GM, thank you very much for taking interest. To avoid frustrations, allow me to quickly explain the motivation of this build:
The main intention is not to achieve/copy/imitate the original Altec system. It will be used for loud home listening. The budget allows for 100-200€ per transducer, we are looking at 15" PA woofers in that price category. It is for a person that has chosen this specific cabinet mainly for aesthetic reasons. The cabinet will be built based on the original dimensions and horn profile, but the reflex tuning will be adapted as needed. The goal is to have a powerful two-way system with a 15" woofer crossed over to a large compression driver.
I had a look at those old measured specs of the 803 woofer.... they are crazy! is there anything like it nowadays? 23 grams Mms, BL 23, refr. eff 12.4% ??? only .9mm xmax though...
regarding bracing, I have found this previous thread for inspiration
Altec VOTT A7 using CAD and CNC
The main intention is not to achieve/copy/imitate the original Altec system. It will be used for loud home listening. The budget allows for 100-200€ per transducer, we are looking at 15" PA woofers in that price category. It is for a person that has chosen this specific cabinet mainly for aesthetic reasons. The cabinet will be built based on the original dimensions and horn profile, but the reflex tuning will be adapted as needed. The goal is to have a powerful two-way system with a 15" woofer crossed over to a large compression driver.
I had a look at those old measured specs of the 803 woofer.... they are crazy! is there anything like it nowadays? 23 grams Mms, BL 23, refr. eff 12.4% ??? only .9mm xmax though...
regarding bracing, I have found this previous thread for inspiration
Altec VOTT A7 using CAD and CNC
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are you referring to the HR input page of post #13 in this thread?
i assumed the driver cutout forms the throat, hence I used a value of 640. Apparently the correct value would be simply the whole 20"x40" baffle area at the start of the horn?
At least mouth size, horn length and expansion (exp) should be correct?
Sorry you lost me there, what does "CR" stand for?
now if i knew how to model all that....
Thank you for your advice Cal!
1)will do
2)that seems very small to me, but lets see!
3)will do
You might can find one with ~the same Fs, Vas, Qts, but not the rest as these were designed for max efficiency, speech articulation behind a cinema screen when coupled to a matching impedance tube system: Altec 515A, 515B, 803A, 803B, 416A
Anyway, a number of prosound drivers have specs similar to the later 416C except with a lot more power handling, but you'll ideally want one with a high frequency response ~like the 515B to match up to the horn: http://www.lansingheritage.org/images/altec/specs/components/515b/page02.jpg
Even then, the 515B was designed for a 70 Hz horn, so the HF gain ideally needs to start earlier to fill in the otherwise 1-2 kHz dip [top response plot]: http://www.lansingheritage.org/images/altec/specs/components/515g/page3.jpg
GM
You might can find one with ~the same Fs, Vas, Qts, but not the rest as these were designed for max efficiency, speech articulation behind a cinema screen when coupled to a matching impedance tube system: Altec 515A, 515B, 803A, 803B, 416A
Anyway, a number of prosound drivers have specs similar to the later 416C except with a lot more power handling, but you'll ideally want one with a high frequency response ~like the 515B to match up to the horn: http://www.lansingheritage.org/images/altec/specs/components/515b/page02.jpg
Even then, the 515B was designed for a 70 Hz horn, so the HF gain ideally needs to start earlier to fill in the otherwise 1-2 kHz dip [top response plot]: http://www.lansingheritage.org/images/altec/specs/components/515g/page3.jpg
GM
are you referring to the HR input page of post #13 in this thread?
i assumed the driver cutout forms the throat, hence I used a value of 640. Apparently the correct value would be simply the whole 20"x40" baffle area at the start of the horn?
At least mouth size, horn length and expansion (exp) should be correct?
Sorry you lost me there, what does "CR" stand for?
now if i knew how to model all that....
Yes.
Sorry, no; between the wrong throat and not factoring in that its axial length is sloped down some, the 110 Hz flare couldn't be made.
Compression ratio, i.e. horn throat [St] = driver effective piston area [Sd].
Yeah, though judging by some sims I've seen posted recently it may be possible in HR now, but a very low priority for me, and none for you since tuning will be done empirically.
GM
Attachments
You're welcome! Understood, I happen to be intimately familiar with this cab alignment, having used it as an example when being taught horn design basics way back when, so knowing the flare frequency, etc., makes it easy in HR, though if you know it you can juggle mouth area Vs length till it calcs the correct one.
HR can be confusing WRT truncated horns in that the pioneers designed a full size horn [this one was originally described as a 1/2 size 55 Hz expo], then cut a 'slice' out of it at the desired throat area and further down as required to meet the needs of the app.
GM
HR can be confusing WRT truncated horns in that the pioneers designed a full size horn [this one was originally described as a 1/2 size 55 Hz expo], then cut a 'slice' out of it at the desired throat area and further down as required to meet the needs of the app.
GM
I corrected the input parameters, now I have the correct flare frequency of 110 Hz. Marginal differences. I did 0.5PI and 2PI, comparing the Beyma SM115N to Fane Sovereign Pro 15-600. Due to a bit higher xmax and higher tuning, the Fane would take a few watts more and be 2-3 dB louder, but with an uneven response. The beyma still comes out with a smoother curve in 0.5 PI.
125 dB with 40 Watts
Any thoughts on these response curves?
(Couldn't resist setting S1 to 640 cmsq, since that is the actual baffle cutout)
125 dB with 40 Watts
Any thoughts on these response curves?
(Couldn't resist setting S1 to 640 cmsq, since that is the actual baffle cutout
)Attachments
GM, since you seem to have some A7 records in your hornresp, would you mind sharing some frequency plots, and which woofers you have simulated. It would be nice to compare. Also it would be much appreciated if you have any comments in regards to how these simulations correlate with your experience? Do you happen to have measurements of any A7 configuration?
best regards,
Bob
Actually, I don't, just the 803A I did to show you the horn inputs. As for measurements, we had no need way back when as all Altec designs were well documented by them, though sadly, EV destroyed any paperwork they didn't need, so limited to a relative few plus whatever DIYers have posted.
Note too that available drivers were for the most part all of a 'sameness' for max interchangeability for each genre of speaker types with W.E./Lansing/Altec being the most copied. Haven't paid much attention to current production, but from what little I've noticed, nothing's really changed in prosound, cinema, M.I. apps beyond the usual improvements in CAD, etc., materials, manufacturing.
As for choosing drivers, the horn 'rings' at ~220 Hz, the mean of its 110-440 Hz BW, so in T/S parlance we ideally want the driver mass corner [Fhm = 2*Fs/Qes'] to be ~220 Hz and ~440 Hz like the average 803A if driven with a period correct matching impedance to drop it back down.
Later Altec drivers don't spec too close until one factors in thermal power distortion, so somewhat misaligned for HIFI/HT apps, ergo ideally one would dial in a bit of some form of series resistance to smooth it out, though few do, or use whatever Fs, Qes driver that meets the 'magic' ~220 Hz Fhm spec and of course there's still the issue of having the right amount of breakup modes BW to fill in above the horn's upper roll-off.
The sims are fine for comparing basic horn response for comparison, but that's it as there's not enough there to have any real correlation with how they sound, though if we can properly sim the back box we might can get an idea of how it sounds, though frankly, it's been so many decades since I've been exposed to them, especially in a HIFI app, that I wonder if I would recognize it if blindfolded since they don't sound like horns at all when properly 'voiced', damped, just very open, efficient, dynamic speakers with excellent [projected] vocals combined with a rolled off bass if not hard in a corner.
Most folks though seem to prefer them as the cinema/PA/MI sound systems they were meant for though, so too 'raw', harsh for me except as dance party speakers or behind screens in the neighborhood cinemas and the couple of early HTs I was exposed to.
Even consumer speakers with horns I prefer with grills and what we nowadays call CD horn EQ, but most don't, though with the M19's mouth foam combined with its more adjustable XO, one can do similar and of course designed as a whole system with period correct matching impedance tube amps with variable DF tone controls + horn baffles, all of this becomes moot to all but the inveterate tinkerer.
GM
fast forward four months, summer is almost over, and tonight I had the opportunity to audition one of the finished 825s with a JBL 2445 on a large wooden on top of it for about an hour. Sorry, no pictures......
Cal's and GMs prophecies were fulfilled..... Although it was in mono, in a medium sized wooden workshop shed, quick and dirty Harsch xover set up on a DCX...... Once I got it roughly dialed in, it was very pleasurable to listen to. Still a bit rough around the edges and could definitely be tweaked further, but taking these circumstances into account...... very very nice!
Some quick sweeps showed flat response down to 50 Hz, the vent was not tuned yet, with the opening dimensioned according to plan, but without cloth, it seems to be tuned around 65 Hz, sweeps near the opening showed a broad hump at this frequency. My friend made up some baffles that will be used for the reflex tuning later
With music playback, our smartphone RTA apps registered fundamentals down to 30 Hz, my Samsung plotted them 6-10 db down, my friends iphone at flat equal level with upper bass (don't know which app he has on his phone).
About the sound...... coupled to a big horn with a beefy 2" driver, the sound is BIG, as expected. Crossover frequency was 770 Hz. Once I had the rough balance between 825 and HF horn set (horn a bit hot compared to the 825), I added a 3 dB shelf bass boost.
Due to the small space, and evening time, I didn't dare to crank it very much at all. even so, with suitably dynamic recordings it can rip your head right off.
I had to skip through my music a bit haphazardly, but it was funny to discover how different it sounds compared to the system I have currently been tweaking. I don't have much experience trying to verbalize listening experiences, but i will try. I listen to a lot of jamaican music. Some of it is very well recorded, some not so well, but especially for the combination of beauty and flaws, I find some of this music very useful when evaluating speakers.
Listening to this particular 825 copy and large HF horn combination, I was struck by the very natural and tactile sound that jumped out from some of the recordings. Well recorded vocals sound very good, all the small reverb tails are very clear, the natural and artificial ambiances can be discerned. Another interesting aspect is, that in some songs the vocals might distort just at a certain forte moment, but be otherwise very clean.
"Tonight" by Keith and Tex, a very unassuming song by itself, the guitars
jumped out at me, the strumming was "tangible" and lifelike. It is a very calm song with very static dynamics, that can sometimes sound a little flat or lifeless, but I was surprised how full it sounded at moderate volume on this system. The instrumentation is sparse, but perfectly balanced, and was beautifully rendered.
Please note again that I was listening in mono. I am itching to hear it in stereo.......
aaaaaand now i need some sleep!
Cal's and GMs prophecies were fulfilled..... Although it was in mono, in a medium sized wooden workshop shed, quick and dirty Harsch xover set up on a DCX...... Once I got it roughly dialed in, it was very pleasurable to listen to. Still a bit rough around the edges and could definitely be tweaked further, but taking these circumstances into account...... very very nice!
Some quick sweeps showed flat response down to 50 Hz, the vent was not tuned yet, with the opening dimensioned according to plan, but without cloth, it seems to be tuned around 65 Hz, sweeps near the opening showed a broad hump at this frequency. My friend made up some baffles that will be used for the reflex tuning later
With music playback, our smartphone RTA apps registered fundamentals down to 30 Hz, my Samsung plotted them 6-10 db down, my friends iphone at flat equal level with upper bass (don't know which app he has on his phone).
About the sound...... coupled to a big horn with a beefy 2" driver, the sound is BIG, as expected. Crossover frequency was 770 Hz. Once I had the rough balance between 825 and HF horn set (horn a bit hot compared to the 825), I added a 3 dB shelf bass boost.
Due to the small space, and evening time, I didn't dare to crank it very much at all. even so, with suitably dynamic recordings it can rip your head right off.
I had to skip through my music a bit haphazardly, but it was funny to discover how different it sounds compared to the system I have currently been tweaking. I don't have much experience trying to verbalize listening experiences, but i will try. I listen to a lot of jamaican music. Some of it is very well recorded, some not so well, but especially for the combination of beauty and flaws, I find some of this music very useful when evaluating speakers.
Listening to this particular 825 copy and large HF horn combination, I was struck by the very natural and tactile sound that jumped out from some of the recordings. Well recorded vocals sound very good, all the small reverb tails are very clear, the natural and artificial ambiances can be discerned. Another interesting aspect is, that in some songs the vocals might distort just at a certain forte moment, but be otherwise very clean.
"Tonight" by Keith and Tex, a very unassuming song by itself, the guitars
jumped out at me, the strumming was "tangible" and lifelike. It is a very calm song with very static dynamics, that can sometimes sound a little flat or lifeless, but I was surprised how full it sounded at moderate volume on this system. The instrumentation is sparse, but perfectly balanced, and was beautifully rendered.
Please note again that I was listening in mono. I am itching to hear it in stereo.......
aaaaaand now i need some sleep!
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