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penguin
04-02-2005, 07:38 PM
Hey all,
I have had some 70s JBL and older Altec stuff in my basement for a while and have decided to make some use of at least some of it. I would like to make a pair of studio monitors in the vein of the 4333. The items that I have are live reinforcement gear (E130 guitar speakers, E140 bass instrument speakers, 2461 small format compression driver, Altec 811 horns, Altc 808-8A drivers). I want to use some of what I have. While I don't think the 2461s are as refined as the 2420s that are used in the 4333 I am sticking with them and the plastic horns
:barf:
that I have for the time being. I also went ahead and ordered a pair of 2405 tweeters on ebay a couple of days ago. So those things are givens for now.

The unresolved issues are the crossover design and the bass drivers.
Bass drivers:
On paper the 2231a seems to be a good woofer for this job. It gives a low 30s F3 with the box design and was the driver in the 4333 originally. I have seen postings that say that it was improved upon considerably by (?) the 2235 (I think). I think Iíll need a driver that can cover the mid bass up to 800hz (possibly higher) as I am using a compression driver for mids.

Crossover design:
I think that crossover points of 800hz and 8000hz would be about right. I have some design software that gave me a design for a Linkwictz Riley 4th order crossover. It requires so many capacitors and inductors that I think the board would be a foot square. I bid on a pair of the original 3331a crossovers on ebay but they got away (went for about $425.00). Does anyone have a schematic for that crossover and/or for an appropriate crossover for my design.


Any ideas? Also I have had a hard time finding a source for a pair of suitable bass drivers. Any ideas there? I am new to building crossovers but I am probably going to be giving it a try. Any pointers, pitfalls to avoid???

Thanks
Penguin

Zilch
04-02-2005, 08:36 PM
http://www.jblproservice.com/navigation/Network%20Schematics.html

speakerdave
04-02-2005, 09:02 PM
Hello, Penguin. Welcome to the forum and good luck with your project.

I have some questions about your plans and possibly some suggestions.

Why have you settled on the 4333? I am listening to a factory pair of the 4333A now. I can give you measurements and information about details if you are thinking of making a replica.

But if I were building from scratch a speaker in this vein I would think it well worth the extra few hundred dollars to add a pair of 2122 bass/mid drivers and make the 4344 instead. You will find in this forum (using the search function) detailed account of building its larger brother, the 4345. Actually, since you are talking about buying the woofers you might consider that speaker.

David

penguin
04-02-2005, 09:13 PM
Thanks for pointing me to the network schematics. :)

I have assumed up to this point that the 4220 and the 4205 drivers in the 4333 monitor were both "16 ohms." The 4220 seems to only come as a 16 ohm version.
:blah:
The JBL literature that I have for the 4333 doesn't seem to specify whether the 2405 is 16 ohm.

:blah:
I am also assuming that the LF 2231 is 8 ohms so that the crossover is designed for 8 ohm bass load and 16 ohm mid and high freq. drivers.
:blah:
Is that right?

Thanks much,:)
Penguin

speakerdave
04-02-2005, 09:25 PM
I believe Giskard has posted many times that the 2405 16 ohm and 8 ohm diaphragms are actually identical and that the factory crossovers using this driver are designed around a 10 ohm impedance. We are talking here of the days of Ohmflex impedance specifications.

Yeah, I think the woofers are 8 ohms.

David

penguin
04-02-2005, 09:38 PM
SpeakerDave,
I can see that there are several significant compromises (perhaps hideous compromises to the purists) in the design that I have scratched out. Nevertheless I am committed to certain components and limits of design due to cost and marriage/political considerations.

I see in so many posts the emphasis on the mid bass being covered by a 8" or 10 cone driver. I expect this adds beautifully to the detail and definition of a muted telecaster in Danny Gatton album or the rim shot on a late Bob Marley recording. :bouncy: I have to resist the temptation to expand the project which I'm sure I could get quite carried away with. (I got into homebrewing beer about 10 years ago. A whole shelf in my den is homebrewing books, I brewed about 40 5-gallon batches in 2 1/2 years, and I put on about 40 pounds:blink: )

For now, I'll stick to the three way system. (Maybe by summer I'll have lost control and I'll look at the 4345)

Thanks
Penguin

yggdrasil
04-03-2005, 05:40 AM
Which midranges are you going to use? The 2461 or the 808?

The 2461 have phenolic dia's and will probably not be usable with the 2405 due to lack of detail over 3-4K.

If you have a pair of large horns for the 2461's you could try crossing them in at 500Hz and cross in the 808's at 2K.

I haven't actually tried using the e-series in a monitor, but... Why not try the E-140's?

Tom Loizeaux
04-03-2005, 08:06 AM
A few responses to some of your questions.
I have a few K140s in cabinets that I've A/Bd with 2231s in my 4333 and 4343 monitors. The 2231s have a much deeper and smoother low end.
I've also used some Altec 802 drivers (on Altec 811 horns) with dual K140 bass cabinets, crossing over around 1.2K (because the K140s go a little higher than most 15" woofers), and feel that though they sounded pretty nice playing back recorded music in a PA situation, they don't measure up to a complete system that has been carefully designed for "flat" playback. I suspect you wouln't be satisifed for very long.
You see, that's the heart of the question. Are you willing to build the cabinets, build the 3-way crossovers, buy the needed componants, all based on using your existing musical instrument stuff, hoping that you don't find it not hi-fi enough? If you did, you would then face starting over. At that point it would have been better to buy, or build a system with the componants designed for your application.
I have added 2-10 (JBL 2123H) mid boxes and a JBL 2426H with fiberglass horn to each side of my small PA to bring it up to a reasonable venue quality, and now I'm about to add some 18" subwoofers! I've found you can't cut corners and hope it will be OK when your tastes are really requiring more then "OK".

Best of luck...and keep us posted.

Tom

penguin
04-03-2005, 08:24 AM
yggdrasil,

The plan was to use the 2461 for the mids from about 800 to 8000. Your idea to put the Altec 808-8A in for the upper midrange never crossed my mind. When you say that the 2461 lacks detail in the range above 3-4k my ear had not recognized that yet. The 808s seem to lack detail in the lower half of 800hz up when compared to the 2461 but using the best of each of them in a four way system . . . . hmmmmm.

As to the E140s they are really punchy and if I use the graphic eq to add something below 100hz they are decent. On the other hand I want to make a nice semi-furniture type of box, so I don't want to design for one bass driver and then realize that I would rather have a different one later after the varnish was drying.:banghead:
The flip side of that is part of the logic for sticking with the 2461s. I would only have to redo the baffle to upgrade to a different horn [and louver diffusion things] and put in the 2420.

Thanks for the ideas.:)
Penguin

Zilch
04-03-2005, 11:11 AM
Sell what you have and use the proceeds to get the right stuff.

You're just makin' a sonic mess there....

John
04-03-2005, 12:45 PM
Top the 2461 with a 2405 and you should be fine. You might even prefer the 2461 to the 2420. Some people have said the 2461 sounds warmer in that configuration.:bouncy:

penguin
04-03-2005, 05:27 PM
John,
thanks for the hopeful note on the 2461s. I have always found them to sound pretty good in the slant monitors that they are in, albiet with quite a bit of graphic EQ help.

(Zilch, Thanks again for pointing out the link for the network schematics.)

I have been going over the schematic for the 3133 network used in the 4333 monitors. It all seems pretty straight forward. However, there were a few questions.

a) In the band pass section there is an inductor that is tapped in the middle. The three leads are labeled Rd, Grn, and Blk, so if I can buy an inductor that is tapped and has the leads color coded I be in great shape. However, looking in the PartsExpress catalog I don't see anything like that. Should I be able to find something like that? Can I tap it myself?

b) The values for the inductors are taken to the 100th of a micro farrad in some cases. In many cases there are not equivalent value inductors in the PartsX catalog. How much tolerance is there for these values and/or where can I find inductors with these values?

c) I see that coils are often mounted on the board so as to prevent them coupling and interfering with one another. What are the rules of thumb there?

d) Finally, the adjustable L-pads are labeled 1,2,3, and blk, wht, red on the schematic. I want to use an attenuator out of a trashed VOTT network for the mids and buy one for the highs. I am assuming that 1=gnd and that 2 and three should be interchangable. ?? Is that right?

Thanks to anyone willing to wade through all my questions,:blah:
Penguin