Suitable midrange cone, for bandpass mid in Unity horn.

[Puggie]

I'm looking for a midrange cone, up to 6.5"dia to fit into a Bandpass enclosure which will fire into an odd unity horn (odd because its being re-shaped to fit into a car, but its using the unity concept).

Basically (I think) I need a midrange driver with a relatively high Fs and low Qt, to work in a 4th order bandpass (sealed rear chamber and ported front) and give me a lower cut off of about 200Hz and upper cut of of 1400Hz (-6db) if I can get more bandwidth all the better.

I'd like to go for a single 6.5" driver or smaller, multiple 2" or 3" drivers would be quite acceptable. I would ideally like something that is available in the UK though, importing from the states is an option but something easily available would be prefered. Someone is having reasonable success with multiple AuraSound NS2 'Whisper' drivers, I'm looking at the Eminence Alpha6 as they are cheap and easily available. any other suggestions please?

[moray james]

the pioneer mid (4 inch with a cup) #B11EC80-02F 8 ohms will work in this application. They cost about $25.00 US each. Worth buying one to test out. Regards.

[GM]

Greets!

To get 'in the ballpark', find one that either is a closed back unit that resonates at ~SQRT(200*1400) = ~529 Hz, or if open back, then ~529 = 2*Fs/Qes. How you get there doesn't matter if you're not trying to get max efficiency out of it with 'X' diameter x 'Y' long vents. IIRC, TD's prototype driver's published specs were ~2*250 Hz/0.99 = 505 Hz, so I wouldn't get too hung up on the apparent need for a low Qt just because it's a horn app.

GM

[Patrick Bateman]

Originally posted by GM
Greets!

To get 'in the ballpark', find one that either is a closed back unit that resonates at ~SQRT(200*1400) = ~529 Hz, or if open back, then ~529 = 2*Fs/Qes. How you get there doesn't matter if you're not trying to get max efficiency out of it with 'X' diameter x 'Y' long vents. IIRC, TD's prototype driver's published specs were ~2*250 Hz/0.99 = 505 Hz, so I wouldn't get too hung up on the apparent need for a low Qt just because it's a horn app.

GM

I'm the guy with the Unity Waveguides in my car, as mentioned above.

GM, I had no idea that there was a formula for this! Thanks for posting it. Honestly, I've spent HOURS poring over the Madisound catalog looking for the best candidate. I purchased and measured half a dozen.

Using the measured data from my Unity midranges, here is what we get.

Aurasound Whisper Suitability for bandpass midrange:
2 x fs / qes =
2 x 164hz / 0.85 =
328hz / 0.85 =
386hz

And here's the measured response of my bandpass midranges, in a real enclosure. As you can see, the bandpass is centered at 380hz, with F3 points at 180hz and 650hz.

In other words, your formula is right on the money! Wish I'd known this three months ago :P

:: PB ::


measured response of my mids

[Patrick Bateman]

Originally posted by moray james
the pioneer mid (4 inch with a cup) #B11EC80-02F 8 ohms will work in this application. They cost about $25.00 US each. Worth buying one to test out. Regards.

Moray,

I took a few minutes to evaluate the Pioneer versus the Aurasound Whisper. Here are my thoughts:

The Aurasound resonates a bit higher, and will extend higher than the Pioneer. (386hz vs 325hz.)
The Pioneer will be waaaaay louder. It's sensitivity is dramatically higher.
The Aurasound measures flatter.
The Aurasound has a higher xmax.

While the Pioneer gives you more "bang for the buck", the data suggest that the Aurasound is a marginally better choice. But they're close, for sure.

[Puggie]

Damn, forgot about this thread,

I've gone and bought some Visaton FRS 7 drivers, Fs of 251 and Qes of 2.08

so 2*Fs/Qes = 241

Hmm somewhat low.

So is their any parameter in particular I should be looking for that would suggest I will get a nice wide bandwidth from the bandass enclosure?

[GM]

Originally posted by Patrick Bateman


I'm the guy with the Unity Waveguides in my car, as mentioned above.

GM, I had no idea that there was a formula for this! Thanks for posting it.

In other words, your formula is right on the money! Wish I'd known this three months ago

Greets!

Yes, I've been following your car audio odyssey. Mine peaked in the early '70s when I modded my then wife's '70-1/2 Camaro with four channel horn loaded surround sound and piped in Altec 411-8A BP sub in the trunk. AFAIK it was the first woofer to have a foam surround and 'high' Xmax, so consequently it was probably the first to suffer from foam rot due to the high pressure/heat of a relatively tiny cab and hot trunk.

You're welcome, it's horn design 101, so published all over the place in one form or another by numerous folks including TD, though normally Qts is used in lieu of Qes. Since I use ML's math, Qes is substituted. Frankly, I wondered why ya'll continued to ponder driver suitability in what seemed like a 'blind leading the blind' manner after I posted it.

GM

[GM]

Originally posted by Puggie
So is their any parameter in particular I should be looking for that would suggest I will get a nice wide bandwidth from the bandass enclosure?

Greets!

As the formula shows, the wider the BW required, the lower Qes must be for a given Fs, ergo for a given Qes the lower Fs must be, but there's still the thorny issue of cab Vb and vent trade-offs just like any vented alignment (especially for a Unity concept), so no simple answer comes to mind at the moment beyond Small's 'EBP' grossly general rule of driver selection where values under 50 suggest the use of a sealed alignment, over 100 suggest the use of a vented, and between 50-100 as adaptable for use in either type.

GM

[omarmipi]

So the 529 Hz value allows you to cross at which points? I want to cross my midrange from 160Hz/6db to 2,500Hz/6dB (or any where up to 6,400Hz, which probably isn't realistic). What value should I be shooting for?

I have 4 VIFA 10MD1908 that have parameters:

*L1: .48 mH
*Znom: 8 ohms
*Re: 5.20 ohms
*Frequency range: 300-8,000 Hz
*Fs: 190 Hz
*SPL: 88dB 2.83V/1m
*Vas: .02 cu. ft.
*Qms: 4.80
*Qes: 1.30
*Qts: 1.03
*Xmax: 1 mm

These Vifa's give me a 292.31Hz value, which is not close to the 529Hz value. However, would they be better for my application?

[Patrick Bateman]

LOL, are you starting to see why both John Sheerin and myself had such a hard time finding an appropriate midrange? It's because an ideal midrange doesn't exist!

So back to your question.

You want to go from 160hz to 6400hz in a bandpass. I know intuitively that it's impossible, but let's do the math anyways.

Here's the math:

Fb = SQRT (F1 x F2)
Fb = SQRT (160hz x 6400hz)
Fb = 1012hz

So you'd have to find a mid with a Fb of 1012hz that has enough excursion to go down to 160hz. Good luck with that!

Would you mind if I scaled down the expectations a bit? Your goal was to cover 5.5 octaves. Even with a direct radiator, that's tough. What if we pare it down to THREE octaves? How about 175hz to 1400hz?

Here's the math:

Fb = SQRT (F1 x F2)
Fb = SQRT (175hz x 1400hz)
Fb = 495hz

As you can see, once you scale down your expectations, there are a handful of candidates that will do the job. The Eminence line array midrange will fit this job, and so will the now-discontinued JBL 400gti. I've personally measured the JBL, and I have one of the Eminence drivers on order.

:: PB ::