EQ-ing mic comparison

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Charles Jenkinson
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EQ-ing mic comparison

#1 Post by Charles Jenkinson »

Just thought I'd compare a few different microphone options for EQ-ing my new W8's. The graph shows 3 different mic's on a comparative basis, not an absolute measurement - it was done in a garage with boundaries around.

They were made using a Frequency plotter iPad app, and I took the results off the curve and put them in a spreadsheet and normalised to 1kHz. The sound file was pink noise from a YouTube video, played via my phone headphone jack. The frequency points are 1/3 octave from 100Hz up to 16kHz.

What's bothering me is the dbx rta-m mic results, which I use to auto-eq the PA. Both the iPad and the BM800 curves are closer to one another and the rta-m swings either side of them; underneath and then at 10kHz and 12.5kHz it is above!

After a comment about my PA sounding a bit bright at my annual outdoor gig (which is coming up next Saturday) I think I need a bit more of an objective view on Eq-ing. Looking at these results, it could be the rta-m mic isn't trustworthy in the upper frequencies. I'm trying to obtain a quote for getting it calibrated, but it's probably not a cost effective option and I haven't read of an option to use a cal file with the dbx PA+ anyway - I'd still have to manually compensate for it.

I've seen the Dayton audio imm-6, but ideally I need a solution that plugs into the dbx PA+ for doing auto-eq. It's a bit awkward getting half way there with the dbx setup and then having another go with extra equipment.

Anyone got any other ideas?
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Bill Fitzmaurice
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Re: EQ-ing mic comparison

#2 Post by Bill Fitzmaurice »

I'm not familiar with the DBX PA+, but if it has the ability to do a house curve that should fix the problem.

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Re: EQ-ing mic comparison

#3 Post by Bruce Weldy »

Bill Fitzmaurice wrote:I'm not familiar with the DBX PA+, but if it has the ability to do a house curve that should fix the problem.
I use the "band" curve. A little bump around 60, a cut in the lo-mids from 125-250 or so, then a gentle roll-off at the top end if I remember correctly. But, after running, I always tweak it by ear.

And I use the dbx mic.

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Re: EQ-ing mic comparison

#4 Post by Svartrose »

As far as I know the driverack can only be used with a dbx mic because it has a built in 'calibration file' (which cannot be changed). So if you use other mics that have another curve, the end result won't be flat.
Calibrating a mic won't help you if you use a driverack. It will when you use software like Smaart.
If the combination driverack/dbx mic is really flat and you can route the mic-input to an output you can use that combo with Smaart to generate a calibration file for other mics with Smaart. (but I'm afraid you can't route it that way...)

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Re: EQ-ing mic comparison

#5 Post by djamps »

Could be differing pickup patterns of the mics reacting to the room modes.

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Re: EQ-ing mic comparison

#6 Post by Bill Fitzmaurice »

Measurement mics are omni-directional.

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Re: EQ-ing mic comparison

#7 Post by Charles Jenkinson »

Svartrose wrote:As far as I know the driverack can only be used with a dbx mic because it has a built in 'calibration file' (which cannot be changed). So if you use other mics that have another curve, the end result won't be flat.
Calibrating a mic won't help you if you use a driverack. It will when you use software like Smaart.
If the combination driverack/dbx mic is really flat and you can route the mic-input to an output you can use that combo with Smaart to generate a calibration file for other mics with Smaart. (but I'm afraid you can't route it that way...)
Thank you, that's an interesting perspective. If you've got any information that substantiates the idea that the rta-m and dbx drive rack products are matched, I'd be interested in seeing it.

It's not a view I've seen elsewhere. Harman say the rta-m is "flat frequency response" quoting +/-3db from 20Hz to 20kHz, but AV Leader who make the mics quote much wider tolerance ranges above and below 1kHz. Harman's marketing words imply that they believe it is 'flat' and therefore why would they correct the standard mic with a calibration file and sneak it in the box, so to speak. The only matching to me seems to be marketing hype and an odd phantom voltage coming from the front of the driverack units.
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Re: EQ-ing mic comparison

#8 Post by Bruce Weldy »

Charles Jenkinson wrote: why would they correct the standard mic with a calibration file and sneak it in the box, so to speak. .
The frequency chart is not a calibration file, it's proof that the mic is flat.

Is a $100 mic going to be dead flat? Probably not, but it can be real close. Not sure what the point is though.....it is certainly good enough to EQ a room and get it close to the curve you have selected, then it's up to you to use your ears and get it right.

That said....are you sure that you are using the same curve each time that you've used the auto EQ? There a are options that you pick from when starting the Auto EQ function. There's flat, band, speech, DJ? Seems like my Driveracks have 4 different curves.

Also, don't use the Wizards...just the Auto EQ. And make sure that the feedback eliminator is turned off.

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Re: EQ-ing mic comparison

#9 Post by Charles Jenkinson »

Bruce Weldy wrote:
Charles Jenkinson wrote: why would they correct the standard mic with a calibration file and sneak it in the box, so to speak. .
The frequency chart is not a calibration file, it's proof that the mic is flat.

Is a $100 mic going to be dead flat? Probably not, but it can be real close. Not sure what the point is though.....it is certainly good enough to EQ a room and get it close to the curve you have selected, then it's up to you to use your ears and get it right.

That said....are you sure that you are using the same curve each time that you've used the auto EQ? There a are options that you pick from when starting the Auto EQ function. There's flat, band, speech, DJ? Seems like my Driveracks have 4 different curves.

Also, don't use the Wizards...just the Auto EQ. And make sure that the feedback eliminator is turned off.
Thanks Bruce.  I tend to use the DJ auto-eq preset mostly, and even then we tweak the wider-band bass and treble knobs on the mixing desk for overall shape.

I have to admit to a bit of trepidation with trusting my ears, even if it is the right solution - it's the inner need to have objective substantiation for what is a subjective experience.

I've also written on the yahoo micbuilders group to get some other angles on this, and the main ideas coming out of it were:
- the mic isn't necessarily the issue, though whilst it may not be flat, there are certainly issues with using auto-eq at both low and high frequencies, due to physics; i..e. comb filtering, notches, and reflections are the main culprits.
- beg, borrow or steal a known mic to try the rta-m against.
- use known mic with REW on a laptop to sample different positions and take an average (this functionality is available in REW) for post auto-eq tweaks - No-one explicitly said this but it's what came to me. The minidsp UMIK-1 seems to be a decent solution and has a unique downloadable cal file that loads into REW.
- compile some test tunes and get to know them - I've never really done this - there appears to be some very well recorded stuff out there with great diversity of detail for listening tests of loudspeaker systems. I'd probably have to have a go with Audacity as well to see what I'm hearing and try to train my ears / brain.

A calibration of the rta-m would be a nice-to-have - I've not dug anything up that is cost effective yet in the UK on that, but it is probably not essential if one was to build on the solutions above. There's probably no wrong way of doing this, but just to start and have a go.
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Re: EQ-ing mic comparison

#10 Post by Bill Fitzmaurice »

Charles Jenkinson wrote: After a comment about my PA sounding a bit bright at my annual outdoor gig
Just because someone thought it was a bit bright doesn't make it so. Bright compared to what? Plastic boxes on sticks? In the immortal words of Ricky Nelson, ' ya can't please everyone, so ya got to please yourself.

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Re: EQ-ing mic comparison

#11 Post by Bruce Weldy »

Charles Jenkinson wrote: - compile some test tunes and get to know them - I've never really done this -
This is an absolute must.

A lot of people use Steely Dan tracks (I used to). Now, I use a track called Texas by Chris Rea (He's an Englishman). Starts with low end, adds kick and then vocals.....gives me everything I need to quickly tell if there are issue in the room and where.

When someone tells me something is off, I will definitely have a listen....but, ultimately I have to make the decision as to what it's going to sound like. But, sometimes they hear something I missed....if so, I fix it. No egos involved - just the desire to make it right.

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Re: EQ-ing mic comparison

#12 Post by Charles Jenkinson »

Bill Fitzmaurice wrote:
Charles Jenkinson wrote: After a comment about my PA sounding a bit bright at my annual outdoor gig
Just because someone thought it was a bit bright doesn't make it so. Bright compared to what? Plastic boxes on sticks? In the immortal words of Ricky Nelson, ' ya can't please everyone, so ya got to please yourself.
I don't know the full answer to this, because of the subjectivity involved. But I do know that one of the references for experience is one of the legacy d&b systems - we played (as musicians) on one of these systems a few months back - we weren't the sound guys - the top end sounded like it lacked definition to me. It was a 3 box high stack with 3 horizontally adjacent tops on top, each side: large subs on bottom, then some sort of square shaped sub box in the middle and then tops (...square boxes - series C?). The 3 tops on each side (and I'm told this is the d&b setup advice) were splayed - one inwards by about 30 degrees, one straight out and the other outwards by 30 degrees. And then there was some plastic boxes on sticks just at the inside edge of the stacks, pointing in for what I assume was centre fill - while they were on sticks, the cab was still lower than the top of the 3 high stacks they were next to - it certainly looked impressive. But, there was no sweetness in the HF, for my liking. If it doesn't sound like the real instruments or voices, something is wrong, even if there are EQ tweaks to get it all sitting together nicely.

As to the distance between the stacks either side of stage they were 12metres apart - I paced it out. The bass was better on this occasion than a previous one - probably due to more setup (EQ) time, but previously, I've heard an horrendous resonance / room mode with a canned track that was playing before the event got started.

I will take a picture next time, if I get asked back.

Venue size is about 600-800.

...I'd have set my tops up vertically and centre-clustered the subs.
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Re: EQ-ing mic comparison

#13 Post by Charles Jenkinson »

Bruce Weldy wrote:
Charles Jenkinson wrote: - compile some test tunes and get to know them - I've never really done this -
This is an absolute must.

A lot of people use Steely Dan tracks (I used to). Now, I use a track called Texas by Chris Rea (He's an Englishman). Starts with low end, adds kick and then vocals.....gives me everything I need to quickly tell if there are issue in the room and where.

When someone tells me something is off, I will definitely have a listen....but, ultimately I have to make the decision as to what it's going to sound like. But, sometimes they hear something I missed....if so, I fix it. No egos involved - just the desire to make it right.
Ego is half the battle - hence the need for objectivity. I've ordered a UMIK-1 so maybe that will help in the long run. I've listened to some of the tracks on the following test track article - some very interesting stuff. https://www.soundandvision.com/content/ ... audio-tool
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Re: EQ-ing mic comparison

#14 Post by Bruce Weldy »

Charles Jenkinson wrote: I've listened to some of the tracks on the following test track article - some very interesting stuff. https://www.soundandvision.com/content/ ... audio-tool
The most important part of that whole article is the first two paragraphs. What auto EQ can do for you is help locate the real problem areas in a room...something that might take you a long time to do. But it listens to frequencies, not the content of what you are playing. Don't rely on it to be the final say on what you hear.

Sometime you should try the Band curve instead of the DJ......I feel that it's much more musical sounding.

Another issue is the source material that you are playing through the system. I can put my tracks though the system that I run for a local band and they sound great, but sometimes we use the bass player's (he also a DJ) tracks from his PC for break music - it sounds absolutely awful. I don't know if he has some EQ inserted in his DJ program or whether he's just downloading crap to start with.....but, it really stinks.

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Re: EQ-ing mic comparison

#15 Post by Monomer »

How are you setting up the mic?


If you're pointing the capsule at the speakers, you might be getting skewed high-end results. Every time I see anyone bust out a smaart rig, the mic is on a stand pointed up and at ear level.
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