unidentical woofers in series/parallel?

[Jay]

I want to build an MTM using Focal 5W4211. The Focal has it's fruits in certain aspects but has drawbacks in other aspects. So I want to "combine" the Focal with other mid-woofer in series or parallel. These drivers are almost identical, at least in power, size and sensitivity.

What are the worst effects of doing this? Will you not reccommend this approach? Any ideas or approaches I can use to achieve what I wanted to achieve?

Thanks

[kelticwizard]

Well, if you hook them up in series, when one has a certain frequency area of high impedance, and the other an area of low impedance, the high impedance speaker should interfere with the low impedance speaker.

For instance, if one is at 50 ohms at 200 Hz and the other is at 10 ohms at 200 Hz, I think the speaker at 10 ohms is not going to get much power delivered to it. Just a guess, here. That is if they are hooked up in series.

I don't think that will be a problem if you hook them up in parallel.

Are you going to put them is separate enclosures?

My guess is that if you put them into separate enclosures and hook them up in parallel, you probably will be all right. Don't hold me to it, though. They might work out even if you do not put them into separate enclosures, but why mess around when you are just speculating in the first place?

[Stephen D]

Ditto to Keltic.
Parallel & preferably separate enclosures.
I'm not to hip on the idea of different M speakers for an MTM
in general though. I was kinda under the impresion driver
matching of the M's would be kinda important for proper Xover response to achieve the vertical lobing benefits of the MTM
configuration but I'm no expert on those details.

[kelticwizard]

Originally posted by Stephen D
I was kinda under the impresion driver
matching of the M's would be kinda important for proper Xover response to achieve the vertical lobing benefits of the MTM
configuration but I'm no expert on those details.

If he does not have similar rolloff characteristics for each of the mid/basses, he might need to do a separate low pass filter for each woofer. However, up around 2,000 Hz or so, the components to do that are not so expensive, so maybe that is not such a bad idea.

Might give some flexibility.

Don't MTM's require odd order crossovers like 3rd order, 5th order, etc?

[GRollins]

I don't think parallel is going to be such a hot idea, either. If one impedance spikes at a particular frequency, then the other driver is going to take the brunt of the signal--being the lower Z path--and this would lead to unpredictable frequency response.
I vote for independent crossovers, along with independent enclosures.
That said, proper choice of drivers could work very well, indeed, but precise matching of the peaks and valleys of the response would require more fiddle factor and time than I can afford at present. Those with more time on their hands may be able to come up with an excellent speaker.

Grey

[GM]

Some insight here: http://melhuish.org/audio/DIYBX1.html Others have used other brands with good results also, including me. I agree with the others on series though, avoid it like the plague since even two so-called identical drivers (+/- a few percent) have performance issues.

GM