Many commercial ported speakers come with foam tubular port bung to reduce bass on poor recordings.
If a port is sealed is the air in the tube still resonating? If so, does that cause detrimental effects?
Is a short foam bung, that leaks a little bass, better than a completely sealed port?
If a port is sealed is the air in the tube still resonating? If so, does that cause detrimental effects?
Is a short foam bung, that leaks a little bass, better than a completely sealed port?
I believe you meant to say a Fully Sealed enclosure is better? If so, I believe the optimum enclosure volume for ported vs sealed are different, any comments?
How about a leaky foam bug vs a rubber bung fully sealing the port?
How about a leaky foam bug vs a rubber bung fully sealing the port?
I have often “fixed” badly tuned reflex boxes with some open-cel foam to push th ebox aperiodic.
A fully aperiodic loudspeaker is a very rare thing. There is no bad, only a transition from a relex to sealed as the resistance in the “vent” is increased. Where one would like to end up is a set of compromises that depend on many things, including you and your room.
My miniOnken add R to the vents and push a reflex just a bit towards aperiodic with gains (small box, LF finesse) and losses (won’t go as low)
da e
A fully aperiodic loudspeaker is a very rare thing. There is no bad, only a transition from a relex to sealed as the resistance in the “vent” is increased. Where one would like to end up is a set of compromises that depend on many things, including you and your room.
My miniOnken add R to the vents and push a reflex just a bit towards aperiodic with gains (small box, LF finesse) and losses (won’t go as low)
da e
I'd consider the bung to be having the expected effect.. and not worry that the smaller details are preventing this, if they are having any effect at all.
A Fully Sealed design (obviously an enclosure) is usually better than a bad Aperiodic design (enclosure result).
The added volume from fully sealing a *typical ported enclosure is almost always inconsequential with a very slight lowering in Fs (Fb) along with a slight lowering of Qtc as a result, and a lower Qtc is usually beneficial subjectively irrespective of (net) spl-losses at lower freq.s. (..and really, when you do something like this (plugging a port) you are almost always trying to reduce the output at lower freq.s.)
*ported enclosures are almost always larger in volume than their counter-part sealed designs for the same woofer. Note though that there are exceptions where the port design is more about tailoring the spl for a more limited bandwidth at higher freq.s than increasing low freq. extension as when you want a "bump" result to sum better with a large shallow front horn (sort of acoustic baffle-step compensation on "steroids").
Yes, a good "O" ring around the outside of a port plug can fully seal a port. Perhaps better still if there are more than 1 "O" rings helping to ensure a fully sealed result.
Leaky foam plugs are almost always still resonators. It's easy to test this with an Impedance trace. IF you have a single "hump" of Impedance for the driver in-box with that "hump" having a low magnitude (nearing flat) then you have an Aperiodic result. IF you have 2 Impedance "humps" then you have a resonant condition.
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And if a computer is used to measure impedance, how do you tell if it's damped enough or not?
dave
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Thanks, Scott. I noticed considerable port output using the supplied short foam bungs, so went online looking for rubber bungs & found a 3" rubber trash disposal stopper ($6 each) to be a perfect fit. It does a nice job of curtailing bass on poor recordings. All of which set me off wondering.......
I typically use reticulated foam for plugging vents but sometimes prefer loose sheeps wool or mineral wool. Aquarium foam also works well.
Most of these options aren't intended to create a perfect seal. They're chosen to provide some leakage and tune the system ie. a lossy sealed box with slight aperiodic operating mode. There are many advantages to this but use caution with max LF excursion limits, as the peak excursion will go up for given SPLs and with unfiltered subsonic content from analog sources or from poor recordings.
If you want a true sealed box, I'd suggest closed cell latex foam rubber used for upholstering seat cushions.
The open cell urethane stuff (used for sound absorption) will also provide some leakage and will stay put better in the port. Just watch out for woofer overexcursion. It only takes one hit of the VC on the rear pole plate to permanently damage a woofer, especially with an aluminum VC former.
Most of these options aren't intended to create a perfect seal. They're chosen to provide some leakage and tune the system ie. a lossy sealed box with slight aperiodic operating mode. There are many advantages to this but use caution with max LF excursion limits, as the peak excursion will go up for given SPLs and with unfiltered subsonic content from analog sources or from poor recordings.
If you want a true sealed box, I'd suggest closed cell latex foam rubber used for upholstering seat cushions.
The open cell urethane stuff (used for sound absorption) will also provide some leakage and will stay put better in the port. Just watch out for woofer overexcursion. It only takes one hit of the VC on the rear pole plate to permanently damage a woofer, especially with an aluminum VC former.
What means “better”? In what ways?
What about a bad sealed vrs a bad aperiodic? Or a good sealed vrs a good aperiodic?
How “good” an aperiodic you can get by stuffing a vent is dependent on many things. And if you want to go further you can “restuff" the enclosure. The GM click-test or measured impedance can be used to get as close as you need. Keep in mind that the 1st Jordan/Goodman’s aperiodic and the Scanspeak VarioVents are short stuffed vents,
The impedance of the Perkins PR-2 has always interested me (tweeter responsible for the shelf higher up).
This kind of impedance gives great latitude for amplifier choice.
Lots more tidbits can be teased from the white paper: https://pearl-hifi.com/03_Prod_Serv/PR2/PR2_Content.html
I like using aperiodic TLs for midTweeter enclosures, and they are the first choice for a woofer in a smaller box than it would really like.
And my miniOnken alignment uses longish restrictive vents to add enuff R to push them just a bit towards aperiodic and they work very well.
dave
A sealed box has one impedance hump, a vented box two, As you move towarsd aperiodic they start to flatten. If you get flat — not at all easy — then it is aperiodic. But even a bit can help sometimes.
dave
Um, not really. It reduces the bass to make it easier to locate the speaker in a variety of locations. Also, if you are using a subwoofer, using a plug can really make integration easier, reduce distortion and improve dynamic range thanks to less excursion below the port F.
My application is a floor stander located, after experimentation with acoustic bass recordings, to minimize bass room modes. The bungs are effective at attenuating bass on recordings with exaggerated bass (probably mixed with small studio monitors). Poor location or recording, the use of bungs amounts to much the same thing!
Remember, there was context to the reply - specifically when comparing a bass reflex design that’s modified by inserting some sort of plug with a result of either leakage or sealed.
Bad “sealed” in this context isn’t sealed. Moreover you are far less likely to achieve good aperiodic in this case (as mentioned you are far more likely to still have a resonant condition).
“Better” in context: timing and phase along with lower excursion for a given input over most of the operating bandwidth.
