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How to start measurements when you have multiple subs

16K views 97 replies 6 participants last post by  thsmith 
#1 ·
REW is working for me now and no more manual measurements, yahooooo!

My room (Living room)as most everyone elses is challenging, 4200cf, 8' to 12' sloping ceiling, hardwood floors, fireplace is 10' wide and 12' high. 6' frech door, all windows have heavy drapes and large opening in back of the room to the right from sitting position.

I have a HSU VTF3-MK3 Turbo in front left corner and HSU MBM-12s behind each main.

When I start my measuring I know I need to remove the mains, should I also turn off the MBMs and focus on just the 3 3 T and then turn off 3 3 T and turn on 1 MBM at a time to find best location for subs ?

3 3 T XO is in set at 55hz
MBMs XO out (50hz-150hz)
AVR (Denon 2808) XO set to 120hz

Thanks
 
#3 ·
#4 ·
ANyone with past experience doing testing with multiple subs ?
Your situation is not considered multiple subs. You have a low sub and a couple mid subs.

It's a very difficult job to properly integrate this arrangement into a set of mains, given the obvious time and phase hurdles that have to be overcome.

I would test each sub individually at first, simply to get an idea of how their position is interacting with the room, but I wouldn't get too crazy about trying to get a perfect response at this stage, because you're going to have to get them to play in concert eventually and they will more than likely not react in your favour.

Your low will have to be average phased with the two mid subs, since they're not co-located. Then the phase of each mid will have to be phased with the mains. Since you have them close to each main (and not beside your couch where it is recommended), then this will work in your favour for phasing. You may want to isolate a measure between a mid and its associated main to set the initial phase of each mid.

brucek
 
#5 ·
Thanks Weverb, I have been following that thread.

After more thought I think I will raise my AVR XO to max

Then with measure just the 3 3 T on and XO out do a measurement

Then do the same for each MBM

and see where I have overlap and gaps.

Once I get to a happy place I want to read more about applying filters to see the changes, I think that is what you did before buying an BFD.
 
#7 ·
Let me know if I can help. Have you done the typical pink noise/RS meter 75dB calibration of...

1. Main sub to highs.
2. One MBM to highs.
3. Other MBM to highs.
4. Both MBM's to highs.
5. All subs to highs.

One of your previous graphs looked like your 3.3 was playing really low compared to the MBM mid-bass. You are going to have a lot of fun playing. You have different positions to try out, with and without turbo to try, and max output versus max extension to try. :bigsmile: Good luck.
 
#6 ·
Thanks Bruce, many things to consider and try. For some reason I always seem to do things the hard way.

I tried the MBM in nearfield and did not like it, most likely the large opening to the right and behind me.

The really cool thing is that REW makes taking measurements so much more accurate, fast and easy as opposed to the way I have been doing it with RS meter, Freq cd and Excel.
 
#10 ·
Bruce, I see what you mean about the sub and MBMs not playing well together. With all 3 on I have a bad suck out at 50hz but individually they look good in that area.

1st graph with 3 3 T and both MBMs on
2nd graph with just 3 3 T on
3rd graph just MBMs on
4th graph just left MBM on
5th graph just left MBM on
 

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#12 ·
Have you added the correction file yet? Why does your graph stop before 200Hz?
 
#13 ·
Also, how are your MBM's playing down to 15Hz. They should drop like a brick after 50Hz.
 
#14 ·
agree and why does the 33T play way past 60hz with XO in and set to 60hz ? I remember in one of your post you thought your receivers XO was not working. My case it looks like the AVR, sub and MBMs XO are not working.

Any ideas, could it be a REW or Sound card problem with setup?
 
#17 ·
I agree about the xo not being a brick wall as the frequency increases, but the MBM was design to fall off after 50Hz. It should not continue down to 15Hz. If you look at my post with just the MBM graph (linked to before) you can see how it did not respond after about 40Hz.

The 3.3 looks realistic.

What level are you calibrating to with REW? 75dB?

Taking a note from brucek's advice book, have you tested your sound card calibration file to make sure you get a flat line?
 
#19 ·
Agree with the MBM measurements. Not sure what is going on but will investigate. I was calibrating at 76hz. Below is a graph of loaded calibration files for SPL and Soundcard, dash is Soundcard. I am using the Turtle Beach SMR but no issues with calibration.



Have you tested different placement options with the 3.3 to try and get rid of that dip?

Not with REW but that will be first order of business this weekend if not sooner.
 

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#18 ·
Have you tested different placement options with the 3.3 to try and get rid of that dip?
 
#20 ·
Try a measurement of your loopback cable to test your soundcard cal file, and remove the SPL meter calibration file and uncheck "c weighting". Make sure you are getting as flat a line response as possible. Reference the last graph on my page 6 of my post to see what I mean.
 
#22 ·
Looks good. Now take a measurement of it.
 
#24 ·
With C weight unchecked and SPL cal still unloaded ?
Yes, it should be a flat line.

See anything wrong?
No, everything looks good.

sweep was from 15hz to 135hz
Measure subs with a sweep from 0Hz-200Hz.

but the MBM was design to fall off after 50Hz. It should not continue down to 15Hz.
The response looks about like I would suspect. It does drop off at the assigned 50Hz. Below that the remaining signal is likely enjoying room gain. There also may be some low frequency noise in the room. I don't see a probelm with the MBM response. Take a near field with the sub in the middle of the room (or outside even better) to get a clearer picture.

I see what you mean about the sub and MBMs not playing well together
Ever considered an 80Hz crossover and the 3 3 T as your only sub and not use the MBM's. The 3 3 T is certainly capable enough. What is your intension/goal with the MBM's?

You do need to turn down the level of the MBM's in relation to the low sub. They're too high to integrate well with the low sub from the graphs you've posted so far. They're both peaking over 80dB. Turn them down.

As a side note on REW, it's a lot easier to evalute responses of each sub if you adjust the REW cutoff target line to the desired crossover. So, if you are testing the low sub, set the target line at 50Hz or 60Hz (there is no 55Hz) and when testing the MBM set the target at 120Hz. It has no effect (except when creating filters), but it helps you visualize how close you are to the desired target.

brucek
 
#25 ·
The response looks about like I would suspect. It does drop off at the assigned 50Hz. Below that the remaining signal is likely enjoying room gain. There also may be some low frequency noise in the room. I don't see a probelm with the MBM response. Take a near field with the sub in the middle of the room (or outside even better) to get a clearer picture.
I understand having some room gain, but 70-72dB at 18Hz!?! :huh: Is there a way to test for "low frequency noise in the room"? Can you turn the highs and lows off and run a measurement? Would that show you anything?
 
#26 ·
Thank Brucek, all input and ideas are welcome and I will try your suggestions.

I am not sure what my intent was with the MBMs now, I think I just started aquiring toys which is not good. I should have apllied science first like learning to use REW. No harm done if I find I do not need them, the used market for MBMs look good.

I like your idea of focusing on the sub and may go back to near field with one of the MBMs if needed and see how REW shows it integrating.

I do have a question for you, I had the 3 3 T and MBMs balanced using this method, any issues with this approach?

Using AVR test tone I matched 3 3 T and MBM
Ref test tone was 80dB and measured one MBM to 78dB, then turned off and did the same for second MBM. With both MBMs on it gave me 80dB.

With both MBMs off I measured the 3 3 T to 80dB with the XO out(normally in).

With the 3 3 T and MBMs on I lowered the AVR sub level to 80dB. Then set 3 3 T XO back to in.
 
#27 ·
Using AVR test tone I matched 3 3 T and MBM
A poor way to do it if there are peaks in a subs response. There is a difference in energy returned when using band limited pink noise if there are peaks, compared to a sub that has a flat response across that band. Peaks will always upset a simple SPL meter level check. In your case I would use REW as the best way to tweak the levels. I would first use the receiver test tones to set them all equal (subs, mains, etc) and then use REW to tweak the level of the MTM's (down in your case).

brucek
 
#28 ·
Is there a way to test for "low frequency noise in the room"?
Yes, use the REW Spectrum Analyzer.

Once your levels are setup for a normal response measure, then select the Spectrum tab and the following settings.
Mode = Spectrum, FFT Length = 65536, Averages = 2 or 4, Window = Rectangular, Y Axis = dBFS

Select the Signal Generator and select WhitePN (periodic White Noise).

Press the RED record button on the Spectrum page.

It lets you examine the room for noise energy that you may not be aware of.

Below is a pic of my office with the Spectrum analyzer running with no signal being generated.

You can see my furnace is introducing some low frequency noise. If I shut it off, the noise is eliminated.

You can see I have the typical poor PC computer 60Hz hum and its related harmonics at 120Hz, 180Hz, 220Hz etc.

You can also see (amazingly), my NTSC RPTV CRT's horizontal oscillator frequency of 15.750Khz present in the room.

The TV is several rooms away and happened to be turned on, but the oscillator noise is present in my office (not that I can hear it, but there it is). Shut the TV off and it goes away.

The Spectrum analyzer can tell you a lot about your room and system before you even do a measure.

Sometimes you'll see a waterfall with a strange signal that rings out for many hundred of milliseconds. If you looked at the spectrum, you might see the source, rather than incorrectly deciding it comes from a modal resonance.... My furnace is a case in point on that issue.



The RTA is also quite useful in REW for dynamic measurements, rather than a simple static measure.

Below is a response measure and then a quick RTA. Once this is running, I can then move the microphone around to see what different listening positions look like (all in real time). It is revealing to see the difference a few feet make when you move the mic, and to compare against the simple response measure on the screen at the same time for comparison.

The RTA also allows you to change filters or move equipment and watch the RTA screen for the real time changes. It's also really useful to adjust phase on a subwoofer for the best crossover response. You simply watch the RTA screen as you dial the phase control. A lot better than taking a bunch of measures to accomplish this task.

Here's a pic of RTA and a response measurement on the same screen (measurements are selectable to be placed on the RTA screen for comparison).
I was sure not to move the mic when I took the measure and then started the RTA.

Pay attention to set the RTA up properly. See the setup values on the plot below. (note that the RTA requires switching the Signal Generator to PinkPN (periodic Pink Noise)




I understand having some room gain, but 70-72dB at 18Hz!?!
Well it's about 15dB above the noise floor. Remember, if there's a high noise floor (typical 45dBSPL, but can be much higher), then the meter calibration file will raise the signal level as the frequency drops. A response chart signal can be mis-interpreted as actual signal, when it's really just noise being raised by the meter calibration file. Consider an old analog Radio Shack meter is adding +30dB offset at 10Hz from the cal file. A high noise floor will show as signal. This is the case with the MBM plots on page 1 of this thread. See how the signal drops nicely until about 30-35Hz and then begins to rise as the frequency goes lower than that. The signal below the drop is noise......... ignore it.

brucek
 
#29 ·
WOW BRUCEK, excellent information ! When I was calibrating my SPL before performing a measure test I was seeing 45 or so dB when no one was in the room and no tones being generated. I do think my AC was running (92 degrees hear in Dallas yesterday). Looks like I now have a way to measure the room before taking measurements.

THANK YOU !
 
#32 ·
Thanks weverb for confirming the soundcard calibration.

Soundcard and RS analog cal file loaded and c weight checked.

RS SPL meter at LP set to slow and C weighting.

The graph below represents my starting point. MBMs powered down. HSU VTF3-MK3 turbo off, XO out, balanced with mains and located in left front corner (ceiling height is 8' vs opposing corner with ceiling 12'). AVR XO 80hz, Auddessy off.

I have moved and mesaured the sub within the limits I can move it in front left corner, chart represents best location.

Any tips on next steps would be great !
 

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