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Discussion Starter · #1 ·
When should one use spikes or an isolation riser for a sub? Is there some common wisdom, like use spikes on carpet and a riser on hard flooring?


Specifically, I live in an apartment with carpet and have a sealed front-firing sub. I can't turn the volume up much without bothering the neighbors. I have a set of spikes I can install on my sub. Does it make sense to do that? It seems an isolation riser wouldn't get me much since it's already on carpet, and the spikes may make the floors/walls rattle more. What to do? Leave it as is?


And on another note my main speakers are towers sitting flat on the carpet. What should I do with them?
 

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Isolation platform/riser is the way to go. What they do is they isolate/decouple the subwoofer from the room. It will help hugely with your issue. It will help keep the bass in your room and it will eliminate any rattling or vibrations that you may currently have. It is also said that your bass will become more tight and punchy rather than muddy and boomy. You can also use the isolation platforms for your floor standing towers as well. You can make your own for very cheap.
 

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Discussion Starter · #3 ·
Why would the isolation riser have a much bigger impact than the carpet by itself? Seems the carpet would do a pretty good job isolating the sub vibrations from the flooring underneath already.
 

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Discussion Starter · #5 ·

Quote:
Originally Posted by flickhtguru /forum/post/20823902


As far as subs go carpet basically does nothing except give a softer place for the sub to sit. If you have questions http://www.auralex.com/c_sound_isola..._isolation.asp . The gramma and the subdude are specially made isolation platforms, read up on it.

I have read up on them, and I'm still unsure what the real benefit is over carpet. Is that much vibration getting into the hard floor underneath the carpet and pad that an isolation riser would eliminate?


The fact that Auralex sells a subwoofer isolation riser by using a graph of sound transmission lost whose x axis range is 100 - 5000 Hz doesn't really make me want to trust their marketing materials.
 

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If you want to couple the sub to the floor to prevent movement use spikes. When I have used them, I use them to get through carpet to concrete or a solid wood floor.


If you want to isolate (decouple) the sub from the floor use an isolation pad. This also prevents damaging hardwood floors with spikes.


Neither decouples the sub's sonic output from the room itself so things like room modes still matter. The sonic benefit of either has been debated frequently (and no doubt will be again, probably in this very thread).


Carpet is essentially transparent at bass frequencies; it will allow the sub to "float" over a floor thus potentially allowing greater vibration of the cabinet than if the sub was solidly anchored or decoupled from the floor.
 

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Quote:
Originally Posted by jonnythan /forum/post/20823913


I have read up on them, and I'm still unsure what the real benefit is over carpet. Is that much vibration getting into the hard floor underneath the carpet and pad that an isolation riser would eliminate?

Carpet doesn't have enough give to reduce vibrations by any significant amount, unless your carpet's pad is over three inches thick.


I use a homemade isolation pad made from a piece of MDF and sanding sponges. That's three inches of spongy material underneath. And it sits on shag carpet. It reduced cabinet vibrations transferred to the floor by a very significant amount.
 

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Discussion Starter · #8 ·

Quote:
Originally Posted by Tulpa /forum/post/20824669


Carpet doesn't have enough give to reduce vibrations by any significant amount, unless your carpet's pad is over three inches thick.
Quote:
Originally Posted by DonH50 /forum/post/20824597


Carpet is essentially transparent at bass frequencies; it will allow the sub to "float" over a floor thus potentially allowing greater vibration of the cabinet than if the sub was solidly anchored or decoupled from the floor.

These seem contradictory to me. If the sub is "floating" over a floor, how is it transferring any significant vibrations to the floor?
 

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It's two different things.


The carpet itself won't absorb the vibrations enough to eliminate them going through the floor (and everywhere else.) But it'll allow the sub cabinet to vibrate even more, exacerbating the problem.
 

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Try this equation -



Whatever you put the sub on will have two heights - one with no sub on top and one with the sub on top. The difference between these two heights is called the static deflection (Xst in the equation). Using the equation, a static deflection of 0.624 mm would make the entire system resonate at 20 Hz. For a transmissibility of below 20%, a static deflection 4 or 5 times that of the resonance frequency is required. 10 times higher would be even better. 4 times represents 0.624 mm x 4 = 2.5 mm.


If you think about when you put the sub down on something - does it actually depress that thing by 2.5 mm? If it's rubber then probably not. That's why for very low frequencies, springs are generally used.
 
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