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There's a nice difference in the mid-teens but I expected more of a difference with the PR at around 20hz. Probably not the case due to the very small box used in the test. With a much bigger box, say 12cf, the difference will probably double at 20hz and have even more of an edge vs sealed in the low to mid teens. It still is a nice upgrade considering the box size.
 

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What was the excursion on the PR looking like at tuning? Have you done a high powered test yet?


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Discussion Starter #65
There's a nice difference in the mid-teens but I expected more of a difference with the PR at around 20hz. Probably not the case due to the very small box used in the test. With a much bigger box, say 12cf, the difference will probably double at 20hz and have even more of an edge vs sealed in the low to mid teens. It still is a nice upgrade considering the box size.
It pretty much did exactly what the sim predicted. Remember, 6cuft for a ported 21" driver would be considered silly; the X21, for example, is >1.5x the volume. This is the price you pay when you tune a small(ish) box very low; it looks like a sealed box with the extreme bottom end propped up a few dB, in this case, 7+dB. Similar to a port, the contribution to output decreases further from tune. If you wanted more out of the PR, a more traditional alignment would do exactly that, but remember I'm using a pro-audio driver not designed to hit down to the 12hz range.

Also, regarding the sound, do you like it better with the PR vs sealed?
It's a wash. IMO depends FAR more on implementation and target eq curve. These pro drivers are something special. I'm pulling a TON out up top but it still has punch and impact, TONS of midbass, I have so much midbass I don't even know what to do with it. The extreme bottom sounds a little anemic to me, but let me play with target response curves a bit.

What was the excursion on the PR looking like at tuning? Have you done a high powered test yet?

PR isn't doing that much until extremely low. Excursion always looks less on larger diameter drivers, but in my quick-testing I doubt it exceeded 10-12mm. Nor should it; at 20hz and 1200W, PR excursion is 5.5mm, this increases to 17.3mm at 15hz, and blows up to 52mm at 10hz and 1200W. If I drop tuning a hair I may be able to get by with no additional HPF (remember, everything in the system goes through a subharmonic synth with a 7hz HPF).

Goofing around I did clip the crown into the Lavoce, PR excursion was moderate. I was sitting on the test box to stop it from dancing, and it was blurring my vision. That's 7+ lbs of moving mass on the PR, will definitely want to use them in a force-balanced scenario!

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Very interesting.

The PR puts quite a dent in Hoffman's Iron Law at ULF, where it most applies.
Yes, it'll get nicer with a larger box like everything does, but as-is you get 7dB @ 15hz for the cost of the PR, which was ~$250 shipped.




Overall impressions are favorable. Going from dual UM18's and a dozen nearfield JBL's to ONE farfield 21" driver in a test box is not the way you want to go about things to impress yourself, so I have to check my expectations. This is putting a LOT of low frequency information out into a huge room, and the design is a test-box only, I never had any intention of running a 6cuft PR box long term, sure I want to use it for temp use, but it was always the plan to learn a little about these PR's and incorporate that into a final design, then build a bunch.

The pro-drivers sound light on the bottom end compared to, say, a UM18, and IMO this is reflected in the measurements. What's interesting is that even when you eq things to be very much the same, the bottom end comes up fine but you KEEP the pro-audio punch. It really does everything pretty well, and I'm not one of the guys who thought the UM18 was a slouch.

As to how it compares to sealed... sound wise it's a wash, it sounds about the same. Great for music. Tuning this low in this small of a box doesn't pay big dividends in increased SPL across a wide range -again, this is expected.

I would say the PR designs have merit. With the price of the Mach5 PR's being about $500 for two, and the Lavoce being $450ish each, the question is what does a sealed triple-lavoce look like compared to a dual-lavoce with PR's? The triple is a weird impedance (2.66ohms) which is odd to drive, but if you stick both in 18cuft cabinets, essentially the triple sealed will beat the PR watt-per-watt above 20hz. The PR beats it between 20 and about 10hz, and the sealed wins below 10hz again. Makes sense, Hoffman working again. The triple lavoce with a speakerpower plate amp would be pretty badass.

Chris
 

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That is interesting in a 6cu/f box. I was expecting the slope to be more downward prior to tuning but the PR was kicking in half and octave above tuning. I guess this bodes well for having two PR’s with the Lavoce driver, especially with what you said about the excursion hitting over 50mm!! That must of been cool to see lol. I was hoping that with that much mass the excursion would of hit under the SIM’s, oh well. This seems to be a success overall. The price on these Pr’s is pretty cheap too.


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^^ If i am not mistaking, doubling the number of PR’s does the same as doubling the number of ports: it moves the tune higher.
 

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I'm talking about cancelling the moving mass, not the tuning. 50mm of that much mass is like swinging around a dumb bell.
Yup, or use it as a TR device, as i do :)



PR’s mounted downfiring in nearfield boxes. Why waste a good shaker ;)
 
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Discussion Starter #73 (Edited)
Generally downfiring PR usage is a no-no, but the Earthquake units are a bit of a different animal. The SLAPS are used in some production models, including the Legacy Foundation, on which one is rear firing and the other is down firing. Not sure what they're tuned to, or if there are any tweaks done to the design for their application.

Edit; note (again) that the SLAPS tend to be spec'd to be used in smaller enclosures.
 

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Have you checked how much they sag?
None!

I now have 500grams of mass added, and there is NO sag of the cone. They are built like a tank:)

And not only am i NOT using a HPF, i am using 10dB low shelf at 10hz, and they eat it up ;)
 

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Damn that’s a good idea.


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Affirmative !!

6 of those were more effective as BOSS than 8 X JBL ;) With the added benefit of SPL and punch from the active drivers in the boxes :)

(Sorry for the OT, Chris ;))
 

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Discussion Starter #80
No it's fine, this forum needs more PR discussions.

The earthquake units have very stiff suspensions. You need to add a lot of mass to drive Fs low. They must have some sag, just by way of physics, but I take the "zero sag" as more of a generalization; the take home is that they aren't sloppy soft PR's that flop around when mounted in a downfiring config. 500g isn't that much, at least in my world, with my starting added mass at 2750g lol.
 
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