# One sub, two subs...



## boarder1995 (Mar 28, 2008)

Here are some recent REW measurements of my single and pair of SVS Ultra 13 subs playing together. I've been through all this measurement and placement stuff before and optimized the pair of subs for entire room even response. But I've recently changed the room a little and replaced a sub amp (BASH out and SLEDGE in for one sub, still BASH in other sub), so I thought I'd revisit my REW measurements.

The super flat measurement is the single BASH sub in its optimal place while measuring from the prime spot. I haven't taken any other location measurements yet, mostly because I'm really floored by how this spot looks! This is in the 15Hz tune, room comp small, no other EQ or adjustments from processor or sub amp.









Now, when I add the second sub to the mix it gets a little less pleasant...









I definitely DON'T have the right sub optimized as evident from the combined response looking less than stellar, and it's individual response below...









I'm mostly pleased with the single sub response. Since I'm the primary movie/music guy, I may go back to ONE Ultra sub in this setting if the remaining seating locations turn out reasonably good.


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## aackthpt (Jan 24, 2011)

Wow, interesting. That second sub has some problems, either itself or in placement. Why are they so much different, do you think it's all placement? Would be interesting to switch the two and see the individual responses.


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## boarder1995 (Mar 28, 2008)

I believe it's placement. I'll swap the two, hopefully this evening, and re-measure them.


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## JohnM (Apr 11, 2006)

Unusual looking measurements, especially the very sharp spike at around 180 Hz - maybe 3rd harmonic of the mains, but very unusual to be so prominent. Could you attach one of your measurements, perhaps the first?


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## boarder1995 (Mar 28, 2008)

Here's an overlay of the two versions of the Ultra13, one BASH and the other SLEDGE powered, placed in the same position (pain to move these around!). I turned room comp off and they look very similar, so I'm not worried about individual sub performance with either amp.









The location seems very ideal for the first sub. Now it's just a matter of finding a good place for the 2nd that doesn't upset the balance and flat response. I'm still trying to decide if the two different amps and slight phase shift or group delay (very minor) differences will create any of these valleys.  I may be way off abse with these assumptions though.


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## boarder1995 (Mar 28, 2008)

JohnM said:


> Unusual looking measurements, especially the very sharp spike at around 180 Hz - maybe 3rd harmonic of the mains, but very unusual to be so prominent. Could you attach one of your measurements, perhaps the first?


I'm not too worried about the sharp spike since it's well above the crossover slope even if I have the LFE set to 120Hz for movies. It's likely something resonating in the room, but that's just a guess. I'm just playing the subs from my USB soundcard out to the sub(s) inputs. Not going through the processor/receiver for now. I'm not following what you're asking me to post?


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## aackthpt (Jan 24, 2011)

boarder1995 said:


> I'm not following what you're asking me to post?


He's asking you to post an MDAT file so he can look at the measurement in other ways.


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## boarder1995 (Mar 28, 2008)

Ah, ok...doing that now...

View attachment 7-23 tests.mdat


There are a ton of other runs in that file, so you'll have to read through the text descriptions to decode.


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## JohnM (Apr 11, 2006)

The soundcard calibration file for those measurements is incorrect, it is a measurement of the room, not the soundcard - the spike at approx 185 Hz is because the room measurement being used for the soundcard cal had a sharp dip there. 

For your existing measurements use the Change Cal... button to clear the soundcard cal, you can substitute a correct cal file when you generate one. On some of the measurements you will need to apply approx -75dB offset to correct the levels (can do that on the All SPL graph). 

When making the soundcard calibration the only connection should be from the soundcard output to the soundcard input, no SPL meter connection, and if REW pops up a message saying the calibration looks incorrect because it varies too much, look closely at the result and compare it to the examples in the soundcard calibration help.


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## boarder1995 (Mar 28, 2008)

I did just that with the card cal. file. loop out to right back in, no meter. I even re-did the file again to ensure the file was correct - a nice gradual slope off the bottom. I'll look at this again when I get home (with my laptop I've got here). Thanks very much for your help and guidance since I may have missed something.


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## bentoronto (Dec 3, 2010)

I am puzzled: the best location sub (first chart) is unaccountably flat. Did you use a lot of smoothing? The second sub (third chart) is looking less smoothed and, you might say, a representative display.

Ordinarily the two together should show the beneficial effects of averaging room shortcomings and maybe also individual sub shortcomings (unless they are profoundly identical to one another).

But the joint chart (middle one) does average the two but looks worse than the first chart. Odd.

Ben


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## boarder1995 (Mar 28, 2008)

No smoothing and I've run it multiple times without changing any settings in REW. I also swapped subs and still looks great there. I even rotated the sub ~90 deg and it looked much worse.
I think there might be some phase/group delay differences between the two identical subs in that one has the SLEDGE amp and the other a BASH. That's just a theory though.


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## bentoronto (Dec 3, 2010)

Of course it has smoothing. Otherwise it would be highly jagged.

Ben


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## boarder1995 (Mar 28, 2008)

I haven't added any smoothing on any of the graphs. If I haven't changed anything on any of the graphs, then why would one be "smoothed" and the others not? It would be highly jagged if it was bad placement perhaps. I'll check again to make sure, but I haven't changed any of those settings and I've checked multiple times.


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## JohnM (Apr 11, 2006)

The plots posted are not valid because they included a soundcard calibration curve that was actually a room measurement, so they show the difference between the measurement that was used as a calibration and the actual measurement taken in each case.


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## boarder1995 (Mar 28, 2008)

I looked at the sound card calibration line and it's fairly flat, except at the very low end where it rolls off. I must have something totally screwed up in my arrangement with this new external USB soundcard. I've done the REW thing before without issues, but this time seem to have something(s) off.


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## JohnM (Apr 11, 2006)

The soundcard cal is not visible on the graphs unless you expand to the maximum vertical span, as the values in the cal data are about 75dB more than expected. Here is a plot that shows the soundcard cal:









At the normal vertical span here is the first plot with the invalid soundcard cal:









and here it is after clearing the soundcard cal:









The measurement is offset by 75dB because the effect of the invalid soundcard cal on the SPL meter calibration, the graphs can be drawn at a proper level by adding a -75dB offset to the traces using the All SPL graph controls.


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