100-400 hz in the box, more diffused the better?

[studiophone]

B is always going to be better right? Not so much focusing on the exact size/placement shown but box vs diffused box for that specific range, the idea is diffused will only help right? Is there a good reason not to break it up?

 

[studiophone]

Sorry here’s the pic.

 

[scottjoplin]

Yes Yes No

 

[AllenB]

Is there a good reason not to break it up?

If you have sufficient absorption that box modes are not an issue.

 

[hollowboy]

I found that there is no such thing as sufficient absorption <400Hz.

When I put a sound source into a complete cabinet, I found that almost 100% of the sound was able to leak out through the woofers. Moderate vs heavy stuffing only made a ~2dB difference under 400Hz.

Post 127, 2nd chart here:
Measuring sound output from speaker cabinet walls

 

[bwaslo]

To diffuse 400Hz, you're going to need irregularities of about 4" or more, more than that for below 400Hz. Some small blocks in the box will do pretty much nothing. Think in wavelengths, you need a decent fraction of a frequency's wavelength to do anything at that frequency.

 

[studiophone]

Side joke: don’t we think in waves? ... Any is still better than none right? The box that got me thinking about this is 18L. And the frequency doesn’t do what I want it to as much if I stuff it more than a little padding on the walls. So I’m thinking maybe diffusing is a good precaution just not a lot of room. Or perhaps at that size it’s not so important?

 

[hollowboy]

More info on the dimensions you need: this shows that a 40mm thick acoustic panel absorbs only at the the top of the 100-400Hz range you're talking about.

Sound Absorption

a little padding on the walls

At low frequencies, padding away from the walls works better than padding on the walls. Similarly, with room treatment, curtains and hangings absorb to lower frequencies if they are spaced out from the walls.

Sound-Absorbing Drapery: Theory & Application

"Up to a point, the deeper the spacing, the more improvement to low frequency absorption you will see. Consider spacing the drape 6 to 12 inches from the surface behind."

...so take this into account, but I think your best efforts will only reap ~2dB benefit in the range of interest.

 

[studiophone]

Cool stuff... developed for submarines. Thinking a little more on this. I want to improve as much as I can the + 200hz and diminish as much as I can below 100 in this box. The thought of the sound in the box leaking out thru the driver and walls makes sense that when I stuff it full the plus 100 goes down and sub 100 goes deeper. Adding the “fake larger cubic space” (Close mic’d). So I think my goal is to keep the curve but do what I can to make sure resonates and/or standing waves are as smooth as poss. Not necessarily deaden. That brings up another question. If I’m using a semi live box to eq. The curve am I creating a problem? I know I always... or is this how speakers are designed?

 

[AllenB]

Don't forget, you don't want to absorb the lowest mode. That is the reason for the box in the first place.

 

[studiophone]

I did a little testing. Looks like the smaller the box the bigger the impact. The small box is 18L and the big is 40.3L The image with 2 curves are at 40.3L with 3 diffusers each measurement but in different locations.

 

[AllenB]

Mixing it up might be creating new resonances. The smaller box may also be changing volume the most.

 

[studiophone]

Funny thing is on the small box I compensated for the volume (lines E,1,2,3) and on the bigger I didn’t.