Ported or Passive Radiator ? (1 Viewer)

[Chris Carswell]

Is there an advantage to a PR over a port? I will be making some MTM's with 6.5" drivers soon and wanted to know which is better. I would like for them to play as low as poss.
The towers can be anywhere from 1.8 ft^3 to 3.0 ft^3 and the center .75 ft^3 to 1.0 ft^3.

If I design the speakers (WinISD) with a nice flat frequency response and a port to have an f3 of 40 hZ, what would be the advantage of a PR? Will it play louder or go lower? From what I can tell it looks like the PR wouldn't be as good. I guess PR's really start to shine when used in small sub boxes.

 

[Shawn Solar]

Ports and Pr's do bassically the same thing but using different methods. A pr is used when the port you want to use or need will not fit into the enclosure cuase it is too big or the enclosure is too small. A port is much cheaper than a pr so if it can be used than that would be the way to go. I can't speak from personal experience but I do not think there is a difference in sound quality between the two. To my knowledge they both share the same rolloff characteristics below tuning.

A port can be used vertically or horizontally a pr, can only be mounted vertically and can not be mounted top or bottom of the box.

A port can compress at high excursion levels and produce a chuffing sound. a pr won't. But using 6.5" drivers I don't think it will be a problem. Though I'm sure someone with a more technical opinion could give you a more specific answer.

 

[Patrick Sun]

Ports are cheaper, PRs are lots more expensive. As always, always a trade-off involved in building subwoofers.

 

[Jack Gilvey]

I don't think I'd bother with PR's in anything but a sub, especially with smaller woofers.

 

[Mark_E_Smith]

Peerless has an interesting artical on designing sealed, vented, and PRs here:
http://www.partsexpress.com/pdf/xls12app.pdf
40 hz should not be hard for a ported system if you pick a good driver.

 

[Chris Carswell]

Sounds good guys & thanks to all that replied.
I think I will stick with the port. It's cheaper and will do the same thing. I thought about the PR in lou of the 12" svs subs I had that I wanted to stick in the MTM towers. If I can get ~ 40Hz from a vented 6.5" MTM I think my tempest can do the rest.
Mark, you should know what drivers.........

 

[Andres Arizaga]

Hi there.
IMO PR gives a better performance than bass reflex config.
why dont use the air wich flows by the ports, to move another woofer (PR)?.
A PR config, offered the same performance of a BR one, but in an smaller box; that simple example shows that PR defeats BR.
CYA.

 

[Jack Gilvey]

A PR config, offered the same performance of a BR one, but in an smaller box; that simple example shows that PR defeats BR.

This is a common misconception. A PR doesn't suffer from the compression and noise that small ports do (is that what you mean?), but a given alignment for a woofer still requires a similar Vb. A PR won't magically give a certain curve in a smaller box.

 

[Wayne A. Pflughaupt]

Speaker building is out of my realm of expertise, but it seems to me that a passive radiator would not be subject the “chuffing” and wind noise that plagues some port systems (based on the excellent performance of PR speaker systems I’ve owned in the past).

It also seems that group delay would not be a problem with a PR as it often is with ported subs – true?

Regards,
Wayne A. Pflughaupt

 

[Patrick Sun]

It's all about the benjamins when it comes to PRs.

 

[Jack Gilvey]

It also seems that group delay would not be a problem with a PR as it often is with ported subs – true?

Actually, GD and transient response can be slightly worse, although I haven't found this an audible drawback.

 

[alejo lamadrid]

I can´t compare PR vs Bass Reflex or vented.
I can´t compare a F1's car vs a Nascar's car.

 

[alejo lamadrid]

I can´t compare PR vs Bass Reflex or vented.
I can´t compare a F1's car vs a Nascar's car.

 

[Jack Gilvey]

Umm, ok.

 

[Brian Bunge]

NASCAR is a dirty word to me!

 

[Tim Kilbride]

One of the chief advantages of using a PR over ports is that you get the best of a few worlds.

First, the box is still a "sealed" enclosure, so you get the advantages of a sealed box (ie higher power handling,etc)

Second, you achieve a lower tuning because the PR will work in conjunction with the woofer and act like a larger cone area moving without the extra motor to push (voice coil) therefore affecting impedence and reactance curves.

Third, MUCH more effecient than ported enclosures

It will sound much more like a ported enclosure with none of the drawbacks...


Tim K.

 

[Jack Gilvey]

It will sound much more like a ported enclosure with none of the drawbacks...

Well, it is still a bass-reflex, and is still susceptible to overload below Fb and has inferior transient response on paper. It can approach an ideal reflex more closely than a port in many circumstances.

 

[Shawn Solar]

Hey Jack, was it you that had that link to pr's and how they work? If I remember right a port and pr work in the same manor. They both use a mass of air to resonate at a given frequency. either determined by mass of the pr or length of the port.

They accomplish the exact same thing but are used under different circumstances. like when the port won't fit in the box. Or port 'chuffing' becomes an issue. PRs are expensive so when the equivelent port can be used it becomes a lot more cost effective.

 

[Jack Gilvey]

The best such link I had was the PR FAQ at Lambda Acoustics, but that one died when they got out of DIY. I noticed today that it seems they're still in the game, though, with raw drivers and PR's available on the site. Maybe the FAQ will come back if we ask all nice-like.

 

[Tim Kilbride]

Jack,
The box is still a sealed enclosure means that there is no exchange of air between the inner volume and the outside world. So the characteristics of a sealed box still apply here.

As for the lower tuning...the PR actually works with the woofer not against it...when the woofer extends outward, so does the PR. It is not a push/pull relationship. So therefore the moving mass is the surface area of woofer 1 plus the surface area of woofer 2. However, you do not have to move two voice coil structures, only one (the PR is passive here). Thus all of your electronic characteristics would be the same for a woofer only box.


As for the effeciency...a sealed box is much more effecient than a ported box. See above...It takes a lot more power to move the motor structure of a speaker and air (ported), not to mention your 3db down point is usually tuned below the port tuning; whereas, in a sealed box the 3db down point is within the performance spec of the speaker/box combination...

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Well, it is still a bass-reflex, and is still susceptible to overload below Fb and has inferior transient response on paper. It can approach an ideal reflex more closely than a port in many circumstances.
*********************

I agree with this fully...this is also why you stuff a ported box with acoustic fill and a 'true' sealed enclosure is not stuffed. The fill only helps control the resonances...a sealed box acutally uses the resonances to its advantage (helps with the bottom end). A good example would be some of the older Boston Acoustics and Tannoy loudspeakers. They used very small drivers (6.5" or so) in huge volumes of air...the speakers had excellent bottom end and did not need very much power to run them...but they were 'big'. Paul Klipsch used sealed enclosures tuned to specific frequencies coupled with horn flares to increase the effeciency and increase the power to signal ratio...but look how big the Klipschorns were!!! As for ported boxes, use can use an average size box and get some pretty decent bottom end...but you need a ton of power. You can however, use a very small sealed box, and extra heavy motor assembly (speaker with huge magnet/4 layer coil) and a shitload of power and make it sound good...if you add a passive radiator to the mix it can really get low and loud...just look at the Carver True Subwoofer...a prime example.

Thanks
Tim K.