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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Audio Measurement and Testing => Topic started by: Russell Ault on January 10, 2018, 05:26:07 am

Title: Inexpensive Microphone for Wireless Measurements
Post by: Russell Ault on January 10, 2018, 05:26:07 am
I don't tend to do the sorts system measurements where owning an M30 (or its ilk) would make for a good return on its investment. I have Smaart 8, an Octa-Capture, and three Behringer ECM8000s (no, they don't have a ruler-flat response, but for quick-and-dirty system tuning and aligning, they get the job done). That being said, having to drag a mic cable around a venue sucks regardless of how much your measurement microphone costs, so I wanted to explore the option of making wireless measurements.

The RF platform (for my market range) was pretty easy to settle on: the Line 6 XD-V75. This was an especially easy choice because, in my area (and in most of Canada), one can rent a single channel's worth of XD-V75 for a weekend for less than $20 (Canadian!), and I'd use it infrequently enough that renting would definitely be the way to go. So far, so unimaginative.

Then came the question of a transducer. Given that I already owned three measurement mics, the obvious choice would have been to pick up a battery-powered phantom power supply and an XLR-TA4 adapter and call it a day. But I noticed that the published frequency response for the skimpy-looking omni-directional headset mic that comes with the Line 6 wireless system was 20Hz-20kHz, so I rented a system with the headset mic and compared it to one of my existing mics.

I clipped the headset and one of my ECM8000s into the same mic clip in front of a speaker, set up a transfer function between the two, set the delay manually to the latency induced by the digital wireless (which I had measured earlier with an adapter cable), and then slid the headset back and forth relative to the wired mic until the phase trace flattened out.

I discovered two things in doing this: 1) the microphone (or at least the one I got) was wired to produce pin 3 hot on the receiver, necessitating a polarity flip on the Octa-Capture; 2) even under the relatively slap-dashed, non-laboratory conditions of my basement it was clear that this mic would do no worse a job at basic measurements than any of my ECM8000s, with only minor deviations between the two microphones (and that's despite the fact that the headset was a rental, having spent its entire working life being used by the kind of people who rent from a place that will give you a channel of Line 6 wireless for less than $55CAD per month).

So I've decided that my next measurement-related purchase is going to be a Line 6 HS70 omni-directional headset mic. I may even make a correction curve for it (I have a couple offers from local people to borrow their better measurement mic so I can make correction curves for my mics anyway). The hilarious part: not only is it (obviously) cheaper than getting a "proper" bias-voltage-powered measurement mic like the iSEMic, it's also cheaper than getting a decent battery-powered phantom power supply, and it means I can still use all three of my existing mics for wired measurements.

TL;DR: in my (admittedly limited) testing, the Line 6 HS70 is nearly as good a measurement mic as the ECM8000 and is cheaper than getting a decent battery-powered phantom power supply.

-Russ
Title: Re: Inexpensive Microphone for Wireless Measurements
Post by: brian maddox on January 10, 2018, 03:23:24 pm
I don't tend to do the sorts system measurements where owning an M30 (or its ilk) would make for a good return on its investment. I have Smaart 8, an Octa-Capture, and three Behringer ECM8000s (no, they don't have a ruler-flat response, but for quick-and-dirty system tuning and aligning, they get the job done). That being said, having to drag a mic cable around a venue sucks regardless of how much your measurement microphone costs, so I wanted to explore the option of making wireless measurements.

The RF platform (for my market range) was pretty easy to settle on: the Line 6 XD-V75. This was an especially easy choice because, in my area (and in most of Canada), one can rent a single channel's worth of XD-V75 for a weekend for less than $20 (Canadian!), and I'd use it infrequently enough that renting would definitely be the way to go. So far, so unimaginative.

Then came the question of a transducer. Given that I already owned three measurement mics, the obvious choice would have been to pick up a battery-powered phantom power supply and an XLR-TA4 adapter and call it a day. But I noticed that the published frequency response for the skimpy-looking omni-directional headset mic that comes with the Line 6 wireless system was 20Hz-20kHz, so I rented a system with the headset mic and compared it to one of my existing mics.

I clipped the headset and one of my ECM8000s into the same mic clip in front of a speaker, set up a transfer function between the two, set the delay manually to the latency induced by the digital wireless (which I had measured earlier with an adapter cable), and then slid the headset back and forth relative to the wired mic until the phase trace flattened out.

I discovered two things in doing this: 1) the microphone (or at least the one I got) was wired to produce pin 3 hot on the receiver, necessitating a polarity flip on the Octa-Capture; 2) even under the relatively slap-dashed, non-laboratory conditions of my basement it was clear that this mic would do no worse a job at basic measurements than any of my ECM8000s, with only minor deviations between the two microphones (and that's despite the fact that the headset was a rental, having spent its entire working life being used by the kind of people who rent from a place that will give you a channel of Line 6 wireless for less than $55CAD per month).

So I've decided that my next measurement-related purchase is going to be a Line 6 HS70 omni-directional headset mic. I may even make a correction curve for it (I have a couple offers from local people to borrow their better measurement mic so I can make correction curves for my mics anyway). The hilarious part: not only is it (obviously) cheaper than getting a "proper" bias-voltage-powered measurement mic like the iSEMic, it's also cheaper than getting a decent battery-powered phantom power supply, and it means I can still use all three of my existing mics for wired measurements.

TL;DR: in my (admittedly limited) testing, the Line 6 HS70 is nearly as good a measurement mic as the ECM8000 and is cheaper than getting a decent battery-powered phantom power supply.

-Russ

I like stories of WIN.  Nice!
Title: Re: Inexpensive Microphone for Wireless Measurements
Post by: Lyle Williams on January 10, 2018, 05:18:05 pm
I wanted to go with an omni lav with my XD-V55 that I am setting up.

In the end I got discouraged by not being able to find published flat response curves.  Either the curves went up at the high end, or they weren't published where I could find them.

Glad to hear that you are happy with the headset.  I might try and track one down.
Title: Re: Inexpensive Microphone for Wireless Measurements
Post by: Russell Ault on January 10, 2018, 10:44:33 pm
In the end I got discouraged by not being able to find published flat response curves.  Either the curves went up at the high end, or they weren't published where I could find them.

The curves I was able to find for Line 6 mics (not from an official website, unfortunately) are here (http://warehousesound.com/r/line6HS-LM.pdf). You'll notice a wide-band 3-4dB peak around 12kHz. I'm not worried about this because I don't think it will have a meaningful impact on what I'm looking for in my measurements, and because it should be easy to flatten out with a correction curve, and because it's well within the lines of this (in)famous graph of ECM8000 frequency responses (https://www.gearslutz.com/board/attachments/studio-building-acoustics/319840d1354639026-ecm-8000-a-cross-spectrum-ecm8000_frequency_response_large.jpg).

(Or, I could be smart-ass and say that the HS70 is a diffuse-field omni.)

-Russ
Title: Re: Inexpensive Microphone for Wireless Measurements
Post by: Mark Wilkinson on January 14, 2018, 08:04:18 pm

Thanks for your post Russ, sounds like something i might want to try...