Display Multiple measurements on same SPL graph

[Timothy Ivie]

I am using version 5.20 beta on a Mac. Have always wondered if it is possible to show multiple measurements on a single graph. For instance measurements for sub #1 and sub #2.

 

[John Mulcahy]

Sure, the All SPL graph or for other parameters the Overlays window.

 

[Timothy Ivie]

Sure, the All SPL graph or for other parameters the Overlays window.

Knew I had seen those displays before. If I may raise one other point on this beta version I have noticed. Prior to taking a measurement I used the generator and spl meter to make sure the level is around 75. When I proceed to measurement section and select check levels in every case it says the level is 75.1 and low. Attached is the measurement that resulted. In prior version I did not face this issue. Perhaps there is a setting or two in the latest version that requires change for my situation.

All the best

 

[John Mulcahy]

I'd suspect there is something amiss with the SPL calibration - unless you are measuring at 130 dB? It is possible the SPL meter was calibrated to say 75 dB with little or no input, hence the warning and the very high readings on the later part of that measurement. If the level check was with a sub cal signal then it does indeed look like it would below, about 50 dB below the level at 200 Hz.

Also best adjust the graph range, about 60 dB from top to bottom is normally about right.

 

[Timothy Ivie]

I am measuring a single 12" sub. Are you saying my SPL calibration needs to be adjusted? If so I need to go read that section of the updated manual. When I was in the generator under Tones I see the freq is set to 50. Anyway I took another measurement and changed the graph range... At this point might it be a good idea to delete the app and reinstall? Another donation was made today.

 

[John Mulcahy]

Reinstalling isn't likely to change much really. The measurements look like the output of main speaker(s) set to small rather than the output of a sub. Can you attach the mdat file for a measurement rather than an image?

By a 60 dB range I meant 140 dB at the top and 80 dB at the bottom, for example.

 

[Timothy Ivie]

I should have said install an older version but I fine trying to work this out. Thank you for your support. The mdat file attached is for a measurement taken a few minutes ago. cheers

 

[John Mulcahy]

So, from the cal file you are using a UMIK but you haven't made any selection in the input device and input, so REW doesn't 'know' you are using the UMIK and can't apply the sensitivity calibration. In the REW soundcard preferences select the UMIK as input device and then select the input as well, don't leave either of them as default. You should also select the output rather than leaving that as default.

How are you connected to the system and what does it consist of? The measurement looks like it is from a main speaker rather than a sub, it has the appearance of having passed through a bass management high pass filter.

 

[Timothy Ivie]

Screenshot including my understanding of your last message. Tested and level is much higher than before so I think you may have solved the issue. There is one thing that is not working correctly on my sound card window. In the past if I selected check levels you would be prompted to then select next or cancel. In the latest version both buttons are greyed out. Is there another something else I missed, wouldn't be a first for me. Other than that I think I might be nearly ready to take some accurate measurements.

I am using a minidsp 2x4 and a 2.1 way crossover plugin. I need to make sure to turn off any crossover before making the measurement. There are two subs connected, powered by a Parasound HCA 1000 amp.

Wish I had your patience and knowledge. All the best.

 

[John Mulcahy]

There is one thing that is not working correctly on my sound card window. In the past if I selected check levels you would be prompted to then select next or cancel. In the latest version both buttons are greyed out. Is there another something else I missed, wouldn't be a first for me

Nope, that's a bug, courtesy of yours truly. It has been fixed for the next beta, in the meantime if you open up the signal generator before trying the level check it should work as before.

Ideally select the output as well rather than leaving it as default output.

 

[Timothy Ivie]

Ok no worries your suggestion works for me. Thanks for all you do.

What is troubling me now is when taking measurements the sub level within the minidsp plug in must be greater than -3.5 dB to get the GREEN OK from REW. I went ahead and took the measurement once I had the OK and then ran EQ. Applying the REW generated EQ to minidsp plugin both sealed subs disappear so I need to increase the level to at least -1.5 dB on most of music tracks. In reviewing the plug in settings there are 5 EQ settings. If I bypass just the first then the sub sound is much more noticeable so I reduce the level back to point that sounds ok to me.

Seems to me the parameters I am using to create the filters are not correct but where to begin?

 

[John Mulcahy]

Would need to see the measurement and the filter settings. If the target level for EQ is set too low you end up using filters as a gain control, which isn't the aim.

 

[Timothy Ivie]

Please see attached for measurements and filters. Thanks for taking a peak.

 

[John Mulcahy]

Those measurements still don't make sense for subwoofers, they look like a high pass filter has been applied to the signal so there is no low end to speak of. If you are going through the miniDSP I suggest you remove it until it has been configured correctly to drive your subwoofers. The input device and input are also not selected in REW so the UMIK sensitivity is not being used and so the measurement levels are far from what they should be. The target level for the EQ window is 75 dB, but much of the measurement is sitting at over 120 dB, hence the massive reduction in level - you are asking REW to bring the signal down by 50 dB.

Don't make any attempts at EQ until you get measurements that are at a believable level and look like they come from a subwoofer rather than a satellite speaker. Once the measurements are making sense the rest can follow.

On the graphs use the Limits button at the top right to set a sensible SPL range for the graph, so that the response fills the vertical span.

 

[Timothy Ivie]

Understand the points you have made. The fault must be in my implementation of minidsp and the 2.1 plugin. I have a minidsp 2x4 kit / mini digi stack. There is an optical cable from the computer running to the mini digi. When I go to take a measurement the mini dsp 2x4 is not presented in the drop down. I also just noticed if I go to my macbook volume icon the output device is is digital out. If my memory serves in the past using a Minidsp 2x4HD that device is selectable in REW and on the macbook. Since I have a minidsp 2x4 HD in another system maybe I should use it to confirm that I am not completely crazy and then get in touch with Minidsp. Very sorry to have troubled you with issue.

 

[John Mulcahy]

The optical output is one of the interfaces on the computer, unlike a USB connection you won't see what is on the other end of it, it will just appear as digital out, so that sounds OK. The 2.1 crossover filter setup probably needs some review though.

 

[Timothy Ivie]

From what I read I need to make sure the crossover in the plug in is disabled perhaps I made a mistake.... again.

One quick question if I am getting a low level, for example 55dB when I do the pre measurement check would it be ok to go ahead with the measurement.

Cheers

 

[John Mulcahy]

It's OK to do the measurement, there is no need to check level before each measurement. The level may be low because of the crossover setting, however.

 

[Timothy Ivie]

I have made sure the crossover setting in the plug in is bypassed. I ran a couple of measurements and they are better but feel I am still missing something. Does it appear to you the plug in is still interfering?

BTW I did NOT get the low level message the one time I checked.

 

[John Mulcahy]

Look much better measurements, levels look good. The low end extension is less than one might expect from 12" subs though, probably worth making measurements very close to the subs (say 1" from the driver) to see what the near field response looks like.

Will the subs be driven from the sub output of a processor or will you use the miniDSP to apply the sub low pass filters?

 

[Timothy Ivie]

Now that is encouraging. Measurement from 1" left and right attached.

The system I am working with is for near field listening only. Pair of ATC C1CA stood on end and dual subs. Will you use minidsp 2x4 with 2.1 plugin for crossover and eq. Subs are driven by a Parasound HCA 100A ( disconnected the PA) and the mains driven by Jolida 202a. I bought cheap subs to learn about bass management not necessarily as an end state solution. I just looked on the sub retailer website - frequency response of 50 ~ 250 Hz. Probably not ideal but since these are only for near field music listening seemed ok to me at the time. I think the pair delivered were less than USD 200. I have removed the port, sealed the port opening added un carded wool and recycled cotton fibre just to tame them down for my small room 11' x 15' room.

After applying REW generated EQ I am thinking to set the crossover in the plugin at 90 and doing a bit of listening for a few days.

 

[John Mulcahy]

Fair enough, look to be performing about as might be expected if the port has been sealed.