Phase Plug design for MW65xx

Going to experiment soon on a set of 6502's.
The big question for one design is if a small neodymium magnet would work to attach the billet phase plug/cone to the inner pole piece?
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Comments

  • KennethSwaugerKennethSwauger Moderator Posts: 7,007
    edited March 20
    I would be concerned about the magnetic field generated by the additional magnet causing unwanted interference with the original permanent magnet and voice coil. It might be better to use a moderately sticky adhesive that would hold it in place while you listen to the results.
    "They thought we were too loud, but shoot, I had four army blankets folded over my amp, and the volume level was on 2. I'm used to playin' on 10!" S.R.V.
  • mhardy6647mhardy6647 Posts: 25,403
    xschop wrote: »
    Going to experiment soon on a set of 6502's.
    The big question for one design is if a small neodymium magnet would work to attach the billet phase plug/cone to the inner pole piece?

    What are you trying to accomplish (i.e., what are you trying to fix)?
    Not meant to be as snarky a question as it sounds.

    Not to denigrate @KennethSwauger's observation/comment at all, but in my one and only (to date) experiment/experience with installing a phase plug where none had previously been found was very successful. In my case, I used a magnet-equipped phase plug from Dave Dlugos ("Planet10 Hifi"). This was to improve the HF peformance (extension and quality) on a fairly pedestrian twincone "fullrange" driver, the R/S 40-1354. Subjectively, the result was beneficial, but I am less sure that the Polk midwoofers will benefit (as much?), given that the range of frequencies they're asked to reproduce are limited by the crossover. Don't have that luxury with the 40-1354. :)

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  • xschopxschop Posts: 1,407
    To Ken, that's what I thought would be issue of mag field interference.
    To Mhardy, It will be cool looking and may have an actual sonic benefit. I sold/ traded most my billet 5jr's. So I need to spend some time experimenting again. You of all should understand.
  • GardenstaterGardenstater Posts: 929
    I have to admit I don't know what you are talking about. Is it this that you want to do?:

    d688va76qwpi.png
    George / NJ

    Polk 7B main speakers (1979, orig owner)
    Martin Logan Dynamo sub
    Crown D150 amp
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14 gauge, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,407
    edited March 20
    I have to polish up on my surgical scalpel technique on these dusty coil covers lol.
  • mhardy6647mhardy6647 Posts: 25,403
    edited March 20
    xschop wrote: »
    I have to polish up on my surgical scalpel technique on these dusty coil covers lol.

    A little free* and unsolicited advice: practice on some cannon fodder drivers -- especially if you've never done it before. It's not hard but it requires a certain amoun of confidence (not one of my better things, at least when it comes to fine motor skills).

    The pair of 1354s I performed dustcapectomies on were my spare spare pair. :|


    EDIT: Oh, come to think of it -- if you have any friends or family members who need some minor, elective surgery, and "Bronze" level health insurance... well... it could be a win-win vis-a-vis your gettin' a little scalpel practice in. :)

    FWIW, I actually didn't use a scalpel. I believe I used one of the thinner-handled X-ACTO knives with a brand new pointy blade, like this:

    4mxt7iaczodv.png

    _____________
    * and worth every penny. :#
  • xschopxschop Posts: 1,407
    Which shape would you choose for the MW phase plug and what's the sonic difference if any?

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  • mhardy6647mhardy6647 Posts: 25,403
    edited March 21
    Quick perusal of this thread from DIYaudio (only the first page -- there are 10 pages) suggests it's worth a look.
    https://www.diyaudio.com/forums/multi-way/192215-phase-plug.html

    Bear in mind that phase plugs for compression drivers (although, presumably, intended to improve the focus and dispersion of the output of the driver) are implemented rather differently than phase plugs for direct-radiator cone drivers.

    The whole thing about audio is that the range of frequencies (wavelengths) we have to deal with is quite broad -- a priori I would think some sort of smooth curve is 'better', but that's an opinion with very little to back it up.

    I can remember seeing nice graphics that 'explain' how the phase plug helps to improve higher-frequency propagation &/or dispersion from a (cone) driver, but danged if I can find any of 'em this morning.

    Take a look, also, at Dave Dlugos' products. Dave was sidelined due to some profound health issues a few years back, but he and his cottage business ("Planet10") were very influential in certain circles back in the glory days of 'full extended range' drivers and their care and feeding :)

    https://www.diyaudio.com/forums/planet-10-hifi/39053-planet_10-hifi.html

    439btdaknipx.png

    Dave has always had a sense of humor about hifi! :)
    My 40-1354 phase plugs are his, BTW & FWIW (& in case I didn't say that already!).

    Of course, there're also some of the vintage Lowther designs -- some of which always make me think of Mister Magoo. B)

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  • mhardy6647mhardy6647 Posts: 25,403
    hmmm.. this might be of interest... or maybe not :p

    http://audioprogress.free.fr/
  • mhardy6647mhardy6647 Posts: 25,403
    edited March 21
    so... here's a pretty concise, and I believe accurate (if nontechnical), explanation of the phase plug.
    Most phase plugs look like bullets. They are placed with the (nominally) flat side facing the driver diaphram, with the intention of forcing the frequencies coming from the center of the diaphram to follow an equal path length to those coming from the more outer periphery of the diaphram, thus keeping them in phase with each other.
    source: https://db.audioasylum.com/mhtml/m.html?forum=hug&n=81485&highlight=phase+plug&search_url=/default.mpl?searchtext=phase+plug&b=AND&topic=&topics_only=N&author=&date1=&date2=&slowmessage=&ip=&sort=score&sortOrder=DESC&sortRank=Forum&forum=hug

    This EV description (from their T-35 family of tweeters) might also be of interest -- although, again, this is for a compression driver (and a rather harsh & aggressive tweeter, at least IMO). :p

    https://www.electrovoice.com/binary/T350 EDS.pdf

    oh, and some typically Steve Deckert-esque prose about his phase plugs. :)
    https://www.decware.com/paper46.htm
    (many of his tweaks, in fairness, get very good press)
  • xschopxschop Posts: 1,407
    I read through much of that. Feels like I was given homework hehe.

    Now I can't find my old posts where I thought I mic'd the O.D. of a pole piece I had apart at one time.
  • xschopxschop Posts: 1,407
    How far past the plane of the removed dust cap base will the bullet-shaped plug need to be?
  • xschopxschop Posts: 1,407
    edited March 26
    Thanks to DowninMexico for the dimensions in his magnet resetting thread. I'll be making these 0.990" dia.
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  • xschopxschop Posts: 1,407
    I'm starting with 5" lengths because the part-off has to be near the chuck jaws....

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  • xschopxschop Posts: 1,407
    So quick I could only get finish pass pic....

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  • xschopxschop Posts: 1,407
    Programming a couple thousandths off tip to clean up point....

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  • mhardy6647mhardy6647 Posts: 25,403
    xschop wrote: »
    I read through much of that. Feels like I was given homework hehe.

    Now I can't find my old posts where I thought I mic'd the O.D. of a pole piece I had apart at one time.

    I do (still) teach a grad-level course in my spare time, you know? B)
  • xschopxschop Posts: 1,407
    mhardy6647 wrote: »
    xschop wrote: »
    I read through much of that. Feels like I was given homework hehe.

    Now I can't find my old posts where I thought I mic'd the O.D. of a pole piece I had apart at one time.

    I do (still) teach a grad-level course in my spare time, you know? B)


    All jesting aside, I appreciate your candor and insight. Your link to the D200? plugs was a good starting point for these. Thank you.
  • mhardy6647mhardy6647 Posts: 25,403
    edited March 26
    De nada... and your plugs look great!

  • xschopxschop Posts: 1,407
    edited March 27
    I used precision shim washers...
    I don't have a 4-place scale, but a couple grams worth of weight was removed....


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  • xschopxschop Posts: 1,407
    edited March 28
    To reiterate, I used .0875" O.D. phosphate coated steel shim washers. The magnetic force just from the pole piece holds them nice and tight....

    Listening session tomorrow. About to do surgery to other cone.... Thanks mhardy for the scalpel tips lol....

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  • xschopxschop Posts: 1,407
    A very interesting discovery, from what I can tell by ear, the plugs definitively clear up voices and instruments somewhere around 800-1200 Hz, especially when accompanied by bass notes.
  • GardenstaterGardenstater Posts: 929
    Very intriguing! How much clearance would you say there is, between the ID of the voice coil and OD of the plug?
    George / NJ

    Polk 7B main speakers (1979, orig owner)
    Martin Logan Dynamo sub
    Crown D150 amp
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14 gauge, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschopxschop Posts: 1,407
    edited March 29
    The factory pole piece is 0.995". Phase plugs are 0.990" diameter. However the factory voice coil is a touch larger than pole piece itself obviously, and more than 0.003" difference either side.
    I intentionally made these plugs 0.25" longer in case I didn't hear much difference and would shorten them down, but that's not the case.

    I can make another shorter set and see if that changes anything in the lower octave, but mhardy's links and discussion doesn't seem to warrant that.
  • xschopxschop Posts: 1,407
    edited March 29
    Also, I do not detect any off-axis difference with plugs in or out, however I do have them in a 12x12 carpeted office, if that matters.

    I Indeed detect the removal of tinnyness of Sade's voice in the specific track Stronger than Pride.... I'm enthused.
  • xschopxschop Posts: 1,407
    Add Donald Fagan to the list.
  • FaustinFaustin Posts: 960
    Nice work. When do you start full blown production? B)
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