Rerurn to Romy the Cat's Site
In the Forum: Playback Listening
In the Thread: Remedies the Beauty
Post Subject: LF cont'edPosted by N-set on: 10/28/2022
Looks like the phase response is quite complicated, with two phase flips between the knee and the Fs notch, but the PR phase eventually comes back to be in phase below the Fs:
"I
am sure we have all heard that a passive radiator is like a vented
speaker. This is true in the region of the box tuning frequency. The
passive radiator acts like a mass hanging on the spring and can be used
to tune the box compliance to the desired resonance frequency in much
the same way as a port does.In both cases, port or passive
radiator, the resonance creates a very high internal pressure in the box
at this frequency. This pressure, if there were zero losses, would
force cone travel to come to zero at this frequency as all output would
come from the port or passive radiator at this frequency. However, there
are some losses, so in reality we end up with a notch in the woofer's
response at the tuned frequency (Fb) and most of the output does still
come from the port / PR.Now, as we move below Fb the passive
radiator begins to act very differently than a port. Here's why - You
still have that image of a weight hanging a spring? Well, a passive
radiator is a much more complex mechanical system than a simple port. It
has its own moving suspension and it has its own resonance frequency (
which we will call Fsp). So in your image of the weight hanging from the
spring, you need to attach another spring to the weight and add an
additional weight hanging on it. So, now you have a weight on a spring
hanging from a weight on a spring. Got that, right? In a vented
system the port output and the cone output are in phase with each at the
tuning frequency. Below that both are rolling off at 12 dB/oct. But,
the port is moving out of phase with the cone as the frequency
decreases. This is what causes vented systems to roll-off at 24 dB/oct.
The same thing occurs with a passive radiator until we reach the
frequency of Fsp. At this point (Fsp) the passive radiator
output is out of phase with the output of the woofer cone and a notch in
the summed response occurs. At this point the PR's phase "wraps" or
flips, and below Fsp the PR's phase moves back in phase with the cone.
This means that at very low frequencies the summed response, unlike the
vented system, rolls-off at only 12 dB/oct, just like a sealed system.
In fact, it is a sealed system below Fsp. This means we have the added
benefit of the box no longer unloading at low frequencies like a vented
box does. Excursions of the woofer cone are much better controlled at
very low frequencies. With the Passive Radiator, you get the benefit of a
vented box at the tuning frequency and the benefit of a sealed box at
lower frequencies. You may have never heard this before, which is what
makes this a smarter place to hang out."
https://diy.midwestaudio.club/discussion/909/ported-vs-passive-radiator-designs-thoughts
I understand this violent phase change happening in a short freq interval is one suspect why "glueing" bass/reinforcement channels is so problematic and they sound disconnected?
Ed, would love to learn the details of your reverb application. It is in my plans (after sorting the electronics and a basic room treatment).
Rerurn to Romy the Cat's Site