My previous link was not a good one, here is a better one
And when British engineers decide to minimize reflections they end up with something like this
And when British engineers decide to minimize reflections they end up with something like this
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David, I don't agree here. They can be even, or in case of internal resonance, the air driven movement can be stronger. However, the internal volume resonances can be usually handled by proper stuffing.
A fairly extreme example was a 90 cm tall cabinet made of aluminum producing considerable output at 380 Hz. The result was a quite huge bump in the overall frequency response, nearly 2 dB IIRC. Stuffing reduced the resonance, but was not applicable, because it reduced bass output too much. The solution was bracing at half of the cabinet height.
markus76 said:
A "knock" is (close to) an impulse. An impulse contains every frequency. The response to an impulse fourier transformed gives the frequency response.
An engineer with insight in signal theory would not even consider making this additional test.
Because they move less...
OK, I admit, it's weird, and I'm sure that's why heavy, stiff cabinets are so popular among audiophiles. How can they know? Most of them has no degree in acoustics, mechanics or electronics. And I know guys with such a degree who still promote heavy*, stiff cabinets.
*heavy by itself is not bad. It's the stiffness, which shifts the resonances up to audible frequencies. And most of the time, the weight is achieved by thickness. And thickness increases the stiffness much more than the weight.
one thing I have never liked very much is the coupling of opposite sides, be it with a stick or bracing
but quite funny, I still like to use to the old method with real wood lists to support all glued edges inside
I suppose its the old british way, and probably also still practiced by Harbeth, Spendor, etc
but quite funny, I still like to use to the old method with real wood lists to support all glued edges inside
I suppose its the old british way, and probably also still practiced by Harbeth, Spendor, etc
Lists in corners are just holding the pieces together, they have minimal effect to vibrations. Crossed studs prevent ballooning effect well, the placement has some effect too (uneven distance to edges).
The magnitude of vibration is important but so is duration (damping). Both must be handled.
I am about to make two big closed subwoofer boxes (259L) of spruce plywood. It has lower density than birch, which usually means shorter ringing when thickness is same. The bethod of bracing is open. The sub enclosure is a much easier task than full range because frequencies are so low.
The magnitude of vibration is important but so is duration (damping). Both must be handled.
I am about to make two big closed subwoofer boxes (259L) of spruce plywood. It has lower density than birch, which usually means shorter ringing when thickness is same. The bethod of bracing is open. The sub enclosure is a much easier task than full range because frequencies are so low.
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yes, thats one way to determine plate ressonance
300year old method
A plate is not a box and a speaker driver is not a knocking finger.
I hear a strange voice talking backwards, saying "sutinit"
That was exactly what you were asking.
You wanted to know if a cabinet is resonating at the frequencies identified by a "knock" test. If you excite a panel by a knock, and record the frequency content of the response, then this is close to the frequency response. From this point on it does not matter where and how you excite the panel, you can be sure that all those resonance frequencies seen in the "knock frequency response" will get excited, supposed that the new excitation is sufficiently broadband (which music is).
The only question is how much every resonance will get excited, when you use a driver instead of a knuckle at a complete different position. With this test, it can happen, that a few resonances will not get excited, because the driver is placed at a node of these resonances. But this is very unlikely.
You wanted to know if a cabinet is resonating at the frequencies identified by a "knock" test. If you excite a panel by a knock, and record the frequency content of the response, then this is close to the frequency response. From this point on it does not matter where and how you excite the panel, you can be sure that all those resonance frequencies seen in the "knock frequency response" will get excited, supposed that the new excitation is sufficiently broadband (which music is).
The only question is how much every resonance will get excited, when you use a driver instead of a knuckle at a complete different position. With this test, it can happen, that a few resonances will not get excited, because the driver is placed at a node of these resonances. But this is very unlikely.
I do something similar as a quick test of the effects of an enclosure for midranges / small fullranges. Gently scratch the cone of the bare driver with a fingernail. Mount it in its enclosure and repeat. If there's a significant difference in the sound, the enclosure needs work (stuffing etc).
You probably didn't read all my posts. I didn't want to know anything, I tried to point out that knocking on different boards doesn't tell much about how much a cabinet will contribute to the radiated sound of a boxed speaker. There are more variables to consider as you just pointed out.
and that works quite effectively
you can even use the method to balance the stuffing in both channels equally
weird stuff(ing)
Then your questions doesn't make any sense. Of course you can't compare a cabinet with a single, free hanging panel. The cabinet (each panel) will have a completely different set of eigenfrequencies (resonances), yet alone by the clamped edges.
And yes, you can find the resonances of the cabinet by knocking at it, and yes, these resonances will get excited by a driver during playback.
And yes, you can find the resonances of the cabinet by knocking at it, and yes, these resonances will get excited by a driver during playback.
Just and idea to extend this thread a little.
Timber is hygroscopic, it sheds or takes on moisture to reach "equilibriam moisture content". That means the moisture content of the wood changes as the seasonal relative humidity in the air changes.
So if you were head butt a speaker cab in a dry Canadian winter and did the same to an identical cab in the UK during their wonderful summer this year, you would very likely get a different sound.
No, there is no finish that will prevent this back and forth passage of moisture.
Timber is hygroscopic, it sheds or takes on moisture to reach "equilibriam moisture content". That means the moisture content of the wood changes as the seasonal relative humidity in the air changes.
So if you were head butt a speaker cab in a dry Canadian winter and did the same to an identical cab in the UK during their wonderful summer this year, you would very likely get a different sound.
No, there is no finish that will prevent this back and forth passage of moisture.
Hi,
To get back to the original post and question, and answer. Which is damped
thin wall cabinets are opaque in the midrange whilst stiffer simple cabinets
simply are not and can be almost transparent at some midrange frequencies.
IMO it doesn't work for small speakers or big 3 ways, but is good for 2-ways.
If you've never heard it don't judge it by theoretical conjecture, i.e. that the
bass must be bad, it isn't, and the midrange is truly excellent for a 2-way.
If you have heard it you will know that it works well, but that does not
preclude other approaches, which IMO may have better ultimate bass,
but inevitably intrude on the midrange more in the speakers character.
What suffers more than anything else IMO is drums, the transient stuff,
and its not the attack, more the minor overhang of any sound that by
definition has a wide bandwidth, some minor bass warmth is added.
That is not terrible, in theory or practice, for an extremely lucid midrange.
In the end they sound nice, pretty faultless for classical, acoustic, soft rock,
jazz MOR etc, but they don't do hard stuff allegedly. Poppycock. Any good
aggressive recording sounds still sounds great with the midrange clarity.
rgds, sreten.
Though I accept intelligent bracing, spreading and cancelling panel resonances
is the modern way of doing things, there is now a lot to good cabinet design.
To get back to the original post and question, and answer. Which is damped
thin wall cabinets are opaque in the midrange whilst stiffer simple cabinets
simply are not and can be almost transparent at some midrange frequencies.
IMO it doesn't work for small speakers or big 3 ways, but is good for 2-ways.
If you've never heard it don't judge it by theoretical conjecture, i.e. that the
bass must be bad, it isn't, and the midrange is truly excellent for a 2-way.
If you have heard it you will know that it works well, but that does not
preclude other approaches, which IMO may have better ultimate bass,
but inevitably intrude on the midrange more in the speakers character.
What suffers more than anything else IMO is drums, the transient stuff,
and its not the attack, more the minor overhang of any sound that by
definition has a wide bandwidth, some minor bass warmth is added.
That is not terrible, in theory or practice, for an extremely lucid midrange.
In the end they sound nice, pretty faultless for classical, acoustic, soft rock,
jazz MOR etc, but they don't do hard stuff allegedly. Poppycock. Any good
aggressive recording sounds still sounds great with the midrange clarity.
rgds, sreten.
Though I accept intelligent bracing, spreading and cancelling panel resonances
is the modern way of doing things, there is now a lot to good cabinet design.
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I guess it wont have the same problems as the guy said the PD1550 would have with bottoming because of the short 22mm mechanical xmax
though joking, I am seriously interested in this 'lossy design' principle, as you call it, for my bass guitar cab
but with 18" woofer 