Better port design?

[pierre]

We have seen recently that many cheap speakers have port resonances. It looks to me they do use basic port (a tube).
I have seen a few better designs, KEF or Yamaha comes to mind. Do you have other examples? I am surprised that
designers are not doing better, this is a very well studied fluid dynamics problem.

Yamaha example (from this website):

KEF example (from LS50 meta manual):

 

[pierre]

And now I see this thread ...

 

[dfuller]

I don't understand port design particularly well but it does seem that most of the goals seem to be reducing chuffing/turbulence (which is what flaring the ends does by reducing velocity through the port) vs reducing resonances (which admittedly I don't quite understand how to resolve beyond "stuff the port with polyfill"). I'll have to do some reading on pipe resonances before I can comment further.

 

[Blumlein 88]

On some ports stuffing them with straws helps. Using smoke to see the flow, this seems to keep a laminar flow with less turbulence. I've been surprised this idea hasn't been incorporated into the ports, maybe there are good reasons, but beyond cost I'm not sure what.

 

[q3cpma]

Very relevant: https://www.somasonus.net/box-construction-methods (jump to "Round 3") including the Harman paper linked. Genelec also has some very good ports, which they describe thus (not encompassing the LSE port):

To minimize the air speed in the tube, the cross sectional area of the vent should be large. This in turn means that the vent tube has to be long which presents quite a design challenge.

The long, curved tube maximizes airflow so deep bass can be reproduced without compression. The reflex tube terminates with a wide flare located on the rear of the enclosure for obvious reasons, minimizing port noises and providing excellent bass articulation.

The curvature of the tube has also been carefully designed to minimize any audible noise, compression or distortion. The inner end of the tube has proper resistive termination to minimize once again audible chuffing noise and air turbulence.

Too bad they don't say how they limit resonances.

 

[DSJR]

Many UK speakers seem to use ports to bump up the response into a boomy drone and to hell with chuffing or whatever. I did own one speaker where the port was specifically tuned to the bass driver resonance and barely anything came out of it, let alone the bass driver going mad at that frequency. Hopefully I have this right but no doubt I'll be 'put to rights' if I haven't

 

[MusicNBeer]

First, anything you put inside the port to reduce the resonance will also reduce the desired low bass output. The placing of the port is extremely important in reducing the unwanted midrange resonances. If front ported, the designer needs to place the port as much "out of view" of the woofer(s) as possible. In addition, the box needs to be well internally damped for midrange frequencies.

 

[Kvalsvoll]

We have seen recently that many cheap speakers have port resonances. It looks to me they do use basic port (a tube).
I have seen a few better designs, KEF or Yamaha comes to mind. Do you have other examples? I am surprised that
designers are not doing better, this is a very well studied fluid dynamics problem.

Yamaha example (from this website):

View attachment 124787

KEF example (from LS50 meta manual):
View attachment 124788

The pictures show effect of flaring, which has no significance for resonances and midrange leakage. Flaring reduces turbulence, which gives reduced distortion and noise and increased efficiency due to reduction of losses.

For lower frequencies and higher spl, the only solution that works is to increase port area.

Resonances and midrange leakage is caused by the port changing from behaving like a lumped element acoustic mass at low frequencies into a pipe at higher frequencies. This can be a problem especially in full-range ported speakers, and any resonance or undesired sound leakage will have a negative effect on the speakers sound quality.

This is easy to measure, just put the mic in the port opening, and you have a sufficiently accurate nearfield measurement.

The length of the port decides the frequency of the 1. resonance, and then there will be midrange leakage from sound inside the cabinet. Amount of leakage is determined by port location, cabinet dimensions and placement of damping materials, placement of driver.

This undesired behaviour can be reduced by optimising the design of the cabinet and the port. It may be difficult to achieve a perfect result. Simulation combined with technical competence and measurements is how to do it.

Resonance in a port can be reduced by adding small holes in the port walls, where dimensions and position of holes is best determined by simulation. Typical improvement of more than 10dB is possible, and in some cases this can be the difference between audible coloration or nice sound.

 

[SIY]

Kali.

 

[pierre]

Kali.

True for the in-5 less so for lp6 and in-8.

 

[SIY]

True for the in-5 less so for lp6 and in-8.

Well, I have an LP-6 about two meters away from me and the port sure does look flared in three dimensions.

 

[Ericglo]

Very relevant: https://www.somasonus.net/box-construction-methods (jump to "Round 3") including the Harman paper linked. Genelec also has some very good ports, which they describe thus (not encompassing the LSE port):

Too bad they don't say how they limit resonances.

Beat me to it.

Is the Harman port patented?

Maybe Brandon could try the Technics solution linked above.

http://www.htguide.com/forum/showth...er-Construction-Methods-Shootout-Thread/page4

 

[deprogrammed]

We have seen recently that many cheap speakers have port resonances. It looks to me they do use basic port (a tube).
I have seen a few better designs, KEF or Yamaha comes to mind. Do you have other examples? I am surprised that
designers are not doing better, this is a very well studied fluid dynamics problem.

Yamaha example (from this website):

View attachment 124787

KEF example (from LS50 meta manual):
View attachment 124788

My Polks have an unusual port.

Exclusive Polk Power Port Technology
Power Port® is our patented design that smoothly transitions the air flow from the speaker’s port into your listening area. It also extends the overall bass port, providing greater surface area to eliminate turbulence and distortion, for bigger, more musical, deep bass impact. Plus, it offers 3dB more bass response output than a traditional port.

 

[jkasch]

AFAIK, the only newish port technology lately is KEF’s “soft” port made of closed cell foam.

 

[Zvu]

The most effective port would be a hybrid of Harman's constant radius port with Kef's flexible port... Preferably, used in a three way loudspeaker.

 

[tuga]

The most effective port would be a hybrid of Harman's constant radius port with Kef's flexible port... Preferably, used in a three way loudspeaker.

And tuned to 20Hz

 

[Zvu]

Now wouldn't that be something ?

 

[Zvu]

I'm actually very very surprised that S&R magazine measured JBL M2, but nobody remembered to put the mic at the port.

It would have probably measured stellar but nevertheless, i want to see it. JBL 2216Nd is crossed at 750Hz to M2 waveguide so it probably doesn't upset the resonance frequency of the port.

 

[Putter]

I know this is OT if related, but it's been mentioned that passive radiators have midrange resonances. What causes them and are they of the same magnitude and frequency as port related resonances?

 

[tuga]

What goes into port alignment?
Or, in other words, for the same box-volume and woofer what differs to make the bass reflex tuning over-, under- or critically damped?