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The SideTowers - An F6 Corundum Build

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  • 4thtry
    started a topic The SideTowers - An F6 Corundum Build

    The SideTowers - An F6 Corundum Build

    Greetings to all,

    This will be my entry for InDIYana 2019. I'm calling them "The SideTowers," as I built them to be tower type speakers in the sideways direction. This resulted in a very small front baffle surface area, which I then softened with multiple facets. As a bonus, this configuration gives me a little extra distance between the woofer and the internal rear wall reflection.

    Specs: Drivers: HiVi F6 & Peerless DA25 (corundum dome). Fb: 36Hz F3/6/10: 32/30/28.
    Xover: 1.3kHz; 5 parts. BSC: 6dB. Gross Internal volume: 1.18 cu ft. Weight: 37 lbs.


    This will be a ML-TL, so I modeled the line in 4 sections using the LA TL program. Without stuffing, the optimal position for the woofer was 4.5" down the line. I was going to place a small partition near the front of the line to create this 4.5" trap, but later on discovered that this was not needed. Simply stuffing the first 8 inches with 5.5 ounces of denim flattened out the 1st and 2nd line peaks considerably. And this 5.5 ounces only caused a loss at the main port resonance (Fb) of about 1dB.

    SideTowers drawing

  • 4thtry
    replied
    Update: Prior to Indy, I revised the crossover down from 1.3kHz to 1.05kHz (12dB/octave electrical; LR 24dB/octave acoustical). See attached schematic, which I forgot to post earlier. After I made this adjustment, I re-measured the harmonic distortion at 95dB/1 meter. Attached is a graph showing how the lower crossover and modified baffle improved the on-axis FR plot. This was done with 5 parts only. I did not revise and/or add crossover parts between Indy and MWAF. The same 5 parts were used at both events.

    None of the MWAF judges seemed to hear the 25mm corundum dome tweeter "grunting" or "straining" from the low crossover point. One judge mentioned a slight problem in the upper bass, which I would interpret as being far below 1kHz. He was probably referring to the internal cancellation & re-inforcement effects caused by the 30 inch depth of the enclosure. These resonances, in the 100 to 500Hz range, were dampened, but not completely eliminated, by 4 ounces of denim placed directly behind the woofer.
    Final SideTower schematic with 5 parts HD at 95dB/1 meter One meter on-axis FR

    Leave a comment:


  • 4thtry
    replied
    After adding the extension plates, the speaker seemed very stable front to back. But when I applied pressure from side to side I noticed that the stands started to rack a little bit. So I added two small 4 x 5" pine blocks to the top and bottom for increased stability.

    The racking is now gone and the speakers are stable in both directions. I also gave the original pine lumber a light sanding and then applied three coats of satin wipe on poly. I know my stands are somewhat crude and industrial looking, but that fresh coat of poly really makes them pop!!
    Top block Bottom block Stand with speaker

    Leave a comment:


  • 4thtry
    replied
    To keep my deep speakers stable during playback, I added top and bottom extension plates to my existing pine speaker stands. The new top plate is 7.5 x 13" and the bottom plate is 12 x 15.5". To keep the speaker from sliding off, I added 1/16" thick foam rubber with contact cement.
    Top and bottom extension plates Bottom plate Top plate

    Leave a comment:


  • 4thtry
    replied
    Originally posted by skatz View Post
    Wow Bill, you did all that for a 1 dB effect??
    Seems like a prime candidate for a CNC project to take over.
    Actually, it was more like a 6dB dip at 4.6kHz on axis. (See post 27) And the dip quickly disappeared as you moved off axis, to 15 degrees or more. This was a major design flaw, because this dip was right in the middle of the presence region.

    One of the big issues here is that I am designing the speaker for the best wide angle sound quality, projecting out to a moderately wide listening window. Let's say, a 2 foot by 4 foot wide window about 2.5 meters away. If a listener is sitting on-axis to one speaker and 15 degees off-axis to the other speaker, then the response to this listener will dip down 6dB at 4.6kHz from one speaker, while remaining perfectly flat on the other speaker. Depending on how much the phase angle shifts, the soundstage may completely collapse for this listener. The revised speakers have a very smooth, flat response, both on and off axis. There should be little to no channel to channel phase shift as you move across the listening window.

    Bill

    Leave a comment:


  • 4thtry
    replied
    Originally posted by KEtheredge87 View Post

    I will go ahead and admit that I have the toilet humor mindset of a 12 year old boy (and at this point I'm sure I'll never outgrow it!). I also had a good laugh at the idea of Bill's poor speakers taking a "dump." Whether intentional or not... Thanks for the laugh Bill!

    Leave a comment:


  • KEtheredge87
    replied
    Originally posted by jhollander View Post

    LOL, spit my beer...
    I will go ahead and admit that I have the toilet humor mindset of a 12 year old boy (and at this point I'm sure I'll never outgrow it!). I also had a good laugh at the idea of Bill's poor speakers taking a "dump." Whether intentional or not... Thanks for the laugh Bill!

    Leave a comment:


  • skatz
    replied
    Wow Bill, you did all that for a 1 dB effect??
    Seems like a prime candidate for a CNC project to take over.

    Leave a comment:


  • jhollander
    replied
    Originally posted by 4thtry View Post
    I'm currently modifying my speaker stands with top and bottom extension plates to keep the speakers from taking an unexpected "dump".
    LOL, spit my beer...

    Leave a comment:


  • 4thtry
    replied
    I'm currently modifying my speaker stands with top and bottom extension plates to keep the speakers from taking an unexpected "dump". My current "construction lumber" pine stands have a small 11.5 x 11.5" base with an even smaller 6 x 9" top plate. My modified stands will have a 12 x 15.5" base with a 7.5 x 13" top plate. Total height will be 28.5 inches. I'll post a few pics next week when I get the stands done.

    Leave a comment:


  • 4thtry
    replied
    I was curious as to whether or not the slight horizontal polar response bunching from 2.5-4kHz would negatively impact tonal balance, so I conducted an average listening window test of 19 microphone positions at an average distance of 2.5 meters. As you can see, the curve is very smooth and downward sloping out to 20kHz, with no tendency to peak in the horizontal bunching area. I'm guessing, but this is probably due to an offsetting response in the vertical domain.

    During playback, the speakers seem well balanced from top to bottom. I voiced them against my Plumbers Delight and Totally Flat speakers and I think I have the tweeter level and BSC set about right. Time will tell, as I have made several mistakes on other speakers, thinking that I nailed it only to find out later that I was way off.
    Average Listening Window FR

    Leave a comment:


  • 4thtry
    replied
    HD graph at 95dB:

    HD at 95dB

    Leave a comment:


  • 4thtry
    replied
    Distortion can be a problem with low crossover points, especially when using a small 1 inch dome tweeter. So I set the speaker up on my 27" stand with the microphone at a distance of 1 meter and measured total harmonic distortion at an average playback level of 95dB. As you can see, THD measures 0.31% at my crossover point of 1.3kHz and does not rise at lower or higher frequencies. At 748Hz, it is still only 0.33%

    During playback, I do not notice tweeter strain or harshness. So I think I am good to go in this department.

    Leave a comment:


  • 4thtry
    replied
    Originally posted by KEtheredge87 View Post
    Wow Bill! That's a labor of love and highly impressive to boot! I really dig the new baffle shape with the variable radius. I made a comment a while back on my own build log where sometimes the DIY guy is as much a sculptor as a carpenter. You definitely fit that bill right now. Makes me think there was some value in all that time I played with PlayDoh and clay as a kid! I'm really excited to see how this turns out.
    Thanks, Keith. When I was painting the Linehoppers a few years ago, my next door neighbor, from a distance, said it looked like I was trying to build some type of sculpture in my garage. But I told him it was just a loudspeaker, with woofers and tweeters and such.

    Leave a comment:


  • 4thtry
    replied
    Originally posted by jhollander View Post
    Bill that is impressive, nice work!
    Originally posted by tomzarbo View Post
    Darned if that foam doesn't look like suede in the pics. Pretty

    cool stuff you're doing with the round-overs. This is science at work!
    TomZ
    QUOTE=ernperkins;n1406082]Very cool and ingenious Bill![/QUOTE]

    Originally posted by Kevin K. View Post
    Your tenacity is awe-inspiring Bill! I've noticed it in some of

    your other builds as well. Really cool solution to address the issue. Good luck getting

    it all ironed out. Opps, I meant rolled out.

    Originally posted by KEtheredge87 View Post
    Congrats Bill! Looking forward to seeing these and competing in April!

    Thanks, John, Tom, Ed, Kevin, & Keith. Much appreciated. The foam does have a slight suede texture to it and needs to be cleaned and brushed out to look the best.

    Leave a comment:

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