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[Mark Wilkinson]

I have never seen an LEQ measurement that gave any freq information.

Lets say the sensitivity is 100dB as per your SPL-LEQ reading.

Let's say you have a freq response that has some peaks and dips-or some major peaks

How do you know where the LEQ number (a single number) "sits" on the overall response shape?

Perfect questions.....
With smaart you have to do some work to relate 'whatever' reference db on the transfer function to the SPL-LEQ meter,
with REW it's easier because the transfer function is given as measured SPL magnitude response.
Once that's done, the LEQ fits through the transfer function as a weighted middle average straight line...it has to by definition.
Then you base response + or - to that line, as well as corners. Piece of cake
Really, LEQ is the same thing you're doing when you eyeball a sensitivity level...only it's measured !!!

The simple requirement is that you take an LEQ simultaneously to a pink noise driven transfer function.....

You could take your TEF graphs, and just draw LEQ through it, if you could equate the sine sweep to noise, I guess.

[Ivan Beaver]

Perfect questions.....
With smaart you have to do some work to relate 'whatever' reference db on the transfer function to the SPL-LEQ meter,
with REW it's easier because the transfer function is given as measured SPL magnitude response.
Once that's done, the LEQ fits through the transfer function as a weighted middle average straight line...it has to by definition.
Then you base response + or - to that line, as well as corners. Piece of cake
Really, LEQ is the same thing you're doing when you eyeball a sensitivity level...only it's measured !!!

The simple requirement is that you take an LEQ simultaneously to a pink noise driven transfer function.....

You could take your TEF graphs, and just draw LEQ through it, if you could equate the sine sweep to noise, I guess.

The problem with noise is trying to come up with an actual-accurate reading.

I have seen meters that read the same (or close enough) on a sine wave, but on noise they read differently.

It has to do with the integration time of the meter and how it displays its "average" between display readings.

So which one is correct?

[Mark Wilkinson]

The problem with noise is trying to come up with an actual-accurate reading.

I have seen meters that read the same (or close enough) on a sine wave, but on noise they read differently.

It has to do with the integration time of the meter and how it displays its "average" between display readings.

So which one is correct?

I dunno here Ivan,  you have boatloads more experience here than I do.
All I do know, is that I get consistent SPL-LEQ readings using either smaart, rew, or terrasonde.
And consistent voltage readings using fluke meters and scope.

This is true for fast and slow .....A, C, and Flat measurements, as well.

And LEQ is typically taken over minutes....how much integration error can there be over such a relatively long time span ?

I just don't see the problem ...


D

[duane massey]

It would seem to me (a "layman" with 45+ years in this industry) that the ONLY way for specs to really be useful would be to run tests on every speaker using the same methods and equipment. Otherwise you will never have accurate numbers for comparison.
On a side note, and I believe Ivan has mentioned this several times, specs do NOT tell you what a speaker actually sounds like in the real world.

The spec I'd really love to see is WGI/WGO: what goes in vs what goes out. How accurate is the speaker in terms of reproducing EXACTLY what goes in, and how accurate within it's rated coverage angle?

I realize that digital processing can
correct" a lot of things, but I still believe you are better off starting with a speaker that doesn't have built-in limitations that have to be corrected.

[Chris Grimshaw]

But the curves might not be the same with and without eq vs distortion.

In loudspeakers the distortion is not uniform across the freq range

So are you trying to measure for a number? or is the number trying to tell actual performance?

Big difference

The "frequency response" curve will vary according to whatever EQ the manufacturer implements.

The Max.SPL (10% THD Limited) curve will not.


Working through an example usually helps. I know you're a smart guy, but it feels like we're not quite getting through to each other.

Lets say I have a 15" driver in a small ported box with a built-in amplifier. There's some EQ being applied to get it flat at the low end. The manufacturer has dialled in 6dB of boost towards the bottom end of its bandwidth (40Hz).

At 40Hz, the drive unit and cabinet can produce 123dB before distortion gets too high. This number won't ever ever change with any EQ that's applied. It's a limit of the drive unit in that cabinet. Since there's 6dB of boost being applied at that frequency, at other frequencies we'll probably be able to push the line level input a little further, with the caveat that you note: different frequencies will have different drive levels needed to hit the distortion limit.

But since that's what the test is all about anyway, it really doesn't matter. Play a tone, push the level until you hit 10% THD, measure the SPL. Repeat at other frequencies.
What will be produced is a graph that will show how loud the cabinet can go at any frequency before it starts sounding stressed.


This is starting to sound a lot like Josh's method, except in graph (rather than tabulated) form.


Chris

[Ivan Beaver]

The "frequency response" curve will vary according to whatever EQ the manufacturer implements.

The Max.SPL (10% THD Limited) curve will not.


Working through an example usually helps. I know you're a smart guy, but it feels like we're not quite getting through to each other.

Lets say I have a 15" driver in a small ported box with a built-in amplifier. There's some EQ being applied to get it flat at the low end. The manufacturer has dialled in 6dB of boost towards the bottom end of its bandwidth (40Hz).

At 40Hz, the drive unit and cabinet can produce 123dB before distortion gets too high. This number won't ever ever change with any EQ that's applied. It's a limit of the drive unit in that cabinet. Since there's 6dB of boost being applied at that frequency, at other frequencies we'll probably be able to push the line level input a little further, with the caveat that you note: different frequencies will have different drive levels needed to hit the distortion limit.

But since that's what the test is all about anyway, it really doesn't matter. Play a tone, push the level until you hit 10% THD, measure the SPL. Repeat at other frequencies.
What will be produced is a graph that will show how loud the cabinet can go at any frequency before it starts sounding stressed.


This is starting to sound a lot like Josh's method, except in graph (rather than tabulated) form.


Chris

It all depends on how the data is "presented".

You and I are talking about 2 different ways of presenting the data.

When I say the distortion will vary depending on the freq and boosting, I was talking about using the same drive level into the processor.

The boosted freq will have have more drive signal so possibly higher distortion/

But hwat you are talking about is running each freq up to 10% and then plotting a graph.

Of course this graph would not possibly look at all like the freq response graph.

And you would have to do each freq individually.

I honestly don't think you will ever get manufacturers to do that.

Heck most don't even post a simple response graph.

It can be good to wish, but it is something you would have to do on your own I believe.

If customers don't have anything to compare to, how do they know if it is good or not?

Here is the really scary thing.  I have meet a good number of "professional audio guys who cannot even read a simple response graph.

Give them a response graph and tell them "Let's assume the sensitivity is 100dB.  Can you tell me what the -3dB point is?"

And they can't.

So how can we expect people to understand more complicated issues.

I guess that is why so many manufacturers only give some simple numbers, because that is all some people "think" they understand.

Most don't want to look at graphs and such, they just want a simple number to tell them how loud it is, and they assume that number gives the whole story.

Oh well----------

[Chris Grimshaw]

When I say the distortion will vary depending on the freq and boosting, I was talking about using the same drive level into the processor.

The boosted freq will have have more drive signal so possibly higher distortion/

But hwat you are talking about is running each freq up to 10% and then plotting a graph.

Of course this graph would not possibly look at all like the freq response graph.

And you would have to do each freq individually.

I honestly don't think you will ever get manufacturers to do that.

Heck most don't even post a simple response graph.

Gotchya. It all makes sense now.


It'd be an easy enough test to automate. If they're bothering to publish frequency response charts, it wouldn't be much more difficult to do the distortion test. I note that RCF publish a decent amount of data for their cabinets.

I'd like to think that if we had some kind of standardised test that every manufacturer could use, people would bother to learn to read the graphs. I do suspect, though, that we're in a small minority of people that care enough about these things to come up with a way of testing them. Most DJs will go to a store, do a quick audition, and buy whatever hits them in the chest the most.

Chris

[Josh Ricci]

Ivan brings up a valid point... "What is the bandwidth"? It's not really possible to cover every sub or speaker with a single generic bandwidth. Some subs go below 20Hz and others offer nothing much below 40Hz. The same could be said above 100Hz. It's not going to be fair to rate sensitivity by using the same bandwidth for every cab.

Another thing I agree with Ivan on is NOT using a noise signal for sensitivity, impedance or SPL specs, for the reasons he has brought up. I prefer a swept sine measurement signal.

Like I said in my last post I really think only 3 measurement graphs would be needed to bring subwoofer manufacturer specs back to reality. In fact only 2 for powered subs. Speakers would require a bit more most notably polar data.

1. Impedance. Covering 10-200Hz. That covers the useful frequency range of nearly any sub cab. In my opinion the nominal impedance spec on the sheet should be the minimum impedance in the rated bandwidth of the cab rounded to the nearest whole ohm. If the cab has a measured minimum impedance of 3.6 ohms that would be a 4ohm nominal cab. If the impedance minimum is 3.3 ohms call it a 3 ohm cab. Regardless of the paper spec the measured impedance graph is there to see for yourself and make a judgment call.

2. Frequency response / Voltage sensitivity. Ground plane frequency response measured with a swept sine signal. I'd prefer a 10m measurement distance.  Nominally 100w, 10X voltage for sensitivity. The frequency of maximum sensitivity should be part of the spec.

3. Short term, distortion limited, 1/3rd octave, burst output. This hits a number of areas. This is measured ground plane. No calculated marketing BS with the SPL rating. It's distortion limited, thought the levels allowed can be quite high, so the cab may be starting to sound distressed but it isn't a totally garbage FART sound making that maximum SPL reading. The individual harmonics have their own thresholds. 2nd is allowed to be very high, 3rd a bit less, 6th much less, etc...The SPL at each 1/3rd octave band is known. No guessing whether the SPL rating is made up near 200Hz. This testing will also reveal powered subs using heavy EQ boost on the low end and unable to maintain their LF extension at higher output levels. This is very common and is immediately obvious once the +/3dB response at lower volumes turns into +/-12dB as the output at 80Hz runs away completely from the 31.5Hz output. This is a bit much data to put on a simple marketing spec sheet but it can easily be condensed down into a single SPL number or even a few at different frequencies for that. Above all the test frequency should be noted. 130dB@80Hz for example.

[Ivan Beaver]

1. Impedance. Covering 10-200Hz. That covers the useful frequency range of nearly any sub cab. In my opinion the nominal impedance spec on the sheet should be the minimum impedance in the rated bandwidth of the cab rounded to the nearest whole ohm. If the cab has a measured minimum impedance of 3.6 ohms that would be a 4ohm nominal cab. If the impedance minimum is 3.3 ohms call it a 3 ohm cab. Regardless of the paper spec the measured impedance graph is there to see for yourself and make a judgment call.

NO NO NO

Trust me on this.

If you state anything other than 2-48-16 ohms, it REALLY REALLY confuses a lot of people.

The SH50 was originally speced as a 6 ohm cabinet.

This is what I felt best represented the overall load on the amplifier.

We had a impedance curve on the spec sheet.

You would not believe all the calls I got about that.

"What size amp do I need-I can't find an amp anywhere that is speced at 6 ohms" and so forth.

So I just changed the spec sheet to read 4 ohms.  All of the calls about impedance stopped.

It is truly sad how many "professionals" in our industry don't understand even the basics.

I think this is why a lot of manufacturers have stopped putting useful data on the spec sheet.  "Let's just sell them what they think they want and all will be happy" seems to be the current trend, no matter if it is actually correct.

When you don't put a spec, nobody can hold you to it.

I have seems specs such as "wide" "narrow" but no degrees given.  So how wide is "wide"?

How about the amp rating on a powered speaker that is "adequate".  Yeah-that helps.  For what?

[Chris Grimshaw]

Alright, call it a 2ohm box and give the amp an easier life. I don't think I'd ever put a pair of 3ohm loads across an amp unless it was an absolute emergency.

Chris

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