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P-90 Feedback Stops
Posted: Sat May 14, 2005 3:45 pm
by admin
I have a Reissue Epiphone Casino and I always had trouble with feeback at higher volumes(so what else is new). I recently changed my speakers in my Vox AC-30 Reissue from Greenback to Celestion Blues and the feedback seems to have disappeared at least at fairly high volumes. So what gives? Does this make any sense to anyone?
Posted: Sun May 15, 2005 1:36 am
by wolfgang
Peter, yes, maybe...
Comparing the frequency responses (Celestion website) one can see three minor differences between the Bulldogs and the Greenbacks:
the typical dip at ca. 1.2 kHz is a bit deeper at the Blue Bulldogs, and second the (again typical) peak in the 2- 5 kHz region is smoother at the Blue Bulldogs.
Although these are minor differences in frequency response it may be the cause for the disappearance
of the feedback. The third difference between these speakers is another dip between 6 and 9 kHz
at the Greenbacks. That makes the Blue Bulldogs sound so nice and smooth, but never dull.
I wish I could afford one (there's a 1970 Sound City Celestion speaker in my amp which is not too bad...)
BTW: John Lennon had big feedback problems with his Casino pick ups in Toronto (DVD John Lennon with Plastic Ono Band, Sweet Toronto)
The Casino did almost not feed back (!), but the pickups did (at the end of "John, John, let's hope for peace).
Posted: Sun May 15, 2005 1:46 am
by admin
Wolfgang: Thanks for your comments. Your analysis is most interesting and must explain, at least in part, the change in feedback for the better.
I will now have to get that DVD of the Toronto concert.
Posted: Sun May 15, 2005 2:09 am
by wolfgang
but it is a bit disappointing in so far Lennon used some open tuning and was under pressure, anyway.
There is no fun in this gig. It may be enough to have only the Life Peace at Torronto LP or CD.
Posted: Tue May 17, 2005 11:13 am
by doctorwho
I'm not a sound engineer, only a chemist, but I see a possible connection in Wolfgang's discussion. The 1.2 kHz frequency would have harmonics at 1.2 x 2 = 2.4 kHz, 1.2 x 3 = 3.6 kHz, and 4 x 1.2 = 4.8 kHz, which all fall in that 2-5 kHz range. Because feedback is a resonance effect, harmonics may be contributing to the overall magnitude, and a "deeper dip" at 1.2 kHz for the Blues might result in fewer of these harmonics.
Now, let the sound engineers can rip this to shreds ...
Posted: Mon Jun 13, 2005 12:25 am
by wolfgang
hello Peter,
I was talking about pick up feedback, not guitar body feedback.