dipole subwoofer [or] contrapunt

[kneadle]

Hello,

I have a desire to build a subwoofer. Before I read this thread: http://www.diyaudio.com/forums/showthread.php?postid=418858#post418858 I was going to build a push-push TL around two old 12" woofers I have lying around doing nothing.

But now I'm intrigued by a dipole subwoofer. I have a long, skinny room I just inherited with my BRAND NEW JOB, which will be perfect for monitoring my audio production and should be good for auditioning music and movies. It seems the figure-8 configuration will be just the ticket to controlling those pesky modes and nodes. Or at least a good start.

I'd like to know what is involved in the construction of such beasts. I have an idea - http://www.diyaudio.com/forums/showthread.php?s=&threadid=12769&highlight=spiral - what is required for a TL subwoofer, but not a dipole.

Oh, oh! I've got it! What priorities should I consider?

Thanks,
Dave

 

[sreten]

Chalk and cheese, TL and dipole.

Choice of subwooofer type really boils down to your two 12"
drivers, they will probably suit one type over another, and
may be entirely unsuitable for a dipole, or may not be.

A TL for push pull 12's is not going to be small.

🙂 sreten.

 

[kneadle]

Chalk and cheese, TL and dipole.

Choice of subwooofer type really boils down to your two 12"
drivers, they will probably suit one type over another, and
may be entirely unsuitable for a dipole, or may not be.

What characteristics make a woofer more suitable for one over another? Dipole likes a high qts, but is there anything else?

A TL for push pull 12's is not going to be small.

🙂 sreten.

Size is not a problem.

However, let me see if I understand the terminology. A TL is a TL. Push-Push would be two woofers mechanically attached at 180°. Push-Pull is the same as dipole.

Is that right?

 

[dqswim]

"What characteristics make a woofer more suitable for one over another? Dipole likes a high qts, but is there anything else?"

From what I got out of the dipole woofers was the need to be able to move air, lots of air so xmax is important.

linkwitz had some great information on his webpage

http://www.linkwitzlab.com/woofer.htm

Do to bandwidth limitations it seems he took down most of the usefull information but if you take the above link and copy and paste in into the web archive you can get the full version of the site

paste the above link into this site and viola... lots of dipole woofer information
http://www.archive.org/

-dave

 

[sreten]

However, let me see if I understand the terminology. A TL is a TL. Push-Push would be two woofers mechanically attached at 180°. Push-Pull is the same as dipole.

Is that right?

????????

A TL or a dipole (or sealed or reflex) can be push pull.
Push pull is not a dipole, a dipole need not be push pull.

Push pull is simply a way of using two drivers in parallel or in
isobaric configuration for 2nd harmonic distortion cancellation.

🙂 sreten.

 

[454Casull]

How much output do you require at what frequency, what sound quality do you want, and how much are you willing to spend?

 

[kneadle]

????????

A TL or a dipole (or sealed or reflex) can be push pull.
Push pull is not a dipole, a dipole need not be push pull.

Push pull is simply a way of using two drivers in parallel or in
isobaric configuration for 2nd harmonic distortion cancellation.

🙂 sreten.

Ok, a hierarchy of terms problem here. What, properly speaking, is "dipole"?

How much output do you require at what frequency, what sound quality do you want, and how much are you willing to spend?

I figure I have the woofers, so I'd be free to spend a lot on materials and XO components. I don't actually know how much output I'll need, but I listen to rock music, and I don't like how much bass is being programmed into movies these days. I mean, if a character puts on a jacket, the subwoofer rumbles.

I want to support the low frequencies for the sake of clarity and efficiency in the mid to hi frequencies. That, and I'm itching to do something with those old woofers.

Thanks,

Dave

 

[sreten]

Ok, a hierarchy of terms problem here. What, properly speaking, is "dipole"?
Dave

Something by the sound of it you shouldn't attempt.

I'm not going to describe it, the details of dipole subs are far too
complicated for a synopsis, and they are not suited to very low
bass (unlike TL's).

🙂 sreten.

 

[kneadle]

Well now I REALLY want to 😉

What's so hard about this?

http://www.euronet.nl/users/temagm/audio/dipolesub.htm

It says, right on the web page, "simple."

Dave

 

[Rudolf]

It says, right on the web page, "simple."

Hi kneadle,

what the website says is: The design of the sub woofer is simple,
but at the expense of an extra amplifier and an electronic crossover/correction filter.
So there really isn´t much work with the enclosure, but you might have a hard time with filters etc.

Since you already have the woofers, why don´t you simply state their type and manufacture? There are lots of people here eager to share their knowledge - if they know, what it´s all about 😀

Rudolf

 

[kneadle]

Re: It says, right on the web page, "simple."

Hi kneadle,

what the website says is: The design of the sub woofer is simple,
but at the expense of an extra amplifier and an electronic crossover/correction filter.
So there really isn´t much work with the enclosure, but you might have a hard time with filters etc.

Since you already have the woofers, why don´t you simply state their type and manufacture? There are lots of people here eager to share their knowledge - if they know, what it´s all about 😀

Rudolf

Well, I need to learn filtering and nonesuch anyway. This is actually one reason I'm interested in it.

The woofers are a consumer-grade brand. I bought them at Best Buy 10 years ago. They are in storage; otherwise I'd be more precise. I remember that they weren't bad, but they weren't good.

In any case, they should be perfect for trying on a new DIY method, I think.

Thanks,

Dave

 

[Rudolf]

Hi Dave,

so this will be really an adventure into unknown land. But I remember from your caterpillar project, that for you the journey is the reward.

One 12" woofer per side isn´t much for a dipole, but is worth a try. Best for a dipole woofer would be a highish Qts between 0.7 and 0.9 or even more. Cheap woofers tend to have a higher Qts than expensive ones, so you may be lucky. Another indication of a high Qts is a comparably small magnet.

What you really need is Xmax. You will not gain much with a stiff accordean surround like in a PA-speaker.

So be sure that your woofers have a rubber or foam surround allowing the cone to move at least 1/2" in both directions (without applying too much force!).

If you can confirm that these conditions are met, you could go to the next step - considering the enclosure.

Rudolf

 

[kneadle]

Hi Dave,

so this will be really an adventure into unknown land. But I remember from your caterpillar project, that for you the journey is the reward.

Rudolf

Ah...I couldn't have said it better myself. As to the other stuff, an educated guess says that those requirements are more or less met. I'll double-check when I move the stuff out of storage.

Thanks,

Dave

 

[kneadle]

Due to bandwidth limitations it seems he took down most of the usefull information but if you take the above link and copy and paste in into the web archive you can get the full version of the site

paste the above link into this site and viola... lots of dipole woofer information
http://www.archive.org/

-dave [/B]

For those interested, http://www.woodartistry.com/linkwitzlab/index.htm hosts the archive CD online.

 

[kneadle]

What, properly speaking, is "dipole"?

To answer my own question: A dipole source consists of two monopole sources of equal strength but opposite phase and separated by a small distance compared with the wavelength of sound. While one source expands the other source contracts.

Sorry if I blurted out the super-secret, super-complicated workings of the DIY speaker universe.

Dave

 

[454Casull]

Sorry if I blurted out the super-secret, super-complicated workings of the DIY speaker universe.

Dave

I think everybody is just sitting here and laughing. 😉

 

[Bill F.]

Don't let anyone tell you dipoles are necessarily complicated. And don't feel pressured into soldering up an active EQ, either! 🙂 (Although you certainly may if you want to...)

Here's a deliciously simple recipe for a bass dipole with a cutoff of 30-40Hz:

Take any bass driver with an Fs between 30 and 40Hz—the more Sd and Xmax, the better. (High Qts, like around 1.0, is a bonus.)

Mount it on a baffle—bigger is better.

Power it with any old subwoofer plate amp (gives you an adjustable crossover, variable gain, and maybe a little EQ boost if you're lucky).

Add series resistance between the amp and the driver to flatten response.

Enjoy!

Bill

 

[kneadle]

Add series resistance between the amp and the driver to flatten response.

Enjoy!

Bill

Sounds delicious. Thanks!

Dave

 

[kneadle]

Okay,

I got them out.

They are Cerwin Vega! Re30 Series speakers, including a 12" woofer (gotta love the exclamation point). I've done some initial measurements, with the results posted in the attached picture.

The problem is that I have absolutely no initial parameters. I haven't the foggiest notion how to measure Qts by myself, and I'm a little under-confident with the Vas measurements. All measurements were done with the Wallin Jig II and Speaker Workshop (oh! what a treasure!).

Oh, and DC Res is 3.0

Any help?

Thanks,
Dave

 

[simon5]

Try to measure most parameters by yourself if you can...

http://www.diysubwoofers.org/measure.htm

You'll need your computer with a tone generator, a multimeter, a 5W resistor of 4 or 8 ohms and an amplifier.