The surprising reason why you might need a sub in your studio

This is an issue that comes up often in a studio consult session. Usually my services are engaged to give advice on acoustic treatment for a studio. The first thing I will do after an initial discussion is test how the monitors are performing in the mix position. This is where it's quite common to find a problem that looks like this:

 

 

The mic was placed in the mix position to show how the monitors measure in the room, as they will be used. Clearly there is no bass response. In general this is not necessarily a good reason to add a sub. Decent quality monitors are not necessarily very expensive and it's not hard to find monitors with adequate extension for most music. 

In this case, the monitors themselves were a limiting factor. We brought in a 12" sealed woofer to test the bass response. This woofer had already been calibrated for a flat anechoic response with plenty of bass extension. Here is the nearfield measurement:

 

 

 

Next we tested in the mix position, with comparison to the existing monitors:

We see a similar response without the early roll off. Clearly there is a room related dip of around 17 dB. This is far too much to resolve with EQ due to the headroom required. We need an acoustic solution. 

The first solution is to optimise the position of the monitors and the mix position. This tends to offer limited improvement and normally we don't effectively resolve a dip related to room modes in this way. We can reduce the depth of a null with bass traps but typically this won't remove a null this deep. In situations like this, the most effective solution is usually a sub in an optimised location.

 

We used the same woofer to test every feasible sub position in the room. One of the better positions is shown here. You can see that a sub with a little EQ removes the problem entirely. Just a little EQ is required to shape the response into a flat overall trend.  

One way to know

 

Not every studio needs a sub. The most important factor is how your monitors measure in your particular room. If your monitors have adequate extension and headroom and a reasonably flat response in your mix position, there is no great need to add a sub. It's a solution that I recommend only where it's required. When it comes to buying a sub, many studio owners have a tendency to first try a cheap sub. Whilst it's true that you can actually get decent monitors for a modest price, the same is not true with subs. Generally speaking, most subs below AUD $1500 are not up to the task. This is why I advise people to have the room tested and implement a sub only where it's needed.