subwoofer ampmodule requirements

[keyser]

What does a subwooferamp need to be?
What type of connection is best in under what circumstances?
Which features do you need?

[paulspencer]

For a sub amp you need:

* plenty of power and something with a very solid power supply - bass is very dynamic, much more so than midrange and above, therefore it has a much greater power requirement

* distortion is not really important IMO

* ability to handle the impedance of your driver (are you sure?)

* ability to get rid of heat without fans that are too loud (some are quite ok)

The processor / crossover is another thing. I prefer to separate the two. I consider the following desirable:

* no eq in the case of plate amps as it will almost never be what you want

* rumble filter - defeatable

* variable crossover

* parametric eq, although this is best dealt with in a more sophisticated sep unit like BFD

[keyser]

i am planning to build a large subwoofer for music-use only.
í have been offered a module at a very good price. The amp has lots of power (200 Watts @ 8 ohm). Maybe it can not be used, because the low-pass is adjustable between 40 and 120 hertz. My main speakers already go pretty deep with their dual 8" woofers per side (i guess f3 inroom between 35 and 40 hertz).
The sub features no hi-pass.
I was thinking about integrating the sub on the REL-way (speakers full-range, sub coming in where speaker rolls-off).
REL's have variable cross-overs from as low as 22hz!
Do you think integrating a subwoofer with this module will be possible in my system?

tanx

[paulspencer]

It's a little more complicated than that when you consider room modes. I think it's near impossible to integrate subs properly with the controls available on a plate amp.

This is not to suggest that the amp module isn't worthwhile, but rather that you may need to add parametric eq and experiment with placement.

If you cross as low as you plan then you might not have any modal issues for the sub, but rather for your mains. Here room modes can really mess up the bass. If you have the means it might be worthwhile adding parametric eq to the bass in between the pre and power amp for your mains.

[keyser]

i am sorry paul, but i don't fully understand what you mean with room modes... could you clarify?

[paulspencer]

http://www.silcom.com/~aludwig/Room_...and_calculated

Typically below 200 Hz you will find room modes or resonances that introduce nasty peaks and dips into the response. Above the Shroeder frequency (SF), there is a transition from the modal region to the region where sound travels as rays as the wavelengths of sound are small compared to the dimensions involved. In this region the response is smoother because the modes are densely spaced, but below the SF their spacing makes the response very probemmatic. At a certain point the room is uniformly pressurised and modes are no longer a problem.

Here is an example of room response simulated vs measured: