Here is some correspondence with Buttkicker that I made early on, that might help somebody else. I was cleaning out my mailbox and came across it. I've since stopped worrying about it and just started enjoying them. They are still in use in my theater - I do still like them, and I'd recommend them to others who love as much tactile feedback as they can get.
Sent: Wednesday, December 05, 2012 12:26 AM
Subject: four buttkicker mini LFEs
I bought four buttkicker mini LFEs from a third party on amazon. I’ve determined that each reacts to the exact same wattage somewhat uniquely... Two activate earlier (using less wattage) than two others. Each is slightly different on the amount of power required to activate it. I can simply plug the same power source into each of the transducers in turn on the same clip and it takes different amounts of output power to initiate each one. Is this expected? As best I could tell these were new in box. They looked new and were sealed. I broke the packaging seal on each, and the seller advertised them as new.
One of them seems to behave more like my Clark Transducer TST209 in that if you put your hand on it you can feel it vibrate very early (at low volumes) and by comparison a couple of the units take a pretty sizable amount of power (comparitively) before they activate (literature says 50 watts minimum. I’m just not sure how much precision there should be in these units on the minimum wattage requirement.
As far as I can tell the unit that activates more easily than the other’s doesn’t suffer from any defects in shake or output capability – it just turns on sooner.
I was also somewhat surprised to determine that the buttkicker mini’s don’t seem to handle frequencies below 35hz very well. I’m an experienced home theater personality and have not applied too much wattage to these units, in fact, I have limited the wattage that can be applied to them using the DSP on the INuke DSP 3000 amp that I’m currently utilizing to 225 watts per channel (4ohm). In playing with the HPF on the DSP – I’ve determined that about 35 hz with a 18dB or 24dB octave rolloff seems to suit the mini LFE pretty well. Without the HPF, many bass heavy movies will bottom out the mini LFE’s. Is that expected on these smaller buttkickers? They do market as being able to hit 5 or 10hz, but my experience is without the HPF they just bottom out easily and feel very unnatural when trying to generate shake at those lowest frequencies in movies like Pulse, or War of the Worlds – etc. Again I’m not necessarily bothered by the HPF requirement – just wanted to know if that is expected.
A lot of what you're seeing is because you have referenced your levels at the higher frequencies, then tried to go into the low frequencies where there is no longer any room for internal movement. Let me explain.
The internal moving element, like any other electro-dynamic device, will want to move a greater distance as the frequency goes lower. The difference in motion between 35Hz and 20Hz is very significant. There's nothing wrong with doing that, except that you'll run into the limitations that you've seen (bottoming out at lower freqs). On the other hand, if you lower your power levels you'll be able to allow more of the lower frequencies. I also expect that you'll see more consistency in activation levels than you're seeing in the higher frequencies only.
Also, the minimum and maximum power ratings are, like speaker and other electro-dynamic devices not absolute figures, but rather a more arbitrary guide for the user. For example, a speaker manufacturer may place a minimum power rating on the speaker of 25 watts. This is not to say that nothing will come out of the speaker at lower levels, because the speaker will produce sound at 1 watt and less. Instead, the manufacturer is communicating to the user a level of power that will properly operate the speaker to the level and quality of sound that the manufacturer designed into it.