Speaker cab port placement

[wraub]

Hey all. As King of The Stupid Questions Club, I feel compelled to ask the following:

Does port placement make a darn bit of difference?
Specifically, I have an Avatar 1x12 cab with a slotted port.

Really, just curious. It may help decide placement of the cab in the room.

Thanks.

wraub

[will33]

The placement of the cab in the room can affect things greatly. The placement of the port on the cab makes zero diffrrence. The frequencies the port is responsible for a low enough to be omnidirectional. They spread out in all directions, not just forward so placement doesn't matter.

[BurningSkies]

With the caveat, that with a rear port placement is important, you don't want to see cone though the port...you'll have some mid frequency projection, and your port is for lows.

[DukeLeJeune]

Originally Posted by BurningSkies

With the caveat, that with a rear port placement is important, you don't want to see cone though the port...you'll have some mid frequency projection, and your port is for lows.

Well, there are different schools of thought on the subject... and my such school is no doubt in the minority. I would have agreed with you up until a little over a year ago, when I tried it, at the suggestion of the Eminence engineer who designed my woofer. Through a flared port, the midrange that escapes doesn't have the edginess that it does through a conventional round port (to my ears at least). So I'm deliberately using that midrange energy, which is unorthodox of course, but I think it's a small net benefit.

Imo, ime, ymmv, etc.

Other things port placement can affect include what the cab sounds like when it's mic'd, and how much low end whump! the bass player feels when he's very close to the front of the cab. What port placement has negligible effect on is, how the cab sounds to the audience.

[Downunderwonder]

Unless the port is blocked by a wall or something, the bass from the port is always close enough to be in phase with the woofer bass, that's the whole point of having ported designs.

[Arjank]

Originally Posted by DukeLeJeune

Well, there are different schools of thought on the subject... and my such school is no doubt in the minority. I would have agreed with you up until a little over a year ago, when I tried it, at the suggestion of the Eminence engineer who designed my woofer. Through a flared port, the midrange that escapes doesn't have the edginess that it does through a conventional round port (to my ears at least). So I'm deliberately using that midrange energy, which is unorthodox of course, but I think it's a small net benefit.

Imo, ime, ymmv, etc.

Other things port placement can affect include what the cab sounds like when it's mic'd, and how much low end whump! the bass player feels when he's very close to the front of the cab. What port placement has negligible effect on is, how the cab sounds to the audience.

I have a written article at home with measurements(full anechoic) of a bassreflex system (for hifi, but that does not matter much) and the author tried/measured several port positions. The most optimal position, basswise, is to have the port(s) as close to the woofer as possible. Having ports at the back of the cabinet is of course the most problematic when the distance between the woofer and port in relation to the "listener" differs at a large amount. But, when you place a cab with rear ports near a wall/corner you may get nice results (read: low end boost) but it can also act counterproductive.
For my own designs I try to keep them as close to the woofer as possible.
Midrange "leaking" is not so much related to seeing the cone through the port but bad internal lining, ports with a too large diameter or ports that are to long compared to the internal volume/dimensions of the cab(which can create a port resonance). The latter can be solved by adding a "lowpass" inside the cabinet that makes sure the midfrequencies of the woofer do not "leak" into the port (also read post #120 in this thread Just finished my build for some 12" Kappalite's ).

[countrybass007]

The isobaric design by Orange seems to work combining a front ported speaker and a sealed speaker in one cabinet. I have cabs with round ports, long ports along the bottom of the cab, side ports, and rear ports. The only real difference I've ever noticed is the rear port reacts differently if it's close to wall at the back of the stage.

[wraub]

Ok, thanks to all for the answers.
The placement of the cab in the room is pretty much set, but the cab is on a small wheeled platform (both for isolation from the floor and to fight dust bunny build-up.)
The platform has a lip around the edge which partially hides the port, so the cab was flipped with the port now at the top.
Hard to tell what exactly it did (if anything) to the sound from the cab, was really more curious about wave/freq/eq issues, etc.

Again, Just being the King of the Club, and doing my job.

Thanks, again.

wraub

[Bass Unique]

Position of the port in your cab should ideally be close to the floor so it is between the woofer and the floor. This would tend to raise the woofer up for better audibility and with the port close to a boundary, you will get the maximum benefit.

However, I would doubt you would notice any significant difference - far greater differences by moving the whole cab to and from walls etc.

And, in my experience, for those talking about port placement on a cab, yes it can make a difference in a reflex box and yes midrange can come out of the port if it is lightly lined or unlined. There is little benefit of midrange from a port as it is usually associated with a null as well.

A long port is fine provided the following:

1) The box is lined well.

2) The length of the port does not coincide with a dimension of the box internally (particularly if it is placed by a box boundary)

3) The Q of the port need to be lower than a typical open pipe. This can be done through lightly lining a large diameter port or through folding (bending) the port. This disrupts any midrange resonances.

[Arjank]

Originally Posted by Bass Unique

There is little benefit of midrange from a port as it is usually associated with a null as well.

IMO there is no benefit at all, on the contrary.
If you have e.g. a woofer and a port underneath it and you measure the impulse response, the resulting waterfallplot will show a big delay at the frequency region where "mids" leak through. So, if you want tight/accurate midresponse you do not want to have any "mids" leaking through the port.

[Arjank]

Originally Posted by Bass Unique

A long port is fine provided the following:

1) The box is lined well.

2) The length of the port does not coincide with a dimension of the box internally (particularly if it is placed by a box boundary)

3) The Q of the port need to be lower than a typical open pipe. This can be done through lightly lining a large diameter port or through folding (bending) the port. This disrupts any midrange resonances.

I would not line a port.
Folding a port will not remove much of the midrange resonances.
Best solution is the one I mentioned a few posts ago, an internal "lowpass" integrated in the cabinet.

[billfitzmaurice]

Originally Posted by Bass Unique

with the port close to a boundary, you will get the maximum benefit.

Boundary loading occurs when the radiating plane is less than 1/4 wavelength from the boundary. Port output as part of system output is only significant below 100Hz, 1/4 wavelength at 100Hz is about 2.8 feet, so with most cab configurations orientation won't matter. But you wouldn't want a tall cab with a shelf port located at the top of the cab.

[Arjank]

Originally Posted by billfitzmaurice

But you wouldn't want a tall cab with a shelf port located at the top of the cab.

+1

In that case the best position for the port is in the "middle" of the cabinet.

[wcriley]

Originally Posted by billfitzmaurice

Boundary loading occurs when the radiating plane is less than 1/4 wavelength from the boundary. Port output as part of system output is only significant below 100Hz, 1/4 wavelength at 100Hz is about 2.8 feet, so with most cab configurations orientation won't matter. But you wouldn't want a tall cab with a shelf port located at the top of the cab.

I never thought about it, but I guess I'm losing some boundary/floor loading when I stack my cabs like this:


Seems I'd be better off stacking them horizontally, with the ports to one side and the drivers aligned close together.

[will33]

Originally Posted by wcriley

I never thought about it, but I guess I'm losing some boundary/floor loading when I stack my cabs like this:


Seems I'd be better off stacking them horizontally, with the ports to one side and the drivers aligned close together.

I'd wondered the same thing but I think when you stack them like that the whole thing acts more like one unit, one radiating plane. I'd think that stack would work better than if the port were at the top only. I guess you'd figure it the same as you would any distance in relation to the frequency the ports are operating at.

Be interesting to hear a real explanation although in any case, I'd think the benefits of maintaining vertical alignment would outweigh whatever dip there may or may not be at some particular frequency.

[BurningSkies]

Originally Posted by will33

I'd wondered the same thing but I think when you stack them like that the whole thing acts more like one unit, one radiating plane. I'd think that stack would work better than if the port were at the top only. I guess you'd figure it the same as you would any distance in relation to the frequency the ports are operating at.

Be interesting to hear a real explanation although in any case, I'd think the benefits of maintaining vertical alignment would outweigh whatever dip there may or may not be at some particular frequency.

I use mine in both directions. If the stage is big enough, Then my mid is on top, if the stage isn't that big, or I'm in the practice room, the mid is in the middle. Otherwise what I'm hearing is heavily slated to the mid and not representative of what's going on in the room.

[will33]

Originally Posted by BurningSkies

I use mine in both directions. If the stage is big enough, Then my mid is on top, if the stage isn't that big, or I'm in the practice room, the mid is in the middle. Otherwise what I'm hearing is heavily slated to the mid and not representative of what's going on in the room.

Good point.

At close range anyway, with the mids being that hot, their relationship to your ear would have a greater effect on tone than any moving around of ports. In the far field, audience perspective, when everything is summed together, that effect should go away and you'd better hear some dip in the lows, if there even is any.

Might be able to answer my own question here with some digging and figuring but this is so much easier.

[wcriley]

Originally Posted by will33

I'd wondered the same thing but I think when you stack them like that the whole thing acts more like one unit, one radiating plane. I'd think that stack would work better than if the port were at the top only. I guess you'd figure it the same as you would any distance in relation to the frequency the ports are operating at.

Be interesting to hear a real explanation although in any case, I'd think the benefits of maintaining vertical alignment would outweigh whatever dip there may or may not be at some particular frequency.

Perhaps I wasn't clear about my alternate stacking method.
I'm thinking about placing the cabs on their sides, with the ports to one side and the mid drivers close to each other. All drivers would be vertically aligned, the woofers would be closer together than they now are, and the top of the uppermost port would be about 32" from the floor/boundary, rather than 48" as it now is.

I'll try it and compare when I get time.

[BurningSkies]

Originally Posted by will33

Good point.

At close range anyway, with the mids being that hot, their relationship to your ear would have a greater effect on tone than any moving around of ports. In the far field, audience perspective, when everything is summed together, that effect should go away and you'd better hear some dip in the lows, if there even is any.

Might be able to answer my own question here with some digging and figuring but this is so much easier.

Luckily, with the cabs we're talking about, 'low shy' isn't a problem, so if their is a dip in the lows, there's room to make adjustments as needed by way of EQ.

[will33]

Originally Posted by wcriley

Perhaps I wasn't clear about my alternate stacking method.
I'm thinking about placing the cabs on their sides, with the ports to one side and the mid drivers close to each other. All drivers would be vertically aligned, the woofers would be closer together than they now are, and the top of the uppermost port would be about 32" from the floor/boundary, rather than 48" as it now is.

I'll try it and compare when I get time.

I'd think that might be more effective, technically anyway, from keeping everything bunched together as closely as possible, in the interest of acting as much like a single point source as possible. At least when running all cones. Throw a 40x90 horn or something in the mix and then you'd be changing the dispersion pattern of the highs.