Speaker Power Distribution

Dohh! Way to go Homer!

Yea I meant Parallel. I tried to get all the info perfect so you guys wouldn't be asking for more.

Anyway; my circuit analysis results indicate about ≈111 watts at each driver. Thoughts?

What color are they?

150 watts RMS ? AES? Peak? You should have more information to make a determination of the speaker's capability..

http://www.jbl.com/estore/jbl/us/support/supportProductSupport.jsp

I am assuming your power values are RMS and not some meaningless peak or PMPO value.

Your fine (well your ears might not be). The similar drivers will share the current fine. You are far more likely to damage the drivers with a small amp driven into distortion (coil-killing DC heating) than a large amp over driving the driver coils (mechanical stress damage).

As long as you have selected the crossover setting correctly of course (ie- not too low in this case)

Are we talking car audio or home entertainment by the way, and what do the rest of the low and mid range speakers and amps consist of?

I have been collecting some vintage professional audio gear which I intend to assemble into a medium sized sound reinforcement system for hire.

Eventually these will be powered by a Crown DC 150A with frequency separation provided by a Crown VFX-2 Active Electronic Crossover.

Right now they are power by a Crown XLS series amp. The XLS amp has a built in crossover and can be configured for low/high pass on both channels or low pass on channel one, and high pass on channel two. The current configuration is for testing as I have received some speaker components with blown drivers, amplifiers with fried power transistor or leaky capacitors...etc.

If you drive the amplifiers into square wave with same peak value as rated rms, you will double the watts - twice rated. So the best protection for your speakers is to prevent amplifier "clipping".

How you do this when someone else has hired the gear is a problem - unless you have some kind of limiter or rate your speakers at twice the amplifier. The second is more idiot proof, simple and durable....

If you have an internal limiter (not accessible from the front panel) you are safe. Otherwise some wiseguy WILL find an easy way to overdrive, and destruct.

With older equipment, lower power amp is the only safe way. They may burn out the amp, but the speakers ought to be unburned.

I wish I knew more about the drivers. Are they horns?

I friend an I did some listening experiments with a tube 7-10 W Mcintosh amp, a high bandwidth, high transient response (>100 V/us), 100 W amp and Voice of the theater speakers.

The results were surprising. The low wattage tube amp had louder horn performance than the 100 W solid state amp. The solid state amp had much better Bass.

He preferred Classical music and I liked music with fast transients and thus I like dome tweeters.

His comment was that he did not expect a Solid State amp to sound nearly as good as the tube amp.

It does make sense that the tube amp was louder because the available voltage is higher in the tube amp when the impedance of the speaker goes up. In the solid state amp, the rails are fixed.

We both though that bi or tri-amping the speakers with a valve amp driving the horns and a solid state amp driving say dome tweeters would be ideal.

What you really have to consider here is the difference between programming power and peak power. Depending on the input to the amp, the peak can range from 10 to 1, as you have with a standard record, to as much as 20 to 1, as you have with a "direct to disc" record. This means that if you are programming, the nominal sound level of you input, at 30 watts then a peak could push your amplifier's output to somewhere between 300 - 600 watts. 215 watts of sound and the balance is distortion. At this point you are at risk of destroying the amp and speakers. Many years ago Phase Linear introduced the Phase Linear 700. This was a serious 700 watt power amp. The reviewer went into great detail describing the programming to peak ratio and ended the article with wondering if 700 watts was enough. He also cited a situation in a disco hall where the speakers were rated at twice the power output of the amplifiers and the speakers were constantly blowing out. This was directly due to overdriving the amp into distortion.

I once saw someone connect 2 8 ohm speakers in parallel in series with a third 8 ohm speaker to get a 12 ohm load. The third speaker was a lot louder than the other two, at least for a little while.

Actually it is very hard to have an amp that has too much power. I use Altec Lansing horn speakers and have since 1971. They are rated at 50watts RMS. I use Crown DC300a amps , 2 in bridged mono. These amps can produce near 500watts rms each in this mode. However they also have incredibly clean power when bridged. I have never blown these speakers in this configuration and have really pushed them hard many times. As others have stated above, clean power is the issue when driving speakers. I am curious as to why you are using 2 compression drivers in parallel. Of all the configs I have done in the 50 years since I started building audio systems this is not one of them. You may have some IM distortion in the areas where the sound projected fields overlap which may spoil your definition and clarity. And placement with respect to your mid's and woofers may also be very difficult to keep proper imagery and tonal balance. I am assuming these are the "grill" type radiators JBL used in the early 70's. Let us know how they work out. As far as the power, you should be quite safe with the Crown 150a's I also have 2 of them and they are quite nice.

Other than on the cannon shot on the 1812 Overture, when do you need 215 watts output? Do your ears ever bleed?

How "sensitive" are your speakers? Speakers have multiple power ratings. One is the minimum power required to be "heard". Another is the maximum power they are rated to handle. I used to have a pair of Audioanalyst A200X speakers. They had a very low programming power rating and a max 200 watts. They were powered by a Phase Linear, (pre Pioneer), 400 watt power amp. They worked fine in my 8 X 10 bedroom and also when I took them to the local high school where my setup could easily handle the 1200 seat auditorium. There is a science to matching speakers and amplifiers as well as knowing when to reverse phase your connections. Did I "need" 400 watts? Absolutely! The speakers were running around 20 to 30 watts in the auditorium and using microphones along with music for an input that level of power provided extremely clean sound.

PMoon,

A parallel connection to a voltage source (your amp) means that each speaker is powered 'individually' from the same voltage according to the basic - V2/R

Driving 215W into a load of 8 ohms implies a voltage source of about ~41.5 Vrms, so each speaker is driven with: 41.5*41.5/16=~107.5 Watts.

Any impedance difference between the speakers will affect their individual power as shown above, and thus their power balance accordingly.

In order to prevent damage to the hf drivers, the power amplifier should be rated double to what the drivers can handle.

Gajanan Phadte