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Behringer USB mixer for speaker measurements?
Behringer USB mixer for speaker measurements?
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Old 9th March 2014, 05:42 PM   #1
tcpip is offline tcpip  India
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Default Behringer USB mixer for speaker measurements?

I have been struggling with a Behringer 302USB for speaker measurements, and I decided I badly need help from you guys.

(I have done speaker measurements, both impedance and SPL, in the past, using Speaker Workshop, an old Creative Soundblaster sound card, an impedance jig and a Panasonic mic capsule. So I know the basics, to the extent needed for that set of components.)

I got myself a calibrated Dayton XLR mic through Cross Spectrum Labs, so I needed a USB audio interface with an XLR input, so I bought a Behringer 302USB. I now have doubts about whether it can be used at all. What I need (for impedance measurements) is the following:
  • I have to pump digital audio out of the USB interface of the laptop to the 302USB
  • The 302USB's LineOuts have to feed the analog signal to my impedance jig
  • The outputs from the impedance jig have to hit the LineIns of the 302USB, and
  • The signal going into the LineIns have to be recorded in the laptop
And I have to do this without mixing the signal going out of the laptop with the signals coming into the LineIns.

I don't know whether the outbound signal and the inbound signal can be kept separate in the 302USB. It has something called a "Main Mix" which seems to mix all these signals internally. (Does it? Am I right? Is it controllable?)
  • I can select whether the "From" signal can come from USB or from the LineIn sockets. What am I supposed to select here? I need a signal to come in over the USB cable from the laptop to the 302USB, and I also need a signal to come into the 302USB from its LineIn sockets.
  • I can select whether the "To" signal can go to the "Main mix" or the "phones". What am I supposed to select here? Some signal is suposed to go to the "Main mix", I presume, because that's the signal which the laptop will record from the Behringer over the USB cable. But isn't the "Main mix" the place where my outbound signal (laptop->Behringer) lands up over the USB playback?
Am totally confused.

Did I make an uncorrectable mistake by buying a mixer instead of a USB audio interface like a Creative Soundblaster or a Focusrite Scarlett? Do you recommend any USB audio interface instead of the Behringer which has an XLR mic input as well as unbalanced two-channel analog inputs and outputs, so that I can do both SPL measurement as well as hook up an impedance jig?

Can any of you please help?

Last edited by tcpip; 9th March 2014 at 05:44 PM.
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Old 9th March 2014, 06:42 PM   #2
Ron E is offline Ron E  United States
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Does the 302USB have phantom power, because you need phantom power with that microphone? IS the 302USB also an external sound card, or just a preamp?

To make measurements you connect the left output of your sound card to the left input of the sound card - this is your reference channel. I use 1/8" male to male Left/right RCA jack adapters for output and input, and I use a female-female coupler to connect the left channels together..

You connect the right output of your soundcard to an amplifier, the amplifier to the speaker under test. You then connect the right input of your soundcard to the line out of your mixer (or whatever mic preamp you are using).

Start making measurements with the gain all the way down on the mixer, and bring it up slowly until you get good signal to noise but no clipping.
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Old 9th March 2014, 07:02 PM   #3
Ron E is offline Ron E  United States
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Quote:
Originally Posted by Ron E View Post
Does the 302USB have phantom power, because you need phantom power with that microphone? IS the 302USB also an external sound card, or just a preamp?
I just looked and it seems to have phantom power. I think by its very nature (although I could be wrong) that thing is mainly an input device. and its input and outputs are not separable. You can still use it only on the input side for the right/left channels as I describe above, but you will need to use the soundcard and headphone/speaker out of your laptop to drive the amplifier that is used to drive the speaker under test.
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Old 9th March 2014, 09:53 PM   #4
Elias is offline Elias  Finland
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Quote:
Originally Posted by tcpip View Post
I have been struggling with a Behringer 302USB for speaker measurements

Hi,

The divice is a mixer, that is what it does, mixes the input signals and puts them at the output. Everything you insert to the inputs will appear at the main mix output. So basically you cannot do a loop measuremt with that. If you loop output to the inputs you'll get feedback oscillation and that's bad.

But have faith, you can make it work for loop measurement, but you'll propably have to modify the unit Think about a nice weekend project

I did something similar for Alesis Multimix4 USB mixer. But it had plenty of other issues as well I needed to fix too
http://dl.dropboxusercontent.com/u/2...AlesisMM4.html

I believe Behringer is similar in functionality, so there should be hope.



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Old 10th March 2014, 04:01 AM   #5
tcpip is offline tcpip  India
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Quote:
Originally Posted by Ron E View Post
Does the 302USB have phantom power, because you need phantom power with that microphone? IS the 302USB also an external sound card, or just a preamp?
Behringer 302USB details: from the Behringer site and from Amazon

In short, it is not advertised as a sound card, though I thought it can act as one. (Maybe it can.) It is a small mixer with USB connection (for power and audio), a mic input, and some line inputs and outputs.

It has phantom power. There are extensive criticisms of its phantom power (or lack of it) on Amazon buyer reviews, but its phantom power is more than adequate for the Dayton measurement mic.

Quote:
To make measurements you connect the left output of your sound card to the left input of the sound card - this is your reference channel. I use 1/8" male to male Left/right RCA jack adapters for output and input, and I use a female-female coupler to connect the left channels together..

You connect the right output of your soundcard to an amplifier, the amplifier to the speaker under test. You then connect the right input of your soundcard to the line out of your mixer (or whatever mic preamp you are using).

Start making measurements with the gain all the way down on the mixer, and bring it up slowly until you get good signal to noise but no clipping.
Thanks, but I already know how to do speaker measurements. See my previous projects here: the Asawari and the Asawari Mark II. I have done SPL and impedance measurements in the past with an earlier USB audio interface, and I have discussed those measurements at length on these forums.

My questions are not really about how to do it -- my questions are "can it be done with a Behringer mixer like the 302USB?"
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Old 10th March 2014, 04:10 AM   #6
tcpip is offline tcpip  India
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Quote:
Originally Posted by Elias View Post
The divice is a mixer, that is what it does, mixes the input signals and puts them at the output. Everything you insert to the inputs will appear at the main mix output. So basically you cannot do a loop measuremt with that. If you loop output to the inputs you'll get feedback oscillation and that's bad.
Great. You have confirmed my suspicions.

I will now have to (i) sell this mixer, and (ii) buy something else, probably much more expensive.

I need something which will ideally do:
  • an XLR mic input and unbalanced line outputs for SPL measurements, and
  • unbalanced line inputs and outputs without any bloody mixing for impedance jigs
Any suggestions?

Quote:
But have faith, you can make it work for loop measurement, but you'll propably have to modify the unit Think about a nice weekend project
You are scaring whatever wits I have left. I have already embarked on a project which is my largest so far, and I have invested pots of money getting the pieces for it -- all I can think of is getting the measurements done ASAP so that I can proceed with the project and complete it. The last thing I want to embark on is a project to mod a tightly-built mixer with my (extremely limited) knowledge.
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Old 10th March 2014, 04:35 AM   #7
tcpip is offline tcpip  India
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What USB audio interface would you recommend for speaker measurements?
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Old 10th March 2014, 07:29 AM   #8
THUMP LUMP is offline THUMP LUMP  United States
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You may want to take a look at the Behringer UCA222 or UCA202. BEHRINGER: Computer Audio You might also want to give this a quick read about it as well. NwAvGuy: Behringer UCA202 Review
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Old 10th March 2014, 11:32 AM   #9
Elias is offline Elias  Finland
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Quote:
Originally Posted by tcpip View Post
My questions are not really about how to do it -- my questions are "can it be done with a Behringer mixer like the 302USB?"

This may be the key issue here. Does your measurement system software use one or two channels ?

Why is it so, because I think one channel meaurement can be done with this Behringer without the internal mixer loop 'problem'.
Say, for example, you output the measurement signal from main mix channel L, then insert mic and set the balance slider to R. This way main mix L output will not appear at R input, but the mic signal is available at channel R.

It's worth to try at least


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Old 10th March 2014, 06:02 PM   #10
tcpip is offline tcpip  India
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Quote:
Originally Posted by THUMP LUMP View Post
You may want to take a look at the Behringer UCA222 or UCA202. BEHRINGER: Computer Audio
I believe they don't support XLR mic inputs? And what is the difference between these two models?

Quote:
You might also want to give this a quick read about it as well. NwAvGuy: Behringer UCA202 Review
Will definitely do that. Thanks.
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