Bracing material?

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Generally it is a good idea to make the bracing from a different material than the cab itself and use a lossy adhesive ie one that does not set solid.

Unevenly spaced is also a good move as JRKO said and to make sure that it is not parallel to the cabinet walls.

I figured so. Not to spiral back into mdf vs. the world but my current plan it to use mdf for the cabinet and ply for the bracing base on what I have read so far.
 
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Available data shows that between 500 and 700 Hz the perception of panel resonances is higher than above or below.

Which has the requirement that the panels are excited into resonating.

may be true from an esoteric, but not from an engineering POV.

Not at all. The purpose of speakers is to play music. That is the excitation source for any resonance.

dave
 
may be true from an esoteric, but not from an engineering POV.

Not at all. The purpose of speakers is to play music. That is the excitation source for any resonance.

Just quickly played a 500hz test tone. As far as I can figure theres no way you could excite a stiff ply panel into vibration/excitation at that frequency with a standard design with music at normal listening levels.

If you got a system to the level required you'd be more worried about hearing loss than vibration in the box anyway.

'most' systems just don't get played that loud, or are even capable of that volume. Also I don't know anyone who listens to high volume test tones for pleasure
 
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Which has the requirement that the panels are excited into resonating.

Which they are.

Not at all. The purpose of speakers is to play music. That is the excitation source for any resonance.

Music consists of a combination of tones. Play a special measurement signal, record the output of the panel, and you can predict the response to ANY other signal.

JRKO said:
Just quickly played a 500hz test tone. As far as I can figure theres no way you could excite a stiff ply panel into vibration/excitation at that frequency with a standard design with music at normal listening levels.

How much will a midrange unit be excited at 500 Hz? Have you hit a panel resonance at 500 Hz?

If you got a system to the level required you'd be more worried about hearing loss than vibration in the box anyway.

Panel excitation is mainly a linear process, so no matter how loud you play, the ratio between direct sound from the drivers to radiated sound by the panels is always the same.
 
Just quickly played a 500hz test tone. As far as I can figure theres no way you could excite a stiff ply panel into vibration/excitation at that frequency with a standard design with music at normal listening levels.
Given the size of the typical speaker you guys build, no. But if you have panels of more than a couple square feet, it can be easily done with some rockin' roll.

If you got a system to the level required you'd be more worried about hearing loss than vibration in the box anyway.
Huh? What say? Speak up, son!


BTW, Lowe's sells 1/4 x 2 oak strips that work well to make egg-crate bracing. Braces running across from panel to panel sometimes make it ring more.
 
Panel excitation is mainly a linear process, so no matter how loud you play, the ratio between direct sound from the drivers to radiated sound by the panels is always the same.
Panels have a damping factor, so at low levels, it's not so linear. Saturate the damping - then it becomes linear until the panel goes into breakup mode. That's when it sounds really nasty.

Mind you, I know these things because I've built studio monitors. Real ones. They're big, and they do 110dB without strain. Currently I'm working on guitar boxes. Resonances in the ~500Hz midrange are a real problem. Of course, the pressure levels are stupid loud. ;)
 
How much will a midrange unit be excited at 500 Hz? Have you hit a panel resonance at 500 Hz?

Would be interested to know what volume is required to make an unbraced/undamped sheet of 18mm baltic birch ply that is 95cm x 40cm start resonating at 500hz so that it is audible with music (not test tones)?

Given the size of the typical speaker you guys build, no. But if you have panels of more than a couple square feet, it can be easily done with some rockin' roll.

At some volume i'd guess thou? So with P10 size boxes not an issue. With the Emken, maybe (panel size above) and real big JBL/Atec style its an issue unless you don't brace/damp or brace/damp poorly. Other than that its a pure engineering issue (how do we damp & brace this military supersub that starts earthquakes?), not real world in your lounge playing your fav choons at normal listening levels type issue?
 
Panels have a damping factor, so at low levels, it's not so linear.

Yes, of course, but that's at VERY low levels. It is not damping, but the cause is the same, friction, which is not linear at low stress.

Saturate the damping - then it becomes linear until the panel goes into breakup mode. That's when it sounds really nasty.

JRKO said:
That's the usual working mode of speakers.
Would be interested to know what volume is required to make an unbraced/undamped sheet of 18mm baltic birch ply that is 95cm x 40cm start resonating at 500hz so that it is audible with music (not test tones)?

It is only interesting when the panel is resonating at this frequency, and there are tests made on this topic, unfortunately not very exhaustive, at least to my knowledge. The results hint to a minimum level of -30 dB below direct sound, under best circumstances, and -20 dB with normal music and the usual living environment.
 
It is only interesting when the panel is resonating at this frequency, and there are tests made on this topic, unfortunately not very exhaustive, at least to my knowledge. The results hint to a minimum level of -30 dB below direct sound, under best circumstances, and -20 dB with normal music and the usual living environment.
Well, the BBC reported resonances that were louder than the source (driver), and I'll concur with that.

But....

At some volume i'd guess thou? So with P10 size boxes not an issue. With the Emken, maybe (panel size above) and real big JBL/Atec style its an issue unless you don't brace/damp or brace/damp poorly. Other than that its a pure engineering issue (how do we damp & brace this military supersub that starts earthquakes?), not real world in your lounge playing your fav choons at normal listening levels type issue?
Yes, at some volume. Say, approaching 100dB. Not your typical, 'I'm not worried about the neighbors at this level' sort of thing. But, rather than have someone extrapolate from common practice, where it doesn't happen, that it can't happen, I'd rather mention it can, because you never know who'll be reading through these threads in the future.

Maybe... someone that might start a thread, "And Now for Something REALLY BIG"? :D
 
Generally it is a good idea to make the bracing from a different material than the cab itself and use a lossy adhesive ie one that does not set solid.

Interesting. That idea popped across my radar when I noticed KEF's cutaway of the LS50 in their white paper on that speaker, though they don't really elaborate.

What's the benefit of a lossy brace, compared to a fixed one?
 
But, rather than have someone extrapolate from common practice, where it doesn't happen, that it can't happen, I'd rather mention it can, because you never know who'll be reading through these threads in the future.

Maybe... someone that might start a thread, "And Now for Something REALLY BIG"? :D

Now there is a thread around here called something like that ;) I'll have to remember that my thread is for posterity!!! Didn't actually get round to bracing or even cabinet design. The only thing I want moving is the driver.

It can happen, but would be most likely in a big cabinet that is played very loud, built by someone who ignores all common sense and help offered, rather than most readers/posters here?

An average builder following basic design concepts & instructions shouldn't have an issue
 
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I've not heard that "against the grain" on ply is the weaker direction, it would seem intuitively to me to be stronger.

I should correct myself, and clarify. There is no way to show that ply is stronger than MDF when it is stressed perpendicular to the edge of the board. No such measures exist, to my knowledge. M.O.E. is quoted for stress on the face of the panel. It may well be stronger, and by that token so is MDF. My point being that many materials are comparable in strength, when used as a holey brace. I could answer conjecture with more conjecture, but im staying objective in my point. Ive been kicked enough for making a valid point thanks very much.
 
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