Re-thinking Peterson Dip

For the last decade or so I've experimented with high frequency dips modeled after the Linkwitz Gundry dip (generally characterized as 3dB down at 3kHz with Q of 2, which is between a half octave and a full octave bandwidth) but on the basis that the issue is excess high frequency reverberation in playback compared to the direct sound vs direct because of small relatively live rooms generally, and not just in the region of cochlear resonance centered at 3kHz.  This reverberant field causes more high frequencies to enter the ear canal which begins roughly perpendicular to the direct sound axis than would happen in a live performance with the music sources in front.

I've generally started a roll off around 2kHz and going up to 12kHz or so, above which some added highs are beneficial.  But I also came to feel it imparted a certain dullness.  So I decided to rethink the "Peterson Dip" which is intended for dipolar full range speakers like Acoustats.

People with "box" speakers aren't bothered by this as much as people with full range dipoles like me.  The reverberant field is naturally rolled off in the highs and often the upper midrange as well with box speakers because of limited high(er) frequency dispersion in woofers and tweeters.

Now I'm trying a dip centered at 4kHz with an bandwidth of 2 octaves, and limited to 3dB maximum.  The "cutoff" points are then 2kHz and 8kHz, which includes what I consider most important--the "metallic" range around 6kHz, without necessarily rolling back the higher frequencies which add "air" or suppressing 1kHz which would remove clarity.  The Q is a comfortably low 0.667 with hardly any overshoot whereas a Q of 2 has significant ringing.  Previously I used 3 filters with a octave bandwidths or less to achieve a 2-12kHz dip, but unless you are truly cancelling resonances, which this is not, I think fewer filters are better.

Noting that my Acoustats measure fairly flat in the range 1kHz-16kHz, I decided to simply apply the new dip on top of their pre-existing response without getting deep into achieving the desired response acoustically for the time being.

It seems to provide about the desired effect on taming excess brightness and making it easy to listen at a higher levels too.

Looking at the resulting spectrum, the difference is hard to see on this scale, but the -3 dB cut actually looks a bit smoother too:

The sound is significantly more "laid back" with the cut on pink noise.  The speakers sound very "forward" without it.  You don't have to have golden ears to hear it if playing while adjusting the control, each -0.5dB difference at 4kHz is very audible.  The actual center frequency is 3990 Hz, the closest to 4kHz that the Behringer DEQ 2496 will let me select and I'm going to call it "4kHz" for simplicity.

All measurements are made from back of the room center position with the Movie EQ on the subs, no other PEQ's on the panels.  iPhone is being held with stand.  I'm standing about 18 inches to one side mostly.  Left channel level set in Tact preamp is -1.0 dB (see next post) which gives best measured balance with SPL meter C weighting.

Left Channel No Cut

 

Left Channel, -3dB at 4Khz

Right Channel, No Cut

Right Channel, -3dB at 4kHz

These 4kHz dips are currently the only PEQ's applied to the panels, since I set all the old  PEQ's to 0.0dB with the new Movie EQ in order to "start from scratch."  However I left all the old frequencies and bandwidths in place because they may be useful in setting new PEQ's all over again.  They are historical information.

The new panel EQ settings are now saved unambiguously as a new memory named "Sep26."  The meanings of the older settings are impossible to discern anymore.

I played the entire album Bass Ecstasy by Bass Erotica at -1.4dB total (-1.3 being applied by Roon's album leveling) in the center back at it was captivating.  3D image, wall to wall, with impressively deep powerful tuneful and never unpleasant bass notes.  I remember when I could hardly listen to this at -10dB because of all the room boom.  I measured 93.1 dBC "fast" peaks on my SPL Pro app at the listening position.  dBC de-weights the deepest bass which will have peaks much above that measured flat.

The Movie EQ sounds great all around the house because of suppressing the primary house modes, and the way the Acoustats couple to entire space.  The Hotseat EQ exaggerates some house modes to get flat response at a close seating position.