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[Nathan Riddle]

I was able to pull the TD1's apart last night and today. Here are the traces:

Dats Dropbox link: TD1-ALL_Traces.tzz

TD1-#5 (old mids)
T1 - Woofer 1
T2 - Woofer 2
T3 - Mid1
T4 - Mid2
T5 - Mid3
T6 - Mid4
T7 - HF_InHorn
T8 - HF_OnDesk
T9 - HF

TD1-#6 (new mids)
T11 - Woofer 1
T12 - Woofer 2 - In Horn (all other drivers removed)
T13 - Mid1
T14 - Mid2
T15 - Mid3
T16 - Mid4
T17 - HF_InHorn
T18 - HF_OnDesk
T19 - HF

Tests done on carpeted floor

Note different scales for the different images.

[Nathan Riddle]

I've cleaned the compression drivers multiple times now. Once when I first got them and just now before taking the impedance traces.

The VC gap always seems to have dirt/junk/particulate in it. It is rather annoying. I keep doing the tape in the gap cleaning method.

Also, is the corrosion a big deal? Should I clean it?
This thread mentions Corrosion X, what about break cleaner? http://forums.prosoundweb.com/index.php?topic=4858.0
I believe one of the gaps has some corrosion specs/spots/bumps would it be smart for me to sand it down?

Also, how is the voice coil supposed to align in the VC gap without scratching? These things don't seem to have any alignment methods...

Thanks, in advance!

[Art Welter]

1)The VC gap always seems to have dirt/junk/particulate in it. It is rather annoying. I keep doing the tape in the gap cleaning method.

2)Also, is the corrosion a big deal? Should I clean it?
This thread mentions Corrosion X, what about break cleaner? http://forums.prosoundweb.com/index.php?topic=4858.0
I believe one of the gaps has some corrosion specs/spots/bumps would it be smart for me to sand it down?

3)Also, how is the voice coil supposed to align in the VC gap without scratching?

Nathan,

1)A magnetic gap can hold a lot of junk..
2)Unfortunately, rust/corrosion expands from the surface, reducing the gap, so sanding off the corrosion may be required to open the gap properly. The many different metals, condensation, humidity and electricity make the interior of a driver a great place for corrosion.
Brake cleaner can be used as a solvent to break things free, but Corrosion X will keep corrosion from coming back, and actually seems to "reform" rust to some degree.
If you plan to continue living in Florida, buy a gallon, between trailer hitches, connectors, circuit boards and everything else that corrodes, you will use it up.
3) The usual way- slightly tighten screws, sine wave sweep (1/2 volt is plenty) around 200-500 Hz, listen for buzz, tap diaphragm in the direction to eliminate buzz. After you can do a full spectrum "clean sweep", tighten up the screws fully.

Since you have the cabinets empty, now would be a good time to smooth out the horn throat, the discontinuity makes for rougher response, and may be largely responsible for the large impedance spike and 4kHz dip.

Art

[Nathan Riddle]

Nathan,

1)A magnetic gap can hold a lot of junk..

2)Unfortunately, rust/corrosion expands from the surface, reducing the gap, so sanding off the corrosion may be required to open the gap properly. The many different metals, condensation, humidity and electricity make the interior of a driver a great place for corrosion.
Brake cleaner can be used as a solvent to break things free, but Corrosion X will keep corrosion from coming back, and actually seems to "reform" rust to some degree.
If you plan to continue living in Florida, buy a gallon, between trailer hitches, connectors, circuit boards and everything else that corrodes, you will use it up.

3) The usual way- slightly tighten screws, sine wave sweep (1/2 volt is plenty) around 200-500 Hz, listen for buzz, tap diaphragm in the direction to eliminate buzz. After you can do a full spectrum "clean sweep", tighten up the screws fully.

Since you have the cabinets empty, now would be a good time to smooth out the horn throat, the discontinuity makes for rougher response, and may be largely responsible for the large impedance spike and 4kHz dip.

Art

Thanks Art!

1) Haha thanks! I think what I was asking was, is it a problem for a compression driver? I know the diaphragm/VC aren't moving far (distance), but it just seems like a nice way to rub the VC raw very quickly having an oscillating member rub against dirt/metal at 1000 to 20k cycles per sec... I can keep cleaning it, but somehow this makes me think there's a root problem. I have a hunch it also gives the strange impedance graphs.

2) I ordered a can of: Corrosion-X 90102 Anti-Corrosion and Lubricant, 16-Ounce, Aerosol on Amazon.
Is this the same stuff?
Can I use it everywhere on the unit?

The whole unit is fairly rusted/corroded. Should I be concerned about the xovers (can I spray everything down with the corrosion x)?
I planed on replacing some of the wiring and will attempt to clean things up.

3) This is very helpful. I tried to look up how to do this, but I can't find anywhere (online) that states this/a method. I'm proud of myself though because intuitively I ran pink noise and watched smaart for any inconsistencies while I did the tightening method, though sine waves will be much better.

4) Haha nice image! Does mine look like it needs more sanding for the horn exit & then re apply LineX ?
Would it be smart to smooth the mid holes as well?

[Nathan Riddle]

Side 2

[Art Welter]

Thanks Art!

1) Haha thanks! I think what I was asking was, is it a problem for a compression driver?  I can keep cleaning it, but somehow this makes me think there's a root problem.

2) I ordered a can of: Corrosion-X 90102 Anti-Corrosion and Lubricant, 16-Ounce, Aerosol on Amazon.
Is this the same stuff?
Can I use it everywhere on the unit?
 Should I be concerned about the xovers (can I spray everything down with the corrosion x)?

3) This is very helpful. I tried to look up how to do this, but I can't find anywhere (online) that states this/a method. I'm proud of myself though because intuitively I ran pink noise and watched smaart for any inconsistencies while I did the tightening method, though sine waves will be much better.

4) Haha nice image! Does mine look like it needs more sanding for the horn exit & then re apply LineX ?
Would it be smart to smooth the mid holes as well?

1) The root problem is "crap in the gap", it just takes a lot of time to get rid of it. It also appears that the driver's bug screens are missing, so if the cabinets were ever set with the horn up, all the crap in the horn would have been funneled in. Some sand and dirt is magnetic.
You should replace the bug screens, nylon netting or nylon hosiery fabric works well.
2)That's the stuff. It can be used on almost anything, last century they used to demonstrate a working CRT TV set completely submerged in an aquarium full of Corrosion X! Trade show electrical inspectors probably put an end to that.. 
It's best to use something like DeOxit and a toothbrush to clean circuit boards before applying Corrosion X, though I've also used Corrosion X to "clean" lots of things.
3) Down at 200-500 Hz, the driver's output is quite low, so the odd harmonics (buzz) generated above are easy to hear. Pink noise (or music) will mask the buzzing.
4) Image courtesy of Mark Seaton ;^). It looks like the throat has already been smoothed, though perhaps could use a "touch up". The mid exit ports are not as critical, though smoothing will reduce diffraction.

Art

[Nathan Riddle]

1) The root problem is "crap in the gap", it just takes a lot of time to get rid of it. It also appears that the driver's bug screens are missing, so if the cabinets were ever set with the horn up, all the crap in the horn would have been funneled in. Some sand and dirt is magnetic.
You should replace the bug screens, nylon netting or nylon hosiery fabric works well.
2)That's the stuff. It can be used on almost anything, last century they used to demonstrate a working CRT TV set completely submerged in an aquarium full of Corrosion X! Trade show electrical inspectors probably put an end to that.. 
It's best to use something like DeOxit and a toothbrush to clean circuit boards before applying Corrosion X, though I've also used Corrosion X to "clean" lots of things.
3) Down at 200-500 Hz, the driver's output is quite low, so the odd harmonics (buzz) generated above are easy to hear. Pink noise (or music) will mask the buzzing.
4) Image courtesy of Mark Seaton ;^). It looks like the throat has already been smoothed, though perhaps could use a "touch up". The mid exit ports are not as critical, though smoothing will reduce diffraction.

1) Nice edit, any dollar store pantyhose will work? Presumably, the thinner leg part will do. Looks easy to mount too as I can place a circle between the metal mount and the rubber seal on the driver.

2) That's...awesome! I have DeOxit I'll spray and pray and clean and when the corrosion gets here hit it with that to help protect. Thanks

3) Makes perfect sense. I'm hoping between cleaning the gap, corrosion, correct VC alignment & cleaning the horn I'll get some better results north of 1k

4) When I think 'smoothing' I think 'rounding' the holes to flare a bit (both entry and exit). Is that correct?

---

5) I've been reading up on HF protection (seems really necessary as the 16ohm version diaphragm is hard to find/not in production). I can't seem to find a consensus on Zener Diodes vs TVS vs polyfuse vs lights vs fuse, etc.

For live use I'd prefer a 3dB compression instead of simply turning off.

I'm thinking this:
TE Connectivity Raychem RXEF110 1.10A Polyswitch Speaker Protector
With resistor (say 5ohms 50w) in parallel (drop spl by ~3dB, not just turn off)

Or Ivan's method:
http://forums.prosoundweb.com/index.php/topic,138477.msg1289035.html#msg1289035
http://forums.prosoundweb.com/index.php/topic,109187.msg1019254.html#msg1019254
Zener diodes & lights/resistors

Or both as they seem to do different things (rms vs peak)

Seems to me (via reading, not experience) the typical failure model of compression drivers is peaks.

My calculations are such:

B&C DE25-16
10 ohms minimum impedance (measured)
28v - 80w peak
20v - 40w cont      (2hr pink noise 6dB crest factor)
10v - 10w thermal (based upon 6dB crest factor?) [not sure if this is correct as I am integrating knowledge gleaned from Ivan/others on limiting]

Peak:
28v zener diode 50w
With 10ohm 50w resistor in series (could I double the resistance and drop to 25w to save money?)
Placed across (parallel with) the DE25

This seems to do the trick, 3% as a bonus to the normal 5% kinda expensive for 4x though...
https://www.electronicsurplus.com/motorola-inc-50m28sz3-diode-zener-28v-50w

In re-reading this:
http://forums.prosoundweb.com/index.php/topic,138477.msg1289047.html#msg1289047
I might have flubbed the math for peak vs rms...

Cont:
RXEF110 1.10A (10ohms gives me about a 12w continuous holding & 50w trip)
10ohm 25w resistor will drop me to 16v
Polyfuse & resistor are in parallel.
Series with xover/driver.

Placed after or before the xover?


Okay, I think I did all my math and calculations right...

---

6) Any thoughts on where to find this magical TD-'2' xover?
Seems Tom and Drew fussed around with the TD1 after SPL went outta business, I'd love to see/hear what they came up with... http://forums.prosoundweb.com/index.php/topic,109187.msg1019990.html#msg1019990

[drew gandy]

I'm puzzled about the missing bug screens.  Seems like an odd thing to remove or disappear.  Is it common, down there in Florida, for the screens to simply rust away in that soup you guys call "air"?  Yes, get the gaps in the comp drivers as clean as possible.  And doing the sweeps is one of the most fun parts of fixing compression drivers.  As Art says, the driver has much more limited output down in the lower mid range but I always found that my ear muscles would react when I had a driver at a level that really made the misalignment buzz well.  Problem is that wearing ear plugs diminishes your ability to hear the 'barmonics'. 

5) I've been reading up on HF protection (seems really necessary as the 16ohm version diaphragm is hard to find/not in production). I can't seem to find a consensus on Zener Diodes vs TVS vs polyfuse vs lights vs fuse, etc.

https://www.parts-express.com/bc-mmd02516-diaphragm-for-de25-16--294-634
Appears to be in stock. 

Compression driver protection for these: I have not done any protection for the comp drivers in my TD-x boxes.  But, based on my own mistakes with trying to protect drivers, I would suggest steering clear of anything like a breaker or switch.  You want it to be gradual. 

My second thought was to suspect that your 28v zener voltage is too low.  Just a hunch.  But, the zener concept should cause harmonic distortion when it's doing it's job.  That might be a nice sign to the operator that you're reaching the limit.  The problem might be that it clips higher frequency content (that might have lower actual power) while allowing quite a bit of lower frequency content through.  Because the impedance rises with frequency, the same voltage is producing less thermal rise in the VC at higher frequencies.  And, with actual music, there is likely more sustained tones lower than higher in the spectrum. Couple this with the drooping response with frequency caused by the mass roll off and inductance, and we probably need more voltage at high frequencies (10Khz) than at low (1.5Khz).  That said, this zener protection scheme is more of a transient catch (who unplugged and re-plugged our power?!?) than a long term limiter.  Suffice to say, protection is a complicated thing. 

Since replacement diaphragms are available, I would suggest that you wait until you blow a few and then work up a protection mechanism.  You may not need it at all.  But perhaps someone who has "blown" more diaphragms can chime in.

Looking at your pics, I would be inclined to go through the pcbs carefully and clean up any corrosion while re-soldering every joint.  And probably put some oil on those threaded mounting studs for the drivers. 

6) Any thoughts on where to find this magical TD-'2' xover?
Seems Tom and Drew fussed around with the TD1 after SPL went outta business, I'd love to see/hear what they came up with... http://forums.prosoundweb.com/index.php/topic,109187.msg1019990.html#msg1019990

A few posts back John Halliburton mentioned TD-2s at Schuba's.  This is a topic that I'd like to get straight.  The way I remember it is that SPL brought in someone to design the "TD-2" after Tom left and that only a few of them were made and installed (was the Cubby Bear supposed to get some as well?).  Conversely, when Tom worked up the new schematic several years ago he called it a "TD-2".  As I recall, he didn't know anything about what they did in the SPL "TD-2" and perhaps didn't want to lend it any credence.  John, please correct me if you can.  But ultimately, I think we need a way to differentiate these things because they are indeed different.  btw, Tom's "TD-2" calls for the BMS 4550 driver. 

As usual, Art's suggestions are spot on.  Well, except I have a bone to pick about one thing.  It's my understanding that the perimeter edge of the midrange entrance holes are best left as square as possible.  The idea is that the cross sectional area of any disturbance in the horn wall is a primary factor in how that aberration will affect the response.  If you round-over the hole edge then you increase the cross sectional area of the aberration. 
I've experimented with hole design for Unity/Synergy entrance holes but most of my play has been on the midrange side of the hole.  I would be delighted if someone has some more info about this.  Art, maybe you have some measurements or info from your travels that conflicts with this?   I would certainly say that "smooth" seems more intuitive for a horn than anything with a sharp edge.  But things aren't always as they seem.


Nathan, I haven't looked at all your measurements yet.  I'll try to do that and perhaps make comments (or just ask dumb questions). 

[John Halliburton]

A few posts back John Halliburton mentioned TD-2s at Schuba's.  This is a topic that I'd like to get straight.  The way I remember it is that SPL brought in someone to design the "TD-2" after Tom left and that only a few of them were made and installed (was the Cubby Bear supposed to get some as well?).  Conversely, when Tom worked up the new schematic several years ago he called it a "TD-2".  As I recall, he didn't know anything about what they did in the SPL "TD-2" and perhaps didn't want to lend it any credence.  John, please correct me if you can.  But ultimately, I think we need a way to differentiate these things because they are indeed different.  btw, Tom's "TD-2" calls for the BMS 4550 driver. 

Yes, that is how the TD-2 got completed as far as I know too.

The Cubby Bear and Joe's on Weed St. have original production TD-1 cabinets still in use.

The horn's effect on hf response is done and complete in the first half inch or so of the throat, so that transition from round 1" hole to rectangular flare needs to be nice and smooth and consistent in all four corners, finishing a bit before the midrange openings.  The one pictured does not look consistent on all four corners.

The smoothness of the midrange openings doesn't appear to affect things much-I always smoothed them out when they came in from the cabinetmaker as needed though.

Best regards,

John

[Art Welter]

1)I'm puzzled about the missing bug screens.  Seems like an odd thing to remove or disappear.  Is it common, down there in Florida, for the screens to simply rust away in that soup you guys call "air"? 

2)It's my understanding that the perimeter edge of the midrange entrance holes are best left as square as possible.  The idea is that the cross sectional area of any disturbance in the horn wall is a primary factor in how that aberration will affect the response.  If you round-over the hole edge then you increase the cross sectional area of the aberration. 
 Art, maybe you have some measurements or info from your travels that conflicts with this?   I would certainly say that "smooth" seems more intuitive for a horn than anything with a sharp edge.  But things aren't always as they seem.

1)Likely the screens were removed to give "more highs" ;^).
2)As John said "The smoothness of the midrange openings doesn't appear to affect things much".
I have measured a slight difference with and without offset driver exit ports, but having rounded/smoothed the ports before testing, can't say whether smoothing them actually made a difference in the response. Smoothing does makes them easier to paint, and looks better :^).

Art

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