Speakers -> Spikes, marmorplates, rubber feet -> no one can explain it - AVS Forum
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post #1 of 32 Old 04-04-2013, 07:20 AM - Thread Starter
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I have been googleing for days now. No one can really explain why to use spikes or why to use any of those "weird" setups and what advantages it would bring.

So here is my current situation:
Speakers: 2x Magnat Zero 8 (=2x 30kg / 66lbs)
Floor: Real wood parguet -> a little bit of kork -> cement

Currently they are standing directly on the parguet with just a little bit of rubber/paper to get an even height (stability). So when watching movies, a lot of "bass" gets transferred to the walls/windows/etc in my room. I can hear some shaking from different parts of my room.

What most people seem to use is:
Speakers -> Spikes -> Marmorplate -> Rubber feet -> Parguet

This would mean my speakers have less vibration as the vibration gets transferred to the marmorplate, how ever the rubber feet will prevent the energy to get into my floor/walls/etc ?

What if I simply try to use:
Speakers -> Spikes -> Parguet

I also have one more convern:
I use this stereo setup to watch movies. The speakers with my Sony TA-F690ES amplifier are strong enough to give me a real vibration feeling during explosions/fighting scenes/whatever in movies. If I start using spikes, will I loose the heavy bass feeling for the cost of better bass sound?

Thanks !
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post #2 of 32 Old 04-04-2013, 07:35 AM
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I believe this depends on whether you have dead or live floors. In a basement where it's carpet over concrete, you'd want the spikes to reach down to touch the solid floor underneath so that the speakers are very stably set on the floors. If you are placing the speaker over live floors that readily flex and resonates with the speaker, you'd want there to be as much isolation as possible. I wonder if it would not be better to put a whole sheet of something like 1/8" thick neoprene cut to the shape of the bottom of the speaker to provide this isolation.

This is what makes a separate sub very attractive: you can filter out the bass signals going to the main speakers so that they are not coupled to the floor, and you can put the subwoofer on an isolation pad.
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post #3 of 32 Old 04-04-2013, 08:03 AM
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Next to high priced cables and power conditioners isolation pads and spikes are the biggest scams in audio. The following quoted claims are taken straight from the websites of manufacturers of these devices.

The Isolation Claim: ‘Its purpose is to prevent sound from transmitting through your subwoofer to surrounding surfaces. Subwoofers create big vibrations (low frequencies) that you can feel in the floor and in objects placed nearby. When the source of the vibrations is coupled directly to the floor it causes these objects to vibrate or resonate…’

The Truth: The source of these vibrations is the movement of the driver cone creating pressure waves in the room. The claim would only be true if you coupled the driver cone to the floor. If the cabinet panels vibrate enough to cause the floor to vibrate the speaker is defective.

The Decoupling Claim: ‘Isolators for your speakers…will decouple your speakers from the surface they rest upon, resulting in a more pure, accurate tone. Low frequencies will be projected and will no longer lack the definition you desire. Mid and high frequencies will be crisp and intelligible. Rattles and resonances will be a thing of the past.’

The Spike Claim: ‘By rigidly coupling a loudspeaker enclosure to a floor by means of a spiking system, it is possible to dramatically improve clarity, stereo imaging and bass response. This is very apparent with subwoofer systems.’

The Quandary: These sources claim the same benefits from coupling and from decoupling. Who’s telling the truth?

The Truth: Both are lying. Isolation and coupling makes no difference. To test this I measured the response of my THT sub and my David full range with the test mic in the room, in the next room, and in the room below, with the cabinet sitting on the carpeted floor, on four inches of high density acoustic foam, on rubber feet and on spikes. I’d post the measured results for each set of comparisons, but there would be no point. In each case the measured responses of the four options were identical.
Note that this was on a carpeted floor. There may be some slight benefits to isolation devices or rubber feet on a bare floor, or on a bare shelf or stand. But you never want a bare floor, it’s an acoustical nightmare. If you only have area rugs in your listening room stick a piece of felt carpet padding, a carpet scrap or rubber feet under your speaker. If you're using bookshelves on a bare shelf or stand small rubber feet or felt pads are all you need to prevent spurious vibrations.

The Endorser Claim: ‘I tried them and they work, I know what I’m hearing!’

The Truth: The first thing you learn in an acoustical engineering course is that you don’t know what you’re hearing. If you did you’d be able to listen to a speaker, take pencil and graph paper in hand, and draw a frequency response chart, THD chart and waterfall plot, all with 1/24 octave resolution and 1/10dB accuracy. Our ears just aren’t that good, not by a very wide margin. But our imagination works very well, and that clouds our audio judgment, leading to placebo effect. In short, if you think something will make a difference in the sound, it will.

One item that's always missing from both manufacturers and owners claims are measured results, before and after. We often say 'If you don't have a picture it didn't happen'. In this case that picture is measured in-room response. When virtually anyone who's really serious about their sound has REW or the like that's not a lot to ask for.

Those who make isolation devices are no different than the cable crooks or any of a hundred other outfits who are interested in one thing and one thing only: Your money. You have it, they want it. And like all snake oil merchants they know the less you understand about how audio actually works, the better a mark you are. Caveat Emptor.

For an in depth examination of why we really don’t know what we’re hearing check out this video:
http://www.youtube.com/watch?v=BYTlN6wjcvQ

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post #4 of 32 Old 04-04-2013, 09:12 AM
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I don't see how decoupling subwoofers is a myth. Decoupling subwoofers is not to increase SQ or anything. It is merely meant to reduce the vibrations caused by the moving driver from transmitting to nearby material.
The effect on the driver movement obviously depends on the degree of coupling to the floor, ie. smooth surface, surface area, etc.

You want solid proof? Stick a cup of water on top of a sub. Now lift it off. Unless the sub enclosure is dual opposed, I am quite sure you'll see a noticeable difference.
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post #5 of 32 Old 04-04-2013, 09:47 AM
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Your hand is dampening the vibrations. Decouple the sub, and then put the cup in front of the sub and watch it dance.

Dumb enough to spend lots of cash on this junk!
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post #6 of 32 Old 04-04-2013, 10:16 AM
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Quote:
Originally Posted by yelnatsch517 View Post

Stick a cup of water on top of a sub. Now lift it off. Unless the sub enclosure is dual opposed, I am quite sure you'll see a noticeable difference.
Now measure the frequency at which said vibrations take place. It's not within the subwoofer passband, nor even close to it. For a sub not to be totally defective panel resonances are no lower than 500Hz; with a well made sub they're higher than that. 500Hz vibrations have no more effect vibrating a floor than will a spitball in stopping an elephant. Preventing those vibrations from causing the sub to buzz atop a hard floor only takes rubber feet or a bit of carpet, not a $50 gizmo.

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post #7 of 32 Old 04-04-2013, 10:52 AM
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Quote:
Originally Posted by flyng_fool View Post

Your hand is dampening the vibrations. Decouple the sub, and then put the cup in front of the sub and watch it dance.

Hmm, I'll try that. Maybe not in front of the sub as that is a little cheating, placing the water at highest SPL point.
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Originally Posted by Bill Fitzmaurice View Post

Now measure the frequency at which said vibrations take place. It's not within the subwoofer passband, nor even close to it. For a sub not to be totally defective panel resonances are no lower than 500Hz; with a well made sub they're higher than that. 500Hz vibrations have no more effect vibrating a floor than will a spitball in stopping an elephant. Preventing those vibrations from causing the sub to buzz atop a hard floor only takes rubber feet or a bit of carpet, not a $50 gizmo.

I agree with the rubber feet. Some people just prefer to not have those for various reasons, aesthetics included.
What we're interested in is probably not the cabinet resonance. When the drivers move back and forth at, say 10 Hz, does it not cause the cabinet to want to move in the same way?
Light horizontal firing subs that are not dual opposed tend to rock and crawl around, why is that?
What is the purpose of dual opposed design? I thought it was to stabilize subs so that they don't "crawl" around.
Now if the cabinet is heavy enough, where does that energy go? What I'm saying is a large subwoofer heavy enough not to move around is similar to the driver being bolted directly to the ground, if it is not decoupled by some method, rubber feet or otherwise.
Is this thought incorrect?

Another analogy: If I'm on the second floor of a house and jump up and land with stiff straight legs, how much energy is transferred through the house.
Now I do the same, except I land on my bed (decouple).
In the first scenario, I guarantee it will sound like an earthquake just hit. In the second scenario, not even a mouse would notice.
Can this analogy be applied to subwoofers? I only weigh 140lbs. I'm fairly sure my two LMS 5400 drivers weigh more than that combined.

My theory is decoupling the subs would probably have a larger effect on your neighbors house than your own house.
Logic is that much of the vibrations within "short" distance (within the room or house, obviously dependent on sub capability) is caused by acoustic energy.
The vibrations at further distances is caused by mechanical energy due to subwoofer not being decoupled from the floor.
Is my logic flawed?
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post #8 of 32 Old 04-04-2013, 11:02 AM
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Rubber feet will protect the bottom of a sub from scuffing. Given a potentially very uneven floor (like say: tile) they will also ensure that that sub is resting on four points rather than (possibly) teetering on a pivot point caused by a rise in a tile. Rubber also generally grips better than varnished wood.

Spikes deal with the opposite problem: rugs. For one thing, they get them a bit above the rug line (which helps reduce rug fuzzies on the bottom of the speaker). Also, depending on the speaker weight, and weight distribution, and the strength of the rug pile, the speaker can lean as it compresses some pile more than others. I suppose in an extreme example, it could even become unbalanced and fall over. Spikes mitigate that.

My N801's (pictured in my avatar) actually use small wheels... which also make moving the speaker easier.

And I have no idea where Bill is getting his "$50" from. Neither costs nearly that much.
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post #9 of 32 Old 04-04-2013, 11:07 AM
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Subdudes cost around $50.

Dumb enough to spend lots of cash on this junk!
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post #10 of 32 Old 04-04-2013, 11:12 AM
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Quote:
Originally Posted by flyng_fool View Post

Subdudes cost around $50.
I'm sure someone sells them for $1000, but

$4.25: http://www.parts-express.com/pe/showdetl.cfm?partnumber=240-725
$8.95: http://www.parts-express.com/pe/showdetl.cfm?partnumber=240-660
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post #11 of 32 Old 04-04-2013, 11:40 AM
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I can't believe we are arguing whether the effects of coupling/decoupling is audible. Of course it is audible. All acoustic instruments produce their audible effects based on some type of coupling of a small vibrating part against a large acoustically live surface. Therefore you absolutely want to decouple a speaker from a live surface. But you also have to balance this requirement against the need to keep the enclosure stable. In terms of being "acoustically live", most wood floors are only "live" in the bass region. Thick carpets and padding help keep floors quiet. Bare wood floors are more troublesome - try putting your cellphone on carpeted vs bare floor with the speaker facing down and notice the difference. This is why generally it's more important to decouple subwoofers than normal speakers. Full range towers may be troublesome, however, and the owner may wish to experiment with decoupling.
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post #12 of 32 Old 04-04-2013, 11:46 AM
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This is a Auralex subdude:

http://www.amazon.com/Auralex-SUBDUDE-HD-Isolation-Dampening/dp/B003EM17IK

Dumb enough to spend lots of cash on this junk!
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post #13 of 32 Old 04-04-2013, 11:52 AM
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Quote:
Originally Posted by gtengineer View Post

I can't believe we are arguing whether the effects of coupling/decoupling is audible. Of course it is audible. All acoustic instruments produce their audible effects based on some type of coupling of a small vibrating part against a large acoustically live surface. Therefore you absolutely want to decouple a speaker from a live surface. But you also have to balance this requirement against the need to keep the enclosure stable. In terms of being "acoustically live", most wood floors are only "live" in the bass region. Thick carpets and padding help keep floors quiet. Bare wood floors are more troublesome - try putting your cellphone on carpeted vs bare floor with the speaker facing down and notice the difference. This is why generally it's more important to decouple subwoofers than normal speakers. Full range towers may be troublesome, however, and the owner may wish to experiment with decoupling.
The instruments usually rely on a resonance cavity. The physical movement of the string causes vibrations in the air that gets reinforced in the resonance cavity. The string is the sourceof the sound, but the air is the coupler. At least I'm pretty sure.

As Bill said, he's taken actual measurements and the science doesn't lie.

Dumb enough to spend lots of cash on this junk!
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post #14 of 32 Old 04-04-2013, 11:56 AM
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Quote:
Originally Posted by yelnatsch517 View Post

When the drivers move back and forth at, say 10 Hz, does it not cause the cabinet to want to move in the same way?
It will cause the cabinet to want to move in the opposite direction as the cone. That can be addressed via sheer weight, by dual opposed drivers, with downfiring or, if the floor is carpet, spikes, anything that causes the friction between the cab and the floor to be adequate to resist the motive force exerted by the driver. This isn't de-coupling, it's coupling the cab more firmly to the floor. The ultimate method would be to bolt the cab to the floor.
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Logic is that much of the vibrations within "short" distance (within the room or house, obviously dependent on sub capability) is caused by acoustic energy.
The vibrations at further distances is caused by mechanical energy due to subwoofer not being decoupled from the floor.
Is my logic flawed?
Whenever you apply logic to issues involving sound it's usually incorrect, as there's very little about sound that's either logical or intuitive. As to what your neighbor hears, your speakers create sound waves, which travel via vibrating the gas molecules present in the air. When they hit your walls, floors, ceiling, doors and windows they vibrate those objects. In turn those objects pass those vibrations to their opposite side, where the gas molecules in the air on the other side are in turn vibrated, passing the wave along. The neighbor will hear the bass frequencies at far higher levels than the mids and highs for two reasons. One is that low frequency waves have far higher energy content than higher frequency waves, so less of their energy is absorbed by walls etc. To be precise, the power density of the wave drops by 1/2 for each octave increase in frequency. The other is that within the room where the sub is located room modes will cause cancellations, whereas beyond the room those modes and their associated cancellations no longer exist.
If you do want to apply a bit of logic to the mechanical coupling issue, listen to the sub in the room below the sub, and those above and beside it. There won't be much difference, despite the sub not being in contact with the walls or the ceiling.

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post #15 of 32 Old 04-04-2013, 12:54 PM
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Quote:
Originally Posted by gtengineer View Post

I can't believe we are arguing whether the effects of coupling/decoupling is audible. Of course it is audible. All acoustic instruments produce their audible effects based on some type of coupling of a small vibrating part against a large acoustically live surface. Therefore you absolutely want to decouple a speaker from a live surface.
Which is accomplished by the spider and surround (you do remember that the speaker is that moving cone/dome, right?)

The discussion here is about the enclosure, not the speaker.
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post #16 of 32 Old 04-04-2013, 01:09 PM
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Originally Posted by flyng_fool View Post

The instruments usually rely on a resonance cavity. The physical movement of the string causes vibrations in the air that gets reinforced in the resonance cavity. The string is the sourceof the sound, but the air is the coupler. At least I'm pretty sure.

I am not familiar with *ALL* stringed instruments, but I am with guitars, and this is not how a guitar works. An acoustic guitar's strings excite the soundboard it is attached to through the bridge, which then excites the air inside its resonance cavity. Part of that sound comes out of the sound hole, but most of it is projected directly by the sound board. I have a feeling that violins work the same way. If air was the primary coupler, there would be little difference between the sustain of an acoustic vs electric guitar. But we know that electric guitars have far greater sustain due to its solid body design and therefore the string's vibration energy do not decay as rapidly.
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As Bill said, he's taken actual measurements and the science doesn't lie.
It's only science if it's been peer reviewed. wink.gif

Of course I am kidding. Truthfully, I haven't given too much thought to do actual measurements since a thick slab of acoustic foam is so inexpensive in the grand scheme of things.
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post #17 of 32 Old 04-04-2013, 01:16 PM
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Originally Posted by JerryLove View Post

Which is accomplished by the spider and surround (you do remember that the speaker is that moving cone/dome, right?)

The discussion here is about the enclosure, not the speaker.

Are you arguing semantics? If so, I have never seen anyone refer to the sprung mass of a driver as the "speaker", so I am not sure where the confusion is. Fact is, speaker enclosures, even those used on high dollar well made speakers, have measurable vibrations when playing loud signals. These vibrations when coupled to a live surface will generate sound. The audibility of that sound depends on a variety of factors and is therefore arguable - which is what's taking place in this thread here.
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post #18 of 32 Old 04-04-2013, 01:44 PM
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Quote:
Originally Posted by gtengineer View Post

I am not familiar with *ALL* stringed instruments, but I am with guitars, and this is not how a guitar works. An acoustic guitar's strings excite the soundboard it is attached to through the bridge, which then excites the air inside its resonance cavity.
The string vibration excites the soundboard but the main purpose of the air mass and sound hole is to tune the resonant frequency of the body. That's why cellos are larger than violins. The vibrating top then vibrates the air around it. In that respect it acts like a driver cone, while the rest of the body acts like a speaker cabinet. You don't place the guitar on the floor so that the body will cause the floor to vibrate so that the sound will be heard. Yes, that's a silly notion, but no less silly than to think a speaker cabinet will cause the floor to vibrate.
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If air was the primary coupler, there would be little difference between the sustain of an acoustic vs electric guitar. But we know that electric guitars have far greater sustain due to its solid body design
The sustain of an electric is due to the high mass of the body. The lower mass of an acoustic acts as an absorbing medium, particularly the soft spruce top. With the higher mass of an electric the string's energy isn't absorbed by the body, so it sustains longer. The higher the body density, the longer the sustain. That's why Les Pauls are so heavy, and why Ash body Strats sustain so much better than Poplar. And it's why I make my instruments from rosewood. I'm not just an acoustical engineer, I'm a luthier as well.



This also relates to speakers. Cabinets that are flimsy absorb energy that otherwise would be radiated as sound. Well made cabinets aren't flimsy, and their panels do not vibrate enough for their vibration to even color the sound, let alone vibrate a floor.

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post #19 of 32 Old 04-04-2013, 01:54 PM
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Originally Posted by gtengineer View Post

Are you arguing semantics? If so, I have never seen anyone refer to the sprung mass of a driver as the "speaker", so I am not sure where the confusion is. Fact is, speaker enclosures, even those used on high dollar well made speakers, have measurable vibrations when playing loud signals. These vibrations when coupled to a live surface will generate sound. The audibility of that sound depends on a variety of factors and is therefore arguable - which is what's taking place in this thread here.
You do appear rather interested in semantics.

It's interesting to note the lack of interest in musicians in putting pianos on either spikes nor rubber feet; instead using wheels because it makes movement more convenient or simple legs for appearance. It's almost as though this coupling you are concerned with is a non-issue under most circumstances.

Actually: I have some pro-gear hear and notice the same lack of care regrading footing; though again wheels are common.

So what's a ball-park volume on this vibration? -30db? -50db?
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post #20 of 32 Old 04-05-2013, 07:48 AM
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Originally Posted by Bill Fitzmaurice View Post

The string vibration excites the soundboard but the main purpose of the air mass and sound hole is to tune the resonant frequency of the body. That's why cellos are larger than violins. The vibrating top then vibrates the air around it. In that respect it acts like a driver cone, while the rest of the body acts like a speaker cabinet. You don't place the guitar on the floor so that the body will cause the floor to vibrate so that the sound will be heard. Yes, that's a silly notion, but no less silly than to think a speaker cabinet will cause the floor to vibrate.

While it is the soundboard that generates the bulk of the sound that a guitar makes, the side and back of an acoustic guitar certainly also generate sound and affect the tone of the instrument with far more implications than shape and volume. In this respect, the sides and backs of a guitar are not analogous to a speaker cabinet, whose job is to be as inert as possible. This is getting off on a tangent and is becoming silly, my point is that we should care about coupling, rather than dismiss it entirely based on erroneous understandings.
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The sustain of an electric is due to the high mass of the body. The lower mass of an acoustic acts as an absorbing medium, particularly the soft spruce top. With the higher mass of an electric the string's energy isn't absorbed by the body, so it sustains longer. The higher the body density, the longer the sustain. That's why Les Pauls are so heavy, and why Ash body Strats sustain so much better than Poplar. And it's why I make my instruments from rosewood. I'm not just an acoustical engineer, I'm a luthier as well.
That's fine and all, so why didn't you correct flyng_fool for claiming that string instruments produce sound by the strings coupling the sound through air? Because he was supporting your position?
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This also relates to speakers. Cabinets that are flimsy absorb energy that otherwise would be radiated as sound. Well made cabinets aren't flimsy, and their panels do not vibrate enough for their vibration to even color the sound, let alone vibrate a floor.
Put your subwoofer on some acoustic foam and pump some reference level bass through it. Feel the enclosure and let me know if you feel any vibrations - I am not talking about enclosure wall flex, but the entire enclosure shakes due to the oscillating mass of the cone, which can be quite substantial for larger high excursion subs. It's arguable whether this is audible as it depends on a wide range of factors. But dismissing it entirely as irrelevant is not the correct approach in my opinion.
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post #21 of 32 Old 04-05-2013, 08:23 AM
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Quote:
Originally Posted by JerryLove View Post

You do appear rather interested in semantics.

How so?
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It's interesting to note the lack of interest in musicians in putting pianos on either spikes nor rubber feet; instead using wheels because it makes movement more convenient or simple legs for appearance. It's almost as though this coupling you are concerned with is a non-issue under most circumstances.
Bill really should jump in and share his expertise on issues like this since it's right up his alley. It's not a non-issue at all. A large part of how a piano sounds is its interaction with the room it is in. In the case of a grand piano, the large soundboard is exposed on the bottom and its coupling with the floor has a significant effect on the resulting sound. So whatever coupling and room effect that results, one would chalk that up to being a characteristic of the instrument, rather than a fault. In live sound applications for large audiences, pianos are mic'ed from the top with the lid open and PA'd, so there is no issue with coupling there at all. Stage floors are also typically built with acoustic treatments.

That said, most of the coupling is through the air for a piano, and even a small piano is far heavier than a large subwoofer or speaker, while generating far lower output levels in the bass frequencies.
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Actually: I have some pro-gear hear and notice the same lack of care regrading footing; though again wheels are common.
Pro gear focuses on reliability, performance, and convenience. In live sound applications, the environment presents such tough problems that even getting a reasonably smooth FR becomes a challenge. So things like "vibration coupling" is fairly low on the priority list. People in their homes have a much more controlled and stable listening environment. They also have more time to fiddle with things, chasing after diminishing returns.
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So what's a ball-park volume on this vibration? -30db? -50db?
I have no idea. It would depend on a lot of different variables. Anyone who claims to know a figure or issue a blanket statement is being careless.
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post #22 of 32 Old 04-05-2013, 09:18 AM
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While it is the soundboard that generates the bulk of the sound that a guitar makes, the side and back of an acoustic guitar certainly also generate sound and affect the tone of the instrument with far more implications than shape and volume. In this respect, the sides and backs of a guitar are not analogous to a speaker cabinet.
The sides and back of acoustic instruments are made of high density woods, like maple, to reduce their ability to vibrate, as the waveforms produced by those vibrations interfere with those produced by the vibrations of the top, or in the case of a piano, the soundboard. They would be made considerably thicker if the weight didn't make the instrument too unwieldy.

One of the major advancements in acoustic instrument design was the Ovation guitar, which employed composite construction and a curved shape to significantly reduce the vibration of the back/side compared to wood. Reducing the ability of the sides and back to vibrate is exactly the same as what's done with a speaker, but as a speaker typically doesn't get tucked under the chin or slung on a strap a speaker can be made sufficiently heavy and stiff to render the panel vibrations too slight to color the sound produced by the driver, or to couple vibrations to the floor with sufficient intensity that they have any more effect than rain on a duck's back.

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post #23 of 32 Old 04-05-2013, 09:34 AM
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Bill really should jump in and share his expertise on issues like this since it's right up his alley. It's not a non-issue at all. A large part of how a piano sounds is its interaction with the room it is in. In the case of a grand piano, the large soundboard is exposed on the bottom and its coupling with the floor has a significant effect on the resulting sound. So whatever coupling and room effect that results, one would chalk that up to being a characteristic of the instrument, rather than a fault. In live sound applications for large audiences, pianos are mic'ed from the top with the lid open and PA'd, so there is no issue with coupling there at all. Stage floors are also typically built with acoustic treatments.

Of course the sound traveling through the air interacts with the floor. The question at hand is the acoustic effect of decoupling the enclosure... putting the piano on rubber feet.

And of course stages are treated. In addition to the above: you don't want a squeaky floor drowning out the music.
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That said, most of the coupling is through the air for a piano, and even a small piano is far heavier than a large subwoofer or speaker, while generating far lower output levels in the bass frequencies.
Pro gear focuses on reliability, performance, and convenience. In live sound applications, the environment presents such tough problems that even getting a reasonably smooth FR becomes a challenge. So things like "vibration coupling" is fairly low on the priority list. People in their homes have a much more controlled and stable listening environment. They also have more time to fiddle with things, chasing after diminishing returns.

Resonance aside: I just don't see this as an issue. Then again: I'm not sure how much audible vibration a <1lb cone can hope to impart by transductance to a few thousand cubic feed of poured concrete.
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I have no idea. It would depend on a lot of different variables. Anyone who claims to know a figure or issue a blanket statement is being careless.

But that's the thing: that determines if we have an issue or not.
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post #24 of 32 Old 04-05-2013, 01:09 PM
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Originally Posted by Bill Fitzmaurice View Post

The sides and back of acoustic instruments are made of high density woods, like maple, to reduce their ability to vibrate, as the waveforms produced by those vibrations interfere with those produced by the vibrations of the top, or in the case of a piano, the soundboard. They would be made considerably thicker if the weight didn't make the instrument too unwieldy.
You are being disingenuous given your expertise as a luthier. The woods used for the back and sides of a guitar are denser only so far as to allow the soundboard to be the main excited surface for projecting sound. However, once that primary objective is reached, there is no further effort to make them additionally inert, but plenty to make sure that their tone is in harmony with the soundboard. The wood types, thickness and construction of the sides and back are all done with consideration to the tone as they balance with the top - they do project less sound than the soundboard but they do produce sound and guitar makers have not made an effort to make them dead.
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One of the major advancements in acoustic instrument design was the Ovation guitar, which employed composite construction and a curved shape to significantly reduce the vibration of the back/side compared to wood. Reducing the ability of the sides and back to vibrate is exactly the same as what's done with a speaker, but as a speaker typically doesn't get tucked under the chin or slung on a strap a speaker can be made sufficiently heavy and stiff to render the panel vibrations too slight to color the sound produced by the driver, or to couple vibrations to the floor with sufficient intensity that they have any more effect than rain on a duck's back.
I wouldn't go so far as to call one company's product differentiation as a "major advancement in acoustic instrument design". Takamine and Yamaha aren't rushing to switch their top line guitars from wood back/sides to composites in order to take advantage of such a "major advancement". Ovation's use of composites is primarily to take advantage of the fact that they can make a seamless back structure with arbitrary contours that is difficult if not impossible with traditional wood construction. Doing so allows them to control the chamber resonance to tailor the guitar's sound output. This again is distinctly different from the goal of a speaker enclosure and counter to what you claim.

I'd rather not carry on this conversation if you choose not to deal fairly with the facts. We can just disagree and leave it at that.
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post #25 of 32 Old 04-05-2013, 01:18 PM
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I'd rather not carry on this conversation if you choose not to deal fairly with the facts. We can just disagree and leave it at that.
I only deal with facts. I also only come here to teach, not to argue, and in order to teach the other party must have the desire to learn. You don't, so hasta la vista.

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post #26 of 32 Old 04-05-2013, 02:55 PM
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Originally Posted by Bill Fitzmaurice View Post

It will cause the cabinet to want to move in the opposite direction as the cone. That can be addressed via sheer weight, by dual opposed drivers, with downfiring or, if the floor is carpet, spikes, anything that causes the friction between the cab and the floor to be adequate to resist the motive force exerted by the driver. This isn't de-coupling, it's coupling the cab more firmly to the floor. The ultimate method would be to bolt the cab to the floor.
Whenever you apply logic to issues involving sound it's usually incorrect, as there's very little about sound that's either logical or intuitive. As to what your neighbor hears, your speakers create sound waves, which travel via vibrating the gas molecules present in the air. When they hit your walls, floors, ceiling, doors and windows they vibrate those objects. In turn those objects pass those vibrations to their opposite side, where the gas molecules in the air on the other side are in turn vibrated, passing the wave along. The neighbor will hear the bass frequencies at far higher levels than the mids and highs for two reasons. One is that low frequency waves have far higher energy content than higher frequency waves, so less of their energy is absorbed by walls etc. To be precise, the power density of the wave drops by 1/2 for each octave increase in frequency. The other is that within the room where the sub is located room modes will cause cancellations, whereas beyond the room those modes and their associated cancellations no longer exist.
If you do want to apply a bit of logic to the mechanical coupling issue, listen to the sub in the room below the sub, and those above and beside it. There won't be much difference, despite the sub not being in contact with the walls or the ceiling.

Just so I'm clear, if we were able to somehow completely levitate a subwoofer off the floor (decouple), it wouldn't considerably reduce the vibrations or amount of energy transfer through the ground because energy transfer at below 20Hz is mostly acoustic, not mechanical?
If so, this is hard for me to imagine, but fact is fact. tongue.gif I just always thought most of the energy transfer through the ground was caused by mechanical energy.
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post #27 of 32 Old 04-05-2013, 03:09 PM
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Just so I'm clear, if we were able to somehow completely levitate a subwoofer off the floor (decouple), it wouldn't considerably reduce the vibrations or amount of energy transfer through the ground because energy transfer at below 20Hz is mostly acoustic, not mechanical?
Correct, except that the energy transfer throughout the entire subwoofer pass band is acoustical, not mechanical. BTW, one of the other engineers here, Mark Seaton if I recall correctly, said that's exactly how you should determine if you really need to spend a lot of money on an isolation pad. He also said he too has never found a pad does anything to stop low frequency vibrations, nor have any of the other subwoofer designers here AFAIK.

Where a well made sub can have panel vibrations is well up into the midrange, 500Hz and higher. Those vibrations can cause a glass of water atop the sub to vibrate, or a lamp or knick-nack that weighs up to a few pounds or so. It won't cause a floor weighing a few hundred pounds or more to vibrate. What will cause the floor to vibrate is the acoustic output, and in turn the sub can vibrate atop the floor unless it's isolated. But all it takes is rubber feet or some carpet. To suggest that mechanical vibrations will cause the floor to vibrate is like a tail wagging the dog, and in this case it's a Chihuahua's tail attached to a St. Bernard's body.

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post #28 of 32 Old 04-05-2013, 03:17 PM
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I only deal with facts. I also only come here to teach, not to argue, and in order to teach the other party must have the desire to learn. You don't, so hasta la vista.

One of the problems right there. A discussion board where someone pre-supposes that they are correct in all things.

And no, you deal in tons of your own opinions which you call facts. I've pointed out examples where your opinions violate physics in the past.
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post #29 of 32 Old 04-05-2013, 03:23 PM
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Those vibrations can cause a glass of water atop the sub to vibrate, or a lamp or knick-nack that weighs up to a few pounds or so. It won't cause a floor weighing a few hundred pounds or more to vibrate. What will cause the floor to vibrate is the acoustic output, and in turn the sub can vibrate atop the floor unless it's isolated. But all it takes is rubber feet or some carpet. To suggest that mechanical vibrations will cause the floor to vibrate is like a tail wagging the dog, and in this case it's a Chihuahua's tail attached to a St. Bernard's body.

This is another good example where you've ignored physics in lew of opinion.

Energy cannot stop. Vibration energy can be converted to something else (say: heat), but no amount of mass will reduce vibration to zero (without such conversion). The actual energy remains constant.

This is why you can hear people inside a submarine from outside a submarine (something far heavier and more rigid than your floor).

When a man in a little capsule "orbits the Earth", the reality is that they both orbit a shared barycenter. The difference between the true center and barycenter is incredibly small when such mass disparity is involved; but it is true none the less. Same here. A rigid coupling to a large mass will reduce amplitude, but not energy. Another example is hearing approaching footsteps by putting your ear to the ground. The Earth has a lot of mass.

PS. Dogs do wag to counter-balance the movement in their tails. In fact: a major purpose of a tail is to counter-balance movements of the animal.

Physics doesn't change based on your opinion Bill.
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post #30 of 32 Old 04-05-2013, 05:22 PM
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This is another good example where you've ignored physics in lew of opinion.

Energy cannot stop. Vibration energy can be converted to something else (say: heat), but no amount of mass will reduce vibration to zero (without such conversion). The actual energy remains constant.

This is why you can hear people inside a submarine from outside a submarine (something far heavier and more rigid than your floor).

When a man in a little capsule "orbits the Earth", the reality is that they both orbit a shared barycenter. The difference between the true center and barycenter is incredibly small when such mass disparity is involved; but it is true none the less. Same here. A rigid coupling to a large mass will reduce amplitude, but not energy. Another example is hearing approaching footsteps by putting your ear to the ground. The Earth has a lot of mass.

PS. Dogs do wag to counter-balance the movement in their tails. In fact: a major purpose of a tail is to counter-balance movements of the animal.

Physics doesn't change based on your opinion Bill.

From what I know of conventional physics, what you say is logical and intuitive; however Bill says when it comes to acoustics, many things are not intuitive.
I don't want to start an argument between two sides, but this is extremely simple to test.
All some needs to do is play something like 120db from a sealed system of subs resting on the floor.
Now have two cups of water, one sitting directly on the floor and another on something like a memory foam pillow.
We can easily compare how much of the vibration is transferred acoustically and how much is transferred mechanically.

A funner way to experiment would be:
Create a wall bolted to the wall and foundation. Now mount 8 RE XXX 18" drivers all facing the same direction. Play dubstep and measure how long it takes for the house to come crumbling apart.
Do the same, except using decoupled sealed enclosures and measure the time. Make sure to level match so the same SPL is achieved in both cases.
Anyone volunteer to do this experiment?

I would run the first experiment with the cup, but my subs have rubber feet and weigh like 150lbs so it's somewhat decoupled and it's way to heavy for me to try to remove the feet.
Anyone want to volunteer for that one and post a vid?
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