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Tuesday, November 8, 2011

3 Steps To Adding A Subwoofer

It's not unusual for musicians and engineers that are doing a lot of work in their home studio on bookshelf-sized speakers to crave more bottom end. As a result, the first thing they think about is adding a subwoofer to their monitor system. That's all well and good, but there are a few steps that you can follow that might help your venture into low frequency territory a lot easier.

1. Do you really need a subwoofer? Before you make that purchase, it's a good idea to be sure that a sub is actually necessary. Here are a couple of things to check out first:
  A) Are you monitoring at a loud enough level? This is a trap that people with home studios fall into; they don't listen loud enough, at least for a short period of time. I know from personal experience as I did that for years and found that everything changed for the better when I turned it up for a little while when working.

First of all, if you monitor too quietly, your ears begin to emphasize the mid-frequencies. This is great for balance but bad for judging the low end of things. Crank up your monitors to a moderately loud level, at least when you're working on the low frequency end of the spectrum. If you still don't have enough low end, go on to B.

  B) You have an acoustic problem in your room. Chances are that either your monitors are too close to the wall, or they're placed at a point of the room length where standing waves causes some of the low end to cancel out. This is more likely to be the cause of just one area of the low frequency spectrum rather than the entire low end though.

Just to be safe, move your speakers a foot or so backwards and forwards and see if you get some of the low end back. If not, move to #2.
2. Purchase a subwoofer from the same manufacturer as your main monitors. The easiest way to get a smooth sounding low end that doesn't cause you more grief that it's worth is to buy a sub from the same manufacturer as the monitors you use most of the time. That means, if you're using JBL's, choose a JBL sub that's made specifically for that system; if you're using Genelecs, do the same, KRK's, the same, etc. This will make a huge difference, especially at the crossover frequency point from the mains to the sub. It's usually impossible to get that area to sound natural if you mix brands.

3. Calibrate your sub correctly. Most musicians and engineers that choose to use a sub just randomly dial in the level. You might get lucky and get it right, but it's more than likely that your level will be off, causing a number of funny sounding mixes until you finally figure it out. Here's how to calibrate the sub to your system:
A) Without the sub connected, send pink noise to your main monitors. At the listening position and while listening to one monitor only, use an SPL meter (just about any will do to get you in the ballpark, even an iPhone app) and adjust the level of monitor until it reads 85dB. The SPL meter should be set on C Weight and Slow. Repeat on the other channel and set that so it also reads 85dB.

B) Turn the main monitors off. Send pink noise just to the subwoofer. Set the level of the SPL meter so it reads 79dB. 79 works because there are fewer bands of low frequencies than high (3 for the low and 8 for the high), so this number takes that into account. You might have to tweak the level up or down a dB, but this will get you into the ballpark.

C) If there's a polarity switch on the sub, try both positions and see which one has the most bass or sounds the smoothest in the crossover area. That's the one to select.
If you follow these steps, you'll find that integrating a subwoofer into your system (if you decide you need one) will be as painless as possible. And by the way, don't you just love the picture on the left?
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Anonymous said...

Thanks for this great advice.

Anonymous said...

ok your talking about adding a subwoofer? but why do audio companies make headphones/monitors with flat eq? they actually do this on purpose, its like they don't want you to hear the bass, i been asking people at guitar center/ sweetwater but no one has an answer for this its crazy am i the only person that notices this? they say cause it benefits you listeners but that makes no sense to me

Bobby Owsinski said...

Who says that speaker manufacturers make products with flat EQ? A lot of units, especially the cheaper ones, are very hyped.

Pro monitors are flat because they assume that you'll be listening in a pretty good acoustic environment and won't need any hype on the low end.

That said, every manufacturer really wants you to hear the low end, since that sells monitors.

Carlos said...

Great advice, interesting technique with the pink noise and SPL meter, and I love the picture! Your point about matching brands between the mositors and sub is well-taken, but sometimes it's not practical, for example, if the monitor maker doesn't offer a matching sub (or they went out business!). In these instances, you can really help smooth out the transition band between the monitors and sub by adding the right kind of electronic crossover. You want one preferably with a Linkwitz-Riley response, minimum fourth order, but sixth or eighth orders are even better. These types of crossovers have excellent well-controlled phase characteristics in the transition region, and are better than most of the crossovers that are built into subs. The "sweet spot" for the crossover frequency will be somewhere close to the middle of the transition between the top of the sub's response and the bottom of the monitors' response. Of course, you will want to choose a sub that can go at least 25-50Hz higher than the low end of your monitors, and if the sub does have a crossover built in, then bypass it or just set the crossover frequency to the highest setting.


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