can someone explain passive radiators to me? (1 Viewer)

[Geno]

Vince, thanks.
I got so confused on the sidetracked nonsense that I stopped reading this thread.

 

[Kyle Richardson]

Plus, to get the desired tuning on a high performance driver you usually have to tune quite low. This results in very long vents and even though they may fit inside the enclosure you start to get vent resonant frequencies inside the frequency range that the sub is also playing. This results in large peaks at those particular frequencies.

On another note, thanks Vince. We don't mind differing opinions here, but we DO like evidence to back them up.

 

[Vince Maskeeper]

I do want to be clear to member and lurkers alike- I would never remove someone from this forum for having a differing opinion. The issue of a differing opinion is HOW and WHERE you express that opinion.

Now, back to your regularly scheduled program.

-V

 

[Dan Hine]

I think I see. So it not only has to do with the size of the port/enclosure but also how much volume the driver displaces? I've been getting confused because I've been reading a book by David Weems and G.R. Koonce and they have a table with suggested length ports for different sized enclosures. They list a 4" diameter port at 4.25" long to tune a 10cubic foot box. I guess this is just in theory, depending on what driver you have and its Vd?

 

[Brian Bunge]

Dan,

Those dimensions are merely suggestions for a specific box size, port diameter, and tuning frequency. You can pick any diameter port you want, but once you start talking high Vd drivers, then you start having to look at 8-10" diameter ports to try to alleviate compression. In doing so, you end up with lengths in feet instead of inches in order to tune low.

Brian

 

[Greg Monfort]

> think I see. So it not only has to do with the size of the port/enclosure but also how much volume the driver displaces? I've been getting confused because I've been reading a book by David Weems and G.R. Koonce and they have a table with suggested length ports for different sized enclosures. They list a 4" diameter port at 4.25" long to tune a 10cubic foot box. I guess this is just in theory, depending on what driver you have and its Vd?
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Who? What? Is an intelligent question being asked? How dare you highjack this thread and sully our forum ! Sheesh! Where's a moderator when you need one!
The cab drives the vent no matter what drives the cab, a point lost on our late, unlamented 'he who was educated in his own mind' WRT servo drive Vs point source driven cabs, ergo a 10ft^3 net cab with a given vent will have an Fb dictated by their interaction alone, regardless of what's loading the cab.
It would resonate at the same frequency whether a 15" Tumult or 4" 'woofer' were attached, although the vent's output would be radically different WRT vent mach since obviously a Tumult can pressurize the cab much more than a dinky 4" 'woofer'.
As previously noted the vent mach may be too high for the intended application, so just blindly following this chart can be a recipe for sonic disaster, another point lost on 'he who appeared not to know squat'.
Again, as previously noted, vents have pipe resonances, otherwise neither horns nor reflex vents would work, and if the length of said vent becomes long enough for the pipe modes to be within the vent's Fb BW, then you get a big dip in the system's frequency response, and peaks also, if really long (been there, done that ).
This is where PRs start to look like a viable alternative. It doesn't have any pipe modes, can be as big as manufacturing practices dictate, and if you choose correctly, can be tuned by adding/removing weight. Like pipe vents though, they have their practical usage limitations, the main one being that it needs to be tuned low due to the excessive group delay (GD) it has at its Fs, or ~one octave below Fb. Regardless of which PR or Fb you choose, as long as the GD decays to inaudibility by 30-35Hz, then you're good to go, another tidbit 'he who is no longer with us' didn't seem to know.
GM

 

[Dan Hine]

Greg and others,
Thanks for the knowledge sharing. I just looked back through the thread and saw that John posted a link to a PR FAQ. I'm going to start reading through that and if I have more questions I hope you don't mind if I ask them.
Dan