RTA mic placement - floor or mic stand?

EQ guys are using on their cabs/systems. A good starting place if you don't have your own RTA.
Post Reply
Message
Author
User avatar
Charles Jenkinson
Posts: 1125
Joined: Sat Aug 06, 2011 3:25 pm
Location: Manchester, UK

RTA mic placement - floor or mic stand?

#1 Post by Charles Jenkinson »

The DBX forum and now official advice is to place the RTA mic on the floor on a towel, and not on a mic stand. They also imply it may be done at a shorter distance away from the speakers than the 25ft recommendation for when performed on the stand. It seems the approach is to emulate the Pressure Zoom Mic (PZM) operating characteristic which cuts out half off all potential reflections (and therefore cancellations) by being oriented close to a plate - the floor being the plate in this case.

Has anyone had any better RTA results using the floor approach over the mic stand? I'm thinking it has to be better, as a general average RTA for a room rather a specific 'spot RTA' for where the mic May be on a stand.
2xJ12L (3012HO) switchable/melded
2xT30

Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.

Grant Bunter
Posts: 6915
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: RTA mic placement - floor or mic stand?

#2 Post by Grant Bunter »

I don't know Charles, but if the floor vibrates in any way, the results will be skewed, because a towel won't stop it. Ask anyone who mikes a kick drum!

At least with a mike stand the mike can be almost on the ground and having the benefit of rubber feet to isolate it...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

User avatar
Charles Jenkinson
Posts: 1125
Joined: Sat Aug 06, 2011 3:25 pm
Location: Manchester, UK

Re: RTA mic placement - floor or mic stand?

#3 Post by Charles Jenkinson »

That's an interesting thought Grant. I hadn't considered resonant frequencies and amplitudes of the Mic support structure. I would be interested to know what the average floor and mic stand responses are to the typical excitation from music. It would perhaps be possible to make a low tuned mount, between 10-15Hz, to isolate the Mic, but these naturally have some slop/displacement if anything knocks the mic. It might need to be slightly up off the floor and have the plate/floor integrated with the mic to prevent relative movement, i.e. banging the mic on the floor if knocked. Sounds like the threads of a golden marketing opportunity, even if to sell ice to the eskimos.

Edit: I.e. use a shock mount for miking drum kicks?, but the mass of the Mic used and stiffness of the mount need to be appropriate to stay 40% or more away from the resonant frequency which is driving the problem, I.e. main kick resonance. Soft mount good. Stiff mount bad.
2xJ12L (3012HO) switchable/melded
2xT30

Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.

User avatar
dswpro
Posts: 314
Joined: Sun Oct 30, 2011 3:17 pm

Re: RTA mic placement - floor or mic stand?

#4 Post by dswpro »

Not sure about the floor placement myself, but I've heard of this technique before.
Only problem I have with the technique is that nobody is listening from the floor.
Reflections are part of the real listening experience. Yes they can color the sound.
I prefer to put the mic in a real listening position, actually multiple positions.

Bruce Weldy
Posts: 8301
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: RTA mic placement - floor or mic stand?

#5 Post by Bruce Weldy »

If you are measuring speakers, then use the appropriate locations.

If you are tuning a room where humans will be listening, then put the reference mic where human ears are. Unless, of course, you want to tell everybody how good it sounds with their ear to the floor.

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

User avatar
Bill Fitzmaurice
Site Admin
Posts: 28620
Joined: Tue May 02, 2006 5:59 pm

Re: RTA mic placement - floor or mic stand?

#6 Post by Bill Fitzmaurice »

Bruce Weldy wrote:If you are measuring speakers, then use the appropriate locations.If you are tuning a room where humans will be listening, then put the reference mic where human ears are. Unless, of course, you want to tell everybody how good it sounds with their ear to the floor.
+1. The only time you'd ever want the mic at floor level is when taking a ground plane measurement.

User avatar
Charles Jenkinson
Posts: 1125
Joined: Sat Aug 06, 2011 3:25 pm
Location: Manchester, UK

Re: RTA mic placement - floor or mic stand?

#7 Post by Charles Jenkinson »

Ok. I only have a gut feel about this, not a theoretical-proof-type of understanding or belief, but a general search of 'RTA mic on floor or stand' seems to confirm that floor is on average better than stand, because: you cannot EQ a room, rather, you can only optimise in an 'average sense' the frequency response of the PA in the room. Placing the mic on a stand in a 'one spot' position, in full space, includes bounce (and therefore comb filtering) from the floor reflections - yes, people talk about taking averages in multiple positions, but what sort of average do they take - a mathematically tabulated average, a rack of the eye guess looking at on screen RTA results, or golden ears tweaking (...meanwhile pink noise has been going off for half an hour in the venue!). Striking out comb filtering effects from the half space reflections intuitively seems a bit more of a closer averaging process, for a 'one hit' RTA process. Here is the original DBX forum article that I read and also which CBIERN referred halfway down the Forum EQ-threads page - I was a little surprised no one commented on it back then. The author implies walk around mic-stand type averaging had been done and the singular floor mic result gave a favourable outcome over the mic stand.

http://billfitzmaurice.info/forum/viewt ... 17&t=20324

And here is another thread, from a search using the term 'RTA mic on floor or stand'.

http://www.reddit.com/r/livesound/comme ... st_floors/

And here's a reasonable theory on boundary or PZM mic's:

http://cdn.shopify.com/s/files/1/0247/3 ... 0.pdf?1690

I appreciate that I am proposing this as 'intuitively better', based on others saying it 'is' better - I personally have no proof. Neither am I going to take the time to design an experiment or method to prove it. What I want to gauge is if there is anyone else in this community that it resonates with? I'm just trying to get a feel for which is the better approach for one hit auto-eq'ing, for best average response in a room.
2xJ12L (3012HO) switchable/melded
2xT30

Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.

User avatar
Bill Fitzmaurice
Site Admin
Posts: 28620
Joined: Tue May 02, 2006 5:59 pm

Re: RTA mic placement - floor or mic stand?

#8 Post by Bill Fitzmaurice »

Charles Jenkinson wrote:And here is another thread, from a search using the term 'RTA mic on floor or stand'.
http://www.reddit.com/r/livesound/comme ... st_floors/
There are some very flawed notions there. Foremost is the idea of removing boundary interactions from the measurement. That is something one wants to do if you're trying to take a frequency response measurement of your speaker, and must do so indoors. There are better ways, one being a nearfield gated measurement. But that's not what you want to do in a venue, where the entire purpose of taking the RTA is for the mic to hear what the audience hears, and that includes boundary reflections.

Bruce Weldy
Posts: 8301
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: RTA mic placement - floor or mic stand?

#9 Post by Bruce Weldy »

Charles Jenkinson wrote: you cannot EQ a room, rather, you can only optimise in an 'average sense' the frequency response of the PA in the room.
That's just nonsense. When we use the term "EQ a room" the rest of his sentence is exactly what we are talking about.

What if we said, "you cannot eat a bisquit, rather, you can only optimize it's size in an average sense in order for it to reach your gut". That's what most of us would call eating.

The author implies walk around mic-stand type averaging had been done and the singular floor mic result gave a favourable outcome over the mic stand.
Time for some common sense......when you adjust the volume of your TV, do you put your head right against the speaker, only to find when you get to your chair that it's not loud enough? Or, do you have your wife keep turning it up while you are in the garage until it sounds just right, but when you go back to your chair, it's too loud?

You adjust sound based on the listening position of the environment you are in...period. Not the floor, not the wall, not some mathematical equation.....make it sound good to your ears in the most places possible in the room. And that is best achieved in a short amount of time by placing the RTA mic at ear level somewhere near the middle of the room.

Now, if you just really dig playing with this and trying to prove it one way or the other - then heck, do it and have a ball. But reality is getting the room RTAed quickly, then put on some music and walk the room fine-tuning it with your ears.

Of course, if you expect that the party will be so wild that the majority of the guests end up with an ear next to the floor, then maybe a little RTA of that position would be prudent - but then you have to ask......which ear? The one closest to the floor? Or the other one? :mrgreen:

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

User avatar
Charles Jenkinson
Posts: 1125
Joined: Sat Aug 06, 2011 3:25 pm
Location: Manchester, UK

Re: RTA mic placement - floor or mic stand?

#10 Post by Charles Jenkinson »

Thanks for that Bill, Bruce. The subject had been troubling me.
2xJ12L (3012HO) switchable/melded
2xT30

Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.

Bruce Weldy
Posts: 8301
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: RTA mic placement - floor or mic stand?

#11 Post by Bruce Weldy »

Charles Jenkinson wrote:The subject had been troubling me.

Time for an intervention.....nothing that beer, cigars, and the Good Book can't fix - to get your perspective back in line. :mrgreen:

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

User avatar
Charles Jenkinson
Posts: 1125
Joined: Sat Aug 06, 2011 3:25 pm
Location: Manchester, UK

Re: RTA mic placement - floor or mic stand?

#12 Post by Charles Jenkinson »

I don't know Bruce. I haven't got much fight left, ...I enjoyed Bill's quick and clean kill, but now you're suggesting i should take up smoking and finish reading the Sound Reinforcement Handbook.

En garde!
2xJ12L (3012HO) switchable/melded
2xT30

Words&graphics - Audio&Acoustics - Hardware&DSP; 3 different paradigms.

Bruce Weldy
Posts: 8301
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: RTA mic placement - floor or mic stand?

#13 Post by Bruce Weldy »

Charles Jenkinson wrote:I don't know Bruce. I haven't got much fight left, ...I enjoyed Bill's quick and clean kill, but now you're suggesting i should take up smoking and finish reading the Sound Reinforcement Handbook.

En garde!

:loler:

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

88h88
Posts: 1603
Joined: Mon Jul 04, 2011 10:20 am
Location: Coventry, UK

Re: RTA mic placement - floor or mic stand?

#14 Post by 88h88 »

I'd never heard of putting a mic on a boundary, I slap mine where ears are going to be, so in various spots around the dance floor. I've never got anything other than a particularly amazing clear as hell sound on any occasion.
4xOT12s, 2xT39s@22", TTLS@18", 2xT60@18"

User avatar
Bill Fitzmaurice
Site Admin
Posts: 28620
Joined: Tue May 02, 2006 5:59 pm

Re: RTA mic placement - floor or mic stand?

#15 Post by Bill Fitzmaurice »

88h88 wrote:I'd never heard of putting a mic on a boundary
There are legitimate reasons for doing so, but EQing the system to the room isn't one of them.

Post Reply