Hello,
I guess this question might sound strange to experienced readers: would it make sense to set a port in an enclosure if one doesn't need to extend the frequency response in the low range? Could a port have a pure "pressure equalization" function which would bring other benefits? Which ones? Then, would it be designed in a different way than an usual port (with a smaller section maybe) ?
Thank you for enlightening me!
I guess this question might sound strange to experienced readers: would it make sense to set a port in an enclosure if one doesn't need to extend the frequency response in the low range? Could a port have a pure "pressure equalization" function which would bring other benefits? Which ones? Then, would it be designed in a different way than an usual port (with a smaller section maybe) ?
Thank you for enlightening me!
The only thing I can think of, is the cone excursion dip.
Therefore creating less cone excursion, slightly lower distortion and possible IMD.
But we are talking about a pretty small frequency band here.
Besides the practical issues of getting the response right.
Generally for a passive system, this means a smaller volume, making the port longer.
Leading to a lower port resonance frequency.
The port by itself also has its obvious downsides.
In general, for high SPL applications, this can make sense.
Often combined with an active HP filter.
Therefore creating less cone excursion, slightly lower distortion and possible IMD.
But we are talking about a pretty small frequency band here.
Besides the practical issues of getting the response right.
Generally for a passive system, this means a smaller volume, making the port longer.
Leading to a lower port resonance frequency.
The port by itself also has its obvious downsides.
In general, for high SPL applications, this can make sense.
Often combined with an active HP filter.
Is a port useful if one doesn't need to extend response in the low range?
If it is really the case, then I would stay with a sealed-filled enclosure, with a QTC of 0.7 to 0.8 :- better step response and transient response
- lower rolloff in the bass extension (typically 12dB/Oct 2nd order against 24dB/Oct 4th order for the BR)
- better group delay
- more neutrality
But it's me, OK ? 😉
T
Would you be thinking along the lines of a passive radiator? There’s been quite a few posts about pros and cons. I’m not sure where the weight of opinion has landed. Edited.
Technically you can make a ported enclosure give a response that is very close to a closed box.
Jus tune it very low.
Only the lowest part will have a higher GD.
It's debatable how bad that is or not.
Aw sorry 😕 :
An empty-sealed enclosure :
A filled-sealed enclosure :
Yes indeed, that's what I do, and it's more or less the goal of the SBB4 box alignments, IIRC.
The idea to report the group delay degradation of the BR in the very low frequencies works quite well - assuming the speakers can handle this, of course (large power handling margin, or reasonable listening loudness 😉 ). You have a deeper, less-boomy tone, and better damping - at least in the usual bass range.
But the group delay of the "best" sealed enclosure will always be superior to the "best" bass-reflex enclosure, quite often with a 1 for 10 margin in level (comparing at critical dampings QTC=0.71 sealed vs. N=5.7 bass-reflex).
T
You can use a port to (with different drivers)
- Get deeper bass for a given box size
- Use a smaller box to get a given bass depth
- Get higher effeicency for a given box size and bass depth
- Reduce cone motion for a given bass output.
Loudspeakers are so ridiculously inefficient in the bass that I always prefer a well made bass reflex system over a closed system.
For that I tune as low as possible like 25/30 Hz and linearize with dsp. Damping in the reflex box can be made to suppress dominant standing waves without loosing bass.
If you have 2.1 system then the satellites should have closed ports in order to not interfere with the sub (and it sounds better then closed)
For that I tune as low as possible like 25/30 Hz and linearize with dsp. Damping in the reflex box can be made to suppress dominant standing waves without loosing bass.
If you have 2.1 system then the satellites should have closed ports in order to not interfere with the sub (and it sounds better then closed)
For my 2 cents worth ...
I would say if you've already got a near perfect speaker/room marriage with good bass,
adding a port could 'open a can of worms' you don't want.
Especially if your box volume is far off ideal Theil & Small parameters.
I would say if you've already got a near perfect speaker/room marriage with good bass,
adding a port could 'open a can of worms' you don't want.
Especially if your box volume is far off ideal Theil & Small parameters.
... and when I run out of binding posts I use ports to route cable till I get some.
All things being equal, a port lowers the F3 point at the expense of everything else in relation to sound quality.
For the most part.
Unless you tune low enough it behaves
more like sealed.
Basically tune for no added bass response.
The reflex being maybe 18 to 22 Hz resonance.
Helps cone control further than sealed.
Can add far more bass with a simple shelf filter
or bass EQ. Reflex can be used for control
instead of the usual unloading.
Unless you tune low enough it behaves
more like sealed.
Basically tune for no added bass response.
The reflex being maybe 18 to 22 Hz resonance.
Helps cone control further than sealed.
Can add far more bass with a simple shelf filter
or bass EQ. Reflex can be used for control
instead of the usual unloading.
Something simple like 4" driver
FR10-8 with .7 Qtc Sealed
Same volume ported.
tuned low around 20 Hz
not much added response
but can see reflex help reducing
cone movement.
FR10-8 with .7 Qtc Sealed
Same volume ported.
tuned low around 20 Hz
not much added response
but can see reflex help reducing
cone movement.
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Never seen them, and besides the practical issues, you have to be extremely careful with lower frequencies since the cone excursion will go through the roof below the tuning freq.
Also, the port resonance will most likely be an issue.
Closed back chambers already need proper damping material to get rid of any internal resonances.
Which are pretty significant without.
Hi, yeah thats also what I thought why there isn't one (googling shows there actually are some, but very very rare).
Point is to get into a thought experiment, which could help anyone to think if porting could help their system performance:
As sound interacts with physical objects the same as long as ratio of wavelength to physical object size (and shape) stays constant, then logically same issues that plague ported tweeters would exist on any transducer/system, they just come down in frequency as physical size goes up.
Since there is (practically) no ported tweeters in use, likely for good reason, then it would be better leave ports out from all boxes, except those who can have the issues taken care by limiting bandwidth on the top end, and benefit having the port (some kind of low end augmentation).
Hence, ports are good for subs, but if ported system bandwidth extends further and further into midrange then risk getting into bad sound territory increases, or, if the transducer doesn't benefit from augmented lows, then there is no reason to port in the first place. Since tweeters are small, they must be crossed over to a bigger transducer at some frequency, hence there is not much point trying to extend the low frequency with cost of high frequency performance.
Point is to get into a thought experiment, which could help anyone to think if porting could help their system performance:
As sound interacts with physical objects the same as long as ratio of wavelength to physical object size (and shape) stays constant, then logically same issues that plague ported tweeters would exist on any transducer/system, they just come down in frequency as physical size goes up.
Since there is (practically) no ported tweeters in use, likely for good reason, then it would be better leave ports out from all boxes, except those who can have the issues taken care by limiting bandwidth on the top end, and benefit having the port (some kind of low end augmentation).
Hence, ports are good for subs, but if ported system bandwidth extends further and further into midrange then risk getting into bad sound territory increases, or, if the transducer doesn't benefit from augmented lows, then there is no reason to port in the first place. Since tweeters are small, they must be crossed over to a bigger transducer at some frequency, hence there is not much point trying to extend the low frequency with cost of high frequency performance.
...and where 'critically' damping it comes into play. 😉
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Yes (and no). The B&W Nautilus tweeter loads its own max-flat impedance QW TL.