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10th March 2015
#271
Gear Guru
Delta

Very good. Then back to the other suggestion. i.e Calculate the distance to the reflection which would cause the first big dip.

DD
11th March 2015
#272
Lives for gear

Sorry but I am not sure how to do that.. I don't really understand how a reflection can cause a dip?
Is there an equation?
11th March 2015
#273
Lives for gear

Looks like combing

With a large surface area (of "MLS type" slats) on the rear wall covered by polys it's quite possible IMHO to get strong reflections back to the microphone which resulted in some combing on the display. What does it sound like?

BTW Diffusers will also create lobes and AFAIK the higher "N" the more and narrower the lobes e.g. "better diffusion".

I am sure Jens will comment if I am totally wrong

Best
11th March 2015
#274
Gear Guru
Dips

No worries dddd, it is fairly simple.
Consider a single frequency sine wave. A perfect reflection will cause it to double itself, at a distance from the reflecting boundary where they are exactly in phase. +1+1=2, or 6dB.
BUT, at a distance where they are in opposite phase, +1-1=0. Of course the reflection is not really perfect so we don't get such perfect cancellation. However we readily see narrow nulls of -30dB and so on.

http://www.mh-audio.nl/CancellationFreq.asp

Comb filter delay time dips and peaks comb filters notch frequency - initial time delay gap ITDG - sengpielaudio Sengpiel Berlin

And, as my Maths teacher used to say, The rest is just arithmetic......

DD
11th March 2015
#275
Lives for gear

Ake, They only noticeable was the louder hf energy and that what I was focused to check. mid and highs.
comb wasnt noticed, but again you have to move to notice that which I didnt cause I usually dont while listening or mixing.
I only saw the measurements and noticed that peaks got bigger and nulls deeper.
11th March 2015
#276
Lives for gear

Quote:
Originally Posted by DanDan
No worries dddd, it is fairly simple.
Consider a single frequency sine wave. A perfect reflection will cause it to double itself, at a distance from the reflecting boundary where they are exactly in phase. +1+1=2, or 6dB.
BUT, at a distance where they are in opposite phase, +1-1=0. Of course the reflection is not really perfect so we don't get such perfect cancellation. However we readily see narrow nulls of -30dB and so on.

mh-audio.nl - Acoustic

Comb filter delay time dips and peaks comb filters notch frequency - initial time delay gap ITDG - sengpielaudio Sengpiel Berlin

And, as my Maths teacher used to say, The rest is just arithmetic......

DD
heh Okey, I got it. I will do the calculations, thanks!
btw, every second period gives me a perfect in phase sinewave, for example 1 and 3 will be in phase, right?
edit: wow, great links, thanks a lot!

I want to experiment more with polys and placement. Something is telling me that the narrow long pieces on the side walls and ceiling are the ones responsible for the comb..ish results.

Last edited by almaelectronix; 11th March 2015 at 12:34 AM..
11th March 2015
#277
Lives for gear

Double tutorial...

Quote:
Originally Posted by almaelectronix
Sorry but I am not sure how to do that.. I don't really understand how a reflection can cause a dip?
Is there an equation?
A "reflection" means (in this case) a strong wave, in a certain frequency band, is coming back to the microphone in the opposite direction! (from the rear wall) and will interfere with the first wave. Constructive (max 6 db boost) and destructive (deep null) interference result.
That's a kind of standing wave (position dependent) happening.
It does not have to be a room mode.

Check the *path length difference* (PLD) between direct sound and the reflection. On the ETC display, or in the room (tape measure) between speaker- rear wall- microphone minus (speaker-microphone).

May be you have to filter the ETC to find the strong return. That does not prove you will hear it

When that PLD equals 1/2 wavelength a cancellation results. (first null)

Best

And I noticed you used linear FR display watching the combing
11th March 2015
#278
Gear Guru
Collaboration

That's jammin. +1 Ake, and correct me if I get the Geometry or Arithmetic wrong...
One way to search for the culprit reflecting boundary is to cut a length of string equal to the whole longer bounce path. i.e. Distance from Speaker to Mic PLUS PLD.
Attach the string at both ends, or get friends to hold it. Grab the string and see if you can make it reach any of the suspect possible boundaries.

DD
11th March 2015
#279
Lives for gear

ye yeah, I know about reflection and comb, my question wasn't so clear, sorry.
I just couldn't understand and put it together how I can calculate which reflection causes a specific null and more specific where it is coming from. Now it is clear! Thanks

Quote:
Originally Posted by akebrake
Check the *path length difference* (PLD) between direct sound and the reflection. On the ETC display, or in the room (tape measure) between speaker- rear wall- microphone minus (speaker-microphone).
If I measure speaker to back wall and back to mic, why then remove the speaker to mic.
Wouldn't that be the same as if I measure mic to back wall and back to mic?

I saw a thread somewher for PLD and string method I will check again

Last edited by almaelectronix; 11th March 2015 at 08:17 AM..
11th March 2015
#280
Lives for gear

PLD and String Method

Quote:
Originally Posted by almaelectronix
โฆโฆ.If I measure speaker to back wall and back to mic, why then remove the speaker to mic.
IF we talk distance thats the "total travel path" used in the "String Method"
(I assume back wall is behind the listener...)

Quote:
Wouldn't that be the same as if I measure mic to back wall and back to mic?
NO, this distance does not include position of the loudspeaker. E.g.a side wall reflection. What would the distance mic to side wall and back to mic tell you?

The measurement signal STARTS in the software (if we are picky) and then goes via the sound card to the speakers. If we use NO Loopback compensation we have some latency and then the loudspeaker "responds" and start making sound waves.
They travel through the air to the microphone (some soft ware authors call it "Time of Flight"; TOF)

If your ETC is set up to show direct sound as T0= 0ms you do NOT know the TOF.(or latency)
But you will KNOW how late the reflections are RE: the Direct first spike on an ETC plot. On ETC the PLD is expressed as time

Quote:
I saw a thread somewher for PLD and string method I will check again
https://www.gearslutz.com/board/6133764-post8.html

Best
11th March 2015
#281
Lives for gear

Quote:
Originally Posted by akebrake
NO, this distance does not include position of the loudspeaker. E.g.a side wall reflection. What would the distance mic to side wall and back to mic tell you?
Hahahaha, yes of course It wont tell me but that`s not what I meant! Good one!
I mean that for the polys measurements my speaker to mic distance is always the same so I can just add this to the path of the reflection surfaces of interest.
Sorry, English is not my native language so many times I can't express myself the way I think.

Quote:
Originally Posted by akebrake
The measurement signal STARTS in the software (if we are picky) and then goes via the sound card to the speakers. If we use NO Loopback compensation we have some latency and then the loudspeaker "responds" and start making sound waves.
They travel through the air to the microphone (some soft ware authors call it "Time of Flight"; TOF)
If your ETC is set up to show direct sound as T0= 0ms you do NOT know the TOF.(or latency)
But you will KNOW how late the reflections are RE: the Direct first spike on an ETC plot. On ETC the PLD is expressed as time
Thanks Ake, but don`t you mind about the basics, I am really familiar with all these.
Last year was full of study on the acoustics for me!!! As the last 20 years of my sound engineering journey!!! Heh there is always something new to learn!

Quote:
Thanks for the link, I `ve seen that one before, Sac did a good job there!
Not the one I was looking for though, I will post it when I have the time to search my endless bookmarks!
12th March 2015
#282
Lives for gear

Quote:
Originally Posted by almaelectronix
...Thanks Ake, but don`t you mind about the basics, I am really familiar with all these.
Last year was full of study on the acoustics for me!!! As the last 20 years of my sound engineering journey!!! Heh there is always something new to learn!
Wow, that's great!
I just tried to be clear if anyone else would see that post

(Describing the String method vs ETC with words is complicated IMHO and I will make another try with an illustration. Workin' on it).

Regarding earlier measurements.
I can see some differences, yes. If they will disturb your ability to perform a great mix, I don't knowโฆ

Observations: difference between L /R w angled desk, wo polys:
Something happens at 260 and 460 Hz on all measurementsโฆ
To investigate I used โVar Smoothingโ (e.g. no smooth at lo freq and gradually more at higher freq). Easier to see tendencies than a lot of combing due to the long IR window.
Next step would (eventually) be to find out if that is the floor (and sub-box) alone or in combination with other surface.
May be listening to some pulses in those frequency range and compare L and R.

Measurement from earlier post: "desk angled"
Attached Thumbnails

Last edited by akebrake; 12th March 2015 at 11:51 PM.. Reason: Add on info
13th March 2015
#283
Lives for gear

Akebrake thanks for taking the time to check the mdats and all you help!

I will see how the room contributes to my mixes after I check how these translate to other systems! Hopefully good!

I must investigate deeper and use the right measurements for check any differences/issues.
I read that it is important when using trace arithmetic that the traces are properly time aligned, e.g. by using the option to use a loopback connection as a timing reference and making sure that any t=0 adjustments are applied to both traces.

Quote:
Per the help on the "All SPL" graph, "For meaningful results measurements that have impulse responses or phase data should be properly time aligned before they are combined.". You would need to set up a loopback to provide a timing reference, measure with each mic in precisely the same location and adjust the levels of the traces so that they are aligned (use 'Add offset to data' before doing any arithmetic). It would be best to measure very close to the source with the source as far from room surfaces as possible to minimise the effect of the room on the measurements.

Last edited by almaelectronix; 13th March 2015 at 09:56 AM.. Reason: add quote
14th March 2015
#284
Lives for gear

Quote:
Originally Posted by almaelectronix
Akebrake thanks for taking the time to check the mdats and all you help!โฆโฆ.
Yourโe welcome! I enjoy following the development of your carefully built and documented control room. Very interesting.

Quote:
...
I read that it is important when using trace arithmetic that the traces are properly time aligned, e.g. by using the option to use a loopback connection as a timing reference and making sure that any t=0 adjustments are applied to both traces.
Good point and I totally agree. Donโt take anything for granted in acousticsโฆ

Too many unknown variables and too many functions in REW
...but I think those areas (260-460 Hz) are interesting

Cheers

BTW this post is about locating different reflections
https://www.gearslutz.com/board/6367558-post22.html
14th March 2015
#285
Lives for gear

3rd July 2015
#286
Lives for gear

Quote:
Originally Posted by almaelectronix
Hi Alma !

Just a "bump" to the thread, curious to know about the room :-)

Ciro
3rd July 2015
#287
Lives for gear

Hi Ciro!
unfortunately I run into several problems with a water leakage from underground and we still havent found the real problem.
I now got a rough solution using a pump in order not to flood in there.

So I have just been able to work just a little bit in the room, still try to "tune" with the room acoustics to be honest.

I ve done a couple of works which I am currently testing on different systems to see how they translate, and I am happy with the results so far, but not ready to make final conclusions until I work more in there.

Till now, I can say that the low region is translating really good to other systems, small speakers, headphones etc. and the sound i have is pretty close to what I am trying to achieve in there.

Of course it is different as I am using a 2.1 system on studio, and ATC's sub sounds fantastic, so it's hard to find that low distortion lows from conventional systems. But I am happy with what I get and it is a great oportunity for me to improve my mixing skills.

So, for now I think that the room is really helping me with the Lf as it is quiet easily heard ,not muddy or boomy as it was before and it is now easy to mess with the eq's etc.
It is also tight and I am not getting room sound when stoping the music i.e. , that is probably the low r.t values.
And it is full and rich, really warm, I love it!

The mid region...No problems i have spoted with the mids so far!

The highs..hmm. Not quiet sure.
To be honest even though I messed a lot with many polys, adding to different spots, testing, measuring, listening I finally found that the two large polys on back wall to side corners and one large on back ceiling to wall corner yielded the best results giving me greater r.t. values on mid and highs without altering the frequency responce.

But still I would like to have just a bit more Hf. Maybe a bit more live space would gave me that? not sure.
I can hear on other systems that it translates okey but I find my self holding back a bit with highs when i am inside the room eq'ing in order too achieve that.
It is not much and maybe it is the combination of the speakers-room acoustics I had before which I got used to over the years.

but my friend's genelecs on his untreated room are closer to my taste on highs.
On the other hand I thing that genelecs are a little bright anyhow.
I thing the model is 8040. If anyone owns or has experience and can confirm that?!

These are my first conclusions so far which might change as time goes by and getting use of the room.

if you have any specific things you wanna know , feel free to ask

Last edited by almaelectronix; 3rd July 2015 at 11:51 PM..
22nd September 2015
#288
Lives for gear

So..
You know I tried polys on back wall and ceiling and after all the testing I kept the usefull ones. Also covered the whole front wall, front corners and lower 60cm of all walls with slats for more hf energy. So the rest is mls binary slated and floor highly reflective.

After all that treatment and tweaking with slats polys etc., is there a way to bring some more 6k and 10k region energy back without affecting the frequency responce below that? Narrow Q, lets say +/-1khz or a bit more but not more than 1.5K.
Any suggestions of what to use? Any possible places where would work best to achieve my goal?
24th September 2015
#289
Lives for gear

What can I use to bring back certain band of high frequencies in my room?
29th September 2015
#290
Lives for gear

Any suggestions?
2nd October 2015
#291
Lives for gear

trinnov?
2nd October 2015
#292
Lives for gear

Sorry, I don't really understand, what do you mean? getting more accurate speakers?

okey I now saw your edit and I am with you on "not too live room".

But, I believe the Atc's are performing really good.
Maybe some different speakers will have different results and help getting closer to the sound I want in there
but can not afford to change them at the moment.
let alone that I love the atc's mids..

As for the speaker placement I sure tried a lot of possible combinations.
I am sure you remember my post about it
https://www.gearslutz.com/board/10793803-post206.html

So for now I am trying to find a solution and I am thinking about trinnov or some other room correction hw since I don't know what else could make a difference on specific frequencies of interest.
Just to make the final tweaking for the hf.
I am ok on mid and lows.

Last edited by almaelectronix; 5th October 2015 at 08:48 AM..
3rd December 2015
#293
Lives for gear

So, some update for my room fwiw.

I tried the room eq correction software from mathaudio along with my calibrated ecm.
I tried many different settings and it works well in my room,
the low region was more balanced after bringing 100-200hz and 500-600hz down
these changes on lf also left some space for the top end to appear louder.

But..

working inside this room I found out a lot of things. So I left the correction software aside for now and experiment with the listening position.
I auditioned again the "inside triangle" position as I had some issues when sitting right at the tip which wasn't clear to me at first.
Such as very small sweetspot, combing on mid and highs, blurry sound stage and thin mids.

Now 15cm inside triangle changed the game.
all these issues are gone, instruments are more easily spotted, some highs I was seeking for are back, and mids are more solid.
Bass is not so tight now though, by "tight" I mean like 80 to 120hz?
but extreme lows like 20-40hz are cleared (not really needed though)

I am considering moving futher inside like 30cm. I have already measured this and posted the results on this previous post but I need to audition and check this as I work.
13th August 2020
#294
Here for the gear

Are you still in the same room, after the years? If so, how its today ?
13th August 2020
#295
Lives for gear

Quote:
Originally Posted by pasim123
Are you still in the same room, after the years? If so, how its today ?
Hi, there was a complication with the owner who is a relative of mine and although initially said that I could stay forever, after my father passed away on 2017 I got a call from his lawyer telling me that he is kicking me out of studio and my house...
So no I am not still there but I am building a new control room approx. 50m2 big which is also my property so..
14th August 2020
#296
Here for the gear

Well, that sux! Gladly you're getting now on building a new one! 50m2 is really awesome size for control room.

Quote:
Originally Posted by almaelectronix
Hi, there was a complication with the owner who is a relative of mine and although initially said that I could stay forever, after my father passed away on 2017 I got a call from his lawyer telling me that he is kicking me out of studio and my house...
So no I am not still there but I am building a new control room approx. 50m2 big which is also my property so..

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