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Let's Talk About Bass Ports


Peter P.

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Some speakers come with bass ports. It's known that ported speakers play lower, but they roll off steeper at the low end. Also, their bass attack is not as tight.

 

So why don't manufacturers provide the ability to plug the port and allow the owner to choose their flavor? Has anyone ever plugged ports that weren't intentionally designed that way?

 

Also, anyone notice the difference between speakers that are front ported vs. rear ported?

 

I have a kg sw subwoofer I bought used with no manual, so I have no positioning instructions. That means I'm free to do what I want!

 

I'd been running the ports facing the room and thought the bass was a little missing. This morning I turned the sub around, with the port 5" from the wall. What a difference!

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Technically a sub with a passive is ported and the RSW line is the most accurate subs I've personally ever heard. 

 

As far as positioning goes the room is really going to make the difference in what sounds best and your listening position but generally as far as output goes IIRC a port adds 3db, rear port another 3db and in the corner I believe up to another 3-6db so there should be a pretty drastic difference between the sub port facing forward in the center of your room and the sub facing the rear wall in the corner of the room. 

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9 minutes ago, Peter P. said:

So why don't manufacturers provide the ability to plug the port and allow the owner to choose their flavor? Has anyone ever plugged ports that weren't intentionally designed that way?

 

To over simplify things low frequency depends on air movement, the lower the note the more air needs to be pushed which is why a lot of people use 18" subs. Problem is when the woofer is moving wildly at low frequencies its output and power handling are usually limited to protect the woofer, plugging a port would reduce the amount of movement of the woofer allowing more power handling and output capabilities so its a trade off low extension versus total output I believe anyway

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3 hours ago, jjptkd said:

Technically a sub with a passive is ported and the RSW line is the most accurate subs I've personally ever heard. 

 

As far as positioning goes the room is really going to make the difference in what sounds best and your listening position but generally as far as output goes IIRC a port adds 3db, rear port another 3db and in the corner I believe up to another 3-6db so there should be a pretty drastic difference between the sub port facing forward in the center of your room and the sub facing the rear wall in the corner of the room. 

 

Ports do not add volume, its a tuning device.

 

3 hours ago, jjptkd said:

 

To over simplify things low frequency depends on air movement, the lower the note the more air needs to be pushed which is why a lot of people use 18" subs. Problem is when the woofer is moving wildly at low frequencies its output and power handling are usually limited to protect the woofer, plugging a port would reduce the amount of movement of the woofer allowing more power handling and output capabilities so its a trade off low extension versus total output I believe anyway

 

Plugging a port only lowers tuning and increases the chance of port noise (chuffing).

 

1 hour ago, wuzzzer said:

Several SVS, Hsu and other subwoofer manufacturers have this option.

 

Great idea, bad design.

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Yes.  Marantz Imperial 7s suggested plugging the port in the owners manual.  Their graph showed  a 4 to 6 bdB attenuation around 60 to 80 Hz and 2 to 3 dB more at 40.  When placed in a corner, on stands or the floor, plugging the port made the speaker sound more balanced.

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19 hours ago, jason str said:

 

Ports do not add volume, its a tuning device.

 

 

Plugging a port only lowers tuning and increases the chance of port noise (chuffing).

 

 

Great idea, bad design.

Ports add volume for the frequency they are ported to if tuned properly and of the proper size, though usually negating some of the woofer output.  A very nice graph that shows this is the B&W 802D chart on Stereophile.com.

 

Plugging the port will reduce that volume at the tuning frequency.  If the port is closed there will be no chuffing though you will change the roll off of the speaker to a more gradual level and reduce the gains in the port tuning area.  Cuffing comes in when the speaker is pushed beyond the amount of air that can be moved by the port effectively along with the geometry / design of the port.

 

Many speakers do provide plugs / bungs.  It is a critical design feature of a very good speaker from PSB, the T3.  Multi-woofer, enclosure, port speaker with plugs to help tune the bottom end to the room.

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1 hour ago, pzannucci said:

Ports add volume for the frequency they are ported to if tuned properly and of the proper size, though usually negating some of the woofer output.  A very nice graph that shows this is the B&W 802D chart on Stereophile.com.

 

Plugging the port will reduce that volume at the tuning frequency.  If the port is closed there will be no chuffing though you will change the roll off of the speaker to a more gradual level and reduce the gains in the port tuning area.  Cuffing comes in when the speaker is pushed beyond the amount of air that can be moved by the port effectively along with the geometry / design of the port.

 

Many speakers do provide plugs / bungs.  It is a critical design feature of a very good speaker from PSB, the T3.  Multi-woofer, enclosure, port speaker with plugs to help tune the bottom end to the room.

 

My post simply states porting does not actually make a driver more efficient as mentioned in this thread by jjptkd.

 

There are rules for ports like anything else in designing a cabinet and it is a critical part of the design but tuning by restricting port airflow is a poor design method.

 

 

 

 

 

 

 

 

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30 minutes ago, jason str said:

 

My post simply states porting does not actually make a driver more efficient as mentioned in this thread by jjptkd.

 

There are rules for ports like anything else in designing a cabinet and it is a critical part of the design and restricting port airflow is a poor design method.

 

 

 

 

 

 

 

 

Yes and I was stating that a port is not just a tuning device.

 

The ability to restrict port size and number is not really a poor design if that was the intent, as in the T3 or as in the SVS Ultra series of subs.  This is not discounting things like Aperiodic Venting devices that the restriction causes a different level of filter (since the port can be simulated as an electrical circuit).

 

Using the wall and distance from it with a port can also provide some level of loading.  It is all a design choice and it's good for owners to understand how to manage those choices with positioning.

 

On 11/29/2018 at 6:53 AM, jjptkd said:

 

To over simplify things low frequency depends on air movement, the lower the note the more air needs to be pushed which is why a lot of people use 18" subs. Problem is when the woofer is moving wildly at low frequencies its output and power handling are usually limited to protect the woofer, plugging a port would reduce the amount of movement of the woofer allowing more power handling and output capabilities so its a trade off low extension versus total output I believe anyway

Actually the woofer won't move huge amounts at low frequencies in a bass reflex cabinet unless the frequency asked for is below the cut off of the port.  At that point the woofer unloads to the cabinet/tuning and can exceed safe excursion (withing norms vs trying to destroy the woofer).  That is why you filter below tuning frequency or tune your box to a frequency that doesn't allow this in combination with the woofer, during normal use.  Plugging the port may allow more power handling but in a properly designed box, not increase output capabilities, just how much power the woofer can eat for a given output.  You will reduce the roll off for some possible extension sacrificing efficiency gains of the port.  

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11 minutes ago, pzannucci said:

Yes and I was stating that a port is not just a tuning device.

 

The ability to restrict port size and number is not really a poor design if that was the intent, as in the T3 or as in the SVS Ultra series of subs.  This is not discounting things like Aperiodic Venting devices that the restriction causes a different level of filter (since the port can be simulated as an electrical circuit).

 

Using the wall and distance from it with a port can also provide some level of loading.  It is all a design choice and it's good for owners to understand how to manage those choices with positioning.

 

Actually the woofer won't move huge amounts at low frequencies in a bass reflex cabinet unless the frequency asked for is below the cut off of the port.  At that point the woofer unloads to the cabinet/tuning and can exceed safe excursion (withing norms vs trying to destroy the woofer).  That is why you filter below tuning frequency or tune your box to a frequency that doesn't allow this in combination with the woofer, during normal use.  Plugging the port may allow more power handling but in a properly designed box, not increase output capabilities, just how much power the woofer can eat for a given output.  You will reduce the roll off for some possible extension sacrificing efficiency gains of the port.  

 

If port noise and loss of output due to vent compression is not an unwanted byproduct I'm not sure what is.

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44 minutes ago, jason str said:

 

If port noise and loss of output due to vent compression is not an unwanted byproduct I'm not sure what is.

Plugging the port won't cause noise.  I'm not sure what you mean.

 

If you design the box to be used as a multi configuration as the two I stated prior or using an aperiodic venting, I'm not sure why it is unwanted.  Doing something incorrectly that causes noise, well yes, that's just plain broken.

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14 minutes ago, pzannucci said:

Plugging the port won't cause noise.  I'm not sure what you mean.

 

If you design the box to be used as a multi configuration as the two I stated prior or using an aperiodic venting, I'm not sure why it is unwanted.  Doing something incorrectly that causes noise, well yes, that's just plain broken.

 

Variable tuning by blocking off one or more ports in a multi port configuration to lower tuning frequency.

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