Measurement Microphone Preamp

[HiFiNutNut]

Hi,

I hope this piece of information will help some of you to decide what to buy / use, and at the same time, to see if anybody has more helpful information.

Following the feedback posts in the forum, I have bought the Behringer ECM8000 Mic and the Behringer MIC800 MIC preamp. Actually, nobody recommended the Behringer MIC800 but some recommended the Behringer UB802 mixer. I bought the MIC800 because it was cheap and appeared to do the exact job - loudspeaker measurement.

Upon reading the User Manual, I found the following in the MIC800:

Low Cut Control: To filter floor rumble and other low-frequency sounds, turn this control toward 15 Hz (minimum filtering) or, alternatively 360 Hz (maximum filter).

I was worried. It appears it employs a first order high pass network at 15 Hz, which can cause inaccuracy in measurement.

Then I was looking at the User Manuals of the UB802 and XENYX802 and hoping they didn't have the filter. I found:

In addition, the mono channels (UB1002 and UB1202) are equipped with a steep LO CUT filter (slope at 18dB/oct., -3 dB at 75Hz) designed to eliminate unwanted low-frequency signal components.

Oh, it is even worse!

I hope I don't have to go through the trouble of reverse engineering the circuit board and replace the filter cap with a much larger value!

Would you be happy with a 1st order high pass at 14Hz for your MIC preamp?

Regards,
Bill

[wigginjs]

Well, depends. For the purpose of trying to use gated measurements to produce a semi-anechoic response graph is definitely doesn't matter. For the purpose of calculating a DRC filter for your loudspeakers it probably doesn't matter (as you loudspeakers probably have no usable output below 30Hz or so). For the purpose of measuring the response of your sixteen 18" driver 10000 watt IB subwoofer and EQing it flat, yeah, you need a new preamp.

[MJL21193]

Originally posted by m0tion
For the purpose of measuring the response of your sixteen 18" driver 10000 watt IB subwoofer and EQing it flat, yeah, you need a new preamp.

[Dave Bullet]

Not sure why that is an issue. For low bass response, the room modes will swamp any effect of filtering within the pre-amp.

What slope is employed? If a 6dB HP then even at 15Hz - some attenuation will occur above that.

Reality is - for regular crossover design I would have thought not an issue for you.

Besides unless you get your ECM8000 calibrated, the rolloff on the mic will be probably as great as the rolloff on the pre-amp (ie. you might end up with a combined 12dB+ slope).

PS: I also have a ECM8000 but use an Event EMP-1 pre-amp. The Pre-amp is supposedly flat (+/0.5dB) from 1Hz (?) to 90KHz (when phantom power is used). The EMP-1 preamp has a HP "rumble filter" which you can switch on / off.

The other option would be to bypass?

David.

[HiFiNutNut]

A -3dB point at 15Hz for audio signal is of no issue. I am worried that it alters the phase of the measurement making proper XO design impossible.

It is for this reason, good amps always choose the DC filter below 1Hz and a LP well beyoond 20kHz. The more extended, the better.

[augerpro]

Quote: In addition, the mono channels (UB1002 and UB1202) are equipped with a steep LO CUT filter (slope at 18dB/oct., -3 dB at 75Hz) designed to eliminate unwanted low-frequency signal components.


That doesn't list the 802 as having that filter and I don't think mine has one. Those manuals are generic for the whole line you so you have to read carefully what is and isn't a feature.

[Brett]

Originally posted by m0tion
For the purpose of measuring the response of your sixteen 18" driver 10000 watt IB subwoofer and EQing it flat, yeah, you need a new preamp.

So can I use it for my 16 x 15" IB sub with 1100W/ch?




This is actually what I'm to build soonish.

[Brett]

PS: agree with augerpro about Behringer manuals. They can be misleading at times if you don't read them carefully and double check with the individual product spec sheet off the website.

[HiFiNutNut]

Thanks. The above extracts were from the individual user manuals. Both the UB802 and XENYX802 have the same description.

Should I be ditching the MIC800 and getting the UB802?

[MJL21193]

I built my own, based on Eric Wallins design:

http://mysite.verizon.net/tammie_eri...mp/preamp.html

I left out the waste of time clipping indicator.
This unit works flawlessly.