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wuzzzer

Bug screen removal from K-55-V midrange?

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I've read the past posts about doing this.  Anyone try doing this recently?  I love a very detailed midrange and am very happy with what the soldered lug drivers in my 1980 Heresys provide.  But, always looking for ways to improve the sound. 

 

Can the screens be replaced if they're removed?  I read that some have had difficulty removing them and have ruined the screens in the process.  With the value and scarcity of the soldered lug drivers I don't want to do anything to them that isn't reversible or would decrease their value. 

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  I've removed the screens a few times and feel as though I can hear a noticeable difference.    Some screens come out much easier than others;  the radius is easily deformed.  They can be straightened and they press easily back into place.  

  Pull one screen off,  play your system in mono and compare the modified driver to the stock driver.   It may just prove to be worthwhile!

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39 minutes ago, Zim. said:

Some screens come out much easier than others;

 

Mine must be in the "others" category! I just pulled on this screen with a small hook and it did not budge. When I shine a flashlight into the opening, the screen looks almost transparent.

 

IMG_5965.JPG.f7299c5d940c75b5ff9fcd78382a536b.JPG

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1 hour ago, PrestonTom said:

Out of curiosity, were you able to do any before and after measures?

Nope, just used the only thing I fully trust!

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40 minutes ago, Khornukopia said:

 

Mine must be in the "others" category! I just pulled on this screen with a small hook and it did not budge. When I shine a flashlight into the opening, the screen looks almost transparent.

 

IMG_5965.JPG.f7299c5d940c75b5ff9fcd78382a536b.JPG

A couple years ago I sent an inquiry to Bob Crites on the availability of replacement screens after I slightly mangled a screen from a corroded k55v.  At the time he thought they were pretty much unobtainium.  One may want to factor this in during the removal risk assessment.

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I wondered about opening the driver and pushing the screen from the inside, but I am guessing that the diaphragm wires are soldered to the terminals, and that even if I unsolder it, there might also be a phase plug in the way.

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When I took mine out, I poked through with a screwdriver and tore them out in one piece. Yes, they could no longer be used but they were a commonly found Atlas PD5-VH.

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2 hours ago, Mighty Favog said:

When I took mine out, I poked through with a screwdriver and tore them out in one piece. Yes, they could no longer be used but they were a commonly found Atlas PD5-VH.

 

Did they sound any better without the screens?

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I'm sure things sound different with them removed.  It's got to be a good 25% reduction in "flowable" area with the screens in.  Aside from anything else going on (like developed compression) it seems as though at the least the output level of the driver would change, and possibly not evenly so throughout its range.

 

I don't believe it's something I'd mess with.

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11 hours ago, soundbound said:

 

Did they sound any better without the screens?

 

I can't really say. It was a new build and I was going by the advice of some others.

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On 9/11/2019 at 1:02 PM, PrestonTom said:

Personally, I would not bother. I seriously doubt the screen plays much of a role sound wise.

Slight change in sound.  I had to remove mine in an old set of k-horns because I could actually hear it rattle on certain notes.

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5 hours ago, pzannucci said:

Slight change in sound.  I had to remove mine in an old set of k-horns because I could actually hear it rattle on certain notes.

for those who might share your screen rattle problem but who do not wish to remove the screen a judicious application of krazy glue should silence the rattle.

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I've recently changed amps to a 3W/CH SET 2A3 driving my recapped AA Klipsch Lascala. The clarity this new amp brought about made me acutely aware of a "rattle" type noise coming from my left channel's midrange. I had heard it slightly with my other amps (both tubes and SS) but only barely. I've surmised that the other amps were somehow obscuring/veiling the noise which only happens on certain notes. Pianos seems to be particularly affected. It is such that it actually brought about a shift in channel balance when I am in the listening position, the central image being slightly left of centre (the problematic speaker).

 

I've since taken both K55V drivers off and measured them.They are testing 11.9 (L) and 12.0(R) with my multimeter, so no need to change the diaphragm according to Bob Crites' site. Next I thoroughly cleaned the push pin terminal with deoxit. The driver to horn gaskets had been changed when I recapped the xovers about 12 years ago and all screws are tight in the cabinet. That's when my attention shifted to the bug screen which led me to this thread. From all appearances both bug screens were intact, they fit tightly with no corrosion. For good measure I tried pushing on the problematic driver's screen to see if doesn't eliminate the rattle. They were both reinstalled and I'D say the problem is 80% fixed, even the channel imbalance is much better. Of course, like I mentioned, I'm now painfully aware of the rattle and the 20% remaining buzz is really unbearable.

 

Can anyone think of a step I may have missed before I go ahead and remove the bug screens? They appear to be really tight and I'll likely damage them taking them out. Has anyone found that removing them alters the tonal balance of the speakers? Thoughts?

 

Many thanks,

Daniel

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So I removed, by force the bug screens from both K55V. The good news is that it didn't seem to change the balance or tone from the speakers.

 

The bad news is that the noise persists. Can anyone please advise what I should look at next?

 

The bug screen from the left channel did have some form of corrosion. Could little bits of corroded screen have gotten in the voice coil and be responsible for the buzz? 

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I would run some test tones through the driver/horn. At a somewhat high level, do you hear any harshness? That can be harmonic distortion and could indicate a failing diaphragm.

 

Since this happened after changing amplifiers, take a RMS voltmeter and make sure there is no appreciable DC voltage going to the driver (I am not sure what your crossover is). If the DC voltage is anything over 50 mV or so, let us know. 

 

In answer to your other idea, if any debris got into where the voice coil is, then that could cause your problem also. Again, listen for any harshness.

 

Good Luck,

-Tom

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Actually, it didn't happen after changing amplifiers, I just noticed it much more after having changed amps. 

 

I've got the AA crossovers which had the caps replaced about 12 years ago.

 

Would you mind telling me exactly how to measure the DC voltage going to the driver? I'm quite ignorant when it comes to electronics.

 

Thanks for the reply!

Daniel

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I ran some test tones and it seems to be buzzing from the left channel between approx 260hz - 300hz. Sounds pretty awful.

 

So does this sound like I need a replacement diaphragm?

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Do you have access to an inexpensive voltmeter? If so, place the two probes on the two outputs (+ and -) of the amplifier. Do NOT short the probes across the outputs. Set the meter on volts DC (not AC). Measure both sides. Perhaps, have a friend look over your shoulder if you are not sure of yourself. 

 

If there was an appreciable DC going to the driver, then this could have damaged the diaphragm. This is only speculation on my part.

Has the driver been modified by anyone or has the diaphragm ever been replaced (sometimes the new ones are not self-centering and can lead to this sort of problem). 

Again these are only guesses because we are using words like "harshness" and "rattle". I assume the other driver is not showing this problem?

If there was DC, I believe the the AA has a series capacitor on it. That should have blocked any DC

 

Good luck,

-Tom

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