Is there such a thing as too long of port length?

[Ronny 10+ year member]

Hey all, I'm wondering if there is a downside to having relatively long port lengths?

I'm working on a dual 12" enclosure currently.

Outer dimensions will be 31x15x15

Port dimensions come out to 2.5x13.5x30.5

This will be for two Mach 5 SPL-12s. I'm told they work well in 1cube net per woofer ported, I'm trying to obtain a tuning of 35hz in an enclosure that will come about to roughly 2.1cubes net after all displacements. Drivers displace a total of .4cubes. Port displaces about .5cubes. This will work out to a little over 16sqin per cube.

Also, does anyone recommend a slot port in the middle of the enclosure over a port off to the side utilizing a sidewall?

Thank you,

Ron

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[wickedwitt 10+ year member]

My 18" says no.

Seriously though, I have 2 12's each have a 4" x 24" x 18" port

 

[RAM_Designs 5,000+ posts]

I would use a single port on the side so you don't have to split the port into two narrower ports at the back of the box(if you were to do one down the middle). There's really nothing wrong with having a long port, and 30" really isn't too terribly long. Granted, a shorter port is better because there's less resistance going down a shorter port, but at the same time you need adequate port area for the subs you're using.

As far as box size goes, I don't know where you heard that those SPL-12's work well in 1ft^3 each...try 2-2.25ft^3 each. Do a 4ft^3 common chamber box and use a bigger port as well.

 

[Ronny 10+ year member]

I would use a single port on the side so you don't have to split the port into two narrower ports at the back of the box(if you were to do one down the middle). There's really nothing wrong with having a long port, and 30" really isn't too terribly long. Granted, a shorter port is better because there's less resistance going down a shorter port, but at the same time you need adequate port area for the subs you're using.
As far as box size goes, I don't know where you heard that those SPL-12's work well in 1ft^3 each...try 2-2.25ft^3 each. Do a 4ft^3 common chamber box and use a bigger port as well.

Thanks.

Yeah, that was given directly from the designer and builder of the woofer Mark. I was speaking with him and told him I planned to do 4cubes net shared but he directed me to do 1 cube net per woofer and tune to my liking. Perhaps I'll do both, I'm sure Mark has tested the woofers to hell and back so we'll see.

Or.. Maybe I'll do a happy medium enclosure build

Ron

 

[RAM_Designs 5,000+ posts]

Thanks.
Yeah, that was given directly from the designer and builder of the woofer Mark. I was speaking with him and told him I planned to do 4cubes net shared but he directed me to do 1 cube net per woofer and tune to my liking.

That's very odd. I've never seen anyone use a box that small. Is this for a burp box or what? How much power are you planning on putting to them? I've searched and found a lot of people using 2ft^3 and still being able to put 4kw to them for metering. The bad thing about using such a small box is getting enough port area for them, which they'll need quite a bit of since they're pretty capable woofers. The port area you have right now is too small, in my opinion, but you're going to end up with a very long port if you go any larger in port area.

Kind of a catch-22.

 

[k_schutte 10+ year member]

Yeah, 1ft^3 for sealed would be reasonable... I usually do 2-2.5 for 12"s

 

[jake760 10+ year member]

I read somewhere on this site to try to keep port length under 36". Don't remember why though...

 

[RAM_Designs 5,000+ posts]

I read somewhere on this site to try to keep port length under 36". Don't remember why though...

A longer port means a less efficient port. But then again the only way to make it short, with the same tuning and box volume, is to use a smaller port...so you're losing efficiency there as well. When it actually becomes an issue is completely install dependent, but it's easy to tell that more surface area inside of a port means more air resistance(again, how much of a difference it actually makes is surely minimal). IMO it's worth using long ports to get the tuning and response curve that you're after.

 

[Ronny 10+ year member]

Ahh interesting. Thanks for the tips everyone.

The enclosure is for daily use, I'll be giving each woofer roughly 1400Wrms so no worries about power handling.

Yeah, the 1cube per is puzzling. I think I'll try 4cubes with say, 75sqin of port area at 35hz?

Maybe try the 2.1cube for fun and see while I'm at it.

 

[RAM_Designs 5,000+ posts]

If the box is for daily use I'd go with slightly lower port area and tuning, say 60in^2 and 32-33hz. Just my preference though, yours may be different.

 

[galacticmonkey 5,000+ posts]

I would use a single port on the side so you don't have to split the port into two narrower ports at the back of the box(if you were to do one down the middle). There's really nothing wrong with having a long port, and 30" really isn't too terribly long. Granted, a shorter port is better because there's less resistance going down a shorter port, but at the same time you need adequate port area for the subs you're using.
As far as box size goes, I don't know where you heard that those SPL-12's work well in 1ft^3 each...try 2-2.25ft^3 each. Do a 4ft^3 common chamber box and use a bigger port as well.

x2. Ive never used/heard any Mach 5 stuff, but not a chance Id use 1 cube ported for ANY 12. Maybe 1 cube sealed, not ever that small ported. If you make the box bigger, the port wont need to be as long either. The smalest Id go is like 1.6-1.75 cubes each.