Home Theater Forum and Systems banner

1 - 20 of 27 Posts

·
Registered
Joined
·
20 Posts
Discussion Starter #1
I am in the process of building a dedicated HT. I took a measurement before and right after I installed the acoustic treatments. What surprises me is that there seems little to no decay below 200 Hz after some 250 ms in either situation. Can this be??
 

Attachments

·
Banned
Joined
·
4,838 Posts
All that stuff that is not decaying is noise in your room and/or system that does NOT decay, it is there all the time, just like the diagram says. Looks like some 30 and 60 Hz electrical noise plus a whole lot of other steady stuff to be gotten rid of. Fan noise, furnace, AC, fridge, freezer? It is easy to "tune out" with our hearing and not notice, but the measurements catch it every time if it is there.
 

·
Registered
Joined
·
20 Posts
Discussion Starter #3
Thanks for your reply, AudiocRaver;

Are you certain, this is 'real' noise and not a REW setting or more likely, an user issue?

Hmm, if so this means I would have considerable ambient noise in the below 120 Hz range: north of 50 db, even 70 db+. I had not noticed that yet.
 

·
Banned
Joined
·
4,838 Posts
A user issue is not out of the question, no offense.:wink2:

There could be measurement system noise that you don't hear in the room.

For actual room noise, it is pretty high. LF at 40 or even 50 dB can be overlooked, but at 60 to 70 dB, you usually get pretty annoyed by it. Interesting that it is very broad-bandish, not just a few spikes like 30 or 60 or 120 Hz. That characteristic might make it easier to mask out of the hearing somewhat. But you are correct, if it is in the room itself, that should be very audible. Not sure what to suggest could be producing it.

Had a fan with a broken blade running on the LR floor upstairs once, vibrated at 20 Hz, stood out like a sore thumb in measurements and I could not hear a thing.:rubeyes:
 

·
Registered
Joined
·
431 Posts
Broadband noise... do you live near a freeway or airport? And have you noticed any fluctuations in that noise based on the time of day the measurement is taken?
 

·
Registered
Joined
·
20 Posts
Discussion Starter #6
Appreciate the comments, Guys!


I ran some more measurements:

'Just' the noise floor. It looks 'clean' to me: quiet (measurements confirms that there is no freeway or airport near by :) ) and this huge bump in the lower frequencies is not there.


Measurement over full signal range. This time I expanded time range to 1500 ms. It seems that above 80Hz the signal decays relatively quickly (200ms), but LF takes over a second(!).


This tells me that the measurement setup and method is OK => is my thinking correct?


If so, this leaves me with either:

* an issue with the subs/signal to the subs (3x EP4000, driving dual stacked 18" SI in sealed 4' flat packs, miniDSP, currently with default settings)
//I already tried plugging the amps into a different power outlet - no change//

or


* an issue with the room i. e. my acoustic treatments are not effective

Room:
- dedicated room in basement 23'x14'x8'
- walls: 3x concrete, 1x drywall (side): covered with mix of Knauf and OC703
- ceiling: exposed wood, but partially covered with acoustic foam
- super chunks made of OC 703 in all 4 corners
- riser 14'x7'x14", wood, vented, filled with R35 pink fluffy
- floor: concrete and wood (riser), no carpet/padding yet





Any suggestions where I should go from there?
 

Attachments

·
Registered
Joined
·
6 Posts
I prefer to look at the flat spectrogram.

Can't post images yet :(

What this looks like to me, is you have mains (bottom) outputting frequencies full range instead of crossing over to the subs. The subs are playing at 1xxHz and below... somewhere between 350 and 400ms later than the mains. :rolleyes:

Can you delay the mains or speed up the subs somehow?
 

Attachments

·
Registered
Joined
·
20 Posts
Discussion Starter #10
I did more testing and I think I found the culprit: it's the Audyssey setting in my AVR (Integra DTR-70.4):

Attached are the spectrogram (Thanks much for the tip Joe!) screenshots for the Audyssey settings: Movie, Music, Off. Also the Dynamic EQ on/off has a small effect.

Questions:
1. what are a) desirable and b) acceptable decay values/targets? => how good is my room compare to the target?
2. what is the proper way (which settings) to perform an audio calibration? (is there a step-by-step process that one of you could point me to? Seems like I am not doing it right)
3. as Audyssey seemingly introduces 'ringing', why should I want it?
 

Attachments

·
Registered
Joined
·
13 Posts
There is something horribly wrong with these measurements. I have NEVER seen a spectrogram that looks like that.

What mic are you using?
 

·
Registered
Joined
·
20 Posts
Discussion Starter #12
It's a UMIK-1.

I am new to the spectrogram view (and to a large degree to REW as a whole), but when comparing my screenshots to others, I thought they looked similar. Could you help me understand what a good one should look like?
Thanks much!!
 

·
Registered
Joined
·
13 Posts
It's a UMIK-1.

I am new to the spectrogram view (and to a large degree to REW as a whole), but when comparing my screenshots to others, I thought they looked similar. Could you help me understand what a good one should look like?
Thanks much!!
Sorry for the late reply!

The ones labeled "Audyssey-Music", "Audyssey-Off -- dyn EQ on" and "Audyssey-Off -- dyn EQ off" look right, but the others seem to have TWO separate spectrograms, with the higher one being centered around 450ms.

I'm no REW expert, but that looks just plain weird to me.

For an example, I have attached my spectrogram for subs+CC.
 

Attachments

·
Registered
Joined
·
20 Posts
Discussion Starter #15
Hi Alan;

I get those 'weird' charts when I engage the "Audyssey" mode. With the sub-mode "Movie", the results are even more pronounced than with "Music". I referred to it as "ringing" in the question (#3) I posed. (Not sure if that's the proper term.)


I like to better understand the situation, so I can get optimal audio calibration results. Can you or anyone else help me with these questions:

1. what are a) desirable and b) acceptable decay values/targets? => how good is my room compare to the target?

2. what is the proper way (which process steps/settings/modes) to perform a full HT audio calibration? Is there a step-by-step process that one of you could point me to? Seems like I am not doing it right. (I have the Audyssey Pro Kit. My DTR70.4 has MultEQ XT32 and Sub EQ HT. I ran the automated calibration prior to performing the REW measurements. I would have done fine-tuning with the miniDSP for my subs afterwards.)

3. as Audyssey seemingly introduces 'ringing', why should I want it? (I am talking about Audyssey Movie / Music Modes

I am grateful for any guidance!
 

·
Registered
Joined
·
13 Posts
I still believe that there is something wrong with your measurement process/equipment. If you were listening to the response represented in one of those "bad" spectrograms, it would have to sound absolutely horrible. That begs the question; how does the system sound??

Ideally, you want your sub response to decay by at least -20dB in the first 160ms. I've attached my decay graph and yours...you will see that according to your graph, your signal has not decayed AT ALL. This, to me, is just impossible.

For tips on running Audyssey, try these two links:
Audyssey 101: http://www.avsforum.com/forum/90-receivers-amps-processors/795421-official-audyssey-thread-faq-post-51779-a-1726.html#post21783025
Audyssey FAQ: http://www.avsforum.com/forum/90-receivers-amps-processors/795421-official-audyssey-thread-faq-post-51779-a-1726.html#post21782993
 

Attachments

·
Banned
Joined
·
4,838 Posts
i looked at your measurements you posted awhile back. It still looks to me like a horrendous amount of LF noise.

It looks acoustical but could be electronic. Plug in some headphones and listen to what the mic is picking up. Crank it up and listen close. This should be very revealing and help you see what is going on in your room. Stomp around a little and make some noise. It should be picked up and easy to hear. You will get nowhere until you quiet the noise.

It could be a faulty USB measurement mic, too.
 
1 - 20 of 27 Posts
Top