Why are speakers measured at 1 meter?

[localhost128]

have you clicked the link I posted below that post you are responding?
we hear the room below 800-1000Hz-ish.
you can do a simple test with a tone generator. run a sine wave at let's say 100Hz and move in you room. how come there will be HUGE variations in SPL? because you are not hearing direct sound. you can actualy find frequencies where the SPL directly in front of the sepaker will be quite low, and huge elsewhere in the room. play around with a tone generator since it will show you so much about your room in general

i think you're confused and/or don't quite understand just what the term critical-distance (Dc) entrails/implies.

what you're describing above for simple modal resonances (eg, 100hz) is their inherent localized behavior. localized as in the pressure wave has a vector/direction component (nodes/antinodes for an axial mode, for example) - completely contradictory to the acoustical definition of reverberant sound-field (random/diffuse-incidence; ie, no direction). to even infer 100hz in this discussion is completely erroneous and not valid in the context of critical-distance (Dc).

the link you provided is a calculator, not a measurement or direct, objectionable data that confirms what the user said above that in a normal room, Dc somehow exists at a mere 1meter from the loudspeaker/source - and thus implying at distances beyond (2,3,4meter), the indirect sound-field would completely dominate that of the direct signal. this just simply does not happen and hence why objective data to support the claim was requested.

and added as to what the other user claiming (without any data to support) that "Otherwise statistical properties set in in just about every room at a few hundred hertz above transition frequencies" (ie, 450hz+).

we do not apply absorption statistically in Small Rooms (normal, residential-sized rooms) a few hundred hz above transition frequency (~450hz) because no statistical sound field exists. it is all localized behavior with direction (ie, indirect specular reflections that can all be measured/resolved/and traced back to their incident boundary). ie, we place absorption or other treatment at reflection points to surgically address specific indirect signals - not randomly applying absorption within the room to bring down the Reverberation Time (implying homogeneous sound-field equal throughout the room). statistical equations are not applied in small rooms because the physical characteristics of the sound-field don't exist. they are Large Room equations, not meant/valid for use in Small Rooms. garbage in = garbage out, as i was taught in university.

what i'm starting to question now from this conversation is whether anyone commenting against the basic understandings/foundations of acoustics has even stepped foot and done any analysis in concert halls, auditoriums, churches, etc and other Large Acoustical Spaces that exhibit a reverberant sound field and critical-distance (Dc) that is easily perceived.

but i will gladly be open to reconsider if objective measurements can be provided that show a critical-distance (Dc) at 1meter from loudspeaker, and that at 450hz and about in "just about every room" such is valid/relevant. even from a subjective-perception perspective, it should be easy: listen to your loudspeaker or television set or radio or any other noise-generating device in a "normal" residential/living room and determine if at 1meter (~3ft) the indirect sound-field is equal in gain to the direct signal - and when walking 2,3,4 meters and with your back against the rear wall of the room whether the indirect sound-field completely dominates in magnitude over the direct signal to the point where perception of the direct signal is becoming lost.

 

[dasdoing]

i think you're confused and/or don't quite understand just what the term critical-distance (Dc) entrails/implies.

what you're describing above for simple modal resonances (eg, 100hz) is their inherent localized behavior. localized as in the pressure wave has a vector/direction component (nodes/antinodes for an axial mode, for example) - completely contradictory to the acoustical definition of reverberant sound-field (random/diffuse-incidence; ie, no direction). to even infer 100hz in this discussion is completely erroneous and not valid in the context of critical-distance (Dc).

the link you provided is a calculator, not a measurement or direct, objectionable data that confirms what the user said above that in a normal room, Dc somehow exists at a mere 1meter from the loudspeaker/source - and thus implying at distances beyond (2,3,4meter), the indirect sound-field would completely dominate that of the direct signal. this just simply does not happen and hence why objective data to support the claim was requested.

and added as to what the other user claiming (without any data to support) that "Otherwise statistical properties set in in just about every room at a few hundred hertz above transition frequencies" (ie, 450hz+).

we do not apply absorption statistically in Small Rooms (normal, residential-sized rooms) a few hundred hz above transition frequency (~450hz) because no statistical sound field exists. it is all localized behavior with direction (ie, indirect specular reflections that can all be measured/resolved/and traced back to their incident boundary). ie, we place absorption or other treatment at reflection points to surgically address specific indirect signals - not randomly applying absorption within the room to bring down the Reverberation Time (implying homogeneous sound-field equal throughout the room). statistical equations are not applied in small rooms because the physical characteristics of the sound-field don't exist. they are Large Room equations, not meant/valid for use in Small Rooms. garbage in = garbage out, as i was taught in university.

what i'm starting to question now from this conversation is whether anyone commenting against the basic understandings/foundations of acoustics has even stepped foot and done any analysis in concert halls, auditoriums, churches, etc and other Large Acoustical Spaces that exhibit a reverberant sound field and critical-distance (Dc) that is easily perceived.

but i will gladly be open to reconsider if objective measurements can be provided that show a critical-distance (Dc) at 1meter from loudspeaker, and that at 450hz and about in "just about every room" such is valid/relevant. even from a subjective-perception perspective, it should be easy: listen to your loudspeaker or television set or radio or any other noise-generating device in a "normal" residential/living room and determine if at 1meter (~3ft) the indirect sound-field is equal in gain to the direct signal - and when walking 2,3,4 meters and with your back against the rear wall of the room whether the indirect sound-field completely dominates in magnitude over the direct signal to the point where perception of the direct signal is becoming lost.

ok, I am probably not competent enough to respond you, or it would require for me to research.
the link I provided is from @jlo's webpage. maybe he wants to contribuite

 

[localhost128]

Because 1 meter in a normal room is just about the ”critical distance” where the mic takes up 50% of reverb sound and 50% direct sound from the loudspeaker.

Only if you want it to extend down to 20 Hz. Otherwise statistical properties set in in just about every room at a few hundred hertz above transition frequencies.

are these claims going to be substantiated with any objectionable, measured-data?

 

[Tim Link]

One thought I've had about this is that even if we're listening in an anechoic environment, the speaker's on-axis response will change with distance, even if it's a virtual point source, if the directivity isn't perfectly flat. If its directivity is beamier up top, its on axis response will tilt upward in the treble as you move further away. So it would be good to know what the distance is that the speaker will have flat anechoic response on-axis. If you are not at that distance, you might consider EQing the speaker's direct response to compensate for that. Really cool would be a powered speaker that lets you set that listening distance and re-tunes the speaker accordingly.

I'm assuming here that we really do want the direct anechoic response at the listening distance to be flat and smooth.

I've been measuring my individual horns at 1 meter or less to establish flat quasi-anechoic response and crossover curves, only to find that these don't hold at the listening position. The lower frequencies droop with distance. So now I know I cannot cross the tweeter horns as low as I was. They can't project that to my chair without ridiculous amounts of EQ.

A 2 meter measuring distance is a reasonable bet for most home floor standers because effects of uneven falloff rates due to distance will be lessened overall in most rooms, so the change from 2meter to 2.5 or 3 meters won't be so bad as if the speaker were adjusted flat at 1 meter. A near field monitor should be measured and adjusted closer.

My attempt this evening to get flat response at the listening position using windowing at about 7 cycles looks pretty promising so far. If I turn off the windowing and smooth the response I'm seeing a nice smooth, constant downward tilting slope, which suggests I'm probably close to something reasonably correct. That's the midrange and HF horns. Tomorrow I have to think about how to integrate the bass cabinets, which take over from 300 Hz down. My inclination is just to match the non windowed response curve from there on down. Or I could try windowing the bass the same way, and then see what happens when I turn the windowing off and smooth the overall response.

 

[thewas]

One thought I've had about this is that even if we're listening in an anechoic environment, the speaker's on-axis response will change with distance, even if it's a virtual point source, if the directivity isn't perfectly flat. If its directivity is beamier up top, its on axis response will tilt upward in the treble as you move further away.

Why would such happen? The direct sound only changes at higher distances due to the air absorption of the higher frequencies.

My attempt this evening to get flat response at the listening position using windowing at about 7 cycles looks pretty promising so far.

Yes, because above the bass response we tend to prefer a flat direct sound which together with the reflected sound gives depending on the directivity of the loudspeakers and absorption of the room a decreasing total non-gated response.

 

[gnarly]

Any loudspeaker SPL online calculator don't say it explicitly but there is an implicit ANECHOIC assumption. They use the inverse square law for distance attenuation....so please, forget about reflections! diffuse field or whatever!
Happy new year!
P.S.: the calculated frequency response is anechoic too, ...or with gated response in a room. Designers don't bother with "your" particular room

yeppa !!! Critical distance is an irrelevant topic in this thread....heck, ROOMS are irrelevant in this thread.

Sensitivity @ either 1W, or better 2.83V, @ 1m is simply a normalization technique, for comparison purposes.
Made in either anechoic chamber or free-field measurements ... no damn room involved!! (Only thing that needs knowing is whether measurement is full-space, or half space.)

Actual measurement distance can be any distance that is in the acoustic far field (as some have said, where SPL falls at inverse square law vs distance and phase summations have settled down)
Then it's simply normalized to 1m with a calculator like this..https://sengpielaudio.com/calculator-distance.htm

Interestingly, it typically takes more distance to get into the acoustic far field for high frequency, than for low. https://www.prosoundtraining.com/2010/06/28/far-field-criteria-for-loudspeaker-balloon-data/
(Shows how really cool the Klippel NFS is, which has the mathematics behind it, to extract far-field projections, from near-field scans.)

A rule of thumb for getting into the acoustic far field is that measurement distance should be at least 3X longest speaker dimension.

IMO, CEA 2034's "measure at 2m", rather than assuring being at 3X speaker in the acoustic far field, reflects the market the spec was written for......
....home audio speakers, and on the smaller end of the size spectrum.
Or, maybe assumes you have a NFS

 

[Tim Link]

Why would such happen? The direct sound only changes at higher distances due to the air absorption of the higher frequencies.

Directivity changes fall off rate. If you have a more planar wave front at some frequencies it's not going to act like a point source as much in those regions, so the fall off rate will be slower. I know this is true because I can measure this effect directly. You will only get a flat anechoic on axis response at one particular distance if the directivity is not perfectly constant.

I should modify this slightly because directivity doesn't have to change fall off rate. If a good CD horn is launching a spherical wave front, but only a section of it, then it will have the same fall off rate as a point source. If directivity is narrowing because of the driver getting big relative to the wave length, or a horn launches a flatter wave front, then that will change the fall off rate.