• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required as is 20 years of participation in forums (not all true). Come here to have fun, be ready to be teased and not take online life too seriously. We now measure and review equipment for free! Click here for details.

Why Are Ported Speakers the Dominant Design?

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
5,791
Likes
4,490
Location
Australia
#81
Last edited:

Juhazi

Major Contributor
Joined
Sep 15, 2018
Messages
1,047
Likes
1,342
Location
Finland
#82
Around BR tuning frequency practically all sound comes from the BR which is half cycle delayed to direct sound. You can't hear this group delay with a sine sweep, but how about a bass transient eg. kick drum stroke? Instruments' sound have lots of harmonics and say we use the KEF LS50 above, that kick fundamental is at 50Hz 2 cycles, but 2nd and all other harmonics will be that half cycle ahead of the fundamental beat! It really does sound different from a closed box speaker having same (eq'd) response in a sweep measurement!

 
Last edited:

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
3,075
Likes
1,998
Location
UK
#84
In simple terms, consider, what we would need to do to eliminate a room reflection at the listener's ear. We would send out an impulse from the speaker, and it would be picked up by the ear, followed by a delayed reflection of the impulse. We could eliminate the reflection by sending out an inverted version of the impulse from the speaker at the right moment. This would cancel the reflected impulse at the listener's ear. The listener would then receive an unwanted reflection of the inverted impulse. We would need to eliminate that with a further inverted inverted impulse, and so on, decaying to zero. BUT what if the reflection was louder at the ear than the direct sound? The inversion of the transfer function wouldn't work, because the result would be unstable and would not decay to zero, instead tending to infinite output amplitude.

BACCH has to do something like this with a ping-pong between the speakers. It couldn't work if the crosstalk at the wrong ear wasn't slightly attenuated compared to the direct.

Consider the output of the port as a 'reflection' that is louder than the direct signal from the cone, and you see that you can't invert the transfer function of a ported speaker. But you can with a sealed speaker.
 

maty

Major Contributor
Joined
Dec 12, 2017
Messages
3,742
Likes
2,218
Location
Tarragona (Spain)
#85
Around BR tuning frequency practically all sound comes from the BR which is half cycle delayed to direct sound. You can't hear this group delay with a sine sweep, but how a bout a bass transient eg. kickdrum stroke? Instruments' sound has lots of harmonics and say we use the KEF LS50 above, have that kick fundamental at 50Hz 2 cycles, 2nd and all other harmonics will be that half cycle ahead of the fundamental beat! It really does sound different from a closed box speaker having same (eq'd) response in a sweep measurement!

The best performance usually is with closed box + two or more subs. You always can close the port.
 

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
5,791
Likes
4,490
Location
Australia
#86
In simple terms, consider, what we would need to do to eliminate a room reflection at the listener's ear. We would send out an impulse from the speaker, and it would be picked up by the ear, followed by a delayed reflection of the impulse. We could eliminate the reflection by sending out an inverted version of the impulse from the speaker at the right moment. This would cancel the reflected impulse at the listener's ear. The listener would then receive an unwanted reflection of the inverted impulse. We would need to eliminate that with a further inverted inverted impulse, and so on, decaying to zero. BUT what if the reflection was louder at the ear than the direct sound? The inversion of the transfer function wouldn't work, because the result would be unstable and would not decay to zero, instead tending to infinite output amplitude.

BACCH has to do something like this with a ping-pong between the speakers. It couldn't work if the crosstalk at the wrong ear wasn't slightly attenuated compared to the direct.

Consider the output of the port as a 'reflection' that is louder than the direct signal from the cone, and you see that you can't invert the transfer function.

I believe the math. over subjective intuition. Why are you inverting the transfer function? The loudspeaker transfer function includes the sum of the driver and port components. Damping factor is chosen for port response behaviour and stability.
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
3,075
Likes
1,998
Location
UK
#87
Why are you inverting the transfer function?
To make the output a duplicate of the signal - even in the time domain.
 

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
5,791
Likes
4,490
Location
Australia
#88
To make the output a duplicate of the signal - even in the time domain.
The output of any loudspeaker is an approximation of the source signal. There will be a difference but this does not translate to instability in a properly designed BR system.
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
3,075
Likes
1,998
Location
UK
#89
The output of any loudspeaker is an approximation of the source signal. There will be a difference but this does not translate to instability in a properly designed BR system.
The speaker itself is perfectly stable. I'm talking about using DSP to get to a time domain duplicate (not a frequency domain approximation) of the signal. It is the overall system that would be unstable.
 

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
5,791
Likes
4,490
Location
Australia
#90
Let's test this in the real world. Have any members had a BR speaker go crazy-unstable when applying DSP within the loudspeaker rated power limits?
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
3,075
Likes
1,998
Location
UK
#91
Let's test this in the real world. Have any members had a BR speaker go crazy-unstable when applying DSP within the loudspeaker rated power limits?
I don't think you're quite following the argument..! No one tries to correct a BR speaker in the time domain. If its frequency response shows loads of bass then it's a result!
 

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
5,791
Likes
4,490
Location
Australia
#92
Obviously not. But then the argument could be imprecise.

I'll leave it to others as to its relevance and to what?

Other people's thought bubbles are their's to explain clearly. I do often have difficulty with yours. Your problem or mine, as it is said? ;)
 

Cosmik

Major Contributor
Joined
Apr 24, 2016
Messages
3,075
Likes
1,998
Location
UK
#93
Obviously not. But then the argument could be imprecise.

I'll leave it to others as to its relevance and to what? Other people's thought bubbles are their's to explain clearly.
Let me try to be more precise. The generalised way to correct a system's foibles is to invert its impulse response, so that if you feed an impulse in, you get the same impulse out (but amplified or converted into sound pressure, or whatever). A latency delay may be necessary to achieve this.

I am suggesting that this can be done with a sealed speaker (and often is in practice - as long as multi-way drivers are time aligned), but cannot be done with a ported speaker because of its reliance on a resonator.
 

KSTR

Senior Member
Joined
Sep 6, 2018
Messages
491
Likes
1,149
Location
Berlin, Germany
#94
It really does sound different from a closed box speaker having same (eq'd) response in a sweep measurement!
As I said, this is possible and when it does, something went wrong. If the ported and sealed are superbly designed (notably no port noise, leakage etc), then the difference disappears... or is extremely low level, and then typically can be tracked down to different distortion and overload/recovery profiles, in general: remaining nonlinearities/instabilites. Anything else would violate linear systems theory.
 

DDF

Senior Member
Joined
Dec 31, 2018
Messages
451
Likes
557
#95
As I said, this is possible and when it does, something went wrong. If the ported and sealed are superbly designed (notably no port noise, leakage etc), then the difference disappears... or is extremely low level, and then typically can be tracked down to different distortion and overload/recovery profiles, in general: remaining nonlinearities/instabilites. Anything else would violate linear systems theory.
True in the bass and for port contribution but a ported system has an inherent lack of back wave absorption due to its typically modest box stuffing. Resonances as far as 28 dB below direct can be audible even with very little delay (Toole/Olive study) but you'd have a hard time detecting that coming through a cone on a frequency response measure unless you knew exactly what to look for (creates only ~ 0.8 dB perturbation on axis).
 

pozz

Machine
Forum Donor
Editor
Joined
May 21, 2019
Messages
1,912
Likes
2,747
#96
Practical question: since watts are so cheap and amps so good, why have a port at all? Especially since sealed and ported speakers share most important characteristics and show the same FR.
 

Wombat

Major Contributor
Joined
Nov 5, 2017
Messages
5,791
Likes
4,490
Location
Australia
#97

pozz

Machine
Forum Donor
Editor
Joined
May 21, 2019
Messages
1,912
Likes
2,747
#98
A good brief overview of pros and cons is given in this article:

See Ported vs Sealed Enclosures section.
Err.. That's written by Robert Harley.

But I'm familiar with the fundamentals. I asked because don't see an advantage from the design perspective given the difficulty of tuning and preventing leakage. Low bass extension is also better done with subwoofers. The only thing I can see tipping the scale is commercial considerations and the practicality of keeping it in one box.

Edit: To be clear, my post was in light of @KSTR's comments about the best designs.
 
Joined
Jul 10, 2019
Messages
72
Likes
74
#99
Practical question: since watts are so cheap and amps so good, why have a port at all? Especially since sealed and ported speakers share most important characteristics and show the same FR.
Low-frequency efficiency and displacement requirement. Free-field SPL is given by acceleration, the second derivative of displacement and thus 4x volume displacement per octave. But is this for the tops above the subbass range?
 

pozz

Machine
Forum Donor
Editor
Joined
May 21, 2019
Messages
1,912
Likes
2,747
Low-frequency efficiency and displacement requirement. Free-field SPL is given by acceleration, the second derivative of displacement and thus 4x volume displacement per octave. But is this for the tops above the subbass range?
With today's amplifiers and drivers efficiency is less of a concern, no? Again, I only see the practicalities of selling single full-range speakers with deep cutoffs and cheaper parts as the main reason why they are so prevalent.

Efficiency makes most sense in sound reinforcement or PA settings.
 
Top Bottom