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Ported speaker behavior question

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Posted on October 22, 2023 at 23:13:58
George S. Roland
Audiophile

Posts: 1428
Location: N W Pennsylvania
Joined: March 20, 2004
 I read in some speaker reviews that at some frequency, the balance between the driver, the volume inside the cabinet and the port create a situation where the cone is still. I would like to know a bit more about this incidence and whether, when the speaker is held motionless, the system produces any sound. Are sounds at that frequency simple not produced?

 

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RE: Ported speaker behavior question, posted on October 23, 2023 at 07:48:21
Ozzy
Audiophile

Posts: 7566
Joined: September 21, 1999
 I don't know of this situation you speak of. But I would venture to say that if a speaker cone is indeed motionless, there will be no sound produced. Now there could be minimal excursion which appears to be "zero" motion, then there could be some sound.





Don't worry about avoiding temptation. As you grow older, it will avoid you.
- Winston Churchill

 

Driver not moving but port is at maximum output, posted on October 23, 2023 at 09:54:48
Edp
Audiophile

Posts: 4410
Joined: September 23, 1999

That is then the resonance frequency of the driver/port/enclosure combo

In the Stereophile plot attached the port output is red line. Notice at its peak the driver lot blue has a big dip in output. That is the measurement that shows the event you describe

 

When the port is properly tuned the resonant frequency of the driver . . ., posted on October 23, 2023 at 13:45:48
Brian H P
Audiophile

Posts: 1212
Location: Oregon
Joined: December 18, 2012
 . . . the sound at that frequency is produced almost entirely by the port, not the driver. This is the Helmholtz resonance of the box/port system.

 

RE: Driver not moving but port is at maximum output, posted on October 25, 2023 at 11:00:25
George S. Roland
Audiophile

Posts: 1428
Location: N W Pennsylvania
Joined: March 20, 2004
 Thank you for this clear explanation, including a graph!
I have a follow-up question. The blue line, at its lowest point, looks to read ca. -4dB.
Since I thought, at "no movement", it would be exactly zero. Does this mean that the cone is never actually dead still but instead moves minimally at that point so that energy from the box is at its maximum.
A fascinating phenomenon!

 

RE: Driver not moving but port is at maximum output, posted on October 25, 2023 at 12:47:24
mlsstl
Audiophile

Posts: 1007
Location: Midwest
Joined: September 1, 2015
 Think about it this way -- only the driver is connected to the amplifier providing the music signal. The port is just a hole in the box, connected to nothing except air. The driver cone is the only source of sound generation in a speaker, so must vibrate to some degree for you to hear anything. The port simply allows the air movement generated by the cone movement to resonate more efficiently at certain freqencies.

 

RE: Driver not moving but port is at maximum output, posted on October 25, 2023 at 14:47:57
tomservo
Manufacturer

Posts: 7907
Joined: July 4, 2002
 The port is a mass, the air is a spring. imagine you have a spring with a weight hanging on it, if you move your hand up and down, you will find the resonant frequency.

At this point you may notice your hand is moving the opposite direction as the weight, when the weight is going down, your hand is going up. One has a phase inverter at that resonance, that's how the rear radiation which is out of phase, is turned into something additive to the front radiation.

Yes, in a vented system with low losses, the cone motion nearly stops while the motion of the port is maximum.
Tom

 

Just to clarify, most of the cone motion..., posted on October 26, 2023 at 10:13:12
MWE
Audiophile

Posts: 2179
Location: Burlington, NC
Joined: June 8, 2000
 at the resonant frequency stops, not all of the cone motion.


Mark in NC
"The thought that life could be better is woven indelibly into our hearts and our brains" -Paul Simon

 

Yet another way to look at it..., posted on October 26, 2023 at 11:09:12
mlsstl
Audiophile

Posts: 1007
Location: Midwest
Joined: September 1, 2015
 ... is to disconnect the wires to the driver and then see how much air movement you get out of the port....

 

LOL! nt. , posted on October 27, 2023 at 05:02:11
MWE
Audiophile

Posts: 2179
Location: Burlington, NC
Joined: June 8, 2000
 Nt.


Mark in NC
"The thought that life could be better is woven indelibly into our hearts and our brains" -Paul Simon

 

RE: Just to clarify, most of the cone motion..., posted on October 27, 2023 at 05:56:20
tomservo
Manufacturer

Posts: 7907
Joined: July 4, 2002
 That is correct, port resonance causes an excursion minimum but it is still moving a little bit. Visually, i might look like no motion.

 

RE: Ported speaker behavior question, posted on October 30, 2023 at 23:14:00
dericmc@live.com
Audiophile

Posts: 97
Location: Amarillo Texas
Joined: October 21, 2023
Contributor
  Since: October 31, 2023
 I prefer sealed cabinets bass tighter to me

 

RE: Driver not moving but port is at maximum output, posted on November 20, 2023 at 18:16:00
3db
Audiophile

Posts: 1514
Joined: July 22, 2003
 The cone motion never stops even at the port's resonant frequency or else one would lose all the sound from the different frequencies above the port resonant frequency. It would be more accurate to say that cone stops any movement at the port frequency but remains in motion for all other frequencies.

 

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