Insulation in cabinets

geppy1
geppy1 Posts: 3,076
edited October 2010 in Vintage Speakers
I need a refresher on this subject. If one has Monitor series speakers with a passive and puts more insulation in the cabinet what is the effect?? If one was to use a passive with a weight on back what effect would that have?? i know having a weight on the passive slows the passive down. keith
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  • FTGV
    FTGV Posts: 3,650
    edited October 2010
    geppy1 wrote: »
    I need a refresher on this subject. If one has Monitor series speakers with a passive and puts more insulation in the cabinet what is the effect??
    Adding insulation may help the midrange because of reduced internal reflections but too much will overdamp the box and reduce output from the PR.
    If one was to use a passive with a weight on back what effect would that have?? i know having a weight on the passive slows the passive down. keith
    Adding weight will change it's mass thus lower its tuning frequency,it does not slow it down.
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  • geppy1
    geppy1 Posts: 3,076
    edited October 2010
    tuning frequency ?? I assume that means its resonance frequency.
    The passives on a RTA 12B are SW 120s and a 1C are SW 120s However on the 1Cs they put a 2 inch by maybe .5 inch carridge bolt on the end of the passive. if you put the 1C passive in the RTA12 cabinet what happens??
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  • FTGV
    FTGV Posts: 3,650
    edited October 2010
    geppy1 wrote: »
    tuning frequency ?? I assume that means its resonance frequency.
    Yes
    The passives on a RTA 12B are SW 120s and a 1C are SW 120s However on the 1Cs they put a 2 inch by maybe .5 inch carridge bolt on the end of the passive. if you put the 1C passive in the RTA12 cabinet what happens??
    Installing the PR with the added mass ( carridge bolt) will alter(lower) the enclosure/PR tuning point.
    Edit.In addition a PR's mass is precisely adjusted to work correctly with a specific enclosure volume,changing one or the other will mistune the relationship and in all likelihood degrade bass performance.
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  • geppy1
    geppy1 Posts: 3,076
    edited October 2010
    That is what i would think Bottomline is these RTA 12s have the passive from a 1C (same part number but added weight) and extra insulation. I assume that together this is a bad idea??
    I removed the big bolt from each and now it looks and the motion feels like the ones i have had from RTA12Bs. At this point would puting a little insulation in be a good idea.? As installed the factory stuff in RTA 12Bs is all in the top half of the cabinet with the bottom half pretty much empty. I have had a number of them so i know what it is supposed to look like. Sure helped in this case.
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  • FTGV
    FTGV Posts: 3,650
    edited October 2010
    geppy1 wrote: »
    At this point would puting a little insulation in be a good idea.? As installed the factory stuff in RTA 12Bs is all in the top half of the cabinet with the bottom half pretty much empty. I have had a number of them so i know what it is supposed to look like. Sure helped in this case.
    I would replicate what Polk did originally with the damping material as I'm sure they had a reason for doing it so.Having the damping material only in the top portion behind the midbass drivers is where it will be most effective at supressing internal reflections that can colour the all important midband.
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  • ShinAce
    ShinAce Posts: 1,194
    edited October 2010
    I'm reading GV's last post and I can't help but wonder if loosely stretching some polyfill over the back of the midrange and tacking it down to the baffle would have significant merit. I'd try this first before stuffing the top of the cabinet.

    A quick google search gave me this:
    http://www.speakerbuilding.com/content/1012/print.php


    The last two pics of the speakers show what I'm thinking. Localize the stuffing to the midrange. In this case, the midrage is external to the enclosure, but still physically stuffed like I'm thinking.
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  • Face
    Face Posts: 14,340
    edited October 2010
    I wonder why that type of midrange enclosure(or lack of)never took off? :D
    "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche
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  • FTGV
    FTGV Posts: 3,650
    edited October 2010
    ShinAce wrote: »
    I'm reading GV's last post and I can't help but wonder if loosely stretching some polyfill over the back of the midrange and tacking it down to the baffle would have significant merit. I'd try this first before stuffing the top of the cabinet.
    My thinking would be that a thin layer of poly will have minimal effect on the strong reflections from the rear panel.
    Face wrote: »
    I wonder why that type of midrange enclosure(or lack of)never took off? :D
    Looks to me like a CL35 rethinking of baffle design much like his unconventional theories on filter design.:wink::biggrin:
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  • Toolfan66
    Toolfan66 Posts: 18,005
    edited October 2010
    I have a set of 15" passives without the weight out of a set of 1.2's, I also have a set of 15" passives with the weight out of a set of 1.2tl's.

    I have swap them a few times using the same CD/SACD/Vinyl when doing so, and I find the passives with the weight have a tighter deeper sound it's not night and day but it's there.

    I have an extra set of 10"/12"/15" passives in my collection of Polk parts.. I would like to find a set of 12" passives without the weight to A/B test in my 1C's just to see if my findings are the same there as well.
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