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Keystone Sub Using 18, 15, & 12 Inch Speakers
Keystone Sub Using 18, 15, & 12 Inch Speakers
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Old 14th May 2015, 05:18 AM   #531
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by CRESCENDO View Post
What was the orientation of the subwoofer during this test?
Good question! Turns out it was mounted upright instead of sideways for that measurement. However, at that frequency there's less than 3dB of difference in the FR graph and the distortion graph for the previous measurement that I did with the sub mounted upright. If Art's interpretation of what the graph is supposed to be showing is correct, there would be gross distortion components showing up in the RTA measurement done at that frequency (-3dB THD =~ 71% THD). The distortion components actually observed at that frequency in the RTA measurement will add up to nowhere near that. The highest component is just over 50dB lower than the fundamental.

I will repeat the test sideways when I get the opportunity. I think I have an idea of what may have contributed to the increase in distortion for the sideway measurement however (large flat vibrating panel + uneven floor). Maybe we should take a page from the HiFi people and use 3 spiked feet per sub...
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Old 14th May 2015, 11:27 PM   #532
Brian Steele is offline Brian Steele  Grenada
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I repeated the upright / sideways test, this time correcting one major thing - the gain on the mic was set too low! The output has DSP applied to it to address the out of band peaks and smooth the TH's passband a bit, but the HP and LP filters are turned off. And the FR is smoothed by HolmImpulse's default smoothing algorithm.

In red is the FR/distortion curves with the POC3 upright
In blue is the FR/distortion curves with the POC3 on its side

The blip in the distortion around 100 Hz is due to panel flex. It decreases when I add about 185 lbs of weight to the TH (by sitting on it, LOL). I haven't figured out which panel is the main culprit yet, but my bet is that it's the bottom one. At frequencies nearer to the lower end of the TH's passband, the POC3 shows less distortion when mounted sideways, though I don't think the difference would be audibly significant.
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Old 15th May 2015, 04:24 AM   #533
Scientific is offline Scientific  Dominica
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Originally Posted by weltersys View Post
5) Having only looked at measurements of Th18 or an Othorn, I'd expect them to be similar, with the Keystone having a bit (2 dB, IIRC) more output than the TH18 according to PASC. The Othorn goes lower, which could translate to sounding less "punchy". Art
Art, any idea how the pal12 would sound if widened to around 22 inches and fitted with an 18" ? Do you know if anyone did a sim for it with an 18? I am wandering how it would compare with a TH18 or a KS if it had an 18" driver.

I am also wandering if the keystone shape would increase SPL to a pal12, considering you settled on that shape after much experimentation. The exit on the pal12 seems pretty small. That KS shape seems to have the magic.
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Old 15th May 2015, 07:12 AM   #534
CRESCENDO is offline CRESCENDO  United States
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Art, any idea how the pal12 would sound if widened to around 22 inches and fitted with an 18" ?
You might be able to get close in Hornresp by taking the areas of the Pal12's S1, S2, etc. and adding the percentage of area you get by widening the enclosure to your desired dimension. If, for instance, you're adding 15% to the internal areas of the Pal12, internally - you may be able to add 15% to the Pal12's S1, S2, etc., then enter some 18" driver parameters to see what comes of it.

Someone might chime in to tell me how accurate/inaccurate this method might be.
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Old 15th May 2015, 02:45 PM   #535
Zwiller is offline Zwiller  United States
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Interested whether this is accurate too as I simmed an extended response KS in post 476. This IS the KS thread, right?
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Old 15th May 2015, 03:36 PM   #536
Brian Steele is offline Brian Steele  Grenada
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Originally Posted by CRESCENDO View Post
You might be able to get close in Hornresp by taking the areas of the Pal12's S1, S2, etc. and adding the percentage of area you get by widening the enclosure to your desired dimension. If, for instance, you're adding 15% to the internal areas of the Pal12, internally - you may be able to add 15% to the Pal12's S1, S2, etc., then enter some 18" driver parameters to see what comes of it.

Someone might chime in to tell me how accurate/inaccurate this method might be.
It should work out fine, once the only dimension you are changing is the width and you're using "par" segments for the HornResp model.

Trouble is, once you load the driver in the model, you may find that you need to increase or decrease the ratio between S1 and S4 to improve the response, and that would require more substantial changes to the box.
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Old 15th May 2015, 05:55 PM   #537
weltersys is offline weltersys  United States
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Originally Posted by Scientific View Post
1)Art, any idea how the pal12 would sound if widened to around 22 inches and fitted with an 18" ?
2)Do you know if anyone did a sim for it with an 18?
3)I am also wandering if the keystone shape would increase SPL to a pal12, considering you settled on that shape after much experimentation.
1) Depends on the 18" used, some will sound like crap, others would work OK.
2) I doubt it, since the pal 12 thread was about a Lab 12 TH.
3) The pal12 uses a fold that would not benefit from a keystone shaped exit.
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Old 17th May 2015, 12:20 PM   #538
m R g S r is offline m R g S r  United States
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Originally Posted by Scientific View Post
Art, any idea how the pal12 would sound if widened to around 22 inches and fitted with an 18" ? Do you know if anyone did a sim for it with an 18? I am wandering how it would compare with a TH18 or a KS if it had an 18" driver.

I am also wandering if the keystone shape would increase SPL to a pal12, considering you settled on that shape after much experimentation. The exit on the pal12 seems pretty small. That KS shape seems to have the magic.
I already had that idea. Here...

http://www.diyaudio.com/forums/subwo...38x22-5-a.html
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Old 17th May 2015, 12:28 PM   #539
m R g S r is offline m R g S r  United States
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And I never tested the keystone on the pal 12. I was going to but after building the test cabinet and getting results that I was happy with, I just built a second cabinet.
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Old 18th May 2015, 01:12 AM   #540
Scientific is offline Scientific  Dominica
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MRGSR, How many PAL12s would you say give the same SPL as a Lab horn?

I looked at the sim for the 18. As an 18 has twice the surface are of a 12, shouldn't that give at least a 3 db increase in SPL over the 12? It is pushing more air, twice the amount of air. Shouldn't that show up in the sim?
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