[pufff]

Hi

I have been reading a lot on this forum lately, and have also "ordered" the Martin King Mathcad files today.

I have used open baffles a few years, but have now decided to work some more with the bass. The very good Martin King articles got me started thinking again.

I found out that U frames, as I use, do not have the same SPL level as on a flat, big frame. Then I thought that 2 drivers in parallel could be the answer.

It seems that most people use the same type of woofer, when they use 2 for each side. In the old G. A. Briggs "Loudspeakers" there is a couple af pages describing the benefits of placing two woofers close to each other, if they have a slightly different resonance frequency. It's mainly a question of damping the peaks of the impedance curves.

So, my stupid question is, why aren't there more with different woofers?

I not the best to explain this, so here are the pages in question on the topic "Drivers in parallel":

http://i47.photobucket.com/albums/f199/tubej/Fora/Briggs_1.jpg

http://i47.photobucket.com/albums/f199/tubej/Fora/Briggs_2.jpg

http://i47.photobucket.com/albums/f199/tubej/Fora/Briggs_3.jpg

[Graham Maynard]

Hi pufff,

When picking a LF driver I choose the one that seems to be best, and use two of them in parallel if necessary. 
I would not go and buy a different one which was less good if LF was my main reuirement.

In G A Briggs' day the LF amplifiers were not like today's very low impedance SS types, and we do not know what the T-S characteristics of his chosen drivers were.  It takes a good low output impedance amplifier to properly energise and control two drivers connected in parallel.

Cheers ........ Graham.

[tubamark]

Hi

It seems that most people use the same type of woofer, when they use 2 for each side. In the old G. A. Briggs "Loudspeakers" there is a couple af pages describing the benefits of placing two woofers close to each other, if they have a slightly different resonance frequency. It's mainly a question of damping the peaks of the impedance curves.

So, my stupid question is, why aren't there more with different woofers?

Not a stupid question at all, I'd say.  At this point I'll assume you're talkiing about a passive multi-way setup.  I think folks use matched woofers because things are more predictable that way.  Efficiencies, displacement limits, etc, guarantee a good match-up.  Graham's thoughts about old vs modern amplification make complete sense, but I still think that your idea could have some benefits from a purely acoustic standpoint, impedance issues aside.

There was some discussion last year in the the (still going strong) "Beyond the Arial" thread over at DIY audio about this very notion.  Lynn Olson didn't think it was a bad idea.  Lampizator's site also mentions that strategic woofer mis-matching can be a good thing.  Both OB, BTW.

The (probable) keys to making it worthwhile would be getting reasonably similar efficiencies, Qts figures, and complimentary (different) response curves.
A lot of preliminary simulations (X-baffle is good enough for this, and it's free) could help you see how driver choices stack-up together.

With a little creativity (like use an inductor on just one woofer) you could balance output, Q, etc & produce a really ideal combined response curve.  Then there's baffle variations. . .  the possibilities are endless, but therein is the fun - the hunt for a holy-grail passive combined response.

You will not likely succeed with the slap-it-in-a-baffle-and-Voila! approach that many favor.  It IS extremely possible to achieve with good homework.

Now you got my wheels spinning on this idea again . . . Darn!
-- Mark

[pufff]

Hmm, I understand the idea of buying 4 similar speakers if they are the best

The Briggs book is old, but a bit interesting because he started making a dipole using the normal units back in 1956, after he had heard the Quad ELS57. He also used tube amplification, which probably is why he was concerned to have the parallel speakers to work as good as possible. And with a tube amp in the making I'm a bit concerned too.

My bass now is a single 12" in a U frame, and the bottom is a bit weak. My midrange have a 95 db mark. So it is mostly Lampizator style. Or just thrown together  Anyway, the midrange is wonderful, and I just found the Martin King MathCad models a week ago. So I can build more understanding. And yes, a passive 2 woofer solution in a U frame is what I am seeking, because 2 woofer seems the only solution to get to the 95 db midrange.

I have been playing around with the models today, and there are a lot of possibilities, but appearently not the possibility for 2 different woofers.

I try to find the relevant part in the "Beyond the Ariel" thread, but it is veeeery long.

[Graham Maynard]

Hi pufff,

I believe that Lynn intends using two different types of driver for bass.  A high Q type for lower frequencies, and low Q for higher.
I think he now plans to use separate amplifiers though, where initially he considered series choke drive splitting.

Cheers .... Graham.

[pufff]

I gave up on the "Beyond the Ariel" thread, too many ideas, too little woodworking...........I think my time is better spent measuring Thile Small parameters, explore the worksheets, and work with what I have.

Maybe a pair of Eminence Alpha 12" for each side, with the centering device changed to a thread on one of them could alter the fs enough to have the effect of mutual damping?

I will think some more after my holiday

[G Georgopoulos]

I've read the booklet of G A Briggs' on loudspeakers, it is very good a guide if you're into loudspeaker building,just follow his advise and you wont go wrong

regards

[Graham Maynard]

Good on you Pufff.

MJK (also XLBaffle) are excellent simulators.
There is though no substitute for volume displacement when it comes to LF, which means we need to take X.max into consideration as well, this being a little low on the Alpha-12A with peak above 2kHz.

If you reduce spider stiffness you will simultaneously reduce driver sensitivity and likely end up with a driver you cannot use for anything.  (Been there - done that.)
Reducing the stiffness reduces the Qes - try that in your worksheets - also those Alphas will then distort more as they run through X.max more easily.
Maybe best to leave them as they are in case you can use them for upper bass/low mid/BSC infill between a larger LF driver and a typical wide range driver.

Cheers ........ Graham.