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Dirty-South Blues Harp forum: wail on! >
Straight Talk on Dope for Harp
Straight Talk on Dope for Harp
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blueswannabe
523 posts
Nov 09, 2014
1:39 PM
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I have saved a few vintage speakers over 50 years old. After so many years, the cone dries out, and usually develops a slight tear radiating from the outer edge going toward the center. I have used pieces of paper towel soaked in Elmer's glue which was applied to the tear, followed by a flat black paint, and then to prevent other such tears I have opted to dope the outer circumference of the speaker by applying rubber cement. Every speaker I have repaired has turned out well.
I have read that doping a speaker not only provides strength to the outer edge and longevity to the speaker but it also reduces some of the high frequencies, including ghost notes, and also helps reduce con cry.
Here's what Weber says about doping a speaker! Of course, this is geared toward guitar players:"Doping is the shiny goop you see on the surround of a speaker. Besides extending the life of the surround, it also acts as a shock absorber to help keep the cone under control at higher volumes. The downside is that it also dampens cone vibrations and therefore reduces the potential character and texture of the speaker. If you are going to bend/sustain notes in the area above the 10th fret on the high E string and at high volumes with heavy distortion, then you need the doping to help prevent ghost notes and cone cry that could result from the extreme cone vibrations. Othewise, I would get the speaker undoped. Many players prefer the raw, undamped tone of the undoped speaker and they learn to modulate their finger pressure when noting in the area that causes cone cry.
Pre-Rola Treatment For this doping, the cone is artificially aged and chemically treated. Vibration dampner compound is also applied to the cone body and surround."
Since high frequencies for harp are usually shunned, what are your thoughts about speaker doping? Do any of you have a doped speaker?
Last Edited by blueswannabe on Nov 09, 2014 1:50 PM
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hvyj
2576 posts
Nov 09, 2014
1:57 PM
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When I put a Mercury Magnetics Fat Stack output transformer in my Princeton Reverb Reissue it overwhelmed the stock speaker, so I put in a Weber Vintage 10F150H hemp cone speaker with light dope. I have no idea what effect the dope has on the high frequency response because the hemp cone takes the edge off the treble anyway. Very full bodied tone, especially since the heavier OT increases the low end response of the amp.
That being said, from what I've read, doping may be more necessary on a 12" speaker than on smaller speakers, but I don't really know.
Last Edited by hvyj on Nov 09, 2014 9:46 PM
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Meaux Jeaux
20 posts
Nov 09, 2014
8:15 PM
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I doped an original 10" speaker that Gars Gille used in a Garnet Gnome I came across some years ago. It sounded great, but after a few years of heavy use deteriorated. I replaced it with a Weber P10Q with H dustcap. I liked the original speaker better.
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hvyj
2577 posts
Nov 09, 2014
9:45 PM
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This is a little off topic, but once upon a time I put a Weber H dust cap on a speaker in a Blues Jr. It had absolutely no effect whatsoever--did nothing at all. Nada. FWIW.
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blueswannabe
524 posts
Nov 10, 2014
5:13 PM
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Hvyj, the speaker I'm trying to repair right know is a 10" cts speaker found in a Kalamazoo. It had two pin holes on the outer edge I think from mishandling. It is missing the dust cap, and it had 2 slight holes in the aluminum voice coil. I repaired the holes in the speaker with the paper towel Elmer's glues fix, I used two slivers of aluminum tape in the two holes on the aluminum ring around which the voice coil goes. THe last fix would be a flat felt cap or round dome cap. Your observation on the dome cap is very helpful. I"ll probably go with the flat felt cap. I hate to throw these speakers away as it doesn't take much to put them the back into reasonabke shape. There is light dope around the outer edge which I think will just take away some of the highs.
update: on that kalamazoo cts speaker. This is slightly off topic. Don't use aluminum tape on voice coil. Speaker worked great for 1 minute and then there was a rattling sound. Although the cone is great, the coil blew agai. This time in mUltiple places.
Last Edited by blueswannabe on Nov 10, 2014 5:53 PM
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Barley Nectar
565 posts
Nov 10, 2014
5:56 PM
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Yes, I dope speaker surrounds at times. I use a product called 527 Bond. This must be mixed with acetone to thin it to the proper consistency then applied quickly with a small artists brush. I do this to fatigued speakers after repairing cracks with teabag paper and the same mix of 527 Bond.
Another trick I found is to toughen old, brittle cones. I use Swave liquid hair spray. First clean both sides of the cone of all dust with a small brush. Then apply the liquid hair spray with a brush so as to dampen the cone clear thru. Apply sparingly near the voice coil so as not to gum up the gap. Set, cone down, to dry. The cone will now be tougher and more supple. It will smell nice too :>). I have not been able to hear any difference in tone with any of these methods...BN
Last Edited by Barley Nectar on Nov 10, 2014 5:57 PM
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