Allowing my drivers to roll off

Rory

Member
2001-06-29 4:19 am
What will happen to my sound if I use a piezo tweeter from 27,000Hz down to 3500Hz, and then a 3" woofer from 10,000Hz to 180 Hz, and then a 4" high excursion woofer from 8,000 Hz to 32 Hz (all wired in parallel, without a crossover)? Will the drivers simply not reproduce a frequency they can't? Or will I have ludicrous distortion and honking? These are some replacement speakers for an old boom box, so audiophile-quality sound isn't super-important, but for the sound to be intelligible is very important. I am in a band, and we need a CD player, so I'm building these replacement speakers for that. We just need to hear how things are supposed to sound.
 
Not only will all of those speakers try to reproduce a full range of frequencies, but you risk damaging your tweeter severely by allowing it to try and reproduce these low frequencies. The sound WILL be very harsh and honky. Also, there is very little doubt that a 4 inch woofer will NOT be able to reproduce frequencies down to 32Hz. It simply cannot move enough air to reproduce frequencies that low. You would be much better off using a 5 1/4 inch woofer at the least, and also using a crossover. The sound, in my opinion, would be unbearable without a crossover, but if you must go without one, you need to put some resistance in order to protect the tweeter from damaging low frequencies. This is often seen in very cheap speakers, such as those which come with off the shelf systems.
 
Poor results are likely

The purpose of a cross-over is (at minimum) to keep the high frequencies out of the woofer and to keep the low frequencies out of the tweeter. In each case, the result will be different: Low frequencies will certainly fry the voice coil in your tweeter, while high frequencies in the woofer will cause strange and unwanted harmonics to occur above the frequency that it can faithfully reproduce.

Also, I agree with Bryan that a 4" driver will not handle frequencies down to 32Hz, forcing it to do so will surely cook that voice coil too!
 

Peter

Disabled Account
2001-07-13 7:53 pm
Yes, the piezo tweeter...

...does not need a crossover. Obviously none of the answering knows such a tweeter; maybe because it is really low fidelity.

Damage will be most likely to occur to your midrange (3" and resonance at 180 Hz - you can´t call that a woofer), if you do not block the low frequencies. Take a cheap bipolar capacity for each. The exact value does not matter, something like 10, 15, 22 microF. It does not make much sense to waste money on more crossover elements. Perhaps you first try if you need the midrange at all. I suppose you do better without.

Place the box directly against the wall, if bass sounds too thin.

Greetings from Berlin

Peter
 
I stand corrected

Ooops, I had forgotten that piezzo's don't need a crossover. Its been a long while since I've read anything about them... Sorry for the confusion. Well, at least your tweeter should be OK without a crossover. There are various web resources to help you calculte the value of caps to use in your crossover. I can't seem to find the link I'm thinking of... If I'm able to locate it, I'll post it here.
 
Here's a strange idea that might actually work.

Somewhere, I read that a Piezo tweeter can modeled as though it's a capacitor. Could you just put the piezo and the midrange in series, then place the woofer in parallel with the combination (you might need a capacitor around the piezo)? The additional impedance of the piezo might do other things here. I'm not sure, as I've never worked with them.

On another point, you won't get much bass from a 4" woofer, especially with only 15W to drive it (they're usually VERY inefficient). Check out Parts Express (http://www.parts-express.com/) for high efficiency drivers (or are you only looking for low volume levels?).

Good luck.

Thoth

[Edited by thoth on 07-14-2001 at 01:13 AM]