From ted@speakeasyvintagemusic.com Thu Oct 19 10:50:49 2006
Subject:RE: Leslie question -- 60 Hz to 50 Hz conversion needed?


I assume the phase correction question regards the bass bin thread.

When one has sound coming from two different sources in the same enclosure
(cabinet), the two sources should be in phase. This means that as one cone
is moving out, so is the other.

However, when there are two cabinets involved the issue can get complicated
at low frequencies. The reason is that the physical distance between the
two cabinets CAN result in a situation where when the two sound waves come
together, they aren't in phase anymore. If they were perfectly in phase,
they would reinforce one another, resulting in more volume, if they are out
of phase they would cancel resulting is lower volume.

Of course this relationship changes with frequency, since higher frequencies
have shorter physical wave lengths. Therefore, you might find a situation
where having them in phase (0 degrees) is no good, but then out of phase
(180 degrees) is also no good. You might find that 15 degrees is best, if
your gear can do that.

Here's a real world problem I once faced. It doesn't exactly illustrate the
bass issue, but it does illustrate the principal of phase cancellation.

It involved a Baldwin church organ. The organ had 5 channels of audio, 1
bass, and 4 manual channels. The channels spoke from speakers in the
console. 1 was for bass, a big 15", the others were as follows; 2 in front
of the players knees (like an A100, but each speaker was a different
channel) and 1 from each side of the organ.

The problem was that there was a point on the manuals where the volume would
drop and then go back up if you ran up and down the scale on certain stops.

As it turned out, the organ was near a wall at one end, and the problem was
that the distance from the speaker to the wall was 1/2 the wavelength of the
quietest note. Move the organ, and the problem went away.

Cheers!

Ted Thompson
General Manager - Speakeasy Vintage Music
____________________

Maryland Organ Service
- A Division of Speakeasy Vintage Music

http://www.speakeasyvintagemusic.com
http://www.mosweb.com
> -----Original Message-----
> From: CloneWheel@yahoogroups.com [mailto:CloneWheel@yahoogroups.com] On
> Behalf Of rafael2pop
> Sent: Thursday, October 19, 2006 12:05 PM
> To: CloneWheel@yahoogroups.com
> Subject: [CWSG] Leslie question -- 60 Hz to 50 Hz conversion needed?
>
> Hi All,
>
> Last posting I wondered if SE actually makes such
> thing as "frequency converter" as was responsded in
> the 50/60 hz thread ?
>
> Could be post was a talk about a induction motor being
> 50/60 hz ?
>
> Anybody knows such thing "frequency converter" for
> Leslies ?
>
> My electrical literacy doen't doesn't come from a
> finished degree on Elect. Engineering to know about
> all stuff about, but except Trekii conversion addon
> to work on Hammonds I never heard of such "frequency
> converter" for a Leslie as something "plug and play"
> thing.
>
> Also expecting somebody clarifies about "phase
> overlapping" mostly when talking about 0/180 degrees.
>
> What unit of measuremente are such degrees ?
>
> Opinions will be highly appreciated.
>
> Rafael
>
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