Ported FH Enclosure

[pikipupiba]

I've seen a bunch of folded horn designs which put the sub in a sealed box at the end of the horn. What would happen if you ported that enclosure? Pros? Cons?

MOST IMPORTANT PART!!!!! If this isn't readily doable, is there a way to make it work?

[chris661]

If you port the enclosure, the driver will unload completely below port tuning, so you'd lose some mechanical security.
At port tuning, the port will be very active, the horn will be very inactive. You'll probably get similar output levels as with a sealed box.

Chris

[pikipupiba]

Originally Posted by chris661

If you port the enclosure, the driver will unload completely below port tuning, so you'd lose some mechanical security.
At port tuning, the port will be very active, the horn will be very inactive. You'll probably get similar output levels as with a sealed box.

Chris

So really low tuning frequency? And could you explain driver unloading to me? I haven't gotten that yet...

[Rademakers]

Most portable front loaded bass horns are of insufficient size to get decent output below 40 -50 Hz (at least in singles). The port in the chamber can be tuned below the Fc of the horn to add some extra output in the lower regions of the spectrum.
If the chamber and port are of sufficent size the output that is gained is higher around tuning then would be the case for the sealed cabinet. It's however generally lower then the output from the horn itself.

Most chambers on front loaded horns are pretty small and therefore very low tuning would be hardly effective. It's best to model this in a programm such as Hornrresp to see what an effective tuning will be.

Below the tuning frequency excursion needs will rise rapidly above that of a sealed chamber a.k.a the unloading of the driver. It will justify the use of high pass filter set at or around the tuning frequency. At and above the tuning the excursion need is lowered. In that way it can be used as an physical filter for excursion control.

Best regards Johan

[pikipupiba]

Originally Posted by Rademakers

Below the tuning frequency excursion needs will rise rapidly above that of a sealed chamber a.k.a the unloading of the driver. It will justify the use of high pass filter set at or around the tuning frequency. At and above the tuning the excursion need is lowered. In that way it can be used as an physical filter for excursion control.

Best regards Johan

But WHY does this happen?

[Top Shelf]

A sealed box provides damping to the cone thru pneumatic compression and rarefaction and has a linear 12 dB/ Oct slope where cone motion increases with lower frequencies. A ported box uses box volume / port and driver mechanical damping eg. surround, spider to control cone motion above fb. @ FB all/ most of the acoustic power is radiated by the port(maximum driver damping). Below fb the port cannot control the motion of the cone , so the cone acts like it were in free air and only has the driver mechanical suspension ( and a little bit of back emf) to control motion. So power handling drops and the cone easily bottoms out. CLACK CLACK.

[pikipupiba]

Ok, that makes sense. Any good sites that really go into the physics of every enclosure type like you just described?

[Top Shelf]

I have a pyramid 1811 ous-x that hits its thermal limit at 1000w rms 20-50 hz without bottoming out in a 50 hz FLH with the ports in the "throat chamber". So I would say pick your drivers carefully. There is discussion about this going on in the horn resp thread, though I don't think anything has come of it.

Not off- hand. But the Loudspeaker Cookbook covers this and quite a bit more