Speaker Enclosure Design

I think you're trying to find the resonant frequency of the speaker right?

This is in 'free air'... I guess you're adjusting the frequency to see the peaks and troughs of the voltage across the speaker coil?

I'm not sure this is a good way to find the resonance of the speaker as you have damped the response using the 1000 ohm resistor... The easiest way I've used is to drive the speaker from a low impedance source and wind up the frequency until you can see the peak movement of the cone, and hear it!

If you're using a computer generated sine wave I would also guess its a bit distorted and so your multimeters will be reading the harmonics - which might be at a resonance frequency, giving a 'dirty' sine wave into the multimeters, in which case they are going to be in error, depending on the crest factor etc...

You really must stick a 'scope on and see what's happening...

John.

Thanks for the input. I think I will have to use the oscilloscope to analyze what is going on. From what I read (and somewhat understand) at the resonant frequency, the impedance of the speaker will be the highest. So when you have the speaker in series with a 1000 ohm resistor (after you have calibrated your system with a 10 ohm resistor in place of the speaker, and set the output so there is 10 mV across the 10 ohm), then you adjust the frequency until you notice a peak in the voltage. The voltage across the speaker will correspond with the resistance, because of the 1000 ohms in series with it. So 0.015 volts will be 15 ohms. I didn't think this was a very good way to do this either, only because the speaker is only getting voltage along the lines of 20-30 mV at the resonant freq, and they don't make much of a vibration, but I didn't really think about the damping effect of the resistor. I don't know if the total change in the phasor diagram would change the response at all. Did I just say something that had absolutely no relevance to this? I don't know, it would make it mostly a resistive load, instead of inductive.

But even if you have a clean sine wave, will a standard multimeter give accurate values for varying frequencies or do you need a "true rms" meter? I should know that I suppose...

And I would hope that the sine wave would be fairly clean, because I am using audio equipment to reproduce it, but I see your point.

Thanks

-Nick

If you have a good clean sine wave then you wont need a true RMS one.....

True RMS responding meters are for use with dirty signals and can even be correct with a square wave input.

Remember that the response and circuit analysis of a loudspeaker is intensly complex, similar to a motor... if you test with the voice coil stationary i.e. low signals, you wont see the effect of the coil moving in a magnetic field and being damped by the contruction of the cone as it moves in the air...

So loudspeaker impedances are invariably complex, but put that together with an enclosure with its own resonances and you really do have a massive problem in testing a speaker in 'free air'... You will get an idea of what needs to be done but only from a great deal of experience, I would assume.... Maybe the designs you have incorporate that experience in which case please carry on...

I'm not an audio designer so I can only tell you what I understand, which for this particular application isn't much!!

John.

I really see what you are saying, I can see how that can be a such a complicated problem. I was questioning the methodology of that website from the beginning because of my screwy results and their suggested setup... it just didn't make sense. I think I did what they said to do as good as is technically possible with the given instrumentation that I have. It looks like I have a lot more research to do for making a good enclosure. I'm actually still an undergrad working on my Mechanical Engineering degree so I don't really have that much experience with anything haha. I DO have senior status, but that doesn't really mean anything as far as real world experience...

But thanks again, that clarified a few things for me, especially about the meters. Maybe eventually I will make an enclosure that sounds better than a $5 speaker from the 1960's at a rummage sale!

Nick

I want to point out that the enclosures are absolutely crucial to speaker performance. Depending on the space your trying to fill will dictate your cabinets. I've found plywood and solid hardwoods aren't very accommodating. Fiberboard seems to work much better. Most speakers I've built (about 7 pair) I used open venting to compensate for bass. Here is a site that may help with some basic questions. http://members.aol.com/mycarstr/Help/box_build.htm P.S. Thank you CR4 for adding the spell check function.

Thats a good page. In addition to that page, I should add that a speaker box dimension in the ratio of 1 to 1.618 to 0.618 makes for the best sounding box. That's the "golden ratio." I think the reason is that certain sound waves cancel (something called standing waves) out before exiting the box, so the sound will be less muddy to the listener. That's why a lot of door speakers in autos don't sound great (or at least that's my theory), because of the odd shapes they have to put in there.

Now do you try to design around the specs of the driver or do you just use some general rules for making your box, like that website shows?

I have lots of OSB plywood, that I was making prototypes with. I also have some very dense 3/4" particle board, same as which I've seen "real" enclosures made out of. Do you think OSB is good enough? It's strong, fairly dense and most importantly... cheap.

My project was to make the best sounding system with the cheapest possible components, and engineer around the minor flaws to make them sound good. I mean look at the $40 computer speaker set you can get. Sure, it won't make some awesome bass thumping noise, but it's amazing how well balanced and good sounding they can make a couple two inch drivers, and a 4 inch "woofer" sound. It's crazy! Now if I just had the means to make these much larger speakers sound that good, that would be awesome.

Definitely go with the particle board, not the OSB.

Don't just tack them together, use construction adhesive (like liquid nails) or even better, slow-set epoxy (then I'd still 'caulk' the corners with adhesive) for a permanent and completely sealed enclosure.

There is a reason why most of the "cheap" speakers are approximately the same dimension-ratio...it's the easy way to maximize the sound quality without doing any engineering/tuning by design.

The overall volume of the cavity is important, but as Bose has demonstrated, the length of the waveguide for bass response will make a difference, and your cross-over electronics will make a big difference in keeping it clean.

Decide on whether you are going sealed or vented (my recommendation). Use WinISD or another to get the box itself close.
If you are going to try to size a bass-port opening for the enclosure, it really may be easiest for you to do what I did: I gave up trying to find a perfect-enough theoretical design and used the 'empirical' method for my last set. Cut your tube hole and start with the longest tube that will fit. (I used cardboard tubing from plotter-paper roll)

Play a reference low-frequency-heavy sample and record the sound pressure levels, then pull the tube back out and band-saw 1/4-1/2" off each time, recording the results. Go back and permanently install a tube cut to length that gave you the best peak response.

I used a pair of 'low-compliance woofers' in each box with response chart showing down to about 30 hz flattish before the curve dropped off to it's 3dB line at 20 with an Fs about 22, which were low enough for me...but get high efficiency drivers. *Mine were 4 Ohm coils, which 'plays the game' of artificially giving higher efficiency numbers than an equivalent 8 Ohm would, since the reference voltage used is the same, but they will still suck more current and produce more volume at equiv. amp output voltage.

I was looking at instrumental bass, not techno/rap, but kept a small volume and chose to do a "4th order" design tuned to just above 30 Hz reference.
umm...don't use a piezo mid-range, make sure everything (including any jack or crossover knobs, etc.) are sealed up tight and well secured...

Oh - this is for car audio.

Have fun!

Hi Nick, as we are into the infinitesimal, better get that golden ratio right, OK approximately right. (Joke)

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616429

Not so funny, and a subject that gives applied mathematicians sleepless nights, you would not think that dropping off the '616429' from the bottom, just to tidy up, would make a blind bit of difference.......WRONG..... "The butterfly effect" sorry....but in a fractal iteration, it certainly does. Delving into the 'Dark Energy/Zero Point Energy Matrix, the precipice where the 'Mandelbrot Set' plunges into the black, That is where minute changes change everything. Dr. J.P. Boyde in his treatise "The Devil's Invention, Asymptotic Superasymptotic and Hyperasymptotic series" stated that investigation into these phenomena was of the utmost urgent engineering priority. Nick you have probably made a Zen Transmission Line...not by luck, but by serendipity.

www.partsexpress.com

The absolute best speaker design I read up on and believe to be true, as it was in a technical magazine.

Was the bass speaker being mounted in the best infinite baffle enclosure you could possibly have, and that was to chimney!!

The guy had sealed the living roon chimney with the bass (woofer) speaker in it so the infinite baffle was the chimney and outside...

He might have stuffed tonnes of glassfibre up the chimney, I'm not sure about that...

John.

Ah ah Electroman, you can improve on that, get a single point loudspeaker like a Tannoy Dual Concentric, you will need four, and have 'stereo' in two rooms.

Second the comment above --- www.partsexpress.com ---- loud speaker cookbooks and software. as far as material i won't use anything other than 13 ply birch ply. expensive, but with the right enclosure size will make almost any speaker of mediocre or better quality rock. I have built enclosures for home stereo, p.a. with built in crossovers, and many enclosures for guitar rigs. Hope this helps.

oops --- I almost forgot. One other factor often overlooked is the cloth that you will cover the front of the enclosure with. (if any) Make sure you use "speaker grille cloth" that is acoustically transparent. If you don't think this makes a difference, just have someone hold a t-shirt or some or other type of cloth in front of the speaker while you stand about ten feet away.

Both points, well made Guest. We call it 25mm Birch Ply here in UK. I have about three sheets always in stock. It is beautiful stuff to work with, and with care you can paint it with a surface you could shave in. Elbow grease & a lot of under/overcoats. Thin ply can be a problem. 7 ply would not be the same at all. Folk often make the mistake of mounting the speaker on thin ply, thinking it won't matter, as the box was made from thick material. If you can find a pair of those old style ceramic kitchen washing basins. Then fit a front of 13 ply to hold the speakers, it can sound fairly impressive. I agree about speaker cloth, like listening through a curtain. even a net curtain makes a difference. Put up a 'mist net' fine as you like, to try and catch bats, (to ring them, whatever) the bats are not fooled. so you have to startle them with loud noise to get them to fly into the almost invisible net.

Mmmm. 'Nickid' I have always found Transmission Line Loudspeakers are very accomodating, as you can 'tune' them up later. I first built a pair about 1966 after reading up the 'recipe' in Wireless World. The basic principle is a 'backwards' folded horn. The loudspeaker goes at the 'big' end. There are free air designs that tend to be BIG and there can be smaller designs which utilise a fibre to increase the effective 'air mass' So if you want a small transmission line loudspeaker the best fibre to use is triple 'OOO' cabinet makers wire wool. The finer the better. It is vital that this wire wool is directional with the 'horn' and it needs to be 'carded' out nice and thin.

If you like contemporary sculpture, why not make it look like a 'Nautilus' Sea Shell. to make it you will need to research pappier machee techniques. You only need to wrap the wet paper strips round a flexible foam/whatever removeable former that you could roll up to form the shell. Myself,.... I would go for sheets of beeswax and make a 'lost wax' mould, which I would fill with Organ Pipe Alloy, essentially old solder It can form rather lovely crystal patterns as it cools. You could paint it with transparent layers of opalescent paint. BUT DO NOT ACCEPT LESS THAN $5000 for the pair when you are done with it. Add baby Sea Shells for the mid range and tweeter make into a giant pearl....... That should turn heads.

I was looking at making some kind of transmission line enclosure. It looks like it would be fairly easy to make it out of particle board, but the problem I foresee is determining the dimensions, but I suppose you just make it so that the path is close to 1/4 of the wavelength the desired tuned frequency? For the woofer for example, would I choose something like 80 or 160 Hz? It all depends on the way I want it to sound, but I honestly have no clue. That "Nautilus" sea shell idea sounds really interesting. I imagine if you did it right, you could make something fairly compact, and still sound very good. It's just a little beyond my time constraint for now...

John, that "infinite baffle" idea is intriguing. I always thought that an enclosure should never be too big, so that the sound waves will resonate and bounce back.

Sandman, I want to try what you are saying about measuring the sound pressure levels. I probably have everything I would need to do something like that, but I'm not familiar with any method of doing so. That sounds like a very good way of tuning the port.

Looks like I'm going to make some kind of transmission line enclosure now... But I have some very nice Pioneer speakers, that seem to have a very good high and low response. I just need to figure out how to make the transmission line enclosure that will sound good with a nearly full range speaker. I have some woofers, so maybe I should just count on having 2 woofers, the two pioneer mids, and two tweeters, in separate enclosures with good crossovers.

Nick

I found something interesting when I put the stock speakers back in my car, before I sold it. They didn't look like anything special, not even the premium speakers. The only design difference between the fairly expensive auto speakers that I had in it and the stocks, were that the stock speakers cones were "flatter", and they had a grill and a little foam on the top around the edge of the grill. The thing that I noticed while putting them back into the car doors, was that the stock speakers sounded just as good in the car door, as outside of the car door. This confused me, so I hooked the after market speakers back in, and they of course, sound terrible outside the enclosure, and sounded much better in it. Why would they sound the almost same outside the enclosure? They surprised me how good they sounded too, the bass wasn't damped out either. The after market and stock were very similar, except the cone design. The stamped metal frame was almost identical in design.

Totally unrelated, I bought some 4" Yamaha speakers (no enclosure, just a driver), just for playing around with, because they were like 3 bucks a piece, at allelectronics.com. The interesting thing about them, the back of the cone is completely sealed off from the environment. All you can see is two felt pieces, acting as a severely damped vent I suppose (each one maybe 1/4"x1" around the perimeter of the metal frame) . It looks like a regular speaker, except the back is mostly sealed off (the stamped metal frame has two rectangular holes, that has thick felt pieces glued in place). Does this mean that this driver is tuned, and wouldn't benefit from an enclosure? It's an interesting design, and I've never seen anything like it before. They sound like a midrange speaker, with little bass response, and mediocre high range response. I found this interesting, because my experience with yamaha speakers, is that they don't really make any just plain crappy speakers. So I saw these, and thought it would be fun to find a use for them. Anyone ever seen a speaker with a semi-closed back?

Nick -

Here's the newer version of the inexpensive SLM from Radio Shack (the best cheap one I was able to find at the time)

If you use Allistair's info links and go through with the TL type of design, be sure to take lots of digi pics along the way, and post your blog/album to share the results!

He's got some great ideas for funky shell-forms, but I don't personally know anyone with the time to try it - hope someone does, I'd love to see/hear how they come out! What I do know, is that it is quite easy to form and work with Bondo, which you mix with a cream catalyst from a tube and start pressing the plastic clay into or onto shapes...and can easily sand smooth afterward and paint with glossy automotive paints if you wish...no need to 'fire' it to get it hard. We did all of my new boat designs; curved rear forms, organic dash displays, new lines and details like insets for cup holders, etc. with industrial 'bondo' (comes in a 50 gallon drum) on fiberglass as well as on wood frames. You'd be surprised how easy it is to frame-up block shapes with MDF and fill-in all the curved and smooth details with bondo.

Anyway, the point is, have fun with the process!

Thanks Sandman, now I know what 'Bondo' is, and also discovered that Senator Barack Obama of Illinois is second nominee after Hillary Clinton for the 2008 US Presidential Elections.......What that has to do with 'Bondo'......Not to worry, it's an off thread topic. My oh My potentially the first Black President of America. My first commission was for voluntary service overseas in his parental Luoland roots. I can say having been born and raised in Kenya, that the Luo Tribe are great musicians and great fun, and have had a very hard time.(Ido not want to wet too many hankerchiefs......a very hard time)...and now I cant even see the screen.

First may I offer my deepest condolences to the Family and friends of Alastair Robertson-Aikman of SME, who passed on this 29th October (Just seen his Obituary..."and those saints of superlative engineering go marching in" R.I.P.)

http://www.newformresearch.com/electrostatic-ribbon-planar-speakers.htm?gclid=CNjOjJzmgYkCFScoZwodiy37VA

Nickid, the above link will introduce you to some of the folk Old 'Blue Eyes' Frank Sinatra would regard as Acoustic Gurus, i.e. The Legendary Peter Walker of Quad.

If you even have the slightest suspicion, however minute, when you close your eyes and suspect the sound is coming from a loud speaker. IT IS NOT High Fidelity.

Loudspeakers should be capable of not sounding like a loudspeaker. You should be utterly convinced there is a person in the room. (OK a Philharmonic Orchestra in the room would be a tall order)

Here ...now..is where the engineering version of the Yellow Brick Road starts. Wikipedia has a good page on Acoustic Transmission Line Loudspeakers with an excellent 1/4 Wave link.

As it happens, for less than a hundred bucks, and not overmuch effort, you could build a full-spectrum ribbon loudspeaker, for about a hundred bucks. but you would need several grand to buy amplifiers etc. to match (Second Hand Bargains at that)

A full-spectrum ribbon similar to the 'Walker Wonder' the afore mentioned genius who spent most of his time travelling up to Buckingham Palace London to receive his next engineering award. thought a well designed full wave ribbon with a full wave undamped acoustic transmission line would be impossible to beat, but rather large and cumbersome. Naturally the magnets would be neodymium etc. and cost a blooming fortune.Thankfully for a lot less you can buy hundreds of feet of flexible 1cm x 0.5cm high performance ferrite magnetic strip, a lot cheaper.....Just a tip.

I appreciate your 'Time Constraints' and suggest you use 1 inch block-board as it is acoustically very dead = good. This link will keep you busy:-

http://www.quarter-wave.com/ I note 'OOOO' steel wool comes as stainless, but walnut oil thinned with turpentine with a soak-n-dry will keep rust at bay. The above link fails to mention that the strands of damping fibre (usually Dacron Hollofill II) MUST follow the general direction of the folded horn. otherwise a 'muffled pillow' sound results. Remember bass vibrations will tend to settle the stuffing, a way round this is to use very thin strips of split bamboo poked through the stuffing to hold it in place. Actually you can, as everything you make is going to be 'square' OK 'wedge'....make a little thin wood/bamboo frame. then take some nice thin fluffy Angora Goat knitting yarn and just make a sort of stretched loom affair. Then slip the frame into the wedge shaped cavities with a drop of white glue to hold in place. use strong sewing tread to make the 'Grid' top and bottom of the wedge that you wind the wool on. YOU WILL NEED TO WEIGH THE WOOL as overall air/wool density is what tunes it. You want to leave clear air space behind the loudspeaker cone. allow the waves to travel a foot or at least the diameter of the cone before encountering any stuffing. Steel Wool, just means you can build much smaller cabinets. If size is important, plywood can be used. When you have plenty of free time, think about those Sea Shells. There is one way they could be built from an excellently 'dead' material. Potters Modelling Clay which is always heavily 'grogged' so will fire to stoneware temperatures. A biscuit fire in an old dustbin filled with sawdust 'lit from the top...not bottom', or if you want a cold fire, just mix the clay with White PVA glue, and varnish/decorate after. The clay would need to be at least 1/2 inch thick, and if fired NO AIR BUBBLES. If it survived the sawdust then a local potter might allow kiln space for a Glaze Firing? Good Luck

I just bought plenty of 3/4" particle board. I have some basic ideas of how to make the most basic transmission line enclosure, but I still don't understand the very basics of what dimensions I should be modeling.

Like this for example, I have the length from the speaker 70 some centimeters to the center of the port at the bottom. From what I probably (don't) understand, that will make it tuned to somewhere around 120 Hz, because the wavelength of 120 Hz is around 280 cm. Is my reasoning close at least?

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Now for this example, I have the total length from the speaker to the middle of the opened port around 134.5 cm. This makes the quarter length tuned frequency around 64 hz. I made these to scale, to the speakers that I would be putting in them...

Now I don't know that much about this kind of thing... does this seem pretty close or not?

Nick-

By the way, all the green lines are supposed to be center lines, but I shrank the image so much, the hashed lines didn't show.

Hi Nikid, the bottom picture looks good, but you need to fit a bit more curvature, the sound wave needs to turn a sharp right-angle bend just behind the speaker, in your drawing the sound wave is hitting a 'flat brick wall'....so to speak....i.e. waves will bounce back, and this will cause distortion.

Fort Halstead Acoustic Weapons Laboratory techniques to the rescue here Nickid....

Can you beg, borrow or make a glass coffee table? (Someone might know of a Javascript software solution that is less messy?)

If you can do so, then just one small light bulb from the Christmas tree is all you need. OK an automotive/bicycle bulb will be brighter.

Also to will need some lengths of wood, and regular clay to stick the wood to the glass. to make a 'Wave Tank' ....i.e. make the coffee table a shallow pool half-an-inch to one inch max. deep. Then you need a cheap vibrator,....but not a cheap one if you get a better 'variable speed' vibrator. Wear dark glasses and a false beard when you go to purchase this ....ahem....item......

Then have lengths of hardwood strips to sink into the coffee table pool that you are now going to use as an acoustic design studio. Put some cushions down on the floor, and look up to the ceiling.....groovey man....bell bottom trousers a flower print shirt a head band will add to the general feeling of 'Retro Chic'.....In case a girlfriend happens to disturb you.......hide the vibrator from view.....You will see the wave pattern projected onto the ceiling by the small filament light bulb i.e. a point source of light. You will be able to design your loudspeaker to scale.

Now to establish the resonant frequency of the drive unit. just get a bowl of popcorn. and your PC should provide a variable sine wave. small bits of popcorn even puffed rice, will show you the resonant frequency by bouncing the highest.

From then on it's mathematics.....I will search for a good table for you to work from. i.e .....F.H.A.W.L. at your service, Salute.

Alistair .... that sounds an intriguing idea!!

Far out man!!

John

I forgot to mention.....ahem.....Lumps of plasticine , stick one of those long Ostrich Feathers into a lump of plasticine anchored at the side of the coffee table. Theatrical shops sell them in all shades of colour. The sort Dita Von Teese uses for her Champaign Stage Act......Tie the thingy-a-majig...to the feather with elastic band/whatever....and have thread suspend a float made of balsa-wood/expanded polystyrene/whatever where the L/S is situated. even make this float angled to mimic the speaker cone, the waves are formed by the bobbing up-n-down of the float. Best to buy a whole bunch of feathers, and place them in a vase as a sort of flower display, so that if interrupted by 'whoever' you can just say it was the nearest thing to hand......Be ultra cool, with an air of dispassionate attention to the vital design task in hand.....make no moves.... and keep the receipt for the ...ahem, in case challenged....I hope these vital pieces of acoustic engineering are not too far off thread.

Postscript:- As the old saying goes "If Music Be The Food Of Love Play On"

And when quite a few years back I was appointed Chaplain to The Lord High Constable of Scotland (The finest Gentleman you could ever meet) his only stipulation was "That's OK Alastair, but please, I do hope you won't be too much of a prude"

Sorry, got carried away there, Chaplains are often (like yesterday) asked to advise on matrimonial arrangements, often leading to the patter of little engineers feet up the wooden hill...... PLASTECINE......You will need the big lump to play 'Transmission Line L/S" design.

First you pat the plasticine into a oblong/whatever block, then with a blunt kitchen knife try to make 'cuts' that when pulled apart form into a 'sort of horn',

Try different combinations, The cross-section area is the important bit, i.e. a square can turn to a rectangle in a 'wedge' shape.....now cut the wedge like a loaf of bread, and see if you can make 'squares' from the progressively 'rectangular' slices? ....when you have done that, you can stack the 'nest' of transformed 'squares', and you are learning a whole lot about 3D geometry......Soon they will be awarding you prizes!

As I remember, the exit port should have an approximate equivalent area to the speaker cone itself, but minus the roll surround. certainly no less than half the area.

Remember, 5 x 5 =25, 4 x 4 =16, 3 x 3 = 9 and 2.5 x 2.5 = 6.25 and which? of these is 'half' the 'area' ......not 6.25, ......Purists like the vent furthest from the speaker, i.e. at the back and at floor level. It's well trendy to put loudspeaker cabinets on spikes, because then vibrations to the floor boards are minimised. This means you can vent to the underside of the L/S cabinet if you desire, but the speaker cone area still applies, so tall spikes needed, if the cone is large.

When you have settled on a set of plasticine cuts, it is time to get out the scissors and cardboard to make a small prototype to scale. Your final scale model should be in something like an expanded polystyrene ceiling tile, but let's not go back there again. This will show you how the final speaker will assemble. It is best if you happen to have made an asymmetric = good, folded horn, to make the pair a 'mirror immage'... that may sound complicated, but all it usually means is the identical components are assembled like you were "Alice through he Looking Glass" if it works behind the mirror it works in front as well....but-jointing is fine with a good glue like Strong as Nails etc.

If you go the 'steel wool' route, you can 'radius' the corners etc. by packing it in tight, & held in place with glue. a bit like a 'steel wool' lined horn. The idea of the exercise is to 'LOSE' the sound waves down the tunnel/ horn. but allow the pressure to escape.

Don't fret, if time constraints etc. sem like this is too much, I can send you a "Windows" Paint Shop master plan, if I know the resonant frequency. If YOO feel like doing a minimalist loudspeaker that will sound OK, Just cut two squares or diamonds, whatever shape you fancy, stick the say 'square' corner-down on a plynth and mount the speaker in the middle. Well YOOAREHERE.COM eat your heart out Philippe! & Love 2 John......Make a 'Birds Nest' of Steel Wool to go behind the speaker. remember the bigger the baffle, the deeper the bass. Philippe is off into space soon with Richard I hear. Bon Voyage & Happy Landings.

I think there ae many speaker reference in bookshopfor reference

(Almost) all loudpeaker enclosures are cuboidal in shape, which to my mind flaws them from the start. This could be because we draw them on t-square draughting tables, cut the chip-board with right-angle radial saws... But then obsession with the right-angle has also led us to make cuboidal buildings, and thus it is true that if you live in a lighthouse you cannot furnish it in the local IKEA store... But I digress...

Sound waves are reflected from plane surfaces, and if we have parallel planes (in a conventional l/s there are three pairs of them - front/back, top/bottom, sides) a standing wave is formed when the frequency of the sound gives it a wavelength, or a multiple thereof, that corresponds to this distance. At these frequencies the parallel planes act as a resonator, reinforcing the intensity of the note and giving a spike in the frequency response curve. A "honk". This can be most unplesant, especially when in corresponds to one of the repeated notes in the music - boom, bish, tiddly OINK tiddly OINK...

The easiest way to avoid this is to build enclosures that have no parallel plane surfaces - We have built "Triangular Transmission Lines", vented enclosure, which also lean backwards slightly as the top and bottom are not parallel, with great success. Oscilloscopes and frequency analysers are all very well, but we have two of the finest audiometric instruments ever made on either side of our heads...

Mail me, anyone who is interested, and I will supply sketches.

Wow, this is cool. I didn't think I would get this many responses. I read an article about transmission line enclosures and they studied the sound responses with making the "transmission line" decrease in size, or increase in size as it travels away from the speaker. I didn't fully understand everything in it... it seemed to be fairly complicated. From what I was able to understand in it, decreasing in size was better.
www.quarter-wave.com/Theory/Alignment_Tables.pdf

I figured that I would have to smooth the inside corners somehow. I'll see what designs Lapinbleu has too... and wow, Alastair, you really have a lot of tips to offer. I'll have to mess around with some of those ideas... and if you could find any tables from the F.H.A.W.L. that would help with this, that would be awesome too, hahaha. So what is this "F.H.A.W.L."?

Thanks
-Nick

Hi Nickid, what is Fort Halstead? you asked, It is the place where all sorts of Scientific stuff that the Government might be interested in goes on. Civilian and Military. There are always loads of amazing careers for interested Graduates.

Check out:- http://www.dstl.gov.uk/jobs/jobshm.php

Well, I made a prototype pair of transmission line enclosures. The first of the pair sounded so good, that I slapped together another one, exactly the same. I put 6x8" pioneer two way speakers in it, and it really is amazing how good they sound. I'm certainly no audiophile but the frequency response seems to be fairly flat all the way down to below 60hz. Things like drum beats are very well represented. I was surprised, because I didn't think these weren't anything special, and they sound good without a separate woofer and tweeter.

As you can see, I didn't put that much thought into it. I just had the material, speakers, and an amp (not to mention a whole day to waste) and I just couldn't wait to start gluing stuff together. After I already started laying down glue, I realized it was kinda stupid to have the top slanted the way it is, because of the way the speaker is oriented, and a ridiculous amount of space is behind and above it. I actually packed a whole crap load of 'OOO' steel wool inside one of them, and quite honestly, it sounds exactly the same as the other. I will be making some more well thought out transmission line enclosures for some other woofers, and mid range speakers that I have. But still... to my ear, I can't imagine it sounding that much better than it does. To compare it to my VW Jetta, that has an 8 speaker Bose Monsoon setup (premium speaker option) I think my speakers actually have a better sounding low end to it. When you crank that Bose system up, sure it sounds great, but it will sound a little muddy at certain freqs. My home brewed boxes don't have as good of a high end, but that's expected because it doesn't have a 'real' tweeter on them.

Nick-

BRAVO! AND BRAVO once again, A convert.......That fine steel wool need to be fluffed out as much as possible....but it seems like it is done. just shove a bit behing the speaker to damp reflections. i.e. round off/radius the top- back corner with it, but if it is all glued up.....ENJOY!...... Next box will be Super-cali-fragilistic-expialidocious Fantasmogorical.

Eliptical drivers are somehow counter-intuitive, and I am a little surprised to see them here. In the UK, in the days before Value Added Tax, a very complex system was in force called Purchase tax. The rules then stated that any driver over 10" diameter was classed for Public Address use, and so enjoyed (or suffered) a lower rate of tax than drivers for home use, at the time clearly a luxury. A 13" x 8" driver therefore had the equivalent surface to a 10" round, but fell into the lower tax bracket...

There may be fine physics at work here, but I find it hard to imagine how an elliptical driver could be as linear as a round one...

I'm wondering if just by dumb luck, I just happened to make an enclosure that works right even though it doesn't look like it should. I showed them to my dad (who has a masters degree in music theory, and was an audiophile in the 80's and early 90's), and he said they sound as good as his Infinity speakers, and then he actually asked me to build him a set too!

I agree, that an elliptical driver won't be as good as a round one. I've noticed that it is somewhat directional, more so than I would expect. Right in front, it sounds great, but if you step to the side a little, it sounds a little different for some reason. Must be because of the shape, and how I have it oriented.

Hi Nick, 'Gordon Films Resonance Productions' the accompanyment to the Book The Colours of Infinity, 'Almathera' the groovey mandlebrot psychadelic animations, Without ingesting those stupid chemicals so in vogue in the late 1960's early 70's. Almost exactly 40 years ago Wellington College was treated to a technicolour rendition much the same as this insert disc to the book......Buy it. Zat is Mandatory Nick.......Orderz iz Orderz after all. ISBN 1-904555-05-5, just gone past comment 333. ahah!......Zen Ven U Haz seen Ze DVD, played on Zeez Magnificent Speakers U have just made....Congratulations....Ve must dizciuzz ze next project. A Class A Valve preamplifier into a Class A Metal Oxide Semiconductor Field Effect Transistor Power Amp. According to ze recomendations of ze Accoustic vepons Lab at Ze Fort Halstead......I don't zink ve need bozzer about ze loud speakerz You have been awarded sufficient medals, and ze ribbons vil do. But you vil need to locate some big 18 inch long throw bass units for ze low frequency. A zeparate amplifier for zoze.

Vell thank you ans Zalute from all of uz.

Well, I added the pieces to smooth the corners out, and it is very debatable if it is better or not. What I did to compare it to the one with no steel wool, or angled pieces in the corners (still like in the pics), I got a microphone, a volt meter and I used the tone generator on my laptop. At 40 some Hz, the one I added stuff to, had a greater voltage coming out of the mic, and the voltage was the same in front of the cone, and in front of the port (so I'm assuming louder=better=more efficient?). The non improved one was completely different, voltage was less front of the cone, and more than twice that in front of the port. At 84 Hz, the non improved one was significantly better.

Now I'm not sure exactly what the purpose of the steel wool is. I thought the purpose of this type of enclosure was to put the sound from the back of the cone, partially in phase with the front of the cone, so the enclosure is very efficient. But I also understand why you would want damping in there, because I've seen the dB vs. frequency curves of undamped enclosures. There are spikes and dips in the sound level, and you don't want that. BUT, I just couldn't believe how good it sounded w/o any damping inside. The sound just fills the room (actually a barn, where I was doing the wood work), even if I had only one speaker hooked up. The improved one still sounds good, but it sounds different than the other, and I still haven't decided if that's a desirable difference... but there is definitely a different frequency response.
So can you describe the purpose of the steel wool?

Lapinbleu, Could you send me some sketches of your enclosures? My email is nick.dittes@gmail.com

I tried sending you a message via the CR4 service, so I don't know if you actually saw it.

Oh, and I'm not sure about a "Class A Valve preamplifier into a Class A Metal Oxide Semiconductor Field Effect Transistor Power Amp"... that sounds beyond me! I just bought on ebay a used 4 channel Pioneer 400 watt amp, 100 dB signal to noise ratio, with less than 0.008% distortion, for $35 shipped.

Well, I actually made a plot of the arbitrary numbers of loudness, and the one with the steel wool inside is a lot quieter. I went from 50 to 300 hz, and between 125-200 it was very close, but above and below that, even to the ear, the empty enclosure was a lot louder. I didn't notice any reverberation, or muddiness, or any abnormality in the empty one. By looking at Martin J. Kings TL charts, my data follows his somewhat, so I suppose it should be damped by quite a noticeable amount. But what I don't notice in the unfilled one, is the spikes and drops in the noise level (by ear at least). I wonder if it's because of my "it looks cool on the outside" design! It is an attractive shape. I'll do some more tests, and if I still don't notice the spikes and drops in dB, then I guess I don't know....

Very Wise, but you need not build it, just keep your eves peeled for a decent second hand thermionic valve Class A, pre-amp on ebay...who knows you might be lucky, you need to check what it is worth by just monitoring prices for a while, then place a silly low bid. Let the equipment come to you..... be patient. Same with the MOSFET Class 'A' Power amp. (read the reviews in the back issues of Hi Fi magazines.

Transmission line speakers are 'not' intended to gain efficiency by the reverse folded horn, that would put 'loading' onto the drive unit. the perfect loudspeaker 'cabinet' would be a simple hole through the wall. but "How do you move a 'hole' around the room you are listening in?".... Essentially it is there to KILL the 'back-content' of the sound wave, without imposing a 'load' on the speaker cone. The 'resonant' frequency of the cone is the 'maximum criminal' the 'minimal criminals' generally don't matter too much.

Wikipedia Quote:-

"

Theoretically perfect enclosure type. Abbrev. 'TL', for housing a loudspeaker. First described in October 1965 by A.R.Bailey in an article in Wireless world(p483-486). It was known that the rear wave of the loudspeaker needed to be completely absorbed without damping the loudspeaker's motion or modulating it from internal reflections and resonance, so Bailey reasoned that the rear wave had to be channelled down a pipe or line, long enough to resist resonance below the desired frequency (e.g., 8 feet for 30 Hz). Bailey reasoned that if the rear wave resonanted the enclosure it would cause interference, which a line would not. If the line were sufficiently long but evenly stuffed with wadding, then the exiting wave would be relatively inaudible. The difference between a Transmission Line loudspeaker and a Reflex or Labyrinth is clear: the rear wave is audibly absorbed and not used for reinforcement. Also the resonance of the enclosure is virtually gone."

Dr. AR Bailey was my tutor during my 'Gap Year' from London Uni.....I was given a placement with a Loudspeaker Manufacturer....blah blah...many moons ago. Things have moved a long way since those heady days in the very early 1970's. I had my fifteen minutes of fame when Sony brought out their first 'Mini-disk' my name was plastered all over their brochure.....I was doing digital compression as my thesis way back then....blah...load of mathematics.....ahah! the ubiquitous 'Mandelbrot Set'...mmm? ...better hush up. The RMPTA will take me away and either hang me or put me on that cold isolated island up in Scotland....'joke' prison chaplain...No Thanks!

I'll remember to keep an eye out for those amps. So it sounds like if you had a half wave or full wave TL enclosure, it would actually be better. That makes sense. As of last night, I did lot's of comparing the empty enclosure to the filled one, and the filled one sounds a little bit more realistic to the ear. I tried some classical, hard rock, jazz... and it is ever so slightly better. Hey, one last question. The flatter the cone, the less it will need an enclosure? I posted something about that above, but no one saw it probably. Those Ribbon speakers you mentioned, don't really need an enclosure, because the sound off the back is in phase w/ the front (I read that somewhere, don't remember where though). I noticed that with some stock speakers on my previous car (Mercury Sable) the cones were very flat compared to most speakers, but they sounded excellent out of any enclosure even (the car didn't have real enclosures, but they sounded good!!!). My Pioneer speakers are like any other, they sound awful outside of a box. Oh, and next summer, when I will have some more time, I am seriously considering that "Nautilus Shell" speaker... that sounds so cool.

I was playing around with a program that does fractals for non-useful purposes, but it does make some cool art. The Mandelbrot set has something to do with fractals, right? http://www.apophysis.org/ I was also doing some in Mathematica 5.

It takes a little playing around with to get the really cool ones in Apophysis, and to get some with any resolution, they can take a long time. I did one (that actually sucked) that took about 5 hours. Here's a different cool one. Apophysis is cool, you can zoom in for a different render to get more detail.

Heh, no need for the royal military police to get involved...

Hey, Thanks for all the information on electronics and acoustics everyone. Maybe I can build some nice enclosures to sell to noobs on ebay... the ones I built certainly sound good. I just bought some 4 way car speakers, so that should be interesting to see what they can do.

That is one cool 'Mandelbrot' painting 'Nick' as I expect most of the contributors to this thread will acknowledge. I think we need a design for 'lapinbleu's' Light house. Something on a Nautical theme....remember those old Steamship Luxury Liners that raced each other for the 'Blue Ribband' as it happens here in Bonnie Colne Lancashire is the resting place of Mr. Hartley the Bandmaster who played on the Titanic. Struck up a Jazz version of "Nearer to God my Thee" as things looked bleak for all the passengers......bit of musical history for this thread....Well.....have a search on GlobalSpec......In 'ART' provenance is everything.....for some sort of cool tubes with elbow joints to match. Stainless Steel perhaps? Galvanised steel looks well cool with all those lovely patterns formed by the zinc cooling into large crystals....Look very like those ventilation pipes on deck, if we made it from those pipes. a transparent Royal Blue automotive spray might look good? and preserve the pattern?

The transmission line could be formed with just four 'OOOO' steel wool stuffing. A mastic of some kind, as used to waterproof gable-end walls would damp down the steel resonances. mix a bit of sawdust in for good measure and stop creep, also thicken up the layer. You would need to soak the steel wool in a 'drying oil' walnut is best, but any old cooking oil like sunflower will do, remember to thin with plenty of turps substitute. Just make a rolled paper cone with strong packing paper that you can remove after stuffing. The vent would be the space left by raising it a bit off the floor. Tannoy Dual Concentric Drivers would be great......point source of sound. Sell them on ebay with those great pics you take. then build a few more perhaps.

Dr. AR Bailey used KEF B139's for his transmission lines, they had a perfectly flat cone, but were essentially bass drivers. The were made from expanded polystyrene with a thin vinyl layer over the top. It is a great hobby building loudspeakers for friends and folk.....meet loads of interesting people as well. Careful if you use that Bondo, to have plenty of ventilation, the stuff stinks at first, as I recall. but sounds 'ideal' for the nautilus project.

Afterthought....Any old bit of 'Carpet' glued to the inside would damp the resonances, and be a lot less hassle. but also use the compacted/ & fluffed up steel wool to make the cone for the transmission line.

I've already got the ones I built put up in our barn. They sound amazing. I just got my Pioneer 400w mosfet amp, and it's HUGE compared to what I thought it was going to be. Even though I bought it on ebay for $36 shipped, I think that was a fluke. I looked up the price and it was about $200 (this is a few years old model, so when it was new it cost a lot more). Now we have better sounding speakers in our barn, than we do in our living room...

This was the new prototype that I built. It has no parallel sides inside of it. Some are close, but are not supposed to be parallel. For size reference, it is exactly 1 meter high. That amplifier that is sitting next to it is a 400 watt Pioneer amp. It is actually fairly large at around 25 cm by 25 cm. The pioneer speakers are 4-way, and have a max of 280 watts a piece. I was surprised how good they sound they can just pump air through the ports at the base, it's amazing. The extra 3 speakers on this make it have a surprisingly good high and low range. I had it hooked up to a good but old reciever, and had the volume almost all the way up with no distortion. I think it needs something more powerful like the amp in the picture to use it fully! BTW, that pioneer amp has a total distortion of 0.008%... and I've heard that's pretty good.

I will follow your suggestion and try some carpet... I know someone who works at a carpet store, maybe I could get some shag carpet!

Thanks Nick, your enthusiasm does you proud. Take care pumping small speakers with the full 400 Watts You could lose your friendly neighbours. and blow a speaker coil. As it happens, a powerful amplifier is far less likely to wreck a speaker than a weak one......It's known as 'clipping' ...what happens is the capacitors on an underpowered amplifier run out of stored charge on high transients. then when the signal comes back on, the loudspeaker cone is in the wrong place....missed a beat, so to speak, Then all the energy is lost in the coil as 'resistance heating' and not 'impedance' as you would get from an unclipped signal.....result

I once burnt out the coil of a massive 18 inch bass speaker rated at well over 250 Watts, with a measly 15 Watts. I thought it would cope as it was so huge. Wrong!

Sounds like you snipped a bargain with the Pioneer. Cool. Second hand speakers can be a problem, you are probably best off buying new drive units at discount. They should also come with full data sheet, That can be very helpful designing an enclosure. I can recommend the Tannoy dual concentric type design, if you ever plan to make that Nautilus. I have this feeling you will look back at this episode in your life, in years to come, as 'Happy Days'

The time has not been wasted 4 sure.

...what happens is the capacitors on an underpowered amplifier run out of stored charge on high transients...

Yes, capacitors cost money, so normally you get the ones that will just do the job. One time we wanted to party at the beach, and so I looked inside the old H&H 100w instrument amp we had to see if we couldn't run it from batteries. These amps have an earthed centre rail and +30v. -30v supplies, quite common. So, four 12v. tractor batteries are indicated - and even with only +-24v. the sound was, but, stunning! Clipping knocks off the extremes of the waveform, and sounds, well, square. If I was any good at ascii art...