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

Jazzhead

Stogie: That is indeed the 1 1/4 Sonic Barrier - the thickest version. I had almost enough from one sheet to do my cabinets, which are larger than 10's, so one sheet may be enough for you.

Jazzhead

One more thing to add to this discussion... If you do Dave's mod as described above be prepared to experiment with the placement of your speakers, specifically the toe-in. The original Polk instructions recommending quite a bit of toe-in (which I applied to some degree in my room) don't seem to apply any more. I've settled on very little toe-in which now produces the largest, clearest soundstage I have ever heard them produce.

voltz

I got a board and cut it for my 10's to expand the center divider board all the wall to the top and have one speaker finish except for the Sonic-barrier which says monday now for delivery. Have not started no#2 yet.

will report back when finished!

westmassguy

voltz wrote: »

I got a board and cut it for my 10's to expand the center divider board all the wall to the top and have one speaker finish except for the Sonic-barrier which says monday now for delivery. Have not started no#2 yet.

will report back when finished!

Get'r Done! Slacker

stogie

@voltz When you expanded the center divider to the top, how did you get around the tweeter centered above the two MW's? Any pictures? thanks, don

voltz

After it was cut to size and while I was test fitting it, I just mark it with a pencil thru the tweeter hole. then clamp it to my portable table and used a jig saw.

only took about a 3/8 deep cut.

Gardenstater

Great thread! How did the M10 mod turn out?

Edit - I see voltz hasn't been around in quite a while.

Really impressive RTA12 mod. These are the speakers I lusted after circa 1979 when all I could afford were my 7Bs!

Jazzhead

I had great success with this. I really appreciate Dave thinking out of the box on this one and taking the time and effort to help me because it opened up the door for these speakers to perform at a much higher level. One wrinkle I had to work out was the polyfill. When my speakers were built someone stuffed them with so much polyfill that I could not physically get it all up above the PR area. I spent a while listening until I settled on a "just enough" amount to get correct sounding bass. I also fabricated a tweeter diffraction ramp/device much like the 12B/12C (but with a slightly larger footprint) from dynamatted aluminum that was another huge leap forward. The fuses have also been deleted (my amps run at 800 wpc so no danger of clipping). These speakers are now very detailed and are capable of some really "spooky" imaging. Sometimes I play a particularly nice recording and shake my head at how good some 42 year old Polks can sound.

Hansvelton

Jazzhead wrote: »

Polk Folks:

I have a pair of 1980 vintage RTA-12's that I have been modding for months.

Forgive me, but that sounds like the introduction to a 12 step program.....

gp4jesus

More pics please?

Livinloud

🤯 I am going to have to really consider this one… the Monitor 11’s I have would benefit from this. I was considering keeping all mods reversible and I like them how they are but… like I said in another thread, I am enjoying the rabbit hole. The biggest downside is that BH5 is pricey!

rodman53

You might want to try Sonic Barrier from Parts Express. Some say it works about as well as BH5.
Sonic Barrier from Parts Express 1 1/4" thick sheet 18x24 $29.98

westmassguy

The Sonic Barrier works quite well. No, it's not Black Hole 5, but for the price, it's well worth it. As mentioned, purchase the 1 1/4"

plastic_avatar

I've been reading up on this tonight. Great work, guys. Wow.

If I tried this on my Monitor 12:

- it's an extension to the top and to the bottom of the lower mids

- 1.25in Sonic Barrier on the top, back, and sides of the outer mw chambers

- no poly in the outer chamber, but original poly in the inner chamber?

westmassguy

plastic_avatar wrote: »

I've been reading up on this tonight. Great work, guys. Wow.

If I tried this on my Monitor 12:

- it's an extension to the top and to the bottom of the lower mids

- 1.25in Sonic Barrier on the top, back, and sides of the outer mw chambers

- no poly in the outer chamber, but original poly in the inner chamber?

Sounds about right

Jazzhead's photos

joebass3

plastic_avatar wrote: »

- no poly in the outer chamber, but original poly in the inner chamber?

@westmassguy answered this question earlier in this thread. Is that still the preferred method Dave?

"lawdogg wrote: »
» show previous quotes
Thanks - and polyfill, cut it in half and stuff it like normal but just in 2 pieces?
westmassguy wrote:
Divvy up what batting you have equally between each side, behind the woofers".

westmassguy

joebass3 wrote: »

plastic_avatar wrote: »

- no poly in the outer chamber, but original poly in the inner chamber?

@westmassguy answered this question earlier in this thread. Is that still the preferred method Dave?

"lawdogg wrote: »
» show previous quotes
Thanks - and polyfill, cut it in half and stuff it like normal but just in 2 pieces?
westmassguy wrote:
Divvy up what batting you have equally between each side, behind the woofers".

Unless @Jazzhead modified it, no batting in the lined side

Jazzhead

It comes down to where the polyfill will fit without over-compressing it. If you compress it against the entire back of the midwoofers and don't leave a window with both drivers for air/soundwaves to access the PR you'll lose slam, bass, kill the life (@westmassguy knows I learned the hard way, lol) I have little in the damped side, because there wasn't much room left. Different speaker models will have different amounts of room left. There's a reason the Polk engineers chose a given amount so I'd try to stay with the original amount as much as possible. You don't want it below the midwoofers, however. My stock speakers had it stuffed up top, and a large amount down in the PR area (Polk employee error?). I was forced to remove some, but currently have the best bass they've ever produced.

joebass3

I just finished doing this to my Monitor 10's and I can echo everything that @Jazzhead has said. Definitely improved everything about these speakers. Thank you @westmassguy for the advice! I have these and also a pair of 7b's in a small vintage setup and I rarely used these because the 7's just sounded so much better. I still prefer the 7's but it's MUCH closer now! To be honest, the room is very small and the placement of the 10's is not ideal. Maybe I should loose the Kabuki speakers or at least swap positions with the 10's.

plastic_avatar

Put them on the Kabuki stands and try them there, off the floor.

Got the Peerless, too? Nice

Nice stack, too, btw!

I have a little Technics of my Dad's on the fix-it-up stack here...

skipshot12

Westmass,
Has this been tried on the SDA SRS’s?

Jazzhead

@joebass3 It's good to finally get actual feedback from someone with 10's (several expressed interest, but we never heard back). How's the bottom end? They should be imaging better (try them out away from the walls for kicks), and perhaps the presentation is less mid-range shouty? Also, they should play louder without losing composure as quickly. This @westmassguy mod is genius, as it potentially can improve more than one shortcoming on the older models with both drivers operating at identical frequencies. IMHO this mod is fundamental for anyone with these older model speakers that is modding for maximum performance.

joebass3

Jazzhead wrote: »

@joebass3 It's good to finally get actual feedback from someone with 10's (several expressed interest, but we never heard back). How's the bottom end? They should be imaging better (try them out away from the walls for kicks), and perhaps the presentation is less mid-range shouty? Also, they should play louder without losing composure as quickly. This @westmassguy mod is genius, as it potentially can improve more than one shortcoming on the older models with both drivers operating at identical frequencies. IMHO this mod is fundamental for anyone with these older model speakers that is modding for maximum performance.

The bass is less boomy but just not tight like the 7's. I'll put them on the stands, play around positioning and see if they improve. Imaging is hugely improved and not shouty like before. Overall I'm thrilled with the transformation! I guess now I should just finish the job and rebuild the x-overs.

Jazzhead

Giving them some air (away from walls/corners) will help you assess the bass. My recollection is 10's sound inherently bass heavy relative to 7's anyway. The bass/midrange should also sound tighter due to that brace stopping vibration at the PR/midwoofer intersection. Have you installed rings or hurricane nuts (rings are best) as that will further tighten bass, and increase slam. Yes, splurge and do the crossovers. Do you have the stock binding posts (you may have posted this elsewhere - sorry)? Replacing them is an audible improvement (I'm gonna empty your wallet, lol).

joebass3

Bass heavy explains what I am experiencing. Its possible that the slam i get with the 7's can't be duplicated with the 10's. I used hurricane nuts for the 10's but did some serious bracing and semi rings for the 7's.
https://forum.polkaudio.com/discussion/197673/monitor-7-baffle-strengthening#latest
I'm sure those two mods really helped with the slam I get with the 7's. Maybe when I pull the x-overs I'll experiment with bracing at the same time.

Jazzhead

At this point with the newly extended brace you are probably good. You'll know more after you reposition and listen some. Glad you are getting positive results. Some of this bass business is amplification/cable related. My 12's crave current - the more they got, the tighter they sounded. 10's may be different.

xschop

The 10's would benefit from a front to back brace above the 10 and 2 o'clock PR fasteners.

joebass3

Some pics...

Jazzhead

Excellent. I'd dampen that last part behind the tweeter area as well (second photo from the top one). Get every surface.

joebass3

After doing this mod, these speakers sound amazing. Big and wide soundstage! Just wish the bass was tighter. Is being bass heavy just the nature of the beast for the Monitor 10 or is there anything that can be done to bring down the bass response between 70hz-120hz to keep it in line with the rest? You can see in the graphs that there is a jump (red line is peak response) in the 10's that is not there in the 7b's. Either way, I'm enjoying these so much more since doing the mod!