how to mount drivers in cabinets with CLD (constrained layer damping) structure?

[Spilferderber]

THE PROBLEM:

how to mount drivers in cabinets with CLD structure?



if you put the bolt run through all three (or more) layers, then you connect them in a rigid way and the CLD effect if gone?

THE SOLLUTION?

you tell me.. I think the speaker drivers should be mounted only to one (outter) layer.

[ianpengelly]

Try mounting the drivers using Well-Nuts, which are threaded brass inserts mounted in a rubber surround,

[Spilferderber]

I was cosidering more aboutmounting the driver only through outter baffle..

[heater]

I too have been thinking about this recently and came to the conclusion that the driver should be attached to the INSIDE layer only. Basically as a result of reading this: http://www.silcom.com/~aludwig/Louds...struction.html

Which I sumarize like this:

1. The main purpose of the cabinet is to dispose of all backwards sound from the speaker leaving only the clean front firing waves.

2. The walls of a normal box will sing and it is hard to stop it with stiff panels, bracing etc.

3. Building a box within a box gets you along way toward eliminating sound radiation from the sides and back of the box.

In this case CLD is more or less a "box within a box". The driver should therefore be fixed to the inner surface. The CLD construction then reduces vibrations reaching the outside and hence unwanted sound radiation from the front panel.

That article prompted me to a simple experiment: Twang a 440Hz tuning fork, the only one I happen to have, and touch it to the panels of a speaker box. Sure enough all speakers I have tried ring like bells!! Seems possible that more sound could come from the sides of the box than the cone itself.

I would be interested in the results of doing this with your CLD boxes. Perhaps using a little speaker fixed inside the box as a stimulous and see how much ringing gets out.

[Cloth Ears]

Originally posted by heater
I too have been thinking about this recently and came to the conclusion that the driver should be attached to the INSIDE layer only.

heater,

I agree with you regarding attaching the drive to only one layer, but how about this for a reason to attach it to only the outside layer.

If you attach the driver to the inside layer, then the box which you have coupled the driver to is the box directly affected by the back wave of the speaker. Therefore, the driver itself would be affected by vibrations from the inside box - as, by construction, this box would be allowed to vibrate more than a single box construction (as it is generally fixed to the floor). The outside layer would, by reasoning of not being either attached to the driver, or being directly affected by the back-wave from the dirver, would vibrate less than for a single box construction.

BUT, if you attach the driver to the outside box, then the back-wave is now transmitted only to the inside box. Not only is the inside box isolated from the outside world, but the driver itself is not directly affected by vibrations from its own back-wave.

Just a thought.

Maybe ask Geenius (Tony Gee), as his Andromeda used this construction.

Good luck, Spilferderber, I don't have the skills or the patience for this kind of construction.

[nunayafb]

...if you attach the driver to the outside box, then the back-wave is now transmitted only to the inside box.

Actually alot of vibration is transmitted from the mounting flange of the driver through the baffle and to the rest of the walls of the enclosure.

If you are going to go to the trouble of CLD, and would like to isolate the outer box completely, I would suggest mounting the driver by the magnet to the inner layer. This way the only contact between inner and outer is the viscous layer and the whatever material you use for a gasket between driver flange and outer baffle.

[ianpengelly]

Hense my suggestion of well nuts, which if mounted cafefully you could attach the driver to whichever layer you wanted (infact you could try both configurations, it doesn't matter as it should effectively isolate the driver from the enclosure anyway) and then use a compliant gasket around the edge of the driver basket.

I believe this is suggested in the Loudspeaker Cookbook, although not specifically referenced to CLD enclosures.

[Spilferderber]

I'm planning to make cabinets, using CLD structures in the following way:

- outter layer: MDF, 16mm
- damping layer: cork plates, 3mm
- inner layer: birch plywood, 19mm
+ bitumen damping

i have three separated cabinets, one for subwoofer (BR enclosure), one for woofer (sealed enclosure) and one MTM cabinet.. for all three I'm planning to use the described CLD structure.

the issue is how to mount drivers and BR tubes.. a friend on the local DIY page also suggested that there would be no problem even if the layers would be stiff connected with the driver screws since they're connected only on a very small surface.

[simon dart]

There are two things to be considered here: firstly the backwave from the drivers cone and secondly the newtonian reaction from the drivers motor.

If you mount the driver to the inner shell the cabinet wall radiation will be reduced but the motor reaction will try and move the driver in the opposite direction so the inner shell needs to be very high mass to counter this or you'll loose definition and detail.

Couple the driver to the outside shell and the CLD wall damping will be much less effective due to the outer shell being directly exited by the driver motor reaction.

I think mounting the driver to the inner shell but skipping the CLD on the bottom face of the box is likely to be best. The driver must have a clear mechanical path to ground. That way youll get the best of out of the CLD without loosing detail and impact. Ive tried well-nuts -avoid!

Simon

[Spilferderber]

mounting the driver only to the inner layer seems to bring more problems.

the main problem: the driver must somehow lean on the outter layer, right?

it seems that we must resolve one more (fundamental) question:

what causes more vibrations, the air behind cone (hitting the walls) or the mounted driver, attached to enclosure?

I think the air is the bad guy here..