Redesign of JBL L-100 pair

[malovich]

I aquired a pair of JBL L-100 speakers for free a couple of years ago, Cabinets have slight water damage and are not re-usable. One tweeter is reading 0 ohms and the other has a dented dustcap, so what I need help with is selecting a new set of tweeters and a new box design. Box can be anything, Sealed, Ported, Variovent, TL.... I'd like smooth response as low as possible but with box dimensions within reason. I have never built or refurbished a pair of speakers but am handy with woodworking tools and am a mechanical engineering student at Penn State. Budget will be up to $50(this is flexible) for components which does not include shipping or the MDF.

Specs:
12" 123A woofer LINK
FS: 25
QTS: .49
QMS: 8.5
QES: .53
VAS: 235.1
EFF: .68
PE: 50
XMAX: 7.87
RE: 4.4
LE: .6
SD: .049
BI: 8.9
MMS: 85
FLUX: 1

4" LE5-2/2105H midrange LINK
FS: 200
QTS: .53
QMS: 3
QES: .65
VAS: 1
EFF: 1.2
PE: 25
XMAX: 1.52
RE: 6.1
LE: .3
SD: .006
BI: 6.6
MMS: 3.5
FLUX: 1.35

Crossover LINK
Frequencies: 1500Hz, 6000Hz
More specifications are on the pdf.

I'm aware of the site where a guy redesigned and created a kit for the crossover but am only interested in using the stock crossover. If there are cheap modifications I can do with the crossover, i'm handy with a soldering iron too. I could potentially use the dimensions listed on his site but if someone has any alternatives I'd be glad to hear them. I intend these to be a Christmas present for my girl but don't worry, I'll get her something that she would enjoy, not just a pair of big speakers. I'm also interested in a budget amplifier of any age to power these for less than $100 which would encompass shipping.

[infinia]

Originally posted by malovich


SNIP>

so what I need help with is selecting a new set of tweeters and a new box design. Box can be anything, Sealed, Ported, Variovent, TL....


SNIP>


but am only interested in using the stock crossover.


SNIP>


I'm also interested in a budget amplifier of any age to power these for less than $100 which would encompass shipping.

Box
Go with the variovent cabinet described in the article you linked esp. using the same front panel layout. If you use a TL or vented design the box size will be close to double the volume.

Tweeter
Stock paper cone tweeter is 94dB/m and uses a 1st order series cap. A modern drop-in replacement is close to nil. IMO the closest thing to use would be a horn loaded soft dome. The horn getting the eff. up to 93dB/m. Since a first order is used, a dome designed for this is required for lowest distortion. Something like this (see link)
http://www.madisound.com/catalog/PDF/CAT378.pdf



Amp
I own one and search for reviews.

see link http://shop.ebay.com/items/?_nkw=adc...+gfa&_osacat=0

[malovich]

Thanks for the suggestions, what would you think of an Audiosource Amp-100? I have one of these running the shakers in my chair which seem to have plenty of power, I am unsure how one would handle sound reproduction. Anyone have other recommendations? Old receivers would be acceptable too.

As for the tweeter, the one you suggested seems a little expensive(just one is over my budget). What about a Dayton DC25T-8 It has the sensitivity and is rated to 50W RMS, will this be enough or would I risk frying them?

Again I really have no experience when building speakers or selecting components.

[infinia]

Originally posted by malovich
]Dayton DC25T-8 It has the sensitivity and is rated to 50W RMS, will this be enough or would I risk frying them?

Again I really have no experience when building speakers or selecting components.

No it would require a Xover redesign and has some other issues in-band. If you love the metal dome sound you could do better with some other part, but all will require a new Xover.


IMO I would suggest looking for a stock tweeter from ebay, and pulling the dome out on the other. Post picts of the tweeter dome and "slightly water damaged" cabinet for suggestions on repair.

Sorry, I'm just not a big fan of gutting historical name brand speakers and modding them.

[malovich]

I was wrong about the tweeters, the one with the dented dustcap is also the broken one, the other one functions fine. Both would need new foam surrounds.
Cabinet pictures are below
One of them:



The other one:

[badman]

http://www.troelsgravesen.dk/JBL_L100_08.htm

You'd need new tweeters but this would be my choice. You're a lucky guy, those woofers are fantastic to work with. Easy to use and sound great.

[infinia]

Hi
Cabs look a little rougher near front corner and edge, but not imposible to repair. If so inclined you could get ideas from an excellent furniture repair book using more or less an artist's touch.
Looks like your tweeter is the LE25 w/orange surround.
(see last paragraph about using metal domes)


Copied from the web site that was linked.

"Why do you buy all these old JBL tweeters?", one of my friends asked, having noticed quite a few LE26 tweeters on my speaker shelves. "Well, hmm....I just like to have a lot of them...", I replied. "OK, fair enough", he said. I like that attitude. Anyway, there's a good reason I've bought all the LE26 tweeters I can find on eBay at sometimes 50 US$/pair, sometimes 80 US$/pair. I now have 5 pairs and that'll be it - I think - and maybe I'll sell two pairs again, once tested and fitted with waveguides.

1. The LE26 is quite sensitive; average SPL/2.8V is around 94 dB. From 6-15 kHz sometimes up to 96-97 dB/2.8V.

5. The LE26 is better than the LE25 - for some reason. Only difference appears to be the colour of the paper pulp used and coating of the surround fabric, extending the frequency range from 13 kHz to 17 kHz and getting rid of the 12-13 kHz peak of the LE25.
6. Last but not least, high-efficiency paper cone tweeters are becoming rare as hen's teeth these days.

The LE26 tweeters are obviously no longer available but quite often for sale at eBay.

Tweeter Sens.
I needed more than average sensitive tweeters to match this driver. I'd rather have a large dome with an upper limit of 15 kHz compared to most modern 1" domes doing well up to 20 kHz, but not particularly well below 3 kHz. Yes, I know some domes go below even 1 kHz, but they don't sound good - to my ears. The LE26 does well up to 15-17 kHz, more than enough. The current trend of claiming 30-40 kHz is ridiculous. We should rather worry about what our tweeters do between 3 and 12 kHz where "treble" is.


Metal Domes
Serious resonances between 15 and 20 kHz may disturb lower registers, as the terrible alu dome introduced in replacement of the LE 25 and 26. Actually this dome was removed again due to complaints about performance. Later on, a titanium dome was introduced doing better than the alu dome, but they could have stayed with the paper cone tweeter, which became very much out of fashion during the late Seventies and Eighties.

[infinia]

here's something that might work http://www.madisound.com/catalog/pro...oducts_id=8354


Note this is a 4 ohm tweeter. Lowering impedance gives an extra 3dB more than a similar 8 ohm, but requires a new (bigger )capacitor and better than average amp. I really would not recommend using this without a new Xover (2nd order) design. The Morel is drop in and near bullet proof in comparison.

[malovich]

So I could go with an LE26 (rarer) or a LE25 (doesn't sound as good as the 26) or a Vifa BC25SC06-04/similar which would require a re-worked crossover? How many more years can I get out of the old/new tweeters before they degrade? How would the capacitors have lasted all these years, should they be replaced anyways?

I'm aware these components are older than 30 years, does anyone know when these were produced? I want to hand these down to my kids in the future as i'm only 21.

What would be involved in making a new crossover on a budget? I've taken an Electrical Engineering class but didn't learn much with respect to capacitors and inductors, only resistors amps and voltage divider type components.

How many watts would an amplifier need to output to reach moderate listening levels with the L-100's?

Again I appreciate any help that is given here even though some of my questions are noobish. My current setup is posted on AVSforum HERE

[infinia]

Originally posted by malovich
So I could go with an LE26 (rarer) or a LE25 (doesn't sound as good as the 26) or a Vifa BC25SC06-04/similar which would require a re-worked crossover? How many more years can I get out of the old/new tweeters before they degrade? How would the capacitors have lasted all these years, should they be replaced anyways?

How many watts would an amplifier need to output to reach moderate listening levels with the L-100's?

If the caps are the large paper type and look OK, they are fine. If they are elecrolytic they may need replacement with the same.
You can get another 30 yrs years if they are treated with care.
http://www.audioheritage.org/html/profiles/jbl/l100.htm

These are very efficient speakers (unlike 95% of todays) and sound best placed against a wall to reinforce the lower bass. IMO 10-25 watts is more than plenty.