hcsunshine
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question about rear ported speakers
bierfeldt
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I have bungs in my Revel Performa3s because of distance to the wall. The bungs that Revel provides are cylindrical pieces of foam.

It will behave more like a sealed speaker. Bass response will be reduced but sound out of the port won't reflect off the wall. Just not quite as clean as a sealed speaker would be.

hcsunshine
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I placed my hand over the port while the music was playing and the bass response was reduced, but it seemed that the overall response was clearer. I actually like the way they sound "bunged" better. thanks bierfeldt. edit: i noticed the four screws holding the port onto the speaker. I think I will take the port out. then fashion a round piece of say 1/2 inch thick plywood and drill four holes in it. maybe I will even take a piece of rubber, like they have on canning jars and put that in between the speaker and the piece of wood and screw the whole thing together. I was wondering now how my speakers will now differ from a sealed design...?

bierfeldt
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I have no idea what will happen if you actually seal it. If i was to try it, I would get an acoustic adhesive foam from PartsExpress to seal the plug. It is basically weather stripping. I would also get acoustic grade filler which is a cotton like substance to reduce resonance. Others may have a different opinion.

I personally would never try it but I am nervouse about fouling up something. But that is me. I am a big wimp when it comes to messing with any sort of device until it is broken.

commsysman
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The plugs that are supplied by the speakers manufacturers are cylindrical pieces of soft foam rubber about 3 inches thick.

One thing that might work well as a substitute is to just stuff in some fiberfill like they use to put in pillows and sleeping bags.

It's not supposed to "seal" the port; just restrict free air movement somewhat.

hcsunshine
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i contacted the manufacturer of the speaker and he said i could do it but he said something about at higher volumes there would be much longer excursions in the woofer. so i'm not gonna do it.

commsysman
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hcsunshine wrote:

i contacted the manufacturer of the speaker and he said i could do it but he said something about at higher volumes there would be much longer excursions in the woofer. so i'm not gonna do it.

There will be longer excursions WITHOUT the plugs. Plugging the port tends to DAMP the woofer and the excursions will therefore be smaller.

You may have misunderstood what was said.

hcsunshine
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i could have sworn he said the excursions will be longer and the bass will roll off a lil higher with it sealed. maybe i'll ask for clarification...ok, this is what he says: "with a port the excursion increases below the frequency of the ports tuning. a sealed box won't do that; however, it overall requires the woofer cone to move more. this is especially true when using a larger box volume with a lower "Q" (as in this case)." ...and i say i do have good size cabinets, too...so i'm still not sure what to think now...though i'm not gonna seal the box just because it sounds good the way it is now.

andy_
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Your manufacturer is correct. The output from the port adds to that from the woofer and so the woofer does not need to move as far for the same level of total output. In addition since the woofer does not move as far there is less distortion from the woofer. At resonance the woofer motion can be brought almost to a stop by the pressure created within the cabinet by the air flow in the port. You can see this in JA's measurement section for a review of a ported speaker like the recent Wilson Duette. Notice how the woofer and port output varies over the low frequencies.

commsysman
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hcsunshine wrote:

i could have sworn he said the excursions will be longer and the bass will roll off a lil higher with it sealed. maybe i'll ask for clarification...ok, this is what he says: "with a port the excursion increases below the frequency of the ports tuning. a sealed box won't do that; however, it overall requires the woofer cone to move more. this is especially true when using a larger box volume with a lower "Q" (as in this case)." ...and i say i do have good size cabinets, too...so i'm still not sure what to think now...though i'm not gonna seal the box just because it sounds good the way it is now.

Yes, the excursion WILL increase BELOW THE FREQUENCY of the port's tuning.

It is important to realize that the speaker's overall response is dropping off rapidly at those lowest frequencies, however.

Increasing the excursions at those lowest frequencies is actually desirable, because that means the rolloff at the low end will be more gradual.

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