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Topic: Speaker Overtones/Problems |
John Knight
From:
Alaska
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Posted 7 Apr 2001 6:38 am |
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I'm asking this group if they have ever seen/heard this. I am getting nasty octive or double octive overtones on two specific notes F# and A#. The amp is a Nash 400 and it is a JBL 15 speaker. When I have had speakers go its always a distortion sound or fuzzy on every note. This is a new one to me
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D 10 Thomas with 8&6
Nashville 400 and Profex II
Asleep at the Steel |
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Jim Cohen
From:
Philadelphia, PA
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Posted 7 Apr 2001 6:44 am
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Yes, in fact I had a conversation with John Hughey about this last weekend in Chattanooga. On my (and his) Nashville 400 amps, there is sometimes a "harmonic distortion", which is kind of like a low, distant "growl", which I think is sometimes heading in the opposite direction from the musical line (tho' John hadn't heard it that way himself). It doesn't happen all the time, and it's completely unnoticeable on stage; you just hear it from time to time at home at living room/practice volume. I don't like it but I don't know what to do about it. FWIW, John says that the Evans is the only amp he's ever tried that "never" makes that sound. Mike Brown: if you're reading this, any comment or suggestion?
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www.jimcohen.com |
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Jack Stoner
From:
Kansas City, MO
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Posted 7 Apr 2001 7:14 am
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I've noticed some intermittent low level sub-harmonics at certain fret positions - generally above the 12th fret. But, I think it is the Goodrich stuff that is causing it. If I use either my MatchBro (which is an older model with basically a matchbox when it's in bypass) or a Matchbox I tend to hear it more. If I go direct I don't really hear it. Like Jim, at stage levels it's not noticeable.
It's not the amp, as I've heard it on both my Nashville 400, and my Transtube/MosValve 500 rack system. |
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Bob Hoffnar
From:
Austin, Tx
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Posted 7 Apr 2001 10:45 am
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John,
What these guys are talking about are know as "difference tones". They are the result the relationship between the overtones of 2 notes played at the same time. Accenting the odd numbered overtones(ie:distortion) in the interval will make the sub harmonic difference tones louder.
If you are getting that sound when you play only one note at a time something is very wrong with your gear.
If you are getting that sound when you play the F# and A at the same time it can be fixed pretty easy. I use a matchbox to buffer the signal when I bump into that sound and I don't want it. Most likely you are slightly overloading your pre amp imput.
Bob |
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Chris DeBarge
From:
Boston, Mass
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Posted 7 Apr 2001 10:45 am
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| Could be a number of causes, but it's most likely not your speaker. Even things like component layout can cause these stray "ugly" overtones on certain notes. I once had an Ampeg that would do this same thing. Turns out that somebody put "goo" on some of the caps to secure them, but this caused certain frequencies to resonate badly due to the physical coupling of the caps to the chassis. I'm not expert, but if you got the amp to an expert it'd probably be an easy fix. |
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John Knight
From:
Alaska
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Posted 7 Apr 2001 11:23 am
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Thanks Bob, It is just one note. The overtone distortion happens with either the F# or A# but it is really nasty when you play the two noted together. I ran another test today using another amp and that speaker and the problem was there. So it is the speaker. Could this be a voice coil?
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D 10 Thomas with 8&6
Nashville 400 and Profex II
Asleep at the Steel |
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Jim Cohen
From:
Philadelphia, PA
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Posted 7 Apr 2001 3:43 pm
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| Quote: |
| I ran another test today using another amp and that speaker and the problem was there. So it is the speaker. |
Or else it's both amps, or else it's your pickup, or else it's your volume pedal, etc. John Hughey tells me he gets it on EVERY amp he's ever tried except for the Evans, so then it would not be the speaker. |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 7 Apr 2001 4:52 pm
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| Sounds like it might be a voice coil problem. Make sure the dust cap hasn't cracked loose on one side. This will make some really strange noises. It could also be that the baffle is slightly warped. Try removing the speaker, and turning it 90 degrees when you remount it. |
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Bob Hoffnar
From:
Austin, Tx
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Posted 8 Apr 2001 12:15 am
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Jim,
Was John Hughey was talking about a problem that exists when he plays a single note or when he plays 2 notes at the same time ?
Bob |
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Jim Cohen
From:
Philadelphia, PA
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Posted 8 Apr 2001 7:38 am
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| I dunno, Bob. We hadn't isolated it to that level in our conversation. |
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Terry Downs
From:
Wylie, TX US
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Posted 8 Apr 2001 8:30 pm
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I think the problem you are talking about is 3rd order intermodulation distortion.
John said he got that while playing a F# and A#. No amplifier is perfectly linear nor has infinite dynamic range. This means harmonics will be generated. When a note is played, the 2nd, 3rd, 4th, etc harmonics are generated within the amplifier due to its non-linearity.
If TWO NOTES are played together, the mixing of the two notes result in not only the sum and difference of the two notes but all combinations of the harmonic multiples and their sum and differences. Consider the F# and A#. Lets assume they are both octave 4 and the F# is higher than the A#.
f1: A# = 233.0818808 Hz
f2: F# = 369.9944227 Hz
The predominant 3rd order intermodulation slope would be 2f1-f2
(2 * 233.0818808 Hz) - 369.9944227 Hz = 96.16933881 Hz !!!
96 Hz is a horrible sounding note VERY close to a G note 2 octaves down. You can't get anything that sounds worse that a semitone away from the note on any octave!!
Well... it turns out that the Evans is the only amp that I know of that has an adjustment AND a test for intermodulation distortion. I have discussed this with Jim Evans at great length. Most amplifier manufacturers try to make their amplifiers as linear as possible (except tube distortion), but the Evans is the only one (that I know of) that actually tweaks the linearity for maximium supression of the 3rd order intermodulation.
I worked for Texas Instruments before Raytheon bought our defense systems group. This app note below is an analysis I worked on with a similar amplifier. It wasn't for an audio application, but the theory is the same. This app note on the TI website is better documented and easier to read than the one I wrote. You can learn all you want to know about intermod with this.
http://www-s.ti.com/sc/psheets/sboa077/sboa077.pdf
If it turns out that your problem is while playing a single note, then forget all I said.
BTW, Jim Cohen, I really enjoyed your CD. Some awesome playing and a super production. Very impressive.
Terry
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Terry Downs
http://nightshift.net
terry@nightshift.net [This message was edited by Terry Downs on 08 April 2001 at 10:04 PM.] |
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Terry Downs
From:
Wylie, TX US
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Posted 13 Apr 2001 10:40 pm
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| I forgot to mention that you can really hear this effect well if you play through a solid state fuzz box type effect such as a Boss Tone of Big Muff Pi. Play two notes, one fixed in pitch and the other bending with it. You will get a bass guitar note playing in reverse pitch direction. |
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Jim Smith
From:
Midlothian, TX, USA
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Posted 14 Apr 2001 10:24 am
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| All fuzz tones do that, it's the nature of the beast. If that's your "problem" it's not a problem. |
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John Knight
From:
Alaska
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Posted 14 Apr 2001 10:32 am
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| Jack, Please close this thread as the speaker needs to be reconed. Thanks |
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