A DIY lighter cabinet? I'd like one made!

[charic]

[quote name='alexclaber' timestamp='1345204768' post='1774928']
I felt the same about my trusty Peavey combo!
[/quote]

I can see it now :

[b]Barefaced : Fed up of your thieves pulling muscles? Try our new lighter cabinet, guaranteed 100% thief satisfaction[/b]

[b][/b]

[alexclaber]

So far two Barefaced cabs have been stolen, both Midgets! I hate to think how many micro-amps vanish before/during/after gigs...

[xgsjx]

[quote name='alexclaber' timestamp='1345205158' post='1774934']
So far two Barefaced cabs have been stolen, both Midgets! I hate to think how many micro-amps vanish before/during/after gigs...
[/quote]

I'm picturing a couple of dwarfs running off with 2 Dubsters on their backs???

[stevie]

[quote name='Phil Starr' timestamp='1345188542' post='1774636']
I haven't checked the Young's modulus for the various plys (Basically how bendy they are) so I don't know which timber will be more resonant. I might look that up too.
[/quote]

The Young's modulus of birch ply is 300% higher than MDF or chipboard. As we know, stiffness is the key criterion for good bass cabinets.

[thinman]

[quote name='alexclaber' timestamp='1345204768' post='1774928']
I felt the same about my trusty Peavey combo!

Phil, if you maintain (or increase) stiffness through bracing, whilst lowering mass, you raise the resonance of the panels to the point that they are no longer excited by pressure but instead excited by the backwave, and the backwave and the resulting panel emittance can be damped effectively, unlike pressure changes which you don't want to damp (as they excite the port). In the process you also reduce the backwave reflection which exits through the cone. Personally I consider panel resonance in a loudspeaker a horrible thing unless it's being used to cancel unwanted energy - the last thing I'd want is significant acoustic energy radiating from a panel, with particular consideration being given to how it screws up transient response.
[/quote]


I'm with Alex here - you could probably use 12mm birch or poplar ply but you will have the added complexity and marginal weight of the required bracing to eliminate any resonance. Bracing could be web-type braces and/or dowels across the height/width/depth of the cabinet. Probably still a gain over using 15mm or 18mm if done right. Just look at the construction of wooden aircraft for a bit of inspiration!

[Dood]

This is making for very interesting reading! I was hoping to squeeze at least 10kg off the weight, but this might not be possible then? It just might not be worth the work. I could be better off going for a 410XL and maybe porting that 5" driver into the cab.. That will sort me out with a 32Kg box. Bass end will be different, but with the same soeakers in both the 4.5 and 410, hopefully that character will be retained, along with the 18mm birch ply!

[KingBollock]

Isn't part of the difference in weight down to the 5" driver in the 4.5? I imagine it weighs quite a bit it's self.

If you did decide to go for a more dispersal friendly configuration, you could have a wooden frame and cloth grille made, that would be significantly lighter than the current metal grill.

Are there any plywoods that are made up of half low density wood and half high density wood? So that you could have the cab made with the high density on the inside. I don't know if that would help any. Also, what would happen if you were to treat the inside of the cab with something like Plasticote, or some other thick and hard paint? Or even a sheet of plastic or thin sheet of aluminium? I know aluminium wouldn't help with the weight, but I'm curious.

[Mr. Foxen]

Hard shiny inside surface is pretty much what you want to avoid, hence lining with foamy/fluffy stuff.

[Matte_black]

I'd make it vertically aligned with the 5" on top. And sealed too, like two 210XL in one.
12mm plywood is good. I've made a vertical 410 with marine-grade Chilean Poplar plywood... it's nice and doesn't weigh a ton. In the picture the third woofer wasn't bolt-on as it was defective but Thomann promptly sent me a replacement... good guys.

[Phil Starr]

Hi Alex, I don't think we've swapped ideas before but can i add my bit to your fan club here. I have always loved your articles in BGM, intelligent, honest and stimulating.

[quote name='alexclaber' timestamp='1345204768' post='1774928']

Phil, if you maintain (or increase) stiffness through bracing, whilst lowering mass, you raise the resonance of the panels to the point that they are no longer excited by pressure but instead excited by the backwave, and the backwave and the resulting panel emittance can be damped effectively, unlike pressure changes which you don't want to damp (as they excite the port).[/quote]



[quote name='alexclaber' timestamp='1345204768' post='1774928']Personally I consider panel resonance in a loudspeaker a horrible thing unless it's being used to cancel unwanted energy - the last thing I'd want is significant acoustic energy radiating from a panel, with particular consideration being given to how it screws up transient response.
[/quote]


I can't disagree with any of this at a factual level and the little science training I have wouldn't let me want to do it any other way anyway. the sound from any panel is going to be distorted in so many ways.

[quote name='alexclaber' timestamp='1345204768' post='1774928'] In the process you also reduce the backwave reflection which exits through the cone. [/quote]

I'm not sure this is right though, surely an inelastic reflection conserves energy and is the most efficient way of reflecting the sound back through the cone and setting up standing waves.. (Assuming it is parallel to the baffle) A thin flexible panel would radiate some energy backwards and lose some as heat. The best way of avoiding this would be to have no rear panel as in some transmission line cabs or by using an angled panel behind the cone.

I think all I wanted to say to the OP was to give some indication of the weight saving to be gained and what significant changes in sound might occur. Using the current drivers and going for the lightest option 12mm Poplar with some judicious lightweight bracing might save 6kg or thereabouts. Panel resonances would be bound to change upwards as you say and would probably clean up the sound a little but I wouldn't expect there to be a dramatic change in sound.

[Peaty]

Hi dood, you might also check out Robins timber in bristol as a source of light weight ply...try there marine dept.

http://www.robbins.co.uk/general/sheet_materials.asp

[LukeFRC]

I'm sure I used to know someone who had like a normal 4x10 but the back and sides were molded out of one piece o brown fiberglass. Weighed nothing. but was very very unbalanced as all the weight was at the front where the speakers were. Never seen anything like it since

[Dood]

I'm not sure the project will go ahead after all. I'd really hoped to make much more of a weight saving than the suggested figures in this thread. If i coud have saved 10Kg or more then the cost would have made it worth it for my poor back.

Next option would be 2x 2.5XL cabs, but they aren't made any more.

[JPJ]

So if rigidity of the cabinet is the goal, why is nobody using ultra lightweight aluminium honeycomb panels? I can vouch for the rigidity of this stuff and you can get it foam filled so no nasty voids to excite.

[Dood]

[quote name='JPJ' timestamp='1346779817' post='1793144']
So if rigidity of the cabinet is the goal, why is nobody using ultra lightweight aluminium honeycomb panels? I can vouch for the rigidity of this stuff and you can get it foam filled so no nasty voids to excite.
[/quote]

Hmm, I don't know JPJ - I'd hazard a guess at cost and difficulty to machine? Wood is easier to throw in to a CNC and cheaper. Wow, that'd be a pretty ultimate Hartke cabinet! Aluminium cones and aluminium cabinet! but that's one too many 'alooominums' for my liking! heh, ey Larry!!

[JPJ]

[quote name='dood' timestamp='1346797146' post='1793512']
Hmm, I don't know JPJ - I'd hazard a guess at cost and difficulty to machine? Wood is easier to throw in to a CNC and cheaper. Wow, that'd be a pretty ultimate Hartke cabinet! Aluminium cones and aluminium cabinet! but that's one too many 'alooominums' for my liking! heh, ey Larry!!
[/quote]

Well you machine it with a standard router with a carbide cutter, granted you would need some sort of frame to attach it to, but all the jointing is done with adhesives so no nasty fasteners required. Fill it full of wadding (like any good cabinet) and polish the bejesus out of the rest of the cabinet and you'd have a thing of undoubted shiney lightweight beauty.

[Dood]

That's sounds mighty interesting! - If I had the cash I'd love to test the theory, just to have something a bit different!

[Phil Starr]

[quote name='JPJ' timestamp='1346779817' post='1793144']
So if rigidity of the cabinet is the goal, why is nobody using ultra lightweight aluminium honeycomb panels? I can vouch for the rigidity of this stuff and you can get it foam filled so no nasty voids to excite.
[/quote]

It's been done for hi fi speakers the Celestion SL 600 was the first I knew about. Quite a successful design though I found it a little dry sounding, it had an early metal dome tweeter if my memory is good and it cost an arm and a leg.

The thing is that you have to eventually engineer to a budget and you rapidly reach the point of diminishing returns. There's little point in spending an extra £1000 to get the ultimate rigid and light cab when the difference on stage is almost inaudible when compared with the best existing conventional speakers. Give most of us £3000 to spend on guitar amp and cab and the bulk would go on the bass, not many of us would spend £2000 of that on a cab however good.

[alexclaber]

[quote name='Phil Starr' timestamp='1346673590' post='1791725']I'm not sure this is right though, surely an inelastic reflection conserves energy and is the most efficient way of reflecting the sound back through the cone and setting up standing waves.. (Assuming it is parallel to the baffle) A thin flexible panel would radiate some energy backwards and lose some as heat. The best way of avoiding this would be to have no rear panel as in some transmission line cabs or by using an angled panel behind the cone.[/quote]

I have a suspicion that a thin-wall but heavily braced panel can exhibit high rigidity at lower frequencies, thus giving good lows but the sections between the braces can have a degree of damped flexibility at higher frequencies which can absorb unwanted midrange, especially if those braces are positioned to give each part of each panel a different resonant frequency whose harmonics are an non-coincident as possible with each other panel section. Unfortunately I haven't had a chance to scientifically test this but it makes sense from a mechanical engineering perspective and it certainly sounds good in practice!

[Mr. Foxen]

[quote name='alexclaber' timestamp='1346950984' post='1795292']
I have a suspicion that a thin-wall but heavily braced panel can exhibit high rigidity at lower frequencies, thus giving good lows but the sections between the braces can have a degree of damped flexibility at higher frequencies which can absorb unwanted midrange, especially if those braces are positioned to give each part of each panel a different resonant frequency whose harmonics are an non-coincident as possible with each other panel section. Unfortunately I haven't had a chance to scientifically test this but it makes sense from a mechanical engineering perspective and it certainly sounds good in practice!
[/quote]

So the idea point for a brace is the same sort of deal as the idea place for a piano hammer to strike the string, where it doesn't hit any harmonic?

[Phil Starr]

[quote name='alexclaber' timestamp='1346950984' post='1795292']
I have a suspicion that a thin-wall but heavily braced panel can exhibit high rigidity at lower frequencies, thus giving good lows but the sections between the braces can have a degree of damped flexibility at higher frequencies which can absorb unwanted midrange, especially if those braces are positioned to give each part of each panel a different resonant frequency whose harmonics are an non-coincident as possible with each other panel section. Unfortunately I haven't had a chance to scientifically test this but it makes sense from a mechanical engineering perspective and it certainly sounds good in practice!
[/quote]
I think I agree with this in part. moving resonances up moves them away from the low frequencies where the highest energy inputs are in the cab so the problem is reduced. Critical positioning of the braces to spread the panel resonances has to help too as you won't have a single resonance dominating as with an undamped panel. Having said that we are much more sensitive to sound in the midranges which adds another layer of complexity.

The bit I am less happy with is the transmission of sound. My understanding is that the energy is absorbed by the panel and that some of it is converted into kinetic energy in the panel, some will be transmitted laterally within the panel and some vertical movement of the panel will occur which will drive the air outside the panel. This will be frequency dependent so the net effect is that the panel acts as effectively as a frequency dependent filter. The absorption of sound in the panel will depend upon its composition, some will be turned into heat. Ply is quite a lively material compared with MDF or chipboard and is even used in cheap guitars and cajon fronts for this reason. The laterally transmitted energy will either be reflected if it meets a hard junction or absorbed at a soft junction. I would guess that how panels are fixed to each other and how braces are attached is crucial. It's a pretty complex system. I would guess that nowhere near all these resonances would be heard in a real life situation though. A friend of mine has just been appointed to Land Rover to work on this in their cars, I'll have to bore her on this when she gets back to see what modelling they do.

[Phil Starr]

[quote name='Mr. Foxen' timestamp='1346952187' post='1795305']
So the idea point for a brace is the same sort of deal as the idea place for a piano hammer to strike the string, where it doesn't hit any harmonic?
[/quote]
That's exactly right, which is why the advice to put the brace straight across the middle (given by someone who should know better in another thread) wasn't very clever. You don't damp bass string by putting a finger above the 12 th fret after all.

[Mr. Foxen]

[quote name='Phil Starr' timestamp='1347007171' post='1795826']
That's exactly right, which is why the advice to put the brace straight across the middle (given by someone who should know better in another thread) wasn't very clever. You don't damp bass string by putting a finger above the 12 th fret after all.
[/quote]

But I would go for the middle if I was trying to reduce its possible displacement from a force applied along its length. Depends on thinking in resonance or flexibility. Because knocking stuff up an octave might put it out of a bass loss because of bending place, and into a middier place that lining will deal with.

Edited September 7, 2012 by Mr. Foxen

[Phil Starr]

Resonance isn't a necessarily bad thing of course. If you are building a double bass then the resonances of the body are all a critical part of the sound and your design philosophy for an instrument amp could quite reasonably regard the cab as an extension of the instrument and a part of the 'sound'. Many older designs did this though newer ones tend to go for a flat response and use electronics to mimic the 'vintage' sounds as well as offering new timbres to play with.

However if you don't deliberately want a resonant cab then you really should avoid the middle, Even a slight displacement (11th fret?) will have the same effect of raising the frequencies an octave but there will just be much less of them. The cabs we are talking about are lightweight rigid cabs here and are meant to be non resonant.

Stuffing, in the sense of the polyester/fibreglass fluffy stuff doesn't impact on panel resonance at all, it is meant to affect only the transmission in the air in the cab. There are heavy bitumnent or mineral loaded rubber pads that are designed to damp panelk resonance but I don't think you mean these.

[Mr. Foxen]

I sort of assume transmission in the air is the thing exciting panel resonances, and the unevenness from lining meant that the energy reaching the panel was less coherent, and thus less able to excite resonance. Also I was picturing knobbly foam, since that is what I've lined cabs with.