What counts as "the room" in an open plan apartment?

[KenMasters]

This might be a stupid question, but I'll ask anyway - what counts as the room when you have a largely open living space?

This is the floor plan of my apartment. It's a surround system, but I've marked the MLP and L+R speaker positions for orientation:



Thinking in terms of RdT targets, what areas of the apartment should be included as the room? 1 being only the darkest shaded area, then expanding out to 4 (being all shaded areas).

I usually think of the room as primarily being the 1st area, given the proximity of the three surrounding walls, but the last reflection of significance comes off the wall in area 2 (stovetop location).

Add to that the wrinkle that when I close the door to area 4, infrasonic bass response is truncated by about 4Hz. The door there is usually open, but it does make me wonder what influence the downstairs area may also have.

So, how would you look at it, what would you consider "the room" when looking at RdT ranges as prescribed by room size?

 

[RayDunzl]

I have a rectangular room where the left rear is open to the kitchen area.

It affects the deep bass.

Mono bass creates a deep null around 48Hz.

Stereo bass may or may not excite the problem, as the recorded phase may be different between the channels.

Left, Right and Both speakers playing a test tone (mono), unsmoothed.

The waves at the listening position, centered around 48Hz, from left and right speakers, go 180 degrees out of phase around 48hz.

Analysis:

Your "room" extends as far as it can return sound to the listening position from some distant reflective surface.

I never noticed this problem before measuring, and still don't "hear" it musically.

So, ???

 

[KenMasters]

Analysis:

Your "room" extends as far as it can return sound to the listening position from some distant reflective surface.

I never noticed this problem before measuring, and still don't "hear" it musically.

So, ???

So, you would say that the entire open volume should be factored in when estimating target decay time?

 

[Keith_W]

So, you would say that the entire open volume should be factored in when estimating target decay time?

Yes. Bass is omnidirectional, it goes everywhere.

 

[Pareto Pragmatic]

Add to that the wrinkle that when I close the door to area 4, infrasonic bass response is truncated by about 4Hz. The door there is usually open, but it does make me wonder what influence the downstairs area may also have.

I think that effect is from the long distance along that wall, through the hallway, and back, so you are cutting out some long standing waves (shortening them) when you close that door. You might get a similar (larger?) effect if you open the door to the outside balcony/patio/whatever in space 4. Actually, you might have a standing wave from that hallway effect, bouncing off the bay window to the corner of the kitchen and back.

For me, with connected spaces but doorways and stairs and such as opposed to truly open space, I generally considered the end of my "room" to be where I hit -20db spl. That's through two doorways, or a doorway and a sharp direction change. So top of stairs is -10db from my MLP, but the other end of the space at the top of the stairs is -20db. Which should mean reflected sound that gets back to my MLP from that point will be -40db. As a rule of thumb when selecting a sub, that worked fine for me. If I just considered the actual spaces open to the sound, that would result in 2x the volume of space, and if I had enough sub for that 2x I would have wasted my money.

 

[RayDunzl]

So, you would say that the entire open volume should be factored in when estimating target decay time?

You can observe whether it seems to affect you or not.

I'd look at an extended impulse response and see where/when the bumps appear...

Black is my mains MartinLogan reQuest
Red is JBL LSR 308, adjacent to the mains.

Ballpark 1 foot per millisecond speaker to reflection/s to microphone and see if you can figure out where your reflections come back from.

There's not really anything to see further to the right on this graph.

When the level is low enough it becomes "don't care".

For the black trace, the one I care about:
1ms is the top of the sofa or the mic stand standing on it
4ms maybe a floor bounce
7ms is off the wall behind the speakers - they are dipoles
Then nothing to note until 27ms, which is the sound from the speakers hitting the wall above the absorption behind the couch, bouncing back to and off of the wall behind the speakers and back to the mic, as far as I can figure.
The little glitch at 32ms might be the dipole bounce following the same path as immediately above, 7ms after the main.

The red bumps/reflections are due to the wide dispersion of the JBL, so it gives bounces off the floor and walls and ceiling and whatever and I have no idea what the bounce at 33ms might be.

You can compare the linear (below) and decibel representations of the impulse response (not shown here).

The linear is better for finding an area (and time of reflection) than the decibel view.

The decibel view helps decide whether the reflection is within audible levels when compared with the main signal.

The MartinLogans seem to create inaudible reflections, the JBL's (in this relatively untreated room) fall into the middle range below:

I think these are reflection levels compared to the main signal level.

 

[Keith_W]

View attachment 370047

May I ask where you got this image? I just looked through my copy of Toole Ch 7 ("Above the transition freq") and Ch 10 ("Sound fields in reproduction spaces") and I could not find it.

 

[RayDunzl]

May I ask where you got this image?

It's in circulation... For better or worse...

A few hits:

Early Reflections 101

One of the most common “generic” acoustic treatment recommendations is to treat the reflection points. Unfortunately properly managing early reflected sounds is actually very complex psychoacoustically. Blindly treating reflection points with the wrong kind of products can make your sound worse...

acousticfrontiers.com

How do great sounding domestic listening rooms measure?

Speaker spinorama preference seems to be well understood in general, but what about the rooms? Is RT60 suitable for assessing liveliness of small room? What is the preference for RT60 curve? Should the curve be flat from 20hz to 20khz, or downward slope, etc? Do most prefer similar value for...

www.audiosciencereview.com

https://www.semanticscholar.org/paper/Master-handbook-of-acoustics-Everest-Pohlmann/25fc7fc3db69f4e77eabcf08b80b646ef44fa8c5/figure/31

 

[Keith_W]

It's in circulation... Fir better or worse...

Found it! That image attribution at the bottom of the image suggests it's in Toole. It's not, I found it in Ch. 6 of Alton Everest's "Master Handbook of Acoustics". Damn it, I did read that chapter. My brain is so leaky!

 

[RayDunzl]

My brain is so leaky!

So is mine, like when I come across some of the (claimed) 13,265 messages I've posted here, and don't remember at all...

Can it really be that many? I know that many say the same thing.

Un-bee-leeb-uh-bul.

 

[KenMasters]

You can observe whether it seems to affect you or not.

I'd look at an extended impulse response and see where/when the bumps appear...

The last notable reflection is off the kitchen wall (by the stovetop). So you would say when it comes to determining decay target range and such, the area up to 2 should be considered the room volume?

 

[Keith_W]

The last notable reflection is off the kitchen wall (by the stovetop). So you would say when it comes to determining decay target range and such, the area up to 2 should be considered the room volume?

Yes, I would use areas 1 and 2 as your nominal room size.

Bear in mind that all acoustic calculations that are dependent on room size, e.g. RT60 and Schroder, are approximations. They are there as a rough guide, not to be followed to the decimal point. If you want to know your actual RT60, or bass behaviour, measure it.

 

[KenMasters]

Yes, I would use areas 1 and 2 as your nominal room size.

Bear in mind that all acoustic calculations that are dependent on room size, e.g. RT60 and Schroder, are approximations. They are there as a rough guide, not to be followed to the decimal point. If you want to know your actual RT60, or bass behaviour, measure it.

Since it's a living-room, there's only so much I can do while keeping things aesthetically pleasing. I think it's pretty fair, but it is why I was curious as to what counts as the room volume, to get a better sense if my room is in the right ballpark:

 

[Keith_W]

Here you go. I used your room dimensions and used Acourate to calculate the appropriate RT60 targets for your room. Acourate requires a sweep as an input, so I used one of my sweeps. Ignore it, just look at the target.

Your room is slightly smaller than the dimensions that I used as inputs, because Acourate's RT60 calculator assumes you have a rectangular room. This means that the RT60 targets will be slightly lower, but not by much.

 

[RayDunzl]

The last notable reflection is off the kitchen wall (by the stovetop). So you would say when it comes to determining decay target range and such, the area up to 2 should be considered the room volume?

I'm no expert, nor do I play one on the Daytime Soap Operas (are they still a thing?).

If the time and decibel level (relative to the direct sound) are above the "reflection inaudible" time and level from the chart above fall into anything but the "reflection inaudible" range, you might investigate.

Mine:

JBL red
MartinLogan black

Reflection SPL (negative dB) vs Direct Sound (0dB)

Analysis:

ALL of the reflections created by the room from the MartinLogans (beamy devils that they are) fall into the "inaudible" range, and about 10dB difference across the graph compared to the little JBLs.

SOME of the JBL reflections fall into the audible area - "Spaciousness or Image shift".

I find the ML razor sharp at the listening position, the JBL much fuzzier, to the point that at one time we weren't sure if one was polarity reversed or not. It wasn't.

Don't care, because the little JBLs are the econobox daily drivers for TV/Radio/PC whatever, and the MartinLogan/Krell choice is for attentive listening or excessive SPL (700watts available) when that comes up in the schedule.