measurement gives too much bass? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 13 Old 07-28-16, 03:55 AM Thread Starter
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Question measurement gives too much bass?

Heya,

new user here. Iīm currently measuring my "living room" , itīs more of a music, mixing and listening room

Two weeks ago I made a first test measurement (REW version 5.14), and I donīt think I activated any EQ settings or whatever. This old measurement is the red graph in the screenshot.

Today I wanted to set up my first Limp Mass Absorbers that I built, and made a confirmation measurement of the older one. Same settings, same gear, in the same location. Except that I went for 25-400Hz instead of 25-500. However, thereīs substantial differences above 50Hz, the blue graph is much further down in measured volume o.O

http://i66.tinypic.com/2ryhyd4.jpg




I decided to update REW to 5.16 and also to 5.17 beta. The rough SPL curve still is the same.
What could I possibly have done wrong?

(_)o
Attached Thumbnails
measurement gives too much bass?-spl.jpg  


Last edited by MrBongo; 07-28-16 at 04:36 AM.
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post #2 of 13 Old 07-28-16, 03:05 PM
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Re: measurement gives too much bass?

From the overall widening gap looks like the blue measurement is with a low pass crossover filter engaged.
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post #3 of 13 Old 07-29-16, 06:09 AM Thread Starter
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Re: measurement gives too much bass?

thatīs kinda what it looks like, between 50 and 150Hz. Above that itīs flat ~18dB below the older graph. But it doesnīt sound like that, nothing changed to my ears. No options were modified either.
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post #4 of 13 Old 07-29-16, 10:43 AM
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Re: measurement gives too much bass?

Quote:
MrBongo wrote: View Post
...Same settings, same gear, in the same location.
Quote:
MrBongo wrote: View Post
...nothing changed to my ears. No options were modified either.
There are all sorts of possibilities here so it is difficult to pin down what changed during the 2 measurements; something has. The issue is determining what it was.

It's possible to confirm there is no problem with repeatability in REW itself for the same overall setup and configuration. Using repeated measurements over time confirms the high repeatability of the software. Many of us have done that. There are however many configuration options within the overall measuring setup that are easy to overlook.
  • Channel(s) activated
  • AVR listening mode setting
  • Incidental noise as possibly from floor above or adjacent room.
  • Mic/speaker locations
  • AVR EQ setting
  • OS settings
  • SW settings

There is not enough info here regarding your measurement setup to help narrow down the possibilities. If you post the .mdat we can rule out a couple of the possibilities or, less likely, find a setting difference.

Your chart doesn't suggest any one of these listed areas to me, with the possible exception of the first one. I am sure you have also reviewed all these areas and not found the problem so my advice would be not to worry about what changed and instead, just confirm all the settings and start over.
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post #5 of 13 Old 07-29-16, 04:20 PM Thread Starter
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Re: measurement gives too much bass?

Quote:
MrBongo wrote: View Post
new user here
I didnīt touch most of the settings at all, as Iīm just starting to get into the program. However, there can always be that little tick box that suddenly is activated after a restart, or is checked with an accidental click on an icon I didnīt see.

I was able to repeat the somewhat linear graph two weeks ago, yesterday I got the same bass-heavy results over and over. No doubt on the repeatability


.mdat files below.
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post #6 of 13 Old 07-29-16, 05:46 PM
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Re: measurement gives too much bass?

Okay, thanks for the files.

16-07-17 is probably good data. 16-07-28 is definitely bad data. The Impulse chart of the -28 data shows lots of severe ringing. It appears you are using the RME interface for both input and output. Possibly there is a 'monitor' feature active in the RME interface setup that is creating feedback in the measurement. This must be disabled.

It is a good idea to run a loopback measurement before making sound measurements to assure that the basic setup is correct.
> Set the REW 'Preferences/Soundcard' so the 'device' (RME) is selected for input and output and also select the channel that will be used for measurements. Leaving these set to 'default' may work, but it is not best practice.
> Remove the mic and place a cable from the output to the input of the RME channel being used for measurements.
> Adjust the levels and measure full range.

You should get a nice clean SPL trace that is flat except where it rolls off at very low frequencies. If there are problems there the REW help 'F1' has lots of more detailed info regarding the proper 'soundcard' setup that may help.
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post #7 of 13 Old 07-30-16, 03:47 AM Thread Starter
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Re: measurement gives too much bass?

I had to use an analog output for the loopback, my amplifier is fed via SPDIF out.
Results below. (What makes this file ten times bigger than others? )

Thereīs no monitoring set up on any channel, I checked that via RME TotalMix (the control software) and by plugging in a guitar. For monitoring, I always use the Reaper internal functions, because I want the processed output only (guitar amp sim and stuff).
I even had to activate the analog output first, everything but the SPDIF output and headphones is disabled here.


REW preferences says:
Output device: SPDIF (RME Hammerfall)
Input Device: Analog 1+2 (RME Hammerfall). Analog 2 is where I had the mic preampīs output and the loopback cable, 1 is empty for the measurement.

Output: Default. The only other choice is called "Master volume", but I didnīt see that term in any of the RME drivers yet.
Input: Default. Other choice "Line_In (Master Volume)". Same here.


Oh, right: the 49,5Hz ringing is my door. I canīt really seem to dampen it in any way, not even with heavy stuff parked in front of it. Thatīs gonna be changed some time as well
Attached Thumbnails
measurement gives too much bass?-out.jpg  

measurement gives too much bass?-pref.jpg  

Attached Files loopback.mdat (2.42 MB) 

Last edited by MrBongo; 07-30-16 at 03:53 AM.
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post #8 of 13 Old 07-30-16, 05:36 AM
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Re: measurement gives too much bass?

The loopback measurement cable can go from the DAC/AVR line output back to the RME line input, but if that is a problem, using the line output works to identify most all problems.

The file is larger because there is more data saved in a full range sweep.

I will accept your comment that the phones monitor will not impact the REW measurement as I am not a user of complicated mixers. If someone else sees a problem with the mixer settings please jump in.

By full range, I was thinking 2-22050 Hz for a 44100 sample rate but the 20-20k should be okay to spot most any issue. There is no ringing in this Impulse measurement. It is a nice clean Impulse chart. The only apparent issue I see with this measurement is: Why does the HF roll-off ~-7 dB at 20 kHz? It would typically be ~-0.2 dB with a quality interface like this so there still is an apparent issue.

The REW settings look okay to me. Most people with this type of setup would be using an ASIO driver instead of java, but Java shouldn't be a problem other than limited channel selections. I am really out of my depth on this issue however. I'm just thinking that Java still includes the OS sound settings and possibly there is a sample rate difference in the OS vs the RME interface? I think ASIO avoids that type of a problem? Repeat, I am not very knowledgeable in this area so hopefully someone else will provide a more specific answer to the probable cause.

The only other things I noted in the original files was that you used multiple sweeps (2) for the measurements. This is probably okay for SPDIF, but if there is resampling someplace then possibly that may become an issue.

Well this are just thoughts for consideration. Sorry I could not spot the specific issue.
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post #9 of 13 Old 07-30-16, 05:53 AM
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Re: measurement gives too much bass?

The latest measurements have extremely high low frequency distortion. From the overlay I'd say your sub has ended up with its gain set 20 dB higher than it was previously.

measurement gives too much bass?-overlay.png
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post #10 of 13 Old 07-30-16, 10:15 AM Thread Starter
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Re: measurement gives too much bass?

Quote:
jtalden wrote: View Post
By full range, I was thinking 2-22050 Hz for a 44100 sample rate but the 20-20k should be okay to spot most any issue. There is no ringing in this Impulse measurement. It is a nice clean Impulse chart. The only apparent issue I see with this measurement is: Why does the HF roll-off ~-7 dB at 20 kHz? It would typically be ~-0.2 dB with a quality interface like this so there still is an apparent issue.

The REW settings look okay to me. Most people with this type of setup would be using an ASIO driver instead of java, but Java shouldn't be a problem other than limited channel selections. I am really out of my depth on this issue however. I'm just thinking that Java still includes the OS sound settings and possibly there is a sample rate difference in the OS vs the RME interface? I think ASIO avoids that type of a problem? Repeat, I am not very knowledgeable in this area so hopefully someone else will provide a more specific answer to the probable cause.
the loopback cable was an unsymmetric 6m instrument cable. Probably part of the reason.

Java was the default. Will try the ASIO driver when I can find the time to. However, it doesnīt seem to be able to do a stereo measurement, thereīs only one output to be selected (either SPDIF left or right).

Quote:
JohnM wrote: View Post
The latest measurements have extremely high low frequency distortion. From the overlay I'd say your sub has ended up with its gain set 20 dB higher than it was previously.

Attachment 126009
Kinda. The x-over frequency is 90Hz. But it definitely is not any louder than before, and thereīs no accidental turn-up-that-cheet on the controls, since I canīt reach the subwoofer nor the ampīs control panel at the moment. See below:
https://www.dropbox.com/s/cl4wavvmu8...60923.jpg?dl=0

But I have no idea whatīs with the distortion either. One measurement shows more than 100% THD, the next one is below 10% almost everywhere (except the door resonance). The SPL graph was almost the same, high distortion measured or not.
Weīll see whatīs with the next run-through.

Last edited by MrBongo; 07-30-16 at 10:25 AM.
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