Altec 604 8G and 604 8K throat sizes.

Printable View

09-16-2020, 08:14 AM
eso

4 Attachment(s)

Altec 604 8G and 604 8K throat sizes.

It's been a while since I've been here, but I need help from some of the brains here.

For many years I've been playing with and building Urei 801B duplex drivers and custom horns. The parts are pretty readily available make make a great sounding system.

People keep asking me for my custom horns for the Altec based duplexes, but I hadn't made any because I didn't have an 604 to work with to make my tooling.

I just came up with a pair of 811A monitors, one of which needs a recone so it was a perfect choice to dissect and reverse engineer my horns with. After after removing the 801A horn, I find the throat is a 7/8" bore.

With the B or C series duplex–neither of which have any Altec parts–the throat at the horn is ~1 1/4".

Cross section illustrations of earlier 604 drivers also show a conical throat flare from the compression driver through the woofer center pole.

Does a Stock 604 8G have a conical throat flare?

Did Urei add a restrictor to the 604 8K throat? if so, was this also a feature in the original 604 8G based Urei 801?

This is a very curious discovery to me.

Any tech insight will be appreciated.

eso

https://www.dropbox.com/s/cl9iplicjn...0horn.jpg?dl=0

https://www.dropbox.com/s/yh9wuo77s0...5645.jpeg?dl=0

https://www.dropbox.com/s/0pkfdr1jkx...5632.jpeg?dl=0

https://www.dropbox.com/s/7mtb36fvba...5630.jpeg?dl=0
09-18-2020, 05:32 AM
eso

4 Attachment(s)

I'm surprised no one here has any input.

Having these 801AA duplexes to study has raised more questions than they have answered.

I can certainly clone this horn and mounting in my wood horns, but I'm going to need an earlier 604 to compare to. After some web crawling it is looking like the 604 8K/Urei 801AA has a different center pole than earlier Altec 604 models. The 604 8K had the Mantaray horn which also had the tiny throat, a 7/8" cylindrical bore from the phase plug through the center pole the the horn mount. By contrast the 801B duplex using the PAS CX1580 woofer and JBL 2425H compression driver has a conical flare from 1" at the compression driver to 1 1/4" at the horn mount.

That conical flare is also shown in cut-away illustrations of earlier Altec 604 models so it is what I expected to find.
Unique to the 801AA horn is an open-cell foam plug at the horn throat–probably added to help pattern control and limit beaming from that long narrow cylindrical bore in driver.

Another item unique to this model are the small circular Helmholtz resonators in the horn sides.

All of these oddities really seem like a series of bandaids applied to compensate for some core shortcoming.
09-18-2020, 01:10 PM
rusty jefferson

Sorry, no experience with the 604 versions of the UREI monitors, I've got the C version. But it looks like the original 801 was based on the 8g, but could have been sold with 8h or 604e (all Alnico) with the added Mantaray horn. UREI apparently had networks for each. Perhaps based on what was available?

Then the 8k (ferrite) was the 801a with the foam edged horn and modified throat because of the magnet change. There's also mention of the new horn being available as a retrofit to 8g and 604e models. Perhaps one of your pictured horns is from the 8k and 1 is the retrofit horn for Alnico? I've not seen mention of an 801AA previously.

http://www.technicalaudio.com/pdf/Du...04/DUPLEX.html
09-18-2020, 01:49 PM
eso

1 Attachment(s)

Quote:

Originally Posted by rusty jefferson

... I've not seen mention of an 801AA previously.

It's slightly confusing, but the original version of the Urei duplex was based on a 604 8G driver and was called an 801A. It was used in the 811, 813 & 815 monitors.

The 811A, 813A and 815A monitors used a duplex based on the Altec 604 8K and it was called the 801AA.

The B series was more consistent in naming with the 811B, 813B and 815B all using an 801B duplex.

eso
09-18-2020, 02:07 PM
rusty jefferson

I get it. I knew the system model numbers and assumed the 801 numbers followed suit.

Since the 811 (801a) had the Mantaray horn, don't you think one of your pictured 800 horns (foam edged) is the mentioned retrofit horn for 801a?
09-18-2020, 04:53 PM
eso

1 Attachment(s)

The 801A used an Altec 604 8G and had the original blue Urei radial horn, not the Mantaray.

The mantaray horn was introduced on the 604 8K which was the platform for the 801AA, hence the tiny throat on the horn for the 801AA

eso
09-18-2020, 08:03 PM
rusty jefferson

2 Attachment(s)

Quote:

Originally Posted by eso

The 801A used an Altec 604 8G and had the original blue Urei radial horn, not the Mantaray.

The mantaray horn was introduced on the 604 8K which was the platform for the 801AA, hence the tiny throat on the horn for the 801AA

eso

Apologies for playing fast and loose with the term Mantaray. I'd not seen a pair of 811/813 (801a) with anything except the original blue UREI exponential horn (without foam lining or diffraction foam on edges) that sort of looks like the Mantaray horn. I assumed your lower imagine in post #2 was the 801aa and the upper imagine was the upgraded horn made available for the Alnico 801a drivers. I see now there were likely several iterations of horns for (I assume) the 801a I wasn't aware of. Didn't mean to derail.
Attachment 87409
Attachment 87410
10-20-2020, 12:12 PM
joyspring

Altec 604 Duplex throat size and Mantaray(tm) introduction

Quote:

Originally Posted by eso

It's been a while since I've been here, but I need help from some of the brains here.

For many years I've been playing with and building Urei 801B duplex drivers and custom horns. The parts are pretty readily available make make a great sounding system.

People keep asking me for my custom horns for the Altec based duplexes, but I hadn't made any because I didn't have an 604 to work with to make my tooling.

I just came up with a pair of 811A monitors, one of which needs a recone so it was a perfect choice to dissect and reverse engineer my horns with. After after removing the 801A horn, I find the throat is a 7/8" bore.

With the B or C series duplex–neither of which have any Altec parts–the throat at the horn is ~1 1/4".

Cross section illustrations of earlier 604 drivers also show a conical throat flare from the compression driver through the woofer center pole.

Does a Stock 604 8G have a conical throat flare?

Did Urei add a restrictor to the 604 8K throat? if so, was this also a feature in the original 604 8G based Urei 801?

This is a very curious discovery to me.

Any tech insight will be appreciated.

eso

https://www.dropbox.com/s/cl9iplicjn...0horn.jpg?dl=0

https://www.dropbox.com/s/yh9wuo77s0...5645.jpeg?dl=0

https://www.dropbox.com/s/0pkfdr1jkx...5632.jpeg?dl=0

https://www.dropbox.com/s/7mtb36fvba...5630.jpeg?dl=0

hello eso,

Long-time UREI 811 / 811A / Altec 604 user here...

The Altec 604 Duplex changed throat size from 1 inch to 7/8 inch between the Alnico and ferrite magnet models because of the need to maintain a correct expansion rate in the shorter axial length of the ferrite magnet structure. To my knowledge and measurement of both Alnico and ferrite) Altec HF drivers, both have conical throats.

The final Alnico model (and the first to feature a Mantaray constant directivity horn) is the 604-8H, used in the Altec Model 18.

Confusingly enough, the first ferrite magnet Duplex is the 604-8K, which also features the Mantaray. This is the driver used in the UREI 800 A-series.

The horn-throat adapters between the Alnico and ferrite 604s are different because of the different throat size. So far as how this affected the design of the UREI A-series horn compared to the original UREI horn, you can read how this was handled in this dB Magazine article by Dean Austin, one of the UREI Time Align project engineers:

Time-Aligned Loudspeakers Revisited, page 27:

https://worldradiohistory.com/Archiv...DB-1981-08.pdf

What's apparent from the article is that the foam diffraction buffer (foam lips) are to compensate for the shorter path in addition to providing a smoother transition from the reflective horn to air. Interestingly, the size was determined experimentally as the horn mouth is of two different materials.

What's also apparent is the role of the foam vertical walls in the A/B/C- series horns to not only accommodate the smaller throat size and attendant flare rate change but to absorb the corner reflections between the horizontal and vertical horn walls that cause transient distortion (the tone burst figures in the article are very interesting).

BTW, Dean also authored an introduction to the UREI Time Align in the same magazine a couple years earlier:

Time-Aligned Loudspeaker Systems, page 58:

https://worldradiohistory.com/Archiv...DB-1979-03.pdf

Hope that this helps,
Robert
06-03-2023, 08:21 AM
eso

1 Attachment(s)

Quote:

Originally Posted by joyspring

hello eso,

Long-time UREI 811 / 811A / Altec 604 user here...

Robert

Found it.

I had saved the those DownBeat links. That's great info.

Since i had originally posted this, I stumbled across and old 604E with one of the original aftermarket Urei horns. Finding that unit helped me to make my first pair of wood horns for the earlier 604, in this case the OEM units for Big Reds from Audio Marketing.

Most of this entire stream of development was inspired by the success of the Mastering Labs crossover which helped the 604s to keep up with JBLs efforts to gain market share in monitoring.

At some point I came across a listing for another orphan 604E so I picked it up to make a pair. I got GPA cones and Ken at Upland reworked both drivers: Cleaned up, re-mag (one was seriously de magnetized) and reconed. I picked up a pair of Angelo's 3-d printed Altec horns to complete the pair. I also just recently built a cloned pair of Mastering Labs crossovers for them. They do sound very nice, a big improvement over a stock Altec network.

What I'd really like to find now is a schematic for the Urei 824 and/or 834 networks which were the aftermarket 16Ω networks for 604E.

Anyway, what would be needed to extract your original Urei horn from you?

eso
06-03-2023, 09:40 PM
joyspring

Quote:

Originally Posted by eso

Found it.

I had saved the those DownBeat links. That's great info.

Since i had originally posted this, I stumbled across and old 604E with one of the original aftermarket Urei horns. Finding that unit helped me to make my first pair of wood horns for the earlier 604, in this case the OEM units for Big Reds from Audio Marketing.

Most of this entire stream of development was inspired by the success of the Mastering Labs crossover which helped the 604s to keep up with JBLs efforts to gain market share in monitoring.

At some point I came across a listing for another orphan 604E so I picked it up to make a pair. I got GPA cones and Ken at Upland reworked both drivers: Cleaned up, re-mag (one was seriously de magnetized) and reconed. I picked up a pair of Angelo's 3-d printed Altec horns to complete the pair. I also just recently built a cloned pair of Mastering Labs crossovers for them. They do sound very nice, a big improvement over a stock Altec network.

What I'd really like to find now is a schematic for the Urei 824 and/or 834 networks which were the aftermarket 16Ω networks for 604E.

Anyway, what would be needed to extract your original Urei horn from you?

eso

hi eso,

Glad that you found this post and that you downloaded the linked DB magazine articles. They clear up a lot of BS that's all too common in vintage audio forums. Fwiw, Dean Austin became project lead for the UREI 809 and entire monitor range after the JBL acquisition.

And very nice networks! The Mastering Lab network was a huge improvement over the OEM Altec and kept the 604Es relevant through the 1970s. Sunset Sound Factory kept theirs into the 1990s as I recall.

Sherwood Sax solved the main problem of the 6 dB midrange rise though I question the value of some of the audio `tweak' affections, particularly the Litz wire inductors. As an aside, then Altec professional audio head John Eargle was interested in acquiring / licensing the ML network but Altec management felt that their network was perfectly adequate. This is the attitude which made Altec irrelevant in short order and it's also interesting that Eargle, Englebretson and other key Altec folk eventually ended up at JBL. The Sax bros. licensed the ML network to Audiotechniques in CT.

I've obtained the original, A-, B- and C-series schematics from Harmon/JBL in the 1980s and I've seen them online as well; however, I never did see a 824/834 schematic. A friend had the 604E + 824 retrofits in his studio but sold his equipment years ago. I'm certain that examples or even schematics for the 16 ohm TA network are like hen's teeth.

So far as my spare horn, I dispatched my contact info in my initial reply so feel free to contact me. If you require that I resend, please let me know.

thank you and hope to talk soon,

Robert
06-03-2023, 11:34 PM
eso

Quote:

Originally Posted by joyspring

... I dispatched my contact info in my initial reply so feel free to contact me. If you require that I resend, please let me know.

thank you and hope to talk soon,

Robert

Can you PM contact to me? Or just email me at:

[email protected]

Thanks!

eso