Down-Firing or Rear Ports?

[villeneuve]

Hi guys,

Just wondering if it is better to have ports mounted on the bottom or the rear of the enclosure?
The driver itself is down-firing, and the enclosure is on a platform so that whole "carpet" thing isn't an issue.

Cheers.

[Azul Baronis]

Hi!

Make sure the speaker doesn't get out of phase with the bassreflex tube! I dunno how to do that really.
Hope this tip helps!

Kindest Reegards,
Wolfgang

[chris661]

Use winISD to sort out the whole size and diameter of the port

Other than that - down is probably best, as speakers (especially rear ported ones) tend to not like being close to a wall.

[Brett]

Originally posted by villeneuve
Hi guys,

Just wondering if it is better to have ports mounted on the bottom or the rear of the enclosure?
The driver itself is down-firing, and the enclosure is on a platform so that whole "carpet" thing isn't an issue.

Cheers.

If I have to use ports, I prefer to have them on the bottom. Minimises any chance of any any high frequency info coming out and being audible and the carpet will help further with that. Just round over / flare the port outputs and I always ensure there will be 80-100mm between the baffle and the floor surface.

[bottomfeeder]

I have built sealed and ported but always went back to sealed .
From what I read , any driver to be used for down firing must not sag too much , I think 10% max .
ports dont care too much about location but is best on the speaker face .
As the other letter stated any port noise will be absorbed by the ground (which is great )

[Brett]

Originally posted by bottomfeeder
ports dont care too much about location but is best on the speaker face .

There is no reason why placement on the baffle is universally best.

[chris661]

Originally posted by bottomfeeder
I have built sealed and ported but always went back to sealed .
From what I read , any driver to be used for down firing must not sag too much , I think 10% max .
ports dont care too much about location but is best on the speaker face .
As the other letter stated any port noise will be absorbed by the ground (which is great )

I think the sag of the driver etc will have been accounted for

And ports do care about location - even front firing ports can sound boomy when the speaker is near the wall

And why try to cancel the port noises, when you could simply round off the edge of the port, which takes out noises.

Down firing port would care less about location than rear, but it would still matter.

[bottomfeeder]

[QUOTE]Originally posted by Brett
[B]There is no reason why placement on the baffle is universally best

Here is some science..
at 20 hertz the wavelength is 55 feet so location wont matter , but at 100 hz the wavelength is 11 feet , so if the port is 3 feet away from the cone , its 1/4 wavelength away and so the cone and the port will be partially out of phase and cancell a bit .
You definitelly dont want the port 5 feet away from the cone (in like a sonotube)

[Azul Baronis]

that's exactly what I've been trying to tell you. If the tube gets out of phase with the driver, you will end up with even less bass than a sealed. If the driver and the tube are both on the front, it might be tricky to get them to play in phase. If they are on different sides of the speaker, that problem doesn't exist.

[Brett]

[QUOTE]Originally posted by bottomfeeder
[B]

Originally posted by Brett
There is no reason why placement on the baffle is universally best

Here is some science..
at 20 hertz the wavelength is 55 feet so location wont matter , but at 100 hz the wavelength is 11 feet , so if the port is 3 feet away from the cone , its 1/4 wavelength away and so the cone and the port will be partially out of phase and cancell a bit .
You definitelly dont want the port 5 feet away from the cone (in like a sonotube)

Der.

I still stand by my statement that front is not universally best as you stated. To give an example, the last ported sub I built had the driver on the baffle at the very bottom, and the port was on the bottom only a short distance away, so phase difference was minor.

I can always find an extreme example to make a point, but I understand physics well enough to not make the mistake of ports several feet away.