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Passive resonator dead end or worthwhile


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Since getting in to vintage Hi Fi I have noticed a few speakers such as Celestin Dittons  and R t R with passive resonators fitted ,basically a speaker with no voice coil or signal to it.

Was there any value to this design or if you have a pair would you be better off fitting actual speakers instead of them? Any information on them would be appreciated.  

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Passive Radiators (PR) work like a port, so they have a tuning freq without the typical noise a port can create.

They may have made the speaker a PR because the design and box size could not accommodate the length of port required or the air speed was to high for the port diameter for the tuning freq required?

Or it may have well been the flavour of that period!

 

PR's and Ports both have their plus and minuses...

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Since getting in to vintage Hi Fi I have noticed a few speakers such as Celestin Dittons  and R t R with passive resonators fitted ,basically a speaker with no voice coil or signal to it.

Was there any value to this design or if you have a pair would you be better off fitting actual speakers instead of them? Any information on them would be appreciated.  

 

To understand a passive radiator, first one must understand a little about the bass reflex loudspeaker. 

 

A conventional bass reflex loudspeaker utilises a vent, or port, to augment bass response. It does by by port 'tuning'. Tuning a port is a combination of port, length and area, which provides the designer with the mass of the air (yes, Tony Abbott, air does have mass, as does CO2). Essentially, a passive radiator design substitutes the mass of air, with a lump of solid material, coupled to the box via a compliant suspension. 

 

Both systems have their benefits and their drawbacks. Personally, I like passive radiator systems for several reasons, but other may disagree. 

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Was there any value to this design or if you have a pair would you be better off fitting actual speakers instead of them? Any information on them would be appreciated.  

 

Yes

No .... because simply swapping a passive radiator, for an actual speaker driver, creates a new system which won't perform the same (ie. correctly)

 

 

More reading @ http://www.aespeakers.com/PRFAQ.php

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Thanks Dave, does a PR have more of an affect then an equivalent port due to the increased surface area? I am guessing this is a drawback of PRs Trev was referring to. I apologise too if my persistent questions s*** you to tears.

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Further to the OPs question, I have one on speakers like the WLM shown. Won't the PR be 180 degrees out of phase with the driver? Can this timing issue affect the sound?

 

In a correctly designed bass reflex enclosure (whether it be ported or PR design), the output from the port or PR will be in-phase or not in-phase, depending on frequency. So, yes, the timing issue does affect the sound. It is supposed to. 

 

As I mentioned earlier, it is appropriate to treat a PR system in the same way that one would treat a ported system. For all intents, there is no difference. 

Edited by Zaphod Beeblebrox
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Thanks Dave, does a PR have more of an affect then an equivalent port due to the increased surface area? I am guessing this is a drawback of PRs Trev was referring to. I apologise too if my persistent questions s*** you to tears.

 

Its often more practical to have a larger area on a PR than a port.     That is where PRs have an advantage.... in a situation where a port would need to be too large.

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Since getting in to vintage Hi Fi I have noticed a few speakers such as Celestin Dittons  and R t R with passive resonators fitted ,basically a speaker with no voice coil or signal to it.

Was there any value to this design or if you have a pair would you be better off fitting actual speakers instead of them? Any information on them would be appreciated.  

 

Replacing a passive radiator with a driver is exactly analogous to cutting out the port of a bass reflex design and putting a second driver in its place.

 

It will be a completely new speaker that you will have to redesign from scratch. And if the existing bass driver is well-suited to a port (or PR) and not well-suited to a sealed box design, then your speaker will perform worse than stock.

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