Passive radiator speakers… really a benefit?? To bassreflex speaker design

[KehaDNb]

Leaving the technical stuff aside for a moment but I found out that PR sounded not that boomy in my room, the BR systems always were boomy . I had just a acoustic curtain, no room treatment

 

[HarmonicTHD]

Leaving the technical stuff aside for a moment but I found out that PR sounded not that boomy in my room, the BR systems always were boomy . I had just a acoustic curtain, no room treatment

That is mainly because of your room (room modes) and less due to the technology used (PR vsBR).

Regardless wether you use PR or BR, it is always a good idea to run a room FR measurement and compensate the room modes (boomyness).

 

[Hayabusa]

Hi as already noted… how and when can I have a advantage in using passive radiator speakers to bassreflex speakers?

One advantage I see is that sounds (higher frequencies) from inside the box are more dampened than with a port?

 

[sarumbear]

Of course with PR you are more limited to whatever passive radiators you can find, whereas you can design and build any port dimensions, or you might find that sealed works better in your situation.

I am sure you can emulate a port with most PRs as they are adjustable.

 

[sarumbear]

Vandersteen had an odd arrangement they called an active coupler. It acted as a passive radiator, but the voice-coil was fed very low frequencies so below the passive tuning it became actively driven.

Strange. You are limited with the PR/Woofer driver's Xmax at that frequency range, what can you achieve by exciting it further?

 

[Blumlein 88]

Strange. You are limited with the PR/Woofer driver's Xmax at that frequency range, what can you achieve by exciting it further?

I don't know. At various times they've claimed their speakers functioned as a closed box with the Acoustic coupler, but they clearly measured otherwise in terms of impedance. Then they claimed the circuit lets the amp damp the otherwise passive radiator limiting excursion at its resonance and driving it actively at lower frequencies around or below 35 hz.

 

[Deleted member 48726]

Actually no. The voice coil and cone can easily outweigh a PR. The spider return/centering spring is the key to PRs. I use 10-18" PRs
I seldom add several washers. Most of the new PRs are not very sensitive. The issue with very sensitive PRs they historically don't hold up well
because of the light spring and foam surrounds vs Butyl rubber surrounds and dual spider returns. I like tuning with disk to a point (if need)
and adding pliable putty until I get a boom. Then remove just enough to remove the boom. I like the weight that's accessible from the front
vs the back, too.

Your stuck with fixed ports and it better sound good in every room. LOL It can't. PRs can require a little maintenance just like any active
driver. BOTH move, both require, rotation, surround maintenance, connection service if it's not mechanically joined and spot soldered
and of course fastener retorque. A weight adjustment as time goes on (you (remove weight). I remove putty about every 2 years. If the sub is moved,
it is re-tuned to that room, that amp and cables. Add putty until it booms and remove it until it stops.. Then EQ the room.

A different idea all together. Servo subs, Bass columns (as couplers) and room treatment (Helmholtz resonators). The best I've found
for just about any reproduction. Just add a good monitor, I like small planars and ribbons. TM, MTM, LS, and hybrid line source.

Rotation? Of the driver due to sack?
What is your experience with this? -I'm asking because I have two pair of old Infinity Kappas and was wondering if it was due time to rotate the woofers 180 °

 

[Maciek]

S
You are right in that the cone becomes unloaded and excursion goes through the roof. My point was that there is little accoustic output below the Fb which I think is handy as it reduces boomines from room modes and reduces the amount of sound escaping Your room (and spilling over to Your neighbours).

You're saying the box doesn't unload the cone there?

Sag depends on cone weight and also Qm of the suspension, if its a very low loss suspension and a heavy cone then rotation from time to time is recommended.

Rotation? Of the driver due to sack?
What is your experience with this? -I'm asking because I have two pair of old Infinity Kappas and was wondering if it was due time to rotate the woofers 180 °

 

[Deleted member 48726]

S
You are right in that the cone becomes unloaded and excursion goes through the roof. My point was that there is little accoustic output below the Fb which I think is handy as it reduces boomines from room modes and reduces the amount of sound escaping Your room (and spilling over to Your neighbours).

Sag depends on cone weight and also Qm of the suspension, if its a very low loss suspension and a heavy cone then rotation from time to time is recommended.

I don't have data on the injection molded graphite cones in my Kappas. But they should be light weight.

 

[fpitas]

S
You are right in that the cone becomes unloaded and excursion goes through the roof. My point was that there is little accoustic output below the Fb which I think is handy as it reduces boomines from room modes and reduces the amount of sound escaping Your room (and spilling over to Your neighbours).

My point was the cone becomes uncontrolled and needs high pass filtering for a high level situation, to avoid reaching Xmax.

 

[mhardy6647]

The rolloff of a PR alignment is different than BR.

 

[abdo123]

That is mainly because of your room (room modes) and less due to the technology used (PR vsBR).

Regardless wether you use PR or BR, it is always a good idea to run a room FR measurement and compensate the room modes (boomyness).

How? The speaker should more or less have been in the same location.

 

[fpitas]

The rolloff of a PR alignment is different than BR.

Yup, you get an extra null below the F3. That will, among other things, increase the group delay.

 

[mhardy6647]

This is the graphic with which I am familiar, but I must confess that I don't have deep understanding of the physics involved in the PR resonance behavior, so I was loath to offer it earlier, unsupported and unsubstantiated.

Passive radiator speaker design - Box calculation example

Similar to bass reflex, the passive radiator speaker design, uses a resonator to extend the frequency response.

audiojudgement.com

I.e.,, this is "google-learning", which of course should never be mistaken for actual learning!

 

[fpitas]

This is the graphic with which I am familiar, but I must confess that I don't have deep understanding of the physics involved in the PR resonance behavior, so I was loath to offer it earlier, unsupported and unsubstantiated.

Passive radiator speaker design - Box calculation example

Similar to bass reflex, the passive radiator speaker design, uses a resonator to extend the frequency response.

audiojudgement.com

I.e.,, this is "google-learning", which of course should never be mistaken for actual learning!

It's reality. If you have a tiny box and need a low tuning, PRs are great. Yet, I've seen people null the port resonances of enormously long ports, when necessary. All part of engineering a speaker. PRs are also good for not radiating midrange garbage from the cabinet interior. But, they cost considerably more than even a long PVC port

 

[Maciek]

How? The speaker should more or less have been in the same location.

Two things were probably invovled. Firstly, You don't know the transfer function of each speaker's tuning. If it was tuned for flat free field response (that is flat in most free design software) then they become boomy when placed inside a room due to boundary gain. Especially so at tuning frequency, which results in boomy, one note bass, irrespextive of resonator used (BR or PR).
Secondly, PRs have less accoustic output below the tuning frequency, so maybe this one excited fewer room modes at the lowest frequencies, which made the bass sound clearer.

Basic use of EQ can fix both. Just pull the lowest octave down a few (2-3) dBs and the bass should sound faster and clearer, although less thunderous. This should fix the tranfer function related issued. Room modes can add even 10 or more dBs in narrow frequency bands, it can be fixed by ear with tone generator and parametric EQ but room correctiom software is much more convenient.

 

[HarmonicTHD]

How? The speaker should more or less have been in the same location.

As we know too little about the specifics of the two speakers in question (low freq FR) one can only guess: Maybe different tuning which excites different room modes with also different energy? Again - just speculation.

Therefore I recommended a REW sweep if possible so one would have facts. Even if to exclude the above hypothesis.