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In Reply to: RE: "New" Quads and Stands posted by cawson@onetel.com on February 27, 2017 at 11:14:27
Stone bass or something similar would be ideal. You have two goals here: To isolate the speaker from the building structure to prevent the transmission of low frequency vibration, and to add mass (in effect) to the baffle or enclosure with the same purpose. So a massive base is ideal.
The caveat though is that this may not be much of an issue. It depends I think on room materials and structure and on the speaker itself -- some speakers cabinets are massive and well damped, some are resonant and could use help. So hard to know how much of an audible improvement (if any) it will make.
Finally, Jim Smith recently made a good point -- if you have to experiment with speaker placement to get the best results, or if you have WAF compromises that mean you would get better sound if you pulled the speakers out for serious listening, furniture glides will give you more of an improvement than spikes and the like.
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> Stone bass or something similar would be ideal. You have two goals here: To isolate the speaker from the building structure to prevent the transmission of low frequency vibration, and to add mass (in effect) to the baffle or enclosure with the same purpose. So a massive base is ideal.
Interesting but why should a building be vibrating? My own building sways in high winds, but that's at about 1Hz per 5 seconds! Unless I have neighbours with jack hammers, or washing machines spinning, I can't see how building vibrations can adversely affect my speakers. I was under the impression it was the other way round. Spikes were promoted to take vibrations from the speaker cabinet and use the solidity of the floor and thence the building to absorb these vibrations. That's what led me to query the alternative use of absorbers instead of spikes. Curious and curiouser!
Consider the way you feel the bass through a wood floor. The floor is vibrating so much that you can feel it. What's worse, it's acting exactly like a sounding board.
Think of the woofer's vibrating coil as a vibrating string of a guitar, the cabinet or baffle the bridge, and the floor itself as the guitar body. Or of how you touch a tuning fork to a table top, it gets a lot louder. That's the physics of it -- the floor and sheetrock are acting as sounding boards or loudspeaker cones, which are acoustic transformers.
Intuitively, it's the difference between waving your hand back and forth rapidly and waving it back and forth while holding a Japanese fan. In the former case, you'll feel little air resistance, in the latter case much more, because you're pushing on many more air molecules.
But it gets worse than that -- floors and sheetrock are typically resonant at audio frequencies. You can hear the resonances by tapping on them and you'll hear a lot in the audio range. So now they're acting like organ pipes as well and that will tend to give you one-note bass.
So if the floor and sheetrock vibrate, more of the acoustic energy from the vibrating enclosure will be coupled to the air, and more of it will reach your ears rather than being dissipated by the internal damping of the speaker enclosure (turned into heat, or randomly-vibrating rather than systematically-vibrating molecules -- it is the *randomness* here that insures that we can't hear it), and it will tend to resonate at certain frequencies as well.
On the other hand, if that vibrating enclosure could be solidly coupled to a massive, low profile building structure like the studs and joists, you'd potentially have a better situation. The studs and joists are also acoustic transformers, but wired the other way around. They have a high mass density, they're rigid, and their resonances are pretty random. So in effect, they make the mass and stiffness of the enclosure higher if they're well coupled to it. For the most part, the benefit isn't that these solid structures are *absorbing* the vibrations but rather that they're reflecting them because of the extreme impedance mismatch. This, coupled through the enclosure, keeps more of the acoustic energy in the moving mass of the driver where it is dissipated through electrical and mechanical damping.
It's really a complex system though since so many factors can vary -- you have flimsy enclosures that vibrate like crazy, and at the opposite extreme you have speakers like Magicos that take heroic measures to keep the enclosure stiff, massive, and damped. And different kinds of floor and building structures as well -- old resonant wood ones, concrete, what have you. Maggies for example benefit from being coupled to building structures with rigid, massive speaker bases like the Mye.
Thanks Josh. I understand what you're saying but there are often contradictions in audio theory!As I sad earlier it was generally believed 20 years ago that floor-standing speakers should always be spiked to the floor - through the carpet if there was one. It was thought that any vibrations in the cabinet could be largely dispersed by bolting it to the floor. Now that we all use spikes, the snake oil peddlers say no, you need to isolate your speakers from the horribly vibrating floors! They sell us crazily priced "sorbothane" or other substances housed in stainless feet and ask hundreds per speaker. Well, if we just want to isolate our speakers so that vibrations from the floor or the cabinet don't adversely affect the music and we believe that isolation is the best way, why don't we simply put a coir matt under our speakers? No vibration is going either way through a coconut floor mat with tens of thousands of minute fibres supporting the cabinet! Or we could use sound deadening sheets that are installed in boat engine rooms. What's wrong with that and why shouldn't it be just as effective as £1000 worth of "audio industry" priced things that do the same job? I'm intrigued to know.
Edits: 03/02/17
Well, I think the trick in isolation is choosing a suspension that has the right resonant frequency, which in this case would be below that of the lowest frequency vibration of concern, e.g., 16 Hz (but that depends of course on the LF extension of the speakers and also the room and the Fletcher-Munson curve). And the compliance of the suspension would depend on the mass of the speaker. You'd presumably want to add damping to dissipate stored energy. And you'd want the platform on which the speaker rests to be massive and (probably) stiff, to reinforce the cabinet structure -- or maybe you'd want it to damp the cabinet?
I think the science here is pretty straightforward, what isn't as obvious to me is what works best in a given situation -- rooms differ, speakers differ, and how we interpret various stray sounds is quite complex, at one extreme we love the sound and feel of a vibrating wood floor and concert hall designers actually go to lengths to promote that, and at the other extreme something plastic or metallic that rattles drives us up the wall.
I mean, I've often thought that if you're playing a cello recording, the speaker should be spiked to the floor -- a cello is, after all! But a tuba would be a different thing, since there's a well-damped squishy support between the tuba and the ground.
So I guess my philosophy is that there is no single right thing -- a mat might be great with one speaker, terrible with another. Maggies for example aren't very massive and you can feel them vibrating, so the typical approach is to use a very rigid stand like the Myes and couple them to the ground -- that keeps the energy in the diaphragm and improves bass response. However, Peter Gunn has taken the opposite strategy with great success, and used a vibrating wood baffle on the Maggie -- basically the opposite of what the textbooks say to do! As with so much in audio, you have to try it and see what works best.
I'm in the UK and have found this supplier of sound / vibration absorbing pads, strips and sheets. I'll be asking for samples before choosing some that I'll stick permanently to the underside of thick slate slabs. The speakers will be spiked to the slabs (or even bolts directly) to increase the mass of the cabinets and the pad below will eradicate vibration transfer between floor and speaker and vice versa and allow easy re-positioning of the speakers. What can be better or more effective? And at a fraction the price that the audio industry wants from me! Peter
PS Sorbothane also offers numerous industrial products, no doubt at a fraction the price that the audio people charge for adding a "audio" tag to!
Just make sure that you get the resonance frequency and damping right. Remember that we're dealing with a fairly massive item and low frequencies here, you can't just stick something springy under a slab and expect to get the results you want. I think you'll probably have good luck with products sold for pro audio, since they generally have full specification and are designed for this purpose. Or you could go with a product designed for consumer audio, but the markup will probably be higher than it will be for the pro audio stuff.
Thanks. I'll speak with the guys at Quad next week to see if they can offer opinions on whether a slate slab fixed to the underside of the speaker's base plate is good, or if it's better to keep the spikes and place a "loose" slate slab under the spikes. I don't want to add to the height of the Quads though. They're already sounding good after very little time spent adjusting angles, etc. Peter
I found a good compromise for Vandersteens using bluetack and solid core cinder blocks as bases. That was more effective than spikes on vanderstands and spikes on cinderblock. The speaker was vibrating an order of magnetude less when cushioned with 5 balls of blue tack per speaker between the speaker and cinderblocks. the floor was wood.
Yes, isn't it interesting that stand-mount speakers have always used Blutak to secure them to the top of the stand, but the stand itself is traditionally spiked to the floor. With floor-standing speakers, the trend seems to be away from spikes into the floor to more of an isolation method.I'm far from convinced that any of these practices have any over-riding advantage (as otherwise there would be no further discussion) and that what works best after trials of particular speakers on particular floors seems to be far preferable than doing what others say we should do - or spending daft sums of money on what they want us to believe will make a massive difference to the sound!
I think I'll get some thick slate slabs cut to fit the underside of the cabinets and have holes drilled so they can be bolted directly to the speakers (adding 50% to their mass) but also testing using Bluetak between the speaker and slab. I would choose slate over any other stone as it is very dense and has less "ring" than marble or even granite. Peter
Edits: 03/03/17
Agree about slate, just that it is flaky to deal with. I bought a couple of packs of cut slate tiles that I selected for lack of ringing when tapped by a small steel rod for damping purposes.
Spiking is a better method of transferring energy to the slate because of the high pressure contact at the spike. Bolting slate to anything is a difficult proposition and it will fall apart that way, just crumble around the bolt due to the high vibration energy. It has a layered structure and you want to transmit energy to the top layer and have it absorbed into the structure rather than transmit to the structure via the bolt, or the area under the nut that has been weakened by drilling the hole for the bolt.
As Josh suggests, the issue is that each location type requires different strategies. Each type of floor and support structure requires its own particular solution.
Absorption with pliant materials is a good damping method if you can fix one side to a stationary mass. Otherwise it is just another mass being vibrated. It will reduce vibration but not nearly as much as when it is used as a constrained layer in the support. An example of this is with a friend's planar box speaker that had a lively cabinet even after applying gobs of soundcoat damping. The solution we came up with was to build an external box for 3 sides of the speaker and the bottom made of corian and fill the spaces between the boxes with a compliant setting material (bitumen based).. Deadened the bass section. The top section was left on its own to avoid diffraction near the tweeter, so had a bolt run through it with neoprene under the nuts. Now it is amazing.
That's an interesting question. I suspect that the spikes would be superfluous if the speaker is riding on slate and there's no carpet to punch through.
There are pro audio isolators for speakers like the "SubDude" for subwoofers, look it up.
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