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Post by geo on Nov 8, 2012 19:31:25 GMT -5
I'd like to make a leslie cabinet for my brother. Does anyone have good resources for this?
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Post by sumgai on Nov 8, 2012 20:54:14 GMT -5
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Post by geo on Nov 8, 2012 22:23:25 GMT -5
I was thinking about doing something like this:
Except with magnetic induction instead of sliding contacts. It's a little more involved than the basic leslie, so I thought I'd try and reach out to someone who's done the whole whirligig before.
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Post by sumgai on Nov 9, 2012 12:06:26 GMT -5
geo, Magnetic induction? Have you done any research on this yet?  First thing: magnetics are coil based. From the word "coil", you already know that they are frequency sensitive. Regardless of any other properties, you know that in order to pass all frequencies, they are gonna have to be pretty darn large, larger even than the output transformer of a tube amp. In turn, that leads to load loss, where power is wasted in the coil itself due to inefficiencies. Not to mention, you've just doubled the number of inductors in the output circuit to the speaker (unless you use a solid state amp head), thus increasing your "heating value" by quite a bit. And all this is before you even get to the bit about radiating all that power into the ozone - your inductors (plural, one to send and one to receive) are not gonna be shieldable, they'll have to be free-standing, that's a given - you can't 'ground' the shield, because any such shielding can't be 'magnetically induced' to make an electrical connection. Not to shoot down your idea, it's a good one, but in order to overcome these hurdles (and there are several more of 'em), you're gonna need the services of an Electrical Engineer, at the very least. And that can of worms is called "cost"..... at what point do you realize that the project is gonna cost a whale of a lot more than what you can get out of it, all in the name of searching for That Mojo Tone®? While sliding contacts will eventually wear out, they can be replaced with relative ease. They're not frequency sensitive, they don't absorb/waste power, and if installed correctly, they should radiate next to nothing. All of which is why the originator (Don Leslie himself) came to the conclusion that the speaker can remain stationary, all that needs to be done is to rotate the environment containing the speaker. Works a treat.  Even the horn that spewed forth the trebles was actually mounted on a 'tuned chamber', the driver itself was stationary, mounted underneath the chamber. Talk about engineering some tight-tolerance bearings..... I wish you luck, no matter which path you take, but as a FOG, I advise you to walk before you run - start with simple, known, proven principles, then work your way into the more esoteric territories. HTH sumgai |
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Post by ashcatlt on Nov 9, 2012 13:12:21 GMT -5
Just to be a pain, I've got mention that if the sliding contacts are, in fact, sliding - and especially if they are wearing out - then they are wasting power. Course it's motor power being wasted rather than amp power, but sg didn't specify. Conservation of Energy is.
Otherwise, I agree wholeheartedly with what he said. Spinning the drivers themselves is inefficient and prone to all kinda issues.
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Post by sumgai on Nov 9, 2012 15:35:40 GMT -5
Right you are, ash - no matter what materials are used, wear and tear will increase, by some small but not insignificant amount, the mechanical resistance between the stationary and the rotating contacts. While sizing the driving motor to take this into account over the lifespan of the product, the cost factor once again raises its ugly head. One of those "several other problems" I mentioned but didn't discuss, above.  Still and all, mechanical contacts will be/are more easily replaced when needful.  sumgai |
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Post by geo on Nov 9, 2012 15:56:49 GMT -5
Back to the drawing board...
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Post by JohnH on Nov 9, 2012 18:07:09 GMT -5
Id be nervous about sending large signals from a valve powered amp through moving contacts, because when they fail, permanently or intermittently, there will be nasty back emfs through the transformer and risk of damage to the amp.
Keeping the speakers still and whirling the cab around them avoids that issue.
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Post by sumgai on Nov 10, 2012 16:24:52 GMT -5
I admit, I do kinda wonder..... Why would you purposely attempt to keep "that Marshall tone" of the 4x12 speaker cab, only to spin it around, thus changing the tone to something else entirely different. Wasn't the whole point of the spinning sound source to achieve a tone that's quite different from a stationary cabinet in the first place? It's been a long time since I've seen such a classic case of WTFWTT.  sumgai |
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Post by geo on Nov 10, 2012 18:30:32 GMT -5
From the video he said he wasn't happy with the regular leslie cab 'cause the lows weren't particularly satisfying. I'm assuming he spun the Marshall cab 'cause he liked the sound it made and wanted the leslie to have the same characteristics, just... leslie-fied.
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Post by sumgai on Nov 10, 2012 21:37:47 GMT -5
geo, It'd take a lot more verbiage than I'm prepared to dispense here and now, but suffice it to say, the vendor's claim of wanting 'more bass' from a cab, while it's spinning, is not gonna happen. While I don't doubt that his hearing perception is different from mine, I do strongly doubt the veracity of his claim, that of a 'good sounding cab should also sound good when spinning'. Hogwash. It might take a fair amount of Googling (or looking with more specialized search engines), but I'm pretty sure that one could eventually find the papers and studies submitted for peer review regarding the phenomenon of sound sources. My meaning is, to paraphrase Newton's Laws, a stationary object will tend to sound different than an object in motion. Part of that is easily proven (the Q.E.D. variety) by the Doppler effect that we hear as a train passes while we're waiting at a crossing. In conjunction with that, we have the phenomenon of 'standing waves'. In short, a standing wave is one that is cancelled (reduced to effectively zero) either by a reflection of itself, or of some harmonic thereof. Alongside of that property, standing waves also exhibit reinforcement at the antinodes (180° out of phase). That means that for any given environment, a frequency will have a certain location whereby it will appear to the ear as being much louder, or nearly non-existant. I'm sure you've heard of rooms/halls/other locales with so-called 'sweet spots' or 'dead spots', eh? Standing waves are the reason for those spots. Now, it shouldn't take a mental giant to understand that as you rotate a sound source, the generation of standing waves will vary greatly - no longer is the room a static environment, it's now a whole circus caliope of environments for every frequency generated by the sound source (our speaker cab). That means that standing waves are coming and going like crazy, which in turn translates to reinforcements and cancellations shifting all over hellngone. No longer do you seek the sweet spot, it'll now find you no matter where you're positioned within the room! But it'll only last a moment, then it's somewhere else, until the rotation of the source has progressed through 360°. Lather, rinse, repeat. All of this goes to help explain why ball-busting bass from a Leslie setup is not easily obtained - it's a matter of room size as much as anything, and bass frequencies are notorious for being non-directional. My preferred solution would be to let the Leslie cabinet do it's job on the mids and highs, and use a sub-woofer to make the room go 'thump!', when the music calls for it. HTH sumgai |
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Post by cynical1 on Nov 11, 2012 0:14:40 GMT -5
Sometimes reinventing the wheel makes you appreciate the original wheel a bit more.
I'm with SG, and have combined a Leslie with a 15" bass cabinet and found it interesting, but not terribly practical...unless you eat your Wheaties and a protein shake before every gig.
A Leslie does what it does, and the design works. Granted, it works best when you don't have to move it too much...and as previously stated, it works best in the range of those directional frequencies.
Personally, making a functional copy of the original Leslie design is tricky enough to get right. Leave it to a German to rig up a commercial dryer assembly to a speaker cabinet... I can just see it walking itself off the stage at a gig...
Happy Trails
Cynical One
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Post by sumgai on Nov 11, 2012 2:14:43 GMT -5
... I can just see it walking itself off the stage at a gig... Tone Tie-downs? |
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Post by lunaalta on Nov 11, 2012 4:08:42 GMT -5
LOL.......... I once did a stint as security at rock events. One gig was 'Rock At The Oval', in London's cricket ground. When The Who came on, I was on stage to, in theory, keep it clear of fans. As he came on, Pete Townshend asked me to grab a hold of the mic in front of his Lesley cabinet, " 'cause it goes walkabout when I crank it up". Apparantly, the vibrations, from having this chunk of loudspeaker spinning on the stage, shook everything around it up too!  |
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Even the horn that spewed forth the trebles was actually mounted on a 'tuned chamber', the driver itself was stationary, mounted underneath the chamber. Talk about engineering some tight-tolerance bearings.....
