Acoustics Service at Kvålsvoll Design

[Kvalsvoll]

Acoustics Service at Kvålsvoll Design

Working on loudspeakers and sound systems has over the years lead to both practical and theoretical knowledge on how to create rooms with good acoustic properties.

This is now made available as a service:
https://www.kvalsvoll.com/Services/roomacoustics_en.htm

You get to see what it takes to fix the room, with rendered images like this:

This room now looks like this:

Choose between 2 options; complete fix, or just a quick assessment.

Acoustics Project:
https://www.kvalsvoll.com/Services/roomacoustics_en.htm#5

Complete guide for acoustic treatment

We fix your room. Starting from specification, we design it and make a 3D-model of the room, it is built and implemented, then we do evaluation, and make adjustments if needed.


Mini Acoustics Project:
https://www.kvalsvoll.com/Services/roomacoustics_en.htm#6

Quick assessment of acoustic treatment.

You get to see a proposal for acoustic treatment of your room, with overview picture and selected views from inside the room.


For contractors/interior designers/home renovators:

Use our Acoustics Service to deliver complete solutions for rooms. With state-of-the-art acoustic performance, at reasonable cost, it will also look great.

You have the tools, skill and manpower to build this.

 

[Kvalsvoll]

How to validate acoustic performance from measurements

A customer who did a Mini-Acoustics Project had 2x T140 installed, and during the calibration process, I noticed he had fixed the room already, and that it worked very well, a bit towards dead for music perhaps, overall quite good. How can I tell?

I look at decay, with 20ms slice interval, 1ms rise time. How much does the sound drop in level during first 20ms:

Around 20dB down at 20ms, and that is very good.

Then I look at frequency response slope of the decay lines, want a flat, smooth response that does not rise much in the low mids, and does not drop off in the highs:

Reasonably good. Now this is a quite small room, so some deviations from flat is to be expected. Note that the first line, the first direct sound arrival, does not necessarily show a correct frequency response due to to the 1ms rise time, because it may be too short.

Then I look at the decay in low mid in approx. 100Hz - 1KHz range, to see if all resonances are gone and decay is controlled and does not rise:

A room with insufficient damping at lower frequencies tend to show an increase in decay towards low mid frequencies.

Other graphs can be nice to look at, but they do not necessarily show much more information about acoustics that already verified in the decay analysis.

GD- group delay, note scale 120ms, NOT 1.0s or something similar that would only show a perfectly flat line:

IR, impulse response, is popular to look into, tells something about reflections towards higher frequencies:

IR: Good rooms tend to have a fast, huge initial drop, and then a bit later reflection level rises, before it continues to drop.

Spectrogram is a nice way to visualize what happens in time and also see room decay frequency distribution, note scale time range is 100ms NOT 1s or even more, scale range is 40dB:

RT60 measures like this, and tells nothing about the acoustic performance of this room, so please stop using RT60 numbers as specification or performance indicator for acoustic performance of small rooms:

 

[janbth]

RT60 measures like this, and tells nothing about the acoustic performance of this room, so please stop using RT60 numbers as specification or performance indicator for acoustic performance of small rooms:

What is the problem with the RT60 plot? It seems to be consistent with the other graphs.

 

[ernestcarl]

Alternatively, one could also move the reference time to 20ms (and Left window width to zero -- or very close to zero)

Full vs Late FR

*Couch Left BM channel


0.1ms Rise Time

*Too much uneven absorption in the HF? -- yeah, possibly... But that's okay, since I have other ways of dealing with it.

 

[Kvalsvoll]

Alternatively, one could also move the reference time to 20ms (and Left window width to zero -- or very close to zero)

View attachment 284691

Full vs Late FR
View attachment 284692
*Couch Left BM channel


0.1ms Rise Time
View attachment 284693
*Too much uneven absorption in the HF? -- yeah, possibly... But that's okay, since I have other ways of dealing with it.

Most important is to be aware that the 1. line does not necessarily match the normal/full-window frequency response. Easy to fix by changing windows, or simply look at the frequency response chart instead.

 

[Kvalsvoll]

What is the problem with the RT60 plot? It seems to be consistent with the other graphs.

Does not show the important aspects, such as early decay attenuation.

There are threads also on this forum where RT60 and why it is not a good measure for small room acoustics has been explained, so instead of repeating all that, see if you can find any of those excellent answers already written by others. Also makes it more convincing reading the same information from different sources.

 

[Trdat]

So just to understand this correctly you say the second line(20ms) in the decay graph has reduced by 20db and that is good. So the goal is for it to be more than 20db? Is that the gap your always talking about?

I am just confused on if it should be longer or shorter the second line?

 

[ernestcarl]

So just to understand this correctly you say the second line(20ms) in the decay graph has reduced by 20db and that is good. So the goal is for it to be more than 20db? Is that the gap your always talking about?

I am just confused on if it should be longer or shorter the second line?

Suppose the "idealized" room response should not have much strong reflected energy coming back from surrounding boundaries up to around 20ms (by how much exactly? I dunno) :

The way I personally deal with what I feel is missing... or how to alternatively add later "diffuse reflections" is via additional speaker channels and DSP -- simpler, though, fundamentally not all too different to what @Wesayso does in his more elaborate setup.

 

[Trdat]

So the 20ms line is the first reflection and if we desire an attenuated first reflection the bigger the gap between the first line and the second is preferred. I think I got this the right way around.

I am presuming it is hard to achieve this in a small room.

Wesayso is using a plugin so he is adding reverb to a track that is playing in Jriver?

 

[ernestcarl]

So the 20ms line is the first reflection and if we desire an attenuated first reflection the bigger the gap between the first line and the second is preferred. I think I got this the right way around.

I am presuming it is hard to achieve this in a small room.

Wesayso is using a plugin so he is adding reverb to a track that is playing in Jriver?

It just shows a “slice” of the late frequency response (a portion of the spectral decay) in time.

Reverb is added — not necessarily to the direct mains loudspeaker sound — but to the delayed and highly attenuated secondary (e.g. surround) channels.

In very small rooms it is not so easy…
The corner seats of my room’s couch, for example, only has about a foot or more before one’s ear gets the reflections from the direct adjacent sidewall.

 

[Kvalsvoll]

So the 20ms line is the first reflection and if we desire an attenuated first reflection the bigger the gap between the first line and the second is preferred. I think I got this the right way around.

I am presuming it is hard to achieve this in a small room.

Wesayso is using a plugin so he is adding reverb to a track that is playing in Jriver?

Big gap is preferred, but not necessarily significant once beyond a certain attenuation level. The "good" rooms tend to show a reduction around -15dB to -20dB after 20ms. Untreated room with good speakers can have say -5dB to -6dB attenuation, and this difference is very measurable and very audible.

20ms after first direct sound is not only first reflection, it is all sound that has reflected inside the room between all surfaces and has a total travel time >20ms.

It is not very difficult to achieve -20dB after 20ms in small rooms, it is more difficult to keep sufficient later energy. Too little late energy can make the room sound very dry.

 

[ernestcarl]

I’ve gotten used to “very dry” myself over the years — so it’s no longer an issue for me — but, it can definitely give a better feeling of natural envelopment and seamlessness when moving about and turning around one’s head if there’s a bit more late diffuse reflections/reverb in the room space.

 

[Wesayso]

Wesayso is using a plugin so he is adding reverb to a track that is playing in Jriver?

Only on ambient channels. No reverb is added to a song or track on main channel(s).

I have absorbing panels at all mayor first reflection points, to reduce the room signature, and use ambient channels to re-create a feel of a bigger/better space.
It hides the real room and makes the listening more enjoyable, while stealing the first reflections makes sure I get to hear a clear clean direct sound.
You don't notice the ambient channels by themselves, unless they are turned off.
Their level is way below the mains and they don't play any louder than a real untreated room would be. They do mess with perception though, in a good way.

My biggest inspiration for this were a user named werewolf/lycan at diymobileaudio.com and diyaudio.com and the many papers/video's from David Griesinger.

 

[Kvalsvoll]

Only on ambient channels. No reverb is added to a song or track on main channel(s).

I have absorbing panels at all mayor first reflection points, to reduce the room signature, and use ambient channels to re-create a feel of a bigger/better space.
It hides the real room and makes the listening more enjoyable, while stealing the first reflections makes sure I get to hear a clear clean direct sound.
You don't notice the ambient channels by themselves, unless they are turned off.
Their level is way below the mains and they don't play any louder than a real untreated room would be. They do mess with perception though, in a good way.

My biggest inspiration for this were a user named werewolf/lycan at diymobileaudio.com and diyaudio.com and the many papers/video's from David Griesinger.

This can be a good solution, because it simplifies acoustic treatment, not so important to keep late reverb. And it is adjustable.