LSi15 Woofer mod, if a DB840 is good, would an MM840 be better?

I just picked up a mint set of LSi15 towers on Craigslist really cheap, so I can justify throwing a few hundred more at them, to milk the most performance from them.

I'm probably going to upgrade the woofers and the crossovers. The consensus on the forums seems to be that the Polk DB840 SVC woofer is the replacement driver of choice for most.

My question is, would the MM840 be an even cleaner, tighter, louder upgrade than the DB840? Or, what about a Focal 21A1 8, or a Focal 21-V2 8? Or a JL Audio 8W3V3-4? Just seems like those are higher quality choices than a DB series Polk driver. Any reason why one of those more expensive drivers wouldn't be better?

Comments

  • hochpt21hochpt21 Posts: 5,064
    I asked the same question when I did mine. Feedback basically said it hadn't been done. I went with what had been done and was very pleased with the results.

    I know that doesn't really answer your question, but the 840 was great.
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  • F1nutF1nut Posts: 40,664
    Any reason why one of those more expensive drivers wouldn't be better?

    Because the good folks at Polk took the time to figure out that the DB840 was the best upgrade replacement.
    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."


  • davidhawke30davidhawke30 Posts: 2
    edited February 2016
    F1 Nut... So the DB840 is an official recommendation of the Polk engineers? Can you please post the link to the write-up of their "official recommendation" ? I'd like to read their findings. Also, was that recommendation published prior to the release of the MM series driver?
  • pitdogg2pitdogg2 Posts: 11,553
    Link may be a goner it was on the old forum.... Like a lot of stuff we lost with the switch to vanilla.
  • EndersShadowEndersShadow Posts: 16,136
    F1 Nut... So the DB840 is an official recommendation of the Polk engineers? Can you please post the link to the write-up of their "official recommendation" ? I'd like to read their findings. Also, was that recommendation published prior to the release of the MM series driver?

    This was information given by a forum member that doesnt come around much that worked with the Polk engineers directly and this was discussed in person and the recommendation made to install the Db driver as well as add dynamat around the port tube. There is no "official" write up on it from Polk or anyone else and no real testing such as measurements, etc.

    But given the number of people that have done the mod and felt they benefited from it, I'd just trust it and go.

    I've seen one person use the MM drivers and that was in a LSi 25 scenario. Otherwise everyone just uses the db driver.

    Your welcome to make your own decision, but I trust the words of that forum member, and I have done the mod and can tell you it makes a BIG difference.
    "....not everything that can be counted counts, and not everything that counts can be counted." William Bruce Cameron, Informal Sociology: A Casual Introduction to Sociological Thinking (1963)
  • mikeyb128mikeyb128 Posts: 2,752
    I did this mod and was well worth the 150 bucks it cost. I would go with what is proven to work and sit back and enjoy the tunes.
    2 channel:
    Bryston 4B3, Bryston BDA3, Cary SLP05, Shanling CDT1000SE with parts conneXion level 2 mods, Nottingham analogue ace space 294, soundsmith Carmen MKii, Zu DL103 MKii, Ortofon MC 20 MKii, Dynavector XX2 MKii, Rogue Audio Ares, Core power technologies balanced power conditioner, Akiko Corelli power conditioner with Akiko Audio HQ power cable, Nordost heimdall 2, Frey 2, interconnects, speaker and power cables, Focal Electra 1028 BE 2, Auralic Aries Femto, Black diamond racing cones, ingress audio level 1 roller blocks, JL Audio E110 with Auralic subdude, Primacoustics room treatments.
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  • K_MK_M Posts: 1,057
    edited February 2016
    We did this mod a while back, and I think someone did measurements that backed up what it sounded like to us also. We saw that thread about it years ago.

    http://forum.polkaudio.com/discussion/89529/db840-sub-in-lsi15s-replace-the-stock-8-driver/p1

    It seemed that the bass was nearly identical as far as volume and deepness, but it was a good bit less boomy sounding in the upper bass sounds.

    As far as using another better quality woofer, there are a few things to consider.

    The bass port is very close to the stock woofer, and can not be extended for deeper bass sounds.

    The actual volume of the bass section on the Lsi15 is quite compact, and not many woofers will work better in this small a volume.

    We liked the Db840 "upgrade", but wondered why they did not use it to begin with?
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4,SDA 3.1TL, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • EndersShadowEndersShadow Posts: 16,136
    K_M wrote: »

    We liked the Db840 "upgrade", but wondered why they did not use it to begin with?

    Well to state the obvious cost. I also think the LSi line came out before this driver... And let's be honest, I wouldn't think its something MOST people would notice. I hold no illusion that we are are standard consumers lol....
    "....not everything that can be counted counts, and not everything that counts can be counted." William Bruce Cameron, Informal Sociology: A Casual Introduction to Sociological Thinking (1963)
  • K_MK_M Posts: 1,057
    K_M wrote: »

    We liked the Db840 "upgrade", but wondered why they did not use it to begin with?

    Well to state the obvious cost. I also think the LSi line came out before this driver... And let's be honest, I wouldn't think its something MOST people would notice. I hold no illusion that we are are standard consumers lol....

    Hmm.......trying to imagine how that would matter.... o:) Sarcasm Angel!
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4,SDA 3.1TL, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • skrolskrol Posts: 2,678
    I had looked at the specs for various Polk automobile subs comparing to the DB840. I had hoped to simulate with some speaker enclosure design software. The DXi804 looked like it might be a closer match. It isn't just the quality of the sub. The specs (Thiele / Small Parameters) are a bit different and may not match the LSi15's sub enclosure. The MM will is also SPL spec'd at 90dB vs the DB840's 85dB. I have a hard enough time taming the bass with the DB840.

    If anyone is feeling ambitious, I attached a spreadsheet with the Polk sub parameters that I collected. Perhaps someone can simulate for the LSi15 enclosure and report back.
    Stan

    Main 2ch:
    Polk LSi15 (DB840 upgrade), Parasound: P/LD-1100, HCA-1000A; Denon: DVD-2910, DRM-800A; Monster HTS3600-MKII, Grado SR-225i

    HT:
    Denon AVR-888, Polk: RTA11TL (RDO198-1, XO and Damping Upgrades), S4, CS250, PSW10, Marantz UD5005, Panasonic TC-P42S60

    Other stuff:
    Denon: DRA-835R, DCD-660, DRM-700A, DRR-780; Polk: S8, Monitor 5A, TSi100; Pioneer: CT-6R, PL-530; Onkyo CP-1046F; Ortofon OM5E, Marantz: PM5004, CD5004, Polk: RM7, Parasound C/PT-600, HCA-800ii
  • K_MK_M Posts: 1,057
    edited March 2016
    skrol wrote: »
    I had looked at the specs for various Polk automobile subs comparing to the DB840. I had hoped to simulate with some speaker enclosure design software. The DXi804 looked like it might be a closer match. It isn't just the quality of the sub. The specs (Thiele / Small Parameters) are a bit different and may not match the LSi15's sub enclosure. The MM will is also SPL spec'd at 90dB vs the DB840's 85dB. I have a hard enough time taming the bass with the DB840.

    If anyone is feeling ambitious, I attached a spreadsheet with the Polk sub parameters that I collected. Perhaps someone can simulate for the LSi15 enclosure and report back.

    I think the db840 42hz spec is the correct one. I see they list 2 other numbers.
    Rember also, not only is the box size significant, but the Vent, is limited physically, by it's close placement to the speaker magnet.
    It can not be extended any significant amount, to lower the box tuning frequency much at all without coming onto contact with the woofer magnet.
    That may be more of the limitation than anything else, in regards to getting deeper bass.

    Another issue, the Lsi bass enclosure, is quite small. I think about .72-.75 cuft.

    That limits low end extension with many woofers right from the get go!

    I do not think that the 90db sensitivity in itself is a huge issue, but with the the stock woofer and the db840 have an excess of energy in the 90-150 hz range.

    The deepest bass is several decibels lower in level in comparison.
    At our house, we experimented a good bit, with this stuff and even tried running the stock Lsi15 woofers, from an outboard sub amp.

    Boosting the overall level of the stock side mounted "sub", a bit, and rolling off the upper bass made it a lot more listenable overall.
    The deep bass is there, but the upper bass is simply over powering.

    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4,SDA 3.1TL, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • K_MK_M Posts: 1,057
    edited March 2016
    8iy32g0yq32z.jpg


    We measured the stock woofer very near field, and got this.

    as you can see 42 Hz was the frequency of the box tuning and the red curve is the port, the green the woofer itself.
    The levels are not accurate as they were measured very close.
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4,SDA 3.1TL, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • K_MK_M Posts: 1,057
    px3wblcgu3rs.jpg

    This I believe is the stock woofer, with stock crossover, and one we modded to create the curve that is lower in level for the upper bass.
    Looking for all the other files we created, but not finding them all!

    We had several dozen comparing stock woofer, with db840 and other mods we experimented with.

    In the end I think the one above with the rolled off upper bass, was almost exactly like the db840 but using the stock crossover.
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4,SDA 3.1TL, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • K_MK_M Posts: 1,057
    To answer the OP question, yes there are technically better woofers available, including the MM840, but the physical limitations of the port almost contacting the woofer magnet as is, precludes extending it more than a small fraction of an inch, hence not being able to take advantage of deeper bass tuning with a longer port.
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4,SDA 3.1TL, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • Hi all, copying it here from.a other thread.

    Just registered here to say that although the DB840 upgrade does make the LSi15 bass sound tight and nice, the MM840 sub destroyed the DB840 in my LSi15s with modded crossovers. Whereas the db840 makes the bass tight, the mm840 takes the bass even deeper, punchier, more dynamic and even thunderlike. I'd recommend anyone considering db840 swap to try mm840 as well. Make sure you use all 8 screws to make sure your mighty mm840 is secured tight in there.

    I should note that the crossovers in my LSi15s are modded, this is yet another way to make your LSi15s sound much better. Just in case, I drive my LSi15s with a pair of fully modded Adcom GFA-565 monoblocs.
    qudh67zgcj0y.jpeg
    svin7c39fc51.jpeg

    Cheers.
  • F1nutF1nut Posts: 40,664
    The DB840 mod was designed and tested by Polk engineers to blend with the rest of the speaker. Something to consider.
    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."


  • Well it seems it was more of an opinion expressed by someone at Polk concerning LSi woofer upgrade - as stated by some of the Polk forums members.

    There's something else to consider here - the crossovers for the LSi15 speakers were designed and tested by Polk as well and there is a lot to be tweaked there. Check vr3 mod among others.

    Lsi15 is a very good speaker as when carefully tweaked it sounds way, way better. Cheers for Polk designers and testers for that.
  • F1nutF1nut Posts: 40,664
    One of the members worked with the Polk engineers in developing the mod.

    One can modify and improve most speakers because companies have to work with price points.
    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."


  • K_MK_M Posts: 1,057
    mm840lsi15 wrote: »
    Well it seems it was more of an opinion expressed by someone at Polk concerning LSi woofer upgrade - as stated by some of the Polk forums members.

    There's something else to consider here - the crossovers for the LSi15 speakers were designed and tested by Polk as well and there is a lot to be tweaked there. Check vr3 mod among others.

    Lsi15 is a very good speaker as when carefully tweaked it sounds way, way better. Cheers for Polk designers and testers for that.

    Did you try to alter the box tuning frequency at all?
    I posted a graph above showing the measured response of one pair of our Lsi15 with the stock woofer before the db840 change.
    Lsi15, Lsi9, LsiC,Rta11t,M5jr+,M4,SDA 3.1TL, SDA SRS 2.3TL, Rti6....Still listing stuff, a work in progress.
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  • Airplay355Airplay355 Posts: 4,272
    Did you modify the power port tube to accommodate the depth of the larger MM woofer?
  • K_M wrote: »
    mm840lsi15 wrote: »
    Well it seems it was more of an opinion expressed by someone at Polk concerning LSi woofer upgrade - as stated by some of the Polk forums members.

    There's something else to consider here - the crossovers for the LSi15 speakers were designed and tested by Polk as well and there is a lot to be tweaked there. Check vr3 mod among others.

    Lsi15 is a very good speaker as when carefully tweaked it sounds way, way better. Cheers for Polk designers and testers for that.

    Did you try to alter the box tuning frequency at all?
    I posted a graph above showing the measured response of one pair of our Lsi15 with the stock woofer before the db840 change.

    I refitted the dampening material around the tube and all around the box.
    Airplay355 wrote: »
    Did you modify the power port tube to accommodate the depth of the larger MM woofer?

    I did not modify the power port as the mm840 fits nicely without any modification. I wired the subs to 2ohms. The nominal speaker impedance is around 3 ohms now but you know the impedance goes up and down with the frequency played by the speaker. I use my LSi15 with mm840 mod with my Adcom GIA-275, Adcom GCA-510, Adcom GFA-565 monos and GFA-5802 with no issues. Please let me know if you'd like to see additional pics.
  • Airplay355Airplay355 Posts: 4,272
    Oh cool, I thought you'd need more space in there. How come you didn't get the SVC version so you didn't have to lower the impedance?
  • Airplay355 wrote: »
    Oh cool, I thought you'd need more space in there. How come you didn't get the SVC version so you didn't have to lower the impedance?

    I couldn't find the SVC version anywhere so I went for the DVC and from what I could hear, the 2ohm wired DVC sub sounded way punchier and better to my ears that when wired to 8ohm impedance. Having lower impedance didn't really bother me as I use nicely tweaked Adcoms with these beautiful speakers and Adcoms are known to control low impedance speakers with no issues.
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