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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, 12:10 PM   #11
bob4 is offline bob4  Germany
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in the meantime, after locating the GPA 416 datasheet ,I have found this Beyma Woofer with slightly different Q parameters, but fairly low Fs and a VAS close to the actual cabinet volume.

Unfortunately the measured response curve of that beyma looks much worse (=less flat) than the GPA 416 or Faital 15PR400.....

One advantage of the Beyma according to hornresp would be that for a low tuning frequency of 30 Hz, the group delay would be less than with the faital.
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Old 31st March 2019, 02:54 PM   #12
Cal Weldon is offline Cal Weldon  Canada
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Which 15" transducer for Altec VOT/825/A7?
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.
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Old 31st March 2019, 03:01 PM   #13
bob4 is offline bob4  Germany
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back from vacation, I am again tinkering around in Hornresp trying to simulate the Altec A7 cabinet.

I have simulated various drivers, but getting only marginal differences. a few dbs here and there in the freq response, moderate variation in group delay and impedance plots.

my main gripes:

1) i want to make sure first of all that the FLH part is modeled accurately. Once I can trust that part, I can focus on the low end tuning.

2) I copied the values of Vtc and Atc from Phils original simulations. Are these correct?


3) the parameters for the GPA 416 are incomplete, missing Cms and Rms..... I'm not sure how trustable the simulation can be under this circumstance.

4) In halfspace the simulations look like a mountain range, even with the fabled GPA 416. The cabs will be used indoors, probably placed close to or in corners. In Quarterspace the responses even out considerably to a more presentable shape.

(EDIT: copied the part about woofer selection to the other thread in the multiway forum, sorry!!!)
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File Type: png A7BeymaInputs.PNG (57.2 KB, 152 views)

Last edited by bob4; 31st March 2019 at 03:04 PM.
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Old 31st March 2019, 03:04 PM   #14
bob4 is offline bob4  Germany
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I was looking for woofers that have reasonably similar Mms, Qts, Qes and Qms compared with the GPA 416. I was concerned if a low Fs would be necessary, but I didn't see any big differences in the simulations. I was also assuming that a low Le would be beneficial for the midrange sound. And what about Vas, would a close match to the cabinet volume bring any benefits? Any comments on my strategy/assumptions?
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Old 31st March 2019, 03:13 PM   #15
bob4 is offline bob4  Germany
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So far on my shortlist:

Faital 15PR400: (was praised somewhere for a great midrange sound)
Beyma SM115N
Fane Sovereign Pro 15-600LF
Fane Sovereign Pro 15-600 (yields a smoother curve than its expensive brother)
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Old 31st March 2019, 03:51 PM   #16
Cal Weldon is offline Cal Weldon  Canada
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Which 15" transducer for Altec VOT/825/A7?
416, 515 and the 421 were all used in that cab. I have Selenium's in mine and I've also heard Eminence and Pyle. I'm not sure the woofers were particularly matched and they all shared the 825 cabinet similarity. It's not a very good cabinet, but for those who like it, they like it a lot. Count me among them.
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Old 31st March 2019, 04:00 PM   #17
bob4 is offline bob4  Germany
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Quote:
Originally Posted by Cal Weldon View Post
I'm not sure the woofers were particularly matched and they all shared the 825 cabinet similarity.
at least that phenomenon seems to be confirmed by my HR efforts....
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Old 31st March 2019, 04:55 PM   #18
bob4 is offline bob4  Germany
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Quote:
Originally Posted by bob4 View Post

2) I copied the values of Vtc and Atc from Phils original simulations. Are these correct?
apparently I DIDN'T copy Vtc, it was calculated by hornresp from my transducer inputs. Phil had manually entered a low value for it. Also, I was able to duplicate the sharp lower cutoff shape of his simulation by setting Rg=5.1 as he did.

I played with the enclosure size, and cut it down to 250 to get rid of the valley between the low cutoff and the midbass hump. I attached a comparison of the Beyma and Fane. The Fane produces a more pronounced midbass hump, while the Beyma is flatter. I then compared different internal cabinet volumes with the Beyma, 250L to 300L, and 300L to 400L. 300L looks like a good compromise, and is probably realistic taking into account that a big and deep port will be needed that will decrease internal volume.
Attached Images
File Type: png BeymaVSFane250L.PNG (61.3 KB, 147 views)
File Type: png Beyma250VS300L.PNG (59.8 KB, 89 views)
File Type: png Beyma300VS400L.PNG (62.0 KB, 89 views)
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Old 31st March 2019, 06:58 PM   #19
GM is offline GM  United States
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Quote:
Originally Posted by bob4 View Post
2) I copied the values of Vtc and Atc from Phils original simulations. Are these correct?
Hmm, strange place to put this! Just now seeing it only because of your other thread.

Regardless, at a glance, I don't see anything technically correct, though the horn response sim isn't all that far off, so got a lot to post re sims, Altec Vs GPA and other replacement driver choices with not much time all at once, hence will be posted piecemeal as time permits.

The highlights/essentials:

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.

Horn is a 110 Hz expo with a 128"^2 x 5/8" [baffle depth] conical throat.

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.

Recommend avoiding GPA if you want a true/best overall Altec A7 performance and find a driver with specs similar to the original 803 it was designed for [tuned to actual Fs] and only use AlNiCo spec 416 if wanting a [much] lower tuning than stock and/or use a high enough XO point to tone down the horn's output, leaving it basically a WG.

Frequency response wise, you want it to look like a lead guitar's where its breakup modes BW fills in/extends the horn's response to ~3.5 kHz/5-6 kHz F12. GPA's OTOH are nominally flat like the last of the series were, leaving the horn a ~ 'one note' honk that they rolled off using a 1.2 kHz XO to 'kill two birds with one stone' with the other of course being to get a much higher HF horn power handling.

Some measured 803 specs here: ASHLEY

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Last edited by GM; 31st March 2019 at 07:06 PM.
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Old 31st March 2019, 07:16 PM   #20
GM is offline GM  United States
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My initial response here: VOT A7

........and ask that you copy/paste as required to consolidate these two threads to here.

TIA,

GM
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