Solution for "Jumping" Subwoofer

[jay21112]

Problem:
So I've had 2 Polk Audio DSW 4000 Micropro subs. I really like them and I got them for a good price (are now discontinued).

Well, the other night, I was watching Insidious and I noticed this "flapping" sound coming from one sub. Insidious itself was a good movie, with ok sound, but there are some points where the bass is incredible (I distinctly remember the bass being out of control when the dad had a flashback to his childhood and he was laying in bed).

Well, I played it over and over and I kept hearing this "flapping sound" which made me think it was a blown voice-coil or something like that. To the point where I called Polk Audio and was talking about getting it fixed and they basically said that they have never heard of one of these subs blowing and that I should inspect the sub thoroughly before sending it for service.

So, I played around with the sub, and realized that on those heavy bass hits...the sub actually JUMPS off the floor, and the "flapping sound" was the entire sub vibrating as it settled back into the grooves made by the spiked feet. When I sat on the sub, to prevent it from jumping, the flapping sound didn't happen.

So, nothing was wrong with the sub except for the fact that Polk Audio should have made it a few pounds heavier (like 50-100lbs).

Solution:
I already have my subs on wood platforms, so I figured I'd just anchor the sub to the platform. Well, try to find tie-down straps at Lowes or Home Depot the day before a Hurricane. Ha. I ended up going to Auto Zone, and all their tie-downs were in stock. I guess I was the only one visiting Auto Zone that day...

Well, I bought a pair of ratcheting tie downs and strapped the sub to the wood platform. First I cut off the hooks (didn't want the hooks damaging the sub), then threaded both ends of the strap through the ratchet mechanism. Then I boosted the platform in the air with some wood, and put the ratchet section of the strap underneath the platform so it would be hidden. Then I tightened it, removed the wood "lift", and set the sub back in place. No more "jumping", no more "flapping", and I would guess that anchoring the sub more firmly will make it more inert and improve overall bass response.

So, my suggestion is if you have a sub on a platform, to go out and buy some ratcheting tie-down straps, and strap that baby down.

 

[its phillip]

Nicely done

 

[Adam]

Agreed - nice, simple solution. If you wanted to get rid of the strap for visual reasons, you might be able to fairly easily anchor the sub to the platform through the feet (easier if the sub feet are attached with bolts) - that would require you to drill four holes through the platform and replace the stock bolts with ones long enough to go through the platform and the sub feet.

 

[jay21112]

Agreed - nice, simple solution. If you wanted to get rid of the strap for visual reasons, you might be able to fairly easily anchor the sub to the platform through the feet (easier if the sub feet are attached with bolts) - that would require you to drill four holes through the platform and replace the stock bolts with ones long enough to go through the platform and the sub feet.

That's actually a great idea, but one that would take a lot of ingenuity with this sub. The sub has a bass radiator on the bottom which is why it jumps off the ground. Therefore, there would have to be a spacer through the bolt between the sub and the platform. Also there is risk of splitting the platform as I drill through it because the holes would be close to the edge.

But, it is a great idea, and one worth doing to maintain the professional appearance of the equipment. I'll keep it in mind. Thanks.

 

[j_garcia]

Auralex Gramma or Great Gramma would probably have done it too, likely without straps, providing the footprint of your subs fits one of them. This would decouple the sub, as opposed to coupling it the way you have with the current platform. The platform appears to be directly coupled to the floor, so it isn't providing much benefit aside from acting as a riser.