Troels' PMS (multilayer assembly) build thread

[Andersonix]

I thought you would have filled that cavity with a highly rigid material like epoxy.

Since we're on the topic, and I just happened to have read a little bit on SL's website about this:

Issues in speaker design - 2
"There are several ways to reduce modal panel vibrations. Because the vibration energy from the driver decreases rapidly with increasing frequency it is advantageous to push the panel vibration modes up in frequency where the excitation energy is small. This is best accomplished by increasing the panel stiffness, but often goes together with increasing the mechanical Q of resonance. Dampening the panel by using a constrained layer that dissipates energy will reduce Q."

In other words it sounds like using a squishy material will lower the Q, and that may not be a good thing?

 

[zimjj]

Bullroar

With all modesty in place, I don't think I'd have a problem, though I wouldn't do it translam.
When you consider that the majority of the "building" was done with a computer controlled router that pretty much eliminates the need for woodworking talent;

...the argument against technology has been going on for years. I know a bunch of people who still build furniture with hand saws, planes, chisels, files and rasps. They will say you're not a woodworker if you have to rely on routers and tablesaws.

The cnc doesn't know whre to cut, it has to be told by the designer. You need to have an exact picture of what you want, and be able to translate that to a design the computer can understand. Assembly also takes patience and skill- how many people mess up model airplane kits?

I'm impressed by what waveflex has accomplished, though I can't imagine a mother naming a child that.

Zimjj

 

[planet10]

Since we're on the topic, and I just happened to have read a little bit on SL's website about this:

"There are several ways to reduce modal panel vibrations. Because the vibration energy from the driver decreases rapidly with increasing frequency it is advantageous to push the panel vibration modes up in frequency where the excitation energy is small. This is best accomplished by increasing the panel stiffness, but often goes together with increasing the mechanical Q of resonance. Dampening the panel by using a constrained layer that dissipates energy will reduce Q."

In other words it sounds like using a squishy material will lower the Q, and that may not be a good thing?

I can't see where Linkwitz says that he believes a high Q panel or a low Q panel is to be prefered. from the way i read the snippet you posted is that low Q is better...

... but this is not the case. I have said that a high Q resonance is prefeerred in any speaker trying to push panel resonances up because they make it harder for the panel resonance to be excited. Toole's book says that research has shown that high Q resonances are also less audible, and he provides measures that show why, even when excited they are.

So a very stiff panel, with high Q panel resonances is both less audible & the resonances are less likely to be excited.

The practise of laying high mass, low stiffness damping material on a panel actually degrades a panels performance in the context of the high stiffness, high frequency panel resonance design approach.

dave

 

[smokinghot]

bull fighter

The cnc doesn't know whre to cut, it has to be told by the designer. You need to have an exact picture of what you want, and be able to translate that to a design the computer can understand.

I completely agree... The OP's programming skills are definitely not to be questioned.

However I have to also agree with MJL here. Numbering layers, placing them together in that order isn't the most difficult thing in the world. I'd imagine the preassembly planning was the most nerve racking part of the build.

With that said... You still have to be impressed by the project.

 

[planet10]

...the argument against technology has been going on for years.

I love CNC tools, my biggest objection to building speakers in stacks is the (often) large waste of materials. WaveFlex has minimized this somewhat by brealing each slice into 4 segments.

Also to keep stiffness up, the wall panels need to be thicker because the material is used in its less stiff direction (perhaps less so with MDF than plywood -- given that MDF is not very stiff to start with), using even more material.

When we do a cabinet, the CNC panel saw cuts most of the panels, the big CNC router reserved for baffles with driver cutouts & rebates (& hopefully holey braces)

dave

 

[MJL21193]

In other words it sounds like using a squishy material will lower the Q, and that may not be a good thing?

What Dave said.
I'm on his wagon now in regards to stiffer panels so adding a soft centre goes against that totally.

...the argument against technology has been going on for years. I know a bunch of people who still build furniture with hand saws, planes, chisels, files and rasps. They will say you're not a woodworker if you have to rely on routers and tablesaws.

You are missing my point.

 

[WaveFlex]

Well...

thanks all for your comments . I will try to answer a couple of questions:

I must admit that the bitumen smells heavily and for long... but I don't expect any further absorbtion once hardened out..Resin would have had exothermic issues... didn't really want to try.

Thanks for telling me assembly looks easy as 1-2-3 , thus meeting project goals. I'll take it as a compliment !

I consider anyone being able to assemble a furniture kit from the famous swedish company will be able to built the PMS.

 

[WaveFlex]

Finishing the woofer area

An externally hosted image should be here but it was not working when we last tested it.

Inside view ready for damping

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

Installing the X-over , connections made, ready to close

An externally hosted image should be here but it was not working when we last tested it.

 

[Salas]

Those rods are magnetic, aren't they? That choke's screw and nut?

 

[WaveFlex]

amagnetics bolt

 

[Salas]

amagnetics bolt

Well done then.

 

[Andersonix]

I can't see where Linkwitz says that he believes a high Q panel or a low Q panel is to be prefered. from the way i read the snippet you posted is that low Q is better...

... but this is not the case. I have said that a high Q resonance is prefeerred in any speaker trying to push panel resonances up because they make it harder for the panel resonance to be excited. Toole's book says that research has shown that high Q resonances are also less audible, and he provides measures that show why, even when excited they are.

So a very stiff panel, with high Q panel resonances is both less audible & the resonances are less likely to be excited.

The practise of laying high mass, low stiffness damping material on a panel actually degrades a panels performance in the context of the high stiffness, high frequency panel resonance design approach.

dave

Dave, I think SL agrees with you about the higher Q being better (which was also the reason I linked to that section of his).

 

[planet10]

Tosh,

I got that impression from your comment, but didn't check deep enuff into linkwitz's site to getanything definitive.

dave

 

[R-Carpenter]

I would guess that bitumen, being a viscous elastomer will transfer mechanical vibrations in to thermal energy, there fore reducing acoustic output of the cabinet.
Wish I had a CNC but alas.

 

[planet10]

I would guess that bitumen, being a viscous elastomer will transfer mechanical vibrations in to thermal energy, there fore reducing acoustic output of the cabinet.

But by adding mass with no stiffness it will lower the panel resonance, thereby increasing the likeliness that there will be mechanical vibrations (energy available to excite a resonance is inversely proportional to the square of the frequency) that need dissapation. It also lowers the Q of the resonance making it more audible (as well as increasing the probability that there will be energy to excite it). A lose-lose proposition in my book.

dave

 

[R-Carpenter]

In this particular case wouldn't it work as a CLD?
Dave, what happens to the magnitude of the resonance then you add a mass with no stiffness ? Also, viscous goo would not be very good at vibration transfer.
Wave, do you have a accelerometer?

 

[planet10]

In this particular case wouldn't it work as a CLD?

I wouldn't think that CLD is very practical for a translam box.

what happens to the magnitude of the resonance then you add a mass with no stiffness ?

Resonant frequency goes down. Q decreases. Therefore more energy available to excite the resonance, and more mass to store the energy in.

dave

 

[WaveFlex]

Thanks for your interesting posts and links.

When designing the PMS the translam way I thought about creating the gap in the rear baffle in order to fill it with a material having a different density, known for its properties.

The construction is indeed a CLD, at least to my understanding.

@planet10

I am not sure to understand why CLD should unpraticable with translam...

 

[planet10]

I am not sure to understand why CLD should unpraticable with translam...

Perhaps just how i intuit it, but a CLD works best when it is layers. The orientaion of the material in a translam is orthoganol to the what you'd want.

dave

 

[WaveFlex]

Well, I do understand where you're coming from concerning the orientation of the MDF, but this doesn't change the fact that is remains a layer... although damping is most propably altered.