Bass Cabinet Stuffing

[Pelliott321]

I agree with Walt and Tom (that is something new)
There are two things. If you want to clean up the sound then mass and bracing is needed. If you lessen the volume you will affect the low end. If you want a better low end then add a sub that is only active from 50hz on down

[Cogito]

Shashi:

Looking at the numbers I got for your driver, you would need a box volume of approximately 16 cu ft to get an fB of 30 Hz. Typically with an optimally stuffed box you can expect an increase in the "apparent" volume of the box of about 25%. Therefore, your box under ideal conditions would look like 10 cu ft. That would give an fB of just under 35 Hz. I don't think any amount or type of stuffing will get you to 30 Hz. When stuffed, your current box would give you a Q around .5 which would result in good transient response.

Tom

[color=#BF0000
Then there is the enclosure. The stiffer the better. You can brace it like Tom has demonstrated or use constrained-layer damping on the outside to save interior volume.

There is no quick fix. Fitting the box with anechoic wedges will not change the resonant behavior of the box other than pushing the box resonance up rather than down and causing unforeseen problems with the overall playback quality.[/color]

Yesterday, I can feel a slight vibration in the backwall when the bass notes are played. That definitely needs stiffening. I will talk to you about it.

That wedges I am considering are not really anechoic in nature, they are just deflection devices. Most of the reflections that reach the cone are from the parallel backwall. By installing the small wedges on the back wall which will alter the angle of the surface there by altering the angle of reflection away from the cone and towards the four side walls (right, left, top and bottom). Since all the walls including the back wall have the acoustic absorption material, each point of incidence will cause loss of energy in the sound waves which eventually die down. Some of them still might reach the cone at significantly lower energy levels. The wedges I a considering are not in place of the stuffing but in addition to and only on the back wall.

[Cogito]

Hey Sashi,

What specifically are you trying to change about the existing response of your bass cabinet?
Chris

Good question.

I have no complaints about the bass cabinet. As it is today, it is very dynamic and detailed. You know, we all have this bug to improve our systems.

Couple of things I aiming to achieve are, lowering the frequency response and eliminating the cabinet resonances. The second is more appealing to me. Recently, I eliminated the resonances in the compression driver of the horn following Walts advice and I am very pleased with the results. If I can get similar results in the bass cabinet....

Mods to the horn is a different animal all together, probably a different thread.

[Cogito]

If you want a better low end then add a sub that is only active from 50hz on down

I am not a fan of subs for audio. Not interested in rumbling effect. Most of them are not musical and to build a musical (read sealed) sub that goes deep down, the volume needed is huge.

[Roscoe Primrose]

Just bite the bullet and build a new box...

Roscoe

[tomp]

Sealed box subs do not need to be huge to work well and go low. You only need large volumes if you want high sensitivity. Remember Hoffman's iron law, you can have low bass, small box size or high sensitivity. You can pick any two of the above but must sacrifice one.

The sacrifices are not always huge. The 12" Dayton drivers I use in the eggs have low resonance, relatively low VAS which is a major contributor to box size and reasonable sensitivity. They achieve this by having a reasonably high mass, stiff suspension, but an exceptionally strong motor with almost 27 Tesla meters BL. That is more than twice a typical 12" driver. WIth that high BL, the sensitivity of the two drivers I have in parallel come up to just over 90 dB/watt. Still far from my old Bozak B199s but the bass extension in a relatively small volume is quite good.

[Cogito]

Just bite the bullet and build a new box...

Roscoe

Yes, that is an option. By increasing the height and depth by 6”, the volume is increased to 13cft Bringing the fs down to 32Hz.

[Cogito]

Tom,

Any disadvantages in using multiple small woofer instead one large woofer?

[SoundMods]

Shashi:

Looking at the numbers I got for your driver, you would need a box volume of approximately 16 cu ft to get an fB of 30 Hz. Typically with an optimally stuffed box you can expect an increase in the "apparent" volume of the box of about 25%. Therefore, your box under ideal conditions would look like 10 cu ft. That would give an fB of just under 35 Hz. I don't think any amount or type of stuffing will get you to 30 Hz. When stuffed, your current box would give you a Q around .5 which would result in good transient response.

Tom

[color=#BF0000
Then there is the enclosure. The stiffer the better. You can brace it like Tom has demonstrated or use constrained-layer damping on the outside to save interior volume.

There is no quick fix. Fitting the box with anechoic wedges will not change the resonant behavior of the box other than pushing the box resonance up rather than down and causing unforeseen problems with the overall playback quality.[/color]

Yesterday, I can feel a slight vibration in the backwall when the bass notes are played. That definitely needs stiffening. I will talk to you about it.

That wedges I am considering are not really anechoic in nature, they are just deflection devices. Most of the reflections that reach the cone are from the parallel backwall. By installing the small wedges on the back wall which will alter the angle of the surface there by altering the angle of reflection away from the cone and towards the four side walls (right, left, top and bottom). Since all the walls including the back wall have the acoustic absorption material, each point of incidence will cause loss of energy in the sound waves which eventually die down. Some of them still might reach the cone at significantly lower energy levels. The wedges I a considering are not in place of the stuffing but in addition to and only on the back wall.

It's apparent you've developed some opinions that don't seem to be subject to change. Good luck!

[tomp]

Shashi:

Off the top of my head I can only think of two problems with multiple smaller drivers that give you the same linear volume displacement as one large driver. The first is cost. Usually that solution costs more. The second is box size. Assuming the same Fs and VAS of two drivers (which probably will not be true) as compared to the one the single driver the single driver will need one box of twice the volume of the two individual drivers. If desired the individual smaller drivers can be put in separate boxes, each with half the volume for easier handling and smaller dimensions that would reduce the possibility of "organ pipe" resonances due to the larger distances of the single box.

If you put both in one box the total surface area to volume relationship will be smaller than the two boxes resulting in lower box material cost and less total weight although the one individual box will be heavier than each smaller box. The larger single box would also need more internal stiffening because of the larger bending moment of the bigger panels. In my main system I put each of the four 15" woofers in their own box. I'm getting too old to move bigger boxes.

Tom