Speaker cabinet design

[moodybuilder]

Got a pair of superpensil 12's . I made the cabinets out of 20mm MDF but they need respaying so I'm wondering if I would be better making a new pair out if 18mm birch ply if what are the advantages.

[Pharos]

From my experience and reading you are better of with MDF because it is a lower Q material, and so more self damping.

In the 60s many cabinets were made from ply which has a higher Q and produces quite noticeable resonances with a knuckle wrap test, many of them making a hell of a racket, but in horn designs not so noticeable because they tended to be coloured anyway.

Chipboard is even lower Q, but is mechanically low quality to work with, and weak.

My choice is MDF with corner bracing with fillets of the scotia profile, using PVA.

[walpurgis]

From my experience and reading you are better of with MDF because it is a lower Q material, and so more self damping.

In the 60s many cabinets were made from ply which has a higher Q and produces quite noticeable resonances with a knuckle wrap test, many of them making a hell of a racket, but in horn designs not so noticeable because they tended to be coloured anyway.

Chipboard is even lower Q, but is mechanically low quality to work with, and weak.

My choice is MDF with corner bracing with fillets of the scotia profile, using PVA.


Yes, I agree with what you say. The use of MDF in speakers has been blighted by negative comments recently, probably by people who have not compared its capabilities. It's my choice of (reasonably economic) materials.

[moodybuilder]

Thank you both. Off to the spray shop, will post the completed pics when done.

[RothwellAudio]

This is a BBC research paper about loudspeaker cabinet materials
http://downloads.bbc.co.uk/rd/pubs/reports/1977-03.pdf

It makes for interesting reading. I don't think MDF was available at the time but quite a few other materials are examined.

[Pharos]

I haven't read the paper, but the BBC had its own philosophy now continued by Harbeth in which they used flimsy panels damped with heavy layers of bitumen, the idea being to put the resonances outside the critically audible ranges.

I'm not convinced that this approach is very beneficial, especially as the flexing can seriously compromise bass performance as the cabinet walls are sucked and blown in and out.

I suggest that if it was a real universally accepted breakthrough technique, it would be more widely adopted.

[RothwellAudio]

I suggest that if it was a real universally accepted breakthrough technique, it would be more widely adopted.

I'm not advocating the BBC's approach as such, just pointing anyone interested in the direction of some interesting reading from a reputable source, based on some research and without a commercial axe to grind.
Actually, I think the principle of minimising panel resonances is very widely adopted - they just don't all take the same approach to it as the BBC did. I think the BBC wanted to reduce audible resonances in the midrange without having extremely thick/heavy cabinets.
Anyway, it's there if anyone wants to read it.

[danilo]

Try particle board? MDF is a semi recent material and anecdotal (at least) info suggests it ,
despite it's pedestrian nature/price point, is a surprisingly decent enclosure medium... superior to MDF by many claims.
Certainly more stable under paint if nothing else.

[Pharos]

Of course you are right about damping Andrew, that is not in question, but that the BBC's technique had not been universally adopted, and so is a relatively 'out on a limb' solution, was my point.

Particle board may well be lower Q, I think ESS used it to an extent.

[SPS]

Got a pair of superpensil 12's . I made the cabinets out of 20mm MDF but they need respaying so I'm wondering if I would be better making a new pair out if 18mm birch ply if what are the advantages.

Your best placed to answer this your self , listen to them with a bit of volume, does all sound well ? Feel the cabinet while playing is there any vibrations / resonate areas of the cabinet thats vibrating, this will colour sound, you may or may not recognise/ hear it.. But its there..

My own experence of materials is is mostly limited to open baffles and large back horns, mdf imparts a dull sound to the music, sort of greyness that is unnatural sounding.
birch ply gives the music a brighness but can resonate suprising easily, (and its easily felt), and if you know what to listen for, quite audible.
Flooring grade chipboard to me is much better sound wise than mdf, its brighter sounding with out the dullness of mdf, it seems to be less resonant in larger panels, using the thicker grades works well,

In slim speakers like yours the sound is likely to be less influenced. But its is unlikely there will be no difference (someone somewhere would point it out.... )
I think scott ( the designer) brought a pair of these round to my house a few years ago and as i remember they sounded very good,
I organise the audio talk meets and have heard alot of speakers over the years, sometimes the material they are built from is easily heard, but with others its not- so good design and construction is the first priority...
Hope thats some use
Steve

[M6NTL]

So what is the consensus on the Plaster of Paris used by Max Townshend in my old Glastonburys as a cabinet material?

Sent from my LG-H850 using Tapatalk

[Pharos]

Unusual, not that heavy a material, maybe quite self damping, probably cheap, but then there are numerous attempts at cabinet designs involving innovative approaches.

Wilson uses 'kitchen tops', ATC uses now quite a lot of aluminium, and I feel sure that certain polymers would make very good cabinets, and be easy to manufacture, but of course plastic has a name associated with cheap and nasty.

I am thinking about using 1' drain pipe for a project.

[walpurgis]

I am thinking about using 1' drain pipe for a project.

I've had similar ideas. Using multiple lengths of 1" pipe each cut to a different length around the quarter wavelength of 35Hz and installed into a cabinet, effectively giving an acoustic column with a broadly spread line resonance around 35Hz instead of the usual transmission line 'hump'. It may be a rubbish idea, but I don't recall seeing it tried.

[danilo]

Apparently this has digressed into the odd materials arena. Fastcal is a superior (harder stronger cheaper than plaster of paris) plaster casting goop.
Some are reporting seriously decent result from enclosures glued together from 1" DOW insulation foam.
Initially adopted for v quickly/cheaply assembled proof of concept enclosure builds.. results have shown that many now view the resultant foamies as keepers.
Who woulda thought?

[Pharos]

I thought that the OP wanted clarification on material choice.

I was thinking Geoff, of 1/4 wave as well, and possibly a passive at the bottom facing the floor.
Pipe may have to be blue or yellow - seen on the street side. Very dead and very tight.

[walpurgis]

I was thinking Geoff, of 1/4 wave as well, and possibly a passive at the bottom facing the floor.

A passive radiator at the exit end of an acoustic line has also crossed my mind in the past. However, I think it may give a somewhat loose bass, as it will rely on the slightly dissipated wave energy from the end of the column.

[walpurgis]

I've also considered an open baffle with an acoustic column pipe at the rear, relying on energy from the rear of the adjacent driver to excite it. The pipe would be open at both ends and would be length tuned to the required resonance. It does not take much energy to stimulate resonance in a pipe. This means the benefits of an open baffle are retained, but a little lower bass reinforcement is provided.

[Qwin]

A few current production speakers are using a sandwich of MDF and Chipboard. (eg Quad, Wharfedale).

MDF on the outside for finish and jointing, Chipboard on the inside for acoustic properties.

DIY possibilities if you can clamp up the sandwich well when glueing them.

I've considered this over 24mm Birch Ply for my next build, still to decide which.

[RothwellAudio]

A few current production speakers are using a sandwich of MDF and Chipboard.

Yes, layering materials seems like a very good and practical idea to me too. MDF and chipboard with a layer of plasterboard between the two might be even better.
Less easy to do but possibly very effective would be two layers of some something (MDF, chipboard, plywood etc) with a void between the two which can be filled with builder's expanding foam.

[walpurgis]

Less easy to do but possibly very effective would be two layers of some something (MDF, chipboard, plywood etc) with a void between the two which can be filled with builder's expanding foam.

Or kiln dried sharp sand? You'll end up with floorstanders that weigh a thousand pounds, but they'll sure be inert!

[Qwin]

I seem to remember a thread somewhere, with 15" Tannoys using a sand filled sandwich.

The guy had scrap partition walling from a portacabin type of structure and used this, with the cavities filled with sand.

Huge and VERY heavy, but said it worked well.

I have built concrete speakers in the past that worked well, they were stolen/recovered a couple of times, the thieves just gave up and abandoned them, they were so heavy. I did investigate Lightweight concrete using Pumice stone and sourced a UK supplier for sacks of Pumice gravel at the time, but never progressed it.

[Pharos]

Yes Geoff I agree with your point in post 16, the passive will have to have a high compliance.

I have found that the join alone between two layers of MDF when done with PVA is a great reducer of excitability of self resonance, The two layers cannot transmit the energy easily through the PVA.

The bi-layer with sand goes way back into the 50s, and surprisingly my new ADAM Gannas use this to pretty good effect, with a Perspex window to show the sand.

[danilo]

:lol: reads like you might also have one of those computer cases with perspex sides and 'colourful' leds

Tannoy featured twin layer 'dampened' (glue actually) enclosures for their DMT series of speakers.
Stripper bars always had a few pairs suspended above their 'stages'

[Pharos]

Actually I loathe all forms of ostentation. Do you remember those jumping energy spectrum bar graphs some years ago?

The sand windows are on the back at least, and ironically taped over with black tape on the inside to hide it by the manufacturers, who I suppose thought twice.

I'm still rather unsure about the speakers though.

[fatmarley]

Less easy to do but possibly very effective would be two layers of some something (MDF, chipboard, plywood etc) with a void between the two which can be filled with builder's expanding foam.

Tried that on my last speaker build and made a right mess of it. An easier way might be to glue foam sheet In between two layers - This looks like It could work - LINK (http://www.ebay.co.uk/itm/UPHOLSTERY-FOAM-SHEET-HIGH-DENSITY-60-x-20-ANY-THICKNESS-GREAT-PRICES-/161850590046?_trksid=p2385738.m2548.l4275)

[walpurgis]

Tried that on my last speaker build and made a right mess of it.

I never make a mess of anything! :lol:

[RothwellAudio]

Tried that on my last speaker build and made a right mess of it. An easier way might be to glue foam sheet In between two layers - This looks like It could work - LINK (http://www.ebay.co.uk/itm/UPHOLSTERY-FOAM-SHEET-HIGH-DENSITY-60-x-20-ANY-THICKNESS-GREAT-PRICES-/161850590046?_trksid=p2385738.m2548.l4275)

Yes, some ideas sound good at the planning stage but start to come unstuck when it comes to implementing them. I once made a pair of speakers with double wall cabinets with a void which I filled with sand. It worked - kind of - but was a proper pain in the backside to do. I think the BBC's idea of using bitumen pads was an attempt to make small-scale manufacture a feasible option and avoid too much complexity in the construction of the cabinets.

[struth]

Q acoustic make double walled cabs. dunno how they do it but they are supposed to sound pretty good. A lot of work for the enthusiast tho

[Pharos]

Possibly Andrew, but I would think weight reduction may also be a factor, don't forget that they move stuff around.

BTW after last night's R2 blues programme with Paul Jones, I am very pleased with my ADAMs, the sound was (for FM), brilliant in clarity, perspective and balance; I will keep them.