Keeping it low

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In my experience getting the very low frequencies to integrate and propagate through the room is the biggest challenge we have placing a subwoofer in the room. That's why in yesterday's post I suggested we start low: both in frequency and level. If you're using one of the low frequency rich discs I suggested yesterday, this shouldn't be too difficult. Whatever disc you use, just make sure it has a good amount of low frequency energy and you're familiar with how that energy should sound at the listening position. There's a bit of work getting this right, so make sure you're patient and prepared to spend the time - pick a Saturday or Sunday afternoon for this exercise. Play the track you have selected with the low frequencies you want to propagate through the room and make sure the sub's volume control is completely down/off. Familiarize yourself with how it sounds without the sub on. Now,turn just the right woofer's volume up to perhaps 1/3 its total level and repeat the track; leaving the left woofer off (or if you're doing a mono sub then no need to worry about the left). If you're lucky, it'll sound like your main speakers just got an extension in the bottom end. In all likelihood you're going to need to tweak the woofer placement a bit. If you're using theSaint-Saënspiece I recommended, track 3, the opening of that piece has the big organ at full range and the bottom end of the instrument should be perfectly balanced with the mid and top, just more room filling and far deeper reaching. If you have that sense when it's being played and all you need is a bit more level, you're in good shape. But if a particular note stands out and booms in the room or if there's little to no increase in energy, you're going to have to move the sub around to fix that. Unlike our setup guide for the main speakers, where we want to make only small changes, the subwoofer deserves big changes to get an idea where it's best to place it. Hopefully you can find a spot where the low frequencies are pretty uniform and are supported in the room. If you find that spot, measure it and then place the left sub in the same relative postion on the opposite side and it should be fine. If you cannot find anywhere in the room that the sub works well, there is a tried and true old trick you can use. You can place the subwoofer in the listening positon and repeat the track. Yeah, I know, it's weird but here's what you do. With your chair or couch moved out of the way and your subwoofer in its place, play the track and while it's playing, walk over to the area where your speakers are. As you walk around behind the loudspeakers you may find a spot where the low bass is what you want. Mark that spot and put the woofer there. The reason this works is because the bass wavelengths are so long that they cover the entire room and work in either direction. Lastly, you can tackle any boominess you might have in the low frequencies with Tube Traps in the corners - something you may want to do in any case if you can aesthetically get away with having them occupy the room. Room conditioning, for bass or imaging, is an entire subject in itself - and one we've covered before - but something very important to your system's well being. Once you've managed to get the low frequencies where you want and without any bass notes jumping out at you, turn the woofer levels up so the organ piece is seamless - this particular track should shake the room - as a real pipe organ would do in your listening room. While it's exciting to have this strong foundational bass, don't get carried away - yes it should shake the room but no, it shouldn't overwhelm or sound unnatural. If you're in a big hall with such an instrument the lowest bass notes move the room but they sound like they're coming from - and part of - the organ itself. Strive to get this seamless and so you don't notice the woofer - you just notice that "this is a big instrument". Now, this is a bit hard since we have the top of the woofer rolled off - so there's going to be a bit of a hole or gap in the response - you'll have to mentally fill that in for the moment. Once you nail the bottom end, you'll understand. When you're finished, play another track that has no low frequencies like track 3 does and make sure the woofer is contributing pretty much nothing - remembering we have the low pass filter frequency turned way down to 50Hz - to the sound. You can turn the level back down to zero and repeat the track and you shouldn't hear much of a change depending on what you're listening to. Tomorrow we'll start raising the frequency and setting the phase control if your sub has one - and I hope it does.
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Paul McGowan

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