Westmassguy's Idea: Employing Damping to Mitigate Comb Filtering and Lobing

Polk Folks:

I have a pair of 1980 vintage RTA-12's that I have been modding for months. I had done most all the standard Polk Forum recommended improvements, the latest being a complete Westmassguy crossover rebuild with Sonicaps/Mills resistors (see David's post "RTA-12 Original Project" in the DIY, Mods & Tweaks category). One job remaining was to install Sonic Barrier or Blackhole 5 inside the cabinet. Before starting David suggested that we experiment with damping material. David explained that since these speakers (and other Polk models) have two drivers side by side, producing the same frequencies, problems can occur such as lobing and comb filtering. He explained that this can affect the virtual point source created by the tweeter and woofers, and that smearing and loss of detail are common problems. Since later versions of the RTA-12 had the outer woofers rolled off by the crossover at 600 Hz, David suggested that we try overdamping the outer woofers and use the standard four-inch strip behind the inner woofers. To accomplish this we needed to extend the original 4x9 inch brace from the top of the cabinet down between the woofers to the exact bottom of the woofer openings. Basically, as David described we needed to create a three-sided box around the outer woofers so all three inner sides could be completely covered with damping material. David explained that deep bass frequencies would not be affected, but upper bass and midrange would be altered on the outer drivers, so less comb filtering and lobing would occur resulting in a more precise image between the two speakers.

The results of this were more than successful. These speakers, which already performed quite well, now have much improved imaging, even greater detail/resolution, improved clarity and they disappear behind a nice wide soundstage. Bass is huge, if the recording goes low, I can really feel it. I did replace the gaskets on the drivers and PRs in this latest project so there is definitely no air leakage. The damping material has also eliminated this speaker's tendency to become "shouty" at high volume (Nightfall has noted this as well in other postings). Also, the relative balance of midrange, bass, and high frequencies is the most realistic I have ever heard from these speakers (midrange was a bit much previously from all that backwave rolling around in the cabinet?).

If you have a Polk model with the dual drivers producing the same frequency this mod will take them to the next level.

The most difficult aspect of this job is cutting and installing the extension to the existing brace. Using a table saw I cut the appropriate amount of 5/8 plywood in an "L" shape to within 1/16 tolerance (and of course each speaker is a bit different...), so that I could wedge the extension in there and epoxy it without fasteners or clamps. You want it bombproof. I used PC Woody wood epoxy as it is a putty, has great gap filling properties, does not drip/run, and does not cure by the evaporation of solvent. I employed a small detail sander that could access the woofer openings to smooth the joints before installing the damping. I used the thickest version of Sonic Barrier. Because of all the flat bracing on the sides and back of in the cabinet, there was very little flat surface, so I had to cut and fit the Sonic Barrier in like the tiles on the space shuttle. I did my cuts with a band saw, which worked very well with next to no waste. The poly batting was reinstalled behind the drivers up above the PR area.

Sorry about the lack of pictures. I was so intent on getting this finished I forgot to photograph what I was doing.

All the credit for this mod goes to Westmassguy (thank you David!). His idea, his genius, his patience, his time and effort to think it through and explain it all. We're the ones that get to sit back end enjoy his fine work (our new crossovers) and his advice.
Polk Audio first generation RTA-12s; 12 inch Polk Stands; DHS Speaker Service upgraded crossovers w/ Sonicap/Mills; the "westmassguy anti-lobing mod" (hyperdamped outer drivers/mirror imaged); tweeter anti-diffraction mod; Cardas binding posts; Neotech UPOCC internal wire; foam-lined inner driver baskets; xschop phase plugs; deleted fuses; Hurricane nuts; Sonic Barrier; Dynamat Xtreme
Ayre K-5xeMP preamplifier
Cambridge Audio 840C CD player; Herbie's Audio Lab Super Black Hole CD Mat
D-Sonic Custom Audio M3a-600M monoblock amplifiers
NAD 4155 FM/AM tuner
Silnote Audio Morpheus Reference II Series II balanced interconnects; Virtue Audio single-ended interconnects
Kimber 12TC speaker cable w/Furez connectors; VH Audio Flavor 4 power cables w/Furutech connectors
Herbie's Audio Lab system isolation: Tenderfeet, Big Fat Dots, Grungebuster Dots, Little Fat Gliders
Dedicated 20A/10 AWG circuit; Furutech GTX-D (G) outlet; Furutech eTP80; Shunyata Research Venom Defender; Synergistic Research Orange fuses
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Comments

  • voltz
    voltz Posts: 5,384
    That sound awesome! WTG Jazz & Dave.

    Dave created these damping boards for my CRS's that also tighten some bass and reduce some shout. His Experience is really paying off for us ;)
    2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge

    HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD
  • westmassguy
    westmassguy Posts: 6,850
    Great write-up Stephen. Glad it did what I thought it would. Never hurts to try new things. It's purpose is simple, reduce the inherent smearing of the image caused by the side by side woofer arrangement.
    Darryl, this would apply to your Monitor 10s too.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • Jazzhead
    Jazzhead Posts: 520
    Just for kicks I thought I would list everything I have done to these speakers:

    -Replaced binding posts with Cardas posts on black painted aluminum discs.
    -Added a layer of dampening material between crossovers and top of cabinet.
    -Westmassguy crossover rebuild with Sonicaps/Mills resistors.
    -Sonic Barrier as described above.
    -Replaced stock internal wiring with Neotech 14 gauge stranded OCC wire.
    -Dynamat on woofer/passive radiator baskets, and inside of binding post plate.
    -Epoxied driver magnets.
    -Added screws to passive radiators where Polk did not install them.
    -Replaced driver and passive radiator gaskets.
    -Sealed the cabinet with Loctite Power Grab.
    -Filled the inside of the crossover coil spools with Mortite to add weight/mass.
    -Filled the inside of the 12 inch Polk Stands with sand and epoxied them together.
    -Speakers are decoupled from stands with Herbie's Audio Labs "Big Fat Dots".
    -Stands decoupled from wood floor with Herbie's Audio Labs "Little Fat Gliders".
    -Periodic application of Deoxit Gold to connections, fuses etc.

    In order of impact, the greatest gains came from David's crossover rebuild, the damping work described above, replacing the binding posts, using the Herbie's Big Fat Dots, and replacing the internal wiring. The other stuff adds up as well, especially isolating the crossover from vibration noticeably improves resolution. I wish you folks could hear these speakers, Matthew Polk would get a kick out of them for sure.


    Polk Audio first generation RTA-12s; 12 inch Polk Stands; DHS Speaker Service upgraded crossovers w/ Sonicap/Mills; the "westmassguy anti-lobing mod" (hyperdamped outer drivers/mirror imaged); tweeter anti-diffraction mod; Cardas binding posts; Neotech UPOCC internal wire; foam-lined inner driver baskets; xschop phase plugs; deleted fuses; Hurricane nuts; Sonic Barrier; Dynamat Xtreme
    Ayre K-5xeMP preamplifier
    Cambridge Audio 840C CD player; Herbie's Audio Lab Super Black Hole CD Mat
    D-Sonic Custom Audio M3a-600M monoblock amplifiers
    NAD 4155 FM/AM tuner
    Silnote Audio Morpheus Reference II Series II balanced interconnects; Virtue Audio single-ended interconnects
    Kimber 12TC speaker cable w/Furez connectors; VH Audio Flavor 4 power cables w/Furutech connectors
    Herbie's Audio Lab system isolation: Tenderfeet, Big Fat Dots, Grungebuster Dots, Little Fat Gliders
    Dedicated 20A/10 AWG circuit; Furutech GTX-D (G) outlet; Furutech eTP80; Shunyata Research Venom Defender; Synergistic Research Orange fuses
  • Nice tweak! Make certain to mark the back of your cabs as you have now made them L & R speakers. This could change how the Monitor 10, 11 & early 12 reputation stands within the lineup.
    HT Optoma HD25 LV on 80" DIY Screen, Anthem MRX 300 Receiver, Pioneer Elite BDP 51FD Polk CS350LS, Polk SDA1C, Polk FX300, Polk RT55, Dual EBS Adire Shiva 320watt tuned to 17hz, ICs-DIY Twisted Prs, Speaker-Raymond Cable

    2 Channel Thorens TD 318 Grado ZF1, SACD/CD Marantz 8260, Soundstream/Krell DAC1, Audio Mirror PP1, Odyssey Stratos, ADS L-1290, ICs-DIY Twisted , Speaker-Raymond Cable
  • westmassguy
    westmassguy Posts: 6,850
    Nice tweak! Make certain to mark the back of your cabs as you have now made them L & R speakers. This could change how the Monitor 10, 11 & early 12 reputation stands within the lineup.
    Yes, you'll have to mark them after the modification. I haven't seen a Monitor 11, but there was an RTA-11, which appears to have a band-pass filter on one of the woofers.
    The schematic is hand drawn, and doesn't specify which woofer the filter connects to.


    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • The Monitor 11 looks like a 10 on steroids. It has a larger cabinet and 12 inch PR. I don't know what the schematic for this model looks like as they are more rare.
    HT Optoma HD25 LV on 80" DIY Screen, Anthem MRX 300 Receiver, Pioneer Elite BDP 51FD Polk CS350LS, Polk SDA1C, Polk FX300, Polk RT55, Dual EBS Adire Shiva 320watt tuned to 17hz, ICs-DIY Twisted Prs, Speaker-Raymond Cable

    2 Channel Thorens TD 318 Grado ZF1, SACD/CD Marantz 8260, Soundstream/Krell DAC1, Audio Mirror PP1, Odyssey Stratos, ADS L-1290, ICs-DIY Twisted , Speaker-Raymond Cable
  • westmassguy
    westmassguy Posts: 6,850
    The Monitor 11 looks like a 10 on steroids. It has a larger cabinet and 12 inch PR. I don't know what the schematic for this model looks like as they are more rare.
    That's what the original RTA-11(Model 11 in the literature) looked like as well.
    The RTA-11 had Peerless Tweeters.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • JPete
    JPete Posts: 295
    The Monitor 11 looks like a 10 on steroids. It has a larger cabinet and 12 inch PR. I don't know what the schematic for this model looks like as they are more rare.
    That's what the original RTA-11(Model 11 in the literature) looked like as well.
    The RTA-11 had Peerless Tweeters.

    I think they look like SDA 2As, not on steroids. But I guess that can go either way.

    The early R.T.A. 11s (Model 11s) are labeled left and right, and the inside mid driver of each cabinet has a foam baffle behind it. Both mid drivers are 6600x, tweets are peerless and passive is 12".

    Which mid would you think has the band pass filter implemented based on the information about foam baffle behind the inside drivers?
    Lexicon RT-10, Parasound P5, McCormack DNA 0.5, Polk SDA CRS+, SVS Sub
    Schiit Modi, Luminous Audio Axiom II, McCormack DNA-1, Digital Phase AP 2
    Marantz AV7701, Emotiva XPA-5, Paradigm 11se Mkii, DCM Time Windows, NHT 2C, SVS Sub

    Spares - Kenwood C1 Pre, NAD 2200PE, Polk Monitor 10B, Polk Model 11, other odds and ends
  • westmassguy
    westmassguy Posts: 6,850
    JPete wrote: »
    The Monitor 11 looks like a 10 on steroids. It has a larger cabinet and 12 inch PR. I don't know what the schematic for this model looks like as they are more rare.
    That's what the original RTA-11(Model 11 in the literature) looked like as well.
    The RTA-11 had Peerless Tweeters.

    I think they look like SDA 2As, not on steroids. But I guess that can go either way.

    The early R.T.A. 11s (Model 11s) are labeled left and right, and the inside mid driver of each cabinet has a foam baffle behind it. Both mid drivers are 6600x, tweets are peerless and passive is 12".

    Which mid would you think has the band pass filter implemented based on the information about foam baffle behind the inside drivers?

    No clue. The schematic is cutoff. the drivers are listed 1 & 2
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • lawdogg
    lawdogg Posts: 449
    Does the new divider go from the top of the cabinet down vertically and meet with the already-existing divider between the midwoofers, bisecting the tweeter? Or does the new divider go from the top of the already-existing divider and extend sideways to the cabinet wall above the outer midwoofer, like a 'cap' to the 3-sided enclosure?

    I ask because I'd love to try this on my Monitor 10s! Nice work!
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
  • westmassguy
    westmassguy Posts: 6,850
    Extend the divider up to meet the top of the cabinet.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • Jazzhead
    Jazzhead Posts: 520
    When I did my damping work, I applied the Sonic Barrier to the back of the cabinet, and to the right and left of the outer woofers - inside that three-sided box that was created by extending the brace. I did not apply any Sonic Barrier to the top inside of the cabinet. Now that we've done this much, David and I think I should go back in and do the top as well and give a listen. I'm going to order some more Sonic Barrier and I will report back after I do the 4th side of the box. My sense is that doing this will only accentuate the positive effects of this mod.
    Polk Audio first generation RTA-12s; 12 inch Polk Stands; DHS Speaker Service upgraded crossovers w/ Sonicap/Mills; the "westmassguy anti-lobing mod" (hyperdamped outer drivers/mirror imaged); tweeter anti-diffraction mod; Cardas binding posts; Neotech UPOCC internal wire; foam-lined inner driver baskets; xschop phase plugs; deleted fuses; Hurricane nuts; Sonic Barrier; Dynamat Xtreme
    Ayre K-5xeMP preamplifier
    Cambridge Audio 840C CD player; Herbie's Audio Lab Super Black Hole CD Mat
    D-Sonic Custom Audio M3a-600M monoblock amplifiers
    NAD 4155 FM/AM tuner
    Silnote Audio Morpheus Reference II Series II balanced interconnects; Virtue Audio single-ended interconnects
    Kimber 12TC speaker cable w/Furez connectors; VH Audio Flavor 4 power cables w/Furutech connectors
    Herbie's Audio Lab system isolation: Tenderfeet, Big Fat Dots, Grungebuster Dots, Little Fat Gliders
    Dedicated 20A/10 AWG circuit; Furutech GTX-D (G) outlet; Furutech eTP80; Shunyata Research Venom Defender; Synergistic Research Orange fuses
  • tophatjohnny
    tophatjohnny Posts: 4,162
    Everything David does is done right. He is a perfectionist! Honored to call him my friend and brother!! Great review!!
    "if it's not fun, it's not worth it & remember folks, "It's All About The Music"!!
    *****************************
  • westmassguy
    westmassguy Posts: 6,850
    Everything David does is done right. He is a perfectionist! Honored to call him my friend and brother!! Great review!!
    Thanks Brother

    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • stogie
    stogie Posts: 230
    Jazzhead, When you're back inside the cabinets could you snap a few pics? I have a pair of 10A's I may try this on.
    Speakers: Polk SDA-SRS xovers rebuilt by David, RDO194's, Dynamat, BH5, glued magnets, new cloth, custom aluminum terminal plates with Cardas posts and Speakon interconnect
    Speaker Cables, Jumpers & Interconnect: DIY Douglas Connection
    Power Amp: Sunfire Architect's Choice Series II
    Preamp: Adcom GFP-750
    SACD/CD: Oppo BDP-95
    Tuner: Sansui TU-717
    TT: Technics SL-MA1
    Phono Pre: Emotiva XPS-1
    Music Server: Mac Mini w/JRiver - iPad w/JRemote
    DAC: Eastern Electric MiniMax Plus
    Other Polks: SDA: 1A, 1C, 2B, CRS+ / Monitor: 10A, 5jr, 4 / RT5
  • Jazzhead
    Jazzhead Posts: 520
    Stogie: I will do that (photos). I regret that I didn't previously. I gather that the bracing is different on my RTA-12's compared to the 10's and others (RTA-12 tweeter sits atop the cabinet) but the idea is the same. Basically, you just have to construct something solid to attach the damping material to so you can do all three sides of the box you have created (and probably the top). just leaving that bottom side open to the rest of the cabinet.
    Polk Audio first generation RTA-12s; 12 inch Polk Stands; DHS Speaker Service upgraded crossovers w/ Sonicap/Mills; the "westmassguy anti-lobing mod" (hyperdamped outer drivers/mirror imaged); tweeter anti-diffraction mod; Cardas binding posts; Neotech UPOCC internal wire; foam-lined inner driver baskets; xschop phase plugs; deleted fuses; Hurricane nuts; Sonic Barrier; Dynamat Xtreme
    Ayre K-5xeMP preamplifier
    Cambridge Audio 840C CD player; Herbie's Audio Lab Super Black Hole CD Mat
    D-Sonic Custom Audio M3a-600M monoblock amplifiers
    NAD 4155 FM/AM tuner
    Silnote Audio Morpheus Reference II Series II balanced interconnects; Virtue Audio single-ended interconnects
    Kimber 12TC speaker cable w/Furez connectors; VH Audio Flavor 4 power cables w/Furutech connectors
    Herbie's Audio Lab system isolation: Tenderfeet, Big Fat Dots, Grungebuster Dots, Little Fat Gliders
    Dedicated 20A/10 AWG circuit; Furutech GTX-D (G) outlet; Furutech eTP80; Shunyata Research Venom Defender; Synergistic Research Orange fuses
  • lawdogg
    lawdogg Posts: 449
    Extend the divider up to meet the top of the cabinet.

    Thanks - and polyfill, cut it in half and stuff it like normal but just in 2 pieces?
    <3 my 3.1TLs

    I will fix your shifted magnets for free. :)
  • westmassguy
    westmassguy Posts: 6,850
    lawdogg wrote: »
    Extend the divider up to meet the top of the cabinet.

    Thanks - and polyfill, cut it in half and stuff it like normal but just in 2 pieces?

    Divvy up what batting you have equally between each side, behind the woofers.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • voltz
    voltz Posts: 5,384
    I figured this would work for my 10's based on how the 12' & 11's & 10's and SDA 2's are so much alike with the 2 side by side drivers.

    Here in a month or so I will do this also and check it out.
    2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge

    HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD
  • westmassguy
    westmassguy Posts: 6,850
    voltz wrote: »
    I figured this would work for my 10's based on how the 12' & 11's & 10's and SDA 2's are so much alike with the 2 side by side drivers.

    Here in a month or so I will do this also and check it out.
    After you sent me your BH5 no less. I can send back what I haven't used Brother.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • voltz
    voltz Posts: 5,384
    No I'm good right now Dave! :) It will be awhile before I'm ready to dig into cabinets, as my free time is a little limited right now. but this has my curiosity up especially after playing around with some SDA 2B crossovers in them for fun!

    But this is a neat little way of adding a little more life & Fun into the M10's! pretty dang cool B)
    2 ch- Polk CRS+ * Vincent SA-31MK Preamp * Vincent Sp-331 Amp * Marantz SA8005 SACD * Project Xperience Classic TT * Sumiko Blue Point #2 MC cartridge

    HT - Polk 703's * NAD T-758 * Adcom 5503 * Oppo 103 * Samsung 60" series 8 LCD
  • So, this would work with SDA SRS 2s ?
  • TForan wrote: »
    So, this would work with SDA SRS 2s ?

    No need as SDAs have different signals in the side by side drivers.
    HT Optoma HD25 LV on 80" DIY Screen, Anthem MRX 300 Receiver, Pioneer Elite BDP 51FD Polk CS350LS, Polk SDA1C, Polk FX300, Polk RT55, Dual EBS Adire Shiva 320watt tuned to 17hz, ICs-DIY Twisted Prs, Speaker-Raymond Cable

    2 Channel Thorens TD 318 Grado ZF1, SACD/CD Marantz 8260, Soundstream/Krell DAC1, Audio Mirror PP1, Odyssey Stratos, ADS L-1290, ICs-DIY Twisted , Speaker-Raymond Cable
  • westmassguy
    westmassguy Posts: 6,850
    TForan wrote: »
    So, this would work with SDA SRS 2s ?

    No need as SDAs have different signals in the side by side drivers.
    This^^^^^^^^^^^^^
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • xschop
    xschop Posts: 4,636
    What would be the inductor value added inline to one of the woofers, if going that route to ameliorate the lobing?
    Don't take experimental gene therapies from known eugenicists.
  • westmassguy
    westmassguy Posts: 6,850
    Something in the 2-3mH range, #18 gauge. You'll see a 90 degree shift in phase, so experiment. You may have to add a shunt inductor too, after the cap, but before the woofer..
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/
  • TForan wrote: »
    So, this would work with SDA SRS 2s ?

    No need as SDAs have different signals in the side by side drivers.

    Ok, thanks.
  • Jazzhead
    Jazzhead Posts: 520
    OK folks, I ordered some additional Sonic Barrier and went back inside my original model RTA-12's and installed some to the top of the cabinet creating a 4-sided box around the outer drivers. As David and I expected, the sonic results were more of a good thing. The imaging is more precise, the music clearer still, and the soundstage is larger and more disembodied from the speakers. This is definitely a mod worth doing. Quality and quantity of bass if anything, is better. I remembered to shoot some pics when I was working which show the 4-sided box of Sonic Barrier, and you can see the extended brace, which comes down to exactly the bottom of the driver openings. Just to remind folks, the inner drivers got the standard 4-inch strip on the back wall of the cabinet.

    3kt8pt3tih82.jpg
    6fqqzixh315q.jpg
    61q0ufp162mc.jpg
    Polk Audio first generation RTA-12s; 12 inch Polk Stands; DHS Speaker Service upgraded crossovers w/ Sonicap/Mills; the "westmassguy anti-lobing mod" (hyperdamped outer drivers/mirror imaged); tweeter anti-diffraction mod; Cardas binding posts; Neotech UPOCC internal wire; foam-lined inner driver baskets; xschop phase plugs; deleted fuses; Hurricane nuts; Sonic Barrier; Dynamat Xtreme
    Ayre K-5xeMP preamplifier
    Cambridge Audio 840C CD player; Herbie's Audio Lab Super Black Hole CD Mat
    D-Sonic Custom Audio M3a-600M monoblock amplifiers
    NAD 4155 FM/AM tuner
    Silnote Audio Morpheus Reference II Series II balanced interconnects; Virtue Audio single-ended interconnects
    Kimber 12TC speaker cable w/Furez connectors; VH Audio Flavor 4 power cables w/Furutech connectors
    Herbie's Audio Lab system isolation: Tenderfeet, Big Fat Dots, Grungebuster Dots, Little Fat Gliders
    Dedicated 20A/10 AWG circuit; Furutech GTX-D (G) outlet; Furutech eTP80; Shunyata Research Venom Defender; Synergistic Research Orange fuses
  • stogie
    stogie Posts: 230
    @Jazzhead, thanks for the pics. is that 1 1/4" sonic barrier? (that's what I have on hand) how much poly-fill batting do you stuff in the new enclosure?
    Speakers: Polk SDA-SRS xovers rebuilt by David, RDO194's, Dynamat, BH5, glued magnets, new cloth, custom aluminum terminal plates with Cardas posts and Speakon interconnect
    Speaker Cables, Jumpers & Interconnect: DIY Douglas Connection
    Power Amp: Sunfire Architect's Choice Series II
    Preamp: Adcom GFP-750
    SACD/CD: Oppo BDP-95
    Tuner: Sansui TU-717
    TT: Technics SL-MA1
    Phono Pre: Emotiva XPS-1
    Music Server: Mac Mini w/JRiver - iPad w/JRemote
    DAC: Eastern Electric MiniMax Plus
    Other Polks: SDA: 1A, 1C, 2B, CRS+ / Monitor: 10A, 5jr, 4 / RT5
  • westmassguy
    westmassguy Posts: 6,850
    Looks great Stephen!
    @Jazzhead just divvy up what you have in there now, between the two sides.
    Home Theater/2 Channel:
    Front: SDA-2ATL forum.polkaudio.com/discussion/143984/my-2as-finally-finished-almost/p1
    Center: Custom Built forum.polkaudio.com/discussion/150760/my-center-channel-project/p1
    Surrounds & Rears: Custom Built forum.polkaudio.com/discussion/151647/my-surround-project/p1
    Sonicaps, Mills, RDO-194s-198s, Dynamat, Hurricane Nuts, Blackhole5
    Pioneer Elite VSX-72TXV, Carver PM-600, SVS PB2-Plus Subwoofer

    dhsspeakerservice.com/