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Author Topic: JBL SRX718 - Basic Distortion Measurements  (Read 38869 times)

Phil Lewandowski

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JBL SRX718 - Basic Distortion Measurements
« on: April 22, 2010, 05:22:17 pm »

Hey All,

Art had asked me to do this, so I figured instead on burying this or adding onto 2 other very long threads, I would start a new one.


Pretty much I will list the data and how all the measurements were taken, then I would probably need Art and others to see what can be gotten out of it, since Art explained what I was looking for but I don't have a ton of experience doing these measurements.


_ _ _ _ _ _ _ _ _ _  Overview _ _ _ _ _ _

So here we go, I placed our DUT, SRX718, with the grill off in the middle of the field on our 3 acre lot here.  (Closest thing was our house at ~125ft)

I placed our measurement mic, ECM8000, and basic Rat-Shack SPL meter at 10 meters away on ground plane.

I used Adobe Audition to produce the test tones and a QSC PL380 with the 718 on channel 1 to power the sub.

I used 60hz to set the levels since I don't know for sure how accurate the multi-meter is at other frequencies.  Once I set the level at 60hz, I didn't change any levels when going to the other frequencies to keep things consistent.



I am going to try and separate the data below I ended up having to set everything at 85V because it seemed like I couldn't get close to 10% distortion without giving it that much power.  I will list some data where I gave it all that the PL380 would give without clipping at 50hz.  It ended up being about 100V with the load.  So I will list that data as well.


On the excursion measurements I would say they are probably in the neighborhood of being with 1-2mm with the eyeballing, as I did do them pretty slowly and several times spread out to see if I got similar numbers.




_ _ _ _ _ _ _ _ _ _  Data - SPL at 10M and excursion _ _ _ _ _ _

First off I seemed to find Fb to be about 40-41hz, as on either side of that the excursion started to increase.


Besides using the RTA function in Smaart in Log view to get the distortion measurements I also took down the Peak to Peak excursion and SPL at 10M, I will list that below:


SPL at 10M

2.83V
60hz - 81dB   (Equates the the 101dB I found at 1W/1M several weeks ago, so that was encouraging)


85V
80hz - 109dB
70hz - 110dB
60hz - 111dB
55hz - 107dB
50hz - 106dB
45hz - 102dB

100V
50hz - 106dB



Peak to Peak Excursion

85V
80hz - 14mm
70hz - 23mm
60hz - 31mm
55hz - 24mm
50hz - 21mm
45hz - 14mm


100V
50hz - 23mm


_ _ _ _ _ _ _ _ Data - Smaart Distortion Measurements _ _ _ _ _ _


So all of these are taken in the same conditions as above.  I ended up using 85V since it seemed like I couldn't get the 2nd harmonic any closer to 20dB below and 85V was already about 900 watts.  The last one will be at 100V, the most I could get out of one side of the PL380 before the "Clip" light came on, with the AC power I had.






Distortion - 80hz @ 85V

http://i717.photobucket.com/albums/ww173/beatmasterphil/SRX718-80hz-85V.jpg




Distortion - 70hz @ 85V

http://i717.photobucket.com/albums/ww173/beatmasterphil/SRX718-70hz-85V.jpg




Distortion - 60hz @ 85V

http://i717.photobucket.com/albums/ww173/beatmasterphil/SRX718-60hz-85V.jpg




Distortion - 55hz @ 85V

http://i717.photobucket.com/albums/ww173/beatmasterphil/SRX718-55hz-85V.jpg





Distortion - 50hz @ 85V

http://i717.photobucket.com/albums/ww173/beatmasterphil/SRX718-50hz-85V.jpg



Distortion - 45hz @ 85V

http://i717.photobucket.com/albums/ww173/beatmasterphil/SRX718-45hz-85V.jpg



Here is the one measurement at 100V

Distortion - 50hz @ 100V

http://i717.photobucket.com/albums/ww173/beatmasterphil/SRX718-50hz-100V.jpg



I decided to stay above Fb for now just for safety reasons, so hopefully there is something useful that I can learn from, and exactly what I am looking at!


The one thing I didn't expect was in a single to be hitting 109-111dB at 10M, equating to about 129-131dB at 1M.  But this is before any decent power compression I am guessing, although the 2268H is rated at only 3.2dB at 800 watts, IIRC. (I was hitting it with the sine waves for about 15-20 seconds at a time, probably about 35 different times in all to check measurements etc...)


Thanks Art again for the directions and looking forward to your insight!


Thanks,
Phil






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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #1 on: April 22, 2010, 06:45:47 pm »

Excellent work, Phil.

Your results show clearly why speakers with the same response can sound so very different, as even the  same speaker generates a different harmonic sequence at different frequencies.

I’ll try to get some figures on some other speakers using the same test protocol to get a comparison.

Interesting to see that the SRX 718 Fb is so high, 40 Hz.

I would be interested in what happens at 34 Hz, the SRX 718 rated 3 dB down point, since a lot of people are pushing them low.

And since the cabinet output level is actually more than 10 dB down at 40 Hz from 60 Hz, to equalize the cabinet flat down low would require 10 times the power.
Comparing the Growler under the same test would be of interest too, since it does not need that boost to be flat.

Back to your SRX 718 tests, at 50 Hz, 85 V the third harmonic (150 Hz) is about 15 dB down from the fundamental, about 18% distortion by itself.

The 21mm peak to peak reading, or 11.5 mm would appear to be slightly above Xmax.

However, the longest excursion you measured, 60 Hz at 31mm appears to be  below 10% distortion , which would indicate an X max of over 15.5 mm.

Both are very good excursion figures, but less than JBL’s stated 26mm Xmax.

For those that don't know about how distortion in a speaker relates to Phil's figures, here is a chart:

index.php/fa/29683/0/

Art Welter
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Mike Christy

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #2 on: April 22, 2010, 07:16:07 pm »

Phil, No, Thank You.

This is great work. It's a little hard to tell by scrolling up and down, but it seems the distortion "signature" remains similar throughout, as you drop down in frequency. Until an input changes drastically, like voltage, then it changes. This seems to chart the character of the system, like Art says.

Im really looking forward to more analysis.

One can, I think, almost imagine the MaxBass plug-in at work here with the even harmonics.

Mike
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Phil Lewandowski

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #3 on: April 22, 2010, 09:55:21 pm »

Thanks Art,

Yes, it would be interesting and I am planning to do the same thing for the Growler.  I might be coming upon 1 or 2 of the new 2010 Growlers in the next couple of weeks so I might wait until that would arrive, as that would be interesting with the new driver.


Take Care!
Phil
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Mike Christy

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #4 on: April 23, 2010, 10:47:29 am »

So Im studying these results, and aside form the distortion numbers it interesting to see that:

@ 85V (900W) 60Hz @ 10m = 111db which equates to 131db @ 1m as Phil says, which is the published spec for the cabinet.

@ 50Hz jumping up to 100V (+1.4db/1250W) we see no increase in output, 106db, but an increase in excursion.

So JBLs published spec of 131db peak output, is really met close to the continuous rating (with sine wave), and the peak rating is really telling us that you have an additional room for VC movement, go ahead if you want, but you wont necessarily get anything more from the system.

Is this thinking correct?
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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #5 on: April 23, 2010, 04:38:43 pm »

Mike Christy wrote on Fri, 23 April 2010 08:47

So Im studying these results, and aside form the distortion numbers it interesting to see that:

@ 85V (900W) 60Hz @ 10m = 111db which equates to 131db @ 1m as Phil says, which is the published spec for the cabinet.

@ 50Hz jumping up to 100V (+1.4db/1250W) we see no increase in output, 106db, but an increase in excursion.

So JBLs published spec of 131db peak output, is really met close to the continuous rating (with sine wave), and the peak rating is really telling us that you have an additional room for VC movement, go ahead if you want, but you wont necessarily get anything more from the system.

Is this thinking correct?

The SRX 718 spec sheet I see lists 130 dB maximum SPL,  which would be consistent with the rated 95 dB sensitivity driven with 3200 watts.

However, the sensitivity appears to be in free space, so half space (as Phil has measured) measures 6 dB higher, hence 131 dB at 900 watts.

You raise a good point, the output did not increase from 900 watts to 1250 watts.

My take is that the 21-23 mm peak to peak relates to an Xmax of around 11 mm.

Once the voice coil is no longer fully in the magnetic gap (above X max) more power (and excursion ) does not increase the output.

Without further testing at higher power levels I wouldn’t say for sure, but it looks like more than 1250 watts won’t make the speaker louder at  frequencies where it will exceed Xmax.
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Phil Lewandowski

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #6 on: April 23, 2010, 04:46:24 pm »

Art Welter wrote on Fri, 23 April 2010 16:38

Mike Christy wrote on Fri, 23 April 2010 08:47

So Im studying these results, and aside form the distortion numbers it interesting to see that:

@ 85V (900W) 60Hz @ 10m = 111db which equates to 131db @ 1m as Phil says, which is the published spec for the cabinet.

@ 50Hz jumping up to 100V (+1.4db/1250W) we see no increase in output, 106db, but an increase in excursion.

So JBLs published spec of 131db peak output, is really met close to the continuous rating (with sine wave), and the peak rating is really telling us that you have an additional room for VC movement, go ahead if you want, but you wont necessarily get anything more from the system.

Is this thinking correct?

The SRX 718 spec sheet I see lists 130 dB maximum SPL,  which would be consistent with the rated 95 dB sensitivity driven with 3200 watts.

However, the sensitivity appears to be in free space, so half space (as Phil has measured) measures 6 dB higher, hence 131 dB at 900 watts.

You raise a good point, the output did not increase from 900 watts to 1250 watts.

My take is that the 21-23 mm peak to peak relates to an Xmax of around 11 mm.

Once the voice coil is no longer fully in the magnetic gap (above X max) more power (and excursion ) does not increase the output.

Without further testing at higher power levels I wouldn’t say for sure, but it looks like more than 1250 watts won’t make the speaker louder at  frequencies where it will exceed Xmax.




That would make sense.  It would seem you might be able to get a bit more peak SPL out of possibly the 60-70hz region where we were measuring only about 2-5% distortion at 85V.  Would that make sense?


I would be curious how much SPL you could get at those frequencies when in instance where it is producing a signal with large dynamic range like a bass drum, if you would be able to get more "peak" SPL out of say the 50hz region, than I got with a sine wave?


Thanks,
Phil
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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #7 on: April 23, 2010, 05:15:45 pm »

Phil Lewandowski wrote on Fri, 23 April 2010 14:46

Art Welter wrote on Fri, 23 April 2010 16:38

Mike Christy wrote on Fri, 23 April 2010 08:47

So Im studying these results, and aside form the distortion numbers it interesting to see that:

@ 85V (900W) 60Hz @ 10m = 111db which equates to 131db @ 1m as Phil says, which is the published spec for the cabinet.

@ 50Hz jumping up to 100V (+1.4db/1250W) we see no increase in output, 106db, but an increase in excursion.

So JBLs published spec of 131db peak output, is really met close to the continuous rating (with sine wave), and the peak rating is really telling us that you have an additional room for VC movement, go ahead if you want, but you wont necessarily get anything more from the system.

Is this thinking correct?

The SRX 718 spec sheet I see lists 130 dB maximum SPL,  which would be consistent with the rated 95 dB sensitivity driven with 3200 watts.

However, the sensitivity appears to be in free space, so half space (as Phil has measured) measures 6 dB higher, hence 131 dB at 900 watts.

You raise a good point, the output did not increase from 900 watts to 1250 watts.

My take is that the 21-23 mm peak to peak relates to an Xmax of around 11 mm.

Once the voice coil is no longer fully in the magnetic gap (above X max) more power (and excursion ) does not increase the output.

Without further testing at higher power levels I wouldn’t say for sure, but it looks like more than 1250 watts won’t make the speaker louder at  frequencies where it will exceed Xmax.




That would make sense.  It would seem you might be able to get a bit more peak SPL out of possibly the 60-70hz region where we were measuring only about 2-5% distortion at 85V.  Would that make sense?


I would be curious how much SPL you could get at those frequencies when in instance where it is producing a signal with large dynamic range like a bass drum, if you would be able to get more "peak" SPL out of say the 50hz region, than I got with a sine wave?

Thanks,
Phil



The speaker can't get louder without more excursion.
Whether more peak power will push the cone further, I don't know.

60 Hz was the frequency you measured the most excursion at, yet it had lower distortion than 50 Hz, which had more excursion.

Some more tests at Fb and below would be informative regarding what the Xmax really is.

The 2268 behaves differently from the distortion specs I have seen before.
I'm going to test a couple Eminence cones and post back.


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Phil Lewandowski

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #8 on: April 23, 2010, 05:37:33 pm »

Art Welter wrote on Fri, 23 April 2010 17:15

Phil Lewandowski wrote on Fri, 23 April 2010 14:46

Art Welter wrote on Fri, 23 April 2010 16:38

Mike Christy wrote on Fri, 23 April 2010 08:47

So Im studying these results, and aside form the distortion numbers it interesting to see that:

@ 85V (900W) 60Hz @ 10m = 111db which equates to 131db @ 1m as Phil says, which is the published spec for the cabinet.

@ 50Hz jumping up to 100V (+1.4db/1250W) we see no increase in output, 106db, but an increase in excursion.

So JBLs published spec of 131db peak output, is really met close to the continuous rating (with sine wave), and the peak rating is really telling us that you have an additional room for VC movement, go ahead if you want, but you wont necessarily get anything more from the system.

Is this thinking correct?

The SRX 718 spec sheet I see lists 130 dB maximum SPL,  which would be consistent with the rated 95 dB sensitivity driven with 3200 watts.

However, the sensitivity appears to be in free space, so half space (as Phil has measured) measures 6 dB higher, hence 131 dB at 900 watts.

You raise a good point, the output did not increase from 900 watts to 1250 watts.

My take is that the 21-23 mm peak to peak relates to an Xmax of around 11 mm.

Once the voice coil is no longer fully in the magnetic gap (above X max) more power (and excursion ) does not increase the output.

Without further testing at higher power levels I wouldn’t say for sure, but it looks like more than 1250 watts won’t make the speaker louder at  frequencies where it will exceed Xmax.




That would make sense.  It would seem you might be able to get a bit more peak SPL out of possibly the 60-70hz region where we were measuring only about 2-5% distortion at 85V.  Would that make sense?


I would be curious how much SPL you could get at those frequencies when in instance where it is producing a signal with large dynamic range like a bass drum, if you would be able to get more "peak" SPL out of say the 50hz region, than I got with a sine wave?

Thanks,
Phil



The speaker can't get louder without more excursion.
Whether more peak power will push the cone further, I don't know.

60 Hz was the frequency you measured the most excursion at, yet it had lower distortion than 50 Hz, which had more excursion.

Some more tests at Fb and below would be informative regarding what the Xmax really is.

The 2268 behaves differently from the distortion specs I have seen before.
I'm going to test a couple Eminence cones and post back.





Gotcha that makes sense, when I next run a test like this, hopefully in the next couple of weeks I will plan to hopefully get some distortion measurements at and below Fb, now that I have a much better idea of what I am looking for.


Thanks,
Phil
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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #9 on: April 24, 2010, 03:02:59 pm »

The conditions were quite bad for outdoor testing yesterday, very windy and cold.
Got hard to type towards the end. After attempting to calibrate the Smaart SPL meter, I decided to quit messing with that and get on with the distortion tests.
The uncalibrated readings are probably about 4 dB lower than the real level.
The tests were done at one meter, the wind was too much to test at 10 meters.

The drum monitor subs used for testing are in no way optimal, the pair were designed to fit in an available space on top of a mixing console in my trailer.
index.php/fa/29707/0/

The  8 ohm Eminence 4015LF is rated at 700 watts, 9 mm Xmax. Tests were done at 350 watts (53 volts) and 700 watts (75 volts), the lower trace is 350 watts.

Excursion was measured peak to peak, I have divided it by two so it is clear when the  Xmax rating was exceeded.
Pictures are labeled with speaker type, frequency, one way excursion at 350 and 700 watts.

Seems I can't remember how to post more than one attachment at a time, next two posts will have the 4015LF distortion pictures.

I will post later with observations and Lab 12 distortion pictures.
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