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Thoughts on Bill Fitz Maurice sub placement recommendations?


Douglas Cyr:
Hello everyone!

I found this article pretty interesting and wonder if the professionals here have any thoughts:

BFM mentions some methods for maximizing subwoofer sensitivity indoors and outdoors. It's my first time ever seeing most of these techniques, and I'm curious as to their effectiveness - especially the techniques he mentions for increasing sensitivity outdoors where there are no boundaries. Would these techniques be genuinely useful? Especially for bass reflex boxes vs horns. Would there be much increase in sensitivity compared to just placing boxes next to each other firing forwards? Will this just give you a funny looking setup?

-The "V" coupling plate
-Tilting the sub down towards the ground at a 30* angle

Note: I don't have any of the BFM subs.

Thanks for any information,

Tim Weaver:
Some bit of old timer's tricks and lots of snake oil salesman.

You'll find that BFM subs are not well respected here, or really, anywhere outside of the BFM forum. There are no real measurements, and there is no one using them for real shows.

The V-plate thing is old. Really old. Folks in the way-back were doing this because and extra couple of dB of efficiency was worth it. No one does it now because power is cheap and new (within the last 30 years) drivers are worlds better at reproducing very low frequencies. We just don't need to carry around plywood and stack the subs in fancy groups to get them to work. Frankly it's a bit insulting to the client to suggest you need to do this in front of a stage.

I doubt the angling-down thing does much of anything outdoors. You aren't appreciably changing the mouth of the horn since there are no sides. If you added sides, it might do something, but what?!?

The corner-loading thing is true. But it's true for all speakers, not just BFM subs. There's no magic there. If you look at manufacturers spec sheets they will (or should) say how they were measured. 1pi, 2pi, 8pi, whatever. Pi in this sense is marketing wank to say it's in free-air (1pi) or on the ground (2pi) or in a corner (8pi), etc. You'll likely only see 1 or 2 pi being used by a decent manufacturer. 1pi being the best way to measure a frequency response, but it's the hardest to make the speaker look "loud" since there is no boundary gain.

BTW, Boundary gain giving you 6dB of boost is the theoretical best case scenario. That's probably like a concrete floor. If you put it against a studwall you won't see as much gain because the wall will flex a certain amount.

Ivan Beaver:

--- Quote from: Tim Weaver on May 19, 2021, 07:42:21 pm ---

I doubt the angling-down thing does much of anything outdoors. You aren't appreciably changing the mouth of the horn since there are no sides.

--- End quote ---
Angling a sub down CAN give you some more gain.

HOWEVER, it will NOT be at any freq that the sub is reproducing.

The amount of the "horn" is simply to short/small to do anything at sub freq.  So worthless for the sub region.

I see things all the time that people do because they "think" it makes a difference.

They often do it simply because it is different, and they think it is "cool".  And anybody they tell about it is probably to ignorant to understand that it doesn't work.

Yeah, but does it do anything at the operating freq range?

THAT is the big question


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