there is this little thing that needs consideration ,
the woofer cone when moving in its enclosure is loaded by the air mass it is displacing
this air load should be as equal as possible on the top half of the cone , as on the bottom half of the cone
in effect each half of the cone should load equal air-masses
internal chambers help in achieving this effectively ,
a pressure drop from a port on one side (side in referance to the woofer) is reduced
while using a back port there are various important issues
critical phase shifts , effect on impedance and linearity of the drive unit
this should be addressed keeping the above in mind
suranjan
transducer design engineer
the woofer cone when moving in its enclosure is loaded by the air mass it is displacing
this air load should be as equal as possible on the top half of the cone , as on the bottom half of the cone
in effect each half of the cone should load equal air-masses
internal chambers help in achieving this effectively ,
a pressure drop from a port on one side (side in referance to the woofer) is reduced
while using a back port there are various important issues
critical phase shifts , effect on impedance and linearity of the drive unit
this should be addressed keeping the above in mind
suranjan
transducer design engineer
I really don't like misinformation.
A rear port obviously cannot be placed against a wall but very
small variations of spacing near the wall will affect tuning, this
is assuming the speaker is designed for near wall placement.
If the speaker is designed for NWP the tuning aspect is beneficial.
Other than that it doesn't matter, rear placement is better as
it reduces any midrange resonance problems with the port.
sreten.
A rear port obviously cannot be placed against a wall but very
small variations of spacing near the wall will affect tuning, this
is assuming the speaker is designed for near wall placement.
If the speaker is designed for NWP the tuning aspect is beneficial.
Other than that it doesn't matter, rear placement is better as
it reduces any midrange resonance problems with the port.
sreten.When we say "against the wall" about how many inches are we talking about?
Would it be fair to say that there is no difference if the rear port is six inches from the wall? How about a foot? If your speaker is twelve inches deep, wouldn't a front firing port on a speaker against the wall be equivalent to a rear firing port on a speaker a foot from the wall?
I'm not denying the rear port-wall interaction, I am just wondering at which point it makes little difference.
Would it be fair to say that there is no difference if the rear port is six inches from the wall? How about a foot? If your speaker is twelve inches deep, wouldn't a front firing port on a speaker against the wall be equivalent to a rear firing port on a speaker a foot from the wall?
I'm not denying the rear port-wall interaction, I am just wondering at which point it makes little difference.
How far is far enough is an interesting question- and I'll bet it turns out to be proportional to the port diameter. The two situations you propose here are different in that the port is firing into free air when front mounted, but into a cavity small compared to wavelength when rear mounted. It may indeed be an insignificant difference, and now you've got me hacked off that I don't have a ported speaker in the house to do some tests with.
You need to consider the size of the airflow out of the port and
the way the wall interacts with the airflow. I'd suggest that a
spacing of near 1/2 port diameter is the minimum spacing giving
the most detuning, and once you get to port diameter spacing
further spacing is not critical for port tuning, but larger spacings
are critical for upper bass/mid balance.
Nearer wall spacing less than 1/2 port diameter by minor
adjustment is more flexible than "port bunging" with foam.
sreten.
the way the wall interacts with the airflow. I'd suggest that a
spacing of near 1/2 port diameter is the minimum spacing giving
the most detuning, and once you get to port diameter spacing
further spacing is not critical for port tuning, but larger spacings
are critical for upper bass/mid balance.
Nearer wall spacing less than 1/2 port diameter by minor
adjustment is more flexible than "port bunging" with foam.
sreten.SY, Sreten:
Figured it would be something like that. That is, just a few inches.
The reason I figured the space would be small is that essentially this situation would be a downfiring port, only using the wall instead of the floor. I have come to understand that this downfiring port configuration has many advantages, and the ones I have seen are never more than an inch or two off the floor.
So I guess once you go more than few inches away from the wall, you are in a situation it doesn't matter much where the port is. But if you move it up closer, you might get some advantages.
Figured it would be something like that. That is, just a few inches.
The reason I figured the space would be small is that essentially this situation would be a downfiring port, only using the wall instead of the floor. I have come to understand that this downfiring port configuration has many advantages, and the ones I have seen are never more than an inch or two off the floor.
So I guess once you go more than few inches away from the wall, you are in a situation it doesn't matter much where the port is. But if you move it up closer, you might get some advantages.
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