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  1. #1

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    Default Advice on sub choice DB or MM 8"

    Hello, I'm new here and searching the forum for a couple of days without finding an answer to my question. So here it is:

    I'm heaving trouble deciding which sub to buy.
    I've got a lot of experience with various brands like RF, alpine, JBL, Kenwood, Clarion.

    My current setup is:

    Head Unit:
    Kenwood KDC-W808 (5v preout)
    4ch amp:
    Kenwood KAC-8401 (4x60W@4ohm)
    D-Class amp:
    Kenwood KAC-8151D (1x400W@2ohm)
    Front speakers:
    Macrom SE2.60 2way (6 1/4")
    Rear speakers:
    4x Macrom 59.10 midrange (4")

    In "storage":
    2x 12" Kenwood KFC-W3009
    1x 12" Rockfort Fosgate RFR2212 DVC (too much is not good for me!!!)

    Recently I bought myself another car. A Swift '94. And it's small. Real small.
    So the problem is, I heaven't got enough space in my trunk. And I really need to leave some useable space there. I don't want to use any of the subs I have.
    I tried to use my RFR2212 but I always end up with a terrible headache. Even when I don't listen at high volumes. It's just an SPL sub, and I really want SQ!!!
    The Kenwood sub doesn't sound right in a small sealed enclosure (0.85 cu ft). Both of these subs only play well at higher volumes. But most of the time I want to listen at lower levels.

    Here's what I made up:
    I want to order a Polk 8". Just one! And place it in a sealed enclosure. My Kenwood KAC-8151D (1x400W@2ohm) is a bit heavy but there's a good stable signal from the HU. And with the input sensitivity at 5v (minimal gain) I think the Polk 8" will play just fine. I know fore sure my amp runs best at 2ohms.

    So which Polk 8" to choose: the db840dvc or the mm840dvc.
    In the Netherland these subs are relatively expensive and I've got a small budget.
    db840dvc sells at €89,- and de mm840dvc sells at €139,-.

    My first choice would be the MM, but I noticed that a ported enclosure is not recommended. That could be a problem when I want to switch enclosures in the future.
    So right now I'm thinking of buying the db840dvc. But I only can find a box plan for the old db804.
    Is 0.35 cu.ft. not a bit small? The MM840 has plans for both 0.35 and 0.68 cu.ft. The 0.68 gives me a better feeling about the result.

    That's a lot of question for one thread (sorry), but here's a summary:

    Will one 8" sub give a nice "add' to my SQ system?
    Is one 8" sub suitable for my D-class amp?
    Is my choice for the DB840 good, or should a MM840 perform very much better?
    Which enclosue to build for the DB840 or MM840?


    Note:
    I've NEVER heard a polk playing, but because of the threads I've read so far, I'm sure they'le be just fine for me!
    Last edited by 809peter; 02-09-2010 at 08:55 AM.

  2. #2

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    The mm line is a step up in SQ over the db. Hits lower notes, handles more power, and a 5 db increase in efficiency is quite a bit. I think if you're used to larger subs a single db might not suit you.

    For the most part, polks are designed with sealed enclosures in mind. That's how you get the best SQ. If what you want is SQ, then the mm840 sealed is a great fit for your vehicle and amp.

    If the budget is tight, you could get your feet wet w/ the db840. There is a reason the mm840 is more expensive though :)

  3. #3

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    I had the mm840 in my truck roughly a year ago, and the sub fills in the bottom end quite well. mm840 isn't overpowering or loud, and will blend in quite well with my sr5250.

    As for the box enclosures, .38-.64 is the recommended sealed enclosure and is the best bet for getting the best sq out of mm840 sub. The more air their is in the box, the less accurate the sub will become in which the sub will produce a boomy/muddier sound. Anyways, you can always go bigger if you wanted, if you like the way the bigger enclosure sounds then who cares? You should just go with what works for you.

    And don't worry about the sealed enclosure being to small. If you really are a sq fan, you will never go back to a ported box again ;)

    And your amp is capable in powering the mm840s, just watch the gains and you will be fine.

  4. #4

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    @ DSkip
    Thanks for your reply.
    With your answer I can make up that the MM840 is better then the MM840. It makes sence. But I don't understand the why you mention the 5 db increase in efficiency. When I compare the specs in the pdf manuals of both subs I don't see the difference in efficiency. They're both 85dB. The only strange thing I noticed is that de MM840 SVC has a 89dB Sensitivity and the DVC 85dB. Strange?!?!?
    Above of all, I don't really know what this variable means in practice. Can you explain this in a few short words?

    Thanks for the advice, I really don't want my feet to get wet. OK it's a bit more expensive, but I rather pay a bit more, and feel satisfied.

  5. #5

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    @ chu

    The way you describe the MM840 nears my expectation of a sub. A nice blend, and not overpowering.

    The thing about the enclosure is not real clear for me.
    I'm used to getting a manuals with minimal, maximal and recommended enclosure size. The MM (and DB840 manuals tell me that the recommended size is .35. But at the box wizard page is see .35 and .68. Is there an explanation on this?
    Look, I don't really want the enclosure to be big (rather not), but I have bad experience with (12") subs in small sealed enclosures (like my kenwoods). (It could be a poor compearance).

    For now, I'm thinking about spending a bit more for the mm840. But I want to be sure to build a good enclosure for this sub. Right now I'm not.

  6. #6

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    http://www.polkaudio.com/caraudio/mm/specs.php#dual

    That's what I was going off. Here's a quick tidbit on efficiency

    http://everything2.com/title/Speaker+efficiency

  7. #7

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    Quote Originally Posted by 809peter View Post
    @ chu

    The way you describe the MM840 nears my expectation of a sub. A nice blend, and not overpowering.

    The thing about the enclosure is not real clear for me.
    I'm used to getting a manuals with minimal, maximal and recommended enclosure size. The MM (and DB840 manuals tell me that the recommended size is .35. But at the box wizard page is see .35 and .68. Is there an explanation on this?
    Look, I don't really want the enclosure to be big (rather not), but I have bad experience with (12") subs in small sealed enclosures (like my kenwoods). (It could be a poor compearance).

    For now, I'm thinking about spending a bit more for the mm840. But I want to be sure to build a good enclosure for this sub. Right now I'm not.
    The recommended space is .35-.5 cubic feet for the mm840dvc, so anywhere within the space will give you the best sq experience you can with the sub. I built mine with .35 sealed enclosure and stuffed it with polyester fiber if that helps any.

  8. #8

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    Quote Originally Posted by DSkip View Post
    http://www.polkaudio.com/caraudio/mm/specs.php#dual

    That's what I was going off. Here's a quick tidbit on efficiency

    http://everything2.com/title/Speaker+efficiency
    That freshens things up.
    The only strange thing on the polk site is there are diffent values from the same product. I get's me a bit confused.
    For example....
    the website http://www.polkaudio.com/caraudio/mm/specs.php#dual
    and the manual on http://www.polkaudio.com/downloads/m..._Sub_WebMN.pdf

    But before running off-topic. The most important thing is that you would surely recommend the mm840 above the db840. Isn't it?

  9. #9

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    Quote Originally Posted by chu View Post
    The recommended space is .35-.5 cubic feet for the mm840dvc, so anywhere within the space will give you the best sq experience you can with the sub. I built mine with .35 sealed enclosure and stuffed it with polyester fiber if that helps any.
    OK thanks.
    But where did you get the .5 from. I cannot seem to find any of this data.
    Do you get it with the manual in the box?

  10. #10

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    That is weird. If I put my money on it, I would expect the ones posted online to be correct. And yes, you will get a manual packaged with the sub.

    mm > db with any speaker, so if you don't mind spending the extra money, then go for the mm. I have two older mm 8"s and I think they are very nice subs.

  11. #11

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    I vote for the MM840. I have the one in my single cab pickup and it's a perfect match for my MM651's. It's a nice tight sound mounted in a sealed truck box stuffed with polyfill.
    Truck system so far...

    2007 Dodge Ram 1500 quad cab Hemi

    Kenwood KDC-X492 HU
    MM651 coaxials in doors

    Family Room:

    Panasonic TC-P50G25 50" Plasma
    Panasonic DMP-BD655K BDP
    XBOX 360 250GB
    Harman/Kardon HK3480(on loan)
    Monitor 70 Series II

  12. #12

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    Quote Originally Posted by 809peter View Post
    OK thanks.
    But where did you get the .5 from. I cannot seem to find any of this data.
    Do you get it with the manual in the box?
    Its off the manual that came with the mm840, buts the spec range is entirely from memory so I could be wrong.

  13. #13

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    Thanks guys !

    I made my mind up. I'm going to buy the MM840DVC because of the better specs and the negative advice of getting the DB840 (cause I was used on 12 inches).
    I also believe it's a better match with my KAC-8151D.
    A week ago, I was almost sure of getting the DB840, so I'm really happy asking this question.
    I don't want to get my feet wet.

    I will be back (in another threads) with questions about the box design.
    Square, sloped backside, etc...
    Last edited by 809peter; 02-14-2010 at 03:10 AM.

  14. #14

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    Mm840

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    Just ordered my Polk Sub MM840DVC.
    Happy and waiting.....

  16. #16

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    Hope it is everything you could ask for. Let us know how you like it after its in.

  17. #17

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    OK, Got my MM840 today.
    Mounted in my .35 sealed enclosure.

    Just did my first testrun. Now I'm sure Polk is the right choice for me.
    It sounds very good! It plays nice and subtle, but my amp can also let it pound very good.
    It's almost unbelievable how good this very tiny sub sounds.
    When I opened the box today, I was a bit in shock.... I thought, this is very small. Yes I never saw a 8"before.

    For now I'm more then satisfied with the result.
    And also surprised, because the .35 enclosure is so small.
    Thanks for the advice !!!

  18. #18

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    Glad you like it. I sold my 12" dbs to run 8" momos, and they sound every bit as good as the 12"s for the music I listen to. I always underestimated the 8" subs and what they were capable of until I got mine.

  19. #19

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    ack this has got me excited to try a few 8s :)

  20. #20

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    congrats, I was a little surprised on how small it looked when I opened my box too. But I can't say enough about the quality of the sound it produces.
    Truck system so far...

    2007 Dodge Ram 1500 quad cab Hemi

    Kenwood KDC-X492 HU
    MM651 coaxials in doors

    Family Room:

    Panasonic TC-P50G25 50" Plasma
    Panasonic DMP-BD655K BDP
    XBOX 360 250GB
    Harman/Kardon HK3480(on loan)
    Monitor 70 Series II

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