It is standard practice to sum all resistances appearing at the terminals of the bass speaker ... output Z of the amplifier + cable resistance + DCR of the series inductor(s) of the lowpass section of the crossover. As mentioned above, this raises the system Qts if the box size is the same, but can be offset if the box size is increased.
The overall goal is to have the Altec/GPA 416 Alnico-magnet driver in a loosely filled closed box, with source Z's between 1 and 2 ohms, and also accounting for "room lift" in the below-60 Hz region. An alternate approach is to use a vented box with about twice the volume, preferably in an alignment with favorable group delay characteristics.
Both LF and HF sections use a passive crossover in the 640 to 800 Hz range, powered by a single amplifier in the 10 to 60-watt range. The expected attenuation in the HF section will be about 10 to 12 dB, with a shelf equalizer if the Yuichi A290 or ES290 type horn is used.
It is a simple 2-way system optimized for vacuum tube amplifiers with zero to moderate feedback. If response down to 20 Hz is desired, that can be provided with a separately powered pair of subwoofers. In that application, Class AB or Class D amplifiers are the best choice, since they have the most power, are the most efficient, and there is limited impression of tonality below 40 Hz.
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Funny you should mention that because I’ve been working on something similar, except with one amp. Current source amps work fine but lots of EQ is needed. However, I could swear it sounds better. Nelson has done a lot of work in this area.
Nelson is welcome to it. I try to minimize equalization, without falling overboard to a full-range driver. Whizzer cones are definitely not my thing ... far too much stored energy, and dynamics that are limited compared to a large-format monitor.
The next step in complexity is a 2-way system. If the drivers are carefully chosen, little or no equalization will be required, and managing the phase transfer and radiation pattern between LF and HF is reasonably simple compared to 3-way systems.
There's always bi-amplification, but that gets gonzo if we are talking about PP all-triode amplifiers. Not ready for that yet.
The next step in complexity is a 2-way system. If the drivers are carefully chosen, little or no equalization will be required, and managing the phase transfer and radiation pattern between LF and HF is reasonably simple compared to 3-way systems.
There's always bi-amplification, but that gets gonzo if we are talking about PP all-triode amplifiers. Not ready for that yet.
I want to thank Joseph (Troy) Crowe for his extensive measurements on the Altec/GPA 416 Alnico in a 100L sealed box enclosure. I suspect the very low IM distortion is the result of the underhung voice coil, which is very rare in modern drivers. I am also gratified to see the cumulative-decay (waterfall) curves are as good as they are.
416 Measurements
I also want to thank Gary Dahl for completing the Beyond the Ariel project with his sealed-box Great Plains Audio 416 Alnicos and the AH425 Azurahorn. He's chosen the extremely rare Yamaha 6688 compression driver, while I will be following Joseph Crowe's guidance on the SB Audience CDN-65T driver, which has remarkable performance for a large format compression driver.
I will be contacting Joseph Crowe for guidance on getting the last mile of this project done: an optimal crossover, most probably using an 1.8 kHz notch filter for the 416, and a 3D-printed or NC-milled adaptor between the 1.4" circular exit of the CDN-65T driver and the 2.0" square entrance of the Athos Audio Yuichi A290 wood horn. Alternatively, using Crowe's own ES-290 wood horn, but I already have both AH425's and A290's horns sitting in the basement, awaiting use. I don't think I need three sets of horns to play with, but who knows?
The measurements referenced above show a crossover in the 640 to 800 Hz region is well-suited to the 416, especially with a moderate notch filter tuned to 1.8 kHz. I still favor large format compression drivers, since they allow a crossover well below 1.2 kHz, in the 500 to 800 Hz region. An octave makes a big difference in this frequency region.
The SB Audience driver is unusual because it extends smoothly to 17 kHz, while most drivers with 3 to 4-inch diameter Ti or Al diaphragms usually have their first resonance around 13 kHz. I don't know what SB has done, but that is exceptional performance, approaching carbon fiber or beryllium diaphragms, at one-third to one-tenth the price.
As for other questions, I have no recommendations for transistor amplifiers, either Class AB or Class D, or bipolar transistor vs GaN FET. From what I heard at the Seattle show, Class D using GaN FETs has come a long way, and has surpassed linear Class AB transistor, but still isn't quite in DHT triode territory yet. But is getting close.
416 Measurements
I also want to thank Gary Dahl for completing the Beyond the Ariel project with his sealed-box Great Plains Audio 416 Alnicos and the AH425 Azurahorn. He's chosen the extremely rare Yamaha 6688 compression driver, while I will be following Joseph Crowe's guidance on the SB Audience CDN-65T driver, which has remarkable performance for a large format compression driver.
I will be contacting Joseph Crowe for guidance on getting the last mile of this project done: an optimal crossover, most probably using an 1.8 kHz notch filter for the 416, and a 3D-printed or NC-milled adaptor between the 1.4" circular exit of the CDN-65T driver and the 2.0" square entrance of the Athos Audio Yuichi A290 wood horn. Alternatively, using Crowe's own ES-290 wood horn, but I already have both AH425's and A290's horns sitting in the basement, awaiting use. I don't think I need three sets of horns to play with, but who knows?
The measurements referenced above show a crossover in the 640 to 800 Hz region is well-suited to the 416, especially with a moderate notch filter tuned to 1.8 kHz. I still favor large format compression drivers, since they allow a crossover well below 1.2 kHz, in the 500 to 800 Hz region. An octave makes a big difference in this frequency region.
The SB Audience driver is unusual because it extends smoothly to 17 kHz, while most drivers with 3 to 4-inch diameter Ti or Al diaphragms usually have their first resonance around 13 kHz. I don't know what SB has done, but that is exceptional performance, approaching carbon fiber or beryllium diaphragms, at one-third to one-tenth the price.
As for other questions, I have no recommendations for transistor amplifiers, either Class AB or Class D, or bipolar transistor vs GaN FET. From what I heard at the Seattle show, Class D using GaN FETs has come a long way, and has surpassed linear Class AB transistor, but still isn't quite in DHT triode territory yet. But is getting close.
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JMLC AH425 vs sectoral horns
First, many thanks again to Lynn and friends who, a decade ago, got me started on this large two way, passive filtered, clean transient DIY speaker design journey.
The drivers I purchased then are the 15 inch TAD TD1601B midwoofer and Radian 745NEO Be 1.4 inch tweeter. I designed a high order low pass filter with a few dBs of baffle step compensation to drive the midwoofer in a sealed bass enclosure. My brother cloned my speakers and has been using his in a room larger than mine. Last year, although satisfied by Martin's JMLC AH425 horn, I could not help myself and acquired gently used Athos clones of the TAD TH4001 for hearing myself how a good sectoral sounds. The TH4001 is a slightly smaller version of the Yuchi A290. I found that I had to tailor the high pass filter to match each horn (for level and EQ) although the driver is the same.
As a side note, in a separate thread I explained the struggle finding a proper adapter for my driver and TH4001 horn. I ended up writing a CAD software to generate the desired throat expansion and got my own adapters 3D-printed. I am satisfied with the result and find that it levels the playing field between the two horn designs. Custom adapters are available made-to-order if anyone is interested.
Listening impressions.
The JMLC and sectoral horns sound superb and I have happily lived with both. The interaction with the room is where differences arise, but I honestly believe that either horn design is well-suited for a high end two way speaker.
JMLC (AH425): One hears very little room reflections when listening inside the sweet spot "cone". It feels a little like wearing headphones, but with all the benefits of a whole body experience (feeling bass, etc). In a typical sized room the sweet spot is wide enough for one or two listeners, but beyond that the tonality starts degrading. One should be aware of this if intending to position listener off axis (e.g. near side or front walls) . The ceiling reflection can add some "height" to the stereo image, which can sound pleasant on some recordings (pipe organ) but otherwise smears details. The JMLC horn sounds even better in my brother's large room than in my own which is of typical size but has a low (7 foot) ceiling. Still, while I use the TH4001 I miss the JMLC experience.
Sectoral (TH4001, A290) : These horns with vanes provide horizontal dispersion wider than is typically needed in a home setting. In practice side wall reflections are alleviated by toeing-in the speakers and haven't bothered me. The sweet spot is very large (width and depth) and the speakers can be listened to closer and further off axis than the JMLC, without noticeable tone degradation. By virtue of its low profile, the sectoral horn allows positioning the two drivers closer together. At short to moderate listening distances one can hear this as tightening the image. A benefit in my room is that the narrow vertical dispersion attenuates ceiling reflection.
If I were to start today, I would be considering the drivers that Lynn mentioned, because we now have extensive measurements confirming their quality (thanks to Troy), as well as their lower cost. A decade ago, jumping in required a leap of faith. Kudos to Gary, Martin and others who led down the path!
In the near future my brother will bring his AH425 and drivers for back-and-forth comparison with the TH4001. I will report any new impressions. In the mean time, I just wanted to share that the JMLC and these sectoral horns don’t sound coloured, and are fun to own and compare, just like fine wine.
First, many thanks again to Lynn and friends who, a decade ago, got me started on this large two way, passive filtered, clean transient DIY speaker design journey.
The drivers I purchased then are the 15 inch TAD TD1601B midwoofer and Radian 745NEO Be 1.4 inch tweeter. I designed a high order low pass filter with a few dBs of baffle step compensation to drive the midwoofer in a sealed bass enclosure. My brother cloned my speakers and has been using his in a room larger than mine. Last year, although satisfied by Martin's JMLC AH425 horn, I could not help myself and acquired gently used Athos clones of the TAD TH4001 for hearing myself how a good sectoral sounds. The TH4001 is a slightly smaller version of the Yuchi A290. I found that I had to tailor the high pass filter to match each horn (for level and EQ) although the driver is the same.
As a side note, in a separate thread I explained the struggle finding a proper adapter for my driver and TH4001 horn. I ended up writing a CAD software to generate the desired throat expansion and got my own adapters 3D-printed. I am satisfied with the result and find that it levels the playing field between the two horn designs. Custom adapters are available made-to-order if anyone is interested.
Listening impressions.
The JMLC and sectoral horns sound superb and I have happily lived with both. The interaction with the room is where differences arise, but I honestly believe that either horn design is well-suited for a high end two way speaker.
JMLC (AH425): One hears very little room reflections when listening inside the sweet spot "cone". It feels a little like wearing headphones, but with all the benefits of a whole body experience (feeling bass, etc). In a typical sized room the sweet spot is wide enough for one or two listeners, but beyond that the tonality starts degrading. One should be aware of this if intending to position listener off axis (e.g. near side or front walls) . The ceiling reflection can add some "height" to the stereo image, which can sound pleasant on some recordings (pipe organ) but otherwise smears details. The JMLC horn sounds even better in my brother's large room than in my own which is of typical size but has a low (7 foot) ceiling. Still, while I use the TH4001 I miss the JMLC experience.
Sectoral (TH4001, A290) : These horns with vanes provide horizontal dispersion wider than is typically needed in a home setting. In practice side wall reflections are alleviated by toeing-in the speakers and haven't bothered me. The sweet spot is very large (width and depth) and the speakers can be listened to closer and further off axis than the JMLC, without noticeable tone degradation. By virtue of its low profile, the sectoral horn allows positioning the two drivers closer together. At short to moderate listening distances one can hear this as tightening the image. A benefit in my room is that the narrow vertical dispersion attenuates ceiling reflection.
If I were to start today, I would be considering the drivers that Lynn mentioned, because we now have extensive measurements confirming their quality (thanks to Troy), as well as their lower cost. A decade ago, jumping in required a leap of faith. Kudos to Gary, Martin and others who led down the path!
In the near future my brother will bring his AH425 and drivers for back-and-forth comparison with the TH4001. I will report any new impressions. In the mean time, I just wanted to share that the JMLC and these sectoral horns don’t sound coloured, and are fun to own and compare, just like fine wine.
I have heard the TH4001 and AH425 at considerable length. Both are superb, and large format compression drivers have a quality of ease and effortlessness you don't get with other drivers. Just stay away from mainstream PA stuff, which is designed for SPLs and durability, but not much else.
It was hearing the Altec A5's in San Francisco, and the Blue Thunders in Zurich, that made me "get religion" about large format horns. So relaxed compared to their little brothers, what a difference.
As transparent as electrostats, but without that slightly nervous quality that makes you tense up when the guitarist really cuts loose, or the singer reaches for that note. (That was the material at the PAF show that made the Class D amps stumble once or twice.)
No matter what you throw at the TH4001's or AH425's, there's always miles of headroom. Once you hear it, even for few minutes, you can't go back.
It was hearing the Altec A5's in San Francisco, and the Blue Thunders in Zurich, that made me "get religion" about large format horns. So relaxed compared to their little brothers, what a difference.
As transparent as electrostats, but without that slightly nervous quality that makes you tense up when the guitarist really cuts loose, or the singer reaches for that note. (That was the material at the PAF show that made the Class D amps stumble once or twice.)
No matter what you throw at the TH4001's or AH425's, there's always miles of headroom. Once you hear it, even for few minutes, you can't go back.
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No, I do not have HF1460's on hand. Nobody had them in stock, and they are several times the price of the SB Audience CDN-65's. So I will start easy at first ... Joseph Crowe's measurements show a driver that is free of the irritating Titanium breakup we see in other drivers. Don't know how they did it.
It might be worthwhile to get two different adapters, one for 2" drivers, and the other for 1.4" drivers. Might as well try 'em all.
I really like Beryllium, but hoo boy, is it expensive. The cheapest route seems to be used JBL drivers with blown diaphragms, carefully cleaning the gap, and installing the Radian replacement diaphragms.
It might be worthwhile to get two different adapters, one for 2" drivers, and the other for 1.4" drivers. Might as well try 'em all.
I really like Beryllium, but hoo boy, is it expensive. The cheapest route seems to be used JBL drivers with blown diaphragms, carefully cleaning the gap, and installing the Radian replacement diaphragms.
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Sorry, if you have already seen this. I stumbled upon this and thought I would share the link as Hiraga has been mentioned from time to time in this thread.
https://www.psaudio.com/blogs/copper/the-munich-high-end-audio-show-2023-and-a-visit-to-jean-hiraga
https://www.psaudio.com/blogs/copper/the-munich-high-end-audio-show-2023-and-a-visit-to-jean-hiraga
Aside from the limited HF response of the Yamaha 6681B driver, is this why you would instead choose the SB Audience CDN-65?
Troy Crowe's measurements of the CDN-65 were quite impressive, along with his subjective report on the sonics. Many compression drivers have more IM distortion than we'd like, but the multi-tone test reveals distortion vs frequency very clearly. And that driver came out very well.
How do the A290 and TH4001 horn differ? Please comment comparatively on their sound. At least if I knew that much it might be a lot easier to decide between them and also Troy's yet unauditioned ES290.
A related matter are questions raised and/or experiences regarding the benefits versus problems caused by vanes in the 290 and 4001. Eso said on post # 145, https://www.diyaudio.com/community/...ompression-drivers-a-discussion.397699/page-8 “………….Many years ago I built a pair of Yuichi A290 radial horns to play with. They are an exceptional radial design with performance very similar to the TAD TH-4001. But I don't like horns with vanes in them for hifi; I find they do great at even horizontal coverage, but the sound stage flattens as a result…………"
More discussion about vanes; posts # 8, 36,
https://www.diyaudio.com/community/...-inch-horn-you-can-actually-buy.390519/page-2 and on the preceding page.
I think they also mentioned that Athos offers those horns with/without the vanes.
But Troy Crowe’s version of the 290 horn apparently has no vanes nor any throat adapter.
https://josephcrowe.com/products/es-290-biradial-wood-horn
https://josephcrowe.com/products/3d-cad-plans-for-es-290-biradial-horn-horn-no-1670
https://www.instagram.com/p/B5VlUlj...d&ig_rid=a2bfbcd5-b7af-4e17-8fbf-2d8c4f895463
What might it be about the geometry of that horn that permits the absence-perhaps advantageously-of both vanes and no throat adapter?
More discussion about vanes; posts # 8, 36,
https://www.diyaudio.com/community/...-inch-horn-you-can-actually-buy.390519/page-2 and on the preceding page.
I think they also mentioned that Athos offers those horns with/without the vanes.
But Troy Crowe’s version of the 290 horn apparently has no vanes nor any throat adapter.
https://josephcrowe.com/products/es-290-biradial-wood-horn
https://josephcrowe.com/products/3d-cad-plans-for-es-290-biradial-horn-horn-no-1670
https://www.instagram.com/p/B5VlUlj...d&ig_rid=a2bfbcd5-b7af-4e17-8fbf-2d8c4f895463
What might it be about the geometry of that horn that permits the absence-perhaps advantageously-of both vanes and no throat adapter?
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Here at 9:33, Troy found the multi-tone test 70db down @ 8kHz ; ~ 0.03 IM distortion.
At 5:34, frequency response measured from 600Hz to 11kHz. With this driver in the 290 or 4001 horn, any particular tweeter suggestions?
Allow me to help Lynn, if he and you do not mind. Lynn can always correct me.
The TAD horn is proprietary but has been measured and copied by Athos and others. The Yuichi horn profile is public. The TAD is slightly smaller and has a 40 x 50 mm entrance versus the Yuichi's 50 x 50 mm. They both have vanes and their surface area expansion profiles are very close. These horns are so similar that I doubt I could hear a difference between them. Measure one yes, hear one...
Splitting hairs... The Yuichi might have a small edge by virtue of its larger size and I would lean towards it if using a 2 inch driver. Go big!
On the other hand, if using a 1.4 inch driver the length of the adapter would make me lean towards the TAD: an adapter for the Yuichi would possibly warrant some kind of support under the driver depending on the driver weight. Still, it is doable. The optimal adapter length for a 1.4 inch driver is 3 inch for the TH4001, and longer for A290 because of the larger surface area difference.
As for depth perception, I have not noticed an issue since using the TH4001. I will be happy to check when doing back-and-forth comparisons with the A425 and report back if I notice anything funny.
Again, putting things in perspective, the low distortion, low coloration of the devices discussed here are revelatory and addictive. The budget conscious DIYer (me included) can always watch the used market. I happen to be aware that a pair of TH4001 clones should come up soon (not mine).
The TAD horn is proprietary but has been measured and copied by Athos and others. The Yuichi horn profile is public. The TAD is slightly smaller and has a 40 x 50 mm entrance versus the Yuichi's 50 x 50 mm. They both have vanes and their surface area expansion profiles are very close. These horns are so similar that I doubt I could hear a difference between them. Measure one yes, hear one...
Splitting hairs... The Yuichi might have a small edge by virtue of its larger size and I would lean towards it if using a 2 inch driver. Go big!
On the other hand, if using a 1.4 inch driver the length of the adapter would make me lean towards the TAD: an adapter for the Yuichi would possibly warrant some kind of support under the driver depending on the driver weight. Still, it is doable. The optimal adapter length for a 1.4 inch driver is 3 inch for the TH4001, and longer for A290 because of the larger surface area difference.
As for depth perception, I have not noticed an issue since using the TH4001. I will be happy to check when doing back-and-forth comparisons with the A425 and report back if I notice anything funny.
Again, putting things in perspective, the low distortion, low coloration of the devices discussed here are revelatory and addictive. The budget conscious DIYer (me included) can always watch the used market. I happen to be aware that a pair of TH4001 clones should come up soon (not mine).
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When I say the Yamaha 6688 is "unobtainium" of course that's not literally true. They're out there, and will last a long term time if not abused.
But the unique tri-finger low-mass suspension of the 6688 diaphragm is not found on any other driver, so if you break it, you will not find any replacements that are made the same way. They might fit, but will not measure or sound the same.
Carbon fiber (Textreme) looks interesting. Very good measurements, but double or triple the price of Titanium or Aluminum. I have heard Beryllium and it is astonishing, with very light weight, incredible strength, and excellent self-damping, unlike Titanium or Aluminum. Very sweet and ultra-transparent sounding. But also really expensive and apparently out of stock everywhere.
Regarding the sound quality of the AH425 or TH4001, I am not aware of any modern high-end speaker, at any price, that can match these. The only thing that would compare would be the long-defunct Hill Plasmatronic that I heard at the 1979 CES show.
But the unique tri-finger low-mass suspension of the 6688 diaphragm is not found on any other driver, so if you break it, you will not find any replacements that are made the same way. They might fit, but will not measure or sound the same.
Carbon fiber (Textreme) looks interesting. Very good measurements, but double or triple the price of Titanium or Aluminum. I have heard Beryllium and it is astonishing, with very light weight, incredible strength, and excellent self-damping, unlike Titanium or Aluminum. Very sweet and ultra-transparent sounding. But also really expensive and apparently out of stock everywhere.
Regarding the sound quality of the AH425 or TH4001, I am not aware of any modern high-end speaker, at any price, that can match these. The only thing that would compare would be the long-defunct Hill Plasmatronic that I heard at the 1979 CES show.
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This one loooks interesting as well:
https://en.toutlehautparleur.com/sp...-kartesian-cmp65-vpa-8-ohm-1-5-inch-exit.html
It seems that it has a lower compression ratio in order to reduce distortion at the cost of reduced efficiency.
Regards
Charles
https://en.toutlehautparleur.com/sp...-kartesian-cmp65-vpa-8-ohm-1-5-inch-exit.html
It seems that it has a lower compression ratio in order to reduce distortion at the cost of reduced efficiency.
Regards
Charles