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Author Topic: JBL SRX718 - Basic Distortion Measurements  (Read 38870 times)

Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #10 on: April 24, 2010, 03:06:09 pm »

Art Welter wrote on Sat, 24 April 2010 13:02

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.

index.php/fa/29708/0/
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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #11 on: April 24, 2010, 03:14:46 pm »

Here are the rest of the 4015LF tests:
index.php/fa/29710/0/
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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #12 on: April 24, 2010, 08:55:46 pm »

The  Eminence 4015LF  fared well regarding distortion, the dB figures are about 4 dB low due to a calibration error.

30 Hz 108 dB 70% distortion (below box tuning, Fb)
35 Hz 114 dB 18% (below Fb)
HP filters are important!
40 Hz 114 dB 2%
45 Hz 118 dB 11%
50 Hz 120 dB 13% (over Xmax)
55 Hz 121 dB 11% (over Xmax)
60 Hz 121 dB 2%
70 Hz 121 dB 8%
80 Hz 119 dB 11% (at Xmax)
Excluding 30 & 35 Hz, an average of 8.29 % distortion.

The 6 ohm Eminence Lab 12 is rated at 400 watts, 13mm Xmax. Tests were done at 200 watts (34.6 volts) and 400 watts (49 volts), the lower trace is 200 watts.
The 50 Hz Lab 12 picture also has a third excursion figure with 655 watts (62.7 v).

30 Hz 100 dB 5% distortion (200 watt figure, 400w was missed in test)
35 Hz 105 dB 3%
40 Hz 107 dB 3%
45 Hz 112 dB 6%
50 Hz 114 dB 7%  116 dB at 655 watts 8% (over Xmax)
60 Hz 113 dB 8%
70 Hz 113 dB 4%
80 Hz 112 dB 5%
An average of 5.13 % distortion.
index.php/fa/29711/0/

Phil tested the JBL SRX 718 at 85 volts (903 watts, a bit above the 800 watt rating) at 10 meters, add 20 dB for a one meter level:

45 Hz 102 dB 9%
50 Hz 106 dB 18%
55 Hz 107 dB 8%
60 Hz 111 dB 5%
70 Hz 110 dB 5%
80 Hz 109 dB 10%
An average of 9.17% distortion.

The Eminence Lab 12 has about half the distortion of the JBL SRX 718, the Eminence 4015LF has slightly less distortion than the JBL.

Both Eminence speakers showed some  power compression, which would increase the percentage  of distortion compared to a cool speaker.

All three speakers are remarkably low in distortion, many commonly used speakers have distortion far greater at one tenth the input power than these have at full rated power.

Art Welter
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Phil Lewandowski

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #13 on: April 25, 2010, 02:16:30 am »

Thanks Art for doing that, I appreciate it a lot, as I found that very education for myself and being able to actually compare to several other designs was very interesting.


Thanks!
Phil
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Phil Lewandowski

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #14 on: April 25, 2010, 11:28:38 am »

Hey Art,

Would it be useful, for comparisons sake, the next time I am out there to test the 2268H with similar power levels that you tested the 4015LF and LAB12 at?  I don't know if that would help for comparison sake since I ended up testing at a bit higher level?


Maybe something like 200, 400, and 800 watts?


Thanks,
Phil
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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #15 on: April 25, 2010, 03:01:43 pm »

Phil Lewandowski wrote on Sun, 25 April 2010 09:28

Hey Art,

Would it be useful, for comparisons sake, the next time I am out there to test the 2268H with similar power levels that you tested the 4015LF and LAB12 at?  I don't know if that would help for comparison sake since I ended up testing at a bit higher level?


Maybe something like 200, 400, and 800 watts?


Thanks,
Phil

Phil,

Testing at decades of power, 9 watts, 90, and 900 would show the  progression of  distortion components, but is a lot of work the way we are doing it.

I tested  at half and full power level, you tested at 1/2 dB more than full power.

The results are real world, subs are often powered with peaks double the full power rating.

For comparison sake, testing at and a bit below Fb would be informative, especially since the SRX 728 specs claim a +/- 3 dB point of 34-220.

However, you will probably find that  the 2268 hits 10% distortion at 33 Hz at only about 1/10 the rated power (100 watts), as  JBL’s chart shows.

Though the SRX 728 has more output above 50 Hz, a pair of Lab 12s, in a box of similar size can put out more clean output below 50 Hz.

This is important to me, since our ears are less sensitive to LF (equal loudness contours), if the sub is rolling off down low, the harmonic distortion may seem equal in level to the fundamental tone even when it is 10-20 dB lower.

This process has been very interesting to me, I have never seen distortion figures at full rated power before, even though it is common to run well above these levels.
index.php/fa/29718/0/

Art Welter
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Phil Lewandowski

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #16 on: April 25, 2010, 03:35:31 pm »

Art Welter wrote on Sun, 25 April 2010 15:01

Phil Lewandowski wrote on Sun, 25 April 2010 09:28

Hey Art,

Would it be useful, for comparisons sake, the next time I am out there to test the 2268H with similar power levels that you tested the 4015LF and LAB12 at?  I don't know if that would help for comparison sake since I ended up testing at a bit higher level?


Maybe something like 200, 400, and 800 watts?


Thanks,
Phil

Phil,

Testing at decades of power, 9 watts, 90, and 900 would show the  progression of  distortion components, but is a lot of work the way we are doing it.

I tested  at half and full power level, you tested at 1/2 dB more than full power.

The results are real world, subs are often powered with peaks double the full power rating.

For comparison sake, testing at and a bit below Fb would be informative, especially since the SRX 728 specs claim a +/- 3 dB point of 34-220.

However, you will probably find that  the 2268 hits 10% distortion at 33 Hz at only about 1/10 the rated power (100 watts), as  JBL’s chart shows.

Though the SRX 728 has more output above 50 Hz, a pair of Lab 12s, in a box of similar size can put out more clean output below 50 Hz.

This is important to me, since our ears are less sensitive to LF (equal loudness contours), if the sub is rolling off down low, the harmonic distortion may seem equal in level to the fundamental tone even when it is 10-20 dB lower.

This process has been very interesting to me, I have never seen distortion figures at full rated power before, even though it is common to run well above these levels.
index.php/fa/29718/0/

Art Welter


Gotcha Art,

I will plan to then do the tests below Fb when I do some distortion measurements on the Growler.

Phil
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Bill Burford

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #17 on: April 26, 2010, 02:00:22 pm »

I wonder what the results would look like with 112/113 V on an amp that wasn't clipping.
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Art Welter

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #18 on: April 26, 2010, 03:31:38 pm »

Bill Burford wrote on Mon, 26 April 2010 12:00

I wonder what the results would look like with 112/113 V on an amp that wasn't clipping.

Bill,

None of Phil’s results were subject to amp clipping.

At 1/10 th power (around 90 watts) the 2268 has only about 1% distortion at 80 Hz.
At full power (around 900 watts) the distortion rises to about 10%.

The PL380 is capable of about 110 V(1500 watts at 8 ohm) continuous sine wave output at 8 ohms, but the JBL 2268 (Pe 800) is not rated for that level.

Results one could expect would be increased  power compression at levels that high, and possibly smoke after a period of sine wave testing .

If the tests were done with a transient signal that did not cause power compression, SPL and distortion would rise very slightly at higher drive levels.

At 1500 watts into one channel, the Pl380  draws 19.15 amps, so a 20 amp 12 gauge circuit of more than a very short length would drop in voltage enough so the amp could not produce that output level with sine wave testing.

Since Phil was testing outside, without setting up a heavy duty AC distribution, voltage drop limited the amp output slightly, by less than one dB (1250w instead of 1500w).

index.php/fa/29736/0/

However, power compression (voice coil impedance rises due to heating, amps produce less power into higher impedance) had set in, the SPL level at 85V(900 watts) was exactly the same as at 100V (1250 watts).
The distortion stayed at the same level since the SPL level did not go up.

Art Welter
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Bill Burford

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Re: JBL SRX718 - Basic Distortion Measurements
« Reply #19 on: April 26, 2010, 10:44:20 pm »

ok ok..

I get confused with music material versus sine-waves sometimes for these applications.  Subwoofer black magic is definitely not my forte.

I was thinking of which amp I would want for a 718 which would be an amp that made 1600 Watts.
but if you put a sine-wave at 1600 Watts into that driver for a test, you'd probably smoke it wouldn't you?
( maybe not immediately but by the end of a test )

Hey where is a good place to learn some of the physics behind things like enclosure-volume, Fb, damping materials, etc as they pertain to subwoofers?  Everywhere I look seems to end up in a car-audio discussion.  I couldn't find anything at the bookstore either.  Are these just well guarded secrets?  
One reason why I like the JBL subs is that they seem to be more "musical" sounding.  Really a lot of subs these days are pretty nice.  but the best example I have would have to do with bass guitar amplifiers.
I notice one thing about a lot of the cheaper rigs:  I don't know if this is caused by Fb or resonant frequencies or what, but a lot of them seem to have this really buzz-saw sound to them where you can still make-out the guitar note they are hitting but there always seems to be a buzz-saw vibration tone that seems to hit hard when they turn the thing up and I can't stand it..  it seems like the frequency is up around 150/160 Hz.  its never a problem in the mix with decent subs but then.. every time I get used to better subs and go back to the older smaller ones, I start to suddenly realize a similar problem with the cheaper subs-- they color the sound at some frequency.
thats why I like 718's and 728's (and better subs)-- they seem a lot more musical ( I guess that distortion factor has something to do with it )
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