Adding the deepest bass to the Movie EQ

 Bass was clearly rolled off in both channels below 31 Hz in the Movie EQ.  But I chose to leave it that way because I hate to use EQ boosts.  They can sound unnatural, they reduce dynamic range, and increase distortion.  Plus in some cases in my all digital system I can get digital clipping.

But when working on the Hotseat EQ this week,  I discovered I had previously been using boosts there up to 9dB (!!!).  In the newer version, now called Hotseat 2, I limited the boosts to 5dB because that worked well enough.  The subs are straining to get these levels at the Hotseat center of the room position, especially at 22.5 Hz, so I didn't want to push them any harder.

Digital clipping is rare in woofer EQ's because you never get 0dB signals below 125 Hz.  Such signals would destroy most woofers, so they are not allowed in recordings.  (I can tell you, having tried to release envelope pushing "Experimental Music" albums myself, streaming music distributors can get very picky about such things.  No clicks or pops are permitted.)

You could have near 0dB signals in the midrange, though I know for certain I reduced the digital level by -6dB in the panel crossover miniDSP's to prevent inter-sample-overs, which then means I could safely use up to 6dB boosts in the panel EQ's.  I'm not sure if I also did that in the bass EQ, where it's not needed to prevent inter-sample-overs, but the previous paragraph explains why there basically no issue with boosts in the bass EQ anyway.  I've never had an issue before, even listening to music at the 0dB level, the bass EQ meters never got close to clipping even with 9dB boosts.

And there's one more factor I'd completely forgotten about.  The Movie EQ has digital "gain compensation" set to -9dB.  Because the back of the room increases bass acoustically.  Meanwhile the Hotseat EQ (1 and 2) has the gain compensation at 0dB because you need all the bass you can get in the center of the room, where most primary room modes tend to cancel bass and you therefore have to pump out way more bass to get flat response there.  At least 9dB more.

This is not a trivial fact.  When I'm playing pink noise (recorded at -20dB) and playing it back at -7dB as I usually do for testing purposes, it sounds only moderately loud at the Hotseat position (around 87dBc or so) with a Hotseat EQ.  But if I walk towards the subs, they are playing very very loudly to the point I wonder if it is safe.  With the Movie EQ, they are just loafing along because it is so easy to get bass in the back of the room, and I hear no huge rumble when I walk towards the subs.

So if I use a +5dB boost in the Hotseat EQ, as I am now doing, that is equivalent to a +14dB boost in the Movie EQ.

So all this means that in the Movie EQ I can boost away in the bass EQ very freely, at least up to +14dB.

I found that +11.5dB boost in the left (sticking with 22.4 Hz and 1/3 octave bandwidth to avoid stimulating those pesky whole house modes below 20 Hz) gave me good near to flat response (with a slight rise) at 22.5 Hz, and +9dB worked best on the right.

But later I decided this was inappropriate for "Movie" mode, which I use when I have movie watching guests over,  mostly elderly people (like myself) including women.  They don't like to hear boomy bass either at the movies or in my home.  Many years ago a guest walked outside because the bass was too loud (that was when I was using something akin to the Hotseat EQ all the time, which did have terribly boomy bass in the back and in fact the entire periphery of the room).  The only quick solution was shutting off the subs altogether.  Later I was dialing them down by -7dB or so for movie watching, and then I'd often forgot to set them back when doing serious listening.  That were the events that motivated me to to have a separate Movie EQ which is automatically controlled by my Insteon/Universal Devices home control system.  (At bedtime, the Hotseat EQ is turned off automatically, and then to turn it back on I use either use either a mini remote or the switch on the Insteon module which controls it by powering a midi device which sends a midi signal to the Behringer DEQ 2496 EQ.  So when I start each day the Movie EQ is active, which is suitable for background music, and then to do serious listening at the Hotseat I press the button.  Sometimes I forget to do that but not for long, because I soon find I'm missing the bass.)

So I decided to take a more conservative approach for the Movie EQ, instead of a slight rise at 22.5 Hz, I'd make it a slight drop at 22.5 Hz (but not too slight either...since the Movie EQ is what I also use for background music).  Measured output is only about 3dB higher at 22.5Hz than it is at 1kHz.  Most of the bass measures higher and some bass measures lower (ideally all the bass below 200 Hz should be readjusted to be level with the 22.5 Hz measurement, which I think represents the best Movie "room curve" compromise).

Rolling back both boosts by 4dB seemed to give me the appropriate response, nearly flat but with a slight reduction at 22.5 Hz (and possibly 25 Hz as well).  The 22.4 Hz boosts are now +7.5dB on the left and +5dB on the right, all at bandwidths of 1/3 octave.

This is now the beginning of "Movie 2" where I intend to get flatter bass response all around using boosts or other measures.

Right Channel before deep bass boost

Right Channel with 9dB deep bass boost

Right Channel with 5dB deep bass boost

Left Channel before deep bass boost

Left Channel with 11.5dB deep bass boost

Left Channel with 7.5dB deep bass boost

I'm thinking now I could raise the Left Channel deep bass boost by another 0.5-1dB to make it match the curve in the right better.  And/Or I will have to see how well this works with actual movies.

Right now the biggest remaining issue in the bass seems to be the depression around the crossover frequency in the Right Channel.  I fixed a very similar depression in the Hotseat EQ by changing the time delay in the sub EQ.  I could do the same thing here most likely with similar results.  But now it bugs me whether that is the correct solution.  It makes no sense because the actual panel to sub distance now seems much too large for such a tiny delay.  And that was not needed in the Left channel which has a local peak at the crossover frequency.  Whether this is better fixed by delay or boost is now a reopened question in my mind.  I might try using larger delay difference instead of a smaller one too.  It seems to me that all the sub electronics ought to have more delay than the simple Class A/B amp used for the panels, and this would only add to the fact that the sub is further back.  Therefore, I would think that the subs would require much less delay than the panels, not just a tiny 0.6ms or so delay that fixed the right channel in the Hotseat position.