1970s Studio Monitor

[grumpy]

Nice detective work

1982-1985 "... It's crossover system dictates unconventional crossover points to obtain smoother and more transparent response. The system requires biamplification." 400w and 200w for LF and HF suggested.

I still have no clue on what the intended crossover points are.

[mech986]

Some additional stuff:

http://194.242.232.16/rubriche/Hobbi...0#.VnSsRtKDFHw

Italian so have google translate.

SPEAKER Gauss Monitor System Model 1984 3-way 7351 years are bi-amped 400 watts 200 watts Low High Sensitivity 93 dB, complete with original paintings and 6500

[mech986]

I would suggest not altering the speaker at present with any kind of new horn but rather work on understanding the way the speaker was designed, and attempt to get it running with the crossover suggestions, measurement, and listening. The picture of it is now much clearer on how it should be oriented, horn on bottom, as typical of some wall-soffit mounted monitors of the day.

I think experimentation with the crossover points and slopes will be key.

The Midrange relief I mentioned is the indentation into the baffle that the midrange is mounted in. Thin felt or 1/4" open cell foam strip deep enough to fit could be used to line the edges of the relief to avoid some diffraction effects of the baffle edges, same could go for the cabinet edges as well.

[mech986]

Interestingly, your speaker is a mirror image to the one pictured a couple of posts above, and is missing the controls, presumably because it is tri-ampable, instead of bi-ampable, so volume is handled by the amps instead. Also, the port is moved further edge-wise instead of being aside the mid and woofer. I'd say these are probably the real mccoy later variant Gauss monitors. Driver complement and horns look identical.

[mech986]

http://thehistoryofrecording.com/Mag...DB-1982-08.pdf

Page 48 of db magazine, August 1982

Product announcement:

"Cetec Gauss has recently introduced a line of studio (control room) monitors to compliment its line of studio monitors. The Model 7351 monitor system offers superior discrete sourcing and higher audio output. The components of the 7351 are blended by using the concept of acoustic crossover, which dictates unconventional crossover points (160 hz to 1400 hz) in order to attain a smooth and transient response. The 7351 delivers a full 35 hz to 18 khz power response and uses a 2080 compression driver on a constant directivity horn with power compensation built into the crossover network."

I typed this out verbatim, including the awkward grammar. There's a couple of pics showing with and without grille. Obviously, this is the one with a crossover built in for the mid and HF.

[grumpy]

"Cool beans"

[gwho]

Wow. Thank you so much for all that information. I did a lot of searching but did not come up with anything. You guys are amazing. That definitely looks similar to what I have. The sound tech I purchased the speakers from said that it was hooked to an active gauss crossover but that he did not get it. Clearly they made a passive crossover version. It appears to have the same drivers and the same horn. One question I have is that they are not symmetrical in design (both are built the same) so when configuring them as shown in the picture, one speaker would have the horn towards the center and the other would have the horn placed on the outside of the speaker. Was this common back in the day.

Best Regards,
gwho

[gwho]

I see that the stereo set up with the 7531 has symmetrical (mirror imaged speakers). Also, thank you for the print out having the crossover frequencies of the 7531 (160hz and 1400hz). Now I've got some targets. Thank you one and all.

gwho

[DavidF]

http://thehistoryofrecording.com/Mag...DB-1982-08.pdf

Page 48 of db magazine, August 1982

Product announcement:

"Cetec Gauss has recently introduced a line of studio (control room) monitors to compliment its line of studio monitors. The Model 7351 monitor system offers superior discrete sourcing and higher audio output. The components of the 7351 are blended by using the concept of acoustic crossover, which dictates unconventional crossover points (160 hz to 1400 hz) in order to attain a smooth and transient response. The 7351 delivers a full 35 hz to 18 khz power response and uses a 2080 compression driver on a constant directivity horn with power compensation built into the crossover network."

I typed this out verbatim, including the awkward grammar. There's a couple of pics showing with and without grille. Obviously, this is the one with a crossover built in for the mid and HF.

Audio detective work at its best, Bart.

The reference to "acoustic crossover" and "unconventional crossover points" suggests to me that the design relied upon the natural roll off/roll on response curves to effect the crossover. Perhaps with some amount of protection allowed for the tweeter horn and some filtering to bring down the lower response of the tweet horn ala the JBL 4430.

The system would be bi amped at the woofer/mid juncture. The outboard crossover would roll off the woofer response around 160 Hz. The natural woofer roll on due to the small sealed enclosure would effect the other side of the transfer. The high end roll off of the mid would be around 1.6k Hz to match up with the point the tweet horn unloads. Although the mid may require some form of circuit to hasten the roll off at the high end. Could be a parallel L-C-R filter rather than an inductor in series. The tweet horn is small suggesting a higher frequency for a natural roll off. Maybe a 2 or 3 uF cap in series to smooth out the response. Then some filtering to deal with driver sensitivity differences, if any, between the mid and tweet.

[gwho]

DavidF

Thank you for the advise and your thoughts on the design. I did not know what they meant by the unconventional crossover but your scenario seems likely. My speakers do not have any crossover and I will be tri-amping them with better power amplifiers, an electronic crossover, and eq in the future to test them out. I will use the 160hz and 1.4K crossover frequencies and see how it sounds. Although I don't have time right at this moment I'm sure it will sound substantially improved when I orient the speakers correctly (per the photos with the horn on the bottom) and crossover adjusted correctly. Once again. Thank you. There is no way I would have figured this out without all your help. I'm glad that everything the retired studio tech told me seems to be true (because I did not have a clue).

I was looking for a hi efficiency speaker but at 93db they might not be as hi efficiency as I thought.

Regards,
gwho

[Tim Rinkerman]

"I was looking for a hi efficiency speaker but at 93db they might not be as hi efficiency as I thought." As I remember them, Gauss speakers usually had 2 spiders and would soak up huge amounts of power because the cones were so hard to move. But, on the other edge of the sword, many people liked them because they were so hard to blow up, the sound being secondary in importance.