How to tune down to 30hz without going under rec. port area?

[ckunke002 10+ year member]

Trying to design a box build online, but can't get as low as i want without my port length extending all the way to the right side of the box or going under the recommended 15sq inches port area per cube.

My build i'm going for is 2.4-2.5 cubes @ 30/31hz port area of 2.5x15". This is the first box build I've ever done so any help would be cool. To reach my desired tuning with that big of port area I have to send it all but a few inches away from the right wall. Would that be problematic?

Thanks

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[T3mpest 10+ year member]

You want to stay at least a port width distance from the back wall, so 2.5 inches in this case. What's the sub in question and how much power are you putting on it? That matters much more than box airspace, although box airspace can get you in a good ballpark 95% of the time.

 

[ckunke002 10+ year member]

You want to stay at least a port width distance from the back wall, so 2.5 inches in this case. What's the sub in question and how much power are you putting on it? That matters much more than box airspace, although box airspace can get you in a good ballpark 95% of the time.

Thank you for the response! I however am talking about the right side wall... I know to turn my port to the right when it reaches port width distance from the backwall to make both port lengths equally wide. Did you mean that I can safely bring the 2nd port length all the way within a port length of the right side?

Sub is a 12" Q 27mm xmax... won't be playing it at 1.5k though probably more like 1k.. Suspension isn't incredibly strong, yet still a lot of xmax so I came to around 15" sq port area

 

[T3mpest 10+ year member]

yes, , as long as your at least a port length away from ALL walls your fine, it's always better to to have more room, but generally it's no big deal if your at least a port width away. Generally an inch here or there won't break your design, you will NOT hear a difference between 31vs32hz, even 31vs34 is going to be subtle. It's more important to give your port room to breathe as choking the port at the entrance is just as bad as undersizing your port area.

 

[ckunke002 10+ year member]

yes, , as long as your at least a port length away from ALL walls your fine, it's always better to to have more room, but generally it's no big deal if your at least a port width away. Generally an inch here or there won't break your design, you will NOT hear a difference between 31vs32hz, even 31vs34 is going to be subtle. It's more important to give your port room to breathe as choking the port at the entrance is just as bad as undersizing your port area.

Good to know ..thank you again. Would you figure 15 sq inches/cube to be just fine for this application? Or would you favor more or less

 

[ckunke002 10+ year member]

This is what I've ultimately come up with.. 14.5 sqinches port per internal cube, about 2.44 internal volume, 35.25 port length. I have about 38 inches width in my trunk so figured I'd utilize most of it and save some depth

 

[thatguy12 10+ year member]

This is what I've ultimately come up with.. 14.5 sqinches port per internal cube, about 2.44 internal volume, 35.25 port length. I have about 38 inches width in my trunk so figured I'd utilize most of it and save some depth

avoid the re calculator at all costs. download torres box calculator, go to 12 volt.com calculators, theres free designs on here. all box calculators differ from each other but the re is way off.

 

[ckunke002 10+ year member]

avoid the re calculator at all costs. download torres box calculator, go to 12 volt.com calculators, theres free designs on here. all box calculators differ from each other but the re is way off.

Really? What part is off exactly? What it gives me for net volume? tuning freq.?

 

[thatguy12 10+ year member]

Really? What part is off exactly? What it gives me for net volume? tuning freq.?

tuning/port area from my experience. torres box calculator is awesome.

 

[mlstrass 5,000+ posts]

I would do around 12^2 for a Q, especially tuned that low...

 

[ckunke002 10+ year member]

I would do around 12^2 for a Q, especially tuned that low...

I was told by somebody in another thread I would need to do about 20^2 for the specific sub... seemed crazy but do you have any idea why that would be suggested?

 

[thatguy12 10+ year member]

I was told by somebody in another thread I would need to do about 20^2 for the specific sub... seemed crazy but do you have any idea why that would be suggested?

i think that much port would be peaky. 12-15 ^2 is what i would shoot for.

 

[T3mpest 10+ year member]

i think that much port would be peaky. 12-15 ^2 is what i would shoot for.

Ports really can't be "peaky". Too small a port will compress under high volume and do the exact opposite, create a dip in response near tuning under high power vs low power useage. However, as the port gets larger response doesn't vary much, it simply stays more linear at high volumes, this is true of almost any normal sized port. Main issue comes in is that as you make the port larger you take away from the box size all things equal which will impact response peaks and there is no reason to use a bigger port than needed.

To OP, anyway the Q is a moderately strong motor, but not overly so. Also as you tune lower you generally need less port area to avoid chuffing as the air is moving less times through the port each second, this stays true until you tune low enough that your below the threshold of hearing. Once you tune at 20hz or so, you need more port again because ANY port noise is audible over the note the port is producing, so you really want to keep the airpseeds as low as possible then. 30hz is a nice are where you can go a bit lower on the port area without impacting things to much. On 1000 watts a 2inch vent would be sufficient. If you ever went to say 2k of power a 2.5 would be optimal.

 

[ckunke002 10+ year member]

Ports really can't be "peaky". Too small a port will compress under high volume and do the exact opposite, create a dip in response near tuning under high power vs low power useage. However, as the port gets larger response doesn't vary much, it simply stays more linear at high volumes, this is true of almost any normal sized port. Main issue comes in is that as you make the port larger you take away from the box size all things equal which will impact response peaks and there is no reason to use a bigger port than needed.
To OP, anyway the Q is a moderately strong motor, but not overly so. Also as you tune lower you generally need less port area to avoid chuffing as the air is moving less times through the port each second, this stays true until you tune low enough that your below the threshold of hearing. Once you tune at 20hz or so, you need more port again because ANY port noise is audible over the note the port is producing, so you really want to keep the airpseeds as low as possible then. 30hz is a nice are where you can go a bit lower on the port area without impacting things to much. On 1000 watts a 2inch vent would be sufficient. If you ever went to say 2k of power a 2.5 would be optimal.

Thanks again for all the info. When you say 2 inches, at that point should I just make it tall enough to cover the 12-15ish square inch per internal cube formula?

And if I'm only going 2 inches wide but still trying to hit those square inches, would that be too narrow and tall of a slot that noise would affect it?

 

[T3mpest 10+ year member]

Thanks again for all the info. When you say 2 inches, at that point should I just make it tall enough to cover the 12-15ish square inch per internal cube formula?
And if I'm only going 2 inches wide but still trying to hit those square inches, would that be too narrow and tall of a slot that noise would affect it?

I thought you height was going to be the 14.5 or so it was before which is why I said 2 inches. Generally I try to stay below a 8:1 ratio of height to width. So at 14inches tall 2 wide is still alright. I wouldn't go any thinner or taller though. If it bugs you 2.25 would be almost the same lol.