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TAD 2001 Bugscreen Removal FAQ — (LONG!)

"The Dread Bugscreen"
by Paul Butterfield
Version 2.3 April 2008

This FAQ covers two methods for bugscreen removal:

METHOD ONE; 'QUICK, DIRTY, & DANGERIOUS' and unreversable.
METHOD TWO; 'PRECISE, CLEAN & SAFER' and reversable.

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DISCLAIMER: The information presented in this FAQ presumes you are either very experienced in audio/speaker repair, or expert level in DIY, or you are highly experienced in audio design and/or audio experimentation. No guarantees expressed or implied. Proceed at your own risk. There Be Dragons Here. The information herein is for academic purposes only. In no event shall PAUL BUTTERFIELD be liable to you or any other person or entity for any damages (whether general, direct, indirect, special, punitive, exemplary or incidental) arising directly or indirectly out of the use or unavailability of this information [[ FAQ: Removing the TAD "Dread Bugscreen" ]], even if such persons have been advised of the possibility of such damages.

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BACKGROUND:

The TAD bugscreen is the fine mesh metal screen in the interior throat of the motor which is held in place by both pressure and glue between the top motor plate and the interior horn throat chamber. Its purpose is to keep foreign objects from migrating to the VC gap area. I have also found (on older models) that the cement that holds the bug screen in place, in some cases, had been grievously over-applied during manufacture, and has caused additional restrictions in the throat area " somewhat like hardening of the arteries. The general opinion among the JoeNet Gurus is to remove it. This is also my advice as well, based on the following:

“It is noteworthy when audio enthusiasts on both sides of the pond are in agreement, but the overwhelming consensus for a significant improvement in sound of the TD2001 is removal of the "Dread Bugscreen." We (the Central Florida Audio Society) had a blind A/B comparison of identical TD 2001 drivers, one with, and one without the bug screen. What was significant " was not that all of the members preferred the sound of the driver without the bug screen " but, in under 30 seconds, everyone that participated in the listen was able to tell which driver had no bugscreen.” ~ CFAS newsletter

TEST CAVEATS:
1) For these listening sessions we used a very fast [NASA surplus] A/B switching relay which all but instantaneously switched between the two horns. The relay was controlled by a push buttons switch, so no one could tell by looking which driver was operating.
2) A pair of exactingly matched TAD 2001 drivers (Measured with LAud w/bug screens in) were used.
3) The small horns were next to each other, with the motors touching each other, so they were as close together as was physically possible.
4) These listening sessions were held in an acoustically damped room. No reflections.
5) The "Dread Bug Screen" listening session have been repeated with consistent results.
6) My reasoned opinion is that by removing the bug screen, one also remove the excess glue wad which compromise both pressure and diffraction.

My personal impressions of the audio presentation without bug screens, in a word, is "unveiled." To my ear (as well as the others who participated in these A/B listening sessions) removing the bug screen resulted in better resolution and transient response with less distortion. IOW, it improved the articulation and speed of the high end. The sound of the horn and driver with the bug screen seemed muffled, harsh and peaky... in a word, " strained. "

The disadvantage to this modification is that the bugscreen is there for a reason: To keep bugs, dirt and ferrous materials from migrating to the voice coil gap. This however, is more of a concern in a pro audio where the TD 200x, 400x are used in commercial sound reinforcement. For example, on one of the TD-2001 drivers I purchased (surplus) from Disney, I soon named "Dirty Harry," which was one of the most used and abused TAD's I have ever seen. Unclean and scurrilous, Dirty Harry seems to have done double duty as a miniature trash container. From the throat of D. Harry I removed chewing gum, candy wrappers, cellophane, a bottle cap, bugs, cigarettes, broken bottle shards and other nasty and unidentifiable FOD. Harry also seems to have had a sticky brown caramel liquid of some kind poured down it's throat, which cemented the voice coil/dome assembly into the motor. After months of applying drops of Marvel Mystery Oil around the VC/dome assembly, I was finally able to remove the voice coil/dome assembly to check the underside for damage from this sticky liquid. Amazingly, there was no damage to either the voice coil, surround or beryllium dome, and, after a thorough and extensive cleaning, Harry is now singing his little alnico heart out. This illustrates the advantage of the bug screen--in a public venue, or homes with curious children. In rare instances [E.g.; DeathMetal 119+db rock shows] the beryllium dome shatters, and the screen keeps the naughty bits confined.

One of the things that our local Chamber of Commerce will never admit to is well known to locals as Florida's' ‘Secret Shame’: An indigenous tropical bounty of airborne and flying insects in the form of: Dozens of varieties of flying cockroaches (which include Palmetto, German, Asian, Cuban, Madeira, dusky brown, brown banded, Blaberus giganteus, and deaths-head), flying ants, love bugs, moths, lady bugs, termites, fleas, sand fleas, midges, mites, citrus gnats, no-see-ums, mosquitos, bees, wasps, yellow jackets, hornets, horse flies, fruit flies, and regular run-of-the-mill houseflies. For those of you with similar environmental problems, I have found that extra large size nylon pantyhose stretched at the junction of horn throat or mouth makes an effective seasonal bug (kid and pet) screen for compression drivers that have had their bug screens removed, as well as traditional drivers (with an exposed gaps area) that have a phase plug or no dust cap.

Incidentally, one of the main advantages of the bugscreen removal method I use (Post me for bugscreen removal pricing if you do not wish to DIY) is that by using a priorprity designed tool for just this purpose, the bugscreen is removed intact and undamaged, so you may re-install if you wish. Or, in the unlikely event you wish to sell/trade your driver, you can offer it in original condition. During my process of removing, cleaning and reinstalling the bugscreens, I completely remove all of the excess glue from the junction of the bug screen and interior throat/phase plug chamber. This obvious restrictive condition occurs in the vintage motors when too much glue has been used during the manufacturing process. Removing these restrictive glue 'bumps' makes for less turbulence in the wave front. I also carefully re-align the VC dome assembly using LAud and my ear. Although removal of the bugscreen results in a marked improvement in the 2001, the improvement is unremarkable in the 4001, 4002. My reccomentadion is to leave the bugscreen of the 4001, 4002, alone and in place.

BEFORE YOU BEGIN!

Use non-magnetic tools in a well lighted area. Apply solvents in well ventilated area.

===================================
METHOD ONE; 'QUICK, DIRTY, & DANGERIOUS'

The easiest way for you remove the "Dread Bugscreen" is with a non-magnetic stainless steel scalpel & blade. Or if a stainless steel scalpel & blade are not available, use an Exacto knife, with a new, unused, knife blade. The downside of the 'QUICK & DIRTY' is that any chaff/FOD/crud may fall into the dome area, migrating to the voice coil gap, and ruining the alignment and sound. Also, it will destroy the bugscreen. This method of bugscreen removal extracts the bugscreen in pieces " an irreversible modification. Let gravity work for you by positioning the motor to allow any chaff/FOD/crud fall out of the throat rather than toward the phaseplug and perhaps into the gap area.

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METHOD TWO; 'PRECISE, CLEAN & SAFER'

STEP ONE:
Remove the VC/dome assembly [DP 2001] for protection during this process. Some DP 2001 units are a tight fit, and if not properly replaced, centered, and torqued, the VC may rub against the pole piece. Improper alignment may cause early failure, and crack or shatter the dome. When you remove the DP 2001, mark where it is located so that you can align it to its original position.

STEP TWO:
Remove the fiber mating gasket (light brown) that is cemented to the top of the motor. This will reveal the junction of the outside edge of the short aluminum interior throat to the inside of the milled hole of the iron motor. At the other end of the aluminum interior throat you will see the bugscreen.

The bugscreen mesh is stainless steel, held in place with a 'contact' like cement applied between the top motor plate and the interior horn throat chamber.

There are two areas that OEM cement is applied to the aluminum interior throat: at both the junctions at the top of the motor, and the interior horn throat chamber at the bugscreen. These glues must be loosened.

STEP THREE:
Before you can remove the bugscreen, the interior aluminum throat needs to be pulled out. The cement holding the aluminum throat has to be softened with acetone and lacquer thinner. This can be a lengthy process, as the cement has to be softened with successive drops of acetone and lacquer thinner and takes successive applications.

Drop solvent with eyedropper directly at the junction where the bugscreen enters the throat. First acetone (or fingernail polish remover) then lacquer thinner. Do not over-apply these solvents. A few drops at a time is sufficient. Keep the junction that holds the bugscreen moist, but not wet, with solvent. This may take several hours to several days"or more"to soften the glues. When the glue is softened, you should be able to pull out the interior aluminum throat. The screen may or may not come out with a the round cylindrical aluminum throat.

After softening of the glue joint takes place between the underside of the top motor plate and the interior (aluminum) throat chamber, remove the interior throat chamber with a strong sticky tape applied to the interior aluminum throat. DO NOT remove the top plate (nickel plated) or the Alnico magnet! Doing so results in a severe loss of gauss, ruining both the efficiency and high frequencu reproduction, and the and the motor will have to be re-magnetized.

The bugscreen comes out with the interior throat chamber. This allows you to completely remove not only the bugscreen, but all the excess glue that may have 'spilled' into the front of the phase plug chamber during the manufacturing process. Removing these glue 'bumps' presents a more uniform wave front.

Then insert the cleaned interior throat chamber back into the motor, and either re-glue the horn throat chamber, or leave it unglued so that the interior throat chamber may be removed to better clean unit in future, or to polish inside of horn throat, or to replace and experiment with hardwood throats, or other damping/ reflective materials. The unglued interior throat chamber will stay in place quite well with a _tiny_ amount of non-hardening clay or putty, and will then be removable. (I use and reccommend Coax-Seal) The interior throat chamber and bug screen may then be removed in the future, to determine which configuration sounds of better: With or without bug screen. Most of my customers choose unglued, but sealed with putty for a 'with and without' A/B comparison.

STEP FOUR:
Replace and re-align the VC/dome assembly. When running LAud, or another IMP program, and the VC is rubbing, you will see a jagged impedance plot instead of a smooth plot. A very obvious saw-tooth pattern. If you only have a pink noise source, you can listen [At low levels]: When the hiss/noise becomes deeper and fuller, you may have a good alignment. Verify while listening to a music source with full Hz range. You should be able to tell by the openness of the shimmer of cymbals, coupled with deep upper mids that you have alignment.

CAUTIONARY WARNING: IRON FILINGS MYSTERIOUSLY APPEAR IN GAP:
They are coming from inside the tapped mounting holes for the rear cover. Obviously an early TAD QC issue, some of the milling did not get cleaned out. To remove, place cleanroom cloth or paper over gap and tape down. [It takes a LONG time to remove filings with stainless steel non-magnetic tweezers!] Use vacuum, then Q-tip with alcohol and oil to remove final mill grit dust.

CLEANING GAP & VOICE COIL:
The method I use to clean the gap is to first use a shop vacuum, with the round vacuum hose placed directly over the gap/phase plug, to remove any of the inaccessible material that has migrated in and under the gap. I then place the motor on a lazy Susan, and with a thin stiff plastic shim wrapped in either laboratory clean wipes [ I only use lab wipes] or well washed cotton, applied with a few drops of isopropyl alcohol, inserted into the gap while I turned the motor on the turntable/lazy Susan. To clean the voice coil I take a lab wipe, and lightly pinch of both sides of the voice coil at the same time. Put several drops of isopropyl alcohol on each surface and clean very, very gently.

On a personal note, I am no longer able to answer email queries regarding above and other TAD modifications. However, you are welcome to email me via AA to set up a no charge telephone consultation [I *am* an educator, BTW] to discuss better audio reproduction. On your dime, though. -Paul B

© (c) Copyright 2004, 2008 Paul Butterfield
NOT to be copied or electronically transmitted without express written or email permission.
Permission granted to recipient to save and print this document for personal, non commercial use only. [FONT: Courier, 12p]

## END FAQ ##

"Those who hear not the music think the dancers mad."
- Angela Monet


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