Measurment Setup w/ the MobilePre USB

[69Stingray]

Hello everyone, my MobilePre USB has arrived and my EMM-6 microphone is on order from Cross-Spectrum, who is having a sale until 15-Jan-2010 by the way.

Time to order cables. I have read 100 or so posts and think I have the proper setup, would some verify?

1.) For sound card calibration, just connect output to input with a mono 1/8" cable.

2.) For measurement, connect microphone to XLR input. Stereo output (with mono 1/8 cable) to AMP, then to speaker.

Am I missing anything?

SPL meter is only needed to set the reference SPL, correct? No need to connect to the MobilePre at all?


(PLEASE SEE THREAD #26 FOR UPDATED SCHEMATIC)

[Smokinghot]

I just did this the other day when setting up my MobilePre USB with HOLMImpluse SW.

1) You'll want to mimic your testing signal chain exactly when doing your sound card calibration. So if you're using the XLR input, then use it when calibrating. I purchased a XLR to 1/4" mono cable for this purpose. **Warning** If you do use this method, be sure to disbale the phantom power for the XLR jacks.

Depending which SW you're using, and what you find convenient, you may rather use the 1/4" mono jacks for your output connections. This amounts to personal preference I believe. I use the 1/4" connections, mainly because I think it's easier to build cable jigs in a mono configuration, and 1/4" mono to whatever patch cables (such as the XLR to 1/4 I mentioned earlier) are in more abundance at audio stores. YMMV

2) Do not use a mono male cable with the stereo jack on the MobilePre. You'll most likely end up shorting the 2 channels to one another.

Before measurement, be sure that you have applied your sound cards calibration test correction file, and installed the calibration file for your mic, if you have one, and if the SW you're using allows for it.

I'm not setting a SPL reference for my tests. I chose rather to dial in the output of my amp to 2.83volts. Which is kinda the defacto standard for measuring at 1 meter.

Hope I helped

[69Stingray]

Thanks for the reply SmokingHot.

• Where did you find XLR to 3.5mm cables? I could only find XLR to 1/4 at Parts Express. Just add an 1/4" to 3.5 mm adapter? Using the actual input is very logical.

• Also, I can't seem to find mono 3.5 mm to mono RCA cables at Parts Express, which seems odd. Any suggestions there? I agree, mono would be better over stereo (elimnates a couple failure modes and errors on my part )

• I am getting a moc with a cal. file, so I should be good to go.

What do you think of this amp?

Pyle Pro PCA1 Mini 2x15W Stereo Power Amplifier

[Smokinghot]

Thanks for the reply SmokingHot.

No prob... Newbs need help too, and I know what it's like to get dead air. :huh:

• Where did you find XLR to 3.5mm cables? I could only find XLR to 1/4 at Parts Express. Just add an 1/4" to 3.5 mm adapter? Using the actual input is very logical.

I didn't. I used XLR to 1/4". I used 1/4" mono throughout my connection process. I didn't buy my cables from the retailer linked, but I thought I'd give you an example, (couldn't find it via PE ). I have a pro music shop near my home, and they had every patch cable / adapter you can come up with. :T

http://www.av-cables.net/pro-audio/pro-audio-40033.html

• Also, I can't seem to find mono 3.5 mm to mono RCA cables at Parts Express, which seems odd. Any suggestions there? I agree, mono would be better over stereo (elimnates a couple failure modes and errors on my part )

Example of what I used: ....again, in the 1/4" mono

http://www.radioshack.com/product/index.jsp?productId=2103711

• I am getting a moc with a cal. file, so I should be good to go.

Nice... Some might say that you can get away without having one specifically for your mic and/or you can make a homebrew file 8O , but IMHO if you're going through the trouble of constructing a measure rig. You should at the minimum insure you've running a flat line before you hit the test button.

What do you think of this amp?

Sorry SR... I decided to educate myself on speakers first before amps. Track me down in another year or so, and I might have the knowledge to give you a useful answer. :lol:

[Bear]

What do you think of this amp?

Pyle Pro PCA1 Mini 2x15W Stereo Power Amplifier

Power output: 2 x 3 watts (4 ohms @ 1% THD), 2 x 4 watts (4 ohms @ 10% THD)

Not Good. 1% THD is only 40dB of headroom before you hit the noise floor for the amp (20 * log(THD)). To get to 60dB of headroom, you need an amp that is less than 0.1% THD at the test voltage. Obviously the above amp should have less than 1% THD at 2.83v, but if it was that dramatic of a shift, then I'd be seriously concerned about the amp's design and suitability to the task.

If you are looking for something compact, then this is probably closer to what you want:

http://www.nuforce.com/hp/products/icon/index.php

Otherwise, I'd look for a good, used stereo or multi-channel amp from someplace like Audiogon. You will want to be careful with Class D amps, though. These use a type of switching power supply that can have audible and measurable artifacts in the upper octave (hence the comment on the NuForce product's website, above, about sensitive speakers and upper octave noise).

[Tyson]

I have a stereo 1/8th inch to XLR cable, when I plug the 1/8th inch mini-plug into the "Stereo Output" on the back, and the other end with the XLR jacks into the Left and Right XLR inputs, I get a clipping indicator along with the signal indicator on the front. Am I doing something wrong?

[ThomasW]

I have a stereo 1/8th inch to XLR cable, when I plug the 1/8th inch mini-plug into the "Stereo Output" on the back, and the other end with the XLR jacks into the Left and Right XLR inputs, I get a clipping indicator along with the signal indicator on the front. Am I doing something wrong?

All that's needed for testing is a standard 'mic' cable (female xlr to male xlr), and a 1/4" mono interconnect with an appropriate connector for your power amp on the other end.

Input signal from the mic goes to the XLR input. Output signal from the 1/4" output goes to the power amp

[Tyson]

I just want to do the loopback right now, is this the correct connection to do that?

[ThomasW]

I just want to do the loopback right now, is this the correct connection to do that?

No a loopback involves hooking the output from one channel to the input of the other channel. The mic inputs aren't used nor are the stereo jacks

[Tyson]

Ok, that clears it up, thanks!

[69Stingray]

Not Good. 1% THD is only 40dB of headroom before you hit the noise floor for the amp (20 * log(THD)). To get to 60dB of headroom, you need an amp that is less than 0.1% THD at the test voltage. Obviously the above amp should have less than 1% THD at 2.83v, but if it was that dramatic of a shift, then I'd be seriously concerned about the amp's design and suitability to the tas

Thanks Bear, I was afraid of that actually. I do have an older stereo reciever, I can just use that. I figured if the Pyle would work, it would be a useful $30 (for convinence).

Also, thanks smokinghot, I may have to visit my local Radio Shack :-)

[Smokinghot]

No a loopback involves hooking the output from one channel to the input of the other channel. The mic inputs aren't used nor are the stereo jacks

odd...

I did my loopback using the 1/4" mono output to the XLR mic input. Worked fine and simulated my testing chain prefectly.

Any reasoning for not doing it that way..?

[Smokinghot]

Also, thanks smokinghot, I may have to visit my local Radio Shack :-)

FWIW...

I found that the local independant pro music store's products were of better quality, and less in price than RadioShack, YMMV. I returned the unopend mic XLR cable I bought from RS once I realized that. That 1/4" to RCA adapter was already out of the packaging so I didn't bother returning it. I also got a screaming deal on my mic tripod from that same independant shop. IMO it's worth dealing with shops that take the effort to remember your name.

Glad I could help...

[gmed]

will this setup work with SoundEasy?
Would I still need the Behringer XENYX 802 mixer?

So confusing. Sorry if this has been explained in the past.

I'm a Doctor, what the hell do I know about these things?

[ThomasW]

odd...

I did my loopback using the 1/4" mono output to the XLR mic input. Worked fine and simulated my testing chain prefectly.

Any reasoning for not doing it that way..?

My statement was addressing the picture showing Tyson's wiring setup.

[ThomasW]

will this setup work with SoundEasy?

Yes

Would I still need the Behringer XENYX 802 mixer?

No

[gmed]

Thank you Thomas. Which one would you recommend? and why?

[ThomasW]

Use a M-Audio Mobile Pre.

[Smokinghot]

My statement was addressing the picture showing Tyson's wiring setup.

The mic inputs aren't used nor are the stereo jacks

Ahh... sorry. You meant that the "stereo mic" input isn't used. "Mic inputs" was a generality that would have to include the two XLR connections. I guess I was being too literal with the plural.

[Tyson]

Thanks everyone, I got it up and running today, and taking measurements using my calibrated mic (well, a Dayton with a calibration file, which I imported into Holm Impulse). Wow, lots more info and detail than my FFT app on my Iphone was giving me! Found a notch between 1.5khz and 2.5khz that was making the tweeter sound "isolated" and "spitty". Plus it showed a few other things that were interesting, but that's for a different thread....

[69Stingray]

Input signal from the mic goes to the XLR input. Output signal from the 1/4" output goes to the power amp

) Do not use a mono male cable with the stereo jack on the MobilePre. You'll most likely end up shorting the 2 channels to one another.

Just to clarify, for the output, use a mono 1/4" in one of the 1/4" unbalanced, outputs correct?

[Smokinghot]

Just to clarify, for the output, use a mono 1/4" in one of the 1/4" unbalanced, outputs correct?

you edited your post before I could paste in all the quotes saying to use the 1/4" connection points.

IMHO, I believe the 1/4" connections are the best way to utilize the MobilePre's outputs.

[69Stingray]

you edited your post before I could paste in all the quotes saying to use the 1/4" connection points.

IMHO, I believe the 1/4" connections are the best way to utilize the MobilePre's outputs.

I was having issues this morning to say the least. My first post was completely not what I wanted to ask. Senior moment at the age of 35.

[69Stingray]

Can I use this cable for output since I will be plugging in my amp's AUX input?

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=241-5674

[Smokinghot]

Can I use this cable for output since I will be plugging in my amp's AUX input?

That's the same connection methodology I'm using. Mono 1/4" to RCA, (however, I'm using a normal RCA cable and the adapter I linked to in my first post). If I didn't already have the RCA cable and the adapter. I'd buy something just like what you linked to.

I would think it's save to assume your amp's AUX input is an female RCA, so you should be good to go. :T

Have fun...!

[69Stingray]

I have updated my schematics in case someone needs them in the future (I know I would of found them useful).

[69Stingray]

Made my first measurement using the above setup. I used Room EQ Wizard, I measured my NHT SuperTwo speaker(s). Mic is approx. on-axis at approx. 6 feet. Speaker is approx 4 feet from the side wall and 6 feet from the back wall.

Room Eq Wizard is ungated, so this is the true in-room freq. response (Note: speaker is not in listening position and mic is not at listening location - this was just a trail).

Smoothing is 1/6 octave.

EMM-6 mic calibrated by Cross-Spectrum .

[kendomusic]

I have updated my schematics in case someone needs them in the future (I know I would of found them useful).

Stingray,
The pictures are very useful. Do you have the connection diagram for the Impedance measurement? I tried to use this recommendation from Purebits but was not successful measuring impedance. I use ARTA-Limp

http://www.purebits.com/appnote17.html

[cjd]

You need to take the left output and feed it both left and right inputs for calibration - without an amp in the chain, you just feed straight through.

For actually measuring impedance you then add a reference resistor (you need to measure this accurately before you use it, the rated value isn't close enough...) into the mix. Lout to Rin direct. Lout to resistor to speaker to Lin (if I recall right).

[69Stingray]

Don't think I can be much help. I have not used ARTA-Limp. CJD's setup sounds correct.

I use the Woofer Tester 3 for impedance measurements. It is very easy.

Image not available

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-803

[cjd]

I should mention, you DO need extra parts in the chain if you're running with an amp in the mix. I was able to fit the 2 resistors and 2 diodes into 1/4" jacks for my rig (I'm using a FastTrack Pro so different device) but I made the mistake of hard-wiring the reference resistor (which can't be in the mix for calibration!)

[joe_B]

Sorry if this is a dumb question but what does the "DUT" stand for in the schematic?

[cjd]

Device Under Test

[kendomusic]

You need to take the left output and feed it both left and right inputs for calibration - without an amp in the chain, you just feed straight through.

For actually measuring impedance you then add a reference resistor (you need to measure this accurately before you use it, the rated value isn't close enough...) into the mix. Lout to Rin direct. Lout to resistor to speaker to Lin (if I recall right).

cjd,
Here 's the jig I use. would you please comment if its correct.

[cjd]

Yes, that's right for measuring impedance. Note that it does nothing with the R input signal, takes everything from L.

Get rid of the resistor and wire straight through for calibration.

[Dennis H]

The Arta/Limp manual recommends using the headphone output if you're not going to use a power amp for impedance measurements. The line out jacks may not be able to supply enough current. For calibration clip both input probes before the resistor and hit the cal button. For measurement the right channel goes before the resistor and the left channel goes after. All the shields of all the wires hook together at the (-) of the driver. He recommends a 100 ohm resistor with the headphone amp, 27 with a power amp. Exact values don't matter as long as you tell Limp what it is. The drawings in the Limp manual are very clear except he just shows the shields going to ground rather than showing how they get there (all hooked together.)

[kendomusic]

The Arta/Limp manual recommends using the headphone output if you're not going to use a power amp for impedance measurements. The line out jacks may not be able to supply enough current. For calibration clip both input probes before the resistor and hit the cal button. For measurement the right channel goes before the resistor and the left channel goes after. All the shields of all the wires hook together at the (-) of the driver. He recommends a 100 ohm resistor with the headphone amp, 27 with a power amp. Exact values don't matter as long as you tell Limp what it is. The drawings in the Limp manual are very clear except he just shows the shields going to ground rather than showing how they get there (all hooked together.)

Thanks CJD and Dennis. I calibrated as recommended by removing the resistor. I then measured the resistor and registered 988 ohms. It was marked 1K ohm. I applied the accurate value in the measurement setting. I also used the "phone out" instead of the of the "stereo line". Tested a 5 1/4 inch woofer from a Klipsch outdoor speaker and attached is what was measured. Did I get it right hopefully?

[cjd]

Can't be sure but it looks like it's about right.

[69Stingray]

A good post from another thread (subject: Speaker Workshop & Mobile Pre)

https://www.htguide.com/forum/showpost.php?p=442929&postcount=14

[norcad]

My experience is that you should use an amp even when you measure impedance. Its pretty tricky to get good results without, and you will never know for sure if they are acurate.

The pictures you see in the post 65Stigray linked to show how to connect when you use "2-channel measurement". This can be used with Arta, REW and Speaker Workshop.
But it isnt easy to adjust the input pots on the M-Audio, they arent made for fine adjustments!

Another very important thing is that you MUST remove all unused cables and plugs from the 1/4" line in sockets when you use the mic.

[kendomusic]

My experience is that you should use an amp even when you measure impedance. Its pretty tricky to get good results without, and you will never know for sure if they are acurate.

The pictures you see in the post 65Stigray linked to show how to connect when you use "2-channel measurement". This can be used with Arta, REW and Speaker Workshop.
But it isnt easy to adjust the input pots on the M-Audio, they arent made for fine adjustments!

Another very important thing is that you MUST remove all unused cables and plugs from the 1/4" line in sockets when you use the mic.

Norcad,
For the purpose of measuring speakers, I understand that I only need a single channel(left). I assume then that the link 69Stingray provided is not the one I should use as a guide.
There is a slight difference when comparing the pictures provided by 69Stingray and how I calibrate it with Arta. In his picture he connects the 1/4" Phono 1/L port to Chan2 XLR port. In Arta, it sees the Chan1 XLR port as the left channel. Does this make any difference?
Is it also a valid calibration if I just plugged in the 1/4" phono 1/L port to the 1/4" Ch1 inst/line port in the front of the unit? Then use the Chan 1 XLR port to connect the mic for measurement.
I am finding out understanding and setting up a measurement rig is an adventure itself.

[norcad]

If you just want to measure the in room response of the speaker, the one channel measurement are just fine. Try the PNPink noise, it makes the measurement a little easier in the low frequences.

It doesnt matter if you use left out/right in or Right out/left in, just change the Arta setting to make it right.

You can do calibration from 1/4" out to 1/4" in, its no problem.
You really dont have to do any calibration at all, the mobile pre is very good from 20-20000hz, many times more acurate than your mic!