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-   -   Why is floor bounce considered only a bass issue? (https://www.diyaudio.com/forums/multi-way/341043-floor-bounce-considered-bass-issue.html)

Defo 5th August 2019 12:28 PM

Why is floor bounce considered only a bass issue?
 
Why is floor bounce considered only a bass issue?

Shouldn't this kind of cancellation affect all frequencies with adequate vertical dispersion? :scratch2:

And also, why is the floor bounce frequency always referenced as singular and not plural? I would imagine more than one narrow band of frequencies being potentially affected.

KaffiMann 5th August 2019 12:32 PM

...?

... Are you talking about halfspace(2*pi) vs full space(4*pi)?
In case you are, perhaps this can help:
Acoustical Space (Free-field, Half-space, Quarter-space, and One-eighth-space)

Edit:
... Or are you talking about the floor-to-ceiling, or wall-to-wall "bounce" as in "room related issues"?
If this is the case, please go to the room treatment part of the forum.
https://www.diyaudio.com/forums/room...tics-and-mods/

JMFahey 5th August 2019 01:32 PM

Just thinking aloud, in any room except an anechoic chamber you will have lots of bouncing around, lots of interaction, peaks and dips allover the place; the analysis being VERY complex.

Now there is *one* important response-altering effect, usually unavoidable unless you float the speaker a significant distance from the floor, which is floor bounce.

Itīs both important and relatively simple to analyze, so people do.

And given the distances involved, it will happen strongly in the Bass frequencies realm, not that other frequencies are not affected but this one is very significant.

chris661 5th August 2019 03:11 PM

Well, the lowest frequency is subject to the least absorption at the floor, so it will make the deepest notch at the listening position.

Wall reflections are a different issue again - you have two sources spread out in the horizontal plane, so perfect cancellations are more rare.

Chris

phivates 5th August 2019 03:21 PM

Is ceiling bounce too variable to be considered of equal concern?

sangram 5th August 2019 03:23 PM

Quote:

Originally Posted by Defo (https://www.diyaudio.com/forums/multi-way/341043-floor-bounce-considered-bass-issue-post5873431.html#post5873431)
Shouldn't this kind of cancellation affect all frequencies with adequate vertical dispersion? :scratch2:

It does.

The answer is in a combination of room modes and transition between half space and omni radiation.

The biggest issue obviously is the actual height of the midwoofer from the floor.

If the speaker is designed to radiate a good amount of power using the floor (down-porting, low-slung ports or woofer close to floor), the primary floor bounce dip is easily eliminated.

Other frequencies cannot be treated in the same way.

So the effect is universal, but the cure can only be applied for bass frequencies.

FredrikC 5th August 2019 03:32 PM

Quote:

Originally Posted by Defo (https://www.diyaudio.com/forums/multi-way/341043-floor-bounce-considered-bass-issue-post5873431.html#post5873431)
Why is floor bounce considered only a bass issue?

Shouldn't this kind of cancellation affect all frequencies with adequate vertical dispersion? :scratch2:

And also, why is the floor bounce frequency always referenced as singular and not plural? I would imagine more than one narrow band of frequencies being potentially affected.

It affects more frequencies, but at a specific frequency the reflection lags exactly half a wavelength behind the direct sound which creates a big dip in the frequency response. At higher frequencies it is more of a discrete reflection, several wavelengths behind the direct sound. At lower frecuencies the reflection goes away as the reflection is in phase with the direct sound.

One can design a system to reduce this, with a line array, or a low mounted woofer crossed to a midrange far from the floor....

Floor bounce also happens with real sources, so it is possible that our hearing is well adapted to it, and don’t perceive this as unnatural. Low frequencies is also perceived from the entire body, not just the ears, so a single point measurement may be exaggerating the effect.

Defo 5th August 2019 04:03 PM

Thanks for the clarification everyone! Makes more sense now.

Quote:

Originally Posted by FredrikC (https://www.diyaudio.com/forums/multi-way/341043-floor-bounce-considered-bass-issue-post5873612.html#post5873612)
One can design a system to reduce this, with a line array, or a low mounted woofer crossed to a midrange far from the floor....

Played around with a calculation for a low mounted woofer and a high mounted midrange now. Pretty neat how you can mitigate the issue this way.
Kind of hard to keep driver spacing within half a wavelength this way though.

Regarding the line array approach - I guess the idea is to cover the dip of the taller mounted drivers with the lower mounted drivers?

sangram 5th August 2019 04:49 PM

Quote:

Originally Posted by Defo (https://www.diyaudio.com/forums/multi-way/341043-floor-bounce-considered-bass-issue-post5873642.html#post5873642)
Pretty neat how you can mitigate the issue this way.
Kind of hard to keep driver spacing within half a wavelength this way though.

Something always gotta give.

Low crossover helps somewhat - 200 to 250Hz is considered the acceptable maximum.

A low port also helps. Not as much as a low slung woofer, but it does mitigate the issue somewhat.

A very large diameter bass driver also works, a 12-15" bass driver can be crossed to a typical 6-7" mid quite easily and be both close to the floor and keep a reasonable C-C spacing.

I chose a 10" woofer and favored closer C-C spacing for better vocal integrity, then used a downfiring port and overdamped the bass a bit in the crossover. This got me a good balance between low end and midbass, with a very good lower vocal range as well.

Not saying that's the only way out - there are others, such as a 2.5 way system with the lower driver down low. C-C spacing is then no longer an issue.

Juhazi 5th August 2019 08:10 PM

Gradient 1.4 by late Jorma Salmi. Downfire bass and a coaxial.
Finnish Gradient 1.4 loudspeaker
Gradient 1.4 loudspeaker, Jorma Salmi | Inner Magazines

http://www.gradient.fi/174-thickbox_...radient-14.jpg


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