 
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
|
|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
Has anyone here built or heard a successful wide range front horn like the Oris combined with a horn to capture the drivers backwave for bass?
A front horn / back horn hybrid?
Follow Ups:
I built a lightweight double loaded horn in about a 2 cu ft enclosure with a 5" auto speaker I had laying around & a RS bullet horn tweeter back in the late '70's which hit about 100hz at 100db/watt. Not real smooth but lively sound from flea power & only weighed about 15 lb.
Haven't built or heard any such beasts, but at least a couple of designs in the literature come to mind. Voigt's domestic corner horn, using the ancestor to the Lowther drivers, front loaded the 8" driver with a horn that terminated with a big clamshell shaped reflector on top, and rear loaded the driver with some sort of labyrinth that exhausted at the ground. Harry Olson designed a compound horn for RCA that front loaded an 8" driver with a short horn in front, and a complex folded rear horn for the low frequencies. These were used in some of the early to mid 1930s Photophone theatre systems.
It already exists- US patent # 2,871,972, 1958. The concept was flawed as the differing path lengths led to a massive out of phase situation between the front and rear waves causing a response hole large enough to drive a small SUV through. It might work if the driver had a tuned rear chamber to delay the rear wave before it went into the rear loaded horn, but the bottom line is that the overall size would still be too large to be worthwhile.
Hi BillI beg to differ. This type of design dates back at least to 1936 when it was presented in the Journal of the Acoustic Soc. of America by Olson and Massa as a "Compound Horn Loudspeaker". It is also discusssed and pictured in Harry Olson's "Acoustical Engineering" as Steve mentions. I am unfamiliar with the 1958 patent you cite, but it would'nt be the first time some prior art by Harry messed up someone's patent. Harry's measurements show some moderate ripple of about 3 dB or so in the crossover region of the front and back horns, much less than seen in the high frequency response which dives around 4K and gets some 5 dB bumps before this. This type of design is also discussed by Dinsdale in his now famous (infamous to some) Wireless World articles of 1974, and the design type is also called the double loaded horn driver. Dinsdale addresses the design consideration that the two sides of the driver are out of phase with each other (like the ported box), and recommends that the combined lengths of the two horns be an odd number of half wave lengths of the frequency at the crossover point. I guess that guy in '58 had some fine tuning to do.
The double horn loaded driver has some advantages:
1. The mid bass horn and the mid range driver can be easily phase alligned with each other, a considerable advantage over designs like the Klipsch horn. Olsons's original design was a 1 way though.
2. It's an all horn design with no mismatch in output between the bass and mid bass like the V.O.T. has.
3. An easy to design compact cabinet is possible. Due to the fact that it is desireable to limit high frequencies coming from the back of the diaphram, 180 degree bends (with a subsequent "muffler effect") in the horn being driven by the rear of the driver are fine. The basic design can be a "W" manifold on top which exits into an "S" horn.
Some disadvantages:
1. Tricky to design by the numbers, as the two horns can be be computer modeled but their combined behavior is somewhat of a wild card as most programs assume reactance annulling with a closed box at one end, or free air termination.
2. Classic reactance annulling with a closed box at the back of the driver is impossible. This is offset to a certain degree by the fact that driver has the acoustic resistance of a horn (albeit different horns) on both sides, but the horns are less easy to adjust than a box.
3. Since Dinsdale, the design seems to have sunk into obscurity, and perhaps seems a relic of the "cut and try" days, and thus unattractive to those who want a + or - 1 dB computer sim even before they start the table saw. But to others this feature places it in the above group.
4. Time delay of about 1 millisecond for every ft. of length of the long horn. This is much more of a purist fault than the crossover overlap IMHO, and I'm surprised no one mentioned it in the other posts, but the many Lowther cabinets have this same delay and whatever else you can say about Lowthers, this is one complaint I have'nt heard yet.
To answer the original question, I have been using a design like this for over ten years (see pic in Members Rigs section of the C.H.C. link quickly before Tom Brennan gets the wanderlust and runs away with the gypsies). The double loader works for me!
Paul. BTW...
I enjoyed the Panel Cutter article in AudioXpress. I have employed panel cutters in the past and can attest to their usefullness, but I gotta confess that I don't have one handy right now (cut and curse method). Well, summers here...
Hi Paul,Double loading briefly crossed my mind for my Ubangi. It should have plenty of space in the rear chamber for a back horn, and it might make driver selection easier. Then I started wondering how much weight the horn would add. The Ubangi is probably 200 lb right now without the ports, or drivers. How do you manage the weight of your double bass horn?
Paul
Hi PaulI manage the weight by ignoring it, and the fact that my rig can be taken apart in several sections. It's too big to fit on a bathroom scale, but hefts around 250 lbs ++, and should exceed 300 lbs when all the experimental styrofoam parts are replaced with wood. Weight only counts in a movable PA, as close only counts in horse shoes and hand grenades.
There sure is a lot of Pauls in this hobby!
Paul
back in 1970 or so- I didn't mention his in the post as the design I did note is far simpler to execute than Harry's maze. Yes, the phase thing can be worked around. Reactance annulling isn't impossible- in this case you can accomplish it with proper sizing of the rear chamber vs. rear throat size but it's an extremely complicated proceedure that is totally empiracle and takes a lot of plywood to figure out. I found that all things considered that the concept was too large and too complicated to be very practical, and that seems to have been born out by the lack of commercial success of the concept.
Hi BillFor someone with your woodworking skills Harry's horn should be a piece of cake. The only slightly tricky part is the "W" manifold, and if you use the same set up on the table saw to cut the height dimension of the dubya, you're okay. The general size of the double loaded bass horns in my rig is about the size of Tom Brennan's Altec A5's, but W.A.F. "z" is always site specific.
The rear chamber in a double loader is more like the compression chamber in a compression driver in that it is a factor for tuning out a resonance rather than an oportunity to generate a resonance to accomplish something constructive as in the reactance annulling box.
As to the lack of commercial succes of the concept, in the circa 1936 era Western Electric saw their cinema sound monopoly overthrown, and the acension of the Altec monopoly followed which lasted all the way into the 70's when JBL took advantage of a chaotic business situation at Altec. RCA (and Harry's lab) was never able to put much of a dent in any of the various theater sound monopolys, and the various technologies suceeded in the market more for prevailing business reasons than technological advances, as they all had smart people and good ideas. My Dad built several double loaders (direct radiator on the front) and sold some to people in his hi-fi club in the '60's. There was one pair that he did'nt sell, and I got them when he had to clean out his garage in the late 70's. In the late 80's a friend brought over some Spica TC 350's, and I felt challenged to match the imaging I heard...
T'was ever thus!
Paul
This jives with my experience with insane speaker experiments. We tried front loading a driver in a TL and discovered that it does not work. Something to be avoided, for sure.Later
D
Hi Dave
I have found some examples but they do seem heavily compromised. There is another thread on this subject at the Full Range Forum. My guess was that there would be big phase problems but in addition Bert Doppenberg says that the back loaded portion of the hybrid with sound very attenuated compared to the front horn.
Sounds to me like a second driver to another bass horn is the ticket .
See you at Bay Area tube fest?
Jay
I don't know about all the studies, but our trials went like this.
Like I said, the PHY TL / Azura test was crude, but it indicated what front load horns do. They increase the efficiency of the driver by about 3 db over the direct radiator function. That leaves an obvious lag in the LF.Our latest work involves a Fostex 168 driver. We have it in a BL horn and in a FL horn...the Big Beast.
First of all, we use a compression chamber behind the driver in the FL horn, which would obviate the use of a BL horn, but more to the point, this arrangement boosts the eff by about 6 db over normal direct or BL horn use. We have it in a tandem use with a 100db ribbon and they match very well.
In the BL horn, this driver will operate at about 96 - 98db eff at best. That is a clear attenuation of the BW. What's more, I don't know how the removal of the compression chamber would further effect the overall response. My guess is that it would lower the FW eff a little [maybe 1/2], but it could also goof with the response itself, since the chamber is mechanically damping and smoothing out the driver's response.
For my money, I will pursue a different path to solve this puzzle. I think that once you get the primary driver to respond below 100hz [in the front horn] you can use a subwoofer of some sort. All the rest is relatively easy, but BL/ FL horns are a difficult [at best] proposition, and will yield questionable results, IMO.
What about a PP FL bass horn. Anybody?
Thanks for the pics.
Later
D
Hi JayThe phase problem is a minor one in Olson's implimentation (see p. 238 of Acous. Eng.) and in mine (if you are still awake after reading my long post above, hey you asked :)). Some cancellation has shown up in measurements, but due to the fact that you have to move the test mic back to a point where the two horns can react, it becomes difficult to seperate any speaker anomalies here from room effects. The fact that the measurements vary quite a bit according to mic location indicates that my room is adding more to the measurements in this respect than the crossover overlap, however there is no reason to feel complacent unless anechoic measurements are done, and none of my buddies have one.
As to Bert's concern that the rear output would be considerably less than the front, this too is not verified in Olson's example nor in mine. The throat of the horn on the front driver should be less than what one would use when applying the classic optimum throat size formula, and this is in order to optimize the front horn for higher frequencies (and it looks like Olson's design could have used some fine tuning here), with the added effect of some attenuation which as luck would have it balances mine out fairly well, with some more experimentation due here. This is just fine tuning and perhaps the least of your problems in a double loader IMHO. Bruce Edgar has pointed out that if you push the horn into a corner, the bass will improve but the mid bass will suffer. Conversely pulling the horn out of the corner and more into the room causes the bass to suffer and the mid bass to improve. This effect makes much more of a difference in the bass/mid bass area than what I can identify as phase cancellation from the two horns.
Paul
No one has mentioned the difference in crossover frequency between Olsen's, Dinsdale's front/back horn and the one the poster has in mind. Also the driver used should be considered as well. If one is going to use a low qts driver with a rising frequency curve like some Lowther or Fostex and crossover the backhorn at about 200HZ to 150HZ, then this idea is very hard to realise.
Hi MichaelzHarry's double loader crosses just under 300 Hz. I don't have Dinsdale's articles handy but his designs seemed largely a suggestion, and he did'nt offer any measurements. Mine cross in the under 200 Hz range depending on how the various drivers and factors are set up, and I feel that the optimum crossover of the bass and mid bas should be around 100 Hz or lower.
Applying this type of design to a Lowther is tempting, but if you open up the "choked" mouth of the average Lowther rear horn, the rear output will over power the direct radiator front, necessitating a horn on the front of the driver, and even in spite of the rising high frequency response there will be some high frequency attenuation. From this follows a tweeter and a crossover, which somewhat defeats the elegant simplicity of the 1 way Lowther configuration with no crossovers to worry about. Some complain about the lack of highs on a Lowther, but I am always amazed at the amount of highs one driver can generate. On the bottom end, the latest inductor gimmick provides plenty of bass even with low powered SET's, but an inductor is a crossover. Perhaps the Lowthers are heading in the direction of a 2 way, but something may be lost in the process: simplicity.
Paul
Don't tell the bumblebee. Or Tannoy.
Chef HenryYeah, the Tannoys too. And the bees! I too have noticed the horn like shape of flowers. The many colors of the flowers are advertisments to the bumble bees (they have better color vision than our own and can see ultra-violet), but the closed end horn shapes of the flowers must reflect back the buzzing sound of their wings and give audio landing instructions to the sweet nectar. I wonder if anyone has studied the hearing of bees?
As in hi-fi, so in life.
Paul
This post is made possible by the generous support of people like you and our sponsors:
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2025, Audio Asylum, all rights reserved ]
