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Nice! Waiting to see what that bad boy can do. Build quality looks good along with the price. If I change my two sealed 21" Eminence NSW subs, it will be to PR's. No port noise issues and a smaller box vs ported. Negatives? More $ and below tune, it will drop off faster vs ported. I'm in the minority but it's what I would do.
 

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Its been about 5 hours.... where are my detailed build photos, REW graphs, and in depth analysis?
 

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C.Pop's New & Improved 21" Mega Journey of Foolishness (with PR's)

Nice! Waiting to see what that bad boy can do. Build quality looks good along with the price. If I change my two sealed 21" Eminence NSW subs, it will be to PR's. No port noise issues and a smaller box vs ported. Negatives? More $ and below tune, it will drop off faster vs ported. I'm in the minority but it's what I would do.

Actually a PR alignment should drop off much shallower than a ported box. A ported box acts more like an open box after port tune and a PR should be somewhere between a sealed and ported post tune ... depending on the size of the box that is.


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PR rolls off faster due to a notch at the resonant frequency of the PR.
This affects transient response in a bad way but I don't know if it is audible. This is a trade-off you make eliminating pipe resonances but you lose output from the system at tuning. Passives do lower distortion induced by the driver's coil movement during large excursions like a port. At tuning the driver is at its minimum motion point. The passive though acts as a notch filter at tuning.
Really deep in frequency, a passive has more output than a port resembling a sealed system.

When you average the PR output above and below Fs, the output roll off is not as steep as a port but from Fs and above it is falling faster than a ported system. Trimlock's wording is proven true when you look at total output.



 

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When you average the PR output above and below Fs, the output roll off is not as steep as a port but from Fs and above it is falling faster than a ported system. Trimlock's wording is proven true when you look at total output.

I don't know, the net conclusion is based on including what I believe is a more or less useless (low SPL) and potentially dangerous parts of the freq range where the driver and PR are exceeding their excursion limits.
 

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Discussion Starter #46 (Edited)
Guys, real world practicality wise "it depends".

I'm going to tune this sucker pretty low, basically that means the output below tune is largely negligible. I have one piece of electronics with a hpf built in, it's currently at about 8-9hz, I can see if I can lower it but not going to be able to lower it a ton -I run out of big resistors that'll fit. Should still be able to get in-room response down to just touch the single digits when all is said and done but that's not a huge priority, the room is very large and room gain is minimal.

As for transient response, same as a big ported box, control group delay appropriately in the audible range and it's a non-issue. Ends up looking like a LLT/EBS type with a shallow rolloff.

Chris

Edit; test box will be tuned higher as it's more practical and gives me a real world data point.
 

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Discussion Starter #47
Its been about 5 hours.... where are my detailed build photos, REW graphs, and in depth analysis?
Right?

I'm juggling a few audio related things right now, including re-calibration of the office system (swapped out for powered JBL monitors), but I assure you some BS is going on with the 21's soon.

Chris
 

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I don't know, the net conclusion is based on including what I believe is a more or less useless (low SPL) and potentially dangerous parts of the freq range where the driver and PR are exceeding their excursion limits.
That would be true of all system alignments if you are talking max SPL. If the volume was just casual listening levels, driver and passives are not necessarily near excursion limits. If you want to exclude response under the passive's resonant frequency, it has already been stated that the passive alignment is falling faster due to the notch.
 

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Discussion Starter #49 (Edited)
Making a little progress, been delayed due to furloughs, covid, etc.

Attached are two graphs, the first is a nearfield mic measurement (in-room) of the LaVoce in a sealed 6 cuft box. The dip at 65hz is a measurement artifact, but the slope of the response can be easily seen.

The second graph, which is a little different from the norm here at AVS but more useful for my usage, is the mic in one of the potential listening positions. Why potential? This is going in the living room, not a dedicated theater, and sometimes things get shuffled around for convenience, the re-style effect, etc. Hey, we've been cooped up in the same place for a while so a furniture-move redecorate can be fun. Important stuff; this is with the mic about 15' away. I wanted to see compression kick in, and I did. Had to cut the upper freq's off on the last run as I was clipping the mic and since I was positioned fairly near the sub itself, it was quite loud and I wasn't interested in continuing. Amp used was a bridged crown xls2502, plenty of power left. Of course, no eq, no filters, no crossover, although I do have one component with about a 7hz HPF, which can be seen in the rolloff.

What's the take home?

I can expect in the vicinity of 7dB of room gain at 20hz, and a little under twice that at 10hz. Not great, not horrible, definitely less than most rooms I've used, but it is a large room.

I'll use the above data to ball park the efficacy of some very low tunes that result in a sloped rolloff not unlike a sealed box.

Next will be to install the PR, run some DATS sweeps to figure out a tuning, then largely repeat the above.

Chris
 

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Making a little progress, been delayed due to furloughs, covid, etc.

Attached are two graphs, the first is a nearfield mic measurement (in-room) of the LaVoce in a sealed 6 cuft box. The dip at 65hz is a measurement artifact, but the slope of the response can be easily seen.

The second graph, which is a little different from the norm here at AVS but more useful for my usage, is the mic in one of the potential listening positions. Why potential? This is going in the living room, not a dedicated theater, and sometimes things get shuffled around for convenience, the re-style effect, etc. Hey, we've been cooped up in the same place for a while so a furniture-move redecorate can be fun. Important stuff; this is with the mic about 15' away. I wanted to see compression kick in, and I did. Had to cut the upper freq's off on the last run as I was clipping the mic and since I was positioned fairly near the sub itself, it was quite loud and I wasn't interested in continuing. Amp used was a bridged crown xls2502, plenty of power left. Of course, no eq, no filters, no crossover.

What's the take home?

I can expect in the vicinity of 7dB of room gain at 20hz, and a little under twice that at 10hz. Not great, not horrible, definitely less than most rooms I've used, but it is a large room.

I'll use the above data to ball park the efficacy of some very low tunes that result in a sloped rolloff not unlike a sealed box.

Next will be to install the PR, run some DATS sweeps to figure out a tuning, then largely repeat the above.

Chris
which passives are you currently using? the Mach5? That's a very nice slope to work with.
 

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Discussion Starter #51 (Edited)
which passives are you currently using? the Mach5? That's a very nice slope to work with.
I will put in a single Mach5 in for initial testing. We'll see how much mass it takes to drop the tuning nice and low.

Haven't heard anything from PSI yet.

Yes, slope is reasonable, obviously these need signal shaping, but worst case scenario a large sealed box, like what it's in now, will do just fine, particularly with multiple drivers. Would make it easy; couple double Lavoce's up front, few singles scattered around.

Chris
 

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Discussion Starter #52
quick and dirty (oh so dirty) impedance sweep of the PR installed with 2.75kg attached.

Dirty because obviously I have some air leaks around the PR, and the enclosure is a slapped together quicky -this can be seen in the ripples. Is it good enough? Yes, as it still aligns with predicted impedance minimum location. I expect this will change some once dialed in, but for what we're doing today there isn't much value in re-running DATS.

Upon firing it up, I definitely have some air leaks around the PR, will re-visit the foam tape stuff, but initial impressions made me laugh. This is going to be frightening once complete. This is around a 15.5hz tuning.

Steve is "helpful" as per normal and Walter popped in since one cat obstructing a sub test really isn't enough, we're going to need two, which roughly equates to the same as around a thousand.

Chris
 

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Discussion Starter #54 (Edited)
2.75kg attached is 3330g total moving mass. MMS unloaded is 580g.

Max? I'll load these SOB's to 50 lbs if I need to. If they die, they die.

Chris
 

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Discussion Starter #56
So basically you're box size is set, you're not going to build them any bigger, no matter what, right?
No, quite the contrary. We'll build them what they need to be -the test box is 6 cuft, final design will be twice the active (and passive, of course), but likely be even larger than the 12cuft doubling expected. How much? Undecided, let's start with 6cuft per and see how that testing goes. Worst case scenario I can always slightly upsize the box if needed to drive PR tuning down for a given loaded mass, but that sort of goes against the point of the PR. I'd rather just make 'em earn their living. ;)

It's exciting and fun times!

Chris
 

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Discussion Starter #58
First run. No eq, blah blah blah, quick and dirty useful apples to apples best I can.

Looks like sim predicted +3.3dB @ 20hz, measured is a little under. Sim predicted +5.9dB @ 14hz, measured is over 1dB more. Sim sealed v PR response crossover is at 10.8hz, measured is at 10.6hz.

It's not a bad day.
 

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Discussion Starter #60
Quick filters to blend:

1: xover LR24db/oct @80hz

Filters:
1: Peak, 23hz, +6dB, Q=1
2: HS 100hz, -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

Gives a nice sloped rolloff going up in freq, helps combat the insane efficiency in the higher frequencies.

Sound is very punchy, tons of impact.
 
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