Seeburg Jukebox Speakers

[Steve Ty]

I?m in the process of refurbishing a pair of old Seeburg Jukebox speakers. I?m replacing the original 811 horn with a 511 (w/902); and replacing the old Utah woofers with a pair of JBL 2226J?s.

Two questions for you audio gurus:

1) When Seeburg made the framing cutouts for the 15? woofers, they left a vertical strip about 1? wide & 1? thick that runs vertically down the middle of each opening. In addition to that strip, they also have a screen material (similar to window screen); a grill cloth; and a metal grill. Seems like a lot of garbage in front of the woofers. Is that okay, or does it screw up the sound? I suppose these were barroom speakers -- so maybe they sacrificed sound quality so they could stand up to the flying beer bottles. It would be easy to remove all that stuff and replace it with an acoustically transparent grill cloth -- is that the answer?

2) Since I?m changing from 811?s to 511?s, I?ll be crossing at 500hz instead of 800hz -- so I?m wondering about modifying the ducts. The existing ducts (two) are 3? x 11? and the cabinets have just over 8 cubic feet of volume -- not counting the stuff in the box. I?d prefer to maintain the 3? diameter, but could easily modify the length -- what?s the ?book? answer for these things?

I?m one of those guys that knows just enough to be dangerous -- appreciate the help -- Thanks.

[joyspring]

Hi Steve,

1. Removing all the stuff in front of the LF driver save a layer of acoustically transparent grill cloth is a good idea. However, the 1" strips are probably alright, particularly if you're crossing over fairly low ( &lt 1kHz).

2. If you're just getting started, I recommend obtaining two books: Vance Dickason's Loudspeaker Design Cookbook and Robert Bullock's Bullock on Boxes. Both are excellent primers on Thiele-Small-derived loudspeaker enclosure design. If you're more ambitious, Richard Small's 1972/3 JAES papers essentially codify his work and that of his predecessors.

However, understanding the concepts in the Dickason and Bullock books will put you far ahead of most on typical audio forums ;-)

Since you already have an existing enclosure, you'll have to use the 2226J's T-S parameters working `backwards' to find the enclosure and port tunings.

Alternately you may use an enclosure design program; LEAP is still the (expensive) industry standard but there are many others for Windows/Mac. I'm afraid I can't help with titles since not at all familiar with Windows/Mac software (I'm on UNIX).

The numbers will get you very close but you will need to measure impedance peaks and conduct listening evaluations to find the desired port tuning.

And use a telescopic duct while experimenting - it'll save you lots of time.

BobR

[Steve Ty]

Bob,

Thanks for the information. It really surprises me how Seeburg built these things. In addition to the wood strip and the metal grill, they also used an adhesive to stick the grill cloth to the screen. The adhesive is smeared all over the screen and blocks about half of it. I?m obviously not an audio wizard, but I?m amazed that these things sounded as good as they did -- maybe it?s not a big deal for the low freqs. I just ordered some grill cloth from Parts Express -- think I?ll remove all that stuff and just use the new grill cloth.

I?ll check out the books you recommended. I have an old book on loudspeakers and enclosures, written by an Abraham Cohen; but after reading a few chapters, I always start feeling like a pig looking at a wrist watch. I guess I?m less interested in learning the how?s and why?s -- and more interested in getting good results.

I built a similar pair of speakers a while back -- copying the JBL 4648 design and then placing those cabinets inside another furniture grade cabinet that also houses a 511 horn (w/909). I?m bi-amping that set-up with a pair of Crown amps and an active crossover -- the sound is magnificent, but these things are about the size of my SubZero. I wanted to build another smaller pair for my rear channel -- which is what these Seeburgs are for. Interestingly, the interior volume of both boxes is the same (8 cu ft) -- although the horn will be inside the Seeburg enclosure, but is not inside the JBL 4648 enclosure. I?ve never been too sure how much to subtract for stuff in the box -- horn/woofers/padding. I suppose its all something of a guess, unless you get a bunch of high tech equipment reading the output. I?m going to cross the Seeburgs at 500hz with a nice old pair of Altec N501-8A?s. I ported the JBL 4648?s for 40hz, but don?t think there?s any way I?ll get that low using the 3? ducts in the Seeburgs -- guess I?ll accept what I get with the existing ducts (two 3? x 11?) -- and see how it sounds. Considering that these will be rear channel speakers, and that I?m half deaf from flying jets for 36 years -- I hope it will be okay. If not, I may have to shoe-horn a larger duct into the enclosure.

Thanks, Steve

[dan fish]

steve I have the T/S parameters for those JBLs U will be using in the seeburg cabs,,If U like I can run them in the speaker design program and give U the port dimentions... I am bettting the ports are not big enough for the JBLs.. I think a guy could pull the old port tubes out, block the old holes and then port them out the back

[dlp4341]

Steve :
1) Yes .
2) Try making port tubes of different lengths.This would allow you to check the low end performance with say : 0.75" (no tube) , 3" , 6" , 9" , ... tubes. To make tubes use a card board box cut and flattened ( a 24 can Coke box is fine ), then roll it up with a 1" overlap. Hold the tube together with masking tape .
to tune your box you will need to measure the speakers impedance @ 10 to 200 Hz . Cut the tube(s) length(s) to get equal height peaks .
See Altec's 1974 Enclosure Manual :
www.lansingheritage.org/html/altec/plans/altec-plans.htm
Also read the 1960 , 1968 , & 1970 manuals.
Good Luck , Don

[MikeInNH]

I bought one of these speakers almost 30 years ago for $10. It was at a bar and they were refubishing the bar and installing a brand new sound system for the entertainment they had there.

I borrowed a friend of mine and his van to get them.

Two real nice things about this.

1) There were actually 3 speakers. All in working order and I got all 3 for $10. The owner didn't know what he had. He just wanted to get rid of them.

2) The bar was a Strip club. My friend and I retreived the speakers at 2 in the afternoon when the bar was open. For some strange reason this 30 minute job took us over 7 hours and a bunch of beers and 1 dollar bills to complete. I think the speakers ended up costing me close to $100. Still worth it though.