Rta15tl Vs Sda-srs

ben62670

I modified some RTA15TL's with MW6502's to take advantage of running at 4 ohms. The inductor needs to be halved, and the cap needs to be doubled for this mod. The RTA's have wonderful sound stage, and are very musical. I love my SDA-SRS's. I also have rekindled my love for my RTA15TL's tonight. The bass is very tight, and the sound stage leaves you wondering if these are SDA's. I have had a few SDA's SRS, 3.1TL's, 2's, 2a's. If you can get your hands on some RTA's at a decent price you really should give these a chance. I am listening to some Fleetwood Mac which is very dynamic, female/male vocals, with slamming bass. these 15's have reintroduced the wow factor. I was at one point contemplating taking them apart. That would have been a shame. Watt for watt these 15's put out more thanthe SDA-SRS's. The SDA-SRS's are more full sounding as in more bass output, and filling the room with sound that shoots through you. Keep in mind that I have modded them for 4 ohms, but even at 8 they were great.

Ben

TroyD

What exactly does making the 4ohm do to the sound?

BDT

ben62670

If you run the same amp for the speakers at 4 ohms my amp puts out 325 watts, and at 8 ohms it puts out 200 watts.

TroyD

And your point is?

BDT

george daniel

Would the difference in speakers (ohms) have any effect on current from the amp.

ben62670

You get more output for free
Why are LSI's 4 ohms?

TroyD

ben62670 wrote: »

You get more output for free
Why are LSI's 4 ohms?

Why are SDA's 6ohms?
Why are Quads 8 ohms?
Why are Dahlquist DQ-10's 8 ohms?

My point being, while I'm not questioning you opinion on the sound of the RTA's.....I think the assumption that lowering the impedance automatically improves the sound quality is a pantload.

BDT

ben62670

The tweeters were slightly over bright with the 8 Ohms MW6503's. Dropping the ohms to the woofers increased their output to compensate for the overly bright tweets. I am not saying that works well with all speakers, it does work with these. the fs is 29 for one driver, and 31 for the other. they both use the same volume per woofer, so it happens to work for this particular application. A lot of speakers are designed to operate at 8 ohms to be more compatible with more amps. I don't have this problem as my amps can handle a 2ohm load. Some SDA's are 4 ohm, some are 6 ohms, and some are 8 ohms.

F1nut

So, the tweeters are still bright and now the woofers are tweaked up too? I don't know, but that doesn't make sense to me. I think a better approach would have been to tame the tweeters by swapping in the RD0's or changing the cap/resistor values.

BTW, none of the SDA's are 8 ohms. Polk started saying that the later versions were compatible with 8 ohm outputs as an marketing move.

ben62670

The RTA's are my rear speakers in my HT setup. Doubling the power increases the output by 3 db. I didn't double the power, but increased it by about 65% so I figure I gained almost 2 db on the woofers. We have all seen resistor values changed through the same lines of speakers. I agree if I wanted to get RDO's for the rears it would have been best to leave them alone. I needed the MW6503's for another project, and had the MW6502's. I would not recommend going out and buying 8 MW6502's for an upgrade. I would recommend swapping in the RDO's. It just happened to be an experiment that worked out well for me. I tried it. There was a definite improvement, so this is how they will stay. The response curve is very flat, and enjoyable to the ear.

Ben

F1nut

Ok, if it works for ya.

ben62670

F1nut wrote: »

Ok, if it works for ya.

Thanks F1 I was getting a little discouraged. I just wanted to share my experiences with you guys. Time for me to sign out.

Good night
Ben

george daniel

Just curious,, what type/brand of caps did you use?

ben62670

george daniel wrote: »

Just curious,, what type/brand of caps did you use?

Solens I don't have the money for the big sonicaps. I actually used the solens up front on the SDA-SRS's with mills resistors. There was a definite improvement over stock. Tighter bass, better sound stage, and smoother vocals. I would love to hear some modified with all sonicaps.For now they just aren't in my budget. I am presently working on some 16 driver (8 stereo, and 8 dimensional)tri amp SDA's with 4 10 inch PRs. I will wrap the cabs in either cherry or mahogany veneer. I am still short 4 drivers for the project. I did get the cabinet volumes from Ken at Polk. Polk has to be the greatest CS company I have ever dealt with.
Enjoy Ben

george daniel

I 've used both, the sonicaps are more expensive, the most noticable difference (to me) was the sonicaps provided a better open midrange than the solens,both increased my perception of bass. I've got a pair of 1C's coming,and I'll use sonicaps as I plan to keep these. I think that I used a .1uf in place of the silver mica,but I recall some talk about eliminating that as well,and I'll most likely use a jumper in place of the poly's.Have fun--george

ben62670

george daniel wrote: »

I 've used both, the sonicaps are more expensive, the most noticable difference (to me) was the sonicaps provided a better open midrange than the solens,both increased my perception of bass. I've got a pair of 1C's coming,and I'll use sonicaps as I plan to keep these. I think that I used a .1uf in place of the silver mica,but I recall some talk about eliminating that as well,and I'll most likely use a jumper in place of the poly's.Have fun--george

Did the sonicaps Open the midrange on the woofers, or the lower end of the tweeters? I had my speakers electronically crossed over, and at high volumes they stayed smoother than being crossed over passively. Let us know how your 1C's turn out:)

Thanks Ben

DarqueKnight

F1nut wrote: »

BTW, none of the SDA's are 8 ohms. Polk started saying that the later versions were compatible with 8 ohm outputs as an marketing move.

I tried to get Polk to explain exactly what they meant by "compatible with 8 ohms". I was not successful in getting a fully satisfactory answer. They just reiterated that the "TL" series SDA's could safely be used with amplifiers that required 8 ohm speaker loads and that they presented a "stable" and "easy load" for almost all available receivers and amplifiers.

The nominal impedance of the TL series SDA's is 6 ohms, but I assume that their impedance does not vary significantly from 6 ohms over its operating range. This impedance response characteristic would make them an easier amplifier load than nominal 8 ohm speakers whose impedance might vary significantly from 8 ohms over a significant portion of their operating range.

dudeinaroom

ben62670 wrote: »

If you run the same amp for the speakers at 4 ohms my amp puts out 325 watts, and at 8 ohms it puts out 200 watts.

Sounds like a GFA 555

ben62670

dudeinaroom wrote: »

Sounds like a GFA 555

It is

heiney9

ben62670 wrote: »

The RTA's have wonderful sound stage, and are very musical. I love my SDA-SRS's. I also have rekindled my love for my RTA15TL's tonight. The bass is very tight, and the sound stage leaves you wondering if these are SDA's.
Ben

There is a lot to be said for a true D'Appolito array. The MTM having both mid's crossed at the same frequency is a very good arrangement, Dr. Joseph D'Appolito knew his stuff. When I had my RTA's I always thought the imaging and soundstage were excellent, even stock. The only draw back is the "meat" of the sweet spot tends to be fairly narrow. Soundstage cues seem to diminish rapidly as you move out of the sweet spot (off axis).

SDA's don't have as drastic a dropoff in soundstage and imaging when listening off axis.

H9

madmax

Many amps start rolling off the treble as you pull more current which could be part of it along with the woofer giving twice the output.
madmax

Edit: Referring to the tweeter brightness...