Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jeff on April 23, 2011, 12:23:30 pm
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I just had an idea, tell me if it's crazy or not.
This may be a possible solution to using a attenuator.
If you had a 4X12" or 4X10" cab and you wanted to crank the amp to get the distortion but didn't want the extra volume, could you add a switch to your cab that would put one speaker out of phase. This way you'd have 3 speakers in phase and one out cancelling some volume?
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It may reduce the volume level , but with one being out of phase with the other I would think it would sound really bad.
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Wouldnt the impedance change as well?
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It wouldn't cancel reliably at all frequencies, and the apparent cancellation may change depending on where you're standing in relation to the speakers and the room.
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Wouldnt the impedance change as well?
I don't think so, 8 ohms in phase is 8 ohms out of phase. I'm only talking about reversing the leads of one speaker. One speaker would be pushing air while the other 3 would be pulling.
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Assuming you have a completely sealed speaker box may be you obtain the situation above named
but if you have a box open in the back what you have in antiphase in front is in phase behind and the sound that reach your ears is anyway composed by reflections coming from front signal and back signal, so not big difference ..............
Kagliostro
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You are thinking of fighting sound with sound?
From my rather limited experience with out of phase speakers I would say that you can expect it to act more as a kind of tone control. As mentioned above only certain frequencies get cancelled and it can make the sound "thinner" rather than cut volume. That can be just what is needed, but most of the time it is to be avoided. I used it a while... in blissful ignorance!
Best, tony
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Wouldnt the impedance change as well?
I don't think so, 8 ohms in phase is 8 ohms out of phase. I'm only talking about reversing the leads of one speaker. One speaker would be pushing air while the other 3 would be pulling.
Yes ok i understand now. I would think that it would not sound too good that way /
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You are thinking of fighting sound with sound?
Yeah, Isn't that how those noise cancellation headphones work? A mic picks up backround noise then the speakers reproduce sound canceling it out? The orignal noise sound wave is disrupted and quited by another wave opposing it?
"Sound is a pressure wave, which consists of a compression phase and a rarefaction phase. A noise-cancellation speaker emits a sound wave with the same amplitude but with inverted phase (also known as antiphase) to the original sound. The waves combine to form a new wave, in a process called interference, and effectively cancel each other out - an effect which is called phase cancellation. Depending on the circumstances and the method used, the resulting soundwave may be so faint as to be inaudible to human ears.
A noise-cancellation speaker may be co-located with the sound source to be attenuated. In this case it must have the same audio power level as the source of the unwanted sound. Alternatively, the transducer emitting the cancellation signal may be located at the location where sound attenuation is wanted (e.g. the user's ear). This requires a much lower power level for cancellation but is effective only for a single user. Noise cancellation at other locations is more difficult as the three dimensional wavefronts of the unwanted sound and the cancellation signal could match and create alternating zones of constructive and destructive interference"
Stereo speakers are usally not as close as guitar speakers. I thought if the speakers were close enough as in a cab it may reduce volume.
But, like you guys said it probally wouldn't work well. There would probally be a zone that sounded loud but out of phase, a zone that sounded loud and in phase, and a small zone that sounded a little quieter and tinny.
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OK, It was a crazy idea.
Once again my fingers were faster than my brain. I gotta stop posting every hairbrained idea that pops into my head. Thanks for talking it out with me.
Jeff
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Now, if you had 5 speakers, you could do a Bessel array:
http://www.angelfire.com/sd/paulkemble/soundf.html (http://www.angelfire.com/sd/paulkemble/soundf.html) :l2:
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OK, It was a crazy idea.
Once again my fingers were faster than my brain. I gotta stop posting every hairbrained idea that pops into my head. Thanks for talking it out with me.
Jeff
No such thing as a hair brained idea. Thats what is so good about this forum. We have a great time and new ideas lead to new designs. Believe me i have had some real hair brained ideas.