speaker repair - shim vs '30hz'

[pierce]

I read with some interest the re-foaming sticky thread, and using the 30hz test tone as a voice coil centering method... Everything I've ever read before, and every (mostly retired) audio pro I've talked to insists you want to shim the voice coil to keep it centered and square. I can see as how running AC (30Hz) into the voice coil would center it on the 'in and out' Z axis, but I can't quite picture how that would keep it properly centered in the gap, radially. Can anyone explain this? I understand electromagnetics and such pretty well as an amateur scientist and general techno-geek.

FWIW, after doing tons of reading, I'm having a local pro sound shop re-foam my 2214H's (L100T) as I don't trust myself to get it right the first time... One of the cones is partially separated from the voice coil too (probably happened in transport), the shop's tech said no problem, he's fixed lots of JBLs like that.

[bigyank]

I have refoamed many woofers over the last few years from 8" to 15" ones without the use of shims. I used gravity, a 30 Hz test tone CD and a LOT of clothes pins. :D

http://i165.photobucket.com/albums/u60/bigyank_19320/RatShack/final_glue.jpg

Search here for Rick Cobb and if you use his install methods, you shouldn't have a problem at all. He comes highly recommended.

Yank

[badman]

How do you apply the pins? I mean, is it in motion when you do?

[bigyank]

How do you apply the pins? I mean, is it in motion when you do?

yes it is in motion and the volume is low so the amount of movement is trivial but enough to keep things centered. Also, I should have noted, and I apologize for not doing so in the previous post is that I work the surround onto the frame as spreakerdave noted carefully and I add the clips in a North-South-East-West pattern until I fill the frame with pins. Don't go all crazy with glue either or you will have some pins left on the surrounds. You will know if you have too much if the glue comes a gushing out from under the surround.

Yank

[duaneage]

And when the wife asks where all the clothes pins are shrug and blame the kids.

[ratitifb]

And when the wife asks where all the clothes pins are shrug and blame the kids.the WAF problem ?

[duaneage]

No, the WAF problem is getting 4 foot monitors with blue faces and blue grill cloth into the living room next to the TV. Or justifying yet another pair of speakers when you already have 11 pairs. How about 5 Yamaha power amps when her friends have the Bose Lifestyle System and it has a cute credit card remote.

Those are WAF problems.

[pierce]

WAF problem numero uno: "Why are there so many wires? can't you hide them?"

[pos]

How about 5 Yamaha power amps when her friends have the Bose Lifestyle System and it has a cute credit card remote.

:D
And then you have to explain her that there is an order to which she has to turn these amps and filters on and off, or baaaaaad things will happen.

[MikeBrewster77]

I find that any conversation that starts with either "I don't know" or "I don't understand" is generally bad news:

"I don't know how this thing works"
(Good - I don't want you touching it anyway)

"I don't understand what was wrong with the last pair of speakers - they sounded fine"
(If I just wanted fine honey, I'd buy Bose.)

"I don't understand how anyone could spend $1,000 for an amplifier"
(Don't get me started on the things I don't understand about you, and trust me $1,000 isn't bad.)

"I don't know why we need all this stuff"
(For the same reason I need you dear - it's love)

I could go on and on- :blah: but as a whole, I have to say my hobby is taken in a fair amount of stride with what can best be described as bemused resignation. Can't complain really...

Best,
- Mike


WAF problem numero uno: "Why are there so many wires? can't you hide them?"

[Beowulf57]

Don't forget that WAF and HAF can be balanced by walking the razor's edge! ;) In my case this is not too dangerous or difficult as we both come from backgrounds with both technical and artistic inclinations. Engineering and art, function and form, pragmatics and aesthetics...all can live in harmony. It may take time, design ingenuity and devotion, but in the end we want sound to become music that attracts us to listen. The same applies to what we see and what we do...so let it be written, so let it be done! :blah: :D

[pierce]

I simply have TWO systems in the house. The 'big stereo' in the living room is my component system, actually, its pretty damn simple, but does have multiple power switches, and you really should juice the power amp 30 secs -after- turning everything else on... but she almost never messes with it, rather, she uses the yamaha a/v receiver based system in the family room (which, btw, is currently stereo and not 5.1, I started finding the rear speakers more distracting than beneficial for all but a few Fx extravaganzas). so its the best of both worlds....

family room system:


yamaha rx-v2092 a/v reciever
ohm model 'h' bookshelf speakers
toshiba dvd player
panasonic laserdisk player (old pioneer LD-S1 bit the big one)
panasonic ag-1980 svhs vcr
vizio 42" 1080p lcd-tv (costco special)

living room system:


adcom gfp-565 preamp
adcom gfa-585 power amp
adcom gft-555-II tuner
yamaha cdx-393 cd deck
denon dp-23f turntable
denon drm-700 cassette
JBL L100T speakers :applaud:

so, everyone is happy ;)

[jcrobso]

When I first got married my complained about the cost of the speakers, $120 in 1966 $$ for JBL D140F and no cabinet!
A few years later one of my wife's best friends came over and my wife played some records for her. My wife's friend was really impressed with sound and just raved about how they sounded like theater speakers.
Ever since then I don't have much of a problem.;) John

[pierce]

Just to achive some closure here, today, I got my speakers back from the local sound shop that re-foamed them, and reinstalled them in my L100T's.

they did a decent job, although it does look like they used a bit too much glue on the dust cap (they removed the cap and shimmed the voice coils the tradititonal way)

grabbed a random CD off the stack, mmm, Talking Heads "Little Creatures"....

DAYUM, I"D FORGOTTEN HOW GOOD THIS SYSTEM SOUNDS.

next on the stack was some Dr John, "Back To New Orleans"... yup, full range bass, I'm loving it.

I do think a bit of crossover tuning may be in order, the tweeters are definitely hot on this system, and a bit too forward.

[hjames]

Just to achive some closure here, today, I got my speakers back from the local sound shop that re-foamed them, and reinstalled them in my L100T's.

I do think a bit of crossover tuning may be in order, the tweeters are definitely hot on this system, and a bit too forward.

grills on or grills off?

Tweeters were beating me on mine when i first got them - just got my crossovers back from Duaneage,
who upgraded them to L100T3 specs for me ... had a brief listen last night - they seems a bit less shrill,
but - Emma will be out Friday night, so I'll get a chance to crank them and let you know if they better ...

Understand that my reference systems are both LE85-mid/2405-tweeter systems, so i am a bit spoiled by their sound ...

[pierce]

grills off at the moment, and worse, they are crowded against the wall, half buried in stuff, and I'm sitting like 2 feet from one. this all conspires against these speakers, I know.

I *need* to clear out some of the clutter in this end of this room and open it up so I can move my computer farther away.

[Oldmics]

I"m sticking with the shims.

I have done the 30 HZ and also a sweep 20-90 HZ wave with mixed success.

I think shims and replacing the dustcap is the one shot guaranteeded method of replacing the surrounds.

Oldmics

[subwoof]

I remove the entire kit on most of the 12 and 15's esp if alnico since buying one here, one there and so on means a smattering of ages, conditions and of course the questionable magnet issue.

Of course then you can actually LOOK at the former / coil to see any bubbling, seperation, glue cracks, etc.

This summer it's off to visit my sister with a vanload of alnicos to get rezapped at a nearby center. Funny how a load in the van that's only 6" high makes the mischlins squish down...

ALWAYS shim. most of the time new litz wires and a good cleaning of the gap is required.

once you scrape a 2203 coil it's all over.