Why are speakers measured at 1 meter?

[gags11]

I’m sorry to post this as a separate thread. But I think there may be many like myself, who wonder why speakers are specked at a meter distance. I also want to say that I am not in any way close to engineering, so excuse me.

First, I understand that if we have a single driver or a book shelf speaker, a 1 meter measurement frequency curve may mean something. What I am curious about, is how say a 60 inch tall speaker measurement at 1 meter have true relevance at 5 meter listening level.

Who came up with this? My non-scientific gut tells me floor standing speakers measured at 2-3 nesters would be more relevant. Would appreciate if you can educate me.

 

[pma]

I’m sorry to post this as a separate thread. But I think there may be many like myself, who wonder why speakers are specked at a meter distance. I also want to say that I am not in any way close to engineering, so excuse me.

First, I understand that if we have a single driver or a book shelf speaker, a 1 meter measurement frequency curve may mean something. What I am curious about, is how say a 60 inch tall speaker measurement at 1 meter have true relevance at 5 meter listening level.

Who came up with this? Thank I say floor standing speakers measured at 2-3 nesters would be more relevant. Would appreciate if you can educate me.

The problem is the in-room measurement with all reflections (reflected delayed sound) and room modes. 1m is probably meant as a compromise. You are right that in case of tall speakers with many drivers it does not make much sense. Even in case of smaller speakers the response has to be combined from near-field measurement (woofer) and 1m measurement (midrange and treble area). The first reflection (usually floor reflection) usually arrives in about 3ms so the range below 300Hz (approx.) is to be measured in woofer near-field.

 

[carlosmante]

I’m sorry to post this as a separate thread. But I think there may be many like myself, who wonder why speakers are specked at a meter distance. I also want to say that I am not in any way close to engineering, so excuse me.

First, I understand that if we have a single driver or a book shelf speaker, a 1 meter measurement frequency curve may mean something. What I am curious about, is how say a 60 inch tall speaker measurement at 1 meter have true relevance at 5 meter listening level.

Who came up with this? My non-scientific gut tells me floor standing speakers measured at 2-3 nesters would be more relevant. Would appreciate if you can educate me.

A short answer could be:
1)The metric system is an Universal reference used un Science.
2) The metric system offers a high "degree of coherence".
3) Electric and Acoustical measures are based in the International System of Electrical and Magnetic Units that is also based on the meter, kilogram and second.

 

[gags11]

A short answer could be:
1)The metric system is an Universal reference used un Science.
2) The metric system offers a high "degree of coherence".
3) Electric and Acoustical measures are based in the International System of Electrical and Magnetic Units that is also based on the meter, kilogram and second.

Agree with metric argument, but why 1 meter? May be I’m being to cynical, do true anechoic measurements at 3 meters line up with the 1 meter measurements for a tall floor standing speaker? I understand that some will be really close, ones that have great vertical dispersion pattern

 

[thewas]

Don't be fooled by the sensitivity rating at 1 meter, most loudspeakers manufacturers don't mention at which distance they measure, often they measure at 2 meters and just recalculate the sensitivity to the 1 meter standard.

 

[Ziltoe]

Hej, [.../] ...often they measure at 2 meters and just recalculate the sensitivity to the 1 meter standard. [\...] interesting, from where did you take that?

 

[thewas]

Hej, [.../] ...often they measure at 2 meters and just recalculate the sensitivity to the 1 meter standard. [\...] interesting, from where did you take that?

One example https://www.audiosciencereview.com/...-dsp-monitor-review.11018/page-16#post-312179 you can find more in the web.

 

[dasdoing]

it's probably a standard from when (true) anechoic chambers where not widely available?
1m seams to be the closest you can get without seperating the drivers

 

[Ellebob]

I don't know where it comes from but it is common to measure at 2 meters and calculate things like sensitivity to 1 meter. The reason is 1 meter is fine to measure if it is a small speaker like most bookshelf type speakers. But larger speakers like towers won't have good driver integration at 1 meter so the frequency measurements will not be accurate for a larger speaker at 1 meter. In those instances it is measured at 2 meters and sometimes further.

 

[wwenze]

Because "1" is easier to use as a starting point to calculate SPL

e.g. 2m? Means double the distance = 6dB less SPL

 

[Tangband]

Agree with metric argument, but why 1 meter? May be I’m being to cynical, do true anechoic measurements at 3 meters line up with the 1 meter measurements for a tall floor standing speaker? I understand that some will be really close, ones that have great vertical dispersion pattern

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. If you measure from 30 cm distance, the mic will measure about 70% direct sound and about 30 % reverb sound from the room. If you are to near the loudspeaker when measuring, you dont measure the impact of the baffle, wich can be huge. So 1 meter is a good compromise, and using gating technique at 5 ms in a normal room is also good when measuring.

Further, in a distance longer than 5 ms sound travel, meaning more than 1,7 meter, the mic will take up ALL information while the ear/brain starts to selecting sound. Its because of the ”precedence effect ” .

Thats why measurements from the listening place 3 meter away with two loudspeakers at the same time can be really misleading, because :

1. You are measuring the room 80 % and the loudspeaker 20 % - because of the ”critical distance” in the room.
2. The measuring results no longer tells the thruth about how it sounds, ”the precedence effect” kicks in after 1,7 meter and longer of distance from the loudspeaker, when you listen to real music.
3. You get comb filtering effects measuring two loudspeakers at the same time.

The most important thing to remember is that the ear/brain and mic works entirely different at a distance of more than 1,7 meter.
The mic monitors all sound, -the ear/brain selects sound.

 

[anmpr1]

Don't be fooled by the sensitivity rating at 1 meter, most loudspeakers manufacturers don't mention at which distance they measure, often they measure at 2 meters and just recalculate the sensitivity to the 1 meter standard.

In his 'mass market, popular oriented' reviews, J. Hirsch (Stereo Review) was measuring harmonic distortion at one meter, comparing the distortion at 1 and 10 watts input, but not reporting SPL, per se. In an October 1971 article he listed the practical problems of citing a single sensitivity figure--room interaction, FR variations, loudspeaker design differences and so forth. Hirsch argued that the most important SPL related criterion for a consumer was loudspeaker distortion--how loud can it play before objectionable distortion sets in--and not simply the box's sensitivity at one watt/meter, or some other arbitrary measurement standard. Accordingly, he gave 'rounded off' power related suggestions in his reviews--whether the speaker needed low, moderate, or high power in a typical living room setting. I think it was roughly 15 to 40, 40 to 60, and more than 60 watts per channel. The JBL L100, AR3a, and AR LST were corresponding examples. Remember, those were days before the prevalence of high powered amps.

By 1974 he sometimes reported sensitivity at 'mid frequencies'. For instance the Avid 103 (a semi-popular mass market loudspeaker from that era) measured 90dB at one watt/meter (April 1974) whereas the (June 1974) JBL L100 was 96dB at 'mid frequencies'. However, JBLs 'official' sensitivity specs at the time were done at 15' (4.57 m) with one watt (78dB for the L100, frequency not specified) By the time of the L100t (mid '80s) JBL was using the one watt/meter spec, frequency not specified.

Alternately, Richard Heyser of Audio, one of the first measurement driven reviewers, took a practical approach with sensitivity. That is, it really depended on the speaker design and listening position. For instance, when reviewing the Klipschorn he used 3.5 meters (98dB), although he did measure it at 1.2 meters--104dB.

 

[Ricardojoa]

Most likely it has to do with the wavelength within the measured frequencies and for the crossover as well. But I remember that klipsch do their measurements at 2 m in some post i have i read before so is not always at 1m. I guess for bookshelf speaker a meter is what is minimum necessary to have accurate measure within down to 300hz or so.

 

[Helicopter]

A short answer could be:
1)The metric system is an Universal reference used un Science.
2) The metric system offers a high "degree of coherence".
3) Electric and Acoustical measures are based in the International System of Electrical and Magnetic Units that is also based on the meter, kilogram and second.

4) only the standard spec is 1m. They only are actually measured at 1m when it makes sense from a practical standpoint. It is just a unit, and in the Metric system one can usually express units as a factor of one, which makes math easier.

 

[Tonygeno]

A short answer could be:
1)The metric system is an Universal reference used un Science.
2) The metric system offers a high "degree of coherence".
3) Electric and Acoustical measures are based in the International System of Electrical and Magnetic Units that is also based on the meter, kilogram and second.

But a longer answer would focus on the number “one”.

 

[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. If you measure from 30 cm distance, the mic will measure about 70% direct sound and about 30 % reverb sound from the room. If you are to near the loudspeaker when measuring, you dont measure the impact of the baffle, wich can be huge. So 1 meter is a good compromise, and using gating technique at 5 ms in a normal room is also good when measuring.

what objective data are you using to arrive at this conclusion that at 1 meter the indirect sound-field will be equal in magnitude to the direct signal?
which then implies that past 1 meter from the loudspeaker in a "normal room" the indirect sound-field is higher in gain.

fact is small acoustical spaces (ie, home residential-sized rooms) do not support a statistically random-incidence reverberant sound-field of which a critical-distance (Dc) would then be present of which beyond one is in the "reverberation".

at no point in a "normal room" will the indirect sound-field become higher in magnitude than the direct signal. the direct signal will always dominate.

 

[anmpr1]

at no point in a "normal room" will the indirect sound-field become higher in magnitude than the direct signal. the direct signal will always dominate.

Depends on the loudspeaker design. I think it is certainly true in dead rooms using forward firing drivers. An omni such as a Walsh driver (or an outlier like the Bose 901) in a 'live' room will have a larger variance between direct and indirect sound. A panel speaker with an equal level out of phase back wave will also show wider variances. A corner horn using walls as a bass enhancer can be said to be sending out an 'indirect' LF signal. Something like the ceiling to floor Beveridge 180 degree lens loaded electrostatic (where the speaker is placed in the middle of the room, facing each other and not the listener) is going to have a large indirect soundfield. What about designs such as the B&O 90? dbx Soundfield or AR LST?

 

[amirm]

Agree with metric argument, but why 1 meter?

As noted, that is the reporting value, not the actual measurement distance. The CEA/CTA-2034 specification mandates 2 meter and reporting at 1 meter:

At very low frequencies, far field is well, very far. So any number picked here is a compromise. They are trying to not put too high a burden as far as the anechoic chamber size you need for the measurements.

Also, there is the issue of signal to noise ratio. The farther you are, the more noise you pick up.

So something had to be picked and 2 meter measuring and 1 meter reporting was picked.

Note that if a measurement does not specify compliance with this standard, it could have used any distance. My measurements are compliant with 2034. But actually measurement is variable and very close to the speaker. This improves the signal to noise ratio but requires heavy computation to generate 2 meter data which then gets reported as 1 meter.

 

[Rock Rabbit]

Well,...is an industry standard (IEC?). The basic idea is that the mic should be measuring in the far field of the loudspeaker (true 6 dB att double the distance) with attenuated reflections (some 20 dB). Typical far field is at least 3x the LS higher dimension...but IEC 60268-5 dictates 1 meter and many boring details for measurements.
Google IEC 60268...have fun

 

[Tangband]

what objective data are you using to arrive at this conclusion that at 1 meter the indirect sound-field will be equal in magnitude to the direct signal?
which then implies that past 1 meter from the loudspeaker in a "normal room" the indirect sound-field is higher in gain.

fact is small acoustical spaces (ie, home residential-sized rooms) do not support a statistically random-incidence reverberant sound-field of which a critical-distance (Dc) would then be present of which beyond one is in the "reverberation".

at no point in a "normal room" will the indirect sound-field become higher in magnitude than the direct signal. the direct signal will always dominate.

This is simply wrong Im afraid .