Passive radiators

[Pearljam5000]

Never really understood the point of these things
What are your thoughts about it?
Good, bad?

 

[Audionaut]

I don't have time right now, but they make a lot of sense, yes.
They are the better alternative to a port opening in a bass reflex system

 

[thewas]

A well tuned PR behaves like a BR but avoids problems like turbulence noises, above tuning frequency sound leakage and large lengths that don't fit in small enclosures, the disadvantage is the relatively higher cost and large area needed (around 2x of the woofer surface).

 

[Arindal]

Never really understood the point of these things

Freely adjusting tuning freq, gettin lower bass from a very small enclosure, or when a traditional port would get too long to fit into the enclosure, preventing cabinet resonances from sneaking out through the port, preventing chuffing and port noise I would see as main advantages of passive radiators. Main trade-offs are: They eat up money and cabinet wall space, are prone to boomy bass if you make mistakes with tuning, and are more complicated to simulate.

For those who stay skeptical about bass qualities with passive radiators in an overly compact enclosure, I recommend to try this one:

Called Detroit, portable Bluetooth speaker looking like a toy, with 4 passive radiators, if I am not mistaken. Pretty amazing.

 

[BeeKay]

and large area needed (around 2x of the woofer surface).

True

 

[Matt_Holland]

A PR doesn’t impinge on internal cabinet volume as much as a port in some cases, so the same bass extension can be achieved with a smaller cabinet.

There are two main factors that go against PRs:
1. Cost vs benefit (this is the big one)
2. Volume displacement limitations in large high SPL systems. You won’t find PRs in many PA bass cabinets. A nice example of an exception to that rule is the K-array Rumble KU315 which uses a single 15” with 2x 15” PRs.

 

[Head_Unit]

Just to note that passive radiators don't *quite* behave like ports acoustically. Not different enough to worry about. I don't remember the details of various papers written over the years but small differences in response IIRC.

 

[dfuller]

A well tuned PR behaves like a BR but avoids problems like turbulence noises, above tuning frequency sound leakage and large lengths that don't fit in small enclosures, the disadvantage is the relatively higher cost and large area needed (around 2x of the woofer surface).

Note that PRs are a 5th order system rather than 4th order, so the roll-off below Fb is steeper and it's more likely to ring audibly.

 

[Ktacos]

I really like PR's for getting bass and not having to worry about upper resonances in a two way. I will say though, making a large portion of the cabinet flexible seems to have some impact on other parts of the speaker. My Mechano23 has a PR on the rear, same one as the pic OP posted, and despite being well braced, the whole speaker just vibrates a ton. I can't help but feel like I'm getting some losses. I also notice that the ~200-300hz region seems to lack definition and impact but I'm not sure if this is contributed by the PR or the main driver. Working on some mixes, I've been finding that I can boost the low impact of a snare drum but audibly it just never really gets much louder or punchier. Strange behavior IMO.

I also curious, what's the typical approach to cabinet fill with PR's? stuff it full, just line the walls?

 

[diyhobby]

I have some cheap decent woofers can I use them as Passive radiator

 

[dfuller]

I have some cheap decent woofers can I use them as Passive radiator

No, you need actual passive radiators.

 

[MattHooper]

I’m not in a position to make a technical case, but my Ltd experience with speakers using passive radiators has been excellent.

One of the things that always attracted me to Thiel speakers was the really excellent bass - punchy solid and very well controlled.
Also, they’ve been among the easiest to place loudspeakers in my room in terms of getting good bass response.

That’s been true of every CS model I’ve had in my room CS6, CS3.7…and my current CS2.7s which use an oval passive radiator:

I’ve had such a positive experience I’ve often wondered why more loudspeakers don’t use passive radiators.

 

[Ropeburn]

Freely adjusting tuning freq, gettin lower bass from a very small enclosure, or when a traditional port would get too long to fit into the enclosure, preventing cabinet resonances from sneaking out through the port, preventing chuffing and port noise I would see as main advantages of passive radiators. Main trade-offs are: They eat up money and cabinet wall space, are prone to boomy bass if you make mistakes with tuning, and are more complicated to simulate.

For those who stay skeptical about bass qualities with passive radiators in an overly compact enclosure, I recommend to try this one:

View attachment 456090

Called Detroit, portable Bluetooth speaker looking like a toy, with 4 passive radiators, if I am not mistaken. Pretty amazing.

A general advantage of using them for portable speakers: you can make them watertight. Impossible with a port.

 

[dfuller]

I really like PR's for getting bass and not having to worry about upper resonances in a two way. I will say though, making a large portion of the cabinet flexible seems to have some impact on other parts of the speaker. My Mechano23 has a PR on the rear, same one as the pic OP posted, and despite being well braced, the whole speaker just vibrates a ton. I can't help but feel like I'm getting some losses. I also notice that the ~200-300hz region seems to lack definition and impact but I'm not sure if this is contributed by the PR or the main driver. Working on some mixes, I've been finding that I can boost the low impact of a snare drum but audibly it just never really gets much louder or punchier. Strange behavior IMO.

I also curious, what's the typical approach to cabinet fill with PR's? stuff it full, just line the walls?

When I've opened them up in the past it's more like a ported box

 

[Waxx]

I don't like them actually, but i can see why people use them to get bass from a very small enclosure. But it does sound forced to me (subjective impression). They resonate on the pressure created by the main woofer, and are tuned by the compliance of the box and the mass of the membrane to a certain frequency. It's mostly tuned by adding mass on the back of the cone.

 

[Arindal]

But it does sound forced to me (subjective impression).

Sounds like a very generalized statement, which can hardly be applied on such a variety of different designs. I wonder on listening to which existing models this is based, and what you mean by ´forced´- why should a passive radiator sound more ´forced´ than let's say air in a port vent or a closed-box woofer being pushed to higher excursion?

They resonate on the pressure created by the main woofer, and are tuned by the compliance of the box and the mass of the membrane to a certain frequency.It's mostly tuned by adding mass on the back of the cone.

Which is basically the same thing occurring in a ported design, you just choose the moving mass by altering the port length. So why should this be a disadvantage?

I would support the statement that vented and PR designs tend to have a slightly different bass character, with the PR designs showing a greater variety between tight bass and boomy bass. I would prescribe the latter to flawed designs, or the will to just maximize the SPL output/lower cutoff frequency of a compound concept.

I’ve often wondered why more loudspeakers don’t use passive radiators.

They are expensive, they need more complicated cabinet designs, they add complexity to the tuning process, they have an inherent excursion limit, and the existing simulation tools are not as precise.

 

[mhardy6647]

I have some cheap decent woofers can I use them as Passive radiator

One would have to remove the voice coil and magnet (and probably the spider as well), and then add mass to achieve the desired loading property for the enclosure.
It could be done, but it's probably better to start with a purpose-built PR. They've gotten expensive, though -- which I find both kind of weird and amusing.

 

[MRC01]

I’m not in a position to make a technical case, but my Ltd experience with speakers using passive radiators has been excellent.

One of the things that always attracted me to Thiel speakers was the really excellent bass - punchy solid and very well controlled.
Also, they’ve been among the easiest to place loudspeakers in my room in terms of getting good bass response.
...

This reminds me of Polk Audio speakers back in the 1980s and 1990s, which also used passive radiators. I thought they had great sound quality and punched above their price class when compared to other brands. They didn't blast as loud as some of the others, so the PR struck me as a tradeoff to sacrifice SPL for cleaner sound.

 

[monx]

I'd rather have a well-engineered port than a passive radiator, based on very irrational aesthetic preferences.

I have one weird question though, can a bass reflex and/or passive radiator be manipulated to make a cardioid design?

 

[mhardy6647]

This reminds me of Polk Audio speakers back in the 1980s and 1990s, which also used passive radiators. I thought they had great sound quality and punched above their price class when compared to other brands. They didn't blast as loud as some of the others, so the PR struck me as a tradeoff to sacrifice SPL for cleaner sound.

Actually the sensitivity of the early (1970s) Polk Monitor Series (7 and 10) is pretty respectable. Since they are not sealed boxes a la Villchur, they're generally a bit more sensitive than the air suspension loudspeakers of the same era.