Subwoofer with a passive radiator, but is otherwise unvented -- should it be considered sealed?

[Forsooth]

Just curious since I read a post a few days ago about a REL sub that has a powered speaker and a passive radiator. I think the poster referred to the sub as "sealed." Thanks.

 

[Verdinut]

With a speaker enclosure using a passive radiator, the air in the cabinet is sealed but the passive radiator acts the same way as the air mass contained in a port. A passive radiator is a type of vent substitute which closely follows vented design methodology and performance.

It has two important advantages over vents: It eliminates vent colorations, wind noises and internal high frequency sound reflected from within the box out of the vent,
and it's practical for small enclosures which would call for vent lengths in excess of internal box dimensions.

It has some downsides too, such as a steeper cut-off and would have less transient stability, a slightly higher cut-off frequency and greater overall losses (Qt) than vented designs.

 

[j_garcia]

That results in a sound that is more similar to sealed than vented, despite the behavior of vented.

 

[Forsooth]

<SNIP>...It has some downsides too, such as a steeper cut-off and would have less transient stability, a slightly higher cut-off frequency and greater overall losses (Qt) than vented designs.

Thanks for the response. Just to make sure I understand...

• by "steeper cut-off," do you mean the lower end roll-off would usually be steeper than with a one-speaker sealed sub?
• by "less transient stability," the word stability is throwing me a little. Do you mean that the passive radiator sub may not produce transients as well as a one-speaker sealed sub, i.e., would tend to be less dynamic?
• "greater overall losses (Qt) than vented designs" goes over my head. I need the dummy's version.

Thanks again.

 

[Verdinut]

Thanks for the response. Just to make sure I understand...

• by "steeper cut-off," do you mean the lower end roll-off would usually be steeper than with a one-speaker sealed sub?
• by "less transient stability," the word stability is throwing me a little. Do you mean that the passive radiator sub may not produce transients as well as a one-speaker sealed sub, i.e., would tend to be less dynamic?
• "greater overall losses (Qt) than vented designs" goes over my head. I need the dummy's version.

Thanks again.

1. You're right 2. The PR sub bass might not be as tight as either a vented box or a sealed one. 3. The "Qt" is one of parameters exposed by two engineers, Thiele and Small, in their research on the function and characteristics of loudspeakers. It has to do with the control of a cone's movement which is mainly dependent on the suspension of the moving mass, the ratio of the strength of the magnet to the moving mass and the enclosure design.

 

[Forsooth]

1. You're right 2. The PR sub bass might not be as tight as either a vented box or a sealed one. 3. The "Qt" is one of parameters exposed by two engineers, Thiele and Small, in their research on the function and characteristics of loudspeakers. It has to do with the control of a cone's movement which is mainly dependent on the suspension of the moving mass, the ratio of the strength of the magnet to the moving mass and the enclosure design.

OK, thanks. I had looked for info on the "Qt" item but was unable to find anything other than there is a speaker company called Qt. I'll do some additional research. 'preciate the information!

 

[Forsooth]

OK, thanks. I had looked for info on the "Qt" item but was unable to find anything other than there is a speaker company called Qt. I'll do some additional research. 'preciate the information!

Forget it! It's based on engineering math formulas.