Best material for new speaker cabs?

I'm planning to build a new pair of cabinets to replace the Lancasters that my Tannoy 12" Golds currently live in. I've found a design that I like (http://melhuish.org/audio/DIYBX18.html) and have obtained dimensional drawings from the (very helpful) author and owner of the cabs from that link.

Next up, what materials shall I use? I'm doing this on a relatively tight budget of maybe £100. Is ply best, if so what type (B&Q cheapo/marine/baltic birch etc), or is MDF perfectly acceptable?

Also, looking at various diy cabs I've seen wall thicknesses that vary from 15mm to 50mm, does thicker really = better or is there an optimum thickness?

 

mdf will give a "dead" sound .....but at leasts its charactor is constant. Oak is good ...but costs

I'd go ply but it may cost more than your budget.

Thickness matters front baffels especially ....the thicker the stiffer its going to be ...but well placed bracing can help a lot.

 

Looks good, similar shape to the Churchill below, if you change the reflex ports. (or you can add another bass driver to make it look like mine):-


Good luck and keep us informed.

 

Hi,

A German magazine made an exhaustive study of this ages ago:

http://www.exdreamaudio.de/Boxen-Baumaterial/boxen-baumaterial.html

A brief summary:

1) 19mm MDF (7.5kg):



The upper response trace is the signal before inserting the test wall into a speaker (so the actual stimulus) the lower is the output after inserting the testwall. Observable is a main resonance around 170Hz which takes long to decay, as the "lossy" mechanism in MDF includes energy storage.

2) 18mm Plywood (6kg):



Same as above, we note that despite having less mass (which would suggest a high resonance) the resonance with plywood has shifted down to 150Hz suggetsing less stiffness, but more crucially, the decay of the resonance is much quicker and very rapid initially and thus suggest a loss mechnism without much energy storage.

3) 44mm coarse fibre board (a little coarser than MDF) 14kG:



The much thicker and heavier material isolates a little better and again due to the coarse and heterogenous structure decay is rapid.

4) For reference - 18mm plywood, 12mm sandfilling, 16mm plywood sandwich (18.5kg):



Only marginally better than cheap, generic thick woodfibre board for a lot of effort.

5) For reference - 20mm Marble (26kg):



Overall, as we can see, attenuation and suppression of the resonance somwhere between 100Hz and 300Hz (paradoxically the resonance seems to go up with added weight, but instead it is actually the increased stiffness from increasing the acthive thickness that does it and outweights the added weight) seems mainly related to weight and thickness (few surprises).

Equally though, going from 19mm MDF to 44mm coarse fibre board does not seem to bring much improvement.

The only real surprise is that Plywood (good grade) decays much quicker than more amorphous and homogenus materials, meaning despite a strong initial resonance peak when excited the audibility of this will be much less as (unlike MDF) Plywood seems to "drone on" much less long.

Okay, what if we apply simple re-inforcements (10cm 18mm board glued on plate edge on):



No material improvement.

How about bitumen Damping Mats (quite expensive in Car Audio Shops):



No material improvement. You need to go to the length the BBC did where they used equal thickness of Bitumen and Plywood to see real improvements.

What if we brace the plate against the opposite board like this?



This is a starting point BTW to the matrix bracing B&W use and which I also recommend.



Wow, now we are cooking with GAS! This is WAY better than 44mm of the same stuff!

What is the upshot?

At similar thickness all materials (except stone and metal - metal was not tested, I used this myself before) resonante in a similar fashion. Plywood will have a less audible and objectionable resonance due to it's lossy nature, if you use a really good grade, (building grade plywood is bad though - see figure 7).

Damping mats and the like improve little. Bracing to opposite walls majorly improves things. If you tie the bracing together in the center of the box so all walls connect together (matrix style) thing get even better.

So, use sensible thickness of Plywood (18 - 22mm) of good grade and brace the heck out of the box will result in the most economical solution.

"Excotic" enclosure materials such as stone and metal are vastly superior but usually not applicable in DIY.

I hope this helps.

Ciao T

 

Wow, that's a pretty comprehensive and very informative reply, thanks very much T!

Ok, decent quality ply with plenty of bracing it is, if I need to stretch the budget a tad then it's probably worth it :MILD:

I'm actually a stonemason so stone cabs would theoretically be possible, but the extreme weight would not be appropriate, nor the cost! Maybe I'll save stone cabs for a 'smaller' project one day.

I'm hoping to persuade a carpenter I know to cut the wood for me, but I intend to do all the rest myself. It'll probably take me a couple of months to complete but am looking forward to the challenge

Dev; I saw someone else's diy version of the Churchills here: http://www.hilberink.nl/codehans/tannoy85.htm

They look great don't they, just not sure I'm capable of that quality of finish!

 

Rather unsual to say this but I think they look much nicer without grills. Can't argue with the quality of finish though.

 

More investigations into material resonance properties here:

http://www.zelfbouwaudio.nl/index.php?option=com_content&task=view&id=18&Itemid=2

The site is in dutch so use babelfish for a crude translation.

It seems that a sandwich of 18mm MDF + 11mm concrete + 80mm fibreglass + bracing yields a near completly inert cabinet material for the frequency range concerned with loudspeakers.

A more sensible proposition is a sandwich of 18mm MDF + 9mm MDF + 10mm concrete + bracing. This is similar to what I used with my cabinets, with the exception of the 11mm concrete which was substituted by 8mm lead bitumen sheets internally. It does yield a dead cabinet.

I'd also recommend building the baffles fairly massively, I use 3" thick MDF construction and then decoupled from the main enclosures using microsorb sheet. This photo better explains:



As you can see the baffles are seperate to the enclosures and attach via long threaded screws which are hidden out of sight behind the driver recesses. The microsorb is placed between the baffle and the enclosure. I also use it to decouple the top enclosure from the bottom one and it works very well here.

The microsorb stuff is available from here:

http://www.percyaudio.com/Catalog.pdf

Look toward page 19 for the description and price.

Also look towards using non-parallel walls to help with standing waves within the enclosure and make sure the cabinet is well braced and try to subdivide large panels into smaller ones and interlock these with the braces to help things further. Again here's a couple more pics to better show what I mean:

Shot of cabinet with some bracing applied:


Shot of subdivided panel interlocked with bracing:



Shot with 9mm MDF 'skin' applied to the whole cabinet:


Construction is nearly as important as the material used.

 

Show off! When you going to make a dedicated website for those Shin? They deserve one.

I'd say moreso. For a sub especially, any MDF vs Ply vs Particle board etc. talk is superfluos IMO, and the manner in which you implement your bracing will have far more effect. Birch Ply is the material of choice, but MDF is fine when you consider the cost (roughly 6x in the UK). If you're an expensive cable loving kinda guy, then Corian or something similarly costly will sound better to you, but otherwise just grab some MDF and brace like hell.

Also if you're going for a very thick baffle then chamfer the inside of the driver cutout.

 

My web authoring skills are pretty poor so I haven't bothered. I do seem to get a fair few questions on the paint finishing process for the gloss black so it might be worth doing something for that.

Agreed.

Which I didn't do

The ATC 9" bass has a pretty crap basket design IMO. Small windows and the spider is virtually butt up against the cone. I think Seas or the Scan sliced papers have the best basket on the market - massive windows, lots of breathing room, minimal reflections back through the cone.

 

Folks,

It is worthwhile noting that the Tannoy Monitor Gold 12" is not a Subwoofer, but a coaxial studio transducer with a crossover of 1KHz and one which needs a whopping big cabinet (say 150 Liter or so).

As a result very large surfaces are unavoidable and the drivers LF coverage up to 1KHz is influenced by the enclosure.

For the kind of enclosure LT has in mind plywood (marine grade or baltic birch) does tend to provide better sound than MDF, even if braced etc. identical. The reasons why are certainly debatable.

What I would PERSONALLY do with a Monitor Gold 12 is to place the driver into fairly compact sealed enclosure, designed to impart minimal colorations and one where the kind of heroic construction methodes evidenced in this thread and others are less rouinous.

This will make them roll off somewhere below 100Hz, suggesting the addition of a power subwoofer of some kind.

That said, I kept my own whopping big Tannoy Corner Yorks untill the bitter and accepted that well braced 40mm multiplex walls still resonante notably in such large enclosures....

Ciao T

 

Surely you could improve on the Tannoy originals by using the many techniques suggested around the net? I do agree that large enclosures aren't particular attractive when considering resonances.

Agreed, although birch ply is extremely expensive around these parts. In the last few years alone I've seen it rise by around 30% at my local Lavers timber yard. If I wasn't such a clutz when cutting stuff I'd use it all the time, as it stands I tend to generate a lot of scrap through trying to perfect cuts. Its a shame because its nicer to work with than MDF, its more stable under moisture and temperature extremes and it possibly makes for a better sounding enclosure, I say that with a heavy heart as an enclosure really shouldn't 'sound' at all ideally.

There's no such thing as overkill regarding enclosure construction, good is never really good enough. I'd like to cast my baffles in a mold and out of concrete at some point, its a matter of finding the time though and also becoming acustom to working with yet another material.

Although what you've suggested here is pretty much what I did with the ATC bass ie. 55ltr critically damped(0.5 Qtc) sealed enclosure rolling off below 100hz with a modelled F3 of 75hz, inroom this extends the F3 to 50hz. So the design clearly needs to be augmented with a subwoofer.

 

thats about what I said at the start...but nice to see why !

 

Hi Pete

Cables arrived today - big thanks

Will give them a serious listen this comming weekend and will report back with the verdict.

 

they have cotton insulation rather than the normal ptfe ....I think it makes them sound rather good !

 

I was wondering what you'd stuffed in the jacket. I've got a good mate who's also heavily into audio over on Sunday so I'll make sure to get some opinions.

I'm using Proel XLR's at the moment, these are the lowest of the low and cost me £5 for a pair of 1mtr interconnects! If there's differences to be heared it should surely show up between your silver and these.

 

Green Glue could be an interesting product http://greengluecompany.com/index.php

 

I have always thought B/BB grade birch ply at 22mm thick, screwed, glued and battoned to be best with removable front and rear, with either a full height figure 8 brace , a couple of standard braces , or a combination depending on cabinet size of course.

Concrete or sand filled bottom, or top , or baffle.
Loads of thick bitumen panels.

Marine grade ply I believe to quite good, it has a central rubber core does it not ? I remember the reviews of a TUG speaker using this material.

I also would prefer a fully sealed and airtight enclosure.

 

Well, picked up all my panels yesterday - pre-sawn at the timber yard to make life a lot easier. Went for 18mm birch ply, grade B/BB. Am doubling up the thickness on baffle. They only had two sheets of 18mm left and one was partially marked so have only got the side panels/baffle and enough offcuts to make the tops and bottoms. All internal bracing will have to be mdf or cheaper ply. Total cost so far: £72 ish.

So far so good.

Difficult bit next; corner fixings. As the cabinet are trapezoidal so no right angles I'm using seperate corner pieces cut/routed to accept/hold the panels. The attached pic shows the corner used by the cabinet designer....

But, I'm considering using circular corners (in section - i.e. poles) instead, as they will be easier to rout the slots for the panels and I won't need to cut tricky angles, and could double up as feet/legs - whaddya reckon?

One more thing, as I intended to sand and polish or varnish the ply to finish them, do you think glue and internal bracing will be enough to hold these together, or should I accept that I'll need put up with visible screws?

 

Glue with internal battons will be fine. This is how I finished mine as I couldnt be arsed to do mitred corners. Be warned, my Birch Ply was a bastard to sand to a decent finish as it seemed to be cut at 90 degree's to the grain.




Paul.

 

Interesting ideas on that site. What can be found around the house? Speak and spell driver, a card box and a drain pipe, lol...

http://melhuish.org/audio/DIYTQ7.html

http://melhuish.org/audio/DIYTQ6.html