Sunday, November 17, 2013

Equalizing the Living Room system with a few digital notches

The need to equalize the living room system became most apparent when I was checking out the sound transfer to the newly remodeled second bedroom I am setting up for a friend.  Despite the soundproof door, there was noticeable bass leakage to the room with the door closed.  But opening the door, then the bass boom was overwhelming.  The excess bass is less noticeable at the listening position, but the bass line still sounded quite blurry there, possibly being affected somehow by the boom in the rest of the room.

I was playing one of my bass test recordings, Bass Ecstacy by Bass Erotica.  I have tuned the bedroom system so that it plays this very well, with bass sweeps audible down below 16Hz, and fairly level from there up.  In fact, I used this recording for the final room tuning in that room, which is why it can play Bass Ecstacy particularly well.

But the recording wasn't sounding as good in the living room.  Still too boomy.  Then I took a look at the digital crossover, a Behringer DCX 2496, thinking about adding some room node suppression, and I noticed I had already added some bass EQ, but I had turned it off.  Ah, yes, I remember doing that some time ago.  I couldn't hear much difference with the EQ turned on, so I decided to leave it off.  I can't remember when I dialed in the EQ a few years before that, some time after I gave up on having the Tact 2.0 RCS adjust the full bandwidth response (only the most recent Tact units permit you to target the bass only, which is the most easily pleasing approach).

The EQ I had set before was an 8dB reduction at 45 Hz with a fairly sharp Q of 4.  That would correspond to a bandwidth about a 1/3 of an octave, a little bit more than 1/3 of an octave actually.  But when I first started playing with the control, I though it was even narrower than that.  Decreasing the Q to 1 made a noticeable difference, but the price for removing the boom was to suck out the bass.

I was determined to solve this problem without doing more measurements (which I've done many times anyway) but simply cut-and-try.  And that actually seemed to work out (refreshingly well).  OK, I did play recorded tones from 16Hz to 160 Hz that I have on my music server.  These tones are supposed to have some warble, but I don't notice it.

Clearly a huge amount of suppression is needed at 45 Hz alright.  The room lights up with bass, even if it's less noticeable at the listening position not far from the center of the room.  But if a Q is used much smaller than 3, the bass cutout affects tones as low as 32 Hz, where there's a nodal suckout.  And the area needing bass suppression is fairly broad, from about 36 Hz to over 70Hz, but with most of the suppression below 50 Hz, with the peak boom at 45 Hz.

All the above mitigates solving the problem with only one notch filter.  I ultimately settled on using two notch filters, one at 45 with a Q of 5.0 and amplitude of -11dB, and another at 57 Hz with a Q of 3.2 and an amplitude of -6.  This cleans up the boomy area pretty well without affecting surrounding areas, particularly at 32Hz which is already weak.  It does create a bit too much loss just around 50Hz, but not too bad.  I dialed in some boost at 30 Hz, 3.5dB of boost with a Q of 5.  Actually, it could use some broader boost below 30 Hz, but hard to dial that in with a parametric.

The result is that Bass Ecstacy is now far more listenable in the Living Room.  It has a coherent and tuneful bass line, not just boom.

I know, some say I should analyze the entire bass with something like RoomEQ Wizard and dial in a few dozen notches.  When that sort of analysis is done with hundreds of notches like the Tact, it's less than impressive to me.  Optimizing the listening position too much doesn't seem good somehow.  It's a lot easier just to use a few notches when tuning by hand, and focus on the really bad room nodes.  I found in adjusting the master bedroom system that combining 1/3 octave graphic EQ (done sparingly) with parametric notches is the most flexible and intuitive, and has given me the most satisfying results.  I have a second Behringer DEQ 2496 to do the graphic as well as the parametric, but it's currently tasked to correcting the European EQ of my Kenwood KT-6040 tuner.

I should remember not to turn off the Bass EQ now.  It sounds much better with it on.

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