Keeping it low

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 the Saint-Saëns piece 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.

Paul McGowan – PS Audio, Intl

The big secret

Sorry about yesterday’s late post, there was a computer glitch with the server but all’s well now.

I promised in that post to let you in on a secret method to making sure your subwoofer integrates with your system well and it’s a two part solution: start low and start low.

I know, but I couldn’t resist.  The first start low is with the frequency.  Even if you plan on crossing over your sub at a higher frequency, perhaps 80Hz or so, don’t use that as your starting point.  Why?  Because there will be too many variables to get right.  Turn your sub’s low pass filter – this is the filter that rolls off the top of the woofer – to no more than 60Hz, preferably more like 40Hz or 50Hz.

The second keep-it-low is the volume.  Perhaps the single biggest problem I see with sub setups is the volume is just too high.  Start low and creep your way up – if you hear the sub working as a separate entity it’s too high in volume.  Subs should never standout out.

In fact, a proper sub never sounds like it’s even working in the system.  Perfectly setup, a subwoofer is like a behind the scenes coach making the star look great, all the while never taking credit.  This is a careful balancing act to give the illusion that your main speakers go down to subterranean levels and can shake the room on appropriate music – it should never sound like it’s coming from the subwoofer itself.

My favorite setup piece for this sort of exercise is a pipe organ.  Why?  Because it’s a fixed instrument that has specific notes and levels that should reproduce properly in your room.  Other bass instruments that are acceptable to me include a bass drum in an orchestra, such as Mahler’s First  – the one I have included a link to is by the ever talented Peter McGrath and the bass drum whacks on the 4th movement are perfect.  However, I would still stay with the organs because the sustained notes are what make it a lot easier to adjust.  My favorite setup piece is the Boston Symphony Saint-Saëns Symphony no. 3, track 3, but I am sure there are many other greats like Reference Recordings Pomp and Pipes and so on.

Here’s the deal – you need a known reference instrument recorded well to make this work for you – and if you’re sure what you have is authentic and “real” – meaning an authentic instrument of some type that goes down to 20Hz – then that’s perfect.

Tomorrow we’ll see how all this comes together but just remember, easy does it.

Paul McGowan – PS Audio, Intl.