[masterxela]

I'm playing around with a sonotube modeling program, and I was wondering how much affect the resonance frequency from the driver to the top of the sono has.


There's no way you can have a tube over 4ish feet and not have that 1/4 wavelength resonance down inside of normal sub material (70hz, down to 48hz w/ a 6 foot tube)


Does this standing wave not have a great affect on the driver and output?


How far outside the xover should it be, to just not deal with it. (not in the mood to try to fix a possibly huge 3hz wide dip)


Because of the number of sonotube's over 4 feet around, I assume people just live with the issue, and try to minimize it with fiberglass/etc on the top plate. But, I read that acoustic "absorbent" material only works down to a wavelength about 4 times as long as it is physically thick. Obviously not possible to address our standing wave then.


Found this on this site, seems to be exactly what I'm talking about. A 10db dip at 65hz from a 4' 6" tube (not 100% sure on length).

Assuming it can't really be avoided without breaking up the rear wave with some kind of deflectors, the best I could model was a 260L 24" tube, tuned to 20hz- that at only 3' 4", pushes the internal resonance up to 90hz. Doesn't look bad with a rl-p18, tc1k, 2k, or ixl....


What precautions need to be taken if I want to curve a port, to get a lower tuning without going taller?


Thanks in advance for any input

 

[Willd]

Hi.


That FR you have there is actually mine. It is of a 15" TC-2000 in a 24" sonosub that is ~48" tall (the actual tube is that long).


However, that dip you see is pretty much entirely due to my room. It manifests itself in measurements of my speakers taken in about the same area, except even worse.

 

[Raymond Leggs]

I didnt know that the voice coil cap had reasonance.

 

[masterxela]

I'm not sure I understand.. What about the voice coil?

 

[soho54]

It really isn't that big of a deal.

When I did my ~6ft sono I did measurements with and without damping materials, unfortunately I dropped that laptop a little later and lost the graphs.

What I found was a ~5dB peak (not a dip) at the resonant frequency, and a lot of ringing. After I added a little batting to the sono sides it dropped considerably. When I added a little foam and batting to the top plate it was no longer a problem. Audibly it was non-existent, the FR peak was gone, and the ringing in the waterfall graph was almost gone, only a small blip left. What was left was nothing compared to what the room was doing to things, elsewhere.

 

[soho54]

I must add that I used the foam on the top plate in a "skyline" diffuser pattern. Four 12" deep sections, four 6" sections, and 4 bare sections. I added a layer of batting a few inches thick circling the port in a ring at 12" down. Right below the diffuser.


This is overkill, but it really helped the waterfall plot. The batting on the sono walls killed the FR peak, and audible ringing on it's own.

 

[masterxela]

thanks