How To Calibrate A Studio Subwoofer

If your studio is lacking the low-end punch you need to hear what you’re doing with the bass frequencies, you might want to add a subwoofer to your setup. You may have even picked up something like Carvin Audio’s TRX3118A active subwoofer, but what you may not have thought about is how to set the level of your new sub.

As it turns out, it matters a good bit how you do this or what you hear (and what you do to your mixes) could be skewed from the rest of the world. This could make your mixes worse rather than better.

Luckily, it’s relatively simple to calibrate a studio sub properly. Let’s get to it!

Pre-Requisites

• SPL Meter - It doesn’t take a lot to get a good calibration, but you will need an SPL meter, either standalone or an app on your phone.
• Proper placement – We’re assuming you have placed your monitors properly, and that your mix position forms an equilateral triangle with your monitors. Your subwoofer’s position is more flexible, but it shouldn’t be in a corner, and it probably sits somewhere under the desk. Make sure you’ve settled on its position before you start.
• Zero out the board – If you’re using a mixer, make sure everything is zeroed out and there’s no funny eq or effects doing anything to the main signal.
• Tone generator – You can use a software tone generator, hardware generator, or a plugin in your DAW. Just make sure it can generate full-bandwidth pink noise.

1 - Make the connection

The first step is to connect your subwoofer. This may be obvious, but there are several options for how. Some subwoofers have an input and an output, so you can connect your monitors to the subwoofer, and the subwoofer to the audio output of your interface or mix console.

This may not be your preference, or you may not have this option, in which case you might send main outputs to your monitors and an aux output or other send to the subwoofer.

Decide this first and make your connections.

2 – Calibrate the monitors

Lo and behold, we’ll actually need to talk about calibrating your monitors too, because after all, we’re trying to get the right relationship between the monitors and the sub.

There are various calibration methods, and all are acceptable, but here we’ll use a standard 85dB at mix position when the output source is at 0dB. When we say output source, that could be your mixing console, or it could be your audio interface, if you’re sending those outputs directly to your monitors. At the software level, you’ll be setting your test tone (pink noise in this case) at unity as well.

To do this, we’ll actually calibrate each monitor separately, shooting for 82dB.

• Step 1 – Turn down monitor inputs all the way (on the back of the speakers themselves). Turn output source down all the way.
• Step 2 – Start playing full bandwidth (20Hz to 20kHz) pink noise.
• Step 3 – Turn up output source to unity (marked as “0” or “U” usually – on an interface unity is often all the way up on the output level dial).
• Step 4 – Hold your SPL meter at the place where your head would be during a mix session and slowly turn up the left speaker input (on the speaker itself) until the meter reads 82dB.
• Step 5 – Turn OFF (leave input level intact) the left speaker and turn up the right speaker’s input level until the meter is at 82dB.
• Step 6 – Turn both speakers on. With both speakers now playing pink noise, your meter should read 85dB at the mix position.

3 – NOW calibrate the subwoofer

Now you’re ready to calibrate your subwoofer.

• Step 1 – Turn off the monitors (don’t mess with the input level!)
• Step 2 – Turn down your subwoofer’s input (on the unit itself) all the way.
• Step 3 – Play full bandwidth pink noise again (at unity in your software).
• Step 4 – Turn up the output source to unity again – remember this might be a separate aux output or send.
• Step 5 – Fade up the subwoofer’s input level until the SPL meter reads 79dB at the mix position.
• Step 6 – Turn your monitors back on and play some music with plenty of bass. Switch the polarity on your subwoofer and listen for an increase or decrease in bass response. Leave the polarity switch in the position that gives you the loudest bass.

4 – Almost done – don’t forget the crossover

Monitor speakers vary in their frequency response, and some may faithfully reproduce audio down to 60Hz or lower. At the same time, your subwoofer may produce only up to 80Hz or its range could extend to as high as 200Hz. First find out the specs of your monitors and your subwoofer.

Next, your monitors may have a high pass filter with one or more options for cutting off their response below a certain frequency. Your subwoofer may have a lowpass filter setting. You may have to experiment with where you let the two cross over to get the best sound.

The best place to start is to set your monitors to cut off right about where your subwoofer cuts off. For example, set the subwoofer’s lowpass frequency to 80Hz and set the monitor’s high pass to 80Hz. If you have a truly variable cutoff (aka a fader or dial rather than a switch) then you have fine control to tweak the crossover.  If not, you can experiment with different switch settings.

The key thing to listen for is cancellation or undue boosting. If you find a setting that makes everything sound worse, don’t use it!

Last thing

That’s it – now you should be properly calibrated, and the only thing left to do is listen to a lot of music and get used to the sound of your new system. The last thing we’ll mention is if you find that 85dB is just too loud for your room, you can set your monitors up for 79dB instead, and decrease the subwoofer’s level to 76dB.

Other than that, enjoy your new room!

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