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[Marjan Milosevic]

  that would be my assumption since most often speakers have one sensitivity measurement instead of multiple.

What we do is measure in steps of 5Hz (the subs) from 20-150hz, and then get the average figure.
Stating a number taken from the peak point is cheating. But marketing departments love those.

[Scott Wagner]

I imagine they can do all kinds of things but the most useful for a speaker would be to measure 1w/1m from the speaker as a system. Those numbers can be toyed with in other ways though given some sort of averaged sensitivity vs a peak sensitivity in the most efficient frequency range.  that would be my assumption since most often speakers have one sensitivity measurement instead of multiple.

I believe JBL (and many other manufacturers) measure the actual speaker system at some distance (10m?), and then calculate the 1m number from that.

[George Friedman-Jimenez]

Listing subs in whole space is just stupid.

Because nobody is listening to them in whole space.

Even if the subs are flown, at the frequencies involved-YOU are in half space. Unless you listen while up on tall ladders.

It does not matter if either the speakers or mic (listener) are in half space-it puts the "whole thing" in half space,

And NO, you do not get to add another 6dB if the speakers are placed on the ground, since the listener (mic) is already within the "groundplane" of the freq involved.

Very interesting, I had never considered this. Ivan, if I understand you correctly, what you are saying implies that if the sub is flown and the listener or mic is close to the ground, there is an additive reinforcement of SPL due to reflection of the wave off the ground near the listener. This makes physical sense for a sub if the phase of the reflected wave is less than 90 degrees (1/4 wavelength) behind the phase of the original pre-reflection wave. That means the listener's ear or mic would need to be less than 1/8 wavelength from the reflecting surface so the round trip distance from ear to floor to ear is less than 1/4 wavelength. 1/8 wavelength would be about 1.4 feet for 100 Hz or 2.8 feet for 50 Hz, assuming the wavefront is perpendicular to the floor but would be even less if the sub were not directly overhead. At 1/4 wavelength from the floor, there would be near complete cancellation of the sound (for that particular frequency) as the reflected wave would be 180 degrees out of phase with the original and only slightly less amplitude. So it is not clear to me how all this factors into the measurement and reporting of SPL levels of subs. What has been your real world experience doing these measurements at Danley?

[Ivan Beaver]

Very interesting, I had never considered this. Ivan, if I understand you correctly, what you are saying implies that if the sub is flown and the listener or mic is close to the ground, there is an additive reinforcement of SPL due to reflection of the wave off the ground near the listener. This makes physical sense for a sub if the phase of the reflected wave is less than 90 degrees (1/4 wavelength) behind the phase of the original pre-reflection wave. That means the listener's ear or mic would need to be less than 1/8 wavelength from the reflecting surface so the round trip distance from ear to floor to ear is less than 1/4 wavelength. 1/8 wavelength would be about 1.4 feet for 100 Hz or 2.8 feet for 50 Hz, assuming the wavefront is perpendicular to the floor but would be even less if the sub were not directly overhead. At 1/4 wavelength from the floor, there would be near complete cancellation of the sound (for that particular frequency) as the reflected wave would be 180 degrees out of phase with the original and only slightly less amplitude. So it is not clear to me how all this factors into the measurement and reporting of SPL levels of subs. What has been your real world experience doing these measurements at Danley?

THe distance from either the sub or the ear (mic) to the floor ONLY applies if all of the devices are in line (or stacked up vertically. to get the "simple distances".

THe argument that putting the subs a couple of feet off of the floor and causing cancellations ONLY applies IF the listener is ABOVE the subs.

They are not

The difference in distances between the direct path of the subs and the reflection off of the floor is what causes the combfiltering.  NOT the distance up off of the floor.

We only measure the subs one way.  The sub is on the ground and the mic is also on the ground.

This eliminates any reflections which would cause cancellations at some freq based to the different path distances.

We also put the mic 10M away (a 20dB loss) and drive the subs with 28.3V (a 20dB gain) so that the "back calculation is equal to a 1M distance.

In order to get a true "free space" measurement requires you to place the sub and the mic VERY HIGH in the air.  Or have a HUGE anechoic chamber.

[Jay Barracato]

I can't help but to think that if the difference between what is measured full space versus half space is actually show critical that is a sure sign of not enough rig for the gig©.

And I am reminded of a humorous story by Patrick McManus about handloaders debating calculated performance versus real performance.

Sent from my DROID RAZR HD using Tapatalk

[Ivan Beaver]

What we do is measure in steps of 5Hz (the subs) from 20-150hz, and then get the average figure.
Stating a number taken from the peak point is cheating. But marketing departments love those.

The problem with that type of "average" is that there are A LOT more points in the average towards the top end.

So between 75Hz and 150Hz The top octave you have 15 points, but in the bottom octave (the one that is harder to reproduce and where most people like to  stretch it a bit) you have 5 points between 20 and 40Hz.

So the part that is already louder (the upper part of the range) gets more points in the average.

So the result could be very misleading-especially if somebody is expecting that sort of sensitivity down at 30hz

[Bob Leonard]

Does any one know if the new SRX800 max SPL listed are measured in FULL or HALF space?

So how did those calls to JBL tech support turn out, and what have you learned from the vast JBL data library at the JBLpro site?

[ProSoundWeb Community]