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I previously posted this question but it was misunderstood this is not about a full range rear and front horn loaded speaker. It is about a MR driver covering only the freq range of 80 to 2K but using rear and front loading horns for efficiency in a linear array setting. All comments apparently missed this and therefore I am posting this again.
The original post was this.
Imagine a MR driver front and rear horn loaded covering 80 to 2KHz with a small front loaded horn easily covering say 240 Hz to 2KHz and a rear folded horn covering 80 to 240Hz. Therefore only 2-3 octave coverage por horn with less distortion and maximal efficiency from only one driver. Then Comp driver taking over above 2KHz and SUBWOOFER taking over below 80 Hz. Easily adapted to linear array use.
An example Imagine the large L dos or copycat large JBL vertex with midline comp drivers, four 8" drivers and two 15" drivers. Now get rid of the 15 inchers and hornload the the rear output of the four 8 inchers while maintaining the front as is (limited front space ("wave"guided) direct firing). Power would be PLENTY and would save mucho bucks and weight.
What do you think!
Rafaro
Follow Ups:
I think you had cone drivers in mind when you asked this question, but the Elctro-Voice CDP-848AT does this with a compression driver (see link). So at lest, with a compression driver, it can be and is done.
Dave
Dave
The related 1828 paging driver is still being sold, and EV used the similar 828 driver in a re-entrant horn in some of the Patricians. PWK did'nt like this driver on top of the K-horn type bottoms he licensed to EV, at least he claimed so in the Bruce Edgar interview published in the Audio Amateur/Speaker Builder as I recall. I have'nt heard a Patrician for many decades, but it would be interesting to compare them with K-horns.
Paul
I do remember seeing those in pictures of Patricians. I have never see or heard a Patrician in front of me, but would like to. I like vintage equipment. The design would have its flaws, but it would be very efficient and wide range. Did you see the specs?
Dave
Dave
I've always liked the 828's, my Dad built his first horn rig with them back in the day. The "big man on campus" in Dad's audio club had an amazing rig with them and an EV30W sub. This was in the early 60's, and this rig could hold it's own with the best stuff I've heard at audio shows today. I mean it actually imaged in the early 60's! As to specs on the Patrician, the later ones had the 30" 30W woofer with an Fs of 16 Hz, and it's a thing unto itself. They were the rage of the first audio show I attended back then. EV made the Patrician well into the mid/late 70's with the entire late output going to Japan (or so I've read), which got the SET craze 20 years before we did here in the US. PWK complained about a hump in the response of the 828 and it's re-entrant horn, but that would be easily addressed today.
Paul
Hi Paul,
Your making me drool! I am a big fan of vintage gear and size does matter. I still have my fathers huge cabinet with a Jensen H-510 coax driver that I want to use in a Mono system.
I wonder how the modern CDP-848AT compares in sound to the 828. I have never heard either.
It is my hunch that the continued popularity of the Patrician in Japan is why Fostex still makes a 30" woofer that is very similar to the EV30W. (Fs is 25Hz). You could build a modern Patrician, and I expect you could make it sound great, but it would cost. You would also need some serious room to play it.
Dave
Dave
You may have heard some EV re-entrant horns inadvertently. Here in Chicago North Ave and Fullerton beaches use them for paging horns. While you mostly hear announcements for lost kids etc, I've heard music through them at times. While I can't comment on the "sound stage" (they're a block apart), the PRaT factor was quite good in spite of the limited bass response.
Paul
The 260 - 10000 Hz frequency response is impressive. Next time I'm in Chicago in the summer ... There are probably some here. I will keep my eye out.
Dave
Rafaro
What you are describing was invented in the 1930's by H.F. Olson. It was called a Compound Horn Loudspeaker in the patent (do a google search to see Olson's original patent which was granted in 1940 right before WW2). This configuration is also known as a double loaded horn. Olson's design used a single cone driver while you propose using 4 8" drivers. You would need to face the 8" drivers toward each other on the horn walls in a manner similar to Tom Danley's Unity horn, which used computer modeling to get the several drivers to work together as I recall. You would need a complex manifold at the rear of the 8" drivers to couple them to the rear horn. Olson's rear horn was bifurcated, that is it split in two parts which joined together further along, and then followed into an "S" bend into the horn mouth. The 80 Hz lower end is realistic, however getting smooth response to 2000 Hz from those 4 facing 8" drivers on the front horn would be tricky, involving a lot of experimentation, "cut and try" and probably EQ (which is going to be there anyway in a PA). This is most likely the reason you don't see designs like this in PA's, it's rather complicated compared to conventional designs. BTW the acoustical crossover between the rear bass horn and the front mid horn in a design like Olson's is typically in the 200 Hz region, and there will a dip in the response in this region where the front and rear out puts add together out of phase, however 200 Hz is well out of the midrange, and the output of the rear horn will also be delayed from the mid by about 1 millisecond for every 1 ft. of bass horn length. Back loaded horns (like many Lowther designs) will have this same dip and delay, and I've never read or heard anyone commenting that it's particularly a problem in them.
It's possible, but don't expect it to be easy.
Paul
Hello Paul.
As always you pinpoint areas of realistic problems in speaker design. I am well aware of Olson`s patent(s) and book(s). He discovered that 60% of the power output of a driver is in the rearwave and actually patented the "Double Loaded Horn" so as not to waste that energy. This design is widely used as you know in the single driver full range horn design circles. The Dinsdale articles etc discuss the benefits and need of hornloading the rearwave of front horn loaded drivers. I refer you to it for the details. As such I am always wondering why this useful technique is not more widely used in Prosound circles were efficiency is most needed!! Granted it will not be realistically useful in Pro circles in a full frequency setting but in a limited freq range such as the critical midrange it has its benefits. As an example the linear array JBL Vertex uses 4- 8" drivers for the MR. These can be easily configured as double loaded horns. A small front horn covering 240 Hz and up....how high up as you point out?? It depends on the center to center (CTC) distance between the 8 inch drivers...Placed in a horn reduces their CTC and when the CTC is 3.3" a crossover at 2Khz will not produce significant nearfield interference lobes!!! One folded expo horn of 48" length, doubling q 11" takes the rear wave of each pair of 8 inchers covers the 70 Hz to 240Hz and replaces the heavy expensive 15" drivers on each side. Since the folds and rearspace behind the driver limit the rear horn freq output above 240 KHz little interference with the front wave should occur. I have used these designs in linear array settings of my own design and find them very useful saving money and weight.
PS: Please tell Don Reid not to be too hard on me...that I know a little about speaker design. Thanks.
Rafaro
Rafaro
In your original post you were proposing a theoretical double loaded horn design, and you asked why this type of configuration was not being used in PA designs. Maintaining the format of a vertical array of 4 8" drivers in a double loaded application presents several design challenges (sorry for going off in another direction with my suggestion to face the drivers towards each other on a horn wall).
_Front horn(s) on the array.
You could use a separate horn on each of the drivers as used in some compression driver PA arrays, but this would add to the size and complexity of the array. The alternative would be to use one large rectangular horn on the front of the drivers, which would tend to require separate phase plugs and/or a sectoral type of design. If the 4 drivers are coupled together on one air chamber (Fhc), this will limit/dictate the high frequency extension (see my post down page here about the Jensen BLH).
_Rear Horns on the array.
You would need to design a manifold to couple the 4 drivers to the rear horn throat (with another Fhc factor), making the array even larger and more complex. The usual formula for designing an optimum throat area (Sr) is based on the T.S. perameters for one driver, and determining this for 4 drivers will involve some estimation plus probable adjustment in the finished design.
In a front loaded horn, the (typically) closed chamber on the rear of the driver is not "wasted", rather it's tuned to resonated to resist the tendency of the mass of air in the horn to move back and forth as a unit (instead of the sound moving through it) and thus limit the bass response near the low frequency theoretical cut off of the horn. This is called reactance annulling. With a double loaded design there is no place for a reactance annulling chamber, so low end performance will be limited by the Fs of the driver (plus horn dimensions), or drivers in the present theoretical design. BTW Dinsdale makes a good suggestion to make sure that the combined horn lengths of the two horns in a double loaded design to be made equal to an odd number of half wave lengths at the acoustical crossover. Due to the muffler effect of the folded horn, this is more likely to be below 200 Hz. than above.
BTW the center to center distance between two 8" drivers is 8" assuming they are on the same flat plane and not a curved array.
These are some things to consider while attempting a design like you propose. Hopefully you will try an experimental prototype and let us know how it goes.
Good Luck!
Paul
Thanks Paul for your courteous patience in reality I just used the well known JBL Vertex as an imaginary example to ilustrate the idea. In reality the design is much simpler. Just one driver 8-10" in each side of a V type "horn" for the front wave and a minimally folded rear horn laterally expanding with a rear space chamber (plus folds) to limit HF output past the front horn LF output. The midline diffraction HF horn in the middle of the V. Please note that time differences between the HF diffraction horn and front horn of the MR drivers is almost nothing (2")and that the rear horn output is only two ms behind the front MR horns output which goes below 200Hz !!Again thanks
Rafaro
Edits: 12/14/14
Rafaro
Hopefully you can build this theoretical design and test it. I should have looked up the JBL VerTec in the beginning to understand what you were suggesting, I would'nt have gone off on some other tangents. Just make sure to follow the Dinsdale rule: total of both HF and LF horn lengths should be an odd number of half wave lengths at the acoustical crossover of the horns.
Paul
Very perceptive of you Paul I have done functional designs along these lines earlier but the latest version is indeed theoretical and pushing the imaginary limits. I been thinking about 1/4 wavelength(WL)reinforcement same as in Tapped horns (TH) but in independent and separate horns! Interestingly the first draft met the necessary criteria so on to sawdust and will see what happens. All my other "crazy" ideas have worked but this one is extreme.
Rafaro
ell, Rafaro, since you asked so emphatically I must say your idea sounds like a sure fire formula for time muddled, phase distorted midrange sound. If you do not understand why this is so you really might consider learning a few more of the basic ideas of sound, speaker design and the such so that you can answer this question for yourself.
Hello Don:
You admitedly have no experience with double loaded horns. In my example do you really think you will be able to "HEAR" a 4ms=48"=4 feet time difference between HF and MR or phase distortion when there is insignificant freq cross over between horns. May I respectfully recommend you take your own advice!
"If you do not understand why this is so you really might consider learning a few more of the basic ideas of sound, speaker design and the such so that you can answer this question for yourself".
Rafaro
"You admitedly have no experience with double loaded horns."I do, they sound poor. PWK (also) wrote about why they sounded bad, about 50 years ago.
" In my example do you really think you will be able to "HEAR" a 4ms=48"=4 feet time difference between HF and MR or phase distortion when there is insignificant freq cross over between horns."
Yes.
Edits: 12/13/14
DJK
The Klipsch Horn itself has a built in delay between the midrange horn and the output of the woofer through the folded corner horn, and this delay reaches up well into the critical midrange over an octave above the 200 Hz region of the acoustical crossover of a typical BLH or double loader. I've heard of attempts to get the mid and woofer in phase with digital delay on a K-horn, but I've never listened to one. I've always liked the K-horns, but due to this delay and it's proximity to the midrange (plus the offset between the mid and tweeter), the K-horns present a rather vague stereo image. For this reason they have been dismissed and ignored by what's left of the audiophile press (Stereophile and TAS), at least until Sound Practices appeared in the early 90's.
When I met PWK back in the 90's I asked him about the subject of time alignment of the drivers. He told me that he had tested this where he had a separate mid and woofer placed in front of him playing music, with an assistant who would move the woofer as he listened with his eyes closed. He had his hand raised and would lower it when he heard a difference. At one point he noticed something had bumped his foot, and when he opened his eyes he saw it was the woofer! Following this story he produced the famous B.S. button from his pocket. He was a grand gentleman and an audio pioneer, but in regards to this he missed the boat in my opinion. BTW I agree that a 48" offset between the tweeter and mid in a K-horn would definitely be audible and not for the good.
Paul
I met PWK in '74, spent a day with him at his factory in Hope. The subject of the LF horn delay didn't come up, but a lot of other things did, so I got some insight into his thought process. I'd bet he was very aware of it, but since the technology of the day didn't offer a simple way of overcoming it he simply chose to ignore it, based on his belief that the speaker still sounded very good. He took the same attitude about placing the mid and HF diffraction horns horizontally instead of vertically. He was much more concerned about the overall result than with nit-picking over what he thought were minor details.
Bill
That's very much the impression I got of him. He had a bit of a curmudgeonly manner, but he very patiently posed for pictures with anyone who wanted one, autographed pics of himself, and answered all questions, even very basic amateur ones. Someone asked him which audio designs other than his he respected. He answered that Altec was one he regarded highly, and Olson too. Asked if he knew Olson, he replied "Well, I met him....".
Paul
I met him because I was playing at a nearby club and he happened to drop in. This being the time when the Shure Vocal Master was the king of the Ramada Inn circuit he took notice of my JBL 4560 style horns loaded with Altec 417s. He was up on the competition, and knew that they weren't JBL or Altec, so after he asked me what they were and I told them I had designed and built them he introduced himself and invited me to his factory. He was further intrigued when I told him I'd built a KHorn clone sans mid and high drivers, using it in a corner for lows, with a pair of smaller speakers flanked to either side for the L/R, sort of a pre-historic sub-satellite arrangement. He then showed me his pet system, KHorns in two corners with a Heresy in the middle of the wall, sort of a pre-historic L/C/R rig.
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