Buttkicker LFE on my small riser underwhelming

I posted this in the construction forum before I realized that there is a Transducer forum. Posted here as well.

I mounted a buttkicker LFE Transducer (from a Buttkicker LFE kit) beneath a 4’ x 5.5’ riser. The riser is constructed of ¾” plywood glued and screwed to a base constructed from 2”x8” lumber. Because of seat mounting requirements, there are 8 2x8s in 4 feet so the riser is very stiff. The transducer is bolted directly thru the ¾” plywood (and thru a piece of 2x8 to stiffen the floor) about 1.5 feet from the rear of the riser, beneath the 2 old style folding theater seats. I used 4 of the rubber isolaters from the kit as feet for the riser. I estimate that the risers and seats weigh around 170 pounds. Pictures:




I have a similar transducer mounted to a loveseat of about the same weight as the riser with 6 K28 isolators. At first, I wired the 2 transducers in parallel to the bk amplifier. When I played a bass heavy movie scene (beginning of Serenity), I noticed that the transducer on the riser overloaded almost immediately and continuously (started rattling – hammering noise), while the one in the couch only rattled once (as it normally does during that scene).

My first thought was to replace the LFE kit isolators with 4 of the heavier K28s that I have. This made it quite a lot better, but it still goes from no shake to overload very quickly. In order to stop the rattling, the amp must be turned down so that I can feel very little shake for most of the movie – kind of defeats the purpose. Removing the feet completely (carpet) reduces shake but not overload.

Anyone have any recommendations that might help? Is it possible that the unit is defective? My next project will be to switch the transducers between the couch and riser to see if they behave similarly, but this requires two people and some effort. Would more power help? I am powering it with a crown 1500 amp. It is rated at 1050 watts at 8 ohms (bridged) – has to be higher for 4. I can switch to a buttkicker 1000, but the amps are difficult to reach at the moment. Would going with the much more expensive large isolaters ($15 each) help? I suppose that it would be possible to cut out parts of the 2x8s to lessen the stiffness of the riser, but that would be a last resort and rather permanent...

Thanks in advance!

bill

The whole thing actually sits on rubber isolators, so they won't hit the floor, but the platform IS very rigid. I could cut down the "joists" if more flex is needed...

Thanks Craig. I wanted stiff joists so that the chairs, which mount on a single leg, would not cause the riser to deform. I think that I overshot some. I am working with Marvin at Guitammer and am a little worried that he will eventually tell me the same thing. If it comes to that, I'll take a reciprocating saw after the joists and see what happens. I'll update with any progress.

I agree that stiffness is a big issue. I experimented some with different amps and configurations last night; there are a few other things going on.

First, I don't think that the banana plugs were fitting into the speaker binding posts properly (my daughter plugged them in and didn't mention that they weren't snug). I switched to bare wire on the binding posts.

Second, power seems important . In order to use my crown amp, I have to crank up the output on the sub-out and max out the gain on the amp due to mismatched line levels. This works fine on the more flexible couch, but I think it leaves a little to be desired on the riser. The buttkicker amp better matches line level and gives more shake before overload. We are now getting a good amount of shake, but it still overloads more often on the the riser. I'm getting closer.

I like the idea of trying the heavier (and taller) feet. The current feet compress some and sink into the carpet so there isn't much space between the riser and the carpet. - I just wish they didn't cost more than the materials in a new riser...

Thanks guys! Really appreciate the input.

bill

Has anyone tried mounting a BK transducer on its side? If I were to use soft isolators and mount the transducer on its side - thru a joist - would I get the desired result? The whole point of the transducer is to move up/down, it would just move the riser sideways. Seems like this would give the seats a pretty good shake...

bill

Also, I heard back from Marvin at BK and he suggested:
1) Try adding another transducer. I can try this, but it takes some work to remove from the couch and install in the riser.
2) Try the larger isolators. I will try the 220s.
3) Make the platform less stiff. Still kind of a last resort - but if all else fails I will go to town with a reciprocating saw.

bill

The top of the riser is glued and screwed to the joists, so no joy on isolating just the top. Also, I don't think that the plywood is strong enough to hold the chairs.

Knowing that there is a lot of pressure applied to the rear of the riser due to the small mounting feet, how much joist should I cut out. The entire riser is made from 2x8s. For example, can I leave the outer joists whole? Cut the inside 2x8s down to 2x4s? It will have to be thicker by the chairs; the lags are 6 inches long. If I cut the outer joists, I have to be much more precise...

Since I will need isolating feet regardless of what I do, I just ordered 4 220s. I would like to get another transducer, but they are running $200 to $240 each now... only paid $100 each for the ones that I have.

bill

So, the 220 feet have been installed. I would say that they made a marginal improvement over the smaller feet, but that could just be my brain trying to justify the $60. Next comes the reciprocating saw; with luck I will get good shake before I cause the collapse of the structure.

bill

Last night I watched Paranormal 4 with my daughter (even she thought it was bad) and we could hear the transducers at times. The movie had a loud low frequency hum during certain parts that caused both transducers to rattle while producing almost no shake. I had never heard this before. I'm thinking that this is the noise made by older transducers that others have referred to - it wasn't an overload, just a semi-quite rattle. The rattle was very distracting from the riser (no carpet to soften sound) and less so from the couch. I hope that this is just good reason to skip Paranormal 4. I don't relish having to turn off amplifiers during certain movies.

bill