isobaric

[keyser]

Hi,
i'm still in the design stadium of building a isobaric subwoofer. I don't like the look of the driving system outside the box. Is it ok to let the woofers fire in a front to back configuration?

 

[richie00boy]

Yes you put a tube inside the box so that the hidden driver is as closely coupled to the visible driver and just wire the phase accordingly to whether you have put it back-back or front-back.

 

[keyser]

Thanks Richie!
working on the drawings, it got me thinking: what if you'd use 3 instead of 2 drivers, or even 4! Not that I'd really wanna do it, but just out of curiosity, would the Vas of the driver combination drop change like this? Vas (1 driver) * (1/n), where n = the number of drivers.

 

[richie00boy]

Hmm I guess it would. You would reach a point though where so much volume would be taken up by the hidden drivers that it's a waste of time. It would also cost a lot and IMO you would be better buying just a single really really good drive unit or two.

 

[johninCR]

IMHO, a better option is to keep the drivers in a clamshell alignment and if the protruding magnet is an eyesore, just build it so the magnet is even with edge of the cab and can be covered with grill cloth. It's the a little less construction effort than having the drivers facing the same direction but you pick up 2 benefits. First, a closer coupling of the driver cones and second, you get the distortion reduction of a push/pull alignment which is especially beneficial using cheaper drivers in my experience.

 

[keyser]

i use isobaric mainly because it halves the needed cabinet size. I already had two woofers. They are of good quality, and cost 110 euro a piece. I got mine from e-bay at 60 euro for the two.
I really prefer to see the front of the woofer, and not the back. Doing as you suggest again increases cabinet size. As long as using a front-back config. doesn't add distortion, i'm ok with it.

 

[johninCR]

If absolute box size and seeing the front of your driver are of primary importance, then you should consider using an aperiodic vented enclosure. You'd have to play with your own tuning to get it right, but to me that's more fun and satisfying anyway that plugging numbers into a program and building what it says. Then you'll have a smaller box, see the cone, and have a woofer left over for a second sub or to sell without sonic sacrifice.

 

[Stocker]

I'll throw in my two bits:

Front-to-back isobaric has the potential for thermal problems with the front woofer when driven to high output levels

If you just want a small box AND your drivers have long excursion AND high power handling capabilities, go for a TINY box and use equalization to get the response you need.

 

[cyclecamper]

If you just want a small box AND your drivers have long excursion AND high power handling capabilities, go for a TINY box and use equalization to get the response you need.

Except the "high power handling capabilities" is a real problem. Compared to an isobaric's two drivers your one would handle half the power, and to get comparable bass from a small box the exact EQ would depend on the particular alignment but the EQ required could require 10 times as much power to really get low or still need a pretty big box. So if you've got a competition automotive woofer that handles 20 times the power, your idea is one way to go. But the EQ means you'll need an even bigger amp than you would for the isobaric.

When you hear a good large isobaric sounding just like something twice as large, it is pretty impressive.

 

[18Hurts]

I built an isobarik sub with two old Cerwin Vega W15P PA woofers,

Main reason was I already had the box (3.85 cubic feet) had two woofers rated at 300 watts RMS 4 ohms each and a Carver amp to punch up to 750 watts into 8 ohms. Did the isobarik trick for 7.3 cubic feet (it's Vas rating) it handles the Carver since the two are wired in series and to further save space, threw an 18" passive radiator on the back. Extended the box sides about 7 inches and built a two piece grill.

I like the Iso-PR setup, it handles twice the power to make up for the sensitivity loss, is reasonable in size, sounds cleaner since it's push/pull and the passive is easily tuned to 21 Hz without giant ports or chuffing.

The front to back thing does not work well since you have a much larger area of air coupling the two woofers...the more air the lower your crossover needs to be. Others have mentioned the voice coils getting hot since it is in such a small space. It also uses a larger enclosure which goes against the point of iso loading.

The other option if you HAVE to see some form of cone is to use a passive radiator--it is very confusing to people that see a clamshell isobarik and just adds to the mayhem with the passive thrown in for good measure. With the grills in place, it looks like a normal box.