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Old 20th August 2012, 08:07 AM   #321
djk is offline djk
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You might try stuffing the back corners with some Dow Corning 703, a resin-coated fiberglass product. It can be carved to fit with an electric knife, or an ordinary steak knife as well.

The secret to the upper frequency bandwidth is reducing the plenum volume, and the front-to-back dimensions as much as practical. I've never tried to use them above 250hz or so, although Les Hudson has made variants that he was able to use up to 400hz.

Are you using the Q=2 HP filter at Fb? That makes it flatter on the low end. Without the filter they tend to sound clean but a bit lean.

Driver Properties
Name: 2226H
Type: Standard one-way driver
Company: JBL Professional Division
No. of Drivers = 2
Mounting = Standard, Push-pull
Wiring = Parallel
Fs = 40 Hz
Qms = 5
Vas = 175.6 liters
Cms = 0.158 mm/N
Mms = 98 g
Rms = 5.029 kg/s
Xmax = 7.62 mm
Xmech = 20 mm
P-Dia = 335.3 mm
Sd = 883.9 sq.cm
P-Vd = 0.689 liters
Qes = 0.33
Re = 5 ohms
Le = 1.75 mH
Z = 8 ohms
BL = 19.2 Tm
Pe = 600 watts
Qts = 0.31
no = 3.3 %
1-W SPL = 97 dB
2.83-V SPL = 99.37 dB
-----------------------------------------
Box Properties
Name:
Type: Vented Box w/ Active HP Filter
Shape: Prism, square (optimum)
Vb = 6 cu.ft
Fb = 37 Hz
QL = 6.197
F3 = 36.59 Hz
Fill = minimal
No. of Vents = 2
Vent shape = rectangle
Vent ends = one flush
Hv = 10.88 in
Wv = 2.5 in
Lv = 13.71 in
-----------------------------------------
Active 12 dB/oct. HP Filter
Fx = 37 Hz
Qx = 2

BBv6.0 shows a 1.1dB rise around 180hz and a smooth roll-off to a shelf of -0.94dB below 80hz. On the upper end it shows a smooth roll-off above 180hz to 320hz, and a 6dB/oct roll-off beyond from the voice-coil inductance.

I have not been able to model what I measure in a real cabinet on the upper end due to the very irregular space created by the plenum and the back of one driver and the front of the other.
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Old 20th August 2012, 11:12 AM   #322
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Interesting- hornrep seems to show a pretty accurate simulation of what I've actually got vs. bbox pro-I wonder why. I presume you mean fill in the corners of the plenum. I made a half hearted attempt at that too, but just took some wood and cut off about 75% of the two back corners, didn't seem to do much but it's worth trying again and doing it right. Thanks for taking the time to sim this.
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Old 21st August 2012, 09:49 AM   #323
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To be or not to be, that is the question.

Did you use the filter (or not)?

You box looks nice, what did you finish it with?
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Old 21st August 2012, 11:59 PM   #324
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DJK, I am using the filter, but did not have it on when I measured for the photo. Initially I thought I was getting a better result just using a bandpass eq vs. the hp, but can test some more. I find my DEQ/Behringer mike to be inconsistent when measuring the very low end. I need to learn to use REW to get a proper view of the output and to eq.
The idea of going to the 500hz horn crossover was just a temp measure anyway till I make space for the midbass front loaded horns (Erik Forker) that I made last year. That horn has a very smooth response from 105hz to 500hz and should sound better handiing those frequencies. So the intent is to end up limiting the PPSL to 40-105hz. I use a HSU original 10" sub for the last two octaves.
For some reason, I never seem to get the same reponse plots in bbpro that you do, mine showed a pretty flat run out to almost 500hz, so I must be doing something wrong in modeling.
Build used home depot 3/4" plywood, stained and water based poly finish with several sandings after each of maybe 4 coats of poly. I routered most of the edges curved, and will eventually turn the boxes vertical to leave space for the FLH's. It looks good enuf unless you examine too closely, and matches the hardwood floor in the room as does the FLH.
I would probably be better off with a sub that can go from 25hz to 100hz vs using both the HSU and the PPSL for the same purpose, but I had the drivers on hand so figured I'd see how it sounded. I also felt that most sub drivers are too slow to mate well with horns, so thought this might be a better solution. I could try to corner load them and apply some eq, I might not need the HSU's at all. Again, Dennis, thanks for your patience and sharing of knowledge.
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Old 25th August 2012, 04:37 AM   #325
OscarS is offline OscarS  United States
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DJK, can PPSL enclosures be modeled in Akabak?
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Old 25th August 2012, 03:02 PM   #326
tb46 is offline tb46  United States
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Default AkAbak PPSL

Hi OscarS,

I exported the Hornresp simulation from Post #320 using: File - Export - AkAbak Script... , and that seems to work just fine. You can then modify the script to suit your design.

I'll attach the AkAbak script file, I had to change the file extension to upload it, to use change it back to "aks".

Regards,
Attached Files
File Type: txt 2226ppsl.txt (2.9 KB, 46 views)
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Old 25th August 2012, 06:56 PM   #327
OscarS is offline OscarS  United States
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Quote:
Originally Posted by tb46 View Post
Hi OscarS,

I exported the Hornresp simulation from Post #320 using: File - Export - AkAbak Script... , and that seems to work just fine. You can then modify the script to suit your design.

I'll attach the AkAbak script file, I had to change the file extension to upload it, to use change it back to "aks".

Regards,
Thanks for the file. Question: So the plenum chamber is modeled as a straight waveguide then, huh? Why is S1=1 cm² in the script, but it is 880 cm² in the HR input screen?
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Old 26th August 2012, 12:38 PM   #328
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It does not work with that model.

I can see no way to model it as it's actually built.
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Old 26th August 2012, 02:50 PM   #329
tb46 is offline tb46  United States
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Hi OscarS,

Post #327: "So the plenum chamber is modeled as a straight waveguide then, huh?"

Yes. By definition in the OD horn the center of the drivers is located at S2, the throat at S1, you cannot change that; but, you can change S2 to the actual area after you subtract the area loss due to the drivers, and you can add S4 and S5 if you want to e.g.: taper the the plenum (chamber/duct/horn/waveguide) from reduced S2 to area without driver influence to mouth. So there is some room for improvement of the model.

Post #327: "Why is S1=1 cm² in the script, but it is 880 cm² in the HR input screen?"

Because some dummy fiddled with the value prior to exporting the simulation. For starters I'd go with the larger value. :-)

Hope the example gets you started anyway.

Regards,
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Last edited by tb46; 26th August 2012 at 02:53 PM.
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Old 3rd October 2012, 08:20 PM   #330
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Oliver: I am wondering how much impact there will be if you don't adjust for driver volumes in the plenum sections? I should think that you want to have identical load on both sides of each driver. Your comments would be appreciated. Thanks and best regards Moray James.
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