Concrete speaker cabinets

[nat8808]

I had a pair of Jordan JX92 single driver speakers for a bit, transmission lines I think, which had a concrete front and rear panels and then veneered.

They were pretty good (but annoyingly sounded much better in the living room of the guy I sold them too! Often happens..). Were home-made (but still a mini commercial exercise) in someone's shed who had a little following in the JX92 world.

[Reffc]

Except that if you have resonant panels which resonate at a frequency different to the natural resonance of the cabinet it can kind of dampen the cabinet resonance.

There was a sound insulating material talked about in New Scientist once which was only a few mm thick - it consisted of a resonant rubber-like membrane attached to a grid in which each square there was a weighted disc suspended. The weighted discs and membrane each had natural resonant frequencies which cancelled each other out (along with all their harmonics) enough so that the result was a massive attenuation of sound trying to pass through it across a wide bandwidth.

3D printing made it possible for economic manufacture which otherwise was too complex.

That sort of misses the point. Any significant amplitude in the sensitive midrange frequency or lower upper frequency is bad, and adding resonant panels of a different frequency isn't really damping since it has no effect on anything other than it's own frequency (or equal multiples thereof). What it does is to shift the system resonance point one way or the other or introduce even more unwanted resonant panel amplitudes further colouring the sound. There are manufacturers using resonant panels for specific frequencies (Broadman acoustics springs to mind) and whilst they may sound great with certain instruments, they may also ultimately be coloured in other areas . Damping, by definition is a shortening of the resonance amplitude duration or a lowering of the amplitude or (preferably) both. Damping can be effected by laminar panel construction using absorbing layers between structural layers, by increasing stiffness (damps amplitude and lifts frequency) or by damping surfaces, (hence the use of bitumen etc) and also by the type of glue used to construct the speakers. Many (if not most) manufacturers have cottoned onto this and use "lossy" glues for panel joints. I used this trick myself for the Rhapsody and Fidelio speakers (as well as using exceptionally rigidly braced cabinet panels).

[tpbholm]

I have a pair of Opus3 Credo speakers that are made of a composite of crushed marble and concrete. They are actually the same shape as yours. The crossover is housed in a bakelite plinth which is bonded to the bottom of the speaker. I've had them for 20+ years. They were manufactured for Opus3 which is a Swedish company. The company is still going strong, it specialises in producing high quality audiophile vinyl LP's.

The speakers themselves sound fantastic and compare well to my more modern B&W 685's. I use them exclusively for vinyl playback fed by my Linn LP12.

Here's a link to some ltd info about them if you're interested: http://www.audiocircuit.com/Home-Audio/Opus-3

[Mr Kipling]

They also make mechanical tangentianal tracking arms.

[nat8808]

That sort of misses the point. Any significant amplitude in the sensitive midrange frequency or lower upper frequency is bad, and adding resonant panels of a different frequency isn't really damping since it has no effect on anything other than it's own frequency (or equal multiples thereof).

Depends... what matters is the final resonant amplitude and frequencies. If all parts combine to create a resonance which is out of important ranges then that could be good.

A panel which resonates at a slightly higher frequency to the tuned air inside (for example) can greatly dampen those resonances as the energy of one will be absorbed by the other rather than resonating in sympathy.

I've no idea what the Bosendorfer speakers actually do or how they work though, just talking very generally here..

[nat8808]

I have a pair of Opus3 Credo speakers that are made of a composite of crushed marble and concrete.

I guess concrete can take many forms..

In which case let's not forget the Celestion Kingston:



Made of a powder and non-toxic resin compound with granite agregate (mainly for appearance). But still pourable and you would use the material just like concrete.

It is this stuff, commercial name Jesmonite: http://www.flints.co.uk/acatalog/Jesmonite_AC100.html

I have some Kingston cabinet/stands and the stands have white sink drainage pipes embedded in them for the cables Seems all very home-made when you examine how things are really constructed!

[Reffc]

Depends... what matters is the final resonant amplitude and frequencies. If all parts combine to create a resonance which is out of important ranges then that could be good.

A panel which resonates at a slightly higher frequency to the tuned air inside (for example) can greatly dampen those resonances as the energy of one will be absorbed by the other rather than resonating in sympathy.

I've no idea what the Bosendorfer speakers actually do or how they work though, just talking very generally here..

Panel harmonic resonance works independently from other panel frequencies. If something is causing a panel to resonate "in sympathy" then it isn't at a different frequency to the natural resonance point of that panel. I see where you're coming from though as it's the effects of resonance decay that can limit alternative frequency resonance effects, but where stiff panels are concerned, the decay times are usually sufficiently small in many designs for that simply not to be effective. Be that as it may, trying to cure one resonance by introducing another another isn't a very good way of trying to control panel resonances, as all muddy the sound to a greater or lesser extent. As you say though, providing those resonances are shifted where it doesn't matter, that, or controlling them is what counts.

[nat8808]

Panel harmonic resonance works independently from other panel frequencies. If something is causing a panel to resonate "in sympathy" then it isn't at a different frequency to the natural resonance point of that panel. I see where you're coming from though as it's the effects of resonance decay that can limit alternative frequency resonance effects, but where stiff panels are concerned, the decay times are usually sufficiently small in many designs for that simply not to be effective. Be that as it may, trying to cure one resonance by introducing another another isn't a very good way of trying to control panel resonances, as all muddy the sound to a greater or lesser extent. As you say though, providing those resonances are shifted where it doesn't matter, that, or controlling them is what counts.

Or creating an artificially "musical" sound, a bloom in some midrange area.. Some people do go for that, often in high-end speakers..

[Reffc]

Or creating an artificially "musical" sound, a bloom in some midrange area.. Some people do go for that, often in high-end speakers..

...yes, and to enhance bass response as in the case of one or two Harbeth/AN speakers (which may sound "musical) but are not exactly accurate in the bass...IMHO

[sq225917]

Patrick Handscombe made concrete speakers for years in the UK under the Electrofluidics brand. They were vibra moulded foamed concrete with some particulate filler. I spoke to him when building a composite loudspeaker cabinet during my degree. I ended up using an epoxy resin base loaded with rubber dust, wood flour and powdered glass. I literally made and NDT'd hundreds of sample tiles before arriving at a mix with high self damping, high mass and stiffness and available to take a great surface finish. Happy days...