Looking for Info on 'Double Box Speaker Cabinets'

[earnrg]

As in an inner box contained within an outer box.. is there wisdom to having a low energy storage inner box with an outer box to then capture/ restrain the audible nature of that box.. the goal being a method to move the energy away from returning through the drivers or having a boxy resonances? I build many things from both wood and metal and I can definitely see and opportunity to make an inexpensive inner-box and build on top of that with an aesthetic/ functional outer box. BUT what are some things to know about this strategy and can you show me examples of other efforts? thx in advance to any feedback!

 

[shadyJ]

I have not heard of this. I wouldn't be surprised if some manufacturers have tried this as a selling point. Just make the cabinet inert. Get some sturdy bracing in there and stuffing with maybe a fabric liner on the interior. Have a thick front baffle. Having an inner cabinet and outer cabinet is pretty silly.

 

[earnrg]

I don't know if it is silly. I know of a couple of examples that suggest otherwise and if you haven't done it how would you be certain. Also it's essentially similar to constrained layer damping which is very popular. perhaps there is an advantage in achieving a quick energy loss inner/ low energy storage cabinet which also has desirable traits.

 

[shadyJ]

Evidence is needed to prove those claims. You need to show cabinet resonance reduction when that is done. The most inert cabinets I have seen just had lots of bracing, not a whole other cabinet inside. It is similar to layered damping materials, but, that being the case, why not just use layered damping materials? Making two boxes will make the speaker much larger and heavier, and now you have to figure out how to handle the front baffle with two boxes. The speaker will be very difficult to port, and now you have two sets of speaker wire terminals to deal with as well. It becomes a mess with very negligible returns. There are much better proven approaches to solving the problem of cabinet resonance. Look at the B&W 800 series or the KEF LS50 measurements. Very little resonance, and that is due to smart bracing.

 

[earnrg]

I didn't make any claims. I'm looking for feedback.
as I'm imagining it the box is open on one side that allows for the inner box to sleeve fit into it. no need for extra anything in the way of cable or terminals. porting shouldn't be a problem and why not make it sealed.
I'm not sure bracing is easier to do than sleeving the boxes. I have a complete wood shop and a 4 X 8 CNC router and run comprehensive CAD. T
The B&W 800s are very complicated with their bracing! not to mention their cabinets. many sophisticated companies have been tuning their bracing for years to optimize the sound so it's not just about bracing. the kef ls50 is so small that there is not much challenge to getting a stiff box in those dimensions.....

 

[shadyJ]

Why not go a small enclosure route then? It is easier, and that is one of the benefits of that approach. The object is to reduce cabinet resonance, and that is a much smarter solution than making two enclosures for a large speaker. Cabinet resonance is a overblown problem anyway- don't believe the hype about it. Crazy bracing and overkill approaches are not needed. Here is a couple articles about cabinet designs that should be eye-opening:
Loudspeaker Cabinet Bracing: A Detailed Look on Do's and Dont's

Myths & Facts about Loudspeaker Cabinets: Identifying Legitimately High Fidelity Designs

 

[speakerman39]

Q-Acoustics uses what they call GelCore TM to make a cabinet within a cabinet approach. At least, this is how I understand it. Here is a link for the OP:

https://www.qacoustics.com/bookshelf-speakers/concept-20-bookshelf-speaker-pair.html

From what I garner over @AVS the Q20's are living up to the hype. Just thought that I would mention this to the OP.

Cheers,

Phil

 

[earnrg]

Thank you for the info.

 

[speakerman39]

Thank you for the info.

Your quite welcome. I have a feeling that Q-Acoustics is going to do really well here in the USA. Their focus is making better cabinets. There is a thread over @AVS. Here is a link:

http://www.avsforum.com/forum/89-speakers/2517105-q-acoustics-owner-s-thread.html


Here is a thread regarding listening impressions of the Q20's:

http://www.avsforum.com/forum/89-speakers/2559041-q-acoustics-concept-20-bookshelf-listening-impressions.html

The Q20's are certainly living up to all of the hype. Might check them out myself one day.

Cheers,

Phil

 

[earnrg]

here is some info from rockport speakers that sums up a central challenge to building speaker enclosures...

"Our composite cabinet walls are constructed from two, high tensile strength, glass fiber reinforced, loaded resin shells that are separated by a proprietary high density, high hysteresis loss, epoxy core material that bonds the inner and outer shells together. This geometry creates an immensely stiff, yet highly damped beam section for the cabinet walls, exploiting the shell’s tensile modulus, and the core’s compression and shear modulus. This kind of composite construction cannot be matched by any single or homogeneous material since the cabinet walls must exhibit high mass, high stiffness, and high damping, a combination of conflicting attributes unobtainable in any single material."

 

[shadyJ]

here is some info from rockport speakers that sums up a central challenge to building speaker enclosures...

"Our composite cabinet walls are constructed from two, high tensile strength, glass fiber reinforced, loaded resin shells that are separated by a proprietary high density, high hysteresis loss, epoxy core material that bonds the inner and outer shells together. This geometry creates an immensely stiff, yet highly damped beam section for the cabinet walls, exploiting the shell’s tensile modulus, and the core’s compression and shear modulus. This kind of composite construction cannot be matched by any single or homogeneous material since the cabinet walls must exhibit high mass, high stiffness, and high damping, a combination of conflicting attributes unobtainable in any single material."

Lol, that is marketing gibberish. Rockport speaker, while very cool, are deliriously over-priced. If you want to separate fact from marketing non-sense, look at the stereophile spectral decay measurements in their speaker reviews. Some surprisingly expensive speakers with elaborate enclosures have some highly resonant cabinets, while some lower cost speakers do quite well. And even then, there is the matter of what is audible and what is not. You do not need to get exotic to have a reasonably good cabinet. Put in some sensible bracing, line the cabinet with stuffing and fabric, and give it a thick front baffle. Then concentrate on the more challenging aspect of speaker design, namely the crossover and driver arrangement. The decisions made there will have a much more significant effect on the sound reproduction than an overbuilt cabinet.

 

[earnrg]

I agree the rockports are likely to be overdone. the same may be said for Wilson or magico etc. however they are all extremely well regarded brands with similarities in regard to their heavily engineered cabinets. there are certainly just as many builder that choose a different approach.. and the common denominator with all of those companines is that they are all still trying to make improvements. the challenges of engineering challenges in material selection and construction methods still have new soulutons waiting to be discovered.
also many very sophisticated builders will not agree with lining the cabinet or stuffing the cabinet with material. I have the other aspects of the speaker design in hand so I'm concentrating on sorting through the various schools of thought related to cabinet construction. I have a complete wood shop with a 4x8 CNC and run CAD. I can go the extra mile for construction. After 25+ years in the audio hobby I've crossed paths with many different strategies for building cabinets and I'd like to entertain something different and better performing that the typical 'reasonably good' approach.

 

[earnrg]

I am also considering using fiberglass and or metal. For me in my daily life I deal with fabricators in many varieties of materials and processes. I also work with a speaker manufacturer. so the scope of what I have available is not a typical diy.

 

[shadyJ]

If you want to take on an overkill cabinet project for its own sake, than I would look at what Magico or the B&W 800 series do with their cabinet. They have been shown to be extremely inert, and what they are doing works. The same is not true for all of these overbaked exotic cabinet designs. The problem is, if you are making a full range speaker like that, then it becomes unmanageable for a single person to lift or move, and you will need a dolly and the help of a friend. I would do bookshelf speakers and subwoofers.

 

[lsiberian]

It is effective and has been demonstrated to be effective in at least these two studies
http://www.audioholics.com/loudspeaker-design/lowering-mechanical-noise-floor-in-speakers
http://www.silcom.com/~aludwig/Loudspeaker_construction.html#Panel_vibration_damping

Manufacturers don't use this technique because it's patented by Sony
https://www.google.com/patents/US5949033

In my discussions with an engineer specializing in CLD he raised the point that it could be the mass loading that helps more than the actual CLD. Either way it's still produced a very resonance free speaker.

The theory is that bracing is sufficient for addressing internal resonances between the back wave and enclosure, but the coupling between the driver and box also causes the transfer of energy and by adding damping it can dissipate that resonance quickly. Andrew and Chris did a lot of research on this, but neither is around anymore.

How it best works is you build the external enclosure first. Then you treat the walls. You don't need full coverage to get most of the effect and full coverage. I used 3 layers Peel-n-Seal roofing material

https://www.amazon.com/Peel-Seal-Aluminum-Roll-Roofing/dp/B005ET3LQC/ref=pd_sim_60_2?ie=UTF8&psc=1&refRID=F1NXG4TMEE9QY5J9VRW3

Being sure to scuff up the aluminum with steel wool for better adherence. Then you adhere panel on the interior of the enclosure to the damping material using PL Construction adhesive.

After that I used Oak 1x2 and/or 1x4 bracing spaced 3 to 4 inches apart to create an internal bracing matrix between the interior panels. I then stuffed the enclosure with cloth wrapped mineral wool.

You can see the full build thread at http://forums.audioholics.com/forums/threads/my-3-way-build.65342/

There are also numerous threads worth reading IMO.

I had plenty of failures along the way until I came up with a solution that works. My speakers also implement bi-polar design in the front sound stage. I doubt you'll find anyone who knows the topic better than I do, but if you do please let me know so I can learn from them as well for my next build. If you do undertake it. I definitely would love to see a build thread.

 

[earnrg]

Hi lsiberian,
thank you for sharing your excellent information. I noticed that you mentioned that you were unsure if the extremely damped cabinet 'sound' was going to work out for your preferences. has that changed? would you do things differently? My idea was that by using a spruce inner box that the sound would have a way to be absorbed and then transmitted to a space to be absorbed/ diffused inside of and outer box. The material for the outer box would rely on a combination of high mass and stiffness. can you tell me what your thoughts are about that concept?

 

[lsiberian]

It definitely worked out for me. You can probably use just about anything for construction material if you plan to use CLD. Be sure to look at the pictures of the build to get some ideas.

I would suggest using plywood. Your speaker will be very heavy if you try to used MDF or anything like it. You can use hardwood.