B&C 8PE21 on Tractrix horn

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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
 
You will need a proper phasing plug to reach 2.5KHz with the 8PE21. Even at that, you’ll 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 can’t 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 can’t 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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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/schede/ps.php?id=101010100
 

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GM

Member
Joined 2003
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
 
tinitus said:
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/schede/ps.php?id=101010100


That would be me. I’ve A/B them in the pictured full size 142Hz tractrix. The faital 5” absolutely smoked the 8PE21 in this horn. Due to the Faital’s 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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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
 
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
 
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
 
jpboyt said:
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
 
Re: JLH: Two question regarding the Faital driver

pk said:
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


It starts to roll off at 135Hz in half space. Its low end is only limited by its high Fs. The Faital could probably still go down to 135Hz in something smaller like ~ 160Hz tractrix maybe.

I also A/B the Faital with Fane Studio 8M. The Faital was better. However, let me make clear how I tested these. The horn has a 4" throat. The Fane did not have a phasing plug, so there was a fair amount of throat reflections. The Faital's actual cone diameter is closer to 4", so there would be almost no throat reflections. The same congestion that was heard with the 8PE21 was present with the Fane. However, due to the much stronger motor of the Fane, the dull tone was gone. IMO, if I would have had a phasing plug for the Fane, it would be the winner over all. But, if you don't have the skills to make a proper phasing plug, the Faital 5' woofer is the one to use.

Rgs, JLH
 
pos said:


Essentially this is what I made with the 8PE21 in the 142Hz tractrix horns. The phasing plug makes a night and day difference in the sound. I’m also working on a phasing plug for the Faital for a 2.5” throat horn. I’ll be making this horn for mid range use. I want to try the Oblate Spheroid and make the horn large enough to hold its pattern down to 600Hz. It should be interesting. No time line on its completion. I’m just working on it as time permits.

Rgs, JLH
 
angeloitacare said:
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

I don’t really care what other people are doing. I’ve already done all the things they are trying to do now. It doesn’t matter how you try to rationalize it; you cannot use a compression driver below Fs and call it high fidelity. All kinds of problems occur when you try to use a compression driver below Fs. The one thing people don’t seem to understand is a horn doesn’t know if it has a woofer or a compression driver bolted to it. The horn behaves the same way. There is nothing magical about a compression drive that allows you to violate good horn design practices. You can use the resonance peak at Fs to cancel some reactance just like you do with a woofer. However, just like with a woofer, below the Fs resonance peak, you lose dampening control and the power response of the horn drops like a rock. You still may be able to measure some output below Fs, but it is due to the narrowing directivity of the horn. All output below Fs is garbage – period. In addition, when you take something like a 150Hz tractrix and extend the throat back to 1” it causes problems too. The throat of the tractrix is exponential in nature this far back. If you don’t believe me, plot the throat section of a 150Hz tractrix and exponential horn starting at 1” diameter and compare them. As most would agree, the exponential horn is not the best sounding horn profile. I happen to be very sensitive to this kind of throat coloration. I can’t stand the sound of long slow tapering throats. It is best to split up the frequency band and use drivers and horns that were intended to be used there.

Rgs, JLH
 
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Joined 2005
I cant say fore sure, but I dont think that CDs are good fore frequencies below 500hz or so...500hz is a wild guess:clown:

btw, those Goto drivers mentioned fore this task are very special creatures and exstremely expencive, supposed to do 200-1khz, prices from 2500EUR to 11000EUR :hot: theres a special double bass-driver to do 20(?)-500hz, cost 10000EUR...e.speaker seem to have it listed, cant imagine how the horn will look like
 
Thank you all for the info again. Based on my learning about a drivers usefullness in a horn loaded application, relative to free space frequency response, I now can see why I could never get Horn Response to give me a good curve that didn't die before 2.5kHz. I think that my best solution is to see if there is a decent waveguide I could us on the 8PE21 and mount the whole mess in a sheet of plywood. Horn loading the drivers looks to be frustrating at best short of some trailer mounted thing to get the lengths and openings right. Most of the stuff I modeled for the frequncy ranges, ended up with extreme loading ratios in the neighborhood of 35/1. Don't think the drivers would like that. Final question, Where do I get info on waveguides?
Thank you for letting me learn from your learning curve.

JPBoyt
 
angeloitacare said:
hi John

thanks for your response.

I didn't know jbl has a commercial product based on the Cone Midrange Compression Driver technical note. I am wondering, if someone has heard the JBL AM4200/95, and if it maiby would perform well for home use. Generally, P.A. speakers sound very harsh.

Angelo


The only problem with listening to a pair is the attenuation in the crossover masks a lot of the tone and dynamics. You would have to disconnect the waveguide from the crossover and drive it directly with an amplifier in order to judge its raw sound quality. Good luck finding a dealer that would let you dismantle one of their speakers. My gut feeling is they could be quite good in the home if multi-amplified.

Rgs, JLH
 
Angelo, tinitus;

Those GOTO Low midrange (SG505, SG570) are purpose designed with low Fs, and have listed frequency response down to 100 Hz, and are recommended to be operated between 200 Hz and 1 kHz with a 150 Hz horn.

A compression driver yes, but quite a different animal from, say a 2441 JBL, etc.
And different from the GOTO High midrange, and tweeter compression drivers...
Robert
 
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