# Ported vs Passive radiators



## ISLAND1000 (May 2, 2007)

Has anyone had the opportunity to compare speakers where the first has a port and the second has a passive radiator?
Is there a discernible sound quality difference between the two?


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## robbo266317 (Sep 22, 2008)

I have only heard one speaker with a passive radiator. 
Theoretically I would assume the PR to respond slower than the air in a ported enclosure. Just my gut feeling....
However, with the wavelengths involved, this is probably not an issue.


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## ISLAND1000 (May 2, 2007)

robbo266317 said:


> I have only heard one speaker with a passive radiator.
> Theoretically I would assume the PR to respond slower than the air in a ported enclosure. Just my gut feeling....
> However, with the wavelengths involved, this is probably not an issue.


Thanks for your observation. Response time was an issue I was wondering about too. The WinISD program includes a delay graph and I can run two box designs at the same time comparing the delay of PR/ported/ AND sealed. Interesting stuff.

Evidently I'm in "No mans" land on this issue. I'm finding very little anywhere.


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## fbov (Aug 28, 2008)

Acoustically, a passive radiator is just a port with very dense air. 

This all goes back to spring-mass systems. You have a driver (mass) exciting a cavity (spring), and a port (mass) resonating with the cavity (spring). It might be easier to visualize if you stop the driver. Then the port mass oscillates like a body on a spring, losing apmplitude to parasitic losses. 

Passives have the ability to carry mass far in excess of the comparable driver's cone mass, and that added mass is adjustable, allowing them to be tuned, like one does port length. Why use them?

When designing small, low-tuned boxes, port length required to trap enough air mass becomes ungainly long, perhaps 2-3x box dimensions. This situation is easily solved with a passive radiator (or two) allowing you to use a far smaller box without a smokestack. 

In my case, a >1 cu ft. subwoofer box, 13" on a side, needed a 20" long port, or a pair of passive radiators. Only later did I realize that a 2 cu ft. box ported worked beautifully! Cie la vie!

HAve fun,
Frank


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## ISLAND1000 (May 2, 2007)

Before you go Frank,
Did you build the 13" cube with the PRs? And if so, what were your thoughts about the quality of the sound?
If you didn't build it, have you ever heard a box with a PR?


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## fbov (Aug 28, 2008)

I built a pair of Triska subs with 2.1 plate amps for my kids. While the system did what I wanted - played loud enough - it didn't have as much extension as I like. That's a result of Hoffman's Iron Law - size, extension, SPL pick 2. 

In general, I like sealed best, then ports then passives. Jim Salk and Jeff Bagby had a monster 3-way with a massive passive, and I just didn't hear the bass extension... could be a lot of things besides the design. 

HAve ufn,
Frank


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## fusseli (May 1, 2007)

I'd think that a PR and a ported sub should sound pretty similar. An advantage of the PR is that it doesn't face air velocity (chuffing or compression) constraints. To me, the only reason to go PR over ported would be to have reduced cabinet size at the higher cost premium of buying the PRs.


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## larft (Jan 30, 2013)

I have a Sunfire subwoofer that is a 13" cube with a PR and it sounds great, but it's a highly engineered $2000 sub, I'm sure part of the design requirement was small size as well as high output. I know it's not really an answer but it sounds like an opportunity for experimentation, if properly implemented it should sound quite good in comparison to a port in my opinion.


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## ISLAND1000 (May 2, 2007)

Your Sunfire mini sub was one of the reasons I'm asking questions.
I heard one years ago. Of course I don't remember the quality of sound but I remember being amazed at what I thought was loud quality back then.
I'm looking at using a small passive that could possible handle the power and excursion from a 10" Beyma woofer. The Beyma woofer has a linear excursion of 6,5 MM and a xmax limit of 13MM.
Parts Express sells a 10" Dayton passive for $26.00. or a 12" for $36. Either one could be over driven by the Beyma but who cares? they're just a passive.
I'm more interested in the sound quality since this latest project of mine is supposed to be the end all sound quality using the best of everything and getting the flattest response with the least distortion and the most accurate phase relation.


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## larft (Jan 30, 2013)

It does indeed have the capability to play VERY loud, which is not how I use it, I can't say that the sound quality is superb since I don't currently have a better comparison, it's the best sounding sub I have. In general terms as you have probably read you usually get the smoothest response and best phase properties from a sealed, not ported or PR augmented enclosure, certainly from the perspective of ease of design and implementation especially if you have a very capable low frequency driver. The port and PR approach in general terms is less accurate frequency and time wise but is more efficient.


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## larft (Jan 30, 2013)

I should also mention that I have plans to build either a single sub or dual subs for my 2 channel system that currently uses the Sunfire and my initial direction would be to do a passive sealed enclosure, depending on the results I might revise my opinion.


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## fusseli (May 1, 2007)

ISLAND1000 said:


> Your Sunfire mini sub was one of the reasons I'm asking questions.
> I heard one years ago. Of course I don't remember the quality of sound but I remember being amazed at what I thought was loud quality back then.
> I'm looking at using a small passive that could possible handle the power and excursion from a 10" Beyma woofer. The Beyma woofer has a linear excursion of 6,5 MM and a xmax limit of 13MM.
> Parts Express sells a 10" Dayton passive for $26.00. or a 12" for $36. Either one could be over driven by the Beyma but who cares? they're just a passive.
> I'm more interested in the sound quality since this latest project of mine is supposed to be the end all sound quality using the best of everything and getting the flattest response with the least distortion and the most accurate phase relation.


You don't want to over-drive a PR or there could be consequences. Manufacturer's usually list a mechanical excursion limit for PRs, which would be the same as Xmech (a.k.a. Xlim) for a woofer, not the same thing as linear excursion (Xmax) with a little excursion beyond that to spare (perhaps a specific driver has an Xmech that's 110% of Xmax).


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## ISLAND1000 (May 2, 2007)

Thanks for the warning Fuselli. 
The Dayton passives have an Xmech of 10MM. 
Although I crank the system once in a while, the mains with the Beyma woofer are limited by the receiver to 80Hz where the sub takes over in a 2.1 or a 5.1 speaker setup. I could even crossover higher say 120Hz.
I know it's cutting it close and I could regret it but what's life without taking a few chances? The PRs are only $26 ea.
I got rid of most of my old drivers and now wish I had kept some for experimentation. I could make PRs out of them.
Do you know of anybody with throw away 10"/12" drivers?


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## fusseli (May 1, 2007)

Tuning the PRs by adding/removing mass to the cone might be tricky with a home made PR. Most of the purpose-built PRs make it easy by having provisions added that you can add steel washers to.


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## ISLAND1000 (May 2, 2007)

Years ago I made a PR out of an old driver. I tuned it by gluing strings of solder in a circle onto the front of the cone where the cone met the "cap". It definitely lowered the Fs of the driver but without test equipment I had no idea what the adjusted Fs was. The end result though was that the driver played lower and used as a PR the combination of driver and PR was interesting but unpredictable. Never DID finish that project.


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