3015 design

[acmebass]

The "still" air in the rear flare belongs to both the port AND the enclosure. As soon as that ports starts to produce sound the air immediately starts vibrating back and forth from the interior of the port (including the flares obviously) to the "enclosure's" air space.

That aside, on the designs that you've seen with 4" ports closers than 4" to the side walls (assuming they were professionally designed and built cabinets), the shift in port tuning (Fb) is accounted for, measured, and re-adjusted to hit the initial targed Fb (or at least it should be).

The shift that happens as ports get closer and closer to side walls, the more the tuning shifts downward. This can actually be a good thing because this artificial lengthening will allow you to shorten the port requirements and still hit your particular Fb. Unfortunately, it is you that will have to do the empirical testing to see how much it affects the Fb, and then work with either equations or modeling software to figure out a new (shorter) port length to achieve your desired tuning.

Now when a port is closer than it's diameter to a side wall is a slightly different thing. At low volumes nothing is happening all that much, because (frequency aside), the velocity in the port is directly dependent on the power fed to the woofer. But at high power levels where the air velocity in the port is great enough, not only may it change the Fb, but you may suffer 'port compression' if it is severe enough, meaning you lose port output dBs as well as shifting the effective tuning, even a complete loss of proper port operation if it is severe (where the port now only acts as a leak in a sealed box and not a resonator of sound.

It's not as detrimental as it may sound IF you have enough port area to maintain as low of a port velocity as possible (and this depends on getting enough port cross sectional area). The lower the port velocity at the power you are going to throw at the speaker, the higher that this threshold is raised before noticeable (negative) effects start to rear their ugly heads.

Simulation is key, but more importantly, testing/tuning the final product is just if not more important.

Almost forgot to state: what I mean by you doing testing/tuning, I mean verifying the actual Fb of the final product via any of the accepted ways to determine port tuning.

Well said.

 

[V63]

I guess I'm asking what "within reason" means in regards to ports.

 

[Krügmeister]

I have a mesa Venture 115 and I swapped out the stock speaker with a 3015. Turns out the stock speaker really was the better option. I love the 3015 but it apparently needs to get closer to specs than my Venture gave

 

[OscarJr]

So in your post above when you say wall or "side" of the enclosure are you talking about the ones running parallel or perpendicular to the ports? Are you saying it doesn't matter about the ones running parallel but only the rear or back of the enclosure perpendicular to the internal port opening that should be at least the diameter of the port. I just want to know the rules.

Sorry 'bout that. When I say "side walls", I mean the walls running parallel to the port itself. For me, the rear wall is termed "rear wall"

except here because I made a typo....in the paragraph that starts

"Now when a port is closer than it's diameter to a side wall...."

should have been....

"Now when a port is closer than it's diameter to a rear wall....."

sorry about that.

That paragraph should have read...

Now when a port is closer than it's diameter to a rear wall is a slightly different thing. At low volumes nothing is happening all that much, because (frequency aside), the velocity in the port is directly dependent on the power fed to the woofer. But at high power levels where the air velocity in the port is great enough, not only may it change the Fb, but you may suffer 'port compression' if it is severe enough, meaning you lose port output dBs as well as shifting the effective tuning, even a complete loss of proper port operation if it is severe (where the port now only acts as a leak in a sealed box and not a resonator of sound.

Sorry about the confusion.

 

[V63]

Thanks for your help. I thought it my have been a typo but wanted to be sure. I really do appreciate people taking to answer my DIY newbie questions.
Thanks again.

 

[OscarJr]

Thanks for your help. I thought it my have been a typo but wanted to be sure. I really do appreciate people taking to answer my DIY newbie questions.
Thanks again.

anytime

 

[Downunderwonder]

So a front port can be right in a corner so long as it's a diameter away at the back?

 

[OscarJr]

So a front port can be right in a corner so long as it's a diameter away at the back?

Yes, but is is a general-rule-of-thumb. There are always things to take into account; but assuming the port has large enough area to keep velocity low enough, then yes ideally you want it at least one-diameter away from the rear wall. You still need to verify Fb, since corner placement will affect it as I outlined in my previous post.