first recone job.. jbl 2205a's surround viabrateing please help - diyAudio
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Old 1st March 2013, 08:04 AM   #1
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Default first recone job.. jbl 2205a's surround viabrateing please help

hey guys got some old alnico jbl 2205a's here and just reconed then to 2225's as it was the only recone kit available for em any more!

these were the ones i used i had to put them together ..
Click the image to open in full size.

now there was a slight difference between the voice coils on my original 2205 cone to these later 2225's ,

the 2225's VC former was taller about 1/2 inch and the voice coil was wider about 1/4inch,
so i just installed them to the height the original 2205's were installed..i had to order a bigger dust cap to cover the former cause it sat a bit higher,

the 2225's seem to have a lighter cone than the 2205's
but the surround seems identical the cloth double roll type that need doping once installed, a latex glue was supplied,

now after all this should i have doped the inside of the surround aswell?
could this vibration be the the inner side of the surround possibly hitting the frame?
or could it be a beginners mistake of not gluing the surrounds evenly to the frame...? that was the only thing i hurried with as racing against some glue cureing....everything else i took my time with nearly two months a bit here a bit there

at first i thought it might leaky box's there in 400lt ported enclosures all braced with a tuneing freq. of 30hz i run them at 85 cut down electronically with a 400w pre/power amp so resealed all the edges of the boxes that didn't help, the drivers have foam shims between the wood and the frame so that cant be it
its happening to both of them so leads me to believe it wasn't me!!!!!
I'm about to pull them from there boxes again and thought id see if any one has come across this problem before
or could maybe give me some advice i have thought of everything and have pulled apart so many times it funny "not for me any more" was going to be some thing great that will shake the house again which is why i was so,so very carefully with
em .... now I'm about pull out what hair Ive got left.....
heres one of them ...
Click the image to open in full size.
the top are "1965" made in Yorkshire Richard Allan 4 inch 15ohm drivers the are 4 of em in each box in a reflex setup i think its called ..there taking 350wrms don't know if the boxes are original or who made em!!! but jeez he new his stuff the mid bass is brilliant !!!!! but anyway
it was only due to a faulty thermostat I'm the central heating wile away for a couple of days in summer
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Old 1st March 2013, 09:27 AM   #2
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Location: Mumbai
Hi ,

Good to see that you attempted to carry out the re-cone job your self , first we need to sort out the setting of the voice coil is in correct position that is the overhang has been marked prior lowering the coil into the magnetic gap (top plate & pole piece) & then the coil has been lowered to this marking , please have a look at the pdf attached with drawings regarding this .

If you have firmly glued the speaker kindly carry out the test in the pdf .

Once this issue is sorted we can go further , the 2225 surround is doped on the outside only .

You need to be sure the lead wires are not touching the spider , to set the roll of a lead wire check the length of the loop from any similar driver

Suranjan Dasgupta
Attached Files
File Type: pdf Voice Coil Placing Guide.pdf (18.5 KB, 34 views)
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Old 1st March 2013, 08:45 PM   #3
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thanks very much for the positive coment
you cant belive how much these have involved my time and thank heaps for that voice coil info,
i have been reserching specs and construction parameters on both drivers and have scribled down about two pages of notes to go over and learn all the paremeters and valuals expressed to those terms of mesurements,
sorry i know you all hate novices but i learn quick !

so it basicly i installed these later kits to the mesurements i took from the old cone once removed and have set the voice coil way to over hung to run that cone kit..

i was under the "visuall asumtion" that they may macanicly bottom out in the frames,

this viabration must be distortion from the coil leaving the magnetic gap to far wich may explain why it affects mostly the deep punchy notes.... would i be right ?

from another post i read some one mentioned the old alnico magnet size and gap depth are the same as the ferite type if they have the same serial no.

the magnet gap depth on the 2225's jbl spec is 71mm would this be the same for the 2205's ?
im finding so hard to find this information jbl has not listed it for em any where i can find on the web "especialy the 2205a's" !

before i can do these calculations it would be very nice to have the top plate,bottom plate and magnet depth on the 2205 frame and the winding thickness and voice coil width of the 2225 VC before i remove the cones


then pull the verniers and dust off the old calculator....

i found some great info here that shal be a great help to me and most inexperianced
http://www.klippel.de/fileadmin/klip...t_Position.pdf

will M.E.K soften hi temp two part epoxy enough to remove it from the cone edge or do i cut very carefully to try and reposition the voice coil
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Old 2nd March 2013, 02:54 AM   #4
OscarS is offline OscarS  United States
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Quote:
Originally Posted by steptoe1111 View Post
or could it be a beginners mistake of not gluing the surrounds evenly to the frame...?
This.

if the surround "inner edge" is not glued to the frame, it will flap up and down and make an annoying noise on the low notes. Happened to me once, and from then on, I made sure to get the surround adhesive all the way to the inside of the rim. I'm not saying it's your problem, since no one here can hear your speaker's vibration (hint: post a video w/ sound), but it is definitely a possibility.
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Old 2nd March 2013, 06:43 AM   #5
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Location: Mumbai
Hi

Good to hear this part is sorted & RCA has showed results , now the fix ,

1) please obtain benzoyl acetate , you will have to work with benzoyl acetate in well vented (or a place with an exhaust fan is running) and using latex gloves ,
2) Please obtain amyl acetate

A) Clean off the doping from the surround with amyl acetate
B) Apply some amyl acetate to the dustcap & prise very lightly for it to enter
C) Apply generous amount of Benzoyl acetetate to the surround & spider (at the joining edges) with a painting brush
D) Let it be for some time & prise it a bit
C) With continuous applying & prising all should come off , please do not be impatient just rest assured that many people has been able to open up drivers w.o. damaging any component much
D) Do not attempt the voice coil yet once you get the dustcap off
E) Once the surround & spider is free - you will find working on the voice coil will be much easier , here you can also use a sharp cutting blade to help very dexterly

Regarding the travel space for the coil in the alnico motor structure vis a vis 2225 parts , the shortest would be if you can send me pictures with dimensions of :-

The voice coil
The Alnico Motorstructure
The spider mounting distance with reference to the basket bottom (including rivets or fixing screw top

I will attempt to let you know whether the voice coil may bottom , if it bottoms the way around etc.

Internet search and pouring over information & infirance thereof will be time consuming if you really want to find out the answers which are intriguing you regarding voice coil winding height size , motor structure gaps , designs , my advise would be to obtaine an impulse charger with a de-magnetizing capacity , demagnetize the magnets & open up the entire motor structure to its individual parts & open up all the drivers you can get your hand on & keep records of your findings

Make a simple test jig with a spring balance a& weights to check the component linearity , you don't need klippel just common sense and observance and the ability to understand the steps taken by loudspeaker makers with respect to component selection from the records of your findings

I have taken this route ...

As in my opinion no manufacturer will ever let anything be published which gives an indication of the above therefore it is difficult to find documents with actual measurements & internal drawings of their products

Suranjan Dasgupta
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Old 2nd March 2013, 09:05 AM   #6
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thanks Suranjan,
will do but i wont be surprized if it taks me another month or so to do so and remove them again ,
when i glued the surround and spider to the frame i used tarzarns grip general purpouse glue because i heard it "may" be benzoyl acetate based glue! it has acetone in it so i asumed it would be easy to remove with the m.e.k again in future,
if i ever had to of corse, glad i took that one into acount !

but in the mean time ...i was going to go through and teach myself about all those parrameters,mesurements and how to calculate them .

again about the novice factor thankyou everyone for your patiance and time,

i relised ages ago in the idustry of electronics that they dont like shareing information and makes me think if its due to the loss of picking up a job,cause your going to atempt to do it yourself and when you do and it blows up the device,electricutes you into hospital or burns your house down...
well most might say he told me thats how to do it.....
from my opinion anyway,
my knolege is all self tought i missed out on high school "im only 30 by the way"
but have moved on to speakers after learning enogh to fix diagnose and repair amps and equipment but havent been so far yet as to learn the full operation of the ocilliscope as 95%of faults ive found with digital multi meter,
even fixed a few plasma and lcd monitor psu's
seven years ago i blew my first amp my old mate gave me.. coneting it wrong,him, dick smith and jaycar kits helped get me on my
way plus the small helpfull hand full of people out there

but its due to my avid apreciation i have for good quality sound
that fuels the spark for devotion to learn.
but back to the facts..
im goin to try a little more glue on that iner endge on under side of surround just to rule out the iner edge is not flapping on it..
but would be great to have some of you guys check my calculations to make sure ive got it ..

i played em for an hour today and put some power through em it take a bit more to get em moveing than the old on ones and the viabration gets hidden alot when blended with the top end but still jumps out on a deep note ..on there own with no top end playing at all just bass at 85hz i think they should sound alot cleaner than they do even takeing into acount the room there in is 4 times smaller than the last and not concreet

i hope its what the other poster mentioned but will se in a few days
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Old 3rd March 2013, 04:17 AM   #7
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Location: Mumbai
Hi ,

Firstly my take would be to encourage people to amps , opening making speakers , and they make bigger amps & bigger speakers , and soon as linkin park would say " make some noise " , noise attracts others and more to this field ... more the better , more customers for the proper audio market . Else soon you will find the entire population behaving as robots with an mobile phone ear phone / i pod type devise to their heads , all you need is for Jim Carry to design the magma (or whatever it was in the Batman movie) to take control of everyone .

Regarding fixing amplifiers with a multimeter w.o. access to costlier tools , please keep going i think it works like this ,

when you see a circuit board something inside you tells you can repair it & most probably the problem lies in xxx part

thats a sign of a natural engineer , the theory part can & should always be cought up with as soon as the opportunity presents itself

theory bores , specially mathematics may be difficult one way to go about it is first create interest to kick start the drive for knowledge ,
1 find a patent related topic that really interests you
2 down load it
3 go over it & appreciate (& here is the start)
4 check the bibliography
5 get all the books , sometimes we may not have been born with that silver spoon , take a membership of British Library / Usis libraries
6 and you are on your way .

Suranjan
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