port and PR in the same box?

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Gotta love advertising!

Gotta love advertising: Same old sh*t with a different label, or plain old making something "new" just to be "different" from the rest, not necessarily better...

A port and a PR serve (very nearly) the same function in box design. They help tune the box & driver combination to a certain resonant frequency to help optimize the performance of the combination. I have never seen any simulation that allowed you to do both at the same time. All of the formulas I have read deal strictly with one or the other, not both, so I wouldn't know where to even begin to calculate theoretical values for such an arrangement!

I'd recommend going with strictly a ported or PR design. Typically, a PR is used where the port dimensions are too great to fit into the box.
Right, you've all had a good laugh at Rory's expense, but nobody has tried to answer his serious (to him) question. Has no-one heard of a 'stagger-tuned' reflex arrangement?


It is possible to tune a vented enclosure to two separate frequencies. This is done to extend and smooth the bass response for a given enclosure size and to reduce the two impedance peaks that are a characteristic of reflex designs. The 'dual' tuning could be accomplished by using two separate ports, but in this case one of the ports has been replaced with an ABR, probably because of space/size limitations.

The design of a 'stagger-tuned' enclosure is not easy as the ports interact with each other, though I believe some simulation software will handle it (I can't remember which, but I am sure I have seen at least one program that will do so). A lot of trial and error adjustment will be required after simulation to achieve a reasonable result and I don't think that this is a realistic option for DIY (unless you have access to equipment capable of performing a Fourier analysis of single-shot pulses). I have only seen one DIY design that used 'stagger tuning' and that was for a full range speaker, not a sub-woofer.

Hope this helps


You posted whilst I was composing my reply to Rory, hence this addendum.

I must disagree with you regarding the relative non-linearities of air and passive radiators. H D Harwood of the BBC Research Department published the results of his investigations into the non-linearities of air in speaker cabinets and vents back in 1974. From these results, it is clear that the distortion introduced by a port is greater than that for an ABR. In addition, an ABR is relatively stable and doesn't vary the enclosure tuning due to changes in temperature, pressure and humidity of the air in the port.

We're agreed on air being variable & imperfect, which is why I wrote 'for all its faults' in my previous post.
Distortion in the port is largely due to turbulence, which can be diddled back and forth a bit by experimenting with the diameter and tube length (if any), plus other odds and ends like rounding of the ends of the ports to encourage laminar air flow. Still, that too is imperfect. At least passive radiators avoid turbulence, so that's in their favor.
In a sealed cabinet using a passive radiator, the humidity, pressure, etc. changes will be minimized, so the design will retain the benefits you mentioned. However, in a dual port/passive radiator design such as Rory is describing, the problems would be back in full force, since the interior of the cabinet will be open to the atmosphere. Possibly, the problems would be even worse, due to the multitude of inter-related variables: driver/port, driver/passive radiator, changed relative tunings between the port and passive radiator...lotsa things to balance there.
My main objection to passive radiators is the mass; I've yet to hear a design at any price point that I thought had comparable bass to a well-designed infinite baffle or ported design. They always seem to be...well, boomy is too strong a word. Perhaps muffled? Anyway, they seem to lack articulation and tightness. It always seems to me that once the passive radiator gets moving it wants to keep going, which blurs (aha! that's the word I wanted) the impact of whatever is going on in the bass.
I tend to use sealed cabinets, but I have nothing against well-done reflex cabinets, and have used transmission lines to good effect in the past (not a reflex, per se, but they're generally open to the air, hence variable in that sense). Sadly, I'm still waiting to hear a speaker using a passive radiator that convinces me that they're worth the trouble. It's always seemed to me to be a nifty idea that just didn't quite work out.
That said, it's always an intriguing idea to play with if one has a blown driver or two on hand. Pop off the magnet, and you've got a free passive radiator (in addition to a free magnet for other experiments, such as the DIY ribbons I've mentioned elsewhere). Since the characteristics are somewhat free form, you can expect a lot of cut and try as you integrate it into the speaker, but if you're interested in the passive radiator concept, it need not cost extra money (as long as you've already got dead drivers on hand, that is...).
As for software that would help design a hybrid cabinet, alas, I'm no help. I don't remember seeing a program that would handle both a passive radiator and a port. I agree with Geoff that it's likely to be a fair hunk of work before something of that nature could be brought to completion.
I seem to recall that you've mentioned several other speaker design approaches in other threads. It might save you time (and money) if you were to listen to a number of speakers of different design philosophies and see if you can identify a common design characteristic that produces sound that you like. If you spend all your time reading White Papers (9 times out of 10, just thinly disguised sales literature, although there are exceptions), you're going to end up being convinced that every idea is the greatest idea in the world. Common sense tells you that out of any random group of ideas, perhaps 10-20% will be winners, 50% so-so, and the remainder absolute duds. Unfortunately, the proponents of the dud ideas squawk as loudly (and sometimes louder) than the winners. This is where experience comes into the picture.
Go forth and listen.
You'll soon be able to separate some of the wheat from the chaff. That will give you more focus as to how to proceed with your DIY projects.

Geoff: It seems that in order to provide two different tuning frequencies, the enclosure would have to have at least two separate chambers with the driver located in between them. This way, chamber #1 could be tuned to one frequency while chamber #2 could be tuned to another frequency.

Providing two tuning points with only a single chambered enclosure doesn't seem possible. If a single chamber had two ports with different dimensions or a port and a PR, it would seem that the two would interact to provide one poorly tuned box rather than a box with 2 different tuning points.

Building a single box with two chambers is substantially more work in both design and construction (not to mention cost of materials) than simply building a traditional vented box. As a result, dual chambers are not generally recommended for beginning builders.

My earlier criticms were not directed at Rory, but a general criticism for marketing/advertising in general.


If you think back to the basics of the Helmholtz resonator, its method of operation is due to the mass of the air in a port or tube resonating with the acoustic compliance of the air in the enclosure. Two different sized ports will have two air masses and two distinct resonant frequencies if placed in a single enclosure. However, as I said in my original posting, there will be considerable interaction between the ports and this will make analysis extremely difficult.

I have only seen this approach used in one design. This was published in the November 1994 issue of Hi-Fi World (a UK magazine).

Goeff, I agree with Eric, that it is not possible to tune a single enclosure to two different frequencies by the use of two different vents. The acoustic masses of the vents will simply add together to give a single mass that resonates with the enclosure compliance. This is simple physics and readilly demonstrated in practice. The justification for multiple vents is either to give a choice of tuning frequencies to try and match the speaker to the room, by simply blocking one or other of the vents, or to spread the frequencies of the standing waves that occur along the length of the vents at higher frequencies.
Take two ports into your listening room?

Some of the Royd loudspeakers used two ports, with staggered tunings.

They did have two internal enclosures thougg, for the two bass / mid drivers in the design (e.g. Royd doublet).

They are one of the best ported loudspeakers I've heard, as a sealed enclosure fan ;)

Rory said:
I noticed something weird about Philips' wOOx subwoofers: they use both a passive radiator and a port in the same speaker box. How would I go about doing something like that?

The previous responses (even the bad jokes) all make the assumption that this is a single-chamber enclosure. There are many designs that use two chambers in the enclosure, where both are ported. Is there any chance that this is a bandpass enclosure of some sort?

As to building one, it would be a lot of work. You'd have to simulate the enclosure with two ports, then replace one of the ports with a passive radiator. Fortunately, the knowledge of how to do this exists, and it's not really too complex. The hard part is to get a good bandpass enclosure. In the simulations I've performed (with LspCAD Pro), they typically have poor transient response.

This is not something I'd suggest to anyone, except a seasoned speaker builder.
Best Buy

Well, there's a Best Buy moving in down the street from my subdivision (within walking distance), so while Best Buy might not be the highest-end place, I can at least hear many, many different types of speakers. What's impressive about this is that wOOx has not gone unnoticed in DIY loudspeaker circles. On the Subwoofer DIY page, we have agreed that wOOx is probably just a Passive Radiator tuned to the same frequency as a port.
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