Bass EQ curves

discman -- Thu, 06/05/2008 - 11:48

Some subwoofers (e.g. Velodyne) allow the user to adjust bass equalization curves. But, particularly below 100hz, what is the right shape for the resulting curve? Flat? Rising with falling frequency (like the rest of the frequency curve does)? Or what?

Steven Stone -- Thu, 06/05/2008 - 16:53

The optimal EQ curve depends on the room and the subwoofer.

Products such as the Revel sub have more than one adjustable EQ point so you can reduce resonant in-room peaks.

It is far more efficient (and practical) to reduce peaks than try to eliminate dips.

Obviously the goal is to achieve flat even in-room response, but the methodology to achieve this may require producing a less linear output from the sub to compensate for room problems.

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

discman -- Thu, 06/05/2008 - 17:37

If by flat, you mean "less lumpy" I get that. But when I set 20hz to the same level as 40hz, and that to = 80hz, the bass sounds rather heavy (seems like flat to me).

Steven Stone -- Fri, 06/06/2008 - 10:05

How do you set the 20Hz to the same level as 40 Hz? Are you using a Radio Shack dB meter? Many dB meters including the RS are notoriously inaccurate below 100 Hz. I have a B&K (with a B&K calibration mic capsule) meter so I can measure down to 50 Hz, but below that I don't trust the B&K either. If such a meter reads "flat" you may actually have a major low end boost in place.

Also are you trying to bring the 20 Hz output UP or the 40 Hz DOWN?

Far easier and more productive to bring peaks down that try to bring troughs up.

Finally if you do get equal output at 20 Hz to 40 Hz you may find that various parts of your room try to "sing along" with sympathetic resonances, which is generally less than musical...16 Hz drives my room nuts - mirrors start rattling and my washer/drier in he next room emits ghostly sounds

:shock:

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

discman -- Fri, 06/06/2008 - 11:46

I'm using the Velodyne-supplied mic, signal generator and software. The Velodyne sub has a built in parametric equalizer (8 band, I think) that operates below 200hz.

Steven Stone -- Fri, 06/06/2008 - 13:50

Since you are using a "turnkey" (all integrated) system we will assume it is properly calibrated.

If you feel the bass is too heavy, perhaps a gentle roll-off starting at 50 or 60 hz so you are down at least 6 dB at 20 would be more to your liking. another thing you should check is how your mains are handling bass below 200 HZ (ideally if your subs start there the mains should be rolling off BEFORE 200 HZ).

I would suggest starting with THX standard 80 Hz hand-off between mains and subs. Some full range speakers will work better with a lower x-over such as 60 Hz. Some small monitor mains work better at a higher x-over point such as 120 Hz.

I usually sweep my mains with a variable tone first to see where they naturally roll off before determining my x-over point. I cross over my Dunlavy Sig VI at 50 Hz even though they go "flat" to 25 Hz. That just works best in my room.

Frankly, flat may be the ideal, but depending on your room and your tastes it may not be the best solution.

Steven Stone
Contributor to The Absolute Sound, EnjoytheMusic.com, Vintage Guitar Magazine, and other fine publications

discman -- Sun, 06/08/2008 - 08:29

Thanks!

Chris Martens -- Wed, 07/16/2008 - 13:39

Discman,

One solution I might suggest would be trying the Audyssey MultEQ XT system as a means of EQ-ing your subwoofer. Four not necessarily appreciated benefits of the Audyssey system are that A) it provides more EQ points for the lower octaves (because that's where the most egregious room EQ problems tend to occur), B) it not only makes amplitude but time-domain corrections, C) it sets separate crossover points for each channel, and D) it takes into account bass performance over multiple listening locations--not just one or two measurement locations.

I've let many audiophiles hear various Audyssey EQ'd 5.1-channel system setups in the Playback audio lab, and two of the most frequent comments I've heard have been that post-EQ bass response sounds notably "taut and deep," and that bass integration with the main system sounds "unusually smooth and seamless." While I would not characterize Audyssey EQ as a "bass panacea," per se, my experience has been that it does tend to help many subwoofers sound better damped and "faster" (in terms of LF transient response) than they otherwise might.

Interestingly, and in keeping with Steven Stone's suggestions, Audyssey sets a finite limit on the amount of bass boost it will allow at any given EQ point (if I remember correctly, the limit is +10dB).

Chris Martens
Editor, Avguide.com/Playback/The Perfect Vision 

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