Difference between PR's and Porting (1 Viewer)

[TonyiBe]

I want to know the difference between using Passive radiators and Porting.

Thanks

 

[Seth_L]

There is no frequency response difference in theory. They're both Hemholtz resonators.

However, in practice you can have port compression and issues with the airspeed in the ports, which can cause audible chuffing. A PR bypasses these issues.

I don't have my Tumult, so I can't comment on the sound of a PR'd enclosure yet, but I'm told they sound different from ported enclosures, more like a sealed box, despite having identical frequency responses (or at least they can have identical responses).

Seth

 

[Travis Cain]

Like Seth said, they both work on the same principal.. I, personally, think that PR's sound a little cleaner and tighter than a port. There are many port advocates that will claim the opposite.

Neither one will yield a higher SPL than the other though.

So, unless you have a personal preference to the type of sound one or the other produces, then you're probably going to be happy either way.

Some things to consider...

Cost- Ports are far cheaper than PR's.

Enclosure size- If you're building a smaller cube sub with a higher excursion driver, it may not be possible to fit enough porting into the enclosure.. PR's will avoid that problem.

Physical appearance- I really think PR's look cool, myself.. I like to see moving cones, the more the better.

Tuning adjustment- Although it's not too often anyone needs to alter the tuning of their box, PR's make it simple.. Add or remove weight. With a port all glued in place, you can always trim it, but you can't make it longer (unless using a flared port kit and you don't actually glue the flares in place)

Either way you go, if it's the same box size and same tuning, you're going to get the same SPL and response, with only slightly differences in the sound which is really just a user preference..

I just bought a Tempest and 2 PR-15's so that shows how strongly I favor PR's over ports..

Hope that helps..

 

[Travis Cain]

Oh, and one other advantage PR's have over ports is driver protection below tuning..

With a port, once you get below it's tuning point, it unloads the driver completely making it very easy to push your driver beyond it's mechanical limits to a point of damage.. Passive radiators will still begin to unload the driver below their tuning point, but not nearly as fast as a port so you still have *some* protection..

 

[Jack Gilvey]

Lots of misconceptions. Try this:

http://www.stryke.com/prfaq.htm

 

[TonyiBe]

Thanks guys for the repsonses.

I knew Jack would chime in. I have seen some of the enclosures you built and i know you know PR designs well. Yuo build some nice enclosures. Thanks for the link as well.

 

[Mark_E_Smith]

As usual I learn something from the "fortunate son" ! I have a comercial pr system that sucks, I thought all prs did, but the Stryke FAQ makes since and has changed my mind. Maybe i'll take a look and see if I can tweek the system I have.

 

[ThomasW]

There are some 'misconceptions' on the Stryke site too.....

Properly design and implimented ports do not chuff or create compression. Nor do they create transient impulse 'ringing/overshoot' inherent with high mass PR's

If you need the smallest box possible then use a PR.

If you want 'vented' sub that has the best pitch definition and least 'coloration' use a port. But understand that the port MUST be flared. And it MUST be of sufficient diameter, to avoid issues like compression/chuffing.

Obviously this is just my $0.02.....

 

[Jack Gilvey]

When space/Vb permits a large enough ("properly designed" ) port, I'd always go/suggest that route.

I do not find that PR alignments sound "somewhere between a sealed and ported box" , as I've seen suggested, and I do not find that they offer more driver protection from unloading below Fb (I don't see how this could be the case unless there was little enough PR Vd available so as to negate the prime {or sole} advantage of PR's anyway).

 

[Seth_L]

Thomas,

I think the problem is how you define a "sufficient diameter" port. How much airspeed is allowable? Most (if not all) commercially available ported subs are underported.

Seth

 

[Jack Gilvey]

I think the problem is how you define a "sufficient diameter" port. How much airspeed is allowable? Most (if not all) commercially available ported subs are underported.

Yep, if you use freeware design programs as the criterion. I do not think that the effect of wide flares such as those on the 4" and 6" Aeroports has been accurately modelled. As I've stated before, I can't imagine what SPL it would take to compress one of the 6" Aeroports.

 

[ThomasW]

Seth

I think the general tendency is for undersized ports everywhere, given the co$t and box volume occupied by larger ones.

IMO 6" flared is the mininium size for a single high excursion 15". And 4" flared is appropriate for 12"s.

Now I'm certain that there are many people that will disagree with this. My experience is that 'overporting' to some degree is the best way to avoid the potential performance drawbacks of a ported design.

I don't get to fixated on mach numbers. It is important with 'woofers' reaching into the lower midrange. Subs on the other hand are more forgiving of slightly higher Mach numbers and or distortion. But unlike some, I feel that 10% distortion is too high

 

[TonyiBe]

Where can i get 6" aeroports. Will one be enough for an AV15...

Thanks Guys, i learned alot from reading the stryke site as well.

 

[Joey_N]

This was a good read, thanks for the info guys!

 

[Jack Gilvey]

Where can i get 6" aeroports. Will one be enough for an AV15...

I think that'll be fine. Go with a big enough box so it'll fit for the Fb you choose. Newfoam can special-order them for you. Not cheap, though, $50/pr. when I got mine. ThomasW is the 6" Aeroport expert 'round these parts.

 

[David Lorenzo]

Dual 3" flared ports would also work well for an AV15. It gives the same mach as a single 6", and they would be much shorter.

 

[Seth_L]

I don't think so David. The cross sectional area of two 3" ports and 1 6" port are not the same. a single 6" port has 2x the cross sectional area of two 3" ports and as a result has twice the length and half the air velocity.

Seth

 

[David Lorenzo]

Well then something weird is going on in WinISD. I never did any math. I just went by what WinISD came up with. A single 6" port measured a mach of .10, of course that would change with different tuning, and with 2 3" ports the mach given is still .10. You are right, however, about the area. So I don't see how the air speed can be equal. Any thoughts? Is WinISD wrong when calculating mach?

 

[Seth_L]

Are you sure you had the same input power? I used WinISD to come up with my numbers.

Seth

 

[Patrick Sun]

WinISD doesn't seem to be strong in calculating the mach numbers.