AndrewT said:
Hi,planet10 said:
it was intended to be and my wording also shows that my view/comment is open to change.
Your next post seems to confirm that high Q has some advantage
certainly some other speaker manufacturers have gone exactly that route with with exotic box materials that are very stiff, very light and adequately braced in proportion to size.
Cal also suggests that the Hi Q sounds nicer.
I think we all accept that a speaker box should add little colouration.
Do we all accept that sufficient bracing MUST be used to minimise panel vibration displacement and/or achieve resonance tuning?
AndrewT said:
The material doesn't even have to be exotic. Take the B&W Nautilus series... construction is a bit exotic (it takes huge dies to press the sheets of plywood into the curved back), and the matrix bracing takes a CNC to do easily.
An intelligent bracing scheme is essential to a box being quiet. No matter what material you are using.
dave
Scottmoose said:
Oh, so this is a forum where a person cannot state his own personal opinion? The only opinion that matters here are the ones that agree with you?
Where's free speech?
Is this a fascist dictatorship?
My mission...patronizing...stir up...contravertial statements. What did I say to you that has offended you so much?
If you don't like what I have to say, put me on your ignore list with all of the rest who don't agree with you.
Re damping and resonance, now I'm getting confused. I thought that they were descriptions of the same thing from opposite 'ends'. So, a well damped box/alignment/piece of wood has less resonance than 'badly' damped box/alignment/piece of wood.
By example, silicon gel is well damped and a tuning fork is badly damped (hit both with a hammer and only one will ring).
Am I looking at these two words slightly askew (my word of the day - substitute 'wrong')?
If I grab a piece of MDF and a piece of ply, same size, same thickness and (almost) same weight - when rapping them with a knuckle, the plywood sounds less 'dead' than the MDF. Which is what I've interpreted to be the MDF is better damped and the ply is more resonant.
I'm not trying to continue the MDF vs ply stoush, but try to understand the terms as they apply to anything.
By example, silicon gel is well damped and a tuning fork is badly damped (hit both with a hammer and only one will ring).
Am I looking at these two words slightly askew (my word of the day - substitute 'wrong')?
If I grab a piece of MDF and a piece of ply, same size, same thickness and (almost) same weight - when rapping them with a knuckle, the plywood sounds less 'dead' than the MDF. Which is what I've interpreted to be the MDF is better damped and the ply is more resonant.
I'm not trying to continue the MDF vs ply stoush, but try to understand the terms as they apply to anything.
MJL21193 said:
I think Planet is wrong and I have been reading the thread.Cloth Ears said:
MDF is fairly well damped (Lo Q). In comparison, plywood is less damped (higher Q). And that rap test is valid if you also take account of the extra stiffness that the plywood has compared to MDF.
Cloth ears,
you're understanding of the terms seems OK to me and that rap test tells much. Plywood is considerably less dense than MDF.
my well document preference for the sonics (vs measurements) of plywood cabinets vs MDF aside, (based on building more than a few pairs from each) - as far as "damping" is concerned, is there not more to it than just the material's density?
cardboard is certainly less dense than aluminum, and yet can be well enough engineered and braced to fabricate light duty furniture
http://www.treehugger.com/files/2006/12/davidgraas_furn.php
(just don't get it wet)
which would be "less" resonant, 2 ft^2 of 18ga aluminum, or 3 ply corrugated cardboard of equivalent mass?
cardboard is certainly less dense than aluminum, and yet can be well enough engineered and braced to fabricate light duty furniture
http://www.treehugger.com/files/2006/12/davidgraas_furn.php
(just don't get it wet)
which would be "less" resonant, 2 ft^2 of 18ga aluminum, or 3 ply corrugated cardboard of equivalent mass?
Colin said:
Thanks Colin. BTW, you're not alone.
chrisb said:
The cardboard would be less resonant (due to high inherent damping, though aluminum has some self-damping quality.). Is it suitable for speaker building? It's possible, but not practical.
With regards to aluminum, it is suitable for speaker building, but untreated, it's not the most practical material either. Also, it is expensive and difficult for the average DIY guy to work with.
MDF has a lot going for it: it's cheap - if you funk up a piece, you're not out much money. It's fairly easy to work with, the only negatives are the toxic dust and the back-breaking weigh. It's fairly well damped, and if proper construction methods are used, it will give a very silent box. It finishes nicely - you can rely on a smooth result whether you choose to paint or veneer.
All in all, a very practical material for speaker building.
planet10 said:
It would definitely store up energy as heat and then slowly leak it out. Plywood would do the same, but probably less. Both should be activated by the air pressure waves (how much depends on thickness and construction) and should vibrate "in sympathy". The plywood (of similar size, shape and thickness) would probably release more energy as sound (or air movement) and less as heat, than the MDF.
[opinion]
For a sealed box (and probably a ported one) I'd go the way of MDF. And I heavily brace. And pack a bit of foam/stuffing/dog hair (Samoyed hair makes great stuffing). Having your sealed box sing along in time with the music is not a good thing. I could probably get the same effect with plywood, but I'd have to do some myself as I tend to use 1" thick walls on my boxes. And I'd probably have to brace a bit more to stop them singing.
For a TL, well I'm experimenting with some 1/2" ply (found some molded kids' benches and thought "what if I stand them on end?") and I guess I'll find out fairly soon. After, that is, the deck is finished and the new car is bought.
And I have no idea about horns or OB. But I've got some things lined up on both fronts. The OB might not be affected so much, and in fact might benefit from being a bit more resonant. The horn possibly also. I'll look at it from the point of view that they are essentially extentions of the cone, and movement may not be a major problem.
[/opinion]
But I do agree with dave on one thing:
"... and i really only need to satisfy me."
MJL21193 said:
I have no problem with you John; life is too short. And I'm all for hearing your views (if you actually knew me, or had read some of my wider posts you'd belive that), but the way you frequently express them makes them appear as if they are somehow facts rather than a personal opinion. To cite your driver post as an example, you remarked that you won't buy anything more than $250 'because there isn't one in production today that is worth more than that.' I didn't see a 'in my opinion' attached to that, so it doesn't come across as a view, but as a blanket statement. This can be rather misleading, especially for newcomers. All I'm asking is that you might take a little more care to stress when something is your view or not. I'm just as guilty I'm sure, but I do make a valiant effort to try to remember to stress if something is my opinion or if it's a fact.
I assume therefore that all of the above makes me a fascist and anti free speech (I trust those phrases have no personal reflection?). Back on planet Earth, as people who know me & have read my posts know perfectly well, I honestly couldn't care less if they agree with me or not. I give my view, people can take it or leave it, but it's always supported with something. If it wasn't, I wouldn't say it. It may interest you to know that this particular fascist (who has spent a great deal of his own time trying to help people, designing well over a thousand cabinets for them to date etc.), has no ignore list. I didn't know there was such a feature.
Re the respective dampings, for those who missed the earlier remarks, here they are again, in condensed form.
Setting the properties of the material itself aside for a minute, and concentrating upon the structure, plywood is made of numerous layers, while MDF has certain layered properties, but these boundaries are far fewer and less defined.
Energy, when travelling through a medium, hates boundaries -you will have losses (I know, I know, you can't just 'loose' something per-se, but you know what I mean) whenever one of these is encountered. Ergo, a panel made from multiple layers is inherently better damped than one made from a single layer of the same material. Nothing novel about that, the physical knowledge has been around for years -I cited the 19th century ship armour a page or two back, and Ron & I have discussed it via PMs in other applications. The physics behind it are somewhat more complicated, but the prinicple is easy enough to follow.
Ergo, if I wanted to use MDF, I'd rather be using multiple thin layers of the stuff than a single thick layer. I still don't like it as the properties of the material itself don't work great for me -you need a thicker (& far heavier) panel to be as stiff as a sheet of decent ply. I agree with John's observation that you can worth with MDF in such a way at to push the panel's natural resonance upward, above the cabinet's passband (as is usually done with ply), rather than downward, as is more usually done (if it is). My only concern with that would be because MDF is inherently less stiff as a material, the structure will be much weaker unless a huge amount of bracing is used.
Setting the properties of the material itself aside for a minute, and concentrating upon the structure, plywood is made of numerous layers, while MDF has certain layered properties, but these boundaries are far fewer and less defined.
Energy, when travelling through a medium, hates boundaries -you will have losses (I know, I know, you can't just 'loose' something per-se, but you know what I mean
) whenever one of these is encountered. Ergo, a panel made from multiple layers is inherently better damped than one made from a single layer of the same material. Nothing novel about that, the physical knowledge has been around for years -I cited the 19th century ship armour a page or two back, and Ron & I have discussed it via PMs in other applications. The physics behind it are somewhat more complicated, but the prinicple is easy enough to follow. Ergo, if I wanted to use MDF, I'd rather be using multiple thin layers of the stuff than a single thick layer. I still don't like it as the properties of the material itself don't work great for me -you need a thicker (& far heavier) panel to be as stiff as a sheet of decent ply. I agree with John's observation that you can worth with MDF in such a way at to push the panel's natural resonance upward, above the cabinet's passband (as is usually done with ply), rather than downward, as is more usually done (if it is). My only concern with that would be because MDF is inherently less stiff as a material, the structure will be much weaker unless a huge amount of bracing is used.
Scottmoose said:
Hi Scott,
Life is too short.
I do, at times, come across a tad harsh. Sometimes I try to (you're right, to stir things up, but no malicious intent), other times it just seems that way (given preconceptions).
Whatever the case, I like to have my say. If you don't agree with my views, argue with me, reason with me or ignore me. Don't ask me to be quiet.
I take every word in every post in every thread here with a grain of salt; as hearsay or the opinions of the author. I expect my own to be taken the same way (there's ample proof that some of my excellent advice is being ignored and pawned off as bluster from a know-it-all newb
). That's ok, we live to fight (discuss) another day. As long as every opinion can be heard, even the controversial ones, the life we have left will be much more interesting.
Scottmoose said:
I know that MDF is less elastic than plywood, but I'm not so sure about the stiffness, especially with the panel sizes used for the average speaker.
One way to find out (if this info is not readily available) is to conduct a deflection test. A piece of MDF and a piece of plywood, same thickness (say 1/2"), same size (say 5" x 20"). Place these strips with their ends supported, put weight on the centre and measure how much each deflects.
I have drawn a crude illustration of what I mean below.
Anyone volunteers? Or should I do that too?
PS. I've been in construction for most of my life, both residential and big-buck commercial. A well built speaker cabinet, even made from MDF, is one of the strongest structures I've seen.
Attachments
ronc said:
Hi Ron,
Mdf is a sandwich layer construct, is it not? Outer compressed "layers" with a less dense core. Doesn't sandwich layer construction have high strength as well? With the nearest layer to the force resisting compression, while the opposite side layer resists tension.
I know, MDF is not the greatest example of a sandwich layer, but still, it has some of it's properties.
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