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Author Topic: JTR Triple 12 and Orbit Shifter  (Read 28309 times)

Robert Patch

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Re: JTR Triple 12 and Orbit Shifter
« Reply #10 on: January 16, 2011, 10:08:39 am »

I believe Evan has checked out.  I set the limiters on the Itech 4000 per Jeff's recommendation at "RMS" 800 watts and peak voltage at 126 volts.

Evan and I are getting together again next month when he gets off tour to do some more test and tune.  If he doesn't post the results, I'll do my best to relay them.
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Art Welter

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Re: JTR Triple 12 and Orbit Shifter
« Reply #11 on: January 17, 2011, 04:01:34 pm »

TrevorMilburn wrote on Sun, 16 January 2011 05:14

Quote:

 
The cabinets do stay pretty clean and pretty smooth as you crank them up, but the HF struggles as you approach limit on the IT4000.


I haven't used SMAART myself, so I am not conversant with the displays shown (I saw the 0dB in the display), but were the measurements taken at full power on the IT4000 or at 1w or some other power? I say this because the speakers IIRC are rated at 1600w program which means that if they were being given the full 2000w the IT4000 is capable of at 4ohms and had a 4db HF eq boost applied, the HF would be pushed well beyond it's comfort zone. I would expect most lesser speakers to be screaming for mercy or completely giving up the fight. Also, is it possible that the coaxial MF/HF was mounted in the centre position (it is a sealed unit so can be moved quite easily from what I have read elsewhere) and the measurements were inadvertently not taken on axis at all?
Just curious.

Regards,
Trevor


Evan stated:
"I measured the horn on axis @ 1m, and ground plane at 1 & 2m. The measurements were all consistent. It's not the mic, as it showed the EV and Mackie boxes flatter out to 16k."

The posted photo clearly shows the coaxial speaker in the top position.

Unless one is specifically testing for distortion or power compression, speaker testing normally is done at a level that will be 20 dB or so above ambient noise.

With speakers like the ones tested, pink noise with peaks of a watt or two is usually plenty of level to be well above ambient noise. You learn to avoid taking screen captures when dogs start barking, vehicles drive by or fly over, or the wind gusts.
If any of those things happen, they will show up as a reduction in the red coherency trace shown on the top of the screen. Evan's coherency traces all look good within the range under test.

That said, it does not take much wind to make the phase change 180 degrees at 16K, even though the frequency response will stay pretty consistent.

Frequency response testing at high SPL levels just makes the neighbors complain, and gives you no better information.

Art Welter
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Jay Barracato

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Re: JTR Triple 12 and Orbit Shifter
« Reply #12 on: January 18, 2011, 10:03:42 am »

TrevorMilburn wrote on Sun, 16 January 2011 06:14




I haven't used SMAART myself, so I am not conversant with the displays shown (I saw the 0dB in the display),





The 0db is the difference between the measured signal and the reference signal. It is independent of the level the speaker is at as long as you are significantly above the background noise (as Art stated).
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Jay Barracato
Solomons MD

Mike Christy

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Re: JTR Triple 12 and Orbit Shifter
« Reply #13 on: January 18, 2011, 12:28:21 pm »

Very odd.

I asked Jeff if the 2010 T-12 has the same HF driver as my T-8s, it does.

My T-8 SMAART plots extended out past 12K, and I hear no evidence of a lack of high frequency from my T-8s. As a matter of fact in some rooms I need to pull 8k down a little for silibance issues.

Maybe a bad xover part/solder joint?

Mike
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Pisces Sound
Seacoast New Hampshire
Southern Maine

Art Welter

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Re: JTR Triple 12 and Orbit Shifter
« Reply #14 on: January 18, 2011, 01:17:35 pm »

Mike Christy wrote on Tue, 18 January 2011 10:28

Very odd.

I asked Jeff if the 2010 T-12 has the same HF driver as my T-8s, it does.

My T-8 SMAART plots extended out past 12K, and I hear no evidence of a lack of high frequency from my T-8s. As a matter of fact in some rooms I need to pull 8k down a little for silibance issues.

Maybe a bad xover part/solder joint?

Mike

Evan's plot shows 8K to be the peak in the HF response.

A cold solder joint on a HF bypass capacitor could make the response droop as shown.

The T-8 is rated 98 dB 1 watt one meter full space, the T-12 101 dB.
If both are  +/- 3dB to 20K, the T-8 tweeter has a minimum of 3 dB more HF attenuation.
I doubt Jeff would use the same crossover for a T-8 as a T-12, so seeing some actual plots of both would be informative.

If you and Jeff could post the HF response it could clear up the issue, and may isolate the lack of HF to the particular unit tested.

Could be a driver, crossover, processor setting, or microphone issue.
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TrevorMilburn

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Re: JTR Triple 12 and Orbit Shifter
« Reply #15 on: January 18, 2011, 06:16:20 pm »

Quote:

Could be a driver, crossover, processor setting, or microphone issue.

If the other speakers you guys tested measured OK, I myself would start looking at driver/crossover issues on the JTRs, or, as I alluded to earlier, the location of the mid/high driver. The results seem to be completely at odds with those of other testers (HT & high-end hi-fi) that I have seen who generally sing the praises of the fidelity of JTR products. I know I have worked with brand new equipment,AV/Computing etc. sometimes from manufacturers renowned for their stringent quality control, which has presented strange problems, not always immediately detectable to the naked ear/eye, due to manufacturing faults or other damage such by transportation is totally at odds with the usual production-run models.
However, one has to accept that items sent out specifically for testing should be checked with extra vigilance before despatch simply to avoid such problems - IMHO testers should report their findings to the manufacturer/dealer/importer before publishing just in case a rogue example has slipped past the post-assembly/despatch checks even if only to avoid embarrassment and with the hope that future quality checks are changed and/or improved. I for one would much rather see a reference to such problems as an addendum to a review along with a response from the manufacturer stating what the problem was and what steps were being taken to prevent further such problems than read a belated, often grovelling response, after a review as been published and remarked/commented on by many of the reviewed equipment's target audience/prospective buyers when damage has already been done.
Just my 2 Cents worth (Oh, and I have trained as an ISO/9000 quality auditor)
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Mike Christy

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Re: JTR Triple 12 and Orbit Shifter
« Reply #16 on: January 18, 2011, 07:00:15 pm »

Here is my T-8 plots, I am pretty sure this is w/o any EQ, and if there were any, it would be to attenuate, not boost.

I agree with you Art, the crossover would have to be different in each cab, but it makes little sense to me that he would set the T-12 HF crossover cutoff as it was measured.

index.php/fa/34807/0/
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Pisces Sound
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Southern Maine

Robert Patch

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Re: JTR Triple 12 and Orbit Shifter
« Reply #17 on: January 18, 2011, 07:03:43 pm »

TrevorMilburn wrote on Tue, 18 January 2011 17:16

I for one would much rather see a reference to such problems as an addendum to a review...


It was a measured characteristic until Jeff reported that it wasn't consistent with his tests.  Evan's off to Brazil now.  When he gets back we can check one speaker against the other.
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Dick Rees

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Re: JTR Triple 12 and Orbit Shifter
« Reply #18 on: January 18, 2011, 07:35:20 pm »

TrevorMilburn wrote on Tue, 18 January 2011 17:16

 IMHO testers should report their findings to the manufacturer/dealer/importer before publishing just in case a rogue example has slipped past the post-assembly/despatch checks even if only to avoid embarrassment and with the hope that future quality checks are changed and/or improved.


You are correct, sir.
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Art Welter

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Re: JTR Triple 12 and Orbit Shifter
« Reply #19 on: January 18, 2011, 07:36:26 pm »

Mike,
Your plot looks little different than Evan’s, it confirms the cabinet is no where near +/- 3 dB to 20 K.
Your  plot shows that 20K is more than 24 dB down from the 8 to 9K peak.
Looks like it is headed south around 12K.
index.php/fa/34808/0/
Thanks for sharing the graph!
Art Welter
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