B&C 8PE21 on Tractrix horn - diyAudio
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Old 26th November 2008, 07:46 AM   #1
jpboyt is offline jpboyt  United States
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Default B&C 8PE21 on Tractrix horn

I am looking for suggestions on the sizing of a tractrix horn for this driver. Crossover points are at 500Hz and 2500Hz. Speakers will end up being in a 3way setup with a Mackie fussion amp. Crossover points are fixed unless I start swapping components out. I was thinking along the lines of an X-tro type box but I supect that the midrange is where I will need the help. Thanks in advance, JPBoyt
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Old 26th November 2008, 01:32 PM   #2
JLH is offline JLH  United States
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You will need a proper phasing plug to reach 2.5KHz with the 8PE21. Even at that, youíll still have a hard time getting the last octave to 2.5KHz. My experience with the 8PE21 is as a mid bass horn in the home Hi-Fi environment. Pro sound applications are different, but not so much that conclusions canít be made. It is possible that a phasing plug along with the narrowing high frequency directivity of the tractrix, you could reach 2.5KHz with the 8PE21. I would suggest a full size 400Hz tractrix with a 29.9cm^2 throat. The real challenge will be getting the back chamber small enough. Since you only want to use it down to 500Hz, the back chamber has to be very small, like less than 500CC. If you canít get the back chamber small enough, then you will have to go to a bigger horn. However, the bigger horn will hurt the high frequency performance even more. You have two forces fighting each other. A smaller woofer would be a better idea here. Then again, depending on your application you may need the power handling capacity of the larger woofer. It seems you are in quite the pickle.

Rgs, JLH

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Old 26th November 2008, 02:01 PM   #3
tinitus is offline tinitus  Europe
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Someone has previously mentioned that the 5" FaitalPro works very well in a frontloaded horn...he actually compared it to an 8" B&C and if used up to 2.5khz it would be quite natural that a smaller unit would be bettter...100USD at USspeaker
I am not sure, but I dont think it will need a backchamber, which makes the horn much simpler

http://www.faitalpro.com/products/sc...p?id=101010100
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Old 26th November 2008, 03:29 PM   #4
GM is offline GM  United States
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It's open back, so unless you design a horn suitable for an open back it will need a back chamber with the smallest Vb obviously being where the basket is sealed up. The latter is best for max BW, high SPL output though, so not practical for a high SQ mids/HF app using a typical cone/dome driver. Better to use a 1.4 or 2" exit compression driver with an Fs < 0.5-0.7x the XO point depending on the horn's cutoff.

GM
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Old 26th November 2008, 04:27 PM   #5
JLH is offline JLH  United States
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Quote:
Originally posted by tinitus
Someone has previously mentioned that the 5" FaitalPro works very well in a frontloaded horn...he actually compared it to an 8" B&C and if used up to 2.5khz it would be quite natural that a smaller unit would be bettter...100USD at USspeaker
I am not sure, but I dont think it will need a backchamber, which makes the horn much simpler

http://www.faitalpro.com/products/sc...p?id=101010100

That would be me. Iíve A/B them in the pictured full size 142Hz tractrix. The faital 5Ē absolutely smoked the 8PE21 in this horn. Due to the Faitalís higher Fs, I was able to leave the back chamber open. The 8PE21 sounded congested, unfocused and dull in tone compared to the Faital. However, when the 8PE21 is equiped with a phasing plug, the gap closes. IMO, the Faital is still a better choice. I must restate this was in a home Hi-Fi system and NOT for PA use. The above may not apply to PA use.

Rgs, JLH


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Old 27th November 2008, 03:54 AM   #6
jpboyt is offline jpboyt  United States
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Thanks for the info. I guess I ought to start over with my list of components and then ask for suggestions. I aquired a couple of the old Mackie Fussion amps, 3ways, that are rated at 1000w, 200w, and 100w into 8ohms. The crossover points are at 500hz and 2500hz. The drivers I have for each box are 2ea B&C 15PZB40 8ohm, 1ea 8PE21 8ohm, and 1ea DE900 8ohm. I own a total of 8-15", 4-8", and 4-1.4". My plan was to end up with two active boxes and two passives. My plan was to run the 2 15PZB40 drivers in series to load up the amp a bit and then be able to run a second passive box, in parallel, with the same driver set. I would end up with 1000w into 16ohm as a single box and 1000w into 8 as double boxes. Mid and highs would be 8ohm single and 4ohm in the active/passive pair combination. These particular components were selected for numerous differing reasons. Price and availability for the most part. The 8PE21 was actually selected for its reasonably flat response between 500hz and 2500hz. Obviously this is not for livingroom use although I love testing the subs next to the piano. Defines sympathetic vibration.
So am I nuts or is there a path to follow through this pile of parts?
JPBoyt
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Old 27th November 2008, 06:26 AM   #7
pk is offline pk  Denmark
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Default JLH: Two question regarding the Faital driver

Jpboyt: I can't help regarding your setup, sorry, but I have two question to JLH - hope it's ok.

JLH: (1) May I ask how far down in frequency does the little Failtal driver load in your 142 Hz tractrix horns? (2) How does the Failtal driver compare to the Fane Studio 8M?

Thanks!

Best regards
Peter
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Old 27th November 2008, 02:27 PM   #8
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hi John

i would like to add another question :
( sorry to the original poster, this is off topic )

some employ instead of a cone driver, a compression driver, to cover the lower midrange band, down to 200hz. examples like the system of experience audo at VSAC, using Goto drivers, comes in mind. Or Vincent Brient's 150hz horn , using the Radian 950pb. You said once, a compression driver used below its resonance frequence distorts a lot. Is distortion not only a matter when high power is required ? I am thinking if it might be worth to make a adapter for my midbass horn, and try out this solution. Have you ever made such a test ?

Angelo
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Old 27th November 2008, 02:50 PM   #9
pos is offline pos  Europe
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some interesting reading:
http://www.jblpro.com/catalog/suppor...=201&doctype=3
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Old 27th November 2008, 03:58 PM   #10
JLH is offline JLH  United States
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Quote:
Originally posted by jpboyt
Thanks for the info. I guess I ought to start over with my list of components and then ask for suggestions. I aquired a couple of the old Mackie Fussion amps, 3ways, that are rated at 1000w, 200w, and 100w into 8ohms. The crossover points are at 500hz and 2500hz. The drivers I have for each box are 2ea B&C 15PZB40 8ohm, 1ea 8PE21 8ohm, and 1ea DE900 8ohm. I own a total of 8-15", 4-8", and 4-1.4". My plan was to end up with two active boxes and two passives. My plan was to run the 2 15PZB40 drivers in series to load up the amp a bit and then be able to run a second passive box, in parallel, with the same driver set. I would end up with 1000w into 16ohm as a single box and 1000w into 8 as double boxes. Mid and highs would be 8ohm single and 4ohm in the active/passive pair combination. These particular components were selected for numerous differing reasons. Price and availability for the most part. The 8PE21 was actually selected for its reasonably flat response between 500hz and 2500hz. Obviously this is not for livingroom use although I love testing the subs next to the piano. Defines sympathetic vibration.
So am I nuts or is there a path to follow through this pile of parts?
JPBoyt

Flat response is the last thing you want in a woofer that is to be horn loaded. What you need is a woofer that has a raising high frequency response. The horn loading will raise the lower frequencies and make the overall response flat again. If you horn load a woofer that has flat response, then it will be bass heavy. Been there, done that. Once you put a woofer on a horn everything changes.

Rgs, JLH
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