Saw Kerfs inside back panel?

kickngas
kickngas Posts: 35
in Vintage Speakers
Why did Polk cut the vertical and horizontal kerfs into the back panel of the 2.3 speaker? This would seem contrary to wanting a rigid cabinet.ax98f3mq52ud.jpg
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  • Gardenstater
    Gardenstater Posts: 4,459
    edited December 2020
    I have read here on the forum that it is to break up standing waves. I suspect that it is a destructive interference diffraction effect that is effective on a certain wavelength based upon the groove spacing and distances from the side panels. Looks like they did it with a CNC router.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • pitdogg2
    pitdogg2 Posts: 25,437
    Correct to break up standing waves.
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  • Gardenstater
    Gardenstater Posts: 4,459
    I think in a sealed enclosure design (no port or passive radiator) you can fill the entire enclosure with polyfill to help eliminate standing waves, but I'm thinking that they want to keep the area behind the passives free of anything that would interfere with the speed of sound transmission from the MW's to the passive. Perhaps the grooves are the best solution in this case.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • F1nut
    F1nut Posts: 50,542
    Freeman built your speakers, you should be honored.

    The grooves are present top to bottom, but are shallow, so no compromise to the rigidity.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • kickngas
    kickngas Posts: 35
    I tip my hat to Freeman, he did a fine job! I feel honored :D . It would be cool if some of those Polk assemblers were present on this forum.
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  • Gardenstater
    Gardenstater Posts: 4,459
    I wonder if Freeman cleaned up the glue squeeze out. Usually there is lots of it visible.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Onkyo A-8017 integrated
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
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  • kickngas
    kickngas Posts: 35
    I will follow behind him with some caulk in the seams just to be sure it it all sealed up.
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  • F1nut
    F1nut Posts: 50,542
    kickngas wrote: »
    I will follow behind him with some caulk in the seams just to be sure it it all sealed up.

    Do not use anything with silicone in it.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • kickngas
    kickngas Posts: 35
    F1nut wrote: »
    kickngas wrote: »
    I will follow behind him with some caulk in the seams just to be sure it it all sealed up.

    Do not use anything with silicone in it.

    Great advice...Power Grab it is!
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  • F1nut
    F1nut Posts: 50,542
    There ya go.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • Jstas
    Jstas Posts: 14,820
    You can use silicone you just have to wait a long time for it to fully cure. Once cured it's pretty inert. But the curing process off-gases chemicals that will degrade speaker components pretty badly.

    When I was building sub boxes for competitions I'd seal the inside with silicone and let it sit with a fan blowing in it for like a week before I put any speakers in. I never had a problem. But I also never rushed it either.

    You gotta really watch the construction adhesives too because they use similar chemicals to keep it pliable so it's does set in seconds. So make sure you read the instructions completely.

    Expert Moron Extraordinaire

    You're just jealous 'cause the voices don't talk to you!
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