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Old 30th October 2008, 09:07 PM   #1
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Default blh driver

i read a thread of another forum, said suitable driver for horn structure should have resonance frequency to Qts ratio should above 120, wonder if that saying real?
and what does this ratio means if it's real.
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Old 30th October 2008, 09:17 PM   #2
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and my purpose is to obtain massive and thundering bass from a blh enclosure. from below 40Hz to about 16~17kHz
can any driver give this result on a blh.
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Old 30th October 2008, 11:10 PM   #3
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No.

Short & sweet wasn't it.

Longer version: actually, you can, sort of. Remember, a BLH only operates over a very narrow passband -Fc to Fh, so, for e.g., 40Hz - 200Hz. It effectively does nothing above that upper corner frequency. Fortunately. Aside from in some cases attenuating the HF / upper midrange. You can certainly go low with a BLH, but it'll have to be big to do it. If that's your design goal, may I suggest a couple of bass horns with 15in woofers per channel, hand over to something else at 200Hz upwards.
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Old 31st October 2008, 01:59 AM   #4
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Default Re: blh driver

Quote:
Originally posted by bigcatdairy i read a thread of another forum, said suitable driver for horn structure should have resonance frequency to Qts ratio should above 120,
Hmm. Well, a driver with an Fs of 30Hz and Qts of .25 works out to be 120. So anything with a Qts of .25 with a higher Fs would be acceptable, according to the rule. That sounds reasonable (Fs of 50Hz would be more believable).

But the rule also implies that a driver with an Fs of 121Hz and a Qts of 1 would also work -- and that does not seem correct.

So maybe it's key to make sure you have a low Qts regardless of Fs? Just guessing here.
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Old 31st October 2008, 03:36 AM   #5
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Interesting, I thought I gave enough info to resolve this seeming conundrum in the other thread: http://www.diyaudio.com/forums/showt...79#post1643579

BTW, the Fs/Qts rule of thumb is for compression loaded horns, not BLHs, and not a particularly good one overall. I just did a mid-bass compression horn that was only ~62.

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Old 31st October 2008, 03:47 AM   #6
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Oops, sorry GM, I hadn't read that thread yet...
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Old 31st October 2008, 09:36 PM   #7
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got that~
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Old 1st November 2008, 07:30 PM   #8
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Quote:
Originally posted by bigcatdairy
and my purpose is to obtain massive and thundering bass from a blh enclosure. from below 40Hz to about 16~17kHz
can any driver give this result on a blh.
I built a pair of Austin 166s, they measure flat to 40Hz, then roll off, when properly corner loaded (walls are sand filled).
"Massive and thundering bass?"
Not even.
Replacing the rear sand filled deflectors with subs, like Scottmoose suggested, gets there though.
Robert
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Old 3rd November 2008, 09:02 PM   #9
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so,can u tell how to obtain a "massive, thundering and low bass"?
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Old 5th November 2008, 02:32 PM   #10
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Quote:
Originally posted by bigcatdairy



so,can u tell how to obtain a "massive, thundering and low bass"?
Hi Guys, haven't been around in a while, but I will try to tackle this one lol

I guess it can be done. Well, yes it can be done. There are definitely going to be some stipulations though. How big is the room you are working with and how big the speaker can be will make a big difference. Realistically speaking, a FR blh will give you great sound down to a certain point. You could build many of these as a way to get great sound and extreme volume down to that point. If you had an extreme amount of room to take up, you could do all that you ask. Being realistic, a single driver blh will not give what you seek though. A pair or 4 pair will still likely fall short unless you have an extremely large (commercial theater?) sized space and a lot of power and money to throw at it. The easiest way would be to build a good sounding blh and add a subwoofer or 2 or 10. They can be smaller than the blh cabs would be and can add lots of thunderous noise. Making them mate well with the blh can be tricky but it is possible.

Let us know your parameters. Size room, size budget, size cabs you can work with etc.

Take care,
Robert
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