A Broad Discussion of Speakers with Major Audio Luminaries

[j_j]

The supposed way to do this is to play pink noise and use an SPL meter. Starting at the speakers, slowly walk away. When the SPL stops dropping, you are at the critical distance.

Bear in mind that the critical distance varies with frequency. Higher frequency = shorter critical distance. So you might get better results by playing test tones instead of pink noise.

TDR works better. When you find the point that the level stops dropping that's too far. You want to go back until the level is 3dB above that constant level. Various effects often make this a tragic problem.

 

[Sokel]

Genelec has a chart about it based both at room volume and speaker size:

https://downloads.ctfassets.net/4zjnzn055a4v/59uPaa9QITsA6tsqhlOv5T/8254aa9ca070ecd1090ecd16b202396b/Monitor_setup_guide_BBAGE125e-lightweight.pdf

 

[j_j]

Genelec has a chart about it based both at room volume and speaker size:

View attachment 477287

https://downloads.ctfassets.net/4zjnzn055a4v/59uPaa9QITsA6tsqhlOv5T/8254aa9ca070ecd1090ecd16b202396b/Monitor_setup_guide_BBAGE125e-lightweight.pdf

Which depends massively on speaker, room treatments (walls,floor, ceilings, furniture, number of people, loudspeaker radiation pattern, and sometimes a partridge in a pear tree. At least if you assume a given speaker (as Genelec has done) and one listener, and you assume a typically treated studio, you're probably doing ok.

However, in general, I'd call it "a good start".

 

[Suono]

Which depends massively on speaker, room treatments (walls,floor, ceilings, furniture, number of people, loudspeaker radiation pattern, and sometimes a partridge in a pear tree. At least if you assume a given speaker (as Genelec has done) and one listener, and you assume a typically treated studio, you're probably doing ok.

The Genelec graph, which I wasn't familiar with, so thanks to whoever posted it, confirms my opinion. Some acoustic laws/rules that apply to live music, large auditoriums, cannot be considered for high fidelity. Having a room larger than 55 square meters to listen to high fidelity in stereo is a rarity.
So talking about critical distance seems pointless to me.

However, in general, I'd call it "a good start".

The Genelec graph, which I wasn't familiar with, so thanks to whoever posted it, confirms my opinion. Some acoustic laws/rules that apply to live music, large auditoriums, cannot be considered for high fidelity. Having a room larger than 55 square meters to listen to high fidelity in stereo is a rarity.
So talking about critical distance seems pointless to me.

 

[rdenney]

In a very live space, it can be surprisingly short. In a large open area, it can be rather a few meters or more.

It would be better to say "ratio of power of direct to all indirect signals". In modern terms it's a bit dated, but it's still a useful measure for places that do not have massive specular reflections. Specular reflections FSCK everything up. 1 means critical distance. Below 1 is in reverberant spaces. well above one is 'near field'. Rather than using the ratio, though, it's usually expressed as "n times the critical distance" which scales more accurately to "perceived distance", GIVE OR TAKE.

To explain, using voice in the old Bell Labs anechoic chamber, you always sound like you're INSIDE THE OTHER GUY'S HEAD when they talk to you, that's because beyond reflection of their body and yours, there is no indirect sound to speak of (well, down a LOT of dB). The critical distance there is above the diagonal of the 40x40 horisontal diagonal. In a small, hard-surfaced space, the critical distance may be a foot. That space will s**k for speech communication.

When I chose the speakers for the sound system in my church, the critical distance was-er-critical. The room is about 60 feet deep including the balcony, and the critical distance is about 15 or 20 feet. Beyond that, specular highlights smear to the point of unintelligibility with many (human) speakers. I needed loudspeakers with a pattern that would punch specular highlights to the back of the room with limited reflection. (The RTA60 of the room is 3-4 seconds—quite reverberant). (I used JBL CBA-50’s.)

I’m thinking specular highlights are the articulations of consonants in speech. When they reflect noticeably, I hear it as echo. Echoey is totally not the same as reverberant. The church has a curved ceiling (24 feet at the peak) which adds reverberant volume but not echo. Reverberation buries the specular highlights. It’s a great room for music, and it was easy to fix for speech.

Rick “the front three pews don’t need the sound system” Denney

 

[NTK]

The Genelec graph, which I wasn't familiar with, so thanks to whoever posted it, confirms my opinion. Some acoustic laws/rules that apply to live music, large auditoriums, cannot be considered for high fidelity. Having a room larger than 55 square meters to listen to high fidelity in stereo is a rarity.
So talking about critical distance seems pointless to me.

The numbers in the Genelec chart is for room volume, which starts at 55 m³, and is not too far off from many domestic listening room.

Why is the distance that (roughly) separates direct field listening and reverberant field listening pointless in a listening room?

 

[Suono]

[QUOTE="NTK, post: 2403877,
Why is the distance that (roughly) separates direct field listening and reverberant field listening pointless in a listening room?
[/QUOTE]
you're right, I read it wrong, you're always in a reverberant field

 

[Keith_W]

TDR works better. When you find the point that the level stops dropping that's too far. You want to go back until the level is 3dB above that constant level. Various effects often make this a tragic problem.

Thanks JJ. I have a couple of questions:

1. What is TDR?
2. Does the critical distance exist in small rooms? I am under the impression that crit distance requires a reverberant field, and there are no reverberant fields in small rooms, only specular reflections.

 

[j_j]

When I chose the speakers for the sound system in my church, the critical distance was-er-critical. The room is about 60 feet deep including the balcony, and the critical distance is about 15 or 20 feet. Beyond that, specular highlights smear to the point of unintelligibility with many (human) speakers. I needed loudspeakers with a pattern that would punch specular highlights to the back of the room with limited reflection. (The RTA60 of the room is 3-4 seconds—quite reverberant). (I used JBL CBA-50’s.)

I’m thinking specular highlights are the articulations of consonants in speech. When they reflect noticeably, I hear it as echo. Echoey is totally not the same as reverberant. The church has a curved ceiling (24 feet at the peak) which adds reverberant volume but not echo. Reverberation buries the specular highlights. It’s a great room for music, and it was easy to fix for speech.

Rick “the front three pews don’t need the sound system” Denney

This is actually why 'critical distance' can mislead. The ratio of energy is only part of the story. Coherent additions with large delays (specular reflections, i.e. echoes) can utterly destroy articulation, as you point out. It being a church, you probably can't go hanging diffusors on the walls, but you know all that detail on cathedral walls? That's all diffusion,and makes the articulation way back THERE much better. You can make a room with a 4 second t60 have good articulation, or zero articulation, depending on how much of the reverberation is diffuse, and how much is coherent.

Which is why I am considering a talk on matlab scripts to measure room impulse response for January. This kind of problem shows up gloriously in the analytic envelope of an impulse response.

 

[Thomas Lund]

Which depends massively on speaker, room treatments (walls,floor, ceilings, furniture, number of people, loudspeaker radiation pattern, and sometimes a partridge in a pear tree. At least if you assume a given speaker (as Genelec has done) and one listener, and you assume a typically treated studio, you're probably doing ok.

Right. The illustration only serves as a priori guidance, based on 200 Hz - 4k average.

This actual measurement is more relevant, attached. It's per monitor in a specific room at the listening location. Here an 8351B in a temporary listening room, in relation to the AES Helsinki conference last month.

 

[Neadych]

I will repeat the question.Will there be a significant difference, and what kind of difference, between a large and a small full-range system with a flat frequency and good directivity, and other significant characteristics, standing in a room in turn, where the small system maximizes its potential? The large system is placed at a distance where the small system's radiation bands are well combined. If there are other conditions for aligning the two systems, they are also met.

 

[Keith_W]

I will repeat the question.Will there be a significant difference, and what kind of difference, between a large and a small full-range system with a flat frequency and good directivity, and other significant characteristics, standing in a room in turn, where the small system maximizes its potential? The large system is placed at a distance where the small system's radiation bands are well combined. If there are other conditions for aligning the two systems, they are also met.

Your question is too vague to be answered. Of course there will be differences, but without knowing what you mean by "large" and "small" we can't get into specifics.

 

[Neadych]

Your question is too vague to be answered. Of course there will be differences, but without knowing what you mean by "large" and "small" we can't get into specifics.

Okay, let's look at the Genelec chart above.
Let's take the 8340 monitors with the 7370 subwoofer and compare them to the 1234 monitors. The room will be 60 m³ and the distance from the monitors to the listening position will be 1.9 m, with a reverberation time of 0.22 s.

 

[Keith_W]

The Genelecs are all the same, they only vary in maximum SPL and bass extension.

 

[dagfinn]

The Genelecs are all the same, they only vary in maximum SPL and bass extension.

Except dynamic power, 4x12" with 4x750w (and more) will outperform the 2x8340+subs hugely all the way to the crossover point to tweeter. The 7370a will go lower, and would be a good match for 1234a under 35Hz. But there are other advantages in bigger speakers too, like less distortion at louder levels, the detail in every frequency range, instrument separation asf. - it's just another level. Tonality will be very similar, but all the same, no .

 

[Neadych]

Will the 1234's dynamic power advantage at 1.9m in the mid-high frequency range be realized compared to the 8340?
And also, at low frequencies, four 12" 1234s versus a single 12" 7370 in a 60m³ room?

 

[dagfinn]

You should go somewhere and listen. Start with 1237a, it is also a much more powerful dynamic speaker then the 8340. The 7370 will go much lower, great sub. But most of the program content will be higher in range, and the explosive dynamic power and punch is not found below 30Hz. But I'm not talking only big and loud, the dynamic detail you get at 80-85dB listening level is a different experience. At 1,9m the 1234 will be totally immersive.

 

[Neadych]

You should go somewhere and listen. Start with 1237a, it is also a much more powerful dynamic speaker then the 8340. The 7370 will go much lower, great sub. But most of the program content will be higher in range, and the explosive dynamic power and punch is not found below 30Hz. But I'm not talking only big and loud, the dynamic detail you get at 80-85dB listening level is a different experience. At 1,9m the 1234 will be totally immersive.
View attachment 478614

And will 1235 create more complete immersion from 1.9m?

 

[dagfinn]

More than totally?

 

[Neadych]

A 1235 will create a more complete immersion from 1.9m, as it is even more powerful and has even less distortion.At what distance and in what room volume can I achieve a complete immersion with an 8340 and a 7370 at an average level of 85 dB? Or is this impossible?What is the maximum distance for a complete immersion with a 1234?What is the distortion level required at the listening location at an average level of 85 dB, and how many dB peaks and how much distortion should be present for the best sound?