The No.1 Website for Pro Audio
Room Modes - Does build style matter?
Old 2 weeks ago
  #1
Gear Head
 

Room Modes - Does build style matter?

It's too late for me now as I wrap up the paint and floor in my new basement studio, but the question just came to me...

We pine over dimensions - tables, calculators, etc - to find the best set we can use in our application that will give us the best starting point in minimizing room modes. The math and resources around are plentiful and seem widely agreed upon. What about the way a room is built and the materials used to build it? Most of what I've found can be summarized as - an array of variables so vast, it will cause some to even disregard their room dimensions; with regards to modes. In other words, if ever the construction of the room is discussed, it basically goes like this - "Hey, I used Bolt range room dimensions, why so many modes? - Welp, it doesn't take into account differences in materials, densities, etc..."

Does anyone know of any literature that discusses the modal impact of different wall types, materials used, etc? Is this something measurable or are there just too many factors to arrive at definitive data?

Could a study such as this one ( https://nrc-publications.canada.ca/e...7-da064b073e7f ) be done with regards to modes?
Old 2 weeks ago
  #2
Lives for gear
 
Jason Foi's Avatar
 

There are always modes. Modes are good. You just want an even distribution of modes. Bad room dimensions cause groupings of modes which makes things harder to treat. Room volume is most important IMO.

You can however build your walls to be treatment, but there can be disadvantages if isolation is required.
Old 2 weeks ago
  #3
Gear Head
 

I suppose if you made your walls out of paper, you wouldn't have many issues with standing waves. There'd be something left to be desired in terms of isolation though... :P

Conversely, if you made your walls out of 10' thick concrete, Motorhead could be playing in there and no one would know. That would probably promote some serious standing waves then, though, eh?

I guess the take away is yes - build style/material does effect the intensity of room modes.

The isolation of my studio turned out very well. I hope I don't have some serious modal problems though. I'm nearly finished laying down the floor and then I can chuck my speakers in there and run some tests.
Old 2 weeks ago
  #4
Lives for gear
 

Quote:
Originally Posted by Jcoop View Post
to find the best set we can use in our application that will give us the best starting point in minimizing room modes
Maybe you are misunderstanding what modes are: Changing the ratio of your room a bit will not "minimize" room modes, and as Jason already pointed out, the goal is NEVER to minimize modes! You don't want to get rid of them.... in fact, the problem is not that you have too many modes, but rather that you don't have enough in the low end! If you had many dozens of modes below 200 Hz, your room would be just fine. But you don't: you probably only have a handful, and that's the issue... there just aren't enough to go around. That's the reason why we try to get a good ratio for the room: because it takes those very few modes that you do have, and spreads them around as evenly as possible. That can help the overall acoustic response of the room.

But getting to your actual question: Assuming that you are isolating your studio to a reasonably good level, different building materials won't have much effect on modes. Because modes form between the solid, hard, rigid, massive boundary surfaces of the room, regardless of what they are made from. Glass, concrete, brick, multiple layers of drywall, etc. all allow modes to form in roughly the same way. It's the dimensions that create the modes, not the construction materials. Now, as Jcoop also pointed out, if you use very light-weight materials that don't isolate well, then your modal response would be much weaker, and for the extreme case he mentioned (paper walls), there would be no modes in the low end... but there would still be some on the very high end, since paper is still reflective enough for that. So even with paper-thin walls, you would still have modes...

Quote:
"Hey, I used Bolt range room dimensions, why so many modes? - Welp, it doesn't take into account differences in materials, densities, etc..."
The number of modes will not change if you use glass walls instead of plywood walls, or concrete walls, or brick walls. Modes are a function of the room dimensions, not the materials. If you build two rooms that have the exact same dimensions, but one is concrete an the other is drywall, then the modal spread would be the same in both cases.

That said, it is possible that some types of construction can act as bass traps (in addition to being walls), which would help damp some of the modes... but even then, it would not change the modal response of the room. Because it is the dimensions of the room that determine the modal response.

- Stuart -
Old 2 weeks ago
  #5
Lives for gear
 
avare's Avatar
 

Quote:
Originally Posted by Jason Foi View Post
You can however build your walls to be treatment, but there can be disadvantages if isolation is required.
Usual walls ALWAYS have MSM resonances. Are you writing to let those be at random?
Old 2 weeks ago
  #6
Lives for gear
 
Jason Foi's Avatar
 

Quote:
Originally Posted by avare View Post
Usual walls ALWAYS have MSM resonances. Are you writing to let those be at random?
Lol, no, i was just vague with my respose.

OP, i meant that you can build your walls in such a way that they target the lowest problem modes. Or even build your inner leaf inside out so that all the insulation is on the inside of the room serving dual purpose. Dampening MSM resonance and providing room treatment at the same time.
Old 2 weeks ago
  #7
Gear Head
 

Quote:
Originally Posted by Jason Foi View Post
There are always modes. Modes are good. You just want an even distribution of modes. Bad room dimensions cause groupings of modes which makes things harder to treat. Room volume is most important IMO.

You can however build your walls to be treatment, but there can be disadvantages if isolation is required.
Quote:
Originally Posted by Soundman2020 View Post
Maybe you are misunderstanding what modes are: Changing the ratio of your room a bit will not "minimize" room modes, and as Jason already pointed out, the goal is NEVER to minimize modes! You don't want to get rid of them.... in fact, the problem is not that you have too many modes, but rather that you don't have enough in the low end! If you had many dozens of modes below 200 Hz, your room would be just fine. But you don't: you probably only have a handful, and that's the issue... there just aren't enough to go around. That's the reason why we try to get a good ratio for the room: because it takes those very few modes that you do have, and spreads them around as evenly as possible. That can help the overall acoustic response of the room.
Of course... It's hard to keep all these concepts in mind when doing a DIY build from scratch. But, yes that makes a lot of sense. It's like passive/subtractive EQ while mixing. You can always tame/pull out problem frequencies but if you're trying to boost something that isn't there (in this case, nulls) then you're in trouble.

Well, I've spent the last couple of evenings listening to music in the new studio and while I'm happy with the stereo image and clarity (for now I just have old panels leaning on the walls while I construct some more robust absorbers) there are a couple glaring modes that need to be addressed.

Anyway. So, the ACTUAL take away from this is that room dimension is the sole dictator with respect to modes and nulls. And, if the room is built with most practical materials and a reasonable amount of isolation, it's not going to matter how you built it or with what.

Side note - as a rough test of isolation I played pink noise from my monitors - measured at 80db standing on the outside of the doorway. When I closed both doors, I achieved nearly 50dB of reduction. I was really happy to have achieved this amount of reduction - the modal issues took a bit of the joy out of that achievement but 1 step at a time, I guess! :P
Old 2 weeks ago
  #8
Lives for gear
 
Jason Foi's Avatar
 

Quote:
Originally Posted by Jcoop View Post
Of course... It's hard to keep all these concepts in mind when doing a DIY build from scratch. But, yes that makes a lot of sense. It's like passive/subtractive EQ while mixing. You can always tame/pull out problem frequencies but if you're trying to boost something that isn't there (in this case, nulls) then you're in trouble.

Well, I've spent the last couple of evenings listening to music in the new studio and while I'm happy with the stereo image and clarity (for now I just have old panels leaning on the walls while I construct some more robust absorbers) there are a couple glaring modes that need to be addressed.

Anyway. So, the ACTUAL take away from this is that room dimension is the sole dictator with respect to modes and nulls. And, if the room is built with most practical materials and a reasonable amount of isolation, it's not going to matter how you built it or with what.

Side note - as a rough test of isolation I played pink noise from my monitors - measured at 80db standing on the outside of the doorway. When I closed both doors, I achieved nearly 50dB of reduction. I was really happy to have achieved this amount of reduction - the modal issues took a bit of the joy out of that achievement but 1 step at a time, I guess! :P
Well, the good news is you can treat the modal range and end up with a good room. Assuming you have enough volume to do so.
Old 2 weeks ago
  #9
Lives for gear
 

Quote:
Originally Posted by Jcoop View Post
Of course... It's hard to keep all these concepts in mind when doing a DIY build from scratch.
Very true! Acoustics is a huge subject, and a lot of it just isn't intuitive at first glance. Its only when you get down into the nuts and bolts that it starts to make sense.

Quote:
But, yes that makes a lot of sense. It's like passive/subtractive EQ while mixing. You can always tame/pull out problem frequencies but if you're trying to boost something that isn't there (in this case, nulls) then you're in trouble.
Just adding to what you said: In the case of room modes (and other nulls... see below), it's not just that you can't EQ it by boosting it, but rather that by attempting to do so, you can make matters worse! Because modes are standing waves, and you are listening in the null, if you try to boost that with EQ you won't get much of a result where you are... but for the rest of the standing wave, the part that is not a null, there will be a dramatic increase in level! But you yourself would not be aware of that, since you are standing in the null. That's why so-called "room correction" hardware and software can only really work for one specific spot in the room, because anything you do with EQ will only be valid for that point: to the detriment of all other points (there's a couple of complicated exceptions to that, but I won't bore you with the details: the statement is correct for most situations and most adjustments). You can only use "room correction" hardware or software as the very last step in tuning your room, AFTER all of the acoustic treatment is in place... because in that case, you are already damping all the modal resonances, killing all the reflections and comb filtering, and the few remaining issues are almost certainly just frequency domain issues, many of which can be attenuated with EQ... but only if the room is treated.

Quote:
Well, I've spent the last couple of evenings listening to music in the new studio and while I'm happy with the stereo image and clarity (for now I just have old panels leaning on the walls while I construct some more robust absorbers) there are a couple glaring modes that need to be addressed.
Have you done the full testing with REW? If not, here's how to do that: How to calibrate and use REW to test and tune your room acoustics REW can reveal a huge amount of very useful information about your room, that will help with both setting things up, and also with deciding how to treat it.

Quote:
Anyway. So, the ACTUAL take away from this is that room dimension is the sole dictator with respect to modes and nulls. And, if the room is built with most practical materials and a reasonable amount of isolation, it's not going to matter how you built it or with what.
True, but with one caveat: that the room is well isolated. I'm pretty sure you were referring to that, but it's an important point to add. If the room is poorly isolated, then you might have modal stuff happening with walls that are not even part of the inner-leaf of your room! And the modes that you do have in your room, might turn out to be at frequencies that are different from what they should be, from the dimensions alone. But if the room is decently well isolated, then the modes should form where they are predicted to form, and the spread should be very close to what the calculators predict.

One other point here: while modal issues are certainly the main culprit for huge peaks and dips in your room response, they are not the only culprit. You can also get dips from SBIR, as well as from strong specular reflections, and a couple of other minor things. Fixing your modal resonances is always the first priority in a small room, but after you do that there might still be some peaks and dips left from other causes. You can usually easily identify which issues are modal and which are "other", by looking at the data REW gives you.

Quote:
Side note - as a rough test of isolation I played pink noise from my monitors - measured at 80db standing on the outside of the doorway. When I closed both doors, I achieved nearly 50dB of reduction. I was really happy to have achieved this amount of reduction - the modal issues took a bit of the joy out of that achievement but 1 step at a time, I guess!
50 dB isolation is actually pretty good! Congratulations! And yes: one step at a time is definitely the way to go with tuning a room. Each time you add a piece of treatment, run REW again. That way you can check that it really did what it was supposed to do, and also see what you need to do next. Occasionally you'll find that as you put in some treatment, and it deals with one problem, it also uncovers another problem that you weren't aware of before, because the first problem was "masking" it...

Ain't acoustics fun!?!?


- Stuart -
Old 2 weeks ago
  #10
Gear Head
 

This all really great information and conceptual reinforcement. Thanks guys.

I have used REW in the past and will run some tests with it (as soon as I find the moving box that has my pc laptop in it... Still unpacking from the summer move )

I think some really important points that people can forget or ignore are that:

- If your room isn't well isolated, you could be experiencing modes/nulls from boundaries outside of your room

- Room Volume - Before addressing modes, make sure none of the nulls are drastically quiet because anything we do to treat modes (short of helmholtz resonators or some membrane absorber) is going to be broadband and will likely make the nulls even quieter. Most of us can't change the room dimensions but could at least alter the speaker placement to optimize the volume of the lowest "nulls."

- Measure with each absorber that you add to the room. This speaks to me in 2 ways. One way is that, as Stuart said, you might be hurting the response with the placement of a given absorber. Secondly, it seems like so many people get to this point and then just "decorate" their room with all kinds of absorption. You could fill your room with absorbers, traps, diffusors but in actuality, you may not need some of them, or their placement is inappropriate for the room response - It's a crap-shoot. Could work out great, but it could be a greatly inefficient use of space and resources. And let's face it, most of us are already working with less space than we would like
Post Reply

Welcome to the Gearslutz Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…
Thread Tools
Search this Thread
Search this Thread:

Advanced Search
Forum Jump
Forum Jump