polk sda 2a crossover upgrade + tl mod questions

JonathanPeterson wrote: »

To reveal the actual build completely it's sda 2a cross overs rdo-198 tweeter and 4 dynaudio 17w75xl 4ohm drivers

Basically I am replacing each 8ohm 6510 driver with 2 17w75xl 4ohm drivers in series.

Everything will be in a sealed box without passive radiators.

OH Boy, Where Do I Start?

Dynaudio makes good stuff. I was not aware you could still buy drivers. I know I had bought and sold Dynaudio mids and tweeters yrs ago.
You however should just build new speakers.
It's been my experience that once you rebuild new crossovers with supreme caps and resistors the speaker no longer have the flaws that you speak of. What you hear are the "cost" effective product Polk put out. When Polk saved .70 per speaker you and I do not see that translates to hundreds of thousands of dollars in actual savings across the board for Polk.

To now build with different drivers and no longer use the passive for the low end I cannot see how that will make a better speaker. Yes the SDA2a is very expensive to recap because of the huge shunt cap required. Solen caps just kill my ears to no end. For the shunt I used the Axon cap and Sonicaps everywhere else. It made a huge difference in how they played and another Polkie is enjoying them as we speak.

Don't butcher them by trying to redesign them

If you don't like the hybridized bass, you could try porting them? At least you're not trying to incorporate titanium tweets.

JonathanPeterson wrote: »

There is this smear or absence in upper midrange in sda that dynaudio drivers seem to resolve. Had sda-2b, crs+ with cross overs redone for many years

From my recent experimenting, the 6510's don't articulate the midrange as nicely as their 6516 counterparts. The 6510's suspension spider is much more loose given the same construction and DCR as 6516's with tighter suspension.

Why don't you just get a different speaker instead of putting all that money into these.

My 2c is that I would do all the mods I could to my Polks to let them be all they can be, FIRST. Blackhole5 behind drivers, anti-diffraction wool on the baffle, anti-diffraction frame on cabinet edges, armacell inside spokes of stamped steel baskets, phase plugs, Rob's rings to stiffen baffle, anti-vibration speaker stands..... Only then will you hear how beautiful the midrange can sound.

I'm all for experimentation though so carry on and report.

Well OK. It seems like the Qm is closer than in the non XL, but still not all that close, Compliance is unknown, DCR of two in series is close, Fs is different, BL is less. We can't really know much else can we? How do you know about sensitivity?

Looks like they used the same voice coil as non XL but changed the magnet motor to a stronger one. Without having the compliance figures for the dynaudio the comparison is tough to make to the 6510.

How are you going to get any bass without a passive radiator when the freq. response shown doesn't go much below something like 50 to 60 Hz?

PS: Great website by the way, thanks!

Try a real amp, no receiver will do the 2a's any justice.

JonathanPeterson wrote: »

Sensitivity is around 88-89db just eye balling from graphs
Vas is 20L. Cms and vas are usually proportional. If Polk vas is 20L and 17w75xl is 20L then their cms are probably the same. I mounted dynaudio in 4 crs boxes and sealed passive radiators. Tweeter and woofers play pretty balanced. I dont want a ton of bass . I use 15" velodyne subwoofer..fsr-15(with parts Express 500w plate amp with dsp). Velodyne plate amps all blow 1 hour after warranty expiration date. Next to 2b Polks these polkdynaudiosteins sounded much more revieling, clean, open and forward smearless. Some voices and string instruments sound very recessed in 2b(crossovers redone using parts Express basic film capacitors. Nothing fancy like clarity)

But where are you getting those values of sensitivity (from what graph?) and Vas (Compliance Volume) from for the MW6510, if the only info. you have is the chart that I posted above^^?

I mean I understand that you are assuming Vas and Cms will be the same if the driver surface area is the same, but are they? It looks like the Polk is around 130cm^2 vs 120cm^2 for the Dynaudio, so Polk is 8.3% greater.

https://mynewmicrophone.com/full-list-thiele-small-speaker-parameters-w-descriptions/#Vas:-Equivalent-Compliance-Volume