I read something a year or two ago that showed asymmetrical flares we better...I think it reduced the port resonance. But I didn't save it. Has anyone ever seen such a study?
I thought about using two layers of sonotube, as the tubes are nested together in the supply houses. Couldn't figure out an easy way to bond them, fill the fit imperfections, other than maybe expanding foam...which proved to be too sticky to allow insertion.
On the box shown, there was an internal divider separating the sub into two single subs. I braced the sonotube off that and the other walls.
Ay any rate, it was one vibrating/rattling mess at higher SPL.
The entire bottom with castors was removeable with the sonotubes glued into the base, removeable to I could trim the monotubes to length after measuring.
Instead, i just threw away that bottom and built a new one with rectangular shelf type ports out of 3/4" ply. Same area and length as the tubes, because the tubes had measured fine.
It did not vibrate anywhere close to the tubes. So I built a pair.
And then found at high SPL, that the front baffle and overall box were the weakest links. Great big cabinets are a bitch to brace !
I ditched those subs, and built a new set based on what learned.
This port, about 9"W x 20"H x 24"D is built like a tank....(as is the whole cab)
So the driver is either high Qts
or something else is going on
with that high Q bump at cutoff.
Curious what driver
if I missed that.
Port resonance or actual
vibrating port can show a bump in the impedance curve.
Ironically not very audible, but measurable for nit pickers.
Port is a basic velocity ramp
is what it is.
Efficiency is what it is as well.
Usual best bet for velocity thingy's .
Is usual basics
Is = Round for best efficiency
and single flare or dual flare helps with
exit velocity at higher SPL.
So yes thicker port might be better.
But as mentioned, its more a issue for higher SPL.
"Boxey"
just sounds like
A driver that is what it is.
And needs some changes to the basic alignment.
To help a suspension that is not exactly happy.
Port tuning should be just plain close to Fs.
Above or below depending on driver compliance
and how much magnet it got.
Hence the excellent description in post #2 by @pkitt
or something else is going on
with that high Q bump at cutoff.
Curious what driver
if I missed that.
Port resonance or actual
vibrating port can show a bump in the impedance curve.
Ironically not very audible, but measurable for nit pickers.
Port is a basic velocity ramp
is what it is.
Efficiency is what it is as well.
Usual best bet for velocity thingy's .
Is usual basics
Is = Round for best efficiency
and single flare or dual flare helps with
exit velocity at higher SPL.
So yes thicker port might be better.
But as mentioned, its more a issue for higher SPL.
"Boxey"
just sounds like
A driver that is what it is.
And needs some changes to the basic alignment.
To help a suspension that is not exactly happy.
Port tuning should be just plain close to Fs.
Above or below depending on driver compliance
and how much magnet it got.
Hence the excellent description in post #2 by @pkitt
But close to what a alignment should be.
The high Q bump is a indicator of not happy
suspension.
Box too small or big
and tuning not near Fs
Of all things it might wanna be tuned lower.
Ports do in all basics.
" Make more bass"
But people tend to over do and think
all kinds of magical thing come about with ports.
the 3 to 8 dB of bass you loose in real world
All comes back with the EQ knob.
Good port is a port that you dont hear.
And way way to often with modeling.
People try to imagine or maximize " more"
bass with some odd interpretation in models.
Bass come back with EQ
and the less port we hear the better when that EQ comes up.
The basic transfer function is what it is.
And should follow the well known basic theory
of following the transfer function of a filter.
If the woofer is High Qts it might not even align.
Not sure till driver data is seen.
TBH I don't think boxy sound comes from 60Hz. It comes in the mid-band exactly where cabinet modes leak from a port (as in the video above) or where the port had secondary resonances. When testing, was the port length extended on the inside or outside of the cabinet?
How about sealing the port fully and adding a sub? Seems a more effective solution than messing with the design.
How about sealing the port fully and adding a sub? Seems a more effective solution than messing with the design.
The boxiness was cured by extending the port. It's no longer an issue.
The port length was extended inside the cabinet but this is a non-issue. It's a 33 litre cabinet with a 6.5" woofer - loadsaroom!
I'm not trying to make a perfect system. I'm simply trying to extract more from a pair of superfluous floor-standers for educational purposes.
An additional sub is out of the question. Typically, a commercially available 8" sub is housed in a 20-25l box. Pro-rata, 2x 6.5" woofers in 70l should be able to compete.
For ported, my goal is no EQ.
I want the combination of port and direct to be flat down to where f-3 roll-off begins.
Ime, a really good ported sub only needs a low-pass for xover to mains. And a high-pass or limiter, for over excursion protection below port tuning.
This is probably what has improved the boxyness. The location of the port inlet has been moved within the enclosure and most likely moved it away from a pressure peak in the enclosure standing waves. It is much like optimising speaker position in a room for a less peaky response.
The lower bass tuning is kind of a side effect. For interest sake, you could try eq'ing 60hz up a few dB to emulate the original tuning and see if the boxy sou d returns. I'd gamble on not.
Boxy = accentuated upper-bass. When listening to dance or R&B, kicks are overly prominent & untrue in relation to bass-line.
A circular cross section/round port is exposed to very even pressure (by low frequencies) from all sides and is geometrically very stiff, even more for curvatures in more than one direction (flared round port). It's different for rectangular ports.
Soft material could reduce the port resonance, see @Tenson 's experiments.
I suppose "boxy" or "honky" sound from ported speakers is probably caused by resonances exiting the port, either caused by enclosure dimension or port length resonances.
Thus except for low crossover woofers i suggest a low resonating and low resonance transmission port. If possible the first longitudinal port resonance should be above woofer pass band.
See my port geometry and resonance absorber thread for a near-ideal (or good compromise) "nfr=0.5" geometry port:
Beta version of excel sheet for calculating the nfr=0.5 port geometry (slight tuning deviation possible, see the following pages of that thread)
@augerpro 's parametric fusion360 model for a nfr=0.5 port
My parametric freecad model.
An explanation how to find suitable port size (exit diameter).
By the way: the latest update of hornresp provides strouhal numbers directly!
Soft material could reduce the port resonance, see @Tenson 's experiments.
I suppose "boxy" or "honky" sound from ported speakers is probably caused by resonances exiting the port, either caused by enclosure dimension or port length resonances.
Thus except for low crossover woofers i suggest a low resonating and low resonance transmission port. If possible the first longitudinal port resonance should be above woofer pass band.
See my port geometry and resonance absorber thread for a near-ideal (or good compromise) "nfr=0.5" geometry port:
Beta version of excel sheet for calculating the nfr=0.5 port geometry (slight tuning deviation possible, see the following pages of that thread)
@augerpro 's parametric fusion360 model for a nfr=0.5 port
My parametric freecad model.
An explanation how to find suitable port size (exit diameter).
By the way: the latest update of hornresp provides strouhal numbers directly!
You realise you're corresponding with a person who made ports out of a washing-up liquid bottle? What you posted is all Greek to me!
My understanding of tuning is pretty basic - nothing is for free. If you tune for power you will lose torque.
In this instance: LF output @40hz can be gained at the expense of SPL @ the 60hz region.
Trimmed 20mm off the ports for 42hz tuning - markedly better performance.
I realised that long after posting very late at night - sorry about that!
Anyhow, my main point was that a slightly softer material could have positive effects regarding port resonance.
see @Tenson 's thread about port variants including partially reduced wall thickness for resonance absorption:
https://www.diyaudio.com/community/threads/design-study-of-3d-printed-loudspeaker-port.408535/