If you pitch your singing such that it does not coincide with the tuning of the string, it will not sing back.
I've said enuff. If you can't grook the concept, no skin off my teeth. Practical examples work.
dave
I've said enuff. If you can't grook the concept, no skin off my teeth. Practical examples work.
dave
Here is practical example: touch the string by the cloth lowering Q. Do you need more or less of energy to excite it?
The energy needed to excite the resonance is related to the area under the curve (and within the bandwidth of that curve)
The concept is very counter intuitive and it took years for me to get there.
dave
The concept is very counter intuitive and it took years for me to get there.
dave
You can get back pretty quickly if you do some real experiments. The resonance is itself the ability to accumulate an energy. Without resonance more energy is needed to get the same displacement than when using resonance. Think of swings if you do not like strings. But what is bad when speakers resonate, they produce tail of oscillations that is still audible when excitation had ceased. You can lower the energy of an excitation using notch-filter, but you can not remove the tail.
Musical notes, their harmonics, no doubt are under that "curve area", withing that "bandwidth of the curve". At least one note or it's harmonic per tune. 😉
And each period of this note (or harmonic) adds an energy to the resonating part of your speaker making it louder and louder.
If the whole octave is louder than the rest of notes it can be equalized electronically. If one note is louder it can't be equalized, and a guitar string continues to oscillate long after you stopped singing near your guitar. It can not be equalized electrically, but can be damped mechanically.
Musical notes, their harmonics, no doubt are under that "curve area", withing that "bandwidth of the curve". At least one note or it's harmonic per tune. 😉
And each period of this note (or harmonic) adds an energy to the resonating part of your speaker making it louder and louder.
If the whole octave is louder than the rest of notes it can be equalized electronically. If one note is louder it can't be equalized, and a guitar string continues to oscillate long after you stopped singing near your guitar. It can not be equalized electrically, but can be damped mechanically.
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For clarification in this discussion, the word resonance is being used for 2 related, but different things, an actual resonance, and the potential for a resonance. We don't get an actual resonance unless sufficient energy is pumped into it to turn it into an actual resonance.
dave
dave
topic is best material for speaker enclosure, strangely enough pages and pages of MDF vs plywood vs different plywood. How come? If the topic was THE cheapest enclosure material, we could go on about Baltic Birch vs MDF and then come to agreement that plywood is slightly stiffer and better suited for woofer encloser and MDF is a little more damped. But the best?
How about 20mm 7000 grade Aluminum walls, lined with 5mm of lead? Steal was mentioned here several times, but why? Aluminium is much stiffer than steal and non magnetic. Of course the high resonances have to be toned down, lead would prolly be ideal, bitumen and other gooey substances would work as well.
Or go ceramic, the stiffest material that can be obtained with reasonable effort. High resonances would have top be dealt with again, of course. Result would be a 'virtually' dead cabinet, whatever resonances the box will have will be so high in frequency and so low in amplitude, even Ceratec driver would produce more distortone than the box, basically we'd have ideal box. There would be no need to perfect the box any further cos it wouldn't be the limiting factor any longer.
Let the kitchen cabinet manufacturers discuss particle board (MDF). It is not a material for a serious loudspeaker cabinet. Unless we go with 10 inch thick walls and our mini monitors using 5 inch Accutons end up with front baffles that are larger than refrigerator doors. or look like coffins aka Avalons
How about 20mm 7000 grade Aluminum walls, lined with 5mm of lead? Steal was mentioned here several times, but why? Aluminium is much stiffer than steal and non magnetic. Of course the high resonances have to be toned down, lead would prolly be ideal, bitumen and other gooey substances would work as well.
Or go ceramic, the stiffest material that can be obtained with reasonable effort. High resonances would have top be dealt with again, of course. Result would be a 'virtually' dead cabinet, whatever resonances the box will have will be so high in frequency and so low in amplitude, even Ceratec driver would produce more distortone than the box, basically we'd have ideal box. There would be no need to perfect the box any further cos it wouldn't be the limiting factor any longer.
Let the kitchen cabinet manufacturers discuss particle board (MDF). It is not a material for a serious loudspeaker cabinet. Unless we go with 10 inch thick walls and our mini monitors using 5 inch Accutons end up with front baffles that are larger than refrigerator doors. or look like coffins aka Avalons
This is something you have to read carefully to understand but I'll try it again since it is often misquoted.
Peter Freyer of Celestian did the original studies. He had an amplifier with flat response and a single path around it of a parametric bandpass. (i.e. a peak with a setable Q, frequency and gain). He wanted to see the effect of "submerged resonances" in a predominately flat system. The experiment was to adjust Q and find the threshold of audibility for various frequencies and levels of the resonant peak. For a given Q he would raise the level of signal going through the resonant bandpass relative to the straight through (flat) path until the resonance was just audible
He found that as the Q was raised the resonance became less audible (as you and Toole have quoted). In fact when Q was doubled the level of the peak needed to be 3 dB higher for equal audibility. Going the other way, cutting Q in half the resonance would have to drop 3dB for equal audibility.
Now this is for the electronic case where Q and peak level are independantly setable. There are electronic networks where Q can be varied while having a constant peak height, not so with mechanical systems. Consider a mechanical system where Q is varied by changing (primarily) damping. For example I have made panels by laminating two layers of MDF together with a thin damping layer. Stiffness and mass would be identical to a single layer of the same combined thickness. Damping of all resonances would be higher.
The result from damping any mechaical resonance is that for cutting Q in half you will see a 6dB drop in peak level. Q is inversly proportional to 20 log damping. So although you have decreased Q in a way that should make the resonance 3 dB more audible, you have reduced its level by 6dB. It is less audible by a net 3 dB.
Again, would you really think that damping resonances would make them more audible?
David S.
So in our 12 tone western system (equal temperment places a musical note in 12th-root-of-2 steps above and below A440) all you have to do is place every cabinet resonance at half a half step on the scale.
It works if nothing noise-like or percusive ever comes along. If Q is such that no skirt residual overlaps the 12th Octave points. If every singer sticks exactly to the scale. (Thank you auto-tune.) If every musician sticks exactly to the scale...and never uses vibrato (string players need not apply). If every orchestra is in tune and hasn't drifted due to humidity. If you never play an LP (off center holes, belt drive drift).
Sure.
David S.
but Speaker Dave, when talking about pushing cabinet resonances higher in frequency, clearly we're talking about lets say, a box that has resonance frequency say, 1000Hz and a a woofer that never does a peep above 80Hz. Would that be a good, effective enclosure for sub? A concrete box that Wavebourn spoke of is just that, as far as woofer in that box is concerened, there are no box resonances. I think thats waht was meant when saying pushing the box resonances higher in frequency. That enclosure would not be suitable in a simple 2 way monitor tho, of course.
a small 2 way with a baffle as narrow as possible. We can reasonably guess the resonance frequency of a 2 inches thick ceramic enclosure, lined with 1 inch of lead, can't we? But that box is so dead, any measurements are of only academic interest. We wont hear them, even driver gaskets will have more audible resonances probably, and awful poly and other cheap cone distortions.
a small 2 way with a baffle as narrow as possible. We can reasonably guess the resonance frequency of a 2 inches thick ceramic enclosure, lined with 1 inch of lead, can't we? But that box is so dead, any measurements are of only academic interest. We wont hear them, even driver gaskets will have more audible resonances probably, and awful poly and other cheap cone distortions.
Lol, I love your out there thinking< I know little enough to still make dangerous new leaps of faith, Hey how about we drill some holes in the aluminium in a grid the lenght of the resonant frequency, and put high presure rubber plugs in there... heh? put that in a calculator and I buy you a banana.
digits, it isn't really Out There Thinking.
Don't you agree that l oudspeaker cabinets are the weakest point in most audio systems? Distortion figures in best Scanspeak, Accuton, Eton are so low now, they are no longer the main issue, cabintes are.
There is no overkill as far as speaker cabinet design is concerned. Cabinet has to be infinetly stiff and infinetly damped. How do you reach that goal? We can attemt to do that and for surely any serious effort to reach that goal could be ridiculed as over kill or All Out There Thinking. Celestion 700 alumiumi honey comb enclosure was considered overkill in 80s, or so I've read. Today it is considered classic and a break trough in cabinet design.
There is no single material, composite or not that would be stiff and damped at the same time, cabinet has to be sandwiche of different materials. Wilson uses Corian I believe and they mix in some non resonant stuff, still the box resonances can easily be measured, probly heard as well. So no such thing as overkill. Aluminuim/lead sandwich is actually pretty basic solution to minimize resonances and far from 'out there' thinking.
Don't you agree that l oudspeaker cabinets are the weakest point in most audio systems? Distortion figures in best Scanspeak, Accuton, Eton are so low now, they are no longer the main issue, cabintes are.
There is no overkill as far as speaker cabinet design is concerned. Cabinet has to be infinetly stiff and infinetly damped. How do you reach that goal? We can attemt to do that and for surely any serious effort to reach that goal could be ridiculed as over kill or All Out There Thinking. Celestion 700 alumiumi honey comb enclosure was considered overkill in 80s, or so I've read. Today it is considered classic and a break trough in cabinet design.
There is no single material, composite or not that would be stiff and damped at the same time, cabinet has to be sandwiche of different materials. Wilson uses Corian I believe and they mix in some non resonant stuff, still the box resonances can easily be measured, probly heard as well. So no such thing as overkill. Aluminuim/lead sandwich is actually pretty basic solution to minimize resonances and far from 'out there' thinking.
I think the page about PHY drivers I read yesterday summed it up best where it described how futile it is to try and fight the backwave, despite them sitting under a 12 tonne roof.
Oh well combining what we know about speakers, they have to be aluminium orbs then 😀
Oh well combining what we know about speakers, they have to be aluminium orbs then 😀
digits, my intention was to go with Beryllium, ok? As you know it is several times stiffer than Aluminum, I only suggested Al to keep cost in check.
So in combining what we know about speakers, they have to be Beryllium orbs!
So in combining what we know about speakers, they have to be Beryllium orbs!
Open baffles are subjected to Newtons third law as much as any box. Secondly there are as much exitations due to pressure differences in an open box as a closed one, that is above the cut off frequency of the baffle. The german magazine showed that a 3 layer approach using MDF-Ceramic tiles-carpet was as effective as MDF/Plywood and fancy damping material. Bracing is also critical. I do belive that a cabinet be it horn, pipe closed box or baffle can not be to well braced or to hevy.
Certainly, in the case of a subwoofer, if we can get the resonances well above the passband, then we can ignore them. For subs high cabinet stiffness is good. We can even ignore internal damping if we want to, as long as the first modes are well above the passband. Of course, a 2way or 3 way speaker is another matter.
For 2" of ceramic and 1" of lead, I still can't say that you will be free of resonance problems. Lead is a great way to add mass and is relatively dead for a metal, but I don't know how good it is as a damping layer. You are pursuing mass and stiffness more than damping in this case. Remember the Harwood case where he had better luck with thinner cabinet walls because the ratio of damping to mass/stiffness was greater when the walls are thinner.
Thats all I'm trying to say in this whole discussion. We need more damping in our cabinets. Increasing mass and stiffness may make our results worse.
David S.
Again, i understand that. But it is incomplete. by adding damping you change other things as well. It also does not take into account the changing of the panel material either.
Damping is only effective if you are trying to kill a resonance that is happening. My aim is to put the panels in a place where the (potential to) resonate is not likely to ever be realized.
dave
Thats not my view of engineering. Its okay if you are a diy-er making your own speakers for fun, but in a comercial world the first question (for every performance parameter) needs to be "how good is good enough"? Spend too much money on one performance aspect and you will be shorting the next.
Again, that is why I like the Harwood approach. His first step was to say, what is a good cabinet? Based on his own listening tests his answer (and others are free to diasagree) was that when the spl off the cabinet panels was 30 dB below the woofer output, then the cabinet is good enough. He then looked into how to achieve that performance level.
That is an engineering approach.
David S.
Or, make them of such shape they don't have resonant frequencies. Like I did in wideband concrete speakers (picture above)
Cars of 1950'th is a good example of such shape. 😉
And concrete is one of the best materials to mold such a way.
An externally hosted image should be here but it was not working when we last tested it.
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