Novice Question: Stereo Woofers in One Box

[joshkrahn]

Hi,

I am designing a boombox for ipods and the like. It will be a single box, roughly the size of a large 80's ghetto blaster. Two woofers and two tweeters, powered by a 12W T.I. evaluation board.

I'm using Unibox and other FRD spreadsheets to do the math, but one question is puzzling me.

Unibox has options for a single drive unit or 2 drive units in series or parallel. But what happens when two woofers are sharing the same volume, but each driver is connected to a separate amp channel (i.e. stereo)?

Can I just use single unit setting? Should I use the series/parallel setting and double/halve the impedance? I'm confused.

Yes, I know this is not the ideal set up, and most DIY'ers would divide the box into two separate volumes, but just humor me for a moment.

Thanks,
Josh

[Saturnus]

I wouldn't do it unless you're dead certain all your mp3s are encoded in joint stereo which basically makes the bass under 200 Hz mono. But would it be very difficult to have a center and bracing wall dividing the 2 chambers?

You run the risk of certain songs not playing bass, or very distorted bass because one channel doesn't play the same as the other channel. In which case both drivers "see" a different size box than they were designed to resulting a very degraded bass response.

[joshkrahn]

Thanks for the reply, Saturnus. By the way, your project is great. In fact, when my colleagues and I were first starting our project, I sent a link to the thread to them for inspiration.

That said, our project is more about aesthetics than audio fidelity (don't shoot me! ). It's actually more of an art project than anything else. We plan to make one or two prototypes and if they sell we'll make more.

We're going to have to have the box built from CNC-cut solid surface (like Corian). It's hard enough getting a fabricator to build us a simple box, let alone something with internal dividers.

So.... let's just say, for poops and giggles, that I HAVE to use a single box even though it's somewhat heretical. What figures should I plug into the simulators to get the best box size and crossover design, all things considered?

Thanks,
Josh

[PeteMcK]

use the single driver setting but double the Vas

[joshkrahn]

Okay, will do. Thanks, Pete!

If anyone else has an alternative approach, feel free to chime in.

Josh

[bjorno]

joshkrahn:

...an alternative approach...

Here is one I’ve built 20 years ago after reading 'Sound System Engineering, 2:nd edition by Don Davis &Carolyn Davis' book page 330 where a similar picture is shown. See the schematic picture 1(2).

Later I also included small Rs and Ls speakers delayed by a MITSUBISHI M65831AP/FP karaoke circuit + another PA: See picture 2(2).

The speaker drivers are obsolete by now, but of course, other suitable ones can be used instead.

Why not build a more powerful ghetto blaster using this concept?

My use of these Speakers where:

If hooked up and placed on or below a small TV set with the small Rs and Ls surround speakers, the wide stereo illusion was in my opinion quite impressive and improved compared to the ordinary built in TV drivers.

b

1(2)

[bjorno]

2(2)

[sreten]

Hi,

FWIW most recordings do not have out of phase bass because it
mostly cancels in room and wastes bass excursion. Occasionally
you do get bass in one channel and none in the other on older
stuff but this does not cause a serious problem.

There is not much advantage to seperating a boom-box.

The box should be designed for two drivers, series / paralllel does
not matter, but as stated doubling Vas does the same thing.

/sreten.