Question about frequency response

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depechefan

Audioholic
Hi,

I'm calibrating my home theater. I have the Denon avc-x8500h receiver and using Audyssey on my ipad. I see this for my center channel:

Image-1.jpg

Is the dip around 500 hz something I might be able to correct with absorption or diffusion panels?

My room looks like this:
20201028_154515.jpg


I haven't done REW measurements yet. Still sounds great but if I can improve things then why not :)

Thanks for your thoughts
Morten
 
ryanosaur

ryanosaur

Audioholic Overlord
That suckout is, at first guess, something to do with the set up in the room (not necessarily the room itself). What is your MLP? (Center Front Seat?)
What is the whole room layout, and where in the room is that seat? Smack in the middle is just as bad as being on the back wall. :)
 
D

depechefan

Audioholic
Yeah, true. The MLP is 3 meters back from the TV. So 2.6 meters from the back wall. That was what I had to do pretty much...
 
ryanosaur

ryanosaur

Audioholic Overlord
If you ran some measurements at different points in the room, you might see some different behavior. Depending on spacing and your need for both rows, you could push that back row to the wall and slide your main seats back a foot or two.
REW might give you the easiest way to measure the responses rather than going through Audyssey sessions.
Either way, I think you may benefit in the long run from getting some decorations up in there that will create natural defraction and absorption... or else some treatments... BUT! I would only do this after you have done everything else to dial in the room.
Double checking everything from your speaker placements (pulling them in from the front corners a bit, for example) to you seating... perhaps building stands to elevate your surrounds slightly (tweeters above ear level is recommended)... basically, all the stuff that is FREE! :D
Once those options are exhausted, then look toward treating to solve the rest.

I'm about halfway through Master Handbook Of Acoustics Sixth Ed. and just finished the absorption chapter. Learning about this stuff is important, and I have a much greater understanding now of why its a bad idea to just start throwing panels up because you were told to treat your room. ;) I've seen some very experienced HT cats say they treated their rooms for years, only to find greater happiness and enjoyment after removing most of it!

Now... refresh my memory... didn't you have the room that was long and narrow, with your gear set up on the long wall, and MA Subs? :)
 
mtrycrafts

mtrycrafts

Seriously, I have no life.
Yes, definitely measure at different locations to see what the changes are. May need to move chairs a bit so that they don't block mic as you go backwards.
Your dip is closer to 400Hz though and with all the bare walls visible, not the best.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Hi,

I'm calibrating my home theater. I have the Denon avc-x8500h receiver and using Audyssey on my ipad. I see this for my center channel:

View attachment 41156
Is the dip around 500 hz something I might be able to correct with absorption or diffusion panels?

My room looks like this:
View attachment 41157

I haven't done REW measurements yet. Still sounds great but if I can improve things then why not :)

Thanks for your thoughts
Morten
That looks like a classic crossover null to me. It is right at where the mid is likely to be 180 degrees out of phase with the mid. This is a very common issue with three ways. Sometimes if you reverse phase then it is out of phase with the tweeter. It may have been tolerated to allow the center to be used with other speakers. In HT if you correct the phase of a center three way for instance, then you put the mid out of phase with two way mains for instance. It may not be as bad as you think as the dip is often much less severe off axis.

I had this exact same problem with my three way center I designed for my in wall system. I could get a perfect FR by reversing the phase of the center mid. However that put it out of phase with the two way left and right speakers, which was worse, and sounded awful.



The cross is actually 400 Hz, but no filters are brick wall and the maximal phase aberration was an octave and a half above crossover. The black trace is axis, the others are off axis.

The good new is that this is not audible as the room response is excellent.
 
D

depechefan

Audioholic
That's very interesting. I am not super worried about it because as you say, TLS Guy, I can't actually hear it. And for the center I've let Audyssey correct up to 1 KHz. Don't know I you guys would do the same? The rest of the speakers I only calibrate with Audyssey up to 300 Hz. That seems to work well. Compared to going all the way up to 20 KHz it sounds like I get more definition at higher frequencies.
With the setup I have I get phenomenal stereo imaging. To the point where I frequently check if the center channel is on because dialog and vocals seem to be directly centered so happy with that. Only small issue I have is that surrounds can be too loud when I'm sitting to either side of the MLP. So probably not a bad idea to get them on a stand to get the tweeter a bit above ear level.
Good memory, Ryanosaur. I did use to have the narrow room with a complete set of MA speakers. Including sub. Following your advice I bought some MA Silver 500s for FR and FL and upgraded my subs. It sounds great, very happy with the setup. Of course I have also moved and my home theater is now a dedicated room. Need to get a platform for the back row. And probably some acoustic treatment but it's not bad as it is :) Btw I'm reluctant to move MLP too much because it's aligned with my ceiling speakers. 6 of those (KEF CI160QR).

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