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Understanding low-frequency reproduction....room or speaker

Hi all, I have a question about low-frequencies and whether my speakers are doing it or its my room.  Allow me to explain...

I own BMC PureVOX speakers, and in our living room space approximately 16x17 with open hallways and a half-wall (not a fully closed square area) if I play the opening track of the "Titanic" soundtrack the low-frequency effects will shake my wife's trinkets off the wall if I'm not careful with the volume.   This is with the speakers out into the room, about 8 feet apart, not close to side walls and at least 2+ feet from the wall behind them.

Just for info, the PureVOX is a bipolar speaker, aluminum cabinet, sealed enclosure, with (2) 6.9" kevlar drivers in addition to the AMT tweeters.  BMC does not provide frequency specs, I assume this is because measuring frequency response is less relevant with bipolar designs.

We recently went to hear the new B&W 802D3, just out of curiosity, and when listening to that same track the 802D3 barely produced any of that low-frequency effect.   This surprised me, because just in terms of size (and price) the 802D3 is in a different league - it's much larger than the PureVOX.

In trying to understand, I pulled up one of those websites where you can listen to low-frequency tones to test audio system boundaries, and on the PureVOX the test tone becomes audible in between 20hz and 30hz.   

So my question is...does this mean the PureVOX actually goes that low, OR is this all just a function of my living room size and configuration, which also explains why my speaker did something the much-larger 802D3 couldn't do?   In my smaller office, I know my Wilson Benesch Arcs sound fuller when they're closer to the wall, so I at least superficially understand wall proximity and room reinforcement and want to understand if that's also what's happening with the PureVOX.


bcgator
davehrab's avatar
davehrab
380 posts
 

bcgator ...  you got it ... walls by their dimensions have a natural P/R/Freq, ... when your speaker produces this frequency the wall will resonate and vibrate in sympathy with the speaker

This is very hard to cure as it is based on your rooms dimensions that you can't  change ... you're more or less stuck with the walls vibrating at their P/R/Freq point

If there is any solace in this ... at least you know exactly what the problem is ... where it is occurring  and what is causing it ... this way you are not making yourself crazy trying to figure it out

The other issue not related to the walls vibrating is the peaks and nulls created by the rooms dimensions which can be very easily to deal with

Peaks and Nulls can effect the sound dramatically and need to be measured

If you can try the Test CD test of listening from 200hz down to 20hz ... you should clearly hear the walls vibrating when you hit the right frequencies    

bcgator's avatar
bcgator OP
356 posts
 
davehrab, I want to clarify something - and I think George had the same idea - the bass response I'm getting, and the resonance, is absolutely not a problem.  It's not something I'm trying to cure, or eliminate.   The purpose of my question wasn't to complain about the low-frequency effects, or figure out how to remove them.  The purpose of my question was to understand how I was getting such great bass response from relatively small speakers (albeit sealed cabinets, and bipolar), in a room that I wouldn't consider small or closed-in, and with the speakers out in free space away from the walls.  I've had larger speakers in that same space, with bass response not close to this.  As I mentioned, BMC doesn't publish frequency response for these, and I figured from the size that if they got down to the 40hz level I'd be happy with them.  But it seems they're going lower.  I just didn't understand if it was the speakers themselves, or as Nonoise mentioned I was just getting lucky with the way this particular speaker was interacting with this particular room.  
georgehifi's avatar
georgehifi
10,312 posts
 

maplegrovemusic

How does one isolate the speakers from a "suspended" floor ? Thought that’s what the spikes are for .


Many get this confused, spikes couple the speaker or stand to the floor, this is fine for cement slab floors, and the best. 

But with any suspended floor the speaker or stand should be de-coupled from it to get the best bass response, as the manufacturer would have voiced it. As they would have been crazy to voice it spiked into a suspended floor acting as a sound board to any bass notes from the speaker.

To de-couple from a suspended floor you need to use an isolating puck or device like a sorbothane filled disc. Like these which you can still use your spikes with 

"Cone/Spike Decoupling Glider"  that are half way down the page.

http://herbiesaudiolab.net/spkrfeet.htm

Or you can substitute your spikes for these "Threaded Stud Glider " a bit further down the page. 


Cheers George

georgehifi's avatar
georgehifi
10,312 posts
 

bcgator 

davehrab, I want to clarify something - and I think George had the same idea - the bass response I’m getting, and the resonance, is absolutely not a problem.  It’s not something I’m trying to cure, or eliminate.  

 I think you probably lucked out with a room standing wave problem that just happens to be just below the natural roll off of that 6.9" bass driver, giving you another octave lower perceived bass. Shh it’s free don’t tell anyone, and whatever you do don't move the speakers or you may loose it.


Cheers George 

geoffkait's avatar
geoffkait
23,365 posts
 
Just thought I mention that one reason why bass response is incorrect or bass shy is that the manufacturer of the speaker simply puts way too much stuffing inside, choking them.  Throw out most or all of the stuffing for best results.  
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