Hanleyster
ambitious but rubbish
Lets say you have your run of the mill cerwin vega 12" 3-way speaker.
What happens if you make it air tight and eliminate the port?
What happens if you make it air tight and eliminate the port?
What happens to the sound when you seal a ported speaker?
- Thread starter Hanleyster
- Start date
twiiii
Lunatic Member
The purpose of a port is to tune the box to the resonant frequency of the speaker, thus extending the Low frequency of the speaker. The port also allows the woofer to move efficiently increasing the out put of the speaker. Close the port and you restrict the movement of the woofer increasing the impedance to the amplifier further reducing the output. Plus as most ported speakers don't have internal sound absorption to stop standing waves and ringing the sealed box will blur the sound of the woofer with multiple reflections imposing on the woofer cone further compromising the sound. If you want to close the port you need to fill the box with fiber glass and hang a curtain of glass behind the woofer to reduce standing waves, prevent ringing and hope fully extend the bass response. But the over all efficiency of the speaker will drop further because a great percent of the energy created by the woofer will be absorbed rather than directed to the former port which supported the overall output of the woofer.
Hanleyster
ambitious but rubbish
So no benefits unless you want to cut bass. Got it.
p.s. Why do sealed speakers like the AR-3a have such good bass when its sooo hard to push the woofer in? Is that why they take a lot of power? It just needs a lot of power to physically move the woofer inwards? Seems like they wouldnt have the same sort of SLAP as a ported speaker's woofer that was much more free to be tossed around by the watts.
p.s. Why do sealed speakers like the AR-3a have such good bass when its sooo hard to push the woofer in? Is that why they take a lot of power? It just needs a lot of power to physically move the woofer inwards? Seems like they wouldnt have the same sort of SLAP as a ported speaker's woofer that was much more free to be tossed around by the watts.
canuckaudiog
On a quest for high fidelity
There are a few reasons to go sealed over ported.
One is some drivers are better suited in a ported box versus sealed (and vice versa). I don't remember the specifics but the thiele small parameters will tell you which one it is better for (and some drivers can work well in both).
The other reason is bass extension. Sealed boxes have a smoother rolloff and extend deeper. They roll off at 12dB per octave.
Bass reflex (vented) rolls off at 24dB per octave.
And of course, the way the bass sounds is different with sealed versus ported.
Finally, efficiency. Bass reflex is more efficient because it has more output, whereas sealed is less so. If you want a very efficient speaker, most likely you are going to be building a bass reflex for the bass loading. The AR 3a is an excellent example of this. The bass is deep and extended, but as you know it is not a very efficient speaker. The driver was designed specifically for acoustic suspension, and I suspect the designers wanted the deeper, extended bass that a sealed enclosure allows so that they could get deeper bass out of a small (ish) enclosure.
There is, also, a third enclosure not discussed, which are transmission lines. However, they are a different animal. Similar to bass reflex in many aspects but different in others.
One is some drivers are better suited in a ported box versus sealed (and vice versa). I don't remember the specifics but the thiele small parameters will tell you which one it is better for (and some drivers can work well in both).
The other reason is bass extension. Sealed boxes have a smoother rolloff and extend deeper. They roll off at 12dB per octave.
Bass reflex (vented) rolls off at 24dB per octave.
And of course, the way the bass sounds is different with sealed versus ported.
Finally, efficiency. Bass reflex is more efficient because it has more output, whereas sealed is less so. If you want a very efficient speaker, most likely you are going to be building a bass reflex for the bass loading. The AR 3a is an excellent example of this. The bass is deep and extended, but as you know it is not a very efficient speaker. The driver was designed specifically for acoustic suspension, and I suspect the designers wanted the deeper, extended bass that a sealed enclosure allows so that they could get deeper bass out of a small (ish) enclosure.
There is, also, a third enclosure not discussed, which are transmission lines. However, they are a different animal. Similar to bass reflex in many aspects but different in others.
Science. Villchur and Kloss got it right. Porting had to wait for Thiel-Small to get it right with science.
Think of them as a ported enclosure with very rigid enclosure re-enforcement.
As stated closing the box increases system resonance and reduces bass output. But, this is not because the woofer moves less; precisely the opposite is true! The port provides damping to the driver and cone excursion is reduced - significantly - around tuning frequency. Running some numbers against a 12" driver I'm working with currently, at 100W input in a 50l box the excursion is the same at 110Hz, 4mm, in both designs. But in the ported box, this reduces steadily to just 0.7mm at resonance (65Hz) whilst the sealed box peaks here at 5.5mm. But what happens below resonance is significant; the port unloads the driver resulting in a massive loss of power handling. In my example, the two are equal again at 45Hz and by 30Hz, the ported design is essentially running the driver free-air with 14.5mm excursion, whilst the sealed driver is still at 5.5mm.
All of this translates to a big increase in power handling and output around the port tuning, and a big decrease below. PA speakers are run with steep active HPF for this reason, in my example I'd be using 24dB/octave HPF at 45Hz with this design.
There is also something to say about the bass quality itself. The ported design introduces a phase shift, but also delay because of it's resonant nature. In my example, at 50Hz the sealed design shows 3ms delay whilst the ported design shows 5ms. And with another (more powerful) driver in the same ported box, this rises to 9ms.
Sealed designs can produce a very linear, deep output with the right driver and a big box with less delay in the bass.
johnr66
Well-Known Member
Reminds me of some one note wonder bass boom wedge speakers I had in the truck once. I could not stand them. I stuffed old socks in the ports and they sounded good afterwards. They were designed with a huge peak in the bass for some reason. Not an ideal fix but it took the peak out of the bass.
Sealed speakers that can deliver deep bass have the driver with proper T/S parameters as mentioned. One important parameter is to select a driver with a low free air resonance (among other things). I built a sealed sub for my computer sound using a 15" driver in a 3 cu ft box. Impressive deep bass. I've never built a bad speaker using modeling software sealed, ported or otherwise. It takes the guesswork out of it.
Sealed speakers that can deliver deep bass have the driver with proper T/S parameters as mentioned. One important parameter is to select a driver with a low free air resonance (among other things). I built a sealed sub for my computer sound using a 15" driver in a 3 cu ft box. Impressive deep bass. I've never built a bad speaker using modeling software sealed, ported or otherwise. It takes the guesswork out of it.
Likely it wasn't designed at all, just random bass drivers thrown in a box that seemed about right and a standard port tube added. Also the SPL crew obviously make use of big resonance to get their crazy SPL numbers.
CopperWizard
Super Member
It has been suggested by others, as well as the technicians who created them, to stuff a sock into the port of the speaker in my avatar(marantz imperial6.) I do on occasion to tighten up the bass but it does cut out some dynamics in the music. I know that's not sealing it though.
nexus
Super Member
the OP mentioned using Cerwin Vega. i would say that CV engineers designed for the market they were aiming for and optimized the speaker to perform it's best.
i am a long proponent of acoustic suspension and sealed box speakers but a well designed big ported speaker like the CVs is very impressive on rock and electronic music.
having said that, i still think one can add some foam damping to the walls of the cab without 'second guessing' the designers. we did this on a friends big CVs and they are much improved.
the deficiency of CV speakers is really not the bass as much as the mid and treble performance. when these are lacking it can tend to make the bass seem muddy or plodding. i have heard a couple of CVs that did okay with large scale orchestral music after careful placement, a couple room treatments and balancing of the trim pots on the speaker.
transmission lines were mentioned but are beyond the scope of the OP's question. yes they are the best but very very hard to get right. i know, i tried for years but was never satisfied in getting them to sound like a good IMF or Fried.
i currently use large sealed box woofers. i have ACI woofers in them which i added a little mass with permagum HVAC sealant (like Infinity used in the early 70's). it lowered the F3 and i still have great transient response and decent power handling. i applied it the same way infinity did, around the dust cap in a flat ring. old issue of Speaker Builder did a feature on the technique.
one thing the OP might try is to lightly stuff the port with acoustic fiberglas or even acoustastuf (from PE). this use to be done to affect an Aperiodic loading as in a Dynaco A25. one has to experiment with this to find the right damping. F3 will be higher than ported but it will be 18db per octave and be flat down to the rolloff point.
i am a long proponent of acoustic suspension and sealed box speakers but a well designed big ported speaker like the CVs is very impressive on rock and electronic music.
having said that, i still think one can add some foam damping to the walls of the cab without 'second guessing' the designers. we did this on a friends big CVs and they are much improved.
the deficiency of CV speakers is really not the bass as much as the mid and treble performance. when these are lacking it can tend to make the bass seem muddy or plodding. i have heard a couple of CVs that did okay with large scale orchestral music after careful placement, a couple room treatments and balancing of the trim pots on the speaker.
transmission lines were mentioned but are beyond the scope of the OP's question. yes they are the best but very very hard to get right. i know, i tried for years but was never satisfied in getting them to sound like a good IMF or Fried.
i currently use large sealed box woofers. i have ACI woofers in them which i added a little mass with permagum HVAC sealant (like Infinity used in the early 70's). it lowered the F3 and i still have great transient response and decent power handling. i applied it the same way infinity did, around the dust cap in a flat ring. old issue of Speaker Builder did a feature on the technique.
one thing the OP might try is to lightly stuff the port with acoustic fiberglas or even acoustastuf (from PE). this use to be done to affect an Aperiodic loading as in a Dynaco A25. one has to experiment with this to find the right damping. F3 will be higher than ported but it will be 18db per octave and be flat down to the rolloff point.
Rule of thumb is a Qts under 0.4 is designed for ported, and a Qts between 0.4 and 0.7 is for sealed. Above 0.7 is for infinite baffle. But that's not a hard and fast rule every single time. There are other characteristics that make some drivers with a Qts of 0.3 work well in a sealed box, and a driver with a Qts of 1.0 work well in a ported box (like DCMs).
It's pretty close. What you are effectively doing is making the port "aperiodic", you are reducing the amount of energy that is transferred through the port. If you measured the response, you'd see that your low cutoff point would be raised in frequency, but the slope will decrease from the signature ported 24 db/octave to something more gradual. If you block the port completely, you'll end up with a sealed box with a slope closer to 6 db/octave. That's why you think the bass is getting "tighter" because you're probably reducing the output of the system to above the resonant frequency of the driver, but you're also losing SPL below the new cutoff point.
nexus
Super Member
actually it will be 12db/octave. aperiodic is more like 18db/octave. only open baffle rolls off at 6db/octave below woofer Fs. just to clarify.
DavidF
Active Member
You need some amount of mass and sheer size in the cone assembly to enhance bass response. The systems at large
The cone put into motion has to have some resistance as a restorative force. Most methods to get deeper bass response involve more cone mass, larger cone surface or combination of both. Adding mass decreases sensitivity.
The typical HiFi speaker in the era of the AR-3 was large in dimension to enclose a 15 inch woofer. In order to preserve sensitivity in the day of low watt amps the woofers were large cones of lighter mass. The large enclosure was to try to find some bass extension. Villchur's solution was to increase the mass of a 12inch woofer to get bass response extension. To avoid a tighter suspension to control the woofer motion he used a "loose" suspension combined with a small enclosure nearly air tight so that the compression of the air would provide a restorative effect to offset the looser suspension. The result was a small enclosure with lower bass response than that of the behemoths. But at the cost of sensitivity.
The cone put into motion has to have some resistance as a restorative force. Most methods to get deeper bass response involve more cone mass, larger cone surface or combination of both. Adding mass decreases sensitivity.
The typical HiFi speaker in the era of the AR-3 was large in dimension to enclose a 15 inch woofer. In order to preserve sensitivity in the day of low watt amps the woofers were large cones of lighter mass. The large enclosure was to try to find some bass extension. Villchur's solution was to increase the mass of a 12inch woofer to get bass response extension. To avoid a tighter suspension to control the woofer motion he used a "loose" suspension combined with a small enclosure nearly air tight so that the compression of the air would provide a restorative effect to offset the looser suspension. The result was a small enclosure with lower bass response than that of the behemoths. But at the cost of sensitivity.
Tim64
Super Member
The woofer design for a sealed enclosure tend to have a much looser surround and spider on older speakers like the AR. The air pressure it self helps stabilize the woofer where as a woofer for a ported enclosure tended to have a more rigid surround and stiffer spider. Today some woofers can be used for either but tend to work best with one or the other.
