sba said:
They are one and the same. Iconic in Seattle has apparently trademarked "Tangerine" for phase plugs, and since these 288's are not made by Iconic, I feel that describing the phase plugs with the name of the inventor is the most respectful thing to do - that's why I linked to the patent.
By the way, both Iconic and Great Plains are staffed by former Altec employees, with Oklahoma City being the last manufacturing plant and repair center for Altec drivers. I understand that GPA uses the original tooling, as well as having some of the same employees. It looks like Iconic is also manufacturing drivers, but I haven't seen those yet. Both groups are a pleasure to talk to, and have lots and lots of Altec information that has not been published on-line or in the literature.
Lynn Olson said:
that is what i am waiting to see. i've been patiently waiting for maybe half this thread.
i have a pair of 12in os waveguides from dr. geddes in transit to me. those three woofers are front runners for my midbass duties. my woofers will be my td15x's, time 2 per baffle.
ps...sorry, the shift key is broke on this keyboard.
what's the difference between this hendricksen phase plug and the phase plug seen here
rank 379 driver
and
cogent driver
rank 379 driver
and
An externally hosted image should be here but it was not working when we last tested it.
cogent driver
Well, this is Steve Schell's area of expertise more than mine, but the 1939 Blackburn patent (2,183,528) is one of the earliest instances. I believe this was used in the WECO/ERPI group, but I could be wrong, it might have been used for RCA instead. There were a lot of patent-sharing agreements at the time.
Here's the original 1978 Henricksen AES Paper. Interesting paper, but the frequency response comparison at the end doesn't look too flattering to the Tangerine. What complicates the comparison are the known irregularities of the horns of the day, and the breakup of the aluminum diaphragm.
Here's a lively quote from Todd W. White (Iconic), posted May 13th, 2001 in the High Efficiency Speaker Asylum forum:
In contrast, my audio-friend John Atwood heard a direct comparison between the circumferential and the Tangerine versions of the 288, and he strongly preferred the Tangerine, even if the Tangerine version used a ceramic magnet, and the circumferential used Alnico. (The Alnico + Tangerine version of the 288 was only in production for about a year, thus the rarity and high price on eBay. The ceramic versions were in production much longer and are easier to find.)
John felt the circumferential versions were "phasey" sounding in direct comparison to the Tangerines, which makes sense to me. As mentioned in the Henricksen paper, circumferential phase plugs only have a few discrete paths - typically 3 or 4 - from the diaphragm to the entrance of the horn, and I would expect sum-and-difference cancellations to appear at narrow, discrete frequencies. These narrow nulls might not look significant in a 1/3-octave smoothed frequency response graph, but they would be much more apparent in the time domain.
I've come to expect the compression-driver fraternity are in constant disagreement with each other, almost as bad as the famous Chevy-Ford disputes in trucks and stock-car racing. Some are Altec all the way, others are JBL enthusiasts, and there are the antiquarians with their love of obscure objects of desire - Vitavox S2's, Klangfilm, and the truly rare RCA MI-9584A compression driver.
Here's a lively quote from Todd W. White (Iconic), posted May 13th, 2001 in the High Efficiency Speaker Asylum forum:
In contrast, my audio-friend John Atwood heard a direct comparison between the circumferential and the Tangerine versions of the 288, and he strongly preferred the Tangerine, even if the Tangerine version used a ceramic magnet, and the circumferential used Alnico. (The Alnico + Tangerine version of the 288 was only in production for about a year, thus the rarity and high price on eBay. The ceramic versions were in production much longer and are easier to find.)
John felt the circumferential versions were "phasey" sounding in direct comparison to the Tangerines, which makes sense to me. As mentioned in the Henricksen paper, circumferential phase plugs only have a few discrete paths - typically 3 or 4 - from the diaphragm to the entrance of the horn, and I would expect sum-and-difference cancellations to appear at narrow, discrete frequencies. These narrow nulls might not look significant in a 1/3-octave smoothed frequency response graph, but they would be much more apparent in the time domain.
I've come to expect the compression-driver fraternity are in constant disagreement with each other, almost as bad as the famous Chevy-Ford disputes in trucks and stock-car racing. Some are Altec all the way, others are JBL enthusiasts, and there are the antiquarians with their love of obscure objects of desire - Vitavox S2's, Klangfilm, and the truly rare RCA MI-9584A compression driver.
Maybe a dumb question here but did original 288s come with Tangential or Circumferential phase plugs?
My next question would be, if the originals were circumferential, is there allot of difference to be heard.
I do quite allot with small format Altec drivers, Ie; the 802-8Gs and the 808s.
I have rebuilt a number of the 808-8As with circumferential plugs and made then into 802s by removing the loading caps, adding felt to the covers and framming them the same.
I honestly can't hear a difference between tangerines and circumfrence plugs if all the rest is the same.
Any thoughts here?
Gary
My next question would be, if the originals were circumferential, is there allot of difference to be heard.
I do quite allot with small format Altec drivers, Ie; the 802-8Gs and the 808s.
I have rebuilt a number of the 808-8As with circumferential plugs and made then into 802s by removing the loading caps, adding felt to the covers and framming them the same.
I honestly can't hear a difference between tangerines and circumfrence plugs if all the rest is the same.
Any thoughts here?
Gary
The 288's used circumferential phase plugs from 1945 through to the mid-Seventies, when Altec changed over to the Hendricksen-designed "Tangerine" phase plugs, which continued to be used until the demise of Altec in the Eighties/Nineties. As mentioned earlier, there was a brief period when the Tangerine and Alnico magnet technologies overlapped, thus the relative rarity of the 288-H models.
It has to be kept in mind that the 515 woofer and the 288 compression driver were the worldwide standard for movie theaters, with more than 10,000 installations - and theaters with 70mm exhibition capability had three sets of A2's or A4's behind the big curved screen. The 515 and 288, by sheer dint of numbers, are the "6SN7" of theater speakers - maybe not the technological ultimate, but there are a lot of them out there.
The transition to THX certification is what replaced Altec with JBL in the mid-Eighties, since Altec never submitted systems to Lucasfilm for approval. In the late Seventies and Eighties, the Altec organization was essentially destroyed by repeated sales to predatory "conglomerate" corporations. This gradually brought R&D to an end, with final result that the name and residual "goodwill" were sold to the Taiwanese Sparkomatic corporation for the low-end car and computer-speaker market. A sad end for a company that grew out of the Bell Labs research organization.
In subjective terms, large and small-format are completely different animals, with different sets of strengths and weaknesses. Large-format is at home in the 500 Hz to 7 kHz region, and has no problem at all filling a large theater with low-distortion sound. In a domestic environment and with a halfway competent crossover, the system will effectively never run out of headroom, except from the grossest abuse combined with an insanely high-powered amplifier. Large-format gets more problematic above 7 kHz, with the technology getting more exotic and weirder in order to persuade it up to the magic 15 kHz figure.
Speaking only for myself, I don't much care for small-format in the 700 Hz to 2 kHz region. It just sounds strained and stressed, like a 1" tweeter being crossed over too low. (In my direct-radiator systems, I've always used a fairly high crossover for my tweeters, since I dislike the sound of overstressed treble drivers.)
Small-format seems to work fine above 2~3 kHz, and of course can go up to 15~20 kHz without too much trouble. When the lower end is "stretched", it seems to go two ways - plastic-film drivers get blurry and indistinct, and lose headroom, while metal drivers get harsh and resonant, and more forward-sounding. This is similar to what happens with direct-radiators, but horn loading seems to really draw attention to the "end of the road" when it comes to the LF limits of the driver.
I admit much of this comes down to personal preference - the blur and veiling of a direct-radiator working at the top of its range versus the ramping-up in distortion of a compression driver working at the bottom of its range. My preference is to take the direct-radiator a bit higher than other folks, and cross the tweeter higher as well - it just sounds better to me. Thus, all of my crossovers seem "too high" compared to industry norms, or prevailing standards of dispersion.
It has to be kept in mind that the 515 woofer and the 288 compression driver were the worldwide standard for movie theaters, with more than 10,000 installations - and theaters with 70mm exhibition capability had three sets of A2's or A4's behind the big curved screen. The 515 and 288, by sheer dint of numbers, are the "6SN7" of theater speakers - maybe not the technological ultimate, but there are a lot of them out there.
The transition to THX certification is what replaced Altec with JBL in the mid-Eighties, since Altec never submitted systems to Lucasfilm for approval. In the late Seventies and Eighties, the Altec organization was essentially destroyed by repeated sales to predatory "conglomerate" corporations. This gradually brought R&D to an end, with final result that the name and residual "goodwill" were sold to the Taiwanese Sparkomatic corporation for the low-end car and computer-speaker market. A sad end for a company that grew out of the Bell Labs research organization.
In subjective terms, large and small-format are completely different animals, with different sets of strengths and weaknesses. Large-format is at home in the 500 Hz to 7 kHz region, and has no problem at all filling a large theater with low-distortion sound. In a domestic environment and with a halfway competent crossover, the system will effectively never run out of headroom, except from the grossest abuse combined with an insanely high-powered amplifier. Large-format gets more problematic above 7 kHz, with the technology getting more exotic and weirder in order to persuade it up to the magic 15 kHz figure.
Speaking only for myself, I don't much care for small-format in the 700 Hz to 2 kHz region. It just sounds strained and stressed, like a 1" tweeter being crossed over too low. (In my direct-radiator systems, I've always used a fairly high crossover for my tweeters, since I dislike the sound of overstressed treble drivers.)
Small-format seems to work fine above 2~3 kHz, and of course can go up to 15~20 kHz without too much trouble. When the lower end is "stretched", it seems to go two ways - plastic-film drivers get blurry and indistinct, and lose headroom, while metal drivers get harsh and resonant, and more forward-sounding. This is similar to what happens with direct-radiators, but horn loading seems to really draw attention to the "end of the road" when it comes to the LF limits of the driver.
I admit much of this comes down to personal preference - the blur and veiling of a direct-radiator working at the top of its range versus the ramping-up in distortion of a compression driver working at the bottom of its range. My preference is to take the direct-radiator a bit higher than other folks, and cross the tweeter higher as well - it just sounds better to me. Thus, all of my crossovers seem "too high" compared to industry norms, or prevailing standards of dispersion.
I also agree with John Atwood. The radial phase plug is the better design. If you take a step back and really look at the circumferential phasing plug, only a few (3 to 4) places on the diaphragm have a straight path to the throat of the driver. However, the various different radius based frequencies always have a straight and unobstructed path to the throat with the radial phasing plug. I believe this is why the radial phasing plug has a smoother, non-phasey harmonic signature to it. It is more harmonically complete. The sonic textures are more natural and realistic with the radial phasing plug. It really is a no brainer.
Rgs, JLH
Rgs, JLH
Eighteensound seem to use a combined radial/annular phase plug design, see patent WO/2004/040942
Maybe that's the best compromise....
- Klaus
Maybe that's the best compromise....
- Klaus
If I had to assign a weighting of how I experience a loudspeaker, it's about 50% subjective, 40% measurement (with strong emphasis on time-domain decay performance), and 10% theory.
This seems the opposite of many modern speakers, where directivity considerations dominate crossover design, and the actual sonics of the driver are not considered all that important.
I've seen a lot of theories come and go in the last 35 years, all of them vigorously proclaimed as the "One True Way" by their apostles and evangelists. Theoretical approaches are useful as long as they conform with the real world - in this case, both measured and subjectively experienced. When measurements and subjective experience diverge, then the model breaks down, and has to be set aside, or at the minimum, examined for unwarranted assumptions.
The Altec bias is there because I heard them in the movie theaters of the 1950s and 1960s, and the sound of the 70mm mag-track movies back then was a LOT better than the sound of modern theaters with their THX certification, kilowatt amplification, constant-directivity horns, 12 dB of HF boost equalization, and JBL titanium diaphragms. The picture was a lot better too ... 70mm Technicolor prints on a curved wide screen are nothing to sneer at, and approached IMAX in immersion and emotional impact.
Believe it or not, movie theater sound was better than all but the most exotic home hifi systems, and was the first introduction to stereophonic sound for millions of people. I've heard a pair of A5's with 288's with 1505 multicell horns with all-triode amplification a few years ago, and the sound was much as I remembered it.
Not so much "hi-fi" in the sense of screeching highs that you get at the theater now, but musically balanced and realistic, and surprisingly spacious sounding - the stereo effect was much more evident than modern movies, for example, which seem to be rather deficient in stereo except for crude sensations of left-center-right panning effects. Orchestral music sounds like spread-out mono instead of the 3D effect of the big Altecs.
Some things show up in the models and measurements, but others don't - they might be measurable ten or twenty years from now, but for now, we can hear things that are hard to fit into theoretical models. It took more than ten years for the significance of jitter, and the requirement for digitally inserted dither when resampling between different rates, to be appreciated in the professional world.
During the meantime, those who complained about the sonics of first-generation digital were treated as if they had been abducted by UFO's. When the obvious defects of first-generation digital were exposed and remedied, were any apologies forthcoming from the Perfect Sound Forever crowd? Not exactly - the invective and ad hominem attacks of the past disappeared into the memory hole.
Go through a few of these wash-rinse-repeat cycles, and you can see the PR Mighty Wurlitzer at work, discrediting the doubters, and convincing the gullible that they're not hearing what they're really hearing. That's why I put perception first, followed by confirmation by measurement (if possible), and last of all, theory, if it serves the first two agendas.
Will the 288's and 414's stay in the lineup? I don't know at this point. It depends on my impressions, the amount of work it takes to straighten them out, and the MLSSA and ARTA measurements. For critical listening, I listen almost entirely to classical and large-scale choral works, so that is the subjective yardstick. Gary Pimm and John Atwood share similar musical tastes and design goals, so we'll be collaborating on various aspects of the project.
This seems the opposite of many modern speakers, where directivity considerations dominate crossover design, and the actual sonics of the driver are not considered all that important.
I've seen a lot of theories come and go in the last 35 years, all of them vigorously proclaimed as the "One True Way" by their apostles and evangelists. Theoretical approaches are useful as long as they conform with the real world - in this case, both measured and subjectively experienced. When measurements and subjective experience diverge, then the model breaks down, and has to be set aside, or at the minimum, examined for unwarranted assumptions.
The Altec bias is there because I heard them in the movie theaters of the 1950s and 1960s, and the sound of the 70mm mag-track movies back then was a LOT better than the sound of modern theaters with their THX certification, kilowatt amplification, constant-directivity horns, 12 dB of HF boost equalization, and JBL titanium diaphragms. The picture was a lot better too ... 70mm Technicolor prints on a curved wide screen are nothing to sneer at, and approached IMAX in immersion and emotional impact.
Believe it or not, movie theater sound was better than all but the most exotic home hifi systems, and was the first introduction to stereophonic sound for millions of people. I've heard a pair of A5's with 288's with 1505 multicell horns with all-triode amplification a few years ago, and the sound was much as I remembered it.
Not so much "hi-fi" in the sense of screeching highs that you get at the theater now, but musically balanced and realistic, and surprisingly spacious sounding - the stereo effect was much more evident than modern movies, for example, which seem to be rather deficient in stereo except for crude sensations of left-center-right panning effects. Orchestral music sounds like spread-out mono instead of the 3D effect of the big Altecs.
Some things show up in the models and measurements, but others don't - they might be measurable ten or twenty years from now, but for now, we can hear things that are hard to fit into theoretical models. It took more than ten years for the significance of jitter, and the requirement for digitally inserted dither when resampling between different rates, to be appreciated in the professional world.
During the meantime, those who complained about the sonics of first-generation digital were treated as if they had been abducted by UFO's. When the obvious defects of first-generation digital were exposed and remedied, were any apologies forthcoming from the Perfect Sound Forever crowd? Not exactly - the invective and ad hominem attacks of the past disappeared into the memory hole.
Go through a few of these wash-rinse-repeat cycles, and you can see the PR Mighty Wurlitzer at work, discrediting the doubters, and convincing the gullible that they're not hearing what they're really hearing. That's why I put perception first, followed by confirmation by measurement (if possible), and last of all, theory, if it serves the first two agendas.
Will the 288's and 414's stay in the lineup? I don't know at this point. It depends on my impressions, the amount of work it takes to straighten them out, and the MLSSA and ARTA measurements. For critical listening, I listen almost entirely to classical and large-scale choral works, so that is the subjective yardstick. Gary Pimm and John Atwood share similar musical tastes and design goals, so we'll be collaborating on various aspects of the project.
Lynn Olson said:
I know a bunch of people that have owned big Altec systems and used to use them in their homes and no longer do - they were a fad a few years back, one that seems to come and go, in the 70's then the late 80's then again in the late 90's with some straglers in the early 2000's and now- I think they (altec systems) sound, resonant, unnatural, honky, bloated in the mid bass with no bottom end, rolled off on the top and at best OK in the midrange. The 288 is really metallic sounding and almost impossible to tame for true hifi sound. The phenolic Altec are far better in the midrange but still sound fake to me but BIG- It's easy to get caught up in the 'thrill' of building a system like the one you propose (big compression drivers and horns) but the results will always speak for themselves.
agent.5 said:
You don't want to restrict the motion of the driver. This means typically having a quite open frame. It also means being quite open under the spider, as most spiders aren't extremely porous. Venting under the spider aids in cooling as well.
A steel frame will affect where the flux travels. It will direct some of the flux into the frame and into directions where it is no longer doing anything positive. This can be a minor or major affect. I've seen drivers where there is 5% decrease in flux in the gap due to the frame being steel vs aluminum.
From a cost standpoint, steel is quite a it cheaper than aluminum. As most steel frames are stamped though, the tooling cost is much higher. You can expect a 15" steel frame to cost maybe $4 where an alum frame will cost $11 or so. The difference is that the steel frame may cost $100,000 in tooling where the aluminum frame may cost $20,000 in tooling. In either case you need to sell a lot of drivers to recover the tooling cost. We're working on some new frame options now that will be more costly per unit, but have little to no tooling cost. It allows us to make a modular frame that we can make as deep or shallow as we want.
John
Three-way
Hello Lynn
Your e-mail has got me pretty fired-up about a three-way using the GPA 288 alnico as the basis of an OB project .
You recently wrote :
"I can now reveal that there will be a new AH-425 Azurahorn, commissioned for this project.
Specifications are: 425 Hz cutoff, T = 0.7071, throat size = 35.4mm (actual measured size of an Altec 288), internal flare rate of matching compression driver = 8 degrees, overall diameter = 418mm, length from front of horn to back of mounting plate = 262mm, diameter as measured from the portion that is at 90 degrees with respect to the central axis (the footprint if it is laid face-down on the floor) = 364mm."
Is this still the state of play ?
If so I might consider getting drivers and horns soon and kick this project off . I will still talk to John A as you suggested .
Now, I'm just unsure about whether 16-ohm on the comp drivers is the way to go . I'll just be running a single 15" of some sort as the bass unit - I can't go for an all-out solution like yours in the space I have at home . Your comment about using a transformer step-down to match-in the horn leaves me a bit unsure about which impedance would be most versatile ...assuming the GPA 288's come in anything other than 16 ohm of course !
Mark
Hello Lynn
Your e-mail has got me pretty fired-up about a three-way using the GPA 288 alnico as the basis of an OB project .
You recently wrote :
"I can now reveal that there will be a new AH-425 Azurahorn, commissioned for this project.
Specifications are: 425 Hz cutoff, T = 0.7071, throat size = 35.4mm (actual measured size of an Altec 288), internal flare rate of matching compression driver = 8 degrees, overall diameter = 418mm, length from front of horn to back of mounting plate = 262mm, diameter as measured from the portion that is at 90 degrees with respect to the central axis (the footprint if it is laid face-down on the floor) = 364mm."
Is this still the state of play ?
If so I might consider getting drivers and horns soon and kick this project off . I will still talk to John A as you suggested .
Now, I'm just unsure about whether 16-ohm on the comp drivers is the way to go . I'll just be running a single 15" of some sort as the bass unit - I can't go for an all-out solution like yours in the space I have at home . Your comment about using a transformer step-down to match-in the horn leaves me a bit unsure about which impedance would be most versatile ...assuming the GPA 288's come in anything other than 16 ohm of course !
Mark
Lynn Olson said:
Hi Lynn, As Nick mentioned, our IB18 is awaiting a cone/surround assembly. Looking at your above post though and the SM 188-N, this drops in line quite well with out TD18M driver. For the 18's we need to jump up to a 2.5" VC instead of the 2" use on all of our other drivers. I received cone samples a couple days ago. Need to get some measurements on a driver, but here is what I have predicted:
Fs: 27Hz
Qms: 6.5
Vas: 563L
Cms: .3mm/N
Mms: 115g
Rms: 3kg/s
Xmax: 6mm
Xmech: 12mm
Sd: 1150sqcm
Qes: .36
Re: 6.6ohm
Le: .3mH
z: 8ohm
Bl: 19Tm
PE: 800W
Qts: .34
no: 3.02%
1W SPL: 97dB
Now this looks quite similar to what you were looking at. The big difference being inductance will be extremely low with the massive copper sleeve over the entire pole. The BL curve will also be much smoother as we have an 18mm thick gap plate and 25mm coil. This should be a much lower distortion driver. Slightly less mass and more efficiency. In this case also the compliance is quite a bit softer making the Fs lower and Q's higher. Simply stiffening up the spider would put Fs in the 38hz range, Qms: 9, Qes: .5, Qts: .48.
I also put another 18" midrange together recently with 2.5" VC motor. This uses the same 18mm gap but with an underhung coil of 12mm. About 3mm underhang but 5.5mm Xmax based on the BL curve. Parameters really come in quite similar as the .5" underhung copper coil and 1" overhung 4 layer alum coil weigh virtually the same and the Bl product comes in very close as well in this case. That may work out extremely well for your needs.
Let me know when and where to get a TD12M to you for this comparison.
John
IslandPink, here's the latest e-mail from Martin Seddon in Perth, Australia, with Martin's photo shown below:
In terms of what we can expect from the 288, scroll down to the last picture on Bjorn Kolbrek's homepage, and look at the red curves. That's an Altec 288B in a plane-wave tube, and you can see the reason I'm considering a crossover in the 5~7 kHz region. The Hendricksen phase plug should be a bit better, but most of the improvement will be in the region above 10 kHz (where it most certainly needs it).
These measurements are exquisitely sensitive to the centering of the mounting on to the flange of the horn/waveguide, and a good match between the 207 Hz internal flare of the 288 driver and the entrance to the horn is also essential. Tiny differences in flare rate in this part of the horn/driver system translate into huge differences on the other end, particularly in the time domain.
I've suggested to Martin that he make a 1.4" flared cylindrical centering tool that can be inserted into the horn when it is mounted onto the compression driver, so centering will not depend on the mounting bolts alone - instead, the tool will be gently slipped into the entire assembly, the bolts tightened, and the tool removed. If the tool gets stuck or visibly tilted to one side or the other, well, the bolts aren't centered, and the mounting holes for the bolts might need to be bored out just a little.
As for impedance, the GPA's can be ordered in 8 or 16 ohms. I chose 16 ohms because I intend to use transformer attenuation, in the following format:
Amplifier -> Crossover set up for 8-ohm resistive load -> 8~9 ohm shunt resistor across primary -> step-down transformer -> compression driver.
If the step-down transformer has a 4:1 turns ratio, that's a 4:1 voltage reduction, or 12 dB attenuation. The entire impedance curve of the compression driver + horn is multiplied upwards 16 times, and then is swamped out by the 8~9 ohm shunt resistor. The driver sees a very low source impedance, and the crossover sees a load very close to resistive. The transformer can be quite small since it does not have to handle any LF energy, thanks to the highpass crossover.
John_J, don't send anything until I get a baffle made - I'll let you know when that happens. That's the next item on the agenda.
In terms of what we can expect from the 288, scroll down to the last picture on Bjorn Kolbrek's homepage, and look at the red curves. That's an Altec 288B in a plane-wave tube, and you can see the reason I'm considering a crossover in the 5~7 kHz region. The Hendricksen phase plug should be a bit better, but most of the improvement will be in the region above 10 kHz (where it most certainly needs it).
These measurements are exquisitely sensitive to the centering of the mounting on to the flange of the horn/waveguide, and a good match between the 207 Hz internal flare of the 288 driver and the entrance to the horn is also essential. Tiny differences in flare rate in this part of the horn/driver system translate into huge differences on the other end, particularly in the time domain.
I've suggested to Martin that he make a 1.4" flared cylindrical centering tool that can be inserted into the horn when it is mounted onto the compression driver, so centering will not depend on the mounting bolts alone - instead, the tool will be gently slipped into the entire assembly, the bolts tightened, and the tool removed. If the tool gets stuck or visibly tilted to one side or the other, well, the bolts aren't centered, and the mounting holes for the bolts might need to be bored out just a little.
As for impedance, the GPA's can be ordered in 8 or 16 ohms. I chose 16 ohms because I intend to use transformer attenuation, in the following format:
Amplifier -> Crossover set up for 8-ohm resistive load -> 8~9 ohm shunt resistor across primary -> step-down transformer -> compression driver.
If the step-down transformer has a 4:1 turns ratio, that's a 4:1 voltage reduction, or 12 dB attenuation. The entire impedance curve of the compression driver + horn is multiplied upwards 16 times, and then is swamped out by the 8~9 ohm shunt resistor. The driver sees a very low source impedance, and the crossover sees a load very close to resistive. The transformer can be quite small since it does not have to handle any LF energy, thanks to the highpass crossover.
John_J, don't send anything until I get a baffle made - I'll let you know when that happens. That's the next item on the agenda.
