Adventures in HomeCinema: Audio /2 Bass woes

Bass woes

Last post finished with flaky bass in movies… sometimes great, sometimes not.

Without some objective measurements it is quite hard to understand the underlying problem, and without understanding the problem it is even harder to find some solution, let alone a good solution.

I bought an USB measurement microphone (UMIK-1) and used REW (room eq wizard) to measure the bass behavior.

Measurements

The first (green) measure is without Audyssey, the second with.

You can see, that Audyssey helped a bit by lowering the peak at 33Hz and filled a bit the valley afterwards. Nonetheless there is a rather big drop of about 15db at 35Hz. It is often said that 10db difference represents a perceived 2-times loudness increase — 20db 4-times.

This certainly can explain the sometimes missing bass response.

I made more measurements and played a bit with difference subwoofer positions and AVR settings, but the problem at around 35Hz always stays the same.

Simulations

There are tools to simulate / calculate these problem frequencies for rectangular rooms.

Amroc clearly shows problems between 33 and 36Hz (and even calculates the Schrödinger Frequency).

REW has a room simulator, where you can place your subwoofer(s) and your main listening position.

Both simulators show inherently the same characteristics that were actually measured. Playing around with REW room simulator shows a few positions for subwoofer / listener, that are unfortunately not possible.

Are there things to fix this situation?

Possible Solutions

position changes

Changing the position of the listener position respectively the subwoofer inherently also changes the loudness of the low frequencies. If possible this is the simplest fix. Not possible for me right now.

Sound Dampening

When building a home cinema from scratch in its own room, there should always be the concern of which (not if) sound dampening measures to install.

Living room cinemas are more constrained, and mostly limited to installing absorbers at the first reflection points.

I have not much clue about sound dampening, because I stopped researching after preliminary results. The needed space and costs are just nut feasible. Lower frequencies are longer, and need thicker and more heavier dampening, which I cannot install here.

AVR

There is the possibility to manipulate the frequency curve in the Audyssey App, or so I thought. Turns out you can only change the target curve the AVR should try to reach. And there are definitely limits how much equalising the AVR does, because it cannot be used to really do great changes unfortunately…

Parametric EQ

There are equalizer boxes (for example the miniDsp 2×4 HD) you can switch between the AVR and subwoofer, which offer the possibility to equalize like we need.

Additional Subwoofer

Additional subwoofer also should help, by basically filling up the valleys and reducing the peaks. Positioning them in opposite corners should do the trick.

The simulation says so! I have to read up, why specifically this should work.

Next steps

The most promising (and possible) things to try are the EQ box, and more subwoofer. I lean on the side of more subwoofer.

I have ordered a suitable cable to try out my kitchen subwoofer. It is better to use the same subwoofer, but this should be ok for a quick proof of concept.

Adventures in HomeCinema: Audio

The home cinema experience depends of course on the picture quality, but also the sound quality, if not more.
    Sound quality is directly reflected by your equipment and your subjective listening experience. Meaning more expensive is not always better for you, even though the equipment might be objectively measurable better.
    My 5.1.2 equipment:
  • Mains: Klipsch RP RP 280F
  • Center: Canton Center
  • Subwoofer: Klipsch R-112SW
  • Surrounds: Klipsch RP 402S
  • Atmos Ceiling: KEF T301
  • AVR: Denon X1600
My basic steps and AVR settings:
  • subwoofer crawl for finding a suitable place
  • Audyssey measurements
  • Set boxes to small and set the the LFE crossover to 120Hz
in the AVR android app (MultiEQ) are some more settings to change:
  • disable “Midrange Compensation”
  • set “MultiEQ Filter Frequency Range” to your rooms Schrödinger Frequency. This effectively restricts the AVR EQ to the lower frequencies.
The Schrödinger Frequency is the limit where your room doesn’t act like a resonator anymore. [1, 2] Bass frequencies up to 100-300Hz get amplified or negated, while everything higher disperses after some reflections.
    Seems easy enough, and sounds pretty good under most circumstances. Unfortunately some movies (for example Deep Water Horizon) that should be very bass-heavy sound / feel pretty tame. Will have to check how to fix this in the next post…
Sources:
[1] https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-1
[2] https://www.soundandvision.com/content/schroeder-frequency-show-and-tell-part-2