I've recently built a pair of Scan-Speak Reference Monitors.
I've deviated a bit from the original design: the back and front are both 50 mm (2 inches) thick and I used cross-bracing.
The box feels rock solid. However, with a tone-sweep I noticed an audible box resonance around 300 hz. The enclosure can be felt to resonate around that specific frequency! This resonance causes a buzzing or rattling sound. To other frequencies the box is practically dead.
I've tried damping materials of different kinds between the driver basket and the baffle, yet the problem remained and is still unsolved.
Has any of you an idea of what might cause this increasingly annoying resonance?
I've deviated a bit from the original design: the back and front are both 50 mm (2 inches) thick and I used cross-bracing.
The box feels rock solid. However, with a tone-sweep I noticed an audible box resonance around 300 hz. The enclosure can be felt to resonate around that specific frequency! This resonance causes a buzzing or rattling sound. To other frequencies the box is practically dead.
I've tried damping materials of different kinds between the driver basket and the baffle, yet the problem remained and is still unsolved.
Has any of you an idea of what might cause this increasingly annoying resonance?
I assume that the front and back panels are separate pieces of plywood or mdf that you glued and screwed together?
Have you been able to localize the physical location of the resonance at all?
You might have coincidentally chosen a set of dimensions where a panel naturally resonates at 300Hz? Is it a very high q resonance or is there a range for frequencies around 300Hz that also trigger it, if very high q it might or might not be as big an issue.
I noticed that you used biscuit joinery, my understanding is that this technique can give rise to really bad buzzes if all surfaces were not glued and tightly clamped. If you did not glue along all the edges of the panels all may not be lost, you may be able to apply hot melt along the edges of all adjoining panels and this should help.
I assume the edges of the braces that touch are glued everywhere.
Glue and screws are the preferred assembly technique to minimize buzzing at joints.
Hope this is helpful to you.
Have you been able to localize the physical location of the resonance at all?
You might have coincidentally chosen a set of dimensions where a panel naturally resonates at 300Hz? Is it a very high q resonance or is there a range for frequencies around 300Hz that also trigger it, if very high q it might or might not be as big an issue.
I noticed that you used biscuit joinery, my understanding is that this technique can give rise to really bad buzzes if all surfaces were not glued and tightly clamped. If you did not glue along all the edges of the panels all may not be lost, you may be able to apply hot melt along the edges of all adjoining panels and this should help.
I assume the edges of the braces that touch are glued everywhere.
Glue and screws are the preferred assembly technique to minimize buzzing at joints.
Hope this is helpful to you.
I'd also recommend getting a stethoscope, but probably not an expensive type like this one: http://www.stethoscope.com/index.cfm?event=ProductDetail&ProductID=279
You then also can use it on turntables, heatsinks, cd-players, general audio-equipment housings, etc. etc. From my experience: In most cases you will find out that you will get a lot to "do something" about unwanted "sound", both emitted, and induced.
regards
You then also can use it on turntables, heatsinks, cd-players, general audio-equipment housings, etc. etc. From my experience: In most cases you will find out that you will get a lot to "do something" about unwanted "sound", both emitted, and induced.
regards
The double 1” MDF panels are indeed glued together, with glue spread over the full surface.kevinkr said:
The full cabinet can be felt vibrating. However, it is strongest near the back of the woofer. Note that just here is the biggest ‘not-braced’ surface of the box.kevinkr said:
As you can see on the pictures, this speaker is very heavily braced considering its size. The resonance is in al small range just above 300 hz. From around 300 to 300 hz. This can be considered pretty high Q, I guess.kevinkr said:
I think every biscuit joint is glued well enough as far as not to make it rattle. All braces are glued on all sides. I have used no screws.kevinkr said:
I simply made this box as rigid as possible. Although the rest of the sound is very good, this rattle came as a big disappointment.
Thanks for the help so far. Still got any ideas?
If you put the entire speaker in your lap while you test, does it still only happen at 300hz? Try hugging it close to your chest (yes I know this will look silly), does it still vibrate at 300hz?
If it doesn't, I would suspect your speaker stands. Some additional weight should drive the resonance down and reduce the magnitude. Maybe you have found the first legitimate use for those audiophile slabs of granite you are supposed to place on top of your speakers.
Dan
If it doesn't, I would suspect your speaker stands. Some additional weight should drive the resonance down and reduce the magnitude. Maybe you have found the first legitimate use for those audiophile slabs of granite you are supposed to place on top of your speakers.
Dan
keyser said:
Of course this should not have been from 300 to 300 hz. It is actually about 300 hz to 330 hz.
My speakers stand on pretty solid speaker stands. I’ve already tried the speakers while holding them in my arms. That doesn’t help.
Yesterday night I screwed the woofer of one of the speakers out, and put it on a pillow. This time it sounded perfectly clean. After that I lay the woofer back into the baffle, but didn’t put the screws in. Strangely, the resonance had not returned!
Somehow the screws must be passing energy from the woofer basket to the box. I still don’t really know what parts exactly cause the resonance inside the box, but decoupling the woofer basket from the box certainly helps.
Gluing might be an option, but is a rather permanent one. Has any of you a better idea?
Any direct wood to wood contact that is not glued is a candidate for buzzing, it is also possible if the speaker basket makes direct contact with the baffle board anywhere via anything but its gasket.
IMO you want the basket pretty tightly coupled to the baffle board to damp vibration in the basket.
Yeah that is a pretty high Q resonance. Do you hear a coloration in this region when you play music?
It is unfortunate that you applied the veneer. I would have recommended installing some screws along the joints.
Applying hot melt glue along the joints may prevent the buzz if it is adjoining panels vibrating against each other.
An earlier post recommending a stethoscope is an excellent idea, drive the box just hard enough to get the buzz and you may be able to localize it..
IMO you want the basket pretty tightly coupled to the baffle board to damp vibration in the basket.
Yeah that is a pretty high Q resonance. Do you hear a coloration in this region when you play music?
It is unfortunate that you applied the veneer. I would have recommended installing some screws along the joints.
Applying hot melt glue along the joints may prevent the buzz if it is adjoining panels vibrating against each other.
An earlier post recommending a stethoscope is an excellent idea, drive the box just hard enough to get the buzz and you may be able to localize it..
keyser said:
At 300 Hz, the wavelength is ~1,15 m, ½ a wavelength is 575 mm. The box looks a bit lower to me, but not too far from it. The bracing inside it will shift the (air) resonance frequencies a bit, which makes me beleive that the resonace actually could be caused by the air cavity rather than the walls themselves.
The damping material you use looks like (I don't find the proper english word, but it looks like packing material) it might not be the best for cancelling resonances. Have you tried fiberglass?
A couple of weeks ago I tried making the cut-out for the woofer basket wider. I'm not sure how to explain it in English. It's not the hole through which the motor falls, but the the cut-out in the baffle to flush mount the woofer basket. In Dutch the tool to do this is called a 'frees'. I don't know the English word.
Who helps me increase my vocabulary?
Anyway, this solved the problem. The resonance must have been caused by the woofer basket vibrating against the wood on the sides of it. This lesson taught me not to make the driver fit too neat and tight. Leave a little space.
Who helps me increase my vocabulary?
Anyway, this solved the problem. The resonance must have been caused by the woofer basket vibrating against the wood on the sides of it. This lesson taught me not to make the driver fit too neat and tight. Leave a little space.
Im sure you are familiar with t-nuts, but you might not be familiar with the ones that "float" on rubber, they are still threaded nuts but now are isolated from the wood, these with some type of gasket (leather rubber whatever) and some rubber washers under the screw head should clear this problem up.
Also, I noticed you did not radius/bevel the back side of the baffle to let the woofer "breathe", does the frame touch the baffle anywhere?
Also, I noticed you did not radius/bevel the back side of the baffle to let the woofer "breathe", does the frame touch the baffle anywhere?
I'm afraid I didn't make myself quite clear. It's not the part of the frame that is supposed to lie on the baffle, but the sides of that part that fit too tightly in the spacing I still don't know the word for.
I didn't know the T-nuts that let de driver float on rubber. I'll look out for those for a future project!
I didn't know the T-nuts that let de driver float on rubber. I'll look out for those for a future project!
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