Measurements make no sense

[clones83]

I’m new to REW and ran measurements at the main seating position, coming up with puzzling results that I can't figure out after much reading in the guides and posts, here and on the AVS forum. I’ve attached the graph of measuring both subs with the crazy results. Hard to understand how I can get any readings below 0. I don't know if this is a setting issue that is just plotting the graph wrong, a setting issue in REW for how I am measuring or if there is a bigger issue with the sub performance.

My set up is a Denon x4200 AVR routed from its sub 1 output to a miniDSP 2x4 HD which has outputs 1 & 2 each to PSA v1800 subs. The high & low pass filters are bypassed for the measurements on the miniDSP. The gains on both subs are at 50%. Output 3 on the miniDSP is going to a Crowson amp for a pair of Crowson MAs but that’s off for the measurements. I’m using a calibrated Umik-1 mic.

Until I get my dedicated home theater room completed next year, I’m in a 21' x 32' finished basement room with an 8' ceiling. Sub 1 is placed right front, between the TV & the RF speaker and sub 2 is mid left wall to the rear of the main seating position. Main seating position is 12' from TV. Subs are not in ideal spots, but the only places they can go in this room.

The obvious issue I see is the extremely low SPL up to 60 hz or so. SPL checks prior to measuring were good; I got 80db with no issues using the REW signal generator with a "Sub Cal" Pink Noise signal at -12dBFS. I can’t begin to do any EQ until I figure out what to do about that. No amount of adjustments in the REW app or with the AVR’s volume makes any difference. Between all the settings on the AVR, REW & miniDSP, I feel like I’m missing something & hopefully there’s a relatively easy setting I’m overlooking to get the overall db up & flattened to a somewhat normal level and the measurements to a point that I can begin to try some EQ. I’d love to have a palm to the forehead, D’oh! moment if anyone can help.

 

[jtalden]

Welcome!
I suggest you delay the closer SW by the difference in the distances of each SW to the LP. For example, if one SW is closer to the LP by 1 ft. it should be delayed by about 1.1 ms in the MiniDSP. If the combined measurement is still poor you can follow one of the many methods suggested to fix this.

You could also measure each sub individually and both together then post the mdat containing those 3 measurements here for us to review. If you can activate the REW acoustic timing feature for those measurements that would be best, but if you haven't used acoustic timing yet then don't bother. It is not required for a general analysis of this situation.

 

[clones83]

Thanks for the welcome! I should have included the individual measurements. The subs are about the same distance from the MLP & I get basically the same results separately and together. Since the 10-30hz range is so incredibly low (below 0db!?) and then an odd ramp up, it seems there's something fundamentally wrong for me to figure out before making adjustments in delay or other areas.

 

[AustinJerry]

Welcome!
I suggest you delay the closer SW by the difference in the distances of each SW to the LP. For example, if one SW is closer to the LP by 1 ft. it should be delayed by about 1.1 ms in the MiniDSP. If the combined measurement is still poor you can follow one of the many methods suggested to fix this.

You could also measure each sub individually and both together then post the mdat containing those 3 measurements here for us to review. If you can activate the REW acoustic timing feature for those measurements that would be best, but if you haven't used acoustic timing yet then don't bother. It is not required for a general analysis of this situation.

Can you explain what a measurement level below 0dB means???

 

[jtalden]

Thanks for the welcome! I should have included the individual measurements. The subs are about the same distance from the MLP & I get basically the same results separately and together. Since the 10-30hz range is so incredibly low (below 0db!?) and then an odd ramp up, it seems there's something fundamentally wrong for me to figure out before making adjustments in delay or other areas.

It looks to me that you sent the REW signal into the Denon right channel. So you probably have a ~80 Hz XO filter set in the Denon. It is then filtering the signal below the XO point.
Either; send the signal to the LFE channel, or temporarily turn off the XO, or set mains to 'large' in the Denon and try again.

 

[jtalden]

Can you explain what a measurement level below 0dB means???

I don't understand that reading.
0 dB is just a very low SPL level, i.e., 20 micro pascal. The part I don't understand is that in practice even a bigtime anechoic chamber will have more SPL at very low frequencies I think and the UMIK mic has self noise that should result in maybe 30-35 dB (just guessing). Maybe someone else can help us out on what is causing this.

 

[John Mulcahy]

The measurements were all made with the Java drivers and the output was the R channel, so they are probably all plots of the right speaker only, showing its high pass crossover. You will need to use ASIO drivers to send signals to the sub channel.

Regarding levels, it is easy to confuse full band SPL meter readings (e.g. the 40 dB or so of a quiet room) with plots of SPL vs frequency, at any given frequency SPL could be very low and below 0 dB.

 

[clones83]

It looks to me that you sent the REW signal into the Denon right channel. So you probably have a ~80 Hz XO filter set in the Denon. It is then filtering the signal below the XO point.
Either; send the signal to the LFE channel, or temporarily turn off the XO, or set mains to 'large' in the Denon and try again.

I don't see a to an option to send to the LFE from REW. The Output drop down options in Preferences and Measure only give me L, R or L+R. In the Denon I set the mains to XO at 250 to take them out of the equation and left the mains as small. I then ran a measurement with the mains set to large. No real difference in the results. I've attached my latest measurements. Is there a way to get REW to give me the drop down option to output to LFE? The help section talked about the option when on a mac or Linux but I'm using a Windows laptop. Does it make a difference if I'm using an HDMI from the laptop to the front (Aux 1) HDMI port of the Denon?

 

[clones83]

The measurements were all made with the Java drivers and the output was the R channel, so they are probably all plots of the right speaker only, showing its high pass crossover. You will need to use ASIO drivers to send signals to the sub channel.

Regarding levels, it is easy to confuse full band SPL meter readings (e.g. the 40 dB or so of a quiet room) with plots of SPL vs frequency, at any given frequency SPL could be very low and below 0 dB.

Thank you John. I'll do some reading about ASIO drivers and give that a try. This is all new to me & computer work is definitely out of my comfort zone but I'm up for the challenge. I'll post back after I've had a chance to do it with ASIO drivers.

 

[AustinJerry]

Thank you John. I'll do some reading about ASIO drivers and give that a try. This is all new to me & computer work is definitely out of my comfort zone but I'm up for the challenge. I'll post back after I've had a chance to do it with ASIO drivers.

Have you looked on your Settings screen to see if you are using the Java drivers? Typically, REW users configure the ASIO driver and use an HDMI connection between the laptop and the AVR. Does your laptop support HDMI connections.

there is a section in this REW guide that explains how to download, install, Nd configure ASIO for use with HDMI:

https://www.dropbox.com/s/zdhq72a1puyyxpr/REW 101 HTS Current Version.pdf?dl=1

Once you have ASIO working, output the measurement sweep to HDMI4, which will measure the subs by themselves.

 

[clones83]

i was definitely using Java, which I thought would work (based on some of my research). Per yours & John’s advice, I’m going to switch to ASIO. Thanks for the link. I also saw some help for this on the miniDSP site. I now also understand what you meant by selecting HDMI4. I’ll report back after doing this.

 

[clones83]

I think I got it! I spent this morning before church loading ASIO drivers and after some fiddling, seem to get proper measurements and confirmed I'm using the correct mic calibration file. I know I have some work to align and EQ, but at least it looks like I'm on the right track. Thank you to everyone who helped.