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Hi
I am interested in constructing the Harry F. Olson rear horn enclosure, as per patent number 2224919 Dated Dec 17, 1940. The rectangular design, and not front/rear horn.
Can anyone help at all.
Can this enclosure be used with 15" driver?
I thank you in advance for your help.
Joh
Follow Ups:
Hi JohnSorry I'm late : ) If you scale the backloaded horn design (from Olson's patent # 2,224,919) up to accomodate your 15" driver, you would wind up with a cabinet about 65" tall. As DJK observes, the original design was for an 8" driver, implying a cabinet about 36" tall. A 65" tall cab would put the center of your driver's coaxial horn at about 55" high. You could easily (?) raise your current OB rig up to this height to see if this will be a problem from your listening position. If not, and you're not put off by a 65" tall box in your listening room, this backloader has some possibilities. Most modern backloaded designs use a narrow profile in the vertical dimension to push the Diffraction Loss/Baffle Step as high as possible, and this design would fly contra to this, with a cab front about 45" wide. The baffle step would in this case be about 100 Hz, where the 15" direct radiator would start to lose it's ability to load the baffle. The design Olson pictured in the 1936 JAES (?) which is the somewhat similar double loader in the patent, had a crossover about 200 HZ or less (where the output of the front and rear of driver crossover into each other). You should be able to adjust this down by modifying the air chamber on the back of the driver (i.e.: making it larger). It's hard to say how much volume you would need here to get it down around 100 Hz, the usual formulas asume a strait horn, and the backloader has several bends which add a muffler effect to the output. Let's say that you find a compromise somewhere you are satisfied with, or just let the crossover fall where it may (probably about 180 Hz), just how low will this beast go? The path of the back horn would be about 150", which should be good for about 45 Hz. The horn mouth would come out to about 202 sq. inches, which should get it down to about 66 Hz. This mouth seems a bit small to me. I would modify the design so that the area below the top manifold, that is to say the final "S" bend, more resembles the double loaded design. So angle the top baffle in the lower end down, and move the last baffle board up at an angle so that you increase the size of the horn mouth as much as you can. To visualize all this, just overlay the bottom part of the double loader onto the top section of the backloader, and adjust the bottom floor up a bit. There is also a possiblilty of opening up a trap door on the back of the cabinet to get more mouth area, which may be useful if there is a corner in the room nearbye for the horn to exhaust into, you can definitely get some more bass extension this way. An interesting project! BTW, I fixed my scanner. The next step is how to attach a scan to an e-mail, which was quite simple when I sent Fred that stuff a few years ago, perhaps less so on OSX. I'll try to get some drawings to you soon.
Good luck in your search!
Thanx Paul
Thats great. My crude measurements put the dimensions of the cabinet similar to your measurements, mine out by a few inches. Indeed this puts it into a huge box. Mmmmmm, the wife factor now comes into it, and I think aesthetically not a great look in the room. I have a biggish room, but need to be practicable. I didn't realise when I actually measured, that i would be so big. My Listening height would be lower than the center of the driver, so again, this doesn't seem practicable.
Paul, what width would be practicable? Is it too much to ask the 15" driver to be used, or a smaller driver required? I guess, when seeking the low end of the spectrum, if can get to 40 or so Hz, that will satisfy my requirements as I don't listen to very low bottom end musical frequencies
I am still learning about horn enclosures,and am thoroughly enjoying the feedback, so thanx to all.
Paul, and everyone else, what programme do you use to calculate horn lengths? Your knowledge and the way you easily confront this enclosure to find solutions is beyond me.
I apologise for my niaevity in the subject and my questions, but eager to learn and understand.
Best wishes
John
JohnWAF* is inversely proportional to cabinet size. Another way to approach the design is to assume a listening level height, let's say at 42". If you put the center of the 15" driver at this height, you would wind up with a cabinet about 52 1/2" high and about 29" wide, with the baffle step coming in around 157 Hz. Another way to address that baffle step is to angle the cabinet front sides back at a 45 degree angle, which you can do by cuting into the top manifold section. There should be no consequences to this as this horn expansion is a rather "geodesic" approximation anyway. If you get the front baffle (where the 15" mounts) to be about 24' wide, this would put the baffle step (at least at this position) at about 190 Hz, right near the projected crossover region of the direct radiator and rear horn. The 42 Hz Fs of your driver and the size of the horn mouth will be the limiting factors in the bass. You can calculate the baffle step by this: F= 4560/W. This is where F=the freq. where the bass will be 3dB down, and W=the baffle width in inches. The horn length tends to follow from the type of horn expansion chosen, which is then adapted to the horn mouth and throat size for the application at hand, and it's somewhat negotiable as you can see if you have been following various recent comments here concerning this. To visualize the various wavelengths you are working with, use 13500/F=W. This is where 13500 is an approximation for the speed of sound in inches per second, F= the frequency, and W=the wavelength in inches. BTW, check your mail.
We like enthusiasm here!
Paul
*WAF=wife acceptance factor, the bane of the horn designer.
Thanx Paul for your advice.
Paul, A 52 1/2 " high speaker is within the WAF area. So i am interested! The height and level make more sense to me and where i listen/position.
I understand the concept of baffle step now after doing some reading on it. However, I don't quite follow what you mean by angling the cabinet front sides to 45 degrees
From my reading of the Paudio BM-15CX38, the Fs is 36Hz. Does this therefore change any enclosure measuremnts?
Also, reading Dr Edgar's article you previously recommended me to read, the fs/Qes ratio of the Paudio takes it to ~156. How does this measurement/value of this driver equate to Dr Edgar's view of what "are good for horns"?
Thanks for all your help, and making me understand these concepts
Best wishes
John
JohnThe spec sheet I have for the BM-15CX38 lists Fs at 42.9 Hz and Qes at 0.322. The Fs/Qes (aka Gross Bandwidth Product/GBP) comes out to 133 Hz, still a candidate for your application which is a hybrid direct radiator and back loaded horn. Dr. Edgar's comments in the Positive Feedback interview were in the context of specifying a driver for a bass horn (which would need to be able to get up to 400 Hz or so, to integrate with a compression mid horn) which his Show Horn and Monolith designs were. I'll send you a sketch illustrating the angled corners for the Olson design adapted for a 15" driver (50" tall, on paper at least ; )
That cabinet is for an 8".
Is there for 15" at all?
the drwaing i saw may suggest that the front/rear horn loaded is ?8" driver. For the rear horn loaded?????
hi DJK - what about "mellow monster" - or whatever Paul Eizik built?
Thanx for that
hopefully can do
best wishes
John
I've got flu and forgot to mention Bill Woods - perhaps he has something, comments, or might be commissioned to design at some point.what drivers are you comsidering? - are there modern 15" coaxial suitable in tone and parameters for back loaded horn?
so called "half-horn" reflex-hybrid run ~6-7 cubic feet bulk - not sure how much more bulk it takes to get near "real horn"
I have the 15'' Paudio coax's, 15BMCXA. In an earlier psot, Paul felt that the Olsen back loaded horn would work for this epaekr, hence my query on the dimensions of the box.
Ypur thoughts on that?
Many thanx
john
I'd trust Paul's guesses (lets see if he catches this thread) - IIRC he modified throat and extended path and rear horn's mouth (an dcabinet depth) plus added a front horn to David B. Weems' basic "Mellow Monster"have you measured CXA's parameters? - Qts is quoted nice and low.
how's CXA's tonal balance and qualities in reflex (or on baffle)? -
-might try CXA or SN15C in Karlson or V-vent box (and have old Eminence 95oz magnet C15CX with 3"x6" horn) SN15C's Q and mass look a bit high for K15 due to 3" coil but if SN15C are tonally lively then may be ok (?) = pig N poke
I have the Paudio in an OB arrangement. JE labs design. extremely happy with the imaging and mid range. However bass is lacking, not tight. top end harsh. I put a post a few weeks back asking about compund horn enclosures, and basically from the advice there, it appeared a rear horn loaded enclosure would be more suitable.
I have so far added a passive 2nd order XO at 1250hz. This has improved the bass quite a lot. I must note that i have supplemented the bass with ahome theatre subbie (not great, loose, but it helps). The mid range is still good. the top end is too harsh. i padded down with an l pad -6dB for top end/tweeter on the driver, and this has helped too.
I think long term, a ribbon or the like tweeter above 10Khz will be needed for this driver.
For long term happiness, i have hence looked at horn enclosures. Paul suggetsed Olson's enclosure, hence my search for this. Under his recommendation and pointers, i looked up the patent, and downloaded drawings. No dimensions however.
I bought a citation of the paper he did with ? Massa in the American Acoustical Soiciety, i think 1936, but the box/horn design is different.
Also, can someone tell me how I can copy a pic onto the body of the letter? that would help to show what i have.
Many thanks
John
(word processor or insert image on another image?)could "half-horn" have any advantage over regular bass-reflex? I believe RCA-Fan looked at a few half-horn for D130 besides the "Hawaii" V-vent. IF CXA Qts is really that low, then 15CXA might work for a box designed for D130.
a Karlson would have mild gain from ~55-200Hz over a reflex, low cone excursion but one may or may not like Karlson artifacts.
(one person's wife did not like the look of V-vent - maybe WAF can be tricky)
Seleninum ST324 slot tweeter might be good for a "helper"
Eminence C15CX in RCA-Fan V-vent box
C15CX impedance in RCA-Fan's V-vent enclosure
one builder's adjustable gap V-vent variant
D130 parameters from listing at Lansing HeritageFs = 40 / Qts = 0.25 / Qms = 4 / Qes = 0.27 / Vas = 297.3 / Eff = 6.7 / Pe = 75 / Xmax = 0.76 / Re = 6.3 / Le = 0.6 / Sd = 0.09 / BL = 18 / Mms = 60 / Flux = 1.2
P-Audio 15CXA listing
BM-15CXA
Description COAXIAL TRANSDUCER
Size (in.) 15.0
Power RMS (Watts) 250
Fs (Hz) 39.0
Xmax (mm) 2.75
Sensitivity 1w/1m (dB) 101
Qts 0.24
Vas (lt) 257.5
Magnet Material Ferrite
Thanx Freddy
The Paudio I have is the BM-15CX38. i am sorry if I have given wrong info. The manufacturers info is:
Fs 36Hz
Qes 0.23
Qts 0.22
Vas 287Lt
Xmax 4.5mm
These alter any of your findings?
Many thanx
John
Hi John - might be even closer to D130's factory specifications.RCA-Fan suggested one half-horn arrangement for D130 but its not been built. I'm not sure if Bill is fond of most coaxial. You might write him a few brief questions from Acoustichorn's website under " Contact "). Coax are an ok tradeoff for me.
AH Pages
Thanx
i emailed him about a month back, and he felt that the sepaker would do well in an Olsen horn enclosure, hence my search for this enclosure now. In the "Horn News April 2006", there is an article on it. I Presume you have seen/already know of it anyway. There is a corner horn enclosure there.
many thanks for your help'
best wishes
john
--had plans from Paul Eizik on an Olson type (which Paul modified to add front horn and extend LF) but got mislaid in mess or lost years back - perhaps Paul can post those or email to me to upload (?) - or at least comment
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