And what about reflections? Might the sound waves that are reflected off the front baffle behave differently whether it's wood or aluminum? Or as in my speakers' case, little plastic pyramids...
An externally hosted image should be here but it was not working when we last tested it.
If the aluminum is bolted down or adhered so it doesn't rattle, the internal damping is irrelevant.
The issue with baffle materials isn't softness, it's acoustic absorbance versus reflectance. That's why felt and open-cell elastomeric foams are so popular; they won't necessarily improve sound, but they will certainly change it.
The little pyramids are mostly for show. They may have some effect in the 10-20K octave, but that's of relatively little importance- and the tweeter will be pretty beamy at that point so that the baffle won't have much effect anyway.
The issue with baffle materials isn't softness, it's acoustic absorbance versus reflectance. That's why felt and open-cell elastomeric foams are so popular; they won't necessarily improve sound, but they will certainly change it.
The little pyramids are mostly for show. They may have some effect in the 10-20K octave, but that's of relatively little importance- and the tweeter will be pretty beamy at that point so that the baffle won't have much effect anyway.
It may very well have an adverse effect on the sound, or it may not, depending on how it is implemented. A stand alone aluminum plate will ring (resonate), you know what that sounds like. When installed as a speaker baffle, the ringing will need to be damped to an inaudible level. This is not as easy as it may appear on the surface.Timn8ter said:
The aluminum will reflect the sound just as wood or plastic. It presents a smooth hard surface for the wave to form. Sometimes this is desired, sometimes not. Your speakers have some sound damping material attached to the baffle. This is typically to "control" unwanted reflected sound at certain frequencies. The designer must have found that the reflected sound was a problem so he tried to eliminate it, or the marketing dept. came in and said "these little pyramids on the front would look cool".Oscar said:
roddyama said:
Yeah, I guess it's mostly for show. Still, the B&W Matrix 3 are a fairly serious set of speakers.
SY said:
Correct. It would be a normal MDF box and then a flat aluminum plate would be bolted onto it, only for looks. So, if he managed to attach it very tightly so it will resonate in inaudible frequencies, there wouldn't be a problem?
Next question then, how to attach? Using lots of bolts maybe could work? But that might cause diffraction since you then have stuff sticking out, right? Glue? (Lots of it.)
Sy,SY said:
Yep, I knew that.
It was an example of the resonate nature of metal plates.Yes they are. I would suspect that, since we're talking about the woofer in the case of your B&W's, that the absorbing material will help to reduce baffle edge reflections as well as make the speaker look cool.Oscar said:
IMO I wouldn't use metal in speaker construction, but that's besides the point. If I did, and partiularly if I had to mount the tweeter on the metal baffle, I would have as much of the plate bolted and bonded to MDF or high damping plastic as possible.Oscar said:
As you stiffen the baffle (metal in this case) the resonant frequency will rise into the tweeters range. The tweeter cone requires very little movement to output signifcant sound levels. For this reason small vibrations in the metal baffle can have a signifcant effect on the frequency response of the tweeter.
Although the metal will "ring" that effect is only really pronounced when you suspend the sheet like a chime. If you bond it evenly to the baffle, it is likely that the material will be effectively deadened. Edge diffraction is another issue and may be reduced by bevelling the edge of the aluminum sheet with a router or sander.
That said, what about using a thin even layer of silicone adhesive to provide additional damping between the aluminum and MDF. A layer of 3M Super 90 spray adhesive may also provide the same effect.
ensen.
That said, what about using a thin even layer of silicone adhesive to provide additional damping between the aluminum and MDF. A layer of 3M Super 90 spray adhesive may also provide the same effect.
ensen.
roddyama said:Yes they are. I would suspect that, since we're talking about the woofer in the case of your B&W's, that the absorbing material will help to reduce baffle edge reflections as well as make the speaker look cool.
Well, they surround the tweeters as well.
An externally hosted image should be here but it was not working when we last tested it.
roddyama said:
No, it's not besides the point. Please, if you care to tell us I would gladly hear your reasons for not using metal in speakers. The resonant behaviour of the material?
purplepeople said:
I've read that for bevelling to have any effect worth mentioning (even though we're talking with audiophiles here...) you need to take away a lot, the width more than a centimeter. That's not feasible when we're talking about a metal sheet.
Well, there's an aluminum sheet of 0.5mm thickness available from the same source. That should work fine, shouldn't it?Vikash said:
However, making holes for the drivers might be a bit tricky to get right perhaps. I don't know about these things, I'm just a computer geek who happens to like music...
Oscar said:
If you have the holes already cut, it's easy. Cut the rough hole in the ally, slightly undersize, and then just use a bearing guided laminate trimmer bit in your router to even up the edges when thr glue is dry.
I don't know about these things, I'm just a computer geek who happens to like music...
Hey, I'm a stage lighting designer!
pm / likes little pyramids...
I was wrong to infer that baffle edge reflection will only affect the woofer range of the spectrum. The full audible range can be affected by baffle edge effects. Whether or not this is the reason for B&W’s use of the absorbing material is purely conjecture on my part.Oscar said:
These are my thought on using a metal baffle (with the possible exception of cast magnesium).Oscar said:
As an example, a tweeter with a diameter of 1.5” (38mm) only need to move several thousandths of an inch (.1 or .2mm) to produce relatively high outputs in the highest octave. A metal plate (I’m thinking 6mm+), even one that is held rigidly on 4 edges, can easily vibrate this much and more. If you happen to excite the resonance that will most likely be in the audible range, the vibrations can be much greater in magnitude. Now, depending on the phase and frequency being reproduced by the driver mounted on that baffle, those vibrations will add or subtract from the effective cone movement.
One could go through all the math required to determine what the actual effects will be, but basically you will have introduced a hi-Q notch filter into the overall response of the speaker. It’s much easier just to make the baffle from a well damped material and cover it with a metal plate for show.
Forgive my poor electrics skills, but what does the Q mean? My elecronics learning book says "A quality factor describing how closely a practical coil or capacitor approaches the characteristics of an ideal component." Umn, different things, right?roddyama said:
Notch filters I know though. I work with them every day
That was, and still is, the idea. And to cure the problems involved with that, you clamp the plate tightly to the baffle and add absorbing materials in between I take it?roddyama said:
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