Precieved Loudness and LF Demand

[garyrc]

Quiet_Hollow,

I’m
confused.

The manual
that came with my AV preamp/tuner (Marantz AV 7005) suggests disabling the low
pass filter in the sub, and setting the low pass to the sub located in the
preamp to 80 Hz. Do I understand
correctly that you think to get a signal at the right SPL (flat) at 80 Hz (and
below), one should set the preamp low pass to the sub at 40 Hz (which is
available on my unit) and then adjust the sub SPL to match the main SPL as closely
as possible?

How about
this? If I understand the Audyssey
people correctly, in the special case of running movies, the primary low
pass to the sub would remain set to whatever the best setting is (40 or
80 Hz), but a special low pass for true LFE only (sound effects in movies, but
not usually the music on the soundtrack) should be set at 120 Hz, because the
filmmakers depend on being able to send sound effects to the sub all the way up
to 120 (ranging down to the 20s and below).
This adjustment on the Marantz is
labeled LPF for LFE. So, the movie score
would be sent to the sub only below 40, 80, or whatever, but the effects would
be sent out of the subwoofer output on the preamp anywhere from 120 Hz on down. Music-only sources, such as CDs, would not be
affected by this special low pass filter, and would be sent to the sub (nominally)
at and below 40 or 80, depending on which one I choose. Does that sound right to you?

[pzannucci]

Quiet_Hollow,

I’m
confused.

The manual
that came with my AV preamp/tuner (Marantz AV 7005) suggests disabling the low
pass filter in the sub, and setting the low pass to the sub located in the
preamp to 80 Hz. Do I understand
correctly that you think to get a signal at the right SPL (flat) at 80 Hz (and
below), one should set the preamp low pass to the sub at 40 Hz (which is
available on my unit) and then adjust the sub SPL to match the main SPL as closely
as possible?

How about
this? If I understand the Audyssey
people correctly, in the special case of running movies, the primary low
pass to the sub would remain set to whatever the best setting is (40 or
80 Hz), but a special low pass for true LFE only (sound effects in movies, but
not usually the music on the soundtrack) should be set at 120 Hz, because the
filmmakers depend on being able to send sound effects to the sub all the way up
to 120 (ranging down to the 20s and below).
This adjustment on the Marantz is
labeled LPF for LFE. So, the movie score
would be sent to the sub only below 40, 80, or whatever, but the effects would
be sent out of the subwoofer output on the preamp anywhere from 120 Hz on down. Music-only sources, such as CDs, would not be
affected by this special low pass filter, and would be sent to the sub (nominally)
at and below 40 or 80, depending on which one I choose. Does that sound right to you?

In theory, Audyssey should take care of all the mess by properly measuring each individual speaker's response in your room, applying the proper gain or not in the correct frequency ranges.

This gets complex because if you don't actually know the response of your sub woofer and main speakers, the overlap between the high pass and low pass could get ugly as they will either sum in the common frequency, be bloated, or null and sound weak. Compound that by the non-flat response of the sub (most don't do reasonably flat unless internally eq'd), the crossover point (filter points which need to actually be spread apart so the summed output is correct), and the roll off of each of the filters, it is hard to do by ear. Additionally, if your subwoofer is set higher than your mains, you have effectively raised the crossover point, conversly the other way.

All of this does not just apply to subs but any filter network design.

[Mongo171]

It's been almost 30 years since I learned about filters, so please excuse the layman in me speaking.

I understand that one can't assume a test's results unless there is a way to see the results. I have downloaded REW to my laptop, just don't have the other pieces yet. Is there something better, besides a Spectrum Analyzer, out there to see the results?

I didn't understand transistor theory until my 2nd Navy school. I finally understood what was going on with Garyrc's last post. I am dense. Takes me a minute to understand things.

Basically, you want the highpass filter to pass freqs over ~80Hz and the lowpass filter to pass freqs lower than ~40Hz. I do understand about the summing of the freqs ~80Hz that will give undesirable results. I set the LPF on my sub to 40Hz and kept my OPPO set to 80Hz. There definitely was an "unloosening" of the bass while watching TV at "TV" levels. There was more bass present at low levels. With that improvement, I can't wait for morning when I can see what that has done to movies and music (my g/f works mornings).