SpeakerTalk

[ahnanowt]

Hi, i recently inherited what i first thought was a pair of concerto's from my father inlaw, then i discovered that he built them himself about 40'ish years ago. I am re-building these speakers soon but my own cabinet design, mainly because they are a tribute to both my inlaws who both died within a year of each other, and they also need to look good too!
The drivers i have are SP1044 x2, SP1003 x2, SP1032 x2 with SP1004 - DN12 crossover and 2x SP1014 - (brand harry spankers) - one of which had cone perfectly inverted or convext or it had an inny not an outty! that was until i managed to pull it back out. The other was going to be a home-made guitar amp before he died, he told me his old loud speakers had to be dimantled along time ago beceause the cabs became damaged and looked tatty!
just when i had finally worked out what i had and what i was doing (hahaha..)
i have just found 1 more t27 and a coles 16ohm tweeter and another pair of crossovers - SP1106 - B2180 with 3way not 2way. I'd appieciate any and all comments,help and advice.

[speakerguru]

Welcome to the forum.

The SP1044, 1003, 1032 and 1004 are a set which will produce a DIY Concerto/Kefkit3 pair of speakers. The B200 SP1014 are not needed. Your relative would have been disappointed with them as guitar speakers. They are far too insensitive and lacking in high frequency response compared to a typical paper cone 12" guitar speaker. The one that was inverted must have been severely overloaded, either electrically or mechanically or both!

[ahnanowt]

Thanks for the welcome, i've been using this site for quite a while now, trying to soak up as much info as i can. The guitar amp was only ever supposed to be a little practice amp, he never finished it but i managed to get it working - doesn't sound too bad even with the very slightly creased cone. I'm going to finish it for him, so my daughter can use his guitar.

[ahnanowt]

I am going to build my kk3 out of 20mm thk solid oak with lignum vitae for added strengh and rigidity. The cabs will be sat on a solid oak plinth - 5 inches thick. I've based my design on the German tall and slim . Has anyone out there actually tried building speaker cabs out of solid oak or do you all just re-gergitate what everyone else says " you've GOT to use mdf or bb ply".
In my opinion the only logical reasons i can think of why people don't use solid oak (or any other hard-wood) is A - the price and B - lack of skill!

[speakerguru]

Personally, I would make guitars or carve green men out of solid oak but each to his own.

If you want a speaker cabinet to be hi-Fi and not add it's own colouration, it should be heavy, rigid AND well damped. Rigidity is better achieved by bracing, a la B&W matrix, rather than thick walls. You could always use the oak for a decorative veneer, if you want that look.

[ahnanowt]

Aren't high-end speakers made from solid wood?
My cabs will be very heavy and ridgit and along with modern dampening materials should resolve any unwanted resonance's.
The oak i am using is older than me and has no knots or imperfections - it is beautiful quater sawn timber which not only looks good but is stronger than "normally sawn" timber. The lignum vitea or iron-wood is extemely hard and heavy. So weight won't be a problem (until i come to move them that is!) nor will rigidity as i will be using proper joinery joins, and bracing internally.

[ahnanowt]

The use of veneers was only invented to keep down the build cost, as a say 3mm or smaller thickness of hardwood is very much cheeper than a regular sized timber!
As a tradesman i will always try to use the best materials to achive the best results, putting on external cladding or veneer is like putting lipstick on a pig!
But thats just my opinion,and like arseholes - everyone has one!
I know several of you's are electronic & or sound engineers and i would never question your knowlege on such matters but i think you proberly spend a fortune on expensive equipment to achive the best quality sound you can, if you spend a little bit more £££'s on quallity timber it will only cost a few quid more than bb ply or mdf with veneer.

[audiolabtower]

The traditional hi fi route was as heavy a cabinet as possible. However the BBC did a lot of research in this area and found the thin wall approach was easier to damp resonances and subjectively better. They found very specific plywoods had inherent self damping, one theory from micro friction between the layers. Residuals were taken care of with bitumen type sheets. A heavy thick solid wood was more difficult to control with resonance lasting longer., and less able to be controlled with added layers. Later the problem was to find a cheaper solution to the specific plywood when it became more expensive and one successful route was the matrix type construction keeping resonances to shorter wavelengths. So without accelerometer tests backed up by subjective tests it is not quite so simple to say what is best.

[SaSi]

You can go the good quality heavy wood with braces and bitumen sheet damping. I have done that for a 200lt enclosure with 20mm high quality plywood, hardwood braces (3 across the height) and 9mm bitumen sheet all around the inner faces of the cabinet.

Works great, removes coloration and even a 12" woofer banging inside this enclosure mounted on a 20lt subenclosure (to get as high a Q as possible) results in minimal output from the outer enclosure and negligible readings from accelerometers mounted dead center on the panels.

There's one catch - assuming cost and effort are unimportant. I have it mounted on wheels (thankfully) and I need another strong person to lift it up to the bench. I can barely slide it to it's back if I want to open the screwed panel to access inside.

As audiolabtower wrote, there are better ways to achieve the same result, other than brute force. And while the late Mr. Briggs even suggested double wall sand filled enclosures or enclosures made of bricks, engineering the issue can come up with more elegant solutions.

The heavier the enclosures are, the more enegry they can store in their mass so the harder it gets to damp that vibration. Braces and bitumen pads become larger and heavier adding to the issue while solving part of it.

The stiffer the wood panel it gets, the higher the Q of the resonances and the higher the frequency. And if you don't do something to dampen that, it gets really audible.

One additional thing that doesn't help solid timber to be a good material is the fact that it's "alive". It absorbs moisture, loses it, expands and shrinks, in every axis, causing several issues from stress to cracks. Plywood is much better than that. MDF is dead dust compacted and glued together, so from a mechanical point of view better than plywood. But has other maladies, not the least of which is being a bitch for your lungs to work with it (cut, route, sand) and generate dust.

Check about constrained layer enclosures, made of alternating materials that damp and stiffen using the least mass possible. Cheap plywood is actually closer to this concept than marine grade birch. Two 4mm pieces of birch with a 3mm bitumen sheet make for an even better panel with dense bracing.

To go to extremes, an acrylic doped carbon fiber enclosure damped by a single layer of bitumen pads may be as good or better than my huge coffin described above and will certainly be way easier to lift.

And in full honesty, nobody said loudspeaker enclosures must be made of wood. There is a list of well built and not cheap enclosures made of composite material, including plastic (the KEF 105 and 107 pods come to mind first), aluminium (JR149, a few elegant looking Technics speakers I collected, like SB-F1, SB-F2, etc) and even carbon fibre.

It was just plain obvious back then, almost 100 years ago, that if you need a stiff panel to mount a speaker driver, a wooden panel was the most readily and production friendly material available. And when baffles turned into boxes, wooden boxes were as obvious as a round wheel is.

I don't argue your point that mdf with veneer is extremely popular among manufacturers due to cost and ease of production, but if you want to see what crazy guys who enjoy spending time and money for material to build loudspeakers are doing, visit www.diyaudio.com and see. Questions about solid timber come from time to time and the documented responses are "avoid this".

You may check this thread, and enjoy:
http://www.diyaudio.com/forums/multi-way/276721-best-cabinet-material.html

and this:
http://www.bbc.co.uk/rd/publications/rdreport_1977_03

[audiolabtower]

Good post.

[ahnanowt]

Thanks for the replies, alot of helpfull info there. Both this and diyaudio are the main sites i've been using for researching the 'dark arts' of speaker building. I have followed all the above links and had to re-read alot/most of it because over the last 11 months i have probely read the majority of posts on both sites and forgotten most of it!