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Signal Chain Loopback Measurements

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I thought I'd get the ball rolling from

 

It would be great if those with REW would do a simple loopback of their AVR, PEQ, Pre/Pro, amplifiers, etc. and post them is a thread dedicated to signal chain loopback measurements. It's so easy to do, I wonder why everyone doesn't do it. REW is free and you don't need a mic or anything else to do the loopback.

 

basic process is just to take an output from whichever device you're measuring and then feed that back to your soundcard (taking due care with levels if measuring an amp) then take a measurement in REW. A few things to bear in mind;

 

* make sure you have an appropriate (soundcard) cal file loaded to counter any purely measurement artefacts (e.g. a hpf on a line in is not that uncommon)

If your measurement covers multiple devices (e.g. perhaps you first loopback over your bd player and then you loopback over your bd player + processor) & you have a measurement for each stage then you can use the "A / B" trace arithmetic function to see the contribution of each individual stage 

 

 

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Can we run a loopback with an HDMI computer?  I have everything using HDMI now so how do I do each component?  Basically I want to know my AVR LFE out, Sanway amp, etc..

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Can we run a loopback with an HDMI computer?  I have everything using HDMI now so how do I do each component?  Basically I want to know my AVR LFE out, Sanway amp, etc..

what do you have for the input side?

 

you can use trace arithmetic here though. Take measurements adding one component at a time (over which you are taking the loopback measurement) then use A / B to see the diff between each measurement, this gives you the contribution of that component to the total rolloff.

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Marantz AV7005 (Red line is XLR, green in RCA)

 

AV7005%20Response%20-%20XLRvsRCA_zpsnqdx

I wonder what the difference between your AV7005 and mine is. Is it just a measurement artefact or some difference in how we have it connected? Also, why would XLR have a different rolloff to RCA? 

 

do we need to post some details about the measurement setup to rule out any such variance perhaps?

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I wonder what the difference between your AV7005 and mine is. Is it just a measurement artefact or some difference in how we have it connected? Also, why would XLR have a different rolloff to RCA? 

 

do we need to post some details about the measurement setup to rule out any such variance perhaps?

 

I wasn't in pure direct mode, and I was measuring from the subwoofer outputs.  

 

My soundcard is a Behringer UCA-202, and I created calibration files for it so the response was perfectly flat before adding the AV7005 or the MiniDSP into the signal chain.  

 

Do ours really measure that differently?

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I wasn't in pure direct mode, and I was measuring from the subwoofer outputs.  

 

My soundcard is a Behringer UCA-202, and I created calibration files for it so the response was perfectly flat before adding the AV7005 or the MiniDSP into the signal chain.  

 

Do ours really measure that differently?

possibly not actually (I'm on a slightly small screen atm), can you zoom in a bit? I used a 20dB wide y axis and 2-40Hz

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possibly not actually (I'm on a slightly small screen atm), can you zoom in a bit? I used a 20dB wide y axis and 2-40Hz

 

Unfortunately, all I saved was the pictures.  I don't have the files I could load into REW anymore,  

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I am using a windows 8 computer with hdmi. I have my yamaha AVR hooked up to my Sanway via sub outs. I usually plug the computer HDMI into the AVR HDMI input 4.

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I am using a windows 8 computer with hdmi. I have my yamaha AVR hooked up to my Sanway via sub outs. I usually plug the computer HDMI into the AVR HDMI input 4.

so you have a line in on a soundcard on the computer? if so, you just need to take the output from each device back into the soundcard and measure. You probably want to use a multimeter to check the output from the amp before you do so to keep it to normal line level voltages (or use something like http://www.avsforum.com/forum/155-diy-speakers-subs/1459739-how-determine-your-receiver-s-maximum-lfe-output-gain-structuring.html perhaps?)

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How do I run the output of the amp to the line in?

I don't know exactly. I googled a bit more on this subject and it seems like it is more involved than I thought, for example http://www.diyaudio.com/forums/everything-else/127882-how-protect-sound-card-during-amp-measurements.html, so basically some sort of resistor network to provide a load to the amp and divide the voltage down to a reasonably level & then possible ground issues to deal with.

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Marchand BASSIS and Bossobass SEQSS MKII:

 

01ff09c7faac51df597d0c0c09b38dba.png

You can stop flexing your mettle now Dave :) Haha. So between the marantz, Mini, and Oppo (which I need to buy), I guess I would be looking at a pretty solid signal chain. The only other variable is the crest 7.5 but I know that has been tested as pretty flat to 2-3hz. Guess that shows pretty well in the speclab measurements we did that day :)

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Here are sweeps of my subs front wall and rear subs. I connected the adcom to the rear subs as well to compare.

 

 

Green: Adcom rear

lower dark purple: clone rear

Maroon: front w/clone

top light purple: clone all subs

 

My UMIK does not have cal files below 10hz. This was at the MLP without touching gain, mic or anything. I tried matching the Adcom upper bass to the clone with the clones gains. The Adcom does not have gain controls. I should run a louder sweep with it maybe?

 

 

 

subs_zpsblfevqpj.jpg

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Hey James isn't that odd how the rear FR matches the front?? Those responses are eerily similar like it was the same subs just another sweep. That green one looks more like a near field response than the dark purple.

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My rear subs are about 6 feet away from the mic. The fronts are 14 feet away. The mic rolls off below 10hz without correction files. It is a UMIK from minidsp. I think I need to turn up the Adcom to get a better representation. My nearfield subs are not within 1 meter so room gain is kicking in but not quite as much as the front. All I did was turn the gain all the way down on each channel. Channel one runs the front array and channel 2 runs the back. The front array is 2 ohms and 8 drivers and the back is 4 ohms with 4 drivers.

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Tons of loopbacks.

 

Note that on a few of the measurements you will see a sharp drop off or spike up near 20kHz. Those are artifacts due to the limitations of the measurements sampling rate and not part of the devices response.

 

EQ Devices:

 
Rane PE-17
post-5-0-84525900-1426777021_thumb.jpg
 
Symmetrix 551E
post-5-0-43713100-1426777006_thumb.jpg
 
Behringer DCX2496
post-5-0-67427800-1426776876_thumb.jpg
 
 
Soundcards:
 
Turtle Beach SRM
post-5-0-68971100-1426777015_thumb.jpg
 
M-Audio Mobile Pre
post-5-0-10373400-1426776955_thumb.jpg
 
Presonus Firebox
post-5-0-93551200-1426776923_thumb.jpg

 

 

Mixers:

 

Peavey PV-14

post-5-0-88557400-1426777057_thumb.jpg
 
Behringer Xenyx 1202
post-5-0-90173900-1426776989_thumb.jpg
 
 
Receivers / Processors:
 
Pioneer VSX-517K SW Out
post-5-0-72855300-1426776996_thumb.jpg
 
Outlaw Audio Model 950 SW Out
post-5-0-19530900-1426776975_thumb.jpg
 
Onkyo TX-SR806 SW Out
post-5-0-86953500-1426776889_thumb.jpg

 

 

Amplifiers:

 

Crown CE4000

post-5-0-57786300-1426776911_thumb.jpg
 
Crest Audio 8002
post-5-0-66197300-1426776898_thumb.jpg
 
AETechron 7560 / Crown M600 (DC coupled)
post-5-0-23889300-1426776895_thumb.jpg
 
QSC PL9.0PFC
post-5-0-64425200-1426777050_thumb.jpg
 
Powersoft K10 / Klein Hummel KPA-2400
post-5-0-27513100-1426776933_thumb.jpg

post-5-0-67427800-1426776876_thumb.jpg

post-5-0-86953500-1426776889_thumb.jpg

post-5-0-23889300-1426776895_thumb.jpg

post-5-0-66197300-1426776898_thumb.jpg

post-5-0-57786300-1426776911_thumb.jpg

post-5-0-93551200-1426776923_thumb.jpg

post-5-0-27513100-1426776933_thumb.jpg

post-5-0-10373400-1426776955_thumb.jpg

post-5-0-19530900-1426776975_thumb.jpg

post-5-0-90173900-1426776989_thumb.jpg

post-5-0-72855300-1426776996_thumb.jpg

post-5-0-43713100-1426777006_thumb.jpg

post-5-0-68971100-1426777015_thumb.jpg

post-5-0-84525900-1426777021_thumb.jpg

post-5-0-64425200-1426777050_thumb.jpg

post-5-0-88557400-1426777057_thumb.jpg

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I still use a Presonus Firebox for most. I have 3. They are about -1dB at 8Hz and -2dB at 5Hz. Small, reliable and built like a tank. I have tried to find something else that perhaps measures a little bit flatter even than that but run into problems with headroom in the mic preamps with everything else I try.

 

The Firebox allows SPL calibrated measurements of right about 140dB using Earthworks M30 or M50 mics before clipping the preamp with the input trim bottomed out and a bit higher than that if I use the ACO rig, but to be honest after doing direct comparisons of the ACO rig versus the EW mics the only differences I could spot worth even mentioning were below 5Hz and they did not amount to much at all. Very close. I usually use an EW because it is a bit quicker and easier to setup due to less cables and one less ac plug. Most of the other interfaces including others from Presonus, M-Audio, Tascam and RME that I've tried just don't accept signals that hot and will clip when the levels reach 120-130dB. For most this wouldn't be an issue but I need the headroom and would have to switch to different mics or add an attenuator to get headroom in the measurement chain. Little bit different priorities for me than most other guys.

 

I'm still hoping to find something a bit better but I have been lazy lately.

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I like Presonus, they seem to have good preamp sections.  I never got good sound out of M-audio's stuff for the price.  RME seems to be the new hot interface these days but I haven't messed with any of it. 

 

That's a boatload of loopthrus, thanks for posting.

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My rear subs are about 6 feet away from the mic. The fronts are 14 feet away. The mic rolls off below 10hz without correction files. It is a UMIK from minidsp. I think I need to turn up the Adcom to get a better representation. My nearfield subs are not within 1 meter so room gain is kicking in but not quite as much as the front. All I did was turn the gain all the way down on each channel. Channel one runs the front array and channel 2 runs the back. The front array is 2 ohms and 8 drivers and the back is 4 ohms with 4 drivers.

Well this is the loopback thread so I think this should be in your own separate thread anyway, but that's exactly my point. Regardless of the rolloff the FR for both sets of subs in your graph are nearly identical. How can subs 6ft away have almost the *exact* same FR as subs 14ft away?? I guess anything is possible but that's highly unlikely. They're almost the same level and shape...

 

Sorry for the off-topic guys.

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