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Multi-Way Conventional loudspeakers with crossovers

Which 15" transducer for Altec VOT/825/A7?
Which 15" transducer for Altec VOT/825/A7?
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Old 31st March 2019, 07:20 PM   #21
Cal Weldon is offline Cal Weldon  Canada
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Which 15" transducer for Altec VOT/825/A7?
I hadn't noticed that. I will merge the other thread into this one.
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Old 31st March 2019, 07:28 PM   #22
bob4 is offline bob4  Germany
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Thank you Cal, this seems like the best solution. Sorry about the confusion....
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Old 31st March 2019, 07:29 PM   #23
Cal Weldon is offline Cal Weldon  Canada
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Which 15" transducer for Altec VOT/825/A7?
You're welcome. I moved only the part where you started in the other one over to this one.
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Old 31st March 2019, 08:28 PM   #24
bob4 is offline bob4  Germany
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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.



Quote:
Originally Posted by GM View Post
Some measured 803 specs here: ASHLEY

GM

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

Last edited by bob4; 31st March 2019 at 08:46 PM.
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Old 31st March 2019, 08:56 PM   #25
bob4 is offline bob4  Germany
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Quote:
Originally Posted by GM View Post
Regardless, at a glance, I don't see anything technically correct,
are you referring to the HR input page of post #13 in this thread?

Quote:
Originally Posted by GM View Post
Horn is a 110 Hz expo with a 128"^2 x 5/8" [baffle depth] conical throat.
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?

Quote:
Originally Posted by GM View Post
Vtc, Atc is irrelevant and can be left blank since it's a 1:1 CR and the driver is pistonic over the horn's gain BW.
Sorry you lost me there, what does "CR" stand for?


Quote:
Originally Posted by GM View Post
Rear chamber is technically a two segment BLH with conical, then parabolic inverse taped TQWT and of course vented [mass loaded]. Note that the 825's open back horn cavities function as a crude band stop filter.
now if i knew how to model all that....
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Old 1st April 2019, 04:24 AM   #26
bob4 is offline bob4  Germany
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Quote:
Originally Posted by Cal Weldon View Post
It is a very forgiving cabinet. The things many persons including myself recommend:
1. Reinforce it
2. Reduce the port size to 75 in^2
3. Fill in the back side of the horn flares, if not already done.
Even if you don't do any of those, you will soon here what that cab can do for a even a mediocre woofer.
Thank you for your advice Cal!

1)will do
2)that seems very small to me, but lets see!
3)will do
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Old 1st April 2019, 04:55 AM   #27
GM is offline GM  United States
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Quote:
Originally Posted by bob4 View Post
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...
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/image...15b/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/image...515g/page3.jpg

GM
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Old 1st April 2019, 04:56 AM   #28
GM is offline GM  United States
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Quote:
Originally Posted by bob4 View Post
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...
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/image...15b/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/image...515g/page3.jpg

GM
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Old 1st April 2019, 05:13 AM   #29
GM is offline GM  United States
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Quote:
Originally Posted by bob4 View Post
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
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File Type: png Altec 825_828 horn dims.PNG (4.0 KB, 80 views)
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Old 1st April 2019, 08:04 AM   #30
bob4 is offline bob4  Germany
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Quote:
Originally Posted by GM View Post
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.
thank you for posting that screencapture GM, I see now what you mean. The flare cutoff frequency is shown in the rightmost column. I am still a hornresp noob. I will adjust accordingly. I'm running an old version of hornresp on my wifes old windows laptop, which doesn't help.....
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