Going w/ passives

leftwinger57

I've been here for years now and own my 2Bs and just re read the SDA Handbook. I followed much of it until it got into the very techno scientific math related stuff. But nowhere does it say why Polk chose to use passive bass radiators(unless I totally missed it) instead of wired woofers or in a lot of the bigger models even a plate amp for a powered sub woofer as done in some makes these days. Anyone know why ? I know I thought my Rectilinears went lower than my 2Bs but since they were sold I'm not that sure anymore. For sure they were older '69/70 compared to my '87 2Bs but modded so much basically a new speaker and totally 2 different systems.

tonyb

Why a speaker designer does what he does is simply a matter of preference. Big speakers were the rage back then and using the cabinet volume to move that passive instead of sucking up amplifier power makes them easier to drive also I would assume. With more power available to the mids, the speaker would have more punch too, which much of the musical bass we hear plays in.

That's my guess anyway, who knows what was in Matt's head at the time. Does it really matter "why" though ?

EndersShadow

I agree with Tony.

A passive radiator allows you to have a sealed speaker, but make it act like a ported one, so by adding in a passive you lower the range of the speaker without needing either a port, or a active woofer (which requires more power).

It also likely simplified the crossover as if you had an active woofer you would be looking at a 3 way speaker instead of a 2 way, which means more parts and complexity in the crossover, etc.

I'm sure the SDA concept was enough of a pain to figure out without overly complicating it by making it a 3 way.

leftwinger57

Well he did say part of the death of the SDAs was the shrinking of speakers, the advent of avr and surround sound. Big also was the WAF effect all leading to ending the SDA series. Good to hear from you Tony....Lew

mhardy6647

Remember that, physically speaking, loading a loudspeaker via a passive radiator is analogous to using a bass reflex port. The mass of the PR itself replaces the mass of air contained in the volume of the port.

Passives have one advantage over an open port -- no potential for port noise ("chuffing"). Many Port Noise Complaints in those days

A PR loaded enclosure will have different (steeper) roll-off characteristics from ports (or acoustic suspension), for better or worse.



The other generic reason to use a passive radiator instead of a port was when the calculated port volume was impractically large for the enclosure volume desired. In that case, sometimes angled port tubes were used; others would use PRs.

Enclosure volume wasn't an issue for most of the SDAs

It is interesting that Polk -- way back when (the Monitor Nine) chose to use PRs rather than the then-fashionable acoustic suspension alignment. The Model Nine brochure does suggest that the driver (no pun intended) was to increase system sensitivity -- but who knows?

My guess is that the "high definition" marketing tag is a clue. The pitch may have been that using small woofers ("midwoofers") improved transient response... the PR still gave the appearance of a big-bu-t-t woofer, which consumers liked and expected. Ports were out of fashion in those days.

Maybe Ken can provide insight?!

heiney9

Polks passives have much less distortion than wired woofers and a flatter response. Today's speakers are slim and deep more advantageous to a port (since the tube can be longer). SDA's by design are wide and not as deep. Not enough real estate for a tube to tune it to hit as low.

That's it in a crude nutshell

mhardy6647

From the aforementioned Polk Audio Model Nine brochure, some clues (perhaps?):




efficiency isn't interchangeable with sensitivity, but both properties, in essence, reflect how well a loudspeaker transforms input electrical power into output acoustic power .



the "definition" thing.

source: https://polksda.com/pdfs/ModelNineManual.pdf

Viking64

"What is that your business?"

https://www.youtube.com/watch?v=5U1-OmAICpU

leftwinger57

Alright grasping all that all you dudes have said. Now what is a model #9. I heard of 4s, 5 5jr,7s,10s and 12s that I don't think anyone liked.
Ok, just did some of my own research and it seems they were not very well liked at all.

mhardy6647

The original Model Nine, with the Motorola piezo tweeter is pretty not great
The later Model 9A, with the Peerless, ain't half bad. Srsly. I've got a pair here -- they ain't bad.

That said -- Good or bad isn't really the issue in this context. The Model Nine was Polk's first consumer loudspeaker and it introduced some pretty durable Polk characteristics, including the use of small, high-excursion "midwoofers" (in the case of the Nine/9A, these were 4-1/2 inch CTS "fullrange" drivers) and passive radiator type 'bass reflex' (Helmholtz resonator) loading.

Tony M

My pair with the peerless tweeters sounds pretty good too. Heavy little buggers too.

mhardy6647

(Marky looks down at the ground and shuffles his feet) -- I... I like... Monitor 9As...

FestYboy

I'll join you in that camp Doc. Love me some 9As.