Room Resonances

Being able to identify room resonances, and then work with and around them are key to producing balanced mixes.

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Most of us working in project studios, are mixing and producing in environments which are far from acoustically perfect, and having to deal with frequency peaks and nulls in different parts of a room are an unfortunate but unavoidable reality. Being able to identify room resonances, and then work with and around them are key to producing balanced mixes.

I faced room resonance issues when mixing my most recent track.  My studio room is far from acoustically ideal, with concrete walls (although covered on 3 sides) and almost-square dimensions (apart from a corridor at the back, forming an overall ‘L’ shape).  My normal sitting position when mixing is centred in the room, and forms an equilateral triangle with the monitors (as is recommended by many tutorials, and monitor instruction manuals).  In the past this position has always sounded balanced in terms of frequency response, but with the last track, i was finding that the mix sounded more balanced when i sat about 50cm in front of my normal position… but as soon as i moved back, the low end of the bass line dropped out significantly.  The bass line centred around a D note (approx 73Hz), and after messing around with sine wave sweep tones, i found that there were significant nulls at that frequency in my normal listening position, and other places in the room.

As a test, I played at 73Hz sine wave through the monitors, and recorded clips of it at two places… one where i thought the mix had previously sounded reasonably balanced, and another where the sine wave seemed to drop off the most (both points being equidistant from the speakers).  These two clips are below (note… please make sure you’re listening on something that can play back 73Hz, or you’re not going to hear anything!)…

Null point:

Balanced point:

Despite the fact that the recordings are of exactly the same sound recorded at the same distance from the speakers, the clip recorded at the null point is roughly 6dB quieter than the clip from the other point.  I was surprised by this… 6dB is really significant, and I assume that the difference between the null point and a peak point in the room could be even as much as 12dB.  If you inadvertently did your whole mix from the null point, it would potentially end up 6dB too loud around 73Hz… that’s a big difference, and would sound noticeably unbalanced when played back on other systems.   It would have been especially problematic in my case given that the null frequency, and the fundamental of the key of the track were the same.

Identifying null and peak points is the first step , and the next question is how to work with/around it?  In my case i changed my listening position slightly, shifting about 40cm forward of the normal position.  I knew from mixing other tracks that this spot usually sounded slightly bass heavy and a little dull at the top end (as it was slightly off-angle of the monitor tweeters).   So I had to be conscious of this when mixing, and very  slightly compensate for it… mixing to be slightly more light in the bass and crisper at the top end than what i thought was an ideal balance.  I also occasionally moved back to the normal position in line with the tweeters, but just to evaluate just the high frequency content.  I also regularly checked the mix on other systems to get some additional perspective (my old monitors plus my tablet and earbuds).

In the end I achieved what I think is a nice, balanced mix through adjusting the mix position as described, and manually compensating for the deficiencies in frequency response at various positions.  This was also coupled with other techniques (which I’ll describe in detail in a future post).  It also helps enormously to ‘know’ the sound of the room you work in… to know and remember any null and peak points, and to be able to anticipate the effect they will have on different parts of a mix, and compensate and balance accordingly.  When I was only producing music in my free time, I didn’t notice the effect of room resonances as much… I think producing full time, and working in the same space regularly lets you get to know the sound of a room much more quickly, and be more conscious of any differences or anomalies.

Interestingly, I checked the wavelength of the low D in which the key was based, and found it was just over 4 metres… which was almost exactly the length of the back wall of the room… and hence probably explained the peaks and nulls at that frequency.

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