Positionning the port on it...

[youyoung21147]

Hello,

I am currently designing a TQWT for a friend, based on a Supravox 165LB. (I gave up the horn, way too big !!)

The previous enclosures I designed all used a frontal port, a solution that always gives satisfaction due to the synchronised driver and port waves.

My friend has a small room, and I'd like to take advantage of corner and floor loading in my design, involving rather a back or side port than a frontal port.

But I'm quite afraid to encounter phase problems and severe dips and peaks with a port that is not on the front of the enclosure.

I have also heard using a rear port could reduce the midrange output through the port, which is a very good thing.

I'm rather looking for a side port, because it doesn't involve leaving space behind the enclosure.


So I'm asking you, port experts, what you think about this port stuff, and what you tried with success !

 

[pinkmouse]

Wavelengths at the frequencies the port is operating at are fairly long, so positioning isn't really a problem. The only issue I can see with side mounting ports is that box width is usually the smallest dimension, so if it's long, you might need to put a bend in the port.

 

[Dumbass]

The previous enclosures I designed all used a frontal port, a solution that always gives satisfaction due to the synchronised driver and port waves.

The back wave is out of phase with the front, so there is absolutely no guarantee that putting the port on front will make the two outputs in phase. To the contrary, in fact.

Rear-firing the port gives a little more boundary reinforcement for lows (expecially if near ground). It also attenuates some of the high freqs that aren't supposed to get through the port, but do.

Unless you plan on having the enclosure flush against the wall, I think rear-firing is the way to go.

 

[youyoung21147]

OK I'll try the side port, so.

Length of the port won't be a problem, I find it even really short on my TQWT. TLs often have big and short ports.

Concerning the shape of the port, which is prefered ?

A tube, a slot, a vertical slot, several tubes ? (my port will not be at the end of the transmission line, but 8" above the the bottom.)

 

[Dumbass]

Concerning the shape of the port, which is prefered?

Round tube is easiest to predict, and I believe least likely to whistle. Flared ports are supposed to prevent turbulence at the ends, perhaps important for big vented subwoofer but probably not too important for full-range project.

 

[pinkmouse]

Yes, round should be fine. It's also easier to tweak if you need to!

 

[youyoung21147]

OK thanks a lot.

I'll go to a DIY shop this week end to see which diameters of PVC pipes are available. Cheap, solid and acoustically neutral .
Just what I need Hope they will have some 100mm + pipes lol !

Greets !

 

[Scottmoose]

Just to add my vote for the round ports. Much less ripple as a rule than a slot port. Remember not to place it right at the bottom of the cab. though. 3" - 4" up is usually a good place to start.
Cheers
Scott

 

[youyoung21147]

Yes, I placed the port above the bottom.

I just have a little question about the speaker's position :

How much space do you usually leave between the port and the wall, not to get a stuffy sound and uneven response ?

 

[pinkmouse]

Good rule of thumb is leave at least the diameter of the port to the wall or any other obstructions. That also applies internally.

 

[youyoung21147]

OK, thanks, so there is no problem in my case !

I'll try this soon and hope it is worth a try, because it must be a solution to baffle step diffraction I think

 

[Scottmoose]

I don't want to sound negative, but it isn't really. For that, you need some form of BSC, or an identical rearward firing driver. Still, it won't do any harm.

 

[youyoung21147]

You mean if I don't want to put the port on the front, I must put it on the back to have the expected bass boost ?

 

[Nuuk]

Before I discovered the joys of open baffles, I played around with issues such as where to place the port.

I tried all the options and settled for having it on the bottom of the cabinet, with the cabinet raised a few inches (cms) off the floor.

 

[youyoung21147]

I unfortunatlely cannot place the port on the bottom, because the optimised geometry for this TQWT is 13" above the bottom !

Otherwise, do rear ports provide a well refined and fast bass, such as front ports ?

 

[Nuuk]

Otherwise, do rear ports provide a well refined and fast bass, such as front ports ?

On the BR boxes I played around with, I didn't notice much difference between front and rear firing. If there is at least some space behind the speaker it shouldn't make much difference but I think if I had to make a choice, I would put a port at the rear!

 

[youyoung21147]

OK thanks for the advice !