First time n00b room measurement - help appreciated - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 12 Old 02-06-12, 08:47 AM Thread Starter
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First time n00b room measurement - help appreciated

Hello,

I have a non symmetrical cnotrol / recording room (see Plan).

I want to know if there's any point in treating the room before I buy nice equipment to put in, or I can use some fancy EQ trick to do the job.

So first things first: understand the room.

I read that it might be best to first make the room more symmetric by adding a wall partition to the left of the listening position, but I thought that it might be a good idea to understand how the room is now and then measure the difference later.

Also, I ran the test through Dell PC speakers
My problem is that I don't want to buy super duper monitors only to find out that I need $4000 of room treatment to use those nice speakers.

Do these 2 things disqualify the measurements?

If not, attached are my files, hopefully posted according to the guidelines.

This is what I noticed:
- lots of ringing because of the small room (see all the modes in the spectrogram and the very long decay times in the waterfall plot)
-response isn't too bad but there is a dip below 50Hz that I don't really understand
-should I worry about the response dips at ~110 / 190 / 260 etc. on the SPL plot?

I don't understand the RT60 & averaged SPL plot

Is there hope for my room?

For less than $4000?
Attached Thumbnails
First time n00b room measurement - help appreciated-plan.png  

First time n00b room measurement - help appreciated-decay.jpg  

First time n00b room measurement - help appreciated-filtered-ir.jpg  

First time n00b room measurement - help appreciated-rt60.jpg  

First time n00b room measurement - help appreciated-spectrogram.jpg  

First time n00b room measurement - help appreciated-spl-averaged.jpg  

First time n00b room measurement - help appreciated-spl.jpg  

First time n00b room measurement - help appreciated-waterfall.jpg  

Attached Files First correct test.mdat (6.38 MB) 
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post #2 of 12 Old 02-06-12, 07:31 PM
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Re: First time n00b room measurement - help appreciated

Initial suggestions.

1. Statistical calculations have no place in Small Acoustical Spaces, Seeing as there is no effective statistically reverberant soundfield, and that the space is dominated by locally variable modal and specular energy distributions, forget RTxx calculations and use the proper tools such as waterfalls for modal evaluation, and ETCs for specular behavior at various listening positions.

2. The mix position lacks fundamental LR symmetry. Consider positioning it facing into the corner to the right.

3. And most importantly, the work surface is a HUGE problem - literally.
The enclosed ETC shows at least one significant destructive early reflection due to the speaker and its mounting.

The very early reflections less than 2ms MUST be addressed. The first indirect arrival is most likely diffraction due to driver signal misalignment. The second is most likely off the megalith of a worksurface.
Lose the large work surface and replace it with a mobile tilted laptop cart capable of holding a keyboard and monitor (and a computer 'below', if desired) - and then mount the monitor on the wall in the corner in front of a 2'x2'x35" floor to ceiling superchunk style bass trap made with cheap 'pink fluffy stuff' Fiberglass.

Once the workstation issue is addressed and the mix position relocated to the corner affording greater L/R symmetry, THEN you can repeat the measurements and begin addressing the bass modes, and following that, the specular reflections via the use of the ETC response.

Last edited by SAC; 02-07-12 at 10:14 AM. Reason: grammar -add "ly" to 'like'
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post #3 of 12 Old 02-07-12, 05:36 AM Thread Starter
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Re: First time n00b room measurement - help appreciated

Thanks for even reading my post

Questions / comments below.

Quote:
SAC wrote: View Post
Initial suggestions.

1. Statistical calculations have no place in Small Acoustical Spaces, Seeing as there is no effective statistically reverberant soundfield, and that the space is dominated by locally variable modal and specular energy distributions, forget RTxx calculations and use the proper tools such as waterfalls for modal evaluation, and ETCs for specular behavior at various listening positions.
Got it.

Quote:
2. The mix position lacks fundamental LR symmetry. Consider positioning it facing into the corner to the right.
Interesting. Wouldn't be completely symmetrical but why not. And why not facing left into the angle? Or keeping the position like it is but build a wall partition to the left of the listening position to mimic the right wall?

But restore symmetry, OK. Got it.

Quote:
3. And most importantly, the work surface is a HUGE problem - literally.
The enclosed ETC shows at least one significant destructive early reflection due to the speaker and its mounting.
OK this I don't get .

It's a desk like I've seen in tens of control room pictures. A simple desk really, flat, probably 4-5 feet wide (size on drawing might be too large, I have to check). What's so bad about that? And why is the mounting bad? Would it be better if the speakers were mounted on monitor supports? Right now they're resting on the desk.

Quote:
The very early reflections less than 2ms MUST be addressed. The first indirect arrival is most likely diffraction due to driver signal misalignment.
The speakers are small PC speakers placed like on the drawing. They're not real studio monitors yet. I do have a subwoofer below the monolith.

Do I need to do anything, I mean besides buying $600 studio monitors?

Quote:
The second is most like off the megalith of a worksurface.
Lose the large work surface and replace it with a mobile tilted laptop cart capable of holding a keyboard and monitor (and a computer 'below', if desired) - and then mount the monitor on the wall in the corner in front of a 2'x2'x35" floor to ceiling superchunk style bass trap made with cheap 'pink fluffy stuff' Fiberglass.
I thought monitors had to have a certain distance to the "front" wall (I remember something like a 35% rule of thumb)?

Quote:
Once the workstation issue is addressed and the mix position relocated to the corner affording greater L/R symmetry, THEN you can repeat the measurements and begin addressing the bass modes, and following that, the specular reflections via the use of the ETC response.
I'll start by changing the listening position alignment with the same surface and we'll see what happens.
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post #4 of 12 Old 02-07-12, 11:06 AM
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Re: First time n00b room measurement - help appreciated

I love how the "multi-Quote "on" is no more functional than "Multi-quote "off""...

My reply is serious but also 'tongue in cheek' as you hit on quite a few commonly held fallacies... My sarcasm is aimed at the Fallacies, not at you personally, as i would love to help you avoid/unlearn a few of them and to help you avoid making them as you expend energy, time and money, possibly to your own detriment. And yes, i am QUITE familiar with studio acoustics!

Quote:
vinnie2k wrote: View Post
Thanks for even reading my post

Questions / comments below.


Got it.


Interesting. Wouldn't be completely symmetrical but why not. And why not facing left into the angle? Or keeping the position like it is but build a wall partition to the left of the listening position to mimic the right wall?

Yes it WOULD provide LR symmetry. What is not symmetrical about 2-45 degree walls to the L & R? Especially considering that you now have absolutely None... And facing Left would provide symmetry How???

But restore symmetry, OK. Got it.
This is ABSOLUTELY necessary.



OK this I don't get .

It's a desk like I've seen in tens of control room pictures. A simple desk really, flat, probably 4-5 feet wide (size on drawing might be too large, I have to check). What's so bad about that? And why is the mounting bad? Would it be better if the speakers were mounted on monitor supports? Right now they're resting on the desk.

LOL! Yes, and you commonly see speakers mounted on bridges laid on there sides, too! Also WRONG! So you are discovering the many (if not most) in the field haven't a clue with regards to acoustics and that they base their 'design'(sic) by copying others who also have no clue who copied others who...you get the idea...! Simply having played a guitar does not impart one with a knowledge of acoustical physics.
And the proverbial status of a large aircraft carrier megalith of a desk is a carryover from the days of old when 128+ channel SSL board was status - as size indicated channels. Unfortunately size was an acoustical detriment then (despite the status of having a large capacity board); and it is even more so now considering folks are now trying to shoehorn studios into closets and the fact that we now have virtual systems that can fit in a laptop! Early high gain reflections are detrimental to imaging, localization, and intelligibility. Period.


And regarding the flawed speaker placement of speakers on or directly over reflective surfaces... Exactly the situation we are talking about (monster desks, bridge mounted speakers,etc.) that resulted in Russ Berger introducing what is now considered "common sense". A minimized and downward sloping work surface featuring Proper speakers selected for their spatial dispersion/Q characteristics mounted properly (minimizing diffraction) and placed several feet BEHIND the deck on mechanically isolated (and use Sorbothane, NOT MoPads!!!...talk about another Common mistake!) stands in order to specifically mitigate early reflections off the worksurface/board. To the degree that you do not have the space to mount them such, you minimize the worksurface to only what is absolutely necessary. And having space for the buffet and 27 groupies fawning over your work is not "absolutely necessary". ...At least not from a qualitative acoustical point of view. Psychological counseling is extra...

As far as how many others do it incorrectly - yes, they are seemingly everywhere - unfortunately an extensive knowledge of acoustics does not rank very high in the hierarchy of necessary skills in audio - I suggest you find new mentors...


The speakers are small PC speakers placed like on the drawing. They're not real studio monitors yet. I do have a subwoofer below the monolith.

Think of how the sub performance might be improved if it were not behind a partition...

Do I need to do anything, I mean besides buying $600 studio monitors?

Oh geesh..."studio" monitors... No, buying something with a label on the box does not insure applicability! Neither do fancily colored cones. What you might want to start investigating are speakers with a more controlled and uniform "power response" - or simply start by attempting to identify some with well made polar dispersion data...That will keep you busy for some time to come. Also, you should consider a signal aligned speaker with MEANINGFUL specs, including a proper impulse response. You will find that anechoic frequency responses are almost worthless. Instead a measured response in the intended mounting location is more useful. But don't hold your breath expecting to find one... In the real world, you will find few free field anechoic spaces away from a boundary to mount your speakers. Thus it should become apparent that specs generated in such spaces have limited applicability or translational value...


I thought monitors had to have a certain distance to the "front" wall (I remember something like a 35% rule of thumb)? And now more "rules" that are but generalizations designed to avoid common modal null locations....as we ignore more significant issues such as SBIR, early reflections, symmetry and other even more critical issues that I wish we could elevate to the status of "rules"!



I'll start by changing the listening position alignment with the same surface and we'll see what happens.
You can, but in an attempt to save you some time (benefiting from those who have already done the legwork and actual tests) the result will simply be a change in the arrival time of the early reflections... hardly a beneficial exercise. Look, I have no personal issue with large work surfaces, Don't misunderstand me. I mean, a place to set your beer, coffee, juice, dinner, girlfriend, video game consoles, rolling tray, etc. is a handy function, but not one related to optimal acoustics that have a very definite impact on the real quality of the mix that I am ASSUMING fits somewhere into the hierarchy of needs (apologies to Maslow) in the process.

I realize that I have been a curmudgeon here (and my ire - and sardonic humor - are aimed at the all too pervasive erroneous ideas, NOT at you!) But it seems beneficial to attempt to 'undo' some significant erroneous assumptions before they become so ingrained as to cause perennial damage. Most are physically easily corrected. Some, primarily the perceptions and ideas about status icons, are a bit harder to remedy... But all are necessary. I know that when I say them, that they carry no clout for you. If you need for me to dig up papers and quotes from folks such as Russ Berger so that you can read them coming from a name that you SHOULD be familiar in order to substantiate the ideas, PM me.
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post #5 of 12 Old 02-08-12, 11:46 AM Thread Starter
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Re: First time n00b room measurement - help appreciated

(I love your tone, you made me LOL a couple of times)

OK so I am now officially aiming for a sticky on this one

Why?

Because I am such a n00b (a ex-physicist type of a n00b, mind you) that I don't have any religion about what needs to be done and why. And because I will ask a lot of very stoopid questions, and SAC is seemingly intent on answering at least some of them.

What I also do, besides asking stupid questions, is read forums (apparently the wrong ones ) and try to understand what experts are saying so that I can build what I need. So, in this respect, SAC, your advice is more than welcome, although I will challenge you on what I don't understand.

So let's go back to what I need.

I am a hobbyist. I plan to spend 5-10 hours a week on music. Max. I have other things in life but I want to do things right, bearing in mind space & money constraints.

I have a MIDI keyboard, an acoustic guitar, an electrical guitar, a DAW, a Tascam US-122L, an LD-74 condenser mic, shitty PC monitors with a shitty subwoofer (and the Titanic as a desk ).

I plan to upgrade to an electronic drum set, a real microphone with a stand and a pop filter and studio monitors (looking at BX8a Deluxe from Studiophile but that might have to change, see above ).

And I have a new room because we just moved.

And this room is supposed to also function as a small office because the family PC (the DAW) is in that room.

So I want to see how I can make the room acoustically better without spending $4000 on EQ and/or treatment.

So I go to John Sayers' site to get some help. By the way, this is the type of stuff they build (can't post link, search for Refinery on his site). Reflections anyone? But I digress.

And over there, someone mentions REW. So I arrive here.

With this in mind:
- I get the symmetry so I'll change things around (face north west corner)
- I need room to put stuff like partitions, take notes, put a folder, etc. If I don't have some form of a desk, where do I put all this stuff? Remember, this is also a part time office... Is the Goliat desk from IKEA too large (can't post link, sorry)?
- Since the "rule" I knew is not appropriate, where do I place my listening position?
- Where do I place my monitors?
- Talking about monitors, the BX8a on m-audio's site have tech specs, but besides the frequency range, I don't really understand how the rest relates to what you are suggesting, can you help me?

Thanks again
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post #6 of 12 Old 02-10-12, 07:10 PM
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Re: First time n00b room measurement - help appreciated

Quote:
vinnie2k wrote: View Post
With this in mind:
- I get the symmetry so I'll change things around (face north west corner)
- I need room to put stuff like partitions, take notes, put a folder, etc. If I don't have some form of a desk, where do I put all this stuff? Remember, this is also a part time office... Is the Goliat desk from IKEA too large (can't post link, sorry)?
- Since the "rule" I knew is not appropriate, where do I place my listening position?
- Where do I place my monitors?
- Talking about monitors, the BX8a on m-audio's site have tech specs, but besides the frequency range, I don't really understand how the rest relates to what you are suggesting, can you help me?

Thanks again
Couple practical suggestions:
If you arrange the desk to face north-west, you would need to place monitors against the wall.(can you mount them in-wall?)
This demands from the monitor that it has a fairly even dispersion and some-kind of boundary compensation possibility. That BX8a has neither. You could look at a JBL 2325 or Mackie HR624-2. Those have fairly uniform, little bit narrower dispersion.
How to minimize desk reflection - As SAC said mount the speakers behind the desk and make the desk angle down towards you so that there is minimal sound reflecting off it towards you. Alternatively you could build a barrier at the edge of the desk to block the sound from reflecting off the desk. Work out the angles and take measurements to confirm. And please take SACs advise and go minimal if possible.

Quote:
vinnie2k wrote: View Post
(I love your tone, you made me LOL a couple of times)
If he could distill more information in a single post the universe would implode.
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post #7 of 12 Old 02-10-12, 08:24 PM
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Re: First time n00b room measurement - help appreciated

There have been many outstanding suggestions made. The desk really needs to disappear and speakers mounted on stands or attached to walls.

Are the yellow rectangles in the room drawing acoustic panels?
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post #8 of 12 Old 02-13-12, 04:00 AM Thread Starter
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Re: First time n00b room measurement - help appreciated

Quote:
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Couple practical suggestions:
If you arrange the desk to face north-west, you would need to place monitors against the wall.(can you mount them in-wall?)
Yes, I could - they are brick walls with standard finishing.
But I was thinking of mounting the monitors on monitor stands, is that good? It offers more flexibility in case I need to fiddle with positioning.

Quote:
This demands from the monitor that it has a fairly even dispersion and some-kind of boundary compensation possibility. That BX8a has neither. You could look at a JBL 2325 or Mackie HR624-2. Those have fairly uniform, little bit narrower dispersion.
How to minimize desk reflection - As SAC said mount the speakers behind the desk and make the desk angle down towards you so that there is minimal sound reflecting off it towards you. Alternatively you could build a barrier at the edge of the desk to block the sound from reflecting off the desk. Work out the angles and take measurements to confirm. And please take SACs advise and go minimal if possible.
I will try to go as minimal as possible. The JBLs are slightly above my price range but I guess they'll do fine.

Can I have a desk / place to store / display stuff behind me then? Like partitions, notes, music books, etc.?
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post #9 of 12 Old 02-13-12, 04:03 AM Thread Starter
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Re: First time n00b room measurement - help appreciated

Quote:
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There have been many outstanding suggestions made. The desk really needs to disappear and speakers mounted on stands or attached to walls.

Are the yellow rectangles in the room drawing acoustic panels?
Well, that was the idea before I got into this fourm, yes

With the listening position being changed, I need to rethink the whole thing anyway.
I only had in mind to block bass reflections with bass traps at primary reflection points (and corners?), but before doing it, I wanted to make some measurements.

So that's why I'm here pestering you
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post #10 of 12 Old 02-13-12, 04:05 AM Thread Starter
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Re: First time n00b room measurement - help appreciated

I will be posting a new layout with the suggestions made here.

I was also thinking of isolating the recording space a bit - can fabric do the job (like curtains) or do I absolutely need sturdy fixed stuff?
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