8" OB driver question?

[Godzilla]

Having recently built an OB using the neat little Betsy (Qts .78) driver and having carefully watched others build OBs with 8" drivers my question is...

When adding helper woofers up to approx 200hz do you need to use drivers with high Qts? I see many happy with low .26 Qts Fostex 207e and the latest TB has a Qts of .44... not typical for OB use. Linkwitz uses an 8" Seas with a Qts of .34...

TIA,
Godzilla

[Zen Mod]

I can't find better answer than - try with MJK's MathCad sheets .

that way you'll skip much of a guessing ......

I simulated even FR drivers , intended for BLH - and they seamlessly blended with Eminence Alpha 15

[just a guy]

The qts and fs, in conjunction with the baffle size determines response (mostly). Narrow baffles need high q bass drivers if you want flat response down to near fs. The best way to determine which drivers will work well is to model them. On the other hand, you can quite easily design an OB without any software at all but it will likely need some (possibly very significant) tweaking after the fact that could be avoided with good modelling in the design process.

Here's how to design OB using no tools except driver specs and your head. Easy as pie, except for the fact that it's not easy to guess where (and how bad) the first big diffraction peak will be without modelling. OB Design (amateur audio)

Nothing beats a good simulation though. In addition to XLBaffle (free) and MJK's software (inexpensive) there's also the new version of Passive Crossover Designer (free - released yesterday) that claims to be more accurate than XLBaffle - and obviously, being a crossover designer, you can model whole speakers, not just the bass driver.

If you have any specific questions and don't feel care to get into modelling, I can model stuff for you.

[godfrey]

Siegfried Linkwitz uses electronic equalization to compensate for the low-frequency roll-off. There's lots of info on his website: Linkwitz Lab - Loudspeaker Design

[lousymusician]

In MJK's '3 driver OB' worksheet (where two of the drivers are woofers and one a wide-ranger), the Fostex FE166 and 167 seem to substitute readily for each other despite one having a lower Qt and being intended for BLH rather than BR use. So, I suspect Qt doesn't matter so much if you're rolling off the bass anyway.

Bill

[Godzilla]

Thanks for your replies! I downloaded xlBaffle and noticed it does not require the Qts measurement when doing its calculation. I thought that was odd... especially for an OB measuring tool. Am i missing something?

Thanks,
Godzilla

[just a guy]

Originally Posted by Godzilla

Am i missing something?

Thanks,
Godzilla

Yes. Qts can be derived from qms and qes, so it knows. How are you doing with it? Is it working out for you? As I mentioned you might also want to try Passive Crossover Designer for it's OB design feature if you have excel.

[pjanda1]

Godzilla,

When you are building a speaker with more of a "play with it till it works" methodology, it can't hurt to have more wiggle room. And, the Betsy's high Qts is going to give you a little more to work with in the midbass than the BetsyK. You could certainly incorporate a lower Qts driver with a helper woofer, but the less energy you have to work with around 150hz, the fewer your options. In an ideal world, you would always have a high pass filter on a fullranger running with a helper woofer. There again, more midbass gives you more options as you might be able to use a steeper and/or higher corner on your filter.

Bill, the Qts difference between the 166 and 167 is not very large, that is probably why you don't see a big difference in the simulations. Either that or you are crossing over high enough that the driver resonance doesn't really matter.

The Betsy's high Qts is necessary so that it will work on an OB all by itself. But, when you add a helper woofer, the BetsyK and it's lower Qts is certainly a viable option too. Neither is necessarily better in that application. The ideal choice will depend on the rest of the design.

Paul
Wild Burro Audio Labs - DIY Full Range Speakers

[mor2bz]

for the fullranger or the helpers on the bottom?

your question is about as clear as mud!

[mor2bz]

I think i understand your q now.

the answer is yes, unless you want to get into eq or a zillion "helpers".