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[Chris Grimshaw]

Hi all,

I'd been meaning to do something like this for a while, and someone asking questions on another forum prompted me to actually get on and do it.

It's a short video on how to use REW to measure your microphones. First one of these I've done, so any feedback or suggestions would be welcome.

So, here it is: https://www.youtube.com/watch?v=uD9HBQ6lSEo&lc

Cheers, all

Chris

[Art Welter]

First one of these I've done, so any feedback or suggestions would be welcome.

Chris,

Nice work, interesting to hear a voice rather than reading!

Worth mentioning that other than omni microphones, most of the mics we use for sound reinforcement have a great deal of proximity effect, so their frequency response is tied very specifically to the measurement distance to the source.
If one wants to check the response at a later date, (to verify that Mr. Mic drop didn't mess your mic up) the measurement distance to the source, and the source placement in the room must be the same as the previous measurement to be useful.

The angle to the source must also be identical, as the source frequency response will vary considerably off axis, your choice of a 2" "full range" driver was good in that regard, but a typical two way monitor would require a very specific alignment and distance to avoid rather large response deviations.

At the short distances required to avoid room reflections, the reflections from the mic face to the speaker also come into play, a large diaphragm omni and a little lav omni could have the same response at 12", but at 2" the large mic size could cause comb-filtering ripples to show up.

Fun stuff.

Art

[John L Nobile]

Very nice video Chris. Informative and kept my interest. A rare combination. Looking forward to more.

[Chris Grimshaw]

Well, here's another one.

https://youtu.be/Pz5aoRrRU5c

Dynamic mics have been interesting to me, because:

- They're very simple devices
- You can apply passive filters to them

In this video, I took an EV RE320 which I didn't like the sound of, and simulated a notch filter to sort out the large 5kHz peak. The result is much more listenable.


Thanks for the feedback so far. Art, I think I'll discuss the things you've mentioned in another video. Right now I don't have much of a plan for these videos - it's just that if I work on something and find the results cool/interesting/whatever, I'll put something together and share them.

Cheers,

Chris

[Yoel Klein]

Well, here's another one.

https://youtu.be/Pz5aoRrRU5c

Dynamic mics have been interesting to me, because:

- They're very simple devices
- You can apply passive filters to them

In this video, I took an EV RE320 which I didn't like the sound of, and simulated a notch filter to sort out the large 5kHz peak. The result is much more listenable.


Thanks for the feedback so far. Art, I think I'll discuss the things you've mentioned in another video. Right now I don't have much of a plan for these videos - it's just that if I work on something and find the results cool/interesting/whatever, I'll put something together and share them.

Cheers,

Chris

Thank you so much. very informational.

[Art Welter]

In this video, I took an EV RE320 which I didn't like the sound of, and simulated a notch filter to sort out the large 5kHz peak. The result is much more listenable.

Chris,

Good work!

After watching your video, and another comparing an RE320 to a Heil mic, seemed that the RE320 has a lot more proximity effect (bass increase at near distance) than I recalled from the RE27, my favorite mic. When I went to compare my RE27 proximity effect to a standard cardioid mic, was horrified to find it's bass response is almost completely gone.

Oh well, better to find out something has died when you test rather than when you need it to work...

I've attached the wiring diagram for the RE27, as an example of response changes with simple passive filters.

Did your notch filter replace all the stock passive filter components, the coil, capacitor & resistor (s) or just the resistor?

Art

[Chris Grimshaw]

Hi Art,

Sorry to hear about your RE27. Missing bass is something that affects a lot of dynamic mics - I have a lot of D12s through here with the same problem. You've taught me a lot over the years, so if you'd like me to take a look for you, it'll only cost the postage.


The RE320 has about 20 components, mostly SMDs, on an internal PCB. I traced most of the schematic, but some of the PCB traces disappear underneath a blob of glue so it ended up difficult to finish off. There's quite a lot of filtering in there, though, which made me wonder why the engineers at EV hadn't come up with something considerably, er, better.

There's a video here which illustrates what I mean: https://www.youtube.com/watch?v=5ruNTeSaNKU

RE20 at 3.56, and RE320 at 5.05.

The RE20 sounds pretty natural to me, while the RE320 clearly has a lumpy rise in the upper midrange and treble.


The literature on the RE320 is mixed, with regards to proximity effect: the datasheet talks about the Variable D technology and how it eliminates proximity effect, and then the frequency response curves clearly show a close-up LF boost of about 12dB. When you consider that the diaphragm starts at the bottom of the head of the mic, that's a lot of proximity effect!


Chris

[Art Welter]

Hi Art,

Sorry to hear about your RE27. Missing bass is something that affects a lot of dynamic mics - I have a lot of D12s through here with the same problem. You've taught me a lot over the years, so if you'd like me to take a look for you, it'll only cost the postage.

The RE320 has about 20 components, mostly SMDs, on an internal PCB.
There's quite a lot of filtering in there, though, which made me wonder why the engineers at EV hadn't come up with something considerably, er, better.
Chris

Chris,

Thanks for the offer to look at the RE27!
Since it has been about 20 years since the element was replaced, thought rotted foam might have migrated into the diaphragm, seizing it up.
The front foam does need to be replaced, though it did not go through the fabric mesh.
There were two very small pieces of  semi rotted foam in the two side ports, it is possible some of it made it’s way into the gap. Tried vacuuming and blowing it out, but no joy.

What has caused the missing bass with the dynamic mics you have looked at before?

In the video Rick Bell mentions the RE320 uses the RE27 element with a different diaphragm. My guess is they used some other stock diaphragm that would give the RE320 a tighter pattern, which then required more passive filtering to flatten out. The tighter pattern also appears to have gained proximity effect- “Semi-Variable D” ;^).

Of historical interest, it appears my late 1980s RE27 does not have several filter components shown on the spec sheet diagram. Some NDym mic diaphragms required redesigns to fix some LF damping problems, the redesigned, “tighter” diaphragms then probably had other other problems needing filters to fix.

Art

[Chris Grimshaw]

No problem, Art.

Well, with the D12s and things I've had, it's been a case of stripping the capsule right down the diaphragm, cleaning and (where possible) re-aligning the diaphragm during reassembly. Can't say much more than that without revealing trade secrets, but if you'd like to shoot me a PM I'd be happy to discuss.

I actually have a lightly-used RE27 on the way, and I'd be happy to share some pictures of the filtering in there. Price was too good to pass up. First things first, though, will be some heavy-duty disinfectant.


To everyone following this thread, I have a few ideas for more videos:
- Mic "bleed" - which mics do well, and why
- DIY Subkicks
- Directionality of cone loudspeakers, particular attention to guitar amps
- Bose MusicMonitor speaker measurements and teardown
- JBL 104 speaker measurements, teardown, mods

I've also been thinking about doing a Live Sound 101 sort of course. Starting with the really basic stuff (identifying cables etc), and then going from a 1980s mixer-amp, through to notepad mixers, medium-sized analogue desks, and then making the jump to digital. I'd also do some parts on mics, speakers etc.
One of the motivations for that is that I have a relative who's active at churches etc, and is often asked to look after the sound without any training at all, but I think it'd be a nice thing to do anyway.

Chris

[Art Welter]

I actually have a lightly-used RE27 on the way, and I'd be happy to share some pictures of the filtering in there. Price was too good to pass up. First things first, though, will be some heavy-duty disinfectant.

Hope your lightly-used RE27 works well!
PM sent to your www contact.

Art

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