Why Do TEF Systems read 3-5 dB high ?

Re: Why Do TEF Systems read 3-5 dB high ?

Art Welter said:
Cool, just use an A.D.A.M. (angular discrepency adjustment module, AKA audio log, AKA 2x4 with gaffer tape cover...) to prop it up.

Of course, EAW is one of the few companies that publish sub cabinet response charts in whole space rather than half space, which mixes mediums ...
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It will take a lot more than just a "road wood" block to get it up.

The question remains on whole space sub measurements. How "whole" is whole space-and down to what freq? When talking subs, you have to get a long way from any reflective surface so that surface does not have an influence on the measurement. That means a VERY Large anechoic chamber (which I don't think EAW has-I have been in their measurement room, and it is just a kinda large room with shipping blankets on the walls-or was anyway) or outdoor with the loudspeaker suspended (and the mic) a good distance from the ground. Not an easy thing to do.
 
Re: Why Do TEF Systems read 3-5 dB high ?

Ivan Beaver said:
It will take a lot more than just a "road wood" block to get it up.

The question remains on whole space sub measurements. How "whole" is whole space-and down to what freq? When talking subs, you have to get a long way from any reflective surface so that surface does not have an influence on the measurement. That means a VERY Large anechoic chamber (which I don't think EAW has-I have been in their measurement room, and it is just a kinda large room with shipping blankets on the walls-or was anyway) or outdoor with the loudspeaker suspended (and the mic) a good distance from the ground. Not an easy thing to do.
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A 6.01 inch (152.7 millimeters) lift is required at the back of an EAW AX cabinet to make the front perpendicular to the ground, a pallet and a 2 x 4 should “get er done” :^)

I agree completely that good measurements are hard to get.

The transfer function required to process semi-anechoic room results into full space results would require some serious software algorithms to yeild good results, though that is what EAW seems to do, reading their notes. Dave Gunness, with his background at EV prior to EAW, probably got that system as good as possible for that type of testing.

It still seems to me that DSLs measurements, though internally consistant, are +3 dB (or more) from other manufactures using half space sub measurements.

Looking at the EAW AX112 Performance data , it says “see notes graphic data for details”,

A couple of the notes:

“5. Environment: Measurements time-widowed and processed to eliminate room effects, approximating an anechoic environment. Data processed as anechoic or fractional space, as noted.
6. Measurement Distance: 7.46 m. Acoustic responses represent complex summation of the subsystems at 20 m. SPL is referenced to other distances using the Inverse Square Law.”

The EAW AX112 sub spec sheet shows a 96 dB “whole space” sensitivity, which appears to be it’s sensitivity at about 70 Hz on the chart they provide.
I would not expect you to try to measure it or any of your subs in whole space, you would need a ten story crane (or taller) to do it right without additional processing.

Although the results of comparing a DSL sub to an EAW sub in half space would be interesting, the test methods that EAW uses makes the comparison a bit apples to oranges, as you have mentioned one can’t simply add 3 or 6 dB to equate a whole space to a half space measurement.

Art Welter
 
Re: Why Do TEF Systems read 3-5 dB high ?

Art Welter said:
A 6.01 inch (152.7 millimeters) lift is required at the back of an EAW AX cabinet to make the front perpendicular to the ground, a pallet and a 2 x 4 should “get er done” :^)

I agree completely that good measurements are hard to get.

The transfer function required to process semi-anechoic room results into full space results would require some serious software algorithms to yeild good results, though that is what EAW seems to do, reading their notes. Dave Gunness, with his background at EV prior to EAW, probably got that system as good as possible for that type of testing.

It still seems to me that DSLs measurements, though internally consistant, are +3 dB (or more) from other manufactures using half space sub measurements.

Looking at the EAW AX112 Performance data , it says “see notes graphic data for details”,

A couple of the notes:

“5. Environment: Measurements time-widowed and processed to eliminate room effects, approximating an anechoic environment. Data processed as anechoic or fractional space, as noted.
6. Measurement Distance: 7.46 m. Acoustic responses represent complex summation of the subsystems at 20 m. SPL is referenced to other distances using the Inverse Square Law.”

The EAW AX112 sub spec sheet shows a 96 dB “whole space” sensitivity, which appears to be it’s sensitivity at about 70 Hz on the chart they provide.
I would not expect you to try to measure it or any of your subs in whole space, you would need a ten story crane (or taller) to do it right without additional processing.

Although the results of comparing a DSL sub to an EAW sub in half space would be interesting, the test methods that EAW uses makes the comparison a bit apples to oranges, as you have mentioned one can’t simply add 3 or 6 dB to equate a whole space to a half space measurement.

Art Welter
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I wonder how they window out the floor? In order to use windowing down to a low freq, the window has to be large. This means you have to be in a LARGE room.
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Anyway-I would love get a sub with a know measurement condition (whole or half space) and a published response chart (that has dB levels-not a 0 and then +-), to do some side by side testing.

For what it is worth, Pat Brown (Synaducon) has pretty much the same SPL results when he measures our full range products as we do. I am not sure what system he is using. He has pretty much all of them
 
Re: Why Do TEF Systems read 3-5 dB high ?

Ivan Beaver said:
I wonder how they window out the floor? In order to use windowing down to a low freq, the window has to be large. This means you have to be in a LARGE room.
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I don't think that windowing alone, even in a Large room, would cut it for valid LF measurement.

My best guess as to how to use a room as a virtual whole space would be to first measure speakers in a real whole space situation, then measure them in the room, and subtract the difference. Considering subs do have different directionality patterns, the room would react differently using a big horn loaded sub compared to a single 15" bass reflex, so LF directionality measurements would have to be done on a variety of subs outdoors, and also included in a room transfer function for it to be valid below the frequency that room absorption works.

Although I can conceptualize how all this could be implemented, I have no idea if that is what EAW has done.
Then again, I have no more than a vague understanding how Gunness Focusing works, but after hearing it and seeing how flat an ordinary appearing speaker's phase and magnitude can be made using it, I think Dave could have pulled off the complex transfer functions needed to turn a semi-anechoic room into a virtual whole space measurement environment.

Of course, assuming EAW's measurements are valid still leaves the whole space to half space comparison difference. Seems odd that EAW would not include half space measurements on their subs, I see more of them sitting on the ground than flown.
Oh well, comparing anything not measured in the same place with the same test gear is difficult.
 
Re: Why Do TEF Systems read 3-5 dB high ?

Art Welter said:
Of course, assuming EAW's measurements are valid still leaves the whole space to half space comparison difference. Seems odd that EAW would not include half space measurements on their subs, I see more of them sitting on the ground than flown.
Oh well, comparing anything not measured in the same place with the same test gear is difficult.
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My opinion is that the measurements and spec sheet numbers should try to convey some useful information about the performance of a product in a way it is intended to be used to the customer. Not just a "bragging" sheet with numbers on it.

For example: While the Danlehy SH100 is a full rnage product-designed to be flown on put on a stand-it is measured in free space. However the current Danley monitors (while using the same horn/driver/crossover) are measured in half space. The idea being that in most cases a floor wedge would be used-well- on the floor.

I just realized that the website is in error regarding the whole/half space issue regarding the measurement of those wedges. I will get the IT guy to change it.

You are correct in the same idea regarding subs. In most cases, the subs will be on the floor. Now maybe those intended to be flown at the top of a line array would be a different argument. But then again-if they are flow high (like up against the ceiling where the boundary would affect it), then the half space measurement would apply.
 
Re: Why Do TEF Systems read 3-5 dB high ?

Ivan,

Just wondering if you had a chance to do a comparative measurement with the EAW AX box you have (had) in house to a DSL product?

Art
 
Re: Why Do TEF Systems read 3-5 dB high ?

Art Welter said:
Ivan,

Just wondering if you had a chance to do a comparative measurement with the EAW AX box you have (had) in house to a DSL product?

Art
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I have not had a chance-and don't forsee a chance any time soon. I will do it when I get a chance, but at least the next week (and possibly more) are completely full from the moment I walk in the door till I leave-which is quite late sometimes. I have a loooong list of things that need to be worked on. You know-stuff that pays the bills.
 
Re: Why Do TEF Systems read 3-5 dB high ?

Ivan Beaver said:
In most cases, the subs will be on the floor. Now maybe those intended to be flown at the top of a line array would be a different argument. But then again-if they are flow high (like up against the ceiling where the boundary would affect it), then the half space measurement would apply.
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And even then it will still be in half space because people are always in half space.
 
Re: Why Do TEF Systems read 3-5 dB high ?

Bennett Prescott said:
And even then it will still be in half space because people are always in half space.
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Hey Bennett,

Is there a moderately easy way to get an idea of where the notch would actually be with flown subs? Since as you say people are pretty much in half space with the ears only being ~6ft off the ground. But if the flown subs where almost directly overhead it seems that is where the notch would be most apparent.

So just trying to get an idea where and how much actual output (even if super small) is lost because of flown subs. Since it would be some since our ears are not on the ground, but with the long wavelengths that would mitigate the effect of flying them.


Thanks,
Phil
 
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Re: Why Do TEF Systems read 3-5 dB high ?

Phil Lewandowski said:
Hey Bennett,

Is there a moderately easy way to get an idea of where the notch woud actually be with flown subs? Since as you say people are pretty much in half space with the ears only being ~6ft off the ground. But if the flown subs where almost directly overhead it seems that is where the notch would be most apparent.

So just trying to get an idea where and how much actual output is lost because of flown subs. Since it would be some since our ears are not on the ground, but with the long wavelengths that would mitigate the effect of flying them.


Thanks,
Phil
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I'm not Bennett, but I'll have a go at this:

Complete cancellation if the subs are directly overhead is given by: Frequency = Speed of Sound / Wavelength, or 1126/24 = 46.91.

I assumed my ears are 6 feet up and I multiplied 6 feet by 4 since complete cancellation would be when your ear is a quarter wavelength from the floor.

Of course, sound that low is heard as well as felt, so I have no idea how the 'feeling' would be degraded by a cancellation at the ears. And if the subs weren't directly overhead, everything changes.
 
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Re: Why Do TEF Systems read 3-5 dB high ?

Silas Pradetto said:
I'm not Bennett, but I'll have a go at this:

Complete cancellation if the subs are directly overhead is given by: Frequency = Speed of Sound / Wavelength, or 1126/24 = 46.91.

I assumed my ears are 6 feet up and I multiplied 6 feet by 4 since complete cancellation would be when your ear is a quarter wavelength from the floor.

Of course, sound that low is heard as well as felt, so I have no idea how the 'feeling' would be degraded by a cancellation at the ears. And if the subs weren't directly overhead, everything changes.
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Thanks Silas, yeah right above is the easy one, but sense the audience with flown subs is usually at a much lower angle than 90 degrees to the subs in relation to the ground, I have always been wondering how much output is really lost by flown subs, since I thought it wouldn't be much at all, but curious about putting some actual numbers to it.

Sense it seems that "complete cancellation" right above is already down is around 45hz, so then that would seem that as the angle gets lowered to say 45 degrees in relation to the ears, sub, and ground, it seems like the frequency that would be affected would go up, as the distance between the floor bounce and ears gets shorter?

{edit} So with a quick sketch, it seeming like it is reasonable to think that in the real world there is going to be a whole bunch of floor bounces reaching the ears at different times, meaning you are creating a bunch of different triangles to figure out what the difference in time arrival is?

Or will there only be a small area of distance in front of the listener that there bounce would have the correct angle to bounce to the listener's ears? (This is all assuming a pretty flat and hard surface in front of the listener, no raked seating, balcony, etc.)

{edit 2} Doing a little calculation, it seems like my last assumption could be wrong, sense, if the listener and flown subs are still; you can move the point along the floor in front of the listener and the total distance traveled of the reflected wave to the listener's ears seems to add up to the same, while the direct sound of course stays the same.


Thanks,
Phil
 
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Re: Why Do TEF Systems read 3-5 dB high ?

Phil Lewandowski said:
Hey Bennett,

Is there a moderately easy way to get an idea of where the notch would actually be with flown subs? Since as you say people are pretty much in half space with the ears only being ~6ft off the ground. But if the flown subs where almost directly overhead it seems that is where the notch would be most apparent.

So just trying to get an idea where and how much actual output (even if super small) is lost because of flown subs. Since it would be some since our ears are not on the ground, but with the long wavelengths that would mitigate the effect of flying them.


Thanks,
Phil
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Think about what having the subs in the air with the mains does for summation at their acoustic crossover.... and think what happens, acoustically, when you have the L/R mains flown and the subs on the floor, no matter what the configuration. You create a dipole in the vertical plane, just as we create a power alley with l/r stacked subs.

What you do about this and how (and maybe why), is for another thread.

Have fun, good luck.

Tim Mc
 
Re: Why Do TEF Systems read 3-5 dB high ?

Tim McCulloch said:
Think about what having the subs in the air with the mains does for summation at their acoustic crossover.... and think what happens, acoustically, when you have the L/R mains flown and the subs on the floor, no matter what the configuration. You create a dipole in the vertical plane, just as we create a power alley with l/r stacked subs.

What you do about this and how (and maybe why), is for another thread.

Have fun, good luck.

Tim Mc
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That is exactly one of the things that I have always brought up when there are those that bring up that you should never fly subs because you lose so much output.

I am personally a much larger advocate of the advantages of flying the subs in a large rig far outweigh the disadvantages. But still being curious, would like to figure out what the exact effect of flying a sub has on output and frequency response.

Maybe I should start another thread on this...hmm...


Thanks,
Phil
 
Re: Why Do TEF Systems read 3-5 dB high ?

I also bet that with flown subs that the amount of floor bounce is strongly related to how packed in the audience members are. In a standing-room-only situation, the people might absorb nearly the entire floor bounce, where seated people might only absorb some of it? There are so many variables, it seems.
 
Re: Why Do TEF Systems read 3-5 dB high ?

Silas Pradetto said:
I also bet that with flown subs that the amount of floor bounce is strongly related to how packed in the audience members are. In a standing-room-only situation, the people might absorb nearly the entire floor bounce, where seated people might only absorb some of it? There are so many variables, it seems.
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Exactly, at lower frequencies like we are talking, I am guessing that the effect of absorbing the floor bounce would be slightly less than in mid to HF realm.

I am thinking more about using an ideal situation with a hard floor a single sub and a single person and seeing what effects there are. Then moving and making connection on what would when variables are changed, such as a crowd etc.. but at least having a starting 'ideal' point seems like a good place to start.

Take Care,
Phil
 
Re: Why Do TEF Systems read 3-5 dB high ?

Phil Lewandowski said:
That is exactly one of the things that I have always brought up when there are those that bring up that you should never fly subs because you lose so much output.

I am personally a much larger advocate of the advantages of flying the subs in a large rig far outweigh the disadvantages. But still being curious, would like to figure out what the exact effect of flying a sub has on output and frequency response.

Maybe I should start another thread on this...hmm...,
Phil
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Phil,

Yes, please do, although interesting, flown vs. ground placed subs as a subject has nothing to do with the measurement disparities I have noted.

You like to test speakers, do you know of any DSL cabinets you could A/B with your JBL SRX718?

The difference in the 2007 NYC comparative test with the TH-115 and the EV2181 showed the TH-115 spec sheet to be exactly 3 dB more than the NYC chart would indicate they should be.

Still hoping for some more side by side comparisons of a DSL sub with another brand sub that has published ground plane measurements to provide examples other than the ones I have already shown.
 
Re: Why Do TEF Systems read 3-5 dB high ?

Art Welter said:
Phil,

Yes, please do, although interesting, flown vs. ground placed subs as a subject has nothing to do with the measurement disparities I have noted.
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Yes sorry, when Bennett mentioned that thing about people being in 1/2 space I just had to throw the question out there since it has been something I have been wondering about for a while.

Art Welter said:
You like to test speakers, do you know of any DSL cabinets you could A/B with your JBL SRX718?

The difference in the 2007 NYC comparative test with the TH-115 and the EV2181 showed the TH-115 spec sheet to be exactly 3 dB more than the NYC chart would indicate they should be.

Still hoping for some more side by side comparisons of a DSL sub with another brand sub that has published ground plane measurements to provide examples other than the ones I have already shown.
Click to expand...


You know, I can't think of anyone nearby that I have heard of that has any DSl speakers. If there is anyone in NE Ohio region I would definetely be up for doing some direct comparisons with a SRX718 and could even do it with a Growler.


I am planning to take a direct comparison Smaart measurement of a SRX718 and Growler, hopefully the weekend of the April 8-10th. Since I want to do a basic test to see what kind of difference we see when fed the same drive voltage.


~Phil
 
Re: Why Do TEF Systems read 3-5 dB high ?

Art Welter said:
If anyone would care to take up Ivan’s gracious offer, I’d be glad to pay for you and Ivan’s expenses.

It is very hard to compare traces in the “blue background jumble” (the blue one) from the 2007 NYC sub shootout that Mark Seaton provided which I posted previously, and the production changes in other speakers used there before do cloud comparisons.

Ivan, IIRC, you and Tom had the TEF data from the 2007 NYC sub shootout, if you still have it, could you please post the TH-115 and the EV-2181 2.83 V results?

Art Welter
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Checking should be fairly simple.
Put a mic near field (about 1/4") from the dust cap or at the same place for both measurements.
Measure with TEF and then with whatever.
taking the baffle step, wall refletions etc out of the picture should give a very clear result.
A 5" driver is ideal (more high end), but larger will work 1000Hz and below
 
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