Does Your Floor Dance?

[Ron Texas]

A few months ago I bought an ML Dynamo 1000W sub on sale. By listening to web based sine wave generators, positioning, fiddling with the controls and the high pass filter on my XLS 1502 amp, it was reasonably close to flat. However, the room seemed to shake too much on low notes. It was bass you could feel way to much. After some experimentation and more listening I found the vibration was centered at 32 hz. It was only a little louder acoustically, but the floor did dance.

I live in the US. Nearly all of our homes are built with a wood frame. Masonry is attached to the outside of the wood frame. The masonry does not support the weight of the frame. My listening room is in a 3rd floor finished attic. It isn't a remodeled attic. The house was built that way from the start. The floor is covered with wall-to-wall (fitted) carpet over a foam pad. Under the pad is plywood which is nailed directly to the wood frame of the structure. It feels solid enough walking on it, but goes crazy at 32 hz.

Out of desperation I needed a cheaper solution than tearing up the carpet and nailing down another layer of plywood. The 1000W is down firing in its default mode, but may also be used as a front firing unit. I had not tried front firing before because it puts the controls on the bottom.

Suddenly, the floor stopped dancing. The good news is the 1000W is convertible. I have to tilt the thing to make adjustments, but I am getting to the point where adjustments have become less frequent and it only weighs 35 Lbs. If your listening room is plywood over wood rafters, think twice before buying a down firing sub or pair of speakers with a built in down firing sub.

File under cheap fixes.

 

[Another Bob]

Interesting. This would seem to indicate that the floor is vibrating in reaction to the moving mass of the speaker cone, rather than the acoustic output. If that is true, you should be able to achieve significant reduction in the effect through a combination of decoupling (using springy/absorbent materials under the sub) and mass loading (putting something heavy on top of it), although your solution is obviously simpler and more elegant.

 

[Soniclife]

A lot of HT people choose down firing for this specific reason, more rumble.

If my concrete floor starts flexing sq will be the last of my worries.

 

[Blumlein 88]

I've a downfiring sub on a wood over wood joist floor. It doesn't do that. I don't have a 1000 watt sub. I think its 250 or 300. I do get a nasty room resonance that will rattle some window panes around 34 hz. It would also rattle a light fixture, but moving the sub a couple feet fixed the light fixture rattle.

 

[Webninja]

Maybe add some isolation pads/feet to reduce the last bit of vibration?

 

[Ron Texas]

Maybe add some isolation pads/feet to reduce the last bit of vibration?

All I had to do was move the feet on the sub to the back and turn it 90 degrees. Since it worked I don't have to experiment with isolation pads. It's designed to either fire down or forward.

 

[Ron Texas]

I've a downfiring sub on a wood over wood joist floor. It doesn't do that. I don't have a 1000 watt sub. I think its 250 or 300. I do get a nasty room resonance that will rattle some window panes around 34 hz. It would also rattle a light fixture, but moving the sub a couple feet fixed the light fixture rattle.

Nearly everything in the room which wasn't nailed down was rattling. The floor vibration was insane. It was perfect for earthquake movies but bad for music and even some video soundtracks sounded overdone.

 

[Ron Texas]

Epilogue: I found another convenient spot where the sub could fire down without shaking the floor wildly.