Altec 604-8h frequency response

[totaltech]

G'day All! Has anyone measured the Altec 604-8h drivers frequency response before? Attached it a measurement taken 1/3 octave smoothed and 10db per division - taken 1 meter on axis, notice the 3khz dip. These are used with the original Altec 604-8h crossovers. I initially thought the compression driver may have been wired out of phase but this is not the case. I have tried all different crossover adjustment and this is the flattest I could get. I have also tried a different mic /measurement system with the same results! Any ideas guys? Both speakers measure the same. Thanks in advance.

[grumpy]

Not crazy different:

http://www.audioheritage.org/vbullet...GPA-604-8H-III

[Ruediger]

With c = 344 m/sec at 3 kHz the wavelength is about 11 cm. If a part of the sound travels 5.5 cm more from speaker to microphone it would add out of phase to the direct sound, leading to cancellation.

Put a quilt, pillows, pullovers and jackets on the floor between speaker and mic and see what happens.

Ruediger

[Horn Fanatic]

With c = 344 m/sec at 3 kHz the wavelength is about 11 cm. If a part of the sound travels 5.5 cm more from speaker to microphone it would add out of phase to the direct sound, leading to cancellation.

Put a quilt, pillows, pullovers and jackets on the floor between speaker and mic and see what happens.

Ruediger

All of the 604 series have phase issues due to the mechanical design of the speaker. Having the voice coils on two different plains is the problem. Bill Hanuschack designed the "Engine" while working for Telex. It was a sound reinforcement driver consisting of an E-V 15" woofer with a 288 driver. That speaker had only one magnet structure leaving the voice coils on the same plane within a fraction of an inch of each other. The down side of that speaker is that the cone IMO, is not suitable for HiFi. Bill also designed the single magnet structure 212-8A 12" CoAx using the 288, which also has a Charles Hughes designed circular horn attached. Even though the driver was designed for commercial installs, it serves quite well for HiFi.

The only way to properly address the phasing problem with a 604 is by electronic time alignment. Ed Long and Ron Wickersham figured that out 40 years ago.

Also, the Mantaray horn on the H & K series has it's own phasing issues, that by it's very design cannot be corrected. Mark Ureda and Cliff Henricksen were well aware of the phasing problem by sighting that the two sets of bends in the middle of the horn are on two different plains, which renders them anything but phase coherent. IMO, using the Mantaray horn for consumer application was a colossal mistake. The horn Bill designed for his 604-8H III is the best thing that ever happend to the 604 save for the T-Plug. I believe the 604 has reached the pinnacle of it's design, unless Bill decides to build a 604 Engine.

H.F.

[totaltech]

Thanks for your response guys! Can the H Series be retrofitted with GPA's series 3 horn? On the reflection issue I will try the blanket idea, this may make sence since I have floorboards but with a rug in the listening area.... I will post results tomorrow!

[andywin]

I' not seen any 604 plots before. It's interesting to compare with my K10A's which date from the mid 50's and use a Jensen / WE 18" cone and 2 cell forn for the CD.

http://www.audioheritage.org/vbullet...highlight=k10A

The K10A's have a small peak at 1.7kHz where the crossover region is. What's the crossover point on the Altecs?

[Horn Fanatic]

Thanks for your response guys! Can the H Series be retrofitted with GPA's series 3 horn? On the reflection issue I will try the blanket idea, this may make sence since I have floorboards but with a rug in the listening area.... I will post results tomorrow!

The screw mounting pattern on the 604 has not changed since it's release date. The UREI horn is a testament to that. The screw pattern on the UREI is a dead match to the multi-cell, egg crate, and Mantaray horns, and as with the series III horn. I recommend that you contact Bill Hanuschak at GPA for the procedure. It may require a re-cone, as the outer spider is bonded the the horn and cone. By changing the horn you would have an ALNICO 604-8H III. Actually, Bill is making that model, and they are quite pretty. A white basket with green Hammertone pot structures.

H.F.

[Altec Best]

All of the 604 series have phase issues due to the mechanical design of the speaker. Having the voice coils on two different plains is the problem. Bill Hanuschack designed the "Engine" while working for Telex. It was a sound reinforcement driver consisting of an E-V 15" woofer with a 288 driver. That speaker had only one magnet structure leaving the voice coils on the same plane within a fraction of an inch of each other. The down side of that speaker is that the cone IMO, is not suitable for HiFi. Bill also designed the single magnet structure 212-8A 12" CoAx using the 288, which also has a Charles Hughes designed circular horn attached. Even though the driver was designed for commercial installs, it serves quite well for HiFi.

The only way to properly address the phasing problem with a 604 is by electronic time alignment. Ed Long and Ron Wickersham figured that out 40 years ago.

Also, the Mantaray horn on the H & K series has it's own phasing issues, that by it's very design cannot be corrected. Mark Ureda and Cliff Henricksen were well aware of the phasing problem by sighting that the two sets of bends in the middle of the horn are on two different plains, which renders them anything but phase coherent. IMO, using the Mantaray horn for consumer application was a colossal mistake. The horn Bill designed for his 604-8H III is the best thing that ever happend to the 604 save for the T-Plug. I believe the 604 has reached the pinnacle of it's design, unless Bill decides to build a 604 Engine.

H.F.

I don't know but my 604-8G's sounded real nice.. They had original 23744 lite diaphragms in them with very little use and came in 612C cabs..

[Horn Fanatic]

The screw mounting pattern on the 604 has not changed since it's release date. The UREI horn is a testament to that. The screw pattern on the UREI is a dead match to the multi-cell, egg crate, and Mantaray horns, and as with the series III horn. I recommend that you contact Bill Hanuschak at GPA for the procedure. It may require a re-cone, as the outer spider is bonded the the horn and cone. By changing the horn you would have an ALNICO 604-8H III. Actually, Bill is making that model, and they are quite pretty. A white basket with green Hammertone pot structures.

H.F.

Update -

I had a conversation with Bill Hanuschak today about converting the 604-8H using the Series III horn. He told me there may be an interface issue regarding the throat diameter of the new horn, and the plastic tube that was used on the ALNICO 604's. He didn't say it couldn't be done, only that he would have to look into it.

H.F.

[Horn Fanatic]

I don't know but my 604-8G's sounded real nice.. They had original 23744 lite diaphragms in them with very little use and came in 612C cabs..

Oh, don't get me wrong, I'm not suggesting the 8G does not sound good, but IMHO Bills new horn sounds awesome. There are times I'm fooled into hearing what I describe as high frequency emanating from a ring radiator. The frequency range of Bill's new horn extends past what the egg crate horn provides. Personally, my favorite of the vintage series is the 604C. I believe the cone sounds much better than the E cone.

H.F.

[voice of theatr]

IMO, using the Mantaray horn for consumer application was a colossal mistake. The horn Bill designed for his 604-8H III is the best thing that ever happend to the 604 save for the T-Plug. I believe the 604 has reached the pinnacle of it's design, unless Bill decides to build a 604 Engine.

H.F.

I am not surprised that Bill's 604 8H III is your favorite of the 604's--I'm a huge fan of his products and parts and service. He's done a phenomenal job at Great Plains Audio not only carrying the (vintage) Altec Lansing torch with his drivers and parts for vintage Altec drivers, but also building on the legacy and pushing the technology forward. However, I would have to disagree about your (sweeping) generalization about using the Mantaray horn for consumer applications. I own a mint pair of vintage Altec Model 14's which feature a Mantaray horn (with 902 h.f. drivers/tangerine phase plugs) and they are some of the best sounding audiophile-home hi-fi speakers that I've ever heard (they rival my Model 19's)!
http://www.lansingheritage.org/html/...s/model-14.htm