SDA bass. How is it done?

ROHfan

While I'm awaiting my crossover mods and upgrades from Trey I did some poking around the web to see, exactly, how the bottom end can be so strong on the SDAs when the woofer is just a passive radiator. These things have very good bass even without the IC which leads me to ponder how one 6.5" driver can produce such low end. I know it must be due to the tuning of the cabinet and such, but how is that the small driver can have that much of an effect on the radiator.

boston1450

Because they are well made Polk SDA's & Mr Polk knows his speaker
Too many drinks

Moose68Bash

It may be only a passive radiator, but it is a big, honking passive radiator!

Schurkey

ROHfan wrote: »

These things have very good bass even without the IC

Does the interconnect cable--on ANY generation of SDA--actually affect the deep bass?

I'm thinking that the SDA connection is rolled-off starting at 100Hz, so bass due to the cable isn't really part of the SDA driver's job. Bass due to the SDA driver of the newest three generations of SDA being driven by the stereo signal at low frequency would affect bass, but that's not the same as when powered by the SDA interconnect.

In short, an SDA 2A or 2B, or the newer SDA-CRS may only have one stereo driver, but they still have two bass drivers because the SDA driver is doing double-duty.

SCompRacer

Basically, bass drivers will roll off early in a sealed cabinet. You could add ports, but then you can get port noise, or chuffing. To prevent chuffing, you can use large diameter ports. To maintain cabinet tuning, the length of the ports can be quite long. Folding a long port can add to an even larger cabinet size.

Enter the passive radiator. Passives work like a port with no noise and complicated port folding. My speakers with dual 8" woofers have one 12" passive radiator on each side.

westmassguy

I'll add to what SCompRacer spoke about. From what I've read, Polk's design goal was a loudspeaker that produced deep bass, with low distortion, and was very fast and accurate (tight). Large woofers have higher mass. When given the same signal, a small woofer will react faster. The cone will start to move and cease to move faster than a larger heavier cone will. I'm over-simplifying here, as there are many other factors in play.
When combining multiple small woofers in a common cabinet, they become acoustically coupled. In other words, when multiple smaller woofers are receiving the same signal, their combined cone area is equivalent to a much larger woofer.
With the 3rd through 5th generation SDAs, the Stereo and Dimensional woofers are fed the same signal below 150Hz. They are acoustically coupled with each other, and fluid coupled (air being the fluid) to the Passive Radiators. The Passive Radiators kick in at around 50Hz, and their output increases as the frequency drops.
That's why the big SRSs, with their large passive radiators, can produce frequencies down to 20Hz and below.
Polk's woofers are also very unique. Their published T/S Parameters are amazing compared to most 6.5" drivers. Their cones are very light, suspensions very relaxed, cone travel is high, resonance frequencies very low, and VAS or how much air the drivers are able to move is also very high. Lastly, the frequency range covered by the drivers is also very wide.

ROHfan

Very interesting. Thanks for the replies.

I've not seen any other speaker brands employing the passive radiator, although I'm sure they must exist. I'm wondering how the accuracy of lower frequencies compare to the SDAs.

westmassguy

ESS comes to mind

Mystery

Many use pr.
Infinity rs series, epi, harms labs etc... and lot of subwoofers.

westmassguy

DSkip, Passive Radiator Designs are considered Bass Reflex, not Acoustic Suspension.
AS designs are sealed, and the air acts as a spring damping the cone. PR Designs are similar to Bass Reflex. They must be tuned, because the Mass of the PR acts the same as the Mass of the air in a Port. The benefit, is zero port noise.

Conradicles

Brian Cheney of VMPS was also a master with passive radiator designs.

Conradicles

Zero port noise rules!

SCompRacer

ROHfan wrote: »

Very interesting. Thanks for the replies.

I've not seen any other speaker brands employing the passive radiator, although I'm sure they must exist. I'm wondering how the accuracy of lower frequencies compare to the SDAs.

Salk uses them. The SoundScape 12's use two 15" PR's. He explained that without them, he would have needed a 9 foot long port of a specific size to prevent chuffing. The SS12's play to an F3 of 18Hz. The SS10's like these (10" woofer) have an F3 of 20 Hz.



My SS8's with dual 8" woofers, an F3 of 25Hz.

Conradicles

Those are beautiful.

Mystery

Conradicles wrote: »

Those are beautiful.

And pricey... Some day...

Mr. Sharpe

ROHfan wrote: »

Very interesting. Thanks for the replies.

I've not seen any other speaker brands employing the passive radiator, although I'm sure they must exist. I'm wondering how the accuracy of lower frequencies compare to the SDAs.

Definitive Technology and Legacy audio. didn't the designer for the vintage polk speakers start designing Definitive speakers? or am I just crazy?

Mystery

How did I forgot to mention this.
All my Klipsch kg2, kg4, forte have passive radiator on the back.
The best passive bass I've heard so far is Sonus Faber. I always think it's active because of the grunt and forceful bass instead of bouncy bass from most other brand pr's.

ROHfan

Man, those Salks are gorgeous!

leftwinger57

Westmassguy, is right again.One of my favorite speakers of the mid 70's and in direct competition to the Bose 901s at the time. Yes a huge foot print but those Heil tweeters and the combo of 12'' speakers in front 12'' passives in the rear were awesome. ESS Heil is still in business out in California. No affiliation....

http://www.audioreview.com/cat/speakers/floorstanding-speakers/ess/amt-1b/prd_119461_1594crx.aspx