PORTS.......what do you actually meant to tune a port to?

[3rutu5]

guys, be gentle, through guidance and having a go, i've managed to work out what i need for a build, but recently it made me think "is the goal to get the 1st port resonance closer to the tuning on the box?" or other. Ive heard people talk about octaves etc, but as i dont really know what that means i thought i would ask the question.

I'll use something i was modelling as the basis of any discussions as that is something i will intend to make. For this one, i've modelled 1x driver and single enclosure assuming 4x 15mm ports each 80mm long, doing such gives a 1st port resonance of 480hz, normally i would have gone 1 or 2 per side which would result in 1000-2000hz and possibly even a 18 or 20mm piece of electrical conduit.which would probably give me close to the 480 but would result in almost twice the single length.

So the question is, as a guide if somebody s tuning boxes between 50-100hz what would a rough rule (range) of thumb be in the 1st port resonance?

the reason i'm using 15mm as i have 1.2m of PVC in my garage and fresh out of the electrical conduit and a trip down to the hardware store would be deemed non essential and i would like to play my part and stay isolated.

[devnull]

There's a rule of thumb for subwoofers that says port resonance should be one octave above the LPF frequency. The problem you may run into is you are trying to use a full range driver which means the resonance will be in the frequency range of what you want the speaker to produce. Probably need to port it out the back.

[fpitas]

Agreed that porting out the back will be your best option.

[3rutu5]

Yes thanks guys, was intending to put them.out the back, got to much weird noise the first build I did when I put a port out the front.

But this was a different build completely, so if I'm turning a full range to hit 90hz I should be getting the resonance to that? Sorry I just got confused

[fpitas]

I know very little about small speakers, but I understand the bass can sound nicer if there's a slight hump near the bottom of the range.

[Chris Roemer]

Purdy sure that a port's resonance is directly related to its length (though maybe it's a mass/x-sectional area thing, just like box tuning?).
You should be able to monkey around in WinISD to verify (or disprove) this.

Avoiding (or trying to target) a certain resonance freq. would certainly be secondary (in my mind) to all the other tuning variables that need to be juggled.

[fpitas]

Purdy sure that a port's resonance is directly related to its length (though maybe it's a mass/x-sectional area thing, just like box tuning?).
You should be able to monkey around in WinISD to verify (or disprove) this.

Avoiding (or trying to target) a certain resonance freq. would certainly be secondary (in my mind) to all the other tuning variables that need to be juggled.

Yes Chris, it's just the pipe resonance, which is mainly a function of length. I *think* we're also talking about the particular port tuning frequency too, but I'm not sure.

[fpitas]

To the OP. Usually one tries to get the port resonances out of the passband of the woofer. In this case that is probably not possible, so you live with them.

Some alternatives you might consider are using a passive radiator, or designing a transmission line enclosure.

[ernperkins]

Did you notice that WinISD is modeling the ports to be about 14"( 358 mm) long? That will be a strange looking beast!

[fpitas]

Did you notice that WinISD is modeling the ports to be about 14"( 358 mm) long? That will be a strange looking beast!

Hang it out the back like a sporty exhaust?

[billfitzmaurice]

A few notes. When you get response like what's in the chart that usually indicates a box that's too small. When the port seems abnormally long that's also an indication of a box that's too small. The port resonance isn't a concern if it's not being excited, which you'd see in the port gain chart. Most of those issues are fixed by making the net cab volume 0.5 cu ft. There's still a hump and dip, but that's unavoidable using a high Q driver in a ported alignment.

[devnull]

A few notes. When you get response like what's in the chart that usually indicates a box that's too small. When the port seems abnormally long that's also an indication of a box that's too small. The port resonance isn't a concern if it's not being excited, which you'd see in the port gain chart. Most of those issues are fixed by making the net cab volume 0.5 cu ft. There's still a hump and dip, but that's unavoidable using a high Q driver in a ported alignment.

So the OP should put a 2" driver in a box that's 20 times bigger than what he's simulating?

[Dukk]

In the past I generally paid little attention to port resonance as I was mostly designing subwoofer boxes and with the LPF far below the resonant frequency, it just wasn't an issue. Certainly any full range, most two way, and even some three way designs will have the driver playing in the port resonance area.
As mentioned, remedies amount to altering the vent to move the resonance out of the pass band, placing the vent on the back to minimize its effect, eliminating the vent (but that's no fun), or just living with it. A lot of designs out there have the vent on the front so while vent resonance is an issue, it is not generally a big one.

[craigk]

Bill M is correct. the box and ports are both to small.

[fpitas]

If he's going large, I'd vote for a transmission line