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Old 29th July 2011, 02:59 PM   #21
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Quote:
Originally Posted by j.michael droke View Post
Hi there Josh & Art: For curiousity and as Art requested, I ran HR using Josh's HR input with 4 Lab 12's in a TH 2s x2p with the following results:

16hz, 13 mm-disp
20hz-103.7spl,236w,7.6mm-disp,05.2ohms-imp (rising spl resopnse)
30hz-116.5spl,334w,0.3mm-disp,04.3ohms-imp (rising spl response)
38hz-126.4spl,039w,6.1mm-disp,34.5ohms-imp (spl peak)
60hz-118.8spl,330w,0.8mm-disp,04.4ohms-imp (spl dip)
90hz-126.6spl,040w,2.6mm-disp,34.8ohms-imp (spl peak)
105hz-123.3spl,313w,1.0mm-disp,04.6ohms-imp (spl dip)
115hz-131.0spl,198w, 0.9mmdisp, 7.2ohms-imp (spl peak)
140hz-120.9spl,325w,0.4mm-disp,04.4ohms-imp (spldip)
above 140hz, repeating peaks and dips
conclusion: from 10hz upward, there was no flat response areas...regards, Michael
Thanks, that response looks terrible.

Looks like the Lab 12s will stay in the ported boxes .
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Old 29th July 2011, 03:12 PM   #22
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Originally Posted by Josh Ricci View Post
4? I am not sure if they would fit without extensive modification or at all. 3 might be workable. I posted the HR input data. You could give it a whirl yourself you know.


Yeah I beefed the bracing a lot but I don't think it will affect things much whether it is skeletonized or not. My gut tells me it is negligible.
My gut says it may be more than negligible difference.

Think in terms of very long ports, a slotted port (port using a cabinet side wall) will tune lower than a “normal” cylyndrical port of the same area and length.

Anyway, you may be right, the difference may be negligible, no way to know for sure without an A/B test.

As far as the me inputting the data, Hornresp is on a computer I have not used in several months, I’d have to figure out how to use it again (and would then want to download the new version of Hornresp), so I was just being lazy .

Art
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Old 29th July 2011, 04:18 PM   #23
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Art,
Part of the reason that I did all of the modeling for this and the Gjallerhorn in Akabak was because of questions like how the bracing will affect the response. I have modeled the paths when split by bracing as separate segments. In the Gjallerhorn this type of detail actually caused me to run out of script. I was told that it was unecessary to go to such lengths but I wanted to be sure. The differences in the simulation with solid bracing and without are very small. Real world driver parameter differences and build differences will amount to more. That's why I am not worried about it too bad. At this point it is time to look at real as built results.
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Old 29th July 2011, 04:40 PM   #24
Xoc1 is offline Xoc1  United Kingdom
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Josh
Nice work!
I'm interested by the Sd/S2 compression ratio that you are using. 4.19 : 1 for a 21" driver.
Most designs posted on the forum seem to use a lower compression ratio.
As a rule of thumb I used approx 2.5 : 1 on the Xoc1 TH18.
This seems to be even more compression than the Gjallerhorn 3.88 : 1.
How does the compression ratio effect the performance of the speaker and driver?
Regards
Martin
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Old 29th July 2011, 05:56 PM   #25
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In practice these are the compression ratios that seemed to provide realistic clearance for the drivers maximum theoretical excursion and a smooth response. A lower compression ratio in the throat results in larger magnitude variations in response. The cones and motors of the drivers used here are very strong. I had some reservations about whether the aluminum LMS ultra cone would hold up in the Gjallerhorn with its extreme amount of stroke but there have been no problems. If it was going to fold up or fail it would have during testing when it had 130 volts dumped into it with sine sweeps and 1/48th octave stepped sine tests covering 10-200hz. I have been using them with out issue. During the conception of this cab I asked Tom D. through email about his thoughts on whether the 21sw152 would take a 4/1 compression well. He thought that it should be fine. I am confident. I sort of march to my own tune, preffering to think about and try things myself rather than accept others doubts as fact. These are not the cones of yesteryear.
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Old 30th July 2011, 05:51 PM   #26
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Originally Posted by Josh Ricci View Post
In practice these are the compression ratios that seemed to provide realistic clearance for the drivers maximum theoretical excursion and a smooth response. A lower compression ratio in the throat results in larger magnitude variations in response. The cones and motors of the drivers used here are very strong. I had some reservations about whether the aluminum LMS ultra cone would hold up in the Gjallerhorn with its extreme amount of stroke but there have been no problems. If it was going to fold up or fail it would have during testing when it had 130 volts dumped into it with sine sweeps and 1/48th octave stepped sine tests covering 10-200hz. I have been using them with out issue. During the conception of this cab I asked Tom D. through email about his thoughts on whether the 21sw152 would take a 4/1 compression well. He thought that it should be fine. I am confident. I sort of march to my own tune, preffering to think about and try things myself rather than accept others doubts as fact. These are not the cones of yesteryear.
Josh,

Although I agree with most all you have said, my most early “expensive mistakes” were back in the days when aluminum (rather than titanium) HF diaphragms were used in the JBL line.

The aluminum diaphragms would develop stress cracks from fatigue over time, in my two years time with Eclipse Concert Systems, I became very adept at changing (and aligning) aluminum four inch 2440 and early 2441 diaphragms.

The aluminum diaphragms would all fail over time, time depending on excursion. There are plenty of 50+ year old aluminum diaphragms still working in low excursion home use, but none in high excursion PA use.

When the titanium diaphragms were introduced (JBL 2425, 2445) we started to use them at STS, and had no failures due to cracking from 1982 through 1992.

I had about twenty 1.75” 2420 aluminum diaphragm drivers which failed from cracking, all failed over several years, but when replaced with the titanium 2425 diaphragms, never failed (other than coil burnout) again.

In fact, JBL wrote in the 2425 spec sheet:

“This titanium diamond structure combines the ruggedness of phenolic and composite type diaphragms with the outstanding frequency response of the fragile aluminum and exotic metal diaphragms. Nontoxic titanium has no fatigue limit, It can last forever if not overdriven.”

It would be interesting to look at the LMS ultra cone under a strobe with a sine wave playing and see if the movement is purely pistonic, or if it does flex some.

Although your short term tests show the aluminum LMS ultra cone has held up fine, I hope they fare well over the long haul.


Art

Last edited by weltersys; 30th July 2011 at 05:54 PM.
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Old 31st July 2011, 12:46 AM   #27
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We will see whether they will or not. If they fail a year or 2 from now from long term aluminum fatigue then I will know. One thing to remember is that these drivers were originally intended for car audio applications. Now that being what it is the one thing I do like about most car audio market drivers is that they are built to take a severe beating in competitions and from general neglect, tough environmental conditions and plain old user idiocy in some cases. We will see.
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Old 31st July 2011, 06:26 PM   #28
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Originally Posted by Josh Ricci View Post
We will see whether they will or not. If they fail a year or 2 from now from long term aluminum fatigue then I will know. One thing to remember is that these drivers were originally intended for car audio applications. Now that being what it is the one thing I do like about most car audio market drivers is that they are built to take a severe beating in competitions and from general neglect, tough environmental conditions and plain old user idiocy in some cases. We will see.
Car audio can be severe, but horn loading is more severe as far as higher and more uneven pressure. I am not all that familiar with the current range of car audio, but I do know that it would take a huge alternator, battery bank and capacitor storage to provide the kind of power that is common in pro PA use.

Do you know what the thickness of the 21sw152 aluminum cone is?
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Old 31st July 2011, 06:29 PM   #29
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21sw152 is heavy paper.
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Old 31st July 2011, 06:37 PM   #30
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Originally Posted by Josh Ricci View Post
21sw152 is heavy paper.
My mistake, you had mentioned "During the conception of this cab I asked Tom D. through email about his thoughts on whether the 21sw152 would take a 4/1 compression well. He thought that it should be fine. "

Do you know what the thickness of the LMS ultra cone aluminum cone is ?
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