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One Last Dip at 150 Hz Mixers (Analog)
Old 3 weeks ago
  #1
Here for the gear
 
Rob Gordon's Avatar
 

Thread Starter
Posts contained private data about my room and were deleted again after there was no further feedback regarding the described space problem.

Rob
Old 3 weeks ago
  #2
Gear Guru
 
DanDan's Avatar
Floor

Interesting speaker. Your dip could well be a result of a floor reflection.
The UMIK-1 has a built in USB interface and it comes with a Cal File which makes the response read flat, and gives you a free SPL meter!
DD
Old 3 weeks ago
  #3
Gear Guru
 
DanDan's Avatar
Blocking

You are welcome. Try the mic on the floor at the suspected bounce point.
Unfortunately these dips can be a collaboration of reflections. REW is a great suite of tools to ferret out which is the biggest contributor.
The bandwidth of the dip is a factor, narrow ones are not necessarily audible.
Also remember we do not hear through the nose. The mic at ear positions might not see the same dip at all.

I haven't had the pleasure of using the Gennie system, but I am told it is good for LF. But no Eq system can fix a dip caused by a nulling reflection.
Your suggesting of substituting removal of everything else by 8-10 is cunning..... But everywhere in the room except a small area would see a spectrum boosted by 10dB at 150Hz. By all means try it though, most of us work in a very small sweet spot.

DD
Old 3 weeks ago
  #4
Gear Guru
 
DanDan's Avatar
Curious

You are welcome Rob. I am very curious about your experiences here. I would have assumed that a large anything there would have an effect.
I was going to suggest blocking next, but you obviously know what you are doing. Because you do, please keep us posted here. Try blocking with an absorbent side. I suspect medium to high density fibre batts might do better than light fibre.
GS here have claimed reductions in the floor bounce using thick carpet and underlay, presumably a big area though. I think that was dinococcus, you could ask him. I don't appear to have a significant floor issue, in my CR with thick carpet and underlay. Although many of us prefer no desk or just enough for keyboard and trackpad, the floor issue can be substantial.
In previous research on this someone pointed out that large mixing desks sometimes included a back panel all the way to the ground, to block.

DD
Old 3 weeks ago
  #5
Lives for gear
 
akebrake's Avatar
 

Quote:
Originally Posted by Rob Gordon View Post
...Walls and ceiling are completely covered with fiberglass / rockwool.
400 mm at ceiling + side walls and 650 mm at front and rear wall.

All hold together by a framework of wood and covered with fabric.
Wood lath attached to the front to bring back the energie in the room.

I use Genelec 8351 speakers. These go down to nearly 30 hz....
Would you mind describing the sidewalls? What kind of "fiberglass/ rockwool"?

Gas Flow Resistivity? Filled completely or airspace?

Just curious...
Old 2 weeks ago
  #6
Lives for gear
 
akebrake's Avatar
 

Quote:
Originally Posted by Rob Gordon View Post
Solved. It is not the floor.

It is the axial room mode across the width of the room. to be exact the 0-3-0 mode...
Hi Rob,

Are you saying you have a strong mode (0-3-0)?

That’s an interesting observation. Especially in a heavily treated room...

Have you measured that? If you place the mic at A, B and C, what would that look like? Eventually spkr moved closer to left wall.

Cheers

BTW Agree with DD re floor bounce. Seems to fit fairly well also.(Collaboration...)

Floor/Ceiling Reflection Calculator
Attached Thumbnails
One Last Dip at 150 Hz-mode-0-3-0-jpg.jpg   One Last Dip at 150 Hz-floor-bounce-.jpg  
Old 2 weeks ago
  #7
Gear Head
 

Quote:
Originally Posted by Rob Gordon View Post
Hello akebrake,

Of course I can do that. But if you are curious because you might have another explanation for the dip then please let me know.

Side walls are 350 mm of low density fiberglass (~5kpa) + 50 mm rockwool (~16 kpa) at the inside of the room

Ceiling is the same.

Front and rear wall are 600 mm of low density fiberglass (~5kpa) + 50 mm rockwool (~16 kpa) at the inside of the room.

No Air Gaps.


Rob
Hey,

Would you care to share a photo of your studio? I saw the diagram you made, but would love to see a photo of the inside.

Thanks,
Old 2 weeks ago
  #8
Gear Guru
 
DanDan's Avatar
ReBoot

Rob, you are getting some of the best help here. Akebrake is kinda Ninja at reading into REW .mdat files. But you, and we, are IMO being hampered by confusing and perhaps dubious information.
I recommend that you eliminate as much as possible between your Computer/REW, and the Speakers.
You have been doing what I call provocative testing, although without REW.
That software or not, just go a bit further with your logical provocations.
Your dip disappeared at floor level? But that could have been a Height thing. Did you move about on the floor. A H mode would not change, anywhere, but a floor bounce would diminish away from it's best bounce spot.
Try a Sine wave at that alleged mode. You should hear the peak resonance easily. Then you should be able to walk the modal patter. Peak, null, peak, null, etc.
This will tell which directions, L W H, and which mode. Or not a mode at all.
Moving the mic (or speakers) will identify a dominant non resonant reflection cancellation. They are a bastard. With you very sensible emulation of boggy's work, you should not be seeing such a null, other than the untreated floor.
But one way or another, we need to be 100% of the cause before trying to fix it, and as I said, you have an REW Ninja..... you will see.
DD
Old 2 weeks ago
  #9
Gear Guru
 
DanDan's Avatar
REW

REW, minimal chain. No SAM, no extra converters if possible, I am not sure if they would get read into the timing. Minimum.

Then measure, post the .mdat file. Let's see what we can see in it.
There may not be a single exact issue.
In many cases I find it best to use Pink Noise PN and the Analyser in REW.
Instant feedback. Thus I can sweep the mic around to prove any particular conclusion.
e.g. Moving towards the Back Wall makes things worse right?
But that is moving away from the Front Wall. It is possible to figure whether this is a FW or BW issue. etc. etc.
Do room modes even matter? - MusicPlayer Forums

No point in adding (or subtracting) things until we know the cause.
Also, no point in doing anything unless we are sure there is an actual problem.
As I said place the mic at actual ear positions, measure and let us evaluate it. Run L, R, L+R at both ear positions. i.e. 6 Measurements.

DD
Old 2 weeks ago
  #10
Gear Guru
 
DanDan's Avatar
AARRGH

Damn, I thought you could use the SAM Mic. The UMIK-1 is a very good investment, it has USB.
DD
Old 6 days ago
  #11
Gear Guru
 
DanDan's Avatar
Progress

REW has grown quite complex over the years. Best to just dive in and take any measurements that spring to mind. Saving and Naming still confuses me!
Try all the toys, RTA and Pink Noise......
I hope the Primer sticky at the top of this forum gets you going quickly and easily.

It is useful to have a full modal view of the room. Speaker on floor in corner, mic in the opposite ceiling corner. This will show all the modes.

Play around with the optimum spot. I would measure at each ear position, rather than the nose. L,R, L+R, for both ears.

You can post .mdat (REW) Files directly here, use the paperclip attachment thing.

DD
Old 5 days ago
  #12
Lives for gear
 
akebrake's Avatar
 

Testing testing

Quote:
Originally Posted by Rob Gordon View Post
Hey DanDan and akebrake.

I now got the interface. If i do some measurements will you take a look at it? ...
Sure! Just upload a "test shot" first (from your usual mic/spkr position) and you can get a quick reply everything looks "normal".

Best

PS If the file is bigger than ≈ 10MB make it two files.
Old 5 days ago
  #13
Gear Guru
 
DanDan's Avatar
Point

It is hard to read posts that long Rob. Please read the Measurement Primer. L,R, L+R, at each ear position, not nose. That is six sweeps.
DD
Old 5 days ago
  #14
Lives for gear
 
akebrake's Avatar
 

Short comment

Quote:
Originally Posted by Rob Gordon View Post
.... I will do the measurements only with the left speaker first.
Then you only know what L spkr plus room will do...

Might work if the room boundaries have the same mass and shape.
Also if the treatment is perfectly symmetrical.
(e.g No windows, pillars, alcoves, racks, furniture, ventilation ducts...)

Do we know that?

Checking L and R separately (L+R optionally) will only take 5 min more and we have a reference.
We don't need evaluating that measurement in depth (if it looks good).

Then you can start moving Left speaker and microphone around searching for modes or non resonant reflections.

Best

PS Everybody have their favourite way of investigation rooms. That's part of the game
Old 5 days ago
  #15
Lives for gear
 
akebrake's Avatar
 

Quote:
Originally Posted by Rob Gordon View Post
Here the first test shot. Infos are in the attached pic...
Interesting.

Couple of questions:

1. Is Genelec SAM disabled?
2. Are you sweeping VERY loud?
Reason for asking is the Distortion figures.(Pic)

3. One speaker at a time. (Around 75dB SPL is enough).
Increase length of sweep to 1M.
Use One sweep.

4. What kind of mic & setup?
5. Is this a quiet place? (Background noise?)
6. Immediately after a sweep is done check the SCOPE Tab for headroom/clipping.

Best
Attached Thumbnails
One Last Dip at 150 Hz-distortion.jpg  
Old 5 days ago
  #16
Lives for gear
 
akebrake's Avatar
 

Much better

Quote:
Originally Posted by Rob Gordon View Post
Please see attached new file. i played a little with positioning in the meantime but put speakers and mic back to place of first test measurement. around 1900 mm apart (+/- 5 cm cause i do it by eye for now)
.....1 sweet with 1M length per speaker - scope does not go over 60 left right...
Nice! Measurement quality looks much better!
(May be the 8000 mic was distorting)

Now I have too scrutinize these graphs and see if they corelate with room dimensions, found reflections etc.

Will come back on that to morrow.

BTW Are speakers standing (woof up/down) or laying (woof left/right)?
(Slightly different directivity in the low end) and

Is there a large desk in place at this measurement? Dimensions?

Cheers

PS You can go on with the diagonal test (if that's convenient...)
Old 3 days ago
  #17
Lives for gear
 
akebrake's Avatar
 

Prefered position?

Quote:
Originally Posted by Rob Gordon View Post
...Tomorrow I will try how much area and thickness of glass wool I would ultimately need in order to achieve a good result in my preferred speaker position. ...
Rob,

If I understand you right, you don’t want to change speaker or listener positions?
You only want to control the floor bounce...?

Cheers
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