Room Node Calculators - What Does It Mean?

[watchnerd]

I thought I understood room nodes reasonably well (I mean, I did my undergrad in applied physics in signal processing, so I can't be too ignorant), but I recently started playing with this calculator:

https://amcoustics.com/tools/amroc?l=22&w=17&h=12&ft=true&r60=0.6

According to this, the Schroeder freq. of my room = 137.5 Hz

Okay, I get that.

But the Bolt Area and Bornello Modes...I'm not really getting those.

Can anyone explain?

Or is this all overkill and should I be using a different, simpler calculator?

 

[Blumlein 88]

Don't know what you are talking about. But some googling shows Bolt ratios come from a 1946 JAES paper by R.H. Bolt. He did something with standard deviation of room modes etc etc. He suggested the 2:3:5 ratio I'd seen before by others.

Here is a bolt graph where height of room is 1. You want your ratios for the other two sides to fall inside the shaded area.

Bonello modes only apply below 200 hz according to this. Yet he also developed a graph that looks pretty much like the Bolt one. His work was later and he tried to take into account frequency regions of modal effects based upon ERBs.
https://www.acousticfields.com/ideal-room-size-ratios-apply-bonello-graph/

This paper here has some good info if you wish to get more involved. I'd say maybe Schroeder and Bonello would be the important things to look at.
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.478.2817&rep=rep1&type=pdf

Or same paper as above. A little cleaner format.
http://eprints.hud.ac.uk/id/eprint/...l_listening_spaces-bfazenda-phdthesis2004.pdf

 

[Blumlein 88]

Oh you should have mentioned the above site can play tones for selected modes. BTW, that software nailed peaks and dips in my room below 200hz. Of course that is the easy part. The calculated modes were exactly where measurements show them to be. Moving the cursor over the mode chart plays a frequency at that mode.

The pressure zones also appear right on for the 3 D display. Some show as stacked vertically and I find standing vs sitting to vary greatly while side to side does little. The others showing horizontal zones standing is the same as sitting while moving side to side makes big differences. Pretty neat visual software with feedback to play the nodes in your room and move around them. Not sure it is more than interesting rather than greatly useful, but their calculations can be verified most directly with hearing them.

The critical distance calculation seems way off from what I measure however. Measurement puts it some where around 9 or 10 feet, they show 3.22 ft.

 

[watchnerd]

Oh you should have mentioned the above site can play tones for selected modes. BTW, that software nailed peaks and dips in my room below 200hz. Of course that is the easy part. The calculated modes were exactly where measurements show them to be. Moving the cursor over the mode chart plays a frequency at that mode.

The pressure zones also appear right on for the 3 D display. Some show as stacked vertically and I find standing vs sitting to vary greatly while side to side does little. The others showing horizontal zones standing is the same as sitting while moving side to side makes big differences. Pretty neat visual software with feedback to play the nodes in your room and move around them. Not sure it is more than interesting rather than greatly useful, but their calculations can be verified most directly with hearing them.

The critical distance calculation seems way off from what I measure however. Measurement puts it some where around 9 or 10 feet, they show 3.22 ft.

It lists my critical distance as 2.72 feet.

I guess the broader question is:

Okay, that's a lot of data...but what do I do with it?

 

[reza]

Okay, that's a lot of data...but what do I do with it?

I read on Linn's page that instead of the usual way of taking an impulse response to correct the system's F.R., they only take measurements of your room dimensions with some general description of what furniture you have in it. They claim it works better than the alternative method. You could give it a shot.

 

[Krunok]

I read on Linn's page that instead of the usual way of taking an impulse response to correct the system's F.R., they only take measurements of your room dimensions with some general description of what furniture you have in it. They claim it works better than the alternative method. You could give it a shot.

Have they published any measurements proving that claim?

And what about the position of the speakers in the room, does that matter or not?

 

[PierreV]

I read on Linn's page that instead of the usual way of taking an impulse response to correct the system's F.R., they only take measurements of your room dimensions with some general description of what furniture you have in it. They claim it works better than the alternative method. You could give it a shot.

Not sure the Linn approach is better than alternatives. It does take speaker position (and supposedly speaker model) into account. When I tried it, yes, there was a difference. Better? I don't know. If your expectations are that the sound will be optimized and it sounds different, I guess that you are primed into thinking the sound is "better".

There was a lot of debate on this in the Linn forums, some of it very nasty and, at the time the Linn forums were abruptly closed, some people thought the closure was linked to that storm in a teacup. People who got sub-par results were often attacked as incompetent and that didn't go too well in general.

IMHO, a lot of the people had the insecure, assisted audiophile flock mentality: the plebs (end-users) should not mess with that stuff, the priests (the dealers) should install and configure the system and God (Linn) rarely spoke, if at all.

 

[Krunok]

Not sure the Linn approach is better than alternatives. It does take speaker position (and supposedly speaker model) into account. When I tried it, yes, there was a difference. Better? I don't know. If your expectations are that the sound will be optimized and it sounds different, I guess that you are primed into thinking the sound is "better".

There was a lot of debate on this in the Linn forums, some of it very nasty and, at the time the Linn forums were abruptly closed, some people thought the closure was linked to that storm in a teacup. People who got sub-par results were often attacked as incompetent and that didn't go too well in general.

IMHO, a lot of the people had the insecure, assisted audiophile flock mentality: the plebs (end-users) should not mess with that stuff, the priests (the dealers) should install and configure the system and God (Linn) rarely spoke, if at all.

Well, IMHO there is only one way to check how well roomEQ process went and that is to measure it. Unfortunately we have yet to see a roomEQ software that does that. From what I have seen here very few users did the control measurement mannually to check how well their roomEQ software did the job, which is also not surprising as if you know how to take good measurement in REW you are half way to do the roomEQ yourself either with REW or with rePhase. In ideal case automated roomEQ software would take into account that measurement and perform another iteration of the correction, but something like that we have yet to see.

What you would also be able to fix mannually, and what neither of the automated roomEQ systems is doing, is to correct FR problems when both speakers are playing that came from phase cancellation. I can hardly imagine Linn's model providing similar results to the result based on actual measurements.

 

[Thomas savage]

 

[Frank Dernie]

I thought I understood room nodes reasonably well (I mean, I did my undergrad in applied physics in signal processing, so I can't be too ignorant), but I recently started playing with this calculator:

https://amcoustics.com/tools/amroc?l=22&w=17&h=12&ft=true&r60=0.6

According to this, the Schroeder freq. of my room = 137.5 Hz

Okay, I get that.

But the Bolt Area and Bornello Modes...I'm not really getting those.

Can anyone explain?

Or is this all overkill and should I be using a different, simpler calculator?

I hadn't seen this but I was certainly aware that the magnitude of the excitation of room modes, and any harmonics, depended strongly on where the air in the room is excited, in the same way the timbre of a stringed instrument varies depending on where you bow or pluck it.
When I did my room that was about all one could do to minimise the excitation of room modes. Sitting near a node of a given mode will obviously be the place where its effect is least heard.
I have always used the speaker position and my seat in the room to optimise the sound I am hearing since I started off when the very idea of "room correction" was not thought of

 

[Blumlein 88]

I did a little experimenting with the web site. A speaker in the wrong position to excite the room still does so with the same pattern as one in a good position (like corners). The level of excitation is not the same. Of course this is with a long tone which gives time for modes to develop fully no matter where the sound energy originates. I could fix it by knocking down all interior walls and lowering the Schroeder frequency.

I've had the idea before that you don't really get good even sound until double the Schroeder frequency and this display and experience using tones on this website seem to corroborate that. The visualizations make me wonder how this all plays out with distributed woofers which seems the only good way to even out response below 200 hz.

Maybe this software needs an evolutionary mode. You tell it how many woofers you are willing to use, and it randomly evolves the best solution. Let it run a few days and show the results.

 

[pozz]

@watchnerd The Bolt and Bornello calculations are about optimal room dimensions. The Bornello one specifically is about the optimal distribution of modes in a given room. They are used mostly by acoustical architects.

I don't know enough about the mathematics to give you more than that.

 

[watchnerd]

@watchnerd The Bolt and Bornello calculations are about optimal room dimensions. The Bornello one specifically is about the optimal distribution of modes in a given room. They are used mostly by acoustical architects.

I don't know enough about the mathematics to give you more than that.

I can see how an acoustical architect could find them useful.

But for a home user who can't change his or her room dimensions, I'm not sure what I'm supposed to do with that info.

 

[Frank Dernie]

I can see how an acoustical architect could find them useful.

But for a home user who can't change his or her room dimensions, I'm not sure what I'm supposed to do with that info.

Weep?

 

[kach22i]

........ but I recently started playing with this calculator:

https://amcoustics.com/tools/amroc?l=22&w=17&h=12&ft=true&r60=0.6

Lots of disclaimers on other websites about minimum room size and using Bolt Area and Bonello graphs.

Can anyone post links on topics with low 7-foor ceilings and proper room dimensions?

I have ceiling drops parallel to the sidewalls planned to act as bass absorbers in anticipation of small room bass issues. Just not sure what else I can built into the design at this early stage of research.

 

[pozz]

Lots of disclaimers on other websites about minimum room size and using Bolt Area and Bonello graphs.

Can anyone post links on topics with low 7-foor ceilings and proper room dimensions?

I have ceiling drops parallel to the sidewalls planned to act as bass absorbers in anticipation of small room bass issues. Just not sure what else I can built into the design at this early stage of research.

Try this calculator: https://www.hunecke.de/en/calculators/room-eigenmodes.html

Enter your room dimensions in meters and it will plot you the resulting modes. Click through them to see where in the room they're situated, which will help you set your listening position.

With a 7 foot ceiling, you'll have a height-based mode which will hit you at 71Hz or so.

If you're building a room from scratch you can shift the position of the modes by changing the angles of the walls, which will also affect the mix of direct vs. reverberant sound for the mids and highs at the listening position. But neither the math nor the construction is trivial.

What I've concluded personally is that calculators help guide where I should put the speakers and listening position, roughly. Then I use a measurement mic to determine placement more accurately since a room model (at least with these tools) and an actual room are very different. I've used membrane-based absorbers and thick broadband absorbers (minimum 6"—8", or 5" with a 1" or 2" air gap) to help with bass and to ensure consistent reverb time. The latter is difficult to control and I've also never been able to affect significantly the response under 70Hz using just add-on treatments.

I've looked into constructing Helmholtz absorbers but, again, the math and construction is non-trivial, and so the acoustic effects are difficult to predict.

I think if I were to do it all again, I would pay a consultant for solid advice and design. Reading the books convinced me that there's only so much I can learn in my free time.

 

[kach22i]

Try this calculator: https://www.hunecke.de/en/calculators/room-eigenmodes.html

Enter your room dimensions in meters and it will plot you the resulting modes. Click through them to see where in the room they're situated, which will help you set your listening position.

With a 7 foot ceiling, you'll have a height-based mode which will hit you at 71Hz or so...................

Thank you for the link, I have not seen that one before.

For my space, 3/4 of the walls are already there, just need to build a little bit of side wall and the back wall.

As I understand it, the rear wall corners is where the real (bass issues) problems lay.

In my layout there is another smaller room behind the back wall where a work desk is located.

The back wall will have a centered full height Ikea record rack, with flanking sliding doors at each rear corner.

So what I will have is a tune-able space via cracking the doors open a bit at the rear with main space of 7" H x 11'W x 15'D, and a rear work room that is closed off from rest of house (via sealed swing door) and will be insulated like the main listening area (lots of MLV).

I will have to enter listening space via the work space, like a lobby to an opera hall.

Choice of listening rooms shall be (courtesy of two sliding doors in opposing rear corners):

(1.) 7" H x 11'W x 15'D

(2.) 7" H x 11'W x 22'D

So where most people would be building bass traps in the rear corners to trap the bass, I can choose to allow it to escape into a chamber half the length of the main listening space filled with books and drawings (in theory).

I have no formal example or precedence that I am emulating, this concept is a formulation of existing home layout constraints and energy management as I currently understand it.

BASS: If you cannot control it, allow it to exit gracefully.

 

[Hipper]

It would be interesting to see measurements of the two arrangements.

Generally though I would see it as changing rather then solving the bass problems. I wouldn't have thought 'books and drawings' would have much impact on bass absorption.

 

[kach22i]

It would be interesting to see measurements of the two arrangements.

Generally though I would see it as changing rather then solving the bass problems. I wouldn't have thought 'books and drawings' would have much impact on bass absorption.

For sure lengthening/venting the room via symmetrical openings, either partially open or closed or fully open/closed will have some interesting and perhaps unexpected results. This is why it must be done.

I only need it to sound good at my listening chair, if not then I will move the chair a few inches (or slide a door open).

Records and books are known to be both absorbers and diffusers, at least according to Bobby Owsinski in the video below.

Bobby Owsinski - Improve the Sound of Your Room

Musician, Producer and Author, Bobby Owsinski (http://www.bobbyowsinski.com/) talks about acoustic theory, and how to affordably improve the sound of your room for under $150, prevent audio leakage and more.

Sure he's talking about mixing and recording studios, but many of the same principals can be applied to stereo and HT rooms.

 

[Hipper]

That video only seems to discuss absorption of the mid to high frequencies. I didn't notice anything about bass although I did skip through it a bit.

Here's a video about diffusion and the effect of book shelves.

There are a lot of myths about all this which are shown to be false.

Check out the other informative videos from this site:

http://realtraps.com/videos.htm

Bass issues are the toughest to deal with and usually require bass traps, a number of sub-woofers or DSP/EQ, or a combination of any of them.