My DIY Rotary Speaker

Discussion in 'Technical Side of Things' started by trlobdell92, Feb 24, 2020.

  1. trlobdell92

    trlobdell92 Gretschie

    128
    Oct 6, 2014
    Cleveland, OH
    So I haven't been fair to this forum, I've been hanging out on our cousin-forum, the Facebook Gretsch group.

    If you're there, you know about the Leslie I built! It's all done, except for tolexing.

    Here is a condensed thought process and photo album for your viewing pleasure!

    My roommate and I decided after seeing Peter Frampton live last August that we needed to get our hands on the real rotary sound. So I did research for three or four months on how to get as close to the real thing for less than $500, and came up with a single axle design, that could be powered by an existing amplifier/combo amplifier in a musician's rig, focusing on the points of cost (as stated), weight, and ease of use.

    For size and weight, it had to be compact. Just big enough to accomplish the motion process of a rotary speaker. A dual motor system would have probably allowed me to design speaker layout differently and make a shorter model, but we've already established cost, and I'm working with plywood. 32" tall by 20" wide by 16" seemed decent enough. I had my friend with a table saw cut dado joints for me since my dovetail jig was too small for any of those dimensions, and soon it would be off to the races.

    For cost, two motors was out immediately. I could have used two stage ceiling fan motors, but then I would have to build a custom control pedal or switch. Having to buy all of the extra parts made no sense when I could use a sewing machine motor with a speed foot control, at 110V, 60 hz, .9A, and 100 Watts (which turned out to be too many, 6000 rpm top speed!!). This is an effective motor, but for full sweep of the pedal it requires a governor in the form of a kitchen light dimmer (triac, 120V, 600W).

    For ease of use as a guitar player, the sewing machine idea operating like a wah or volume pedal made the most sense.

    How then would I go about doing the rotors? I didn't want to buy the real things for hundreds of dollars. My sister is a baker. I thought, oh, cake dummies! Perfect. What would I do for a horn? ...lightbulb, oil funnel!

    So after settling on a single motor design, I had to design a single axle process. I know about basic mechanics from high school physics, so I'll need an axle, at least two bearings, and a pulley system. First I tried to use half inch parts, with the idea of using half inch pipe floor flanges to attach the rotors. The outer diameter of 1/2" pipe though, is not 1/2", and so the pipe did not fit my pulley. Back to the internet we go, to use metric! I came across pulleys used in 3D printer parts, never even considered anything like that existing, but onto amazon and hit buy I went, standardizing my parts at 12mm, close to 1/2" since I already had some holes for my parts drilled.

    I considered using drywall anchors to attach the styrofoam to wooden platforms, but the glue did not hold the anchors when I tried to drive the respective screws in. Back to the drawing board. The 12mm flanges arrived, and holy CRAP were they way smaller than the 1/2" flanges... so the wood platforms shrunk to the width of the flanges, and I realized, glue and dowels! KISS!

    Once the rotors and axle were ready for assembly, I drilled four shelves with pilot holes to line up the axle and speakers. I made a couple of measurement errors along the way that weren't fatal, but definitely made the motor housing chamber more compact than I had wanted, along with the tweeter chamber. This was where I made my first real mistake.

    The plywood is warped a bit. To get the shelves in right, I installed the front panel to open up the sides. I installed the shelves, made their marks for screws, and drilled pilot holes into them and the support beams.

    For some terrible reason, I decided to fix the front panel in. The one side was warped out pretty badly, by a 1/4 inch. So I screwed the front in, and then I clamped and glued the sides to the front panel. I did this before locking down the shelves because I needed to make sure they would go in at the right depth, up against the front panel, I needed to cut and route proper sound holes, and I had the middle two shelves and axle pre assembled. Because of this, only half the shelves are bolted down on all four corners.

    Installing the drive assembly, speakers, and crossover was really easy after I drew up some good schematics. Truthfully the most difficult part of the whole thing, tolex excepted, was cutting the stupid little interface panel on the back. Hole saws for the aux power outlet and speakon jack, jigsaw for the breaker and IEC plug. I hate metal working.

    Front to back from first actual cuts in the wood to theorizing, troubleshooting, and IMG_7978.jpg IMG_7979.JPG IMG_7980.JPG IMG_8051.jpg IMG_8052.jpg IMG_8060.JPG IMG_8061.JPG IMG_8062.JPG IMG_8063.JPG IMG_8064.JPG first test with band practice tonight, this took 7 weekend days to do (Monday and Tuesday).

    If I were to build another one or make a hobby of building this cousin to a Leslie, I have three takeaways:
    1. Do not affix the front panel with glue until the end of the build - secure all shelves at all corners first
    2. Cut a channel down to the axle hole of the middle shelves, the motor chamber shelves, for removing the drive train with ease - shelving installation, then soundhole cutting, then parts installation.
    3. This project was absolutely worth doing.
     
  2. blueruins

    blueruins Country Gent

    May 28, 2013
    Savannah, GA
  3. trlobdell92

    trlobdell92 Gretschie

    128
    Oct 6, 2014
    Cleveland, OH
  4. Ricochet

    Ricochet I Bleed Orange

    Nov 13, 2009
    Monkey Island
    My head is spinning! :) Dude, that is awesome!
     
    trlobdell92 likes this.
  5. hcsterg

    hcsterg Country Gent

    Feb 13, 2012
    France
    What a work ! :eek::eek::eek:

    Congratulations... :cool::cool::cool:

    A+!
     
    trlobdell92 likes this.
  6. DennisC

    DennisC Synchromatic

    Age:
    37
    867
    May 11, 2017
    Germany
    ... cool!

    Absolutely cool.
     
    trlobdell92 likes this.
  7. stevo

    stevo Friend of Fred

    May 1, 2012
    Atlanta
    Oh man - I'm inspired and intimidated. Someone (hint hint) should make and market a nice portable one (as portable as possible) for guitar players. I think it would sell quite well. I want one!
     
    new6659 and trlobdell92 like this.
  8. trlobdell92

    trlobdell92 Gretschie

    128
    Oct 6, 2014
    Cleveland, OH
    I would be glad to build another one :)
     
    new6659 likes this.
  9. wabash slim

    wabash slim Gretschified

    Age:
    70
    Feb 10, 2010
    lafayette in
    They already have---a Leslie Model 16 or18. It's what SRV used.
    They're made from the 12" speaker rotors that can be found in smaller spinet organs online for $100---easy enough to DIY at home. They work on a vertical axis as opposed to the organ version which runs horizontally.

    One major aspect of a Leslie, Triobdell, is that the HF horn and LF rotor turn in opposite directions. That leads to some serious, complex interplay between highs and lows. It also makes a difference how close you are to a wall and corner. That also makes a Leslie nearly impossible to mike.

    I have to give you credit for your ingenuity. You've come up with a far less expensive way to get the rotary effect. Have fun with it. Of course, now you've got another large piece of gear to haul around to gigs.
     
    trlobdell92 likes this.
  10. Setzerhotrod

    Setzerhotrod Country Gent

    Age:
    59
    Oct 26, 2011
    Anchorage Alaska
    I love it when an idea pops into ones’ head, sleepless nights follow, chewing on the idea like a dog with a good bone, not letting go until the hands follow the brain and the idea is born out manifested in physical form!! Oh yes!!!
     
    trlobdell92 likes this.
  11. stevo

    stevo Friend of Fred

    May 1, 2012
    Atlanta
    I'd like to hear one of those in person - I had seen those designations but had never actually looked at one. Looks like it goes out the top and I would have thought the horizontal ports sound better?
     
  12. Alanqa

    Alanqa Gretschie

    199
    Aug 22, 2019
    Lancashire UK
    I was thinking of trying something similar but on a smaller scale using an 8” speaker.
     
    trlobdell92 likes this.
  13. wabash slim

    wabash slim Gretschified

    Age:
    70
    Feb 10, 2010
    lafayette in
    The Leslie 16 and 18 units sound thru the top and sides vertically. The Accordovox version is the same. The standard Leslies are horizontally oriented and totally wash the room in sound with a complex mixture of highs and lows cancelling and reinforcing certain frequencies continuously. They're certainly more "spacial". If you don't know, I'm a retired sound guy and longtime keyboard player and have a long history with Leslies. I'm of the belief that just about everything sounds better thru a Leslie.
     
  14. stevo

    stevo Friend of Fred

    May 1, 2012
    Atlanta
    Yes, I love Leslies. We used to have an organ when I was a kid that had built in Leslie and I loved it. But when I've been near a standalone/standard Leslie and it was heaven, simply wonderful.
     
    trlobdell92 and wabash slim like this.
  15. JeffreyLeePierre

    JeffreyLeePierre Country Gent

    Wow!
    Great work.
    We got the pics, now we want sound samples...
    (For what it's worth after being recorded and uploaded as mp3 or YT video).
     
    trlobdell92 likes this.
  16. wabash slim

    wabash slim Gretschified

    Age:
    70
    Feb 10, 2010
    lafayette in
    The funny thing is that Lorenz Hammond absolutely hated Leslies and wouldn't let his organ dealers sell them.
     
    trlobdell92 and stevo like this.
  17. wabash slim

    wabash slim Gretschified

    Age:
    70
    Feb 10, 2010
    lafayette in
    There are many 8" Leslie units on EBay that came from small spinet organs. Most should be reasonably priced. Just build your own box.
     
    Last edited: Feb 25, 2020
    trlobdell92 likes this.
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