C.Pop's New & Improved 21" Mega Journey of Foolishness (with PR's) - Page 3 - AVS Forum | Home Theater Discussions And Reviews
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post #61 of 130 Old 05-15-2020, 07:53 PM
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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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post #62 of 130 Old 05-15-2020, 08:09 PM
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Also, regarding the sound, do you like it better with the PR vs sealed?
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post #63 of 130 Old 05-15-2020, 09:20 PM
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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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post #64 of 130 Old 05-15-2020, 09:30 PM
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Very interesting.

The PR puts quite a dent in Hoffman's Iron Law at ULF, where it most applies.


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Originally Posted by Chris Popovich View Post
Sealed vs. PR (3330Mms, Mach5 PR). 6cuft enclosure.

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post #65 of 130 Old 05-15-2020, 11:05 PM - Thread Starter
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Quote:
Originally Posted by spanish68 View Post
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.

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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.

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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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Originally Posted by noah katz View Post
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.

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post #66 of 130 Old 05-15-2020, 11:34 PM
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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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post #67 of 130 Old 05-15-2020, 11:44 PM
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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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post #68 of 130 Old 05-16-2020, 01:02 AM - Thread Starter
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Quote:
Originally Posted by Nalleh View Post
^^ 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.
In a given box volume, yes. I'll be more than doubling volume. Tune will drop a little.
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post #69 of 130 Old 05-16-2020, 01:11 AM
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Quote:
Originally Posted by Chris Popovich View Post
In a given box volume, yes. I'll be more than doubling volume. Tune will drop a little.
Sure, i meant per active driver.

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post #70 of 130 Old 05-16-2020, 09:29 AM
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Quote:
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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.
I'm talking about cancelling the moving mass, not the tuning. 50mm of that much mass is like swinging around a dumb bell.
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post #71 of 130 Old 05-16-2020, 09:51 AM
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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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post #72 of 130 Old 05-16-2020, 10:48 AM
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Quote:
Originally Posted by Nalleh View Post
PR’s mounted downfiring in nearfield boxes.

Have you checked how much they sag?

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post #73 of 130 Old 05-16-2020, 10:55 AM - Thread Starter
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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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post #74 of 130 Old 05-16-2020, 11:03 AM
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Quote:
Originally Posted by noah katz View Post
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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post #75 of 130 Old 05-16-2020, 11:04 AM - Thread Starter
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Yeah, they really are stout buggers.
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post #76 of 130 Old 05-16-2020, 11:54 AM
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Quote:
Originally Posted by Nalleh View Post
Yup, or use it as a TR device, as i do



PR’s mounted downfiring in nearfield boxes. Why waste a good shaker

Damn that’s a good idea.


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post #77 of 130 Old 05-16-2020, 12:04 PM
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Quote:
Originally Posted by Nalleh View Post
None!

I now have 500grams of mass added, and there is NO sag of the cone.

Then they must have very high Fs, as cone sag is an inverse function of Fs.

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post #78 of 130 Old 05-16-2020, 12:07 PM
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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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Quote:
Originally Posted by noah katz View Post
Then they must have very high Fs, as cone sag is an inverse function of Fs.
16.7hz.

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post #80 of 130 Old 05-16-2020, 12:41 PM - Thread Starter
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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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Quote:
Originally Posted by Chris Popovich View Post
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.
Indeed. Agreeing with all you said

Well, if there is sag from the 500grams, it has to bee within 1mm! Because it is not percievable.

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post #82 of 130 Old 05-16-2020, 01:23 PM
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Quote:
Originally Posted by Nalleh View Post
16.7hz.

Sag = g / [2*Pi*Fs]^2

= 9.81/[2*3.14*16.7]^2

= .00089 m

= .89 mm

Pretty close (and not as high as I expected).

But is that its Fs when mass loaded?

Seems like the freq response would be a mess.

As an aside, I'm philosophically opposed to high suspension stiffness, as it lowers efficiency same as the box air spring.

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post #83 of 130 Old 05-16-2020, 02:06 PM - Thread Starter
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Noah, that's one of the reasons I didn't try multiples of them with the 21" driver, although a high power motor like these pro-audio drivers is the sort you'd want to use.

The Earthquake SLAPS can be fantastic for small boxes, very quickly become much less optimal as box size increases.
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post #84 of 130 Old 05-16-2020, 02:31 PM
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Chris, I agree regarding the "more midbass that one can use" regarding this new pro drivers, specially the 21". I have my NSW's bottom end boosted and the mid bass still is amazing. On another note, do you have plans on the size of the PR boxes? How many are you planning to make?
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post #85 of 130 Old 05-16-2020, 03:01 PM
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C.Pop's New &amp; Improved 21&quot; Mega Journey of Foolishness (with PR's)

Chris where you located at? I forget.

I will continue to sit back and enjoy the discussion as I’m looking at building some ported subs using the 21” Lavoce SAN driver.

Something along the lines of 14.5 cf give or take internal (before subtracting ports)...

I’d likely have to have active on front, 1 passive on the outer sides (subs would be built as part of a full entertainment center), but I’ve always liked passives....

Did you post the T/S for the passive somewhere (so I can model myself in WinISD)?

Anyway, carry on!


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post #86 of 130 Old 05-16-2020, 07:47 PM - Thread Starter
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I'm in North Phoenix, Arizona.

Re-arranged my silly living room today, spent several hours with the single LaVoce/PR alignment pounding away. No room correction, just the alignment correction. Periodically I'd reach over and feel what the PR is doing, which is exactly nothing most of the time. Remember, we get carried away with what it COULD do more than what it NEEDS to do. I did most of the listening without any subharmonic synth.

This sounds fantastic.

I usually am not an overly big fan of upper bass, it's just so easy for it to be overblown, boomy and muddy. While this absolutely needs to be tamed, it isn't the annoying upper bass you get from crappy bookshelf speakers tuned too high, it's the sort that makes you nod your head and tap your feet. Great impact.

Alignment wise, simply put this behaves like a sealed box until you get down to 20hz or below, then you get a little extra output. It ends up presenting like the same sealed sub but in a room with (much) better ULF gain. Pretty cool.
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post #87 of 130 Old 05-16-2020, 07:49 PM - Thread Starter
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Specs of Mach5 21" PR with no weight added:


Fs: 17.9hz
Qms: 8.7
Vas: 18.33 cuft
Cms: 0.136 mm/N
Mms: 580g
Rms: 7.45 kg/s
Sd: 1640sqcm
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post #88 of 130 Old 05-17-2020, 10:09 AM
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Something I wonder about with a PR that must more massive to overcome suspension stiffness is whether it worsens transient response.

I would suspect so, as higher stiffness and mass with presumably the same damping would raise Q.

This would be evident in the time response showing more prolonged ringing.

I was going to try this with UniBox (a very nice program, especially for PR design http://audio.claub.net/software/kougaard/ubdwnld.html ), but my (Windows 10) computer isn't behaving according to the online instructions for unprotecting an Excel workbook.

Anyone want to give it a try?

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post #89 of 130 Old 05-17-2020, 10:54 AM - Thread Starter
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I was approaching it from a different direction; control group delay.

PR's negatively impact transient response same as ports do (but worse since they're a higher order alignment... ports + mech losses). It's another reason to keep tuning very low; make sure group delay is low in the audible range. The old rule of thumb from Dan Wiggins was 20ms at 20hz. This design is around 11.5ms @20hz . It peaks at a whopping 65ms at 12hz, but it's my position that's inaudible.

Below is group delay for sealed box vs. current PR alignment, no eq.
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post #90 of 130 Old 05-17-2020, 03:01 PM - Thread Starter
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Changed filters a bit (dropped 23hz down to 20, lowered Q from 1.0 to 0.5, dropped 100hz high shelf down to 90hz).


1: xover LR24db/oct @80hz

Filters:
1: Peak, 20hz, +7dB, Q=0.5
2: HS 90hz, -16dB, Q=0.5
3: Peak, 500hz, -80dB, Q=20

You have to do the -80dB filter with biquads, it's this:
biquad1,
b0=0.859483993961542,
b1=-1.71525949967588,
b2=0.859455887949733,
a1=1.71525949967588,
a2=-0.718939881911275
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