Newbie DIY subwoofer builder needs some help with positioning and setup...

Hi all

I'm after a few pointers on how to get the most out of my newly built DIY sub. Overall I am extremely happy with it:

Acoustic Energy 150W amp, 12 inch driver (not the cheapest generic one but still cheap at around $130 AUD - 50 of your finest UK pounds) in a 60 litre 18mm MDF box with twin 66mm ports extended to 225mm as per my calculations using Win ISD...(giving me a supposed -3dB point of just below 30Hz)

If anyone can be arsed to read the ramblings of a semi-newbie then I'd love to hear your comments!

1. Placement - The room is a rectangle, about 4 metres by 10. The TV / amp / centre and the fronts are all at one end, with 3-metre sofas facing each other on each side of the room so you can lie on them on your back and and look forwards at the TV (my sweet spot for watching DVDs is however in a bean bag placed in the centre of the room!). The rears are about 1 metre past the ends of the sofas, toed in to point into the middle of the room.

I can't get the sub into the front corner of the room as the front right speaker is there, and there is a doorway in the front left corner. Anyway I can't have it anywhere near the TV at the front of the room as it is obviously not shielded and the magnet affects the TV from well over a metre away...

So I have placed the speaker in the middle of the side wall, just past the end of one of the sofas. Ok so this is not a corner, but the flat side of the sofa (about 70 cm high, flat and at 90 degrees to the floor) might help? Can anyone comment on this positioning? It certainly works, but is it "far from ideal" or adequate or next best from being in the front corner...?

Should I try and move the sub into the far corner of the room - ie 9 metres away from the kit (about 4 metres behind the rears) and probably about 6 metres through dead air behind where the listener would be sitting? After the ends of the sofas, there is nothing but a dining table and flimsy un-upholstered chairs for it to fire through

The reason I ask this is because at the moment I only have about 5 metres of cable... But if the consensus was "back of the room is the place" then I could easily knock something up...

2. Amplifier Setup - I have been reading the recent thread on volume/gain controls on subs... I'm going to play around with setting the output on the amp down a few dB, and turning up the gain on the sub amp, as per people's experiments reported in that thread. But can someone confirm, once I have the levels the way I want them, does the receiver adjust the power going to the sub in the same way as it does the volume of the other speakers, when I turn the volume knob? In other words, once I get the level the way I want it, I don't have to turn it up if I want to watch a movie with the volume up, and down if I want to watch with the volume down... the amp just increases / decreases the power sent to the sub in proportion?

3. Setup 2 - My Amp (Harmon Kardon AVR4500) has 2 subwoofer crossover frequencies - 60Hz and 40Hz, and a setting to send either the LFE channel only, or the left/right and LFE channels in one. For music (stereo) I have it set to LFE/L/R (I know there is no LFE but this is the only available option) and 60Hz crossover. For DTS and DD I have it set to LFE only, 60Hz.

Then I have the crossover filter on the subwoofer amp set all the way open - assuming that the receiver will have done this work for me. Is this the way to go? It seems like the only benefit I would have from using the crossover on the sub amp is if I wanted to achieve a crossover of *between* 60&40, or below 40 for that matter.

Also - for movies, do most people mix the front channel with the LFE and send to the sub, or just the LFE - is there any common wisdom on this or is it all down to personal preferences? Is it best to change to LFE only for those special movies that have a good .1 track, and use the mixed setting for less well designed movies?

Anyway, if you've got this far, thanks for reading. Greetings from Australia. Midwinter yesterday in Sydney and it was 26 degrees. What am I doing indoors playing with subwoofers?

Cheers

lhalha