Maker Pro
Maker Pro

Bass speaker failure mechanism

N

N Cook

Jan 1, 1970
0
Perfectly ok for a gig and then next time of using nothing.
No reported distortion in last use, hoping there is no problem with the amp
pumping out DC (sporadically?) , the 2SB817 / 2SD1047 driivers are not stuck
at DC rails.
Can a voice coil rub un-noticeably and then at switch on or off a DC pulse
be the final straw and fuses at the rub point ?
There has obviously been rough handling of box - could severe bumping or
dropping of the case damage a speaker ?
 
J

jakdedert

Jan 1, 1970
0
N said:
Perfectly ok for a gig and then next time of using nothing.
No reported distortion in last use, hoping there is no problem with the amp
pumping out DC (sporadically?) , the 2SB817 / 2SD1047 driivers are not stuck
at DC rails.
Can a voice coil rub un-noticeably and then at switch on or off a DC pulse
be the final straw and fuses at the rub point ?
There has obviously been rough handling of box - could severe bumping or
dropping of the case damage a speaker ?
Look for a frozen cone, ie the cone will not move when pushed in...most
often caused by magnet shifting due to hard vertical drop.

jak
 
N

N Cook

Jan 1, 1970
0
jakdedert said:
Look for a frozen cone, ie the cone will not move when pushed in...most
often caused by magnet shifting due to hard vertical drop.

jak

perfectly free movement, all seems perfectly well, except the voice coil is
open circuit
 
R

Ron(UK)

Jan 1, 1970
0
N said:
perfectly free movement, all seems perfectly well, except the voice coil is
open circuit

Check the continuity of the pigtails twixt connectors and cone

Ron(UK)
 
N

N Cook

Jan 1, 1970
0
Ron(UK) said:
Check the continuity of the pigtails twixt connectors and cone

Ron(UK)

--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com

yes full continuity.
I'm loathe to replace the speaker if there is some intermittant problem in
the amp dumping full DC on the speaker, although no reported loud clicks or
bangs.
Is there an interim fudge like putting a 100V, 100W light bulb in series
with a new speaker and running in earnest for a few hours.
Its a high power 250 W or so 12 inch Mackie M1263W
I think I'll ask the owner and then heat up the cone periphery and dust
skirt periphery to remove the cone and look inside.
 
N

N Cook

Jan 1, 1970
0
Ron(UK) said:
Check the continuity of the pigtails twixt connectors and cone

Ron(UK)

--
Lune Valley Audio
Public Address Systems
Hire Sales Maintenance
www.lunevalleyaudio.com

yes full continuity.
I'm loathe to replace the speaker if there is some intermittant problem in
the amp dumping full DC on the speaker, although no reported loud clicks or
bangs.
Is there an interim temporary fudge like putting a 100V, 100W light bulb in
series
with a new speaker and running in earnest for a few hours.
Its a high power 250 W or so 12 inch Mackie M1263W
I think I'll ask the owner and then heat up the cone periphery and dust
skirt periphery to remove the cone and look inside.
 
R

Ron(UK)

Jan 1, 1970
0
N said:
yes full continuity.
I'm loathe to replace the speaker if there is some intermittant problem in
the amp dumping full DC on the speaker, although no reported loud clicks or
bangs.
Is there an interim temporary fudge like putting a 100V, 100W light bulb in
series
with a new speaker and running in earnest for a few hours.
Its a high power 250 W or so 12 inch Mackie M1263W
I think I'll ask the owner and then heat up the cone periphery and dust
skirt periphery to remove the cone and look inside.

Slice the dust dome off first with a razor blade, occasionally the
joints where the pigtails are soldered to the voice coil fail,and you
can make a temporary repair. Chances are the v/c has just failed out of
badness, if there had been dc on the output it would almost certainly be
either locked up solid or be rubbing.

Send it to Wembley Loudspeakers for a recone.

Ron(UK)
 
M

Meat Plow

Jan 1, 1970
0
yes full continuity.
I'm loathe to replace the speaker if there is some intermittant problem in
the amp dumping full DC on the speaker, although no reported loud clicks or
bangs.

You would hear that. And a healthy speaker would handle it. You have the
option of sending the speaker for a recone.
 
yes full continuity.
I'm loathe to replace the speaker if there is some intermittant problem in
the amp dumping full DC on the speaker, although no reported loud clicks or
bangs.
Is there an interim fudge like putting a 100V, 100W light bulb in series
with a new speaker and running in earnest for a few hours.
Its a high power 250 W or so 12 inch Mackie M1263W
I think I'll ask the owner and then heat up the cone periphery and dust
skirt periphery to remove the cone and look inside.

theres no bodge option, its o/c. Time for a coil repair, which normally
means a rewind.


NT
 
J

jakdedert

Jan 1, 1970
0
theres no bodge option, its o/c. Time for a coil repair, which normally
means a rewind.
Didn't he concur that the fault was between the terminals and the voice
coil? That's mechanical failure caused either by age (fatigue) or
over-excursion...not DC. It might be fixable, but it will likely never
be reliable. New speaker (or recone) is definitely indicated.

If DC 'is' suspected, it's easy to test for.

jak
 
N

N Cook

Jan 1, 1970
0
The owner now says that it had been on odd occassions dropping out but
immediately returning.
Now I've removed the cone I can locate where the break is.
About 10 turns of slightly darkened varnish covering the break somewhere
underneath in the lower coil run. I assume a few turns of slightly reduced
diameter so, chain only as strong as weakest link, eventually mechanically
broke due to heating, rather than vaporised , so could make and break until
permanently broke. No other rubbing noticeable.
 
N

N Cook

Jan 1, 1970
0
I had a go at locating the break properly by scraping back small bits of
varnish and the break is just at the point where the flat copper that goes
axially out to the braid joins the round copper wire of the coils.
This suggests a design flaw, would these thin flat copper tails be the round
wire pressed to flat ? so causing a stress point at the change of form , i
could see no trace of solder or anything at the juncture.
The slight browning would be quite normal for those 10 or so turns and under
coil may be perfectly ok, this voice coil remade is 5.7 ohm dc for 8 ohms
speaker , seems reasonable. Shame the cone and skirt are now slashed.
Seems no point in recommending a genuine Mackie replacement speaker.
 
N said:
I had a go at locating the break properly by scraping back small bits of
varnish and the break is just at the point where the flat copper that goes
axially out to the braid joins the round copper wire of the coils.
This suggests a design flaw, would these thin flat copper tails be the round
wire pressed to flat ? so causing a stress point at the change of form , i
could see no trace of solder or anything at the juncture.
The slight browning would be quite normal for those 10 or so turns and under
coil may be perfectly ok, this voice coil remade is 5.7 ohm dc for 8 ohms
speaker , seems reasonable. Shame the cone and skirt are now slashed.
Seems no point in recommending a genuine Mackie replacement speaker.

Just unwind one turn and you've got a 7.2 ohm speaker, moving coil
impedances are a bit all over the shop so it wouldnt be a problem. But
if youve trashed it...


NT
 
N

N Cook

Jan 1, 1970
0
Just unwind one turn and you've got a 7.2 ohm speaker, moving coil
impedances are a bit all over the shop so it wouldnt be a problem. But
if youve trashed it...


NT

Another reason for not recommending a Mackie replacement.
The centre of the magnet is vented to the outside via a wire mesh grill
allowing any iron swarf and crud less than 1mm or so in size to pump in and
out of the voice coil/ magnet space.
 
E

Eeyore

Jan 1, 1970
0
N said:
The centre of the magnet is vented to the outside via a wire mesh grill
allowing any iron swarf and crud less than 1mm or so in size to pump in and
out of the voice coil/ magnet space.

Not so. The magnetic circuit isn't directly in the same location. Besides, there
shouldn't be anything getting in via the grille.

Graham
 
N

N Cook

Jan 1, 1970
0
Eeyore said:
Not so. The magnetic circuit isn't directly in the same location. Besides, there
shouldn't be anything getting in via the grille.

Graham

Do Mackie use a foam formulation guaranteed not to disintegrate to dust over
time ?
 
R

Ron(UK)

Jan 1, 1970
0
N said:
Do Mackie use a foam formulation guaranteed not to disintegrate to dust over
time ?

Nobody does, they all disintegrate eventually.

High power speakers instrument or PA don't generally use foam or rubber
for the surround, they are either paper or paper reinforced with a
material such as linen.

I don't think Mackie make their own speakers, they did own RCF for a
while, but I expect if you cross reference the speaker you have there,
it`s most likely an Eminence.

Ron(UK)
 
M

Meat Plow

Jan 1, 1970
0
Another reason for not recommending a Mackie replacement.
The centre of the magnet is vented to the outside via a wire mesh grill
allowing any iron swarf and crud less than 1mm or so in size to pump in and
out of the voice coil/ magnet space.

I have a pair of Peavey Black Widow 12's in a combo amp that have the mesh
vent through the magnet structure. These are approx 25 years old and are
still in use today. The amp is a 160 watt RMS tube amp. (6x6L6)
 
N

N Cook

Jan 1, 1970
0
Eeyore said:
Not so. The magnetic circuit isn't directly in the same location. Besides, there
shouldn't be anything getting in via the grille.

Graham

If the coarse grill was replaced with 2 larger diameter hemispheres one
inside the other something like the size of a flour seive with proper
filter material between the two, that would be ok
 
R

Ron(UK)

Jan 1, 1970
0
N said:
If the coarse grill was replaced with 2 larger diameter hemispheres one
inside the other something like the size of a flour seive with proper
filter material between the two, that would be ok

It`s really not a problem, Most pro drivers are vented. Any ferrous
stuff which got in there would stick to the metalwork long before it got
to the magnetic gap -not that there should be any iron filings floating
around inside the cabinet. Some speakers don't even have the little
grill, some have a disk of foam in the vent hole, some just have a hole.
Care has to be taken to make sure that there`s no chuffing or other
unwanted noises from the vent. There`s a lot of air moving in and out of
there with a big low frequency driver.

Ron(UK)
 
Top