1970s Studio Monitor

[gwho]

I've been wanting to investigate hi efficiency speakers when I ran across a pair of these speakers (see pictures) being sold in los angeles area which I purchased. They were owned by a studio sound tech that purchased them from a studio in LA in the late 1980s where he worked. He said these replaced a pair of JBL 43XX speakers (in the late 1970s). Apparently they wanted more midrange impact so they had this three way built vs the JBL (which he said was a two way). Eventually these were replaced in the studio which is when he acquired them. He had the speakers rebuilt by orange county speaker in the late 1990s and they have been in storage most of the time since (which is why he was getting rid of them).

I do like the sound but have a few questions. Both speakers are built identically as shown so they are not symmetric. The compression driver is a renkus-heinz SSD-1800, the midrange is a 10" gauss 3184b, and the woofer is a 15" gauss 4583a. The exterior dimensions of the box are 32" x 25" x 18". He said the horn was oriented vertically to control dispersion. Would anyone know what kind of horn this is and what the dispersion characteristics are? The horn is about 7" in the vertical dimension and the discs appear to be solid metal. Similarly, the midrange (gauss 3184b) is in a small sealed box. The dimensions of the box are 10" x 10" x 6". I'd like to find the parameters for this speaker but can't find any data sheets. I believe he said the speaker should be above 95db efficiency.

Right now these are my garage speakers but I would like to improve them if I can. They have no crossover but came with cables and jacks for connecting each speaker to an amplifier. I would appreciate anyone with a knowledge of the horn characteristics or specs on the 3184b. Also, any comments on the speakers for listening to music or any simple design changes that might improve them.

Best Regards and Happy Holidays!
gwho

[Mr. Widget]

I don't have any specific info not these speakers and ideally you'll find more info on them, but I can give you some basic info. You should get a stereo three way active crossover like an Ashly XR-2001 or a Urei or Rane... or a more contemporary DSP based design. You will also need three stereo amps. I would try 200Hz and 1,000Hz as initial frequencies.

To get the most from these speakers you will need to do a lot of experimenting with frequencies, levels, and associated equipment.

Regarding the vertical horn, EV and others have made diffraction horns that were designed to operate vertically. I assume that is also the case here.


Widget

[gwho]

Mr Widget

Thank you, your comments are very helpful to me. I have been using an Ashly xr4001 coupled to a 7 channel receiver to power the speakers (just to mess around with them). The person I bought the speakers from also threw in a couple of old AB International amplifiers but they are big heavy amps and I haven't had a chance to try them yet. I was crossing at 500hz and 2k so I will have to play around with crossover points a bit. I did not know what the specs were on the horn (60 degree? 90 degree? in the vertical configuration). I believe he told me the horn is also Gauss but I could not find any label on it. Because of the small size of the horn (7 inches) I assumed that it was crossed over at a higher frequency. Also, I was assuming that the 10" woofer in such a small sealed box (10x10x6) would not go to low.

Best Regards
gwho

[grumpy]

That horn does look very familiar, but I couldn't find it either. I'd probably keep HF at 1.5K+ ... 200-500Hz on the mid?
it's only an octave (ish). If you don't listen quite loudly, the lower freq range should be ok and might clean up male vocals
if that's an issue.

[Mr. Widget]

I have no idea what is a safe low frequency crossover point for that tweeter, but running the 10" to 1.5K or 2K probably isn't ideal.

Old AB amps if working properly will sound a hell of a lot better than an AVR. Give them a shot.


Widget

[grumpy]

"running the 10" to 1.5K or 2K probably isn't ideal."

Lol. agreed, but that's a pretty small horn so I'll admit I had driver safety in mind ahead of performance. As more is known about the drivers perhaps the performance envelope could be pushed a bit further

[gwho]

Thanks for the replies. Grumpy you were spot on, the one comment I have on the sound quality with the current crossover at 500hz and 2khz is that I do not like how the vocals sound. I do have a data sheet on the ssd-1800 compression driver. It says that the lower limit of the CD is 500hz. I will try out the AB International amps. He said they worked but they look like they been through a war or two. It appears that there could be a disconnect in the design. Hopefully, I can get parameters for the midrange to determine the range of operation for the small sealed box. What happens to a horn if you try to go lower than the capabilities of the horn? Will it sound a certain way? Clearly the ssd-1800 can go lower. I will try 1k/1.5k and 100/200hz and see how it sounds.

Regards,
gwho

[grumpy]

What happens to a horn if you try to go lower than the capabilities of the horn? Will it sound a certain way? Clearly the ssd-1800 can go lower...

You could destroy the diaphragm.
It could sound nasally or megaphone-ish.

A 500 Hz capable horn is quite large, so it's not
the driver that is the limiting factor here.
You might be able to push the HF crossover
lower (perhaps <1KHz), but you would want the
filter slope to be steep (18-24dB/Oct) to keep the
diaphragm from over-excursion
(easy to do as frequencies drop and the horn acts
less like a horn and more like a hole)

[Mr. Widget]

If you like the top end you might decide to go 4-way and add a Westlake or JBL 2397 mid horn crossed at 1.0-1.2KHz and 8KHz or so up top. If the rest of the bits are outstanding, that could really make it.

Definitly take it easy on the power levels until you really know what you have.


Widget

[mech986]

Some thoughts:

The horn looks a bit like a metal version of the Westlake midrange horn but on its side and missing some of the internal vanes. I'd be intrigued to see what it sounds like on its side. Didn't EV also make a few horns like this?

The woofer probably won't operate deep, say below 40hz, due to its construction and the port size. Wonder what it might sound like with the port stuffed or closed since efficiency really isn't necessary and you can easily dial down the mid and HF tweeter.

I'd personally like to stuff the midrange box if it isn't already, plus line the midrange relief area with non-diffraction foam. Apparently used by Westlake in some of their monitors:

Some info from AB Systems, including a write up by none other than our late dear friend Ken Pachowsky and his Westlakes:
http://www.abamps.com/rooms.html
http://www.diyaudio.com/forums/multi...-westlake.html

Looks like you could go as low as 250-500 hz with the midrange.

Eventually, I'd get them up on their sides and place up about 18 inches or so to get the tweeter up, and the whole box off the floor for imaging (such as they have) purposes. If we assume not much low bass, don't worry about the loss of floor reflection/boundary reinforcement, work on getting midbass and crossover transitions right, and better or seamless driver transition.

I'd agree with a 12 or 18db tweeter crossover slope to prevent damage and wouldn't run them below 2K for the moment, maybe start at 3k and see what that gets you.

Horn driver specs:
ftp://ftp.renkus-heinz.com/Legacy_Pr...D1800_data.pdf

Some info on the Gauss woofer:
http://www.audioheritage.org/vbullet...-manuals-pdf-s

[grumpy]

another blast from the past (compares 3148 to 2123):

http://www.audioheritage.org/vbullet...d-with-75-fill

[gwho]

Mech986 and Mr Widget thanks for the input. I've added a couple pictures of the horn in the hope that someone can identify them. It seems that I have two unknowns (horn and midrange speaker). From a design perspective would someone put a midrange (10") to cover a narrow frequency band of around 250/500hz and 1/1.5Khz? I would assume that today it would be a 5" or 4" midrange or large horn. I realize that these speakers are quite old and designed in an era without simulation as is done today.

If I can't get these to sound right a four way might be of interest. Today, what would be a typical frequency of operation of a 10" midrange? Would it be more like 100hz to 1khz?

Mech986 - What is the midrange relief area? Where can you get non-diffraction foam? There is no stuffing in the box so this is something I can easily do. The box port is merely the square hole cut in the box. What would I expect to gain by sealing the port and adding stuffing to the large box. Wouldn't this decrease the frequency response? It is not what I would typically think of as a port (tube with predetermined volume). Thanks for the specs on my other drivers.

Regards
gwho

[Mr. Widget]

If I can't get these to sound right a four way might be of interest. Today, what would be a typical frequency of operation of a 10" midrange? Would it be more like 100hz to 1khz?

Mech986 - What is the midrange relief area? Where can you get non-diffraction foam? There is no stuffing in the box so this is something I can easily do. The box port is merely the square hole cut in the box. What would I expect to gain by sealing the port and adding stuffing to the large box. Wouldn't this decrease the frequency response? It is not what I would typically think of as a port (tube with predetermined volume). Thanks for the specs on my other drivers.

In the JBL 4343 the 10" driver runs between 300Hz and 1250Hz. In the 4345 the 10" driver runs between 290Hz and 1.3KHz. In the JBL 4250 the 12" mid bass driver runs between 250Hz and 1.1KHz.

Assuming the designer of the system knew what they were doing that simple rectangle is a tuned port and you should keep it... then again they may not have had a clue. It is impossible to tell. You would need to take your own measurements and verify the TS parameters, box tuning etc. All quite accessible with todays tools.

I would get some Wrap-on fiber glass and line the walls of the cabinet if there is nothing in there.


Widget

[gwho]

Thank you Grumpy and Mr Widget. The 3184B information will be very useful. Now the only unknown is the horn. Although the box size for the 3184B in my speaker is smaller than 1 cu/ft simulations it gives me an indication of the frequency response will be. The upper limit of the 3184B is probably around 1K-1.5k as you both have mentioned. Perhaps the best mod would be to get a bigger horn such as a 800hz or 1Khz horn and change out the horn that is currently in the speaker. I would then know that I am covered in the critical band.

Regards,
gwho

[Earl K]

Here's a tiny bit of info ;



harvested from Google .