Cabinet resonance question
motorstereo
Posts: 2,133
Last week while doing some rearranging I temporarily placed a 50lb amp (mcintosh 2100) on top of each of my spiked and bass braced 1.2tl's. Surprisingly to me I could feel speaker vibrations very plainly through the tops of those heavy amps even with their rubber feet. When I say I was surprised it's because I can barely feel any vibration with my hand placed directly on the speaker top. So what I'm wondering if a sandbox type device placed on top the speakers would be a good idea. Any thoughts on doing something like this or would this be a wasted effort as the 2100's are somehow amplifying those vibrations?
Comments
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A couple of cat boxes and some sand is cheap and easy. Try it and see what you think.
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The vibrations you felt were caused by the air waves in the room, they were not actually being transferred from the cabinet into the amps.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Hmmm; I never thought of that angle Jesse and I'm betting you're right. I do know I haven't noticed any change in the sound with the amps sitting there vs. not sitting there.
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Of course, I'm right.
Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
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Of course, I'm right.
I vaguely remember Joe having a sack of lead shot plopped on top of each of these speakers back in the day. I can just imagine the arguments there must've been from those 2 different schools of thought.
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He never had them when I was there, which was before he had chemical issues.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Ok here's my findings having done some crude hands on testing. I boosted my 18'' sub which will easily overpower the 1.2s; with the 1.2s off. I could detect little to no vibration on those 2100's until the sub reached uncomfortable (borderline retarded) levels. I did notice the sub's cabinet vibrating though. There's plenty of cabinet resonance there but those soundwaves didn't affect the 2100's sitting on the 1.2s.
The next test was using the balance knob on the polks with the sub turned off. Turning the balance to one speaker and then the other there's no doubt there's more vibration coming from the speaker with all 8 drivers working. The speaker with only 4 working had much less vibration. My uneducated guess is around half the amount.
Last test was to disconnect the sda cable. With a 30hz bass boost there was noticeable vibration coming through the amp on the speaker that was working. Only the very slightest amount could be felt from the other speaker's amp. These very basic tests lead me to believe that the resonance is coming from the cabs and not from the soundwaves in the air. These tests aren't rocket science by any means and if I can do them anyone can try this out on their sda's to see if their findings might be different from mine.
I'm sorry Jesse as I was really hoping your theory was correct. Maybe just maybe Joe was onto something with those lead shot filled bags? Unfortunately I don't have any lead shot filled bags and the best I can come up with is a pair of amps.
Next question.......is it worth the effort to build a sandbox type device? -
Yet, you can barely feel any vibration with your hand placed directly on the speaker top.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Any chance that the soft feet of the amplifier results in a "critical vibration" that just happens to be activated by the minimal speaker cabinet vibration?
Maybe the amplifier chassis/cabinet/suspension has a natural resonance that's being excited. A sand-box wouldn't have that sort of natural resonance, and the cabinets by themselves don't have a natural resonance at whatever frequency is exciting the amplifier.. -
Seems its panel vibration.The rubber feet on the amp are not compliant enough to damp them so they are transmitted to the steel chassis.
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Yet, you can barely feel any vibration with your hand placed directly on the speaker top.
That's right. I never noticed any vibration until I set the amps up there. The cage vibrates noticeably more than the autoformers on the back.Any chance that the soft feet of the amplifier results in a "critical vibration" that just happens to be activated by the minimal speaker cabinet vibration?
Maybe the amplifier chassis/cabinet/suspension has a natural resonance that's being excited. A sand-box wouldn't have that sort of natural resonance, and the cabinets by themselves don't have a natural resonance at whatever frequency is exciting the amplifier..
Yes I was thinking along those lines to. I would think the rubber feet and the weight of the amps though would stifle that resonance though.
But I'm thinking there should not be any resonance with them being both spiked and braced?Seems its panel vibration.The rubber feet on the amp are not compliant enough to damp them so they are transmitted to the steel chassis.
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The speakers should be either spiked or bass braced, but not both.
If I were you, I'd forget about this whole thing. If adding 50lbs. to the top of the speakers didn't improve the sound, it's a non-issue.Political Correctness'.........defined
"A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."
President of Club Polk -
Its sympathetic vibration of the panels, this is why we dynamat.HT Optoma HD25 LV on 80" DIY Screen, Anthem MRX 300 Receiver, Pioneer Elite BDP 51FD Polk CS350LS, Polk SDA1C, Polk FX300, Polk RT55, Dual EBS Adire Shiva 320watt tuned to 17hz, ICs-DIY Twisted Prs, Speaker-Raymond Cable
2 Channel Thorens TD 318 Grado ZF1, SACD/CD Marantz 8260, Soundstream/Krell DAC1, Audio Mirror PP1, Odyssey Stratos, ADS L-1290, ICs-DIY Twisted , Speaker-Raymond Cable -
I remember reading that they shouldn't be both spiked and braced. The spikes are here to stay so it'll be the brace that I'll be removing at some point.
I was thinking the same thing that if those amps didn't make a difference chances are that a sandbox won't either. I was really hoping someone here had tried it and had some thoughts one way or the other. -
I'll add another to spikes only. Ditch the brace. From reading on this site the brace was to pass government tip-over tests anyway. I'll bet you hear the difference without it.
If you're worried about the cabinet roof resonating, line it with Dynamat, then cut pieces of 3/4" or 1" MDF to size and screw them to the underside of the roof with wood screws short enough not to poke through the top. Home made dead-wood. Personally I think it would be a bunch of work for a non-problem. Just get rid of those braces and don't put your amps on top of any of your speakers. Then sit down and enjoy what ya got.
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