RTA-15TL Recap

westmassguy

This was a fun little project. One of the Hi-Pass, 5 Watt Resistors had burned, and taken out the 12uf Electrolytic Cap on one side, and partially melted the plastic spool end on the Inductor. The Inductor's DCR and MH values were checked, and luckily the coil winding was not damaged. Clarity PX Caps, and Mills MRA-12 Resistors were chosen. Due to their enormous size, the layout and smaller size of the late model Circuit Boards, I had to relocate two of the Capacitors to the bottom of the board. The existing standoffs were drilled, tapped, and nylon riser extensions installed. Due to the small size of the boards, nylon wire ties would have been difficult if not impossible to install. Although I despise hot glue, I really had no choice. The original Crossovers were slathered with Hot Glue. I removed as much as possible mechanically, and with Acetone, installed all the new components using 3M VHB tape, and finished them off with as neat a bead of hot glue as possible. The coils were re-glued with Hot Glue, and made a bit more presentable.






They sound quite a bit better now.

Faustin

Nice work as always Dave. Man, those boards are small. Looks like you barely had enough room even relocating caps to the bottom of the board.

EndersShadow

Nice work. One day I need to have my 11TL's done. I have everything for all the other mod's (dynamat, rings) except the RDO's......

westmassguy

Faustin wrote: »

Nice work as always Dave. Man, those boards are small. Looks like you barely had enough room even relocating caps to the bottom of the board.

Thanks Bruce. Just barely enough.

westmassguy

EndersShadow wrote: »

Nice work. One day I need to have my 11TL's done. I have everything for all the other mod's (dynamat, rings) except the RDO's......

Thanks

voltz

Excellent work as always I know it wasn't easy but you sure make it look easy with how clean everything looks.

westmassguy

voltz wrote: »

Excellent work as always I know it wasn't easy but you sure make it look easy with how clean everything looks.

Thanks Darryl

westmassguy

For comparison, this is another 15TL I did a while back, This pair had the old style circuit boards. Clarity caps of similar size were used on this project as well. A bit more real estate to work with.

voltz

It is always wild to see the before and after shots to see how different the caps and inductors are.

here is a pic of my crossover's for my monitor 10's that Dave did for me, I left the old parts in front of it for comparison

westmassguy

Looks familiar

drumminman

Looks good WMG!

westmassguy

drumminman wrote: »

Looks good WMG!

Thank you Sir

voltz

I always wondered what the RTA 15tl's sounded like, Now with you new Crossovers those speakers are going to be something special!

westmassguy

The 11TLs are the sweet spot in my opinion. The 15TLs go deeper, but they have a rear facing PR, which can, under certain circumstances, Interfere with the front PRs. Phase issues.

markamerica

Dave, Nice work, as usual. The comment on the 15TLs and the two PRs per cabinet is interesting to me. You mentioned a phase issue. Could you explain? (My usual curiosity.) Thanks!

Mark

westmassguy

markamerica wrote: »

Dave, Nice work, as usual. The comment on the 15TLs and the two PRs per cabinet is interesting to me. You mentioned a phase issue. Could you explain? (My usual curiosity.) Thanks!

Mark

The front and rear PRs are moving in phase with each other. If the speaker were placed in the center of the room, there wouldn't be a problem per se, since they're producing the same sound waves in phase (I'm, purposely leaving out room interaction). Once you place the speaker in front of a wall, the rear facing PR's sound waves bounce off the rear wall, and are now 180 degrees out of phase and delayed. As they move forward, and combine with the front PRs output, comb filtering can occur. Certain frequencies may be canceled, while others may combine, effectively doubling. This can cause very odd bass response from the speaker. Finding the proper distance from the rear wall is more critical with the 15tls than other types of loudspeakers. The 8t and 11t do not have this problem.

markamerica

I see what you're saying, but I thought that's why Polk used two slightly different PRs, front and rear.

Nightfall

westmassguy wrote: »

The 8t and 11t do not have this problem.

Don't forget about the 12's!

westmassguy

markamerica wrote: »

I see what you're saying, but I thought that's why Polk used two slightly different PRs, front and rear.

The 11TL's have PRs that are tuned differently due to the amount of mass that's added to the cone, not sure about the 15TLs. That has nothing to do with phase however.

westmassguy

Nightfall wrote: »

westmassguy wrote: »

The 8t and 11t do not have this problem.

Don't forget about the 12's!

Love the 12s. When I said sweet spot, I was referring to RTAs with the d'appolito driver arrangement.

markamerica

westmassguy wrote: »

markamerica wrote: »

I see what you're saying, but I thought that's why Polk used two slightly different PRs, front and rear.

The 11TL's have PRs that are tuned differently due to the amount of mass that's added to the cone, not sure about the 15TLs. That has nothing to do with phase however.

Yeah, I went back to verify what my memory said, and sure enough, the PRs in the 15TLs are different.
Here's a link to a pdf of the original sales brochure. You might have to zoom in a little.
http://polksda.com/pdfs/RTA_TL_Sales_Brochure.pdf

I thought the different PRs would address the potential comb effect you mentioned, rather than the phase issue, by having different resonance frequencies.

Anyway, thanks for the answer, as I hadn't considered the phase issue. So much to learn, so little time.

Mark