Floor Bounce

johnny p. -- Tue, 06/19/2012 - 12:34

I just read REG's comments on floor bounce in the April editorial and it looks like a serious problem. Especially when it causes a severe suck-out in the lower midrange.
But since DSP can't correct for this, shouldn't we be looking for speakers that eliminate it acoustically ? Besides a dipole, a compression horn (like Avantgarde), I see that Gradient, Legacy (Whisper) and Amphion (floorstanders) are the only cone-type systems that tackle this problem..
Are there more ? It looks like we need more designs that control their directivity.....

Keladrin -- Thu, 06/21/2012 - 04:13

Hi Johnny,
Couldn't agree more. Floor, wall and ceiling bounce are all problems as what you get is a series of virtual speakers (imagine the walls as mirrors - you also experience the reflection). The sound will reinforce or cancel depending on the wavelength and listening position so DSP only works for one position (and even then it is not totalleffective as it doesn't deal with lack of coherence or phase changes, justthe frequency balance). One source becomes many uncoherent sources.
Like you say the most effective way around this is a more directional speaker or array of full-range speakers. Acoustic treatment around the room also helps, especially using thick carpet rather than solid floors. How do you create a more directional source? By using the correct cone profile and avoiding protruding button tweeters or unfocussed ribbons.
Companies like Bose actually use the high-dispersion approach to create this novel layer of reflection, but this doesn't represent the original sound as it's relying on this reflected room layer. Alot of so-called pseudo-surround or stereo from small central console work like this. It stems from the early attempts to produce an 'expanded' sound from a compact 'stereo' system.

johnny p. -- Thu, 06/21/2012 - 13:41

So DSP really dosen't help the low-mid suck out - or maybe it does partially. I can't believe how few designers are working on this...

Keladrin -- Fri, 06/22/2012 - 03:17

No it doesn't. The problem is any suck-out is listening position dependant and trying to cancel it out will just result in excess output if you move position. Because the effect is caused by phase interactions like I say nothing can easily clean up the sound  - once coherence has been lost it can't easily be recovered as you are effecting a fundamental property of the sound. Any dsp would have to compare the original signal with that observed at the listener and and apply a signal which compleely cancels out the interference. Yes there is a solution - it's called noise cancelling headphones, but then if you are using headphones you won't have the problem anyway. The best non-headphone solution is to minimise the reflections in the first place. Careful positioning of speakers and listener helps.

johnny p. -- Fri, 06/22/2012 - 13:14

But if we don't move our heads while we listen...........

Keladrin -- Wed, 06/27/2012 - 03:19

Still an issue, even if equalised, as you are receiving signals that are out of phase as explained above

brion -- Sat, 06/23/2012 - 22:18

Half-round tube traps work very well on the floor in front of the speakers. Place the reflective side towards the speaker. I've used this for years and it removes a "hollowness" to the sound. Carpeting works well, too, although it's not as flexible, though, as being able to move the tube trap  closer to and furthur away from the speaker.

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