compound(isobaric) subwoofer

[Akrambash]

I'm planning to build a compound subwoofer using two dainty (taiwan made)10 inch subwoofers. Initially I used one 10 inch driver in 4 cft sealed box and the results were ok(good for a cheap driver)
However I'm planning to go isobarik for two reasons. One is half of the original box volume. Two is reduced voice coil excursion at very low frequencies which I'm told will prevent the cone from bottoming out. Are there any more advantages to these two and what are the design parameters I have to take into consideration. To drive these speakers I will be using a plate amp with the capability to drive at 4 to 8 ohms bcs the single driver nominal impedence is 8 ohms and yes I will be connecting them in parellel

[chris661]

I've never heard of reduced excursion at low frequencies. The half (ish) volume is correct.

To design a speaker for them - either use a program that supports iso-brarik loading, or design a box, half the volume (keep tuning frequency the same) and use that.

Another thing with iso-brarik loading is the lower efficiency. You are, effectively, asking more power (2x voicecoils) to shift the same amount of air as one. I think the loss is around 3dB, which isn't the end of the world, but, if your speakers are inefficient as they are, you'll find yourself running out of power quickly.

Chris

[mwmkravchenko]

Originally Posted by Akrambash

However I'm planning to go isobarik for two reasons. One is half of the original box volume. Two is reduced voice coil excursion at very low frequencies which I'm told will prevent the cone from bottoming out. Are there any more advantages to these two and what are the design parameters I have to take into consideration.

Hi

I've built a couple of Isobaric cabinets over the years. The only gain I have really found is in cabinet size. The second driver is basically sacrificed to get you a stronger compound motor. If it is smallest box size you are after then it is the way to go. There is no lessening of excursion at low frequencies by the way. THe driver behaves as a normal one with 3db of gain. And actually the inner driver takes quite a beating if you are unkind to it. I stopped making this kind of box for kids. They shred them in days.

Mark