should speaker port be sealed.

[PSU80]

I wanted to get your thoughts on sealing the rear port on my bookshelf speakers. I'm using a sub crossed over at 80 and have read some articles suggesting the the ports be sealed when used with a sub. Can the speaker be damaged by plugging the port and if not what is the theory and/or potential benefit (if any) of sealing the port?

Thanks

 

[templemaners]

Why don't you contact Aperion and see if they say it's ok if you seal the port? You can do that with some speakers, like Sierra-1's, but not others.

 

[ski2xblack]

Try it out and find out if it works.

Sealed mains seem much easier to blend with subs, at least in my experience. Corking them will raise their lower roll-off by 1/2 octave or maybe more, so you want to make sure their sealed response fits with the current crossover point you're using. If it does, I don't see any issues with what you're considering. With smoother sub blending, it could very well pay dividends.

 

[Swerd]

You shouldn't be able to damage the woofers by blocking the port, you will only loose some bass response. If you are crossing over at 80 Hz to a subwoofer you may not even notice any loss.

Download Aperion's frequency response and impedance curves. On the lower part of page 2 it shows (in turquoise) the bass response of the port. The port on those speakers is tuned to about 40 Hz, and at 80 Hz the port's response is nearly 5 dB lower.

 

[sholling]

You can do that with some speakers, like Sierra-1's, but not others.

There is a time and a place where a plug can help but as long as the port has room to work I wouldn't plug the port, at least not without talking to the manufacturer. Some companies actually include plugs with their speakers s that you can wall mount them. That said I plugged my Sierra-1s only after speaking with the designer and using plugs he designed to prevent pressure within the speaker. Here is Dave F's (Ascend Acoustics designer/owner) opinion as it applies to his products.

http://forum.ascendacoustics.com/showthread.php?t=3781

Simply plugging the port of a properly designed ported loudspeaker is generally a bad idea. A woofer that is designed for a ported enclosure will act differently when installed in a sealed enclosure. The compliance of the woofer is not designed to see the internal pressures created by a sealed enclosure and the speaker then becomes overdamped, subjecting the woofer to greater excursions (often exceeding its mechanical limits) and pre-mature bass roll-off. You can also end up with a higher than normal impedance peak at system resonance.

However, the advantages to plugging a port can outweigh the disadvantages if the speaker is going to be positioned so that the port tube is close to a wall or the speaker is in an enclosure. The challenge we faced was how to offer the flexibility of plugging the port without crippling our woofer which is fully optimized for a ported design.

The solution was to transform the Sierra-1 into an aperiodic enclosure, an enclosure that allows a specific amount of pressure to be released through the cabinet. This allows precise control of woofer damping resulting in improved bass response compared to simply sealing the port while also lowering the high impedance peak.

 

[TLS Guy]

I wanted to get your thoughts on sealing the rear port on my bookshelf speakers. I'm using a sub crossed over at 80 and have read some articles suggesting the the ports be sealed when used with a sub. Can the speaker be damaged by plugging the port and if not what is the theory and/or potential benefit (if any) of sealing the port?

Thanks

If you seal the port the F3 point will rise and probably to around 90 Hz for most bookshelves and it could be a lot higher.

Drivers designed for sealed enclosures have a much looser suspension than speakers designed for ported use. Ported drivers usually have Qts around 0.35 or lower, sealed drivers over 0.4.

The next issue is that if the port is sealed a lot more damping materiel needs adding to the enclosure. The other issue is that the box is likely to be over sized for the drivers sealed alignment, and you may get a lot of ripple above F3.

Sealed is attractive for combining with a sub as roll off is second order below F3 for ported is fourth order.

The receiver high pass roll off is second order, but the low pass is fourth order. So if you have a second order roll off on your speakers you get a better splice. So a sealed speaker with an F3 of 80 Hz can theoretically work very well with a sub.

Your best bet is to buy a woofer tester, to get the Thiel/Small parameters of your driver in the bookshelf and then model the optimal alignment. Don't be surprised if the model requires building new cabinets.

 

[j_garcia]

I would tend to say it won't cause any damage, but as TLS points out, you will lose bass extension.

For the purpose of adding a sub, I dont' think plugging the port will have much impact on their integration with the sub when using a processor that is taking care of bass management. They were designed to be vented, so plugging the port should not be necessary.

 

[Dan]

Try an experiment. Get a sound pressure level meter ($20 odd at the Shack) and a CD with test tones including 20-200 Hz. Try the tones with the ported speaker alone, with the port temporarily sealed with and without your subwoofer. Graph it all out if you like on semilog paper. Go for the response curve that looks best/ is flattest.

 

[ski2xblack]

Try an experiment. Get a sound pressure level meter ($20 odd at the Shack) and a CD with test tones including 20-200 Hz. Try the tones with the ported speaker alone, with the port temporarily sealed with and without your subwoofer. Graph it all out if you like on semilog paper. Go for the response curve that looks best/ is flattest.

Be extremely careful if you do this. When ported, the driver and port get more and more out of phase as you go below the port's resonance. This is a recipe for overexcursion of your drivers using test tones.

When sealed, playing the same freq of the port's resonance in the first case, the driver will move much more, but still probably within it's capabilities, unless you're pushing the volume excessively. (The different damping characteristics others mentioned still stand, those were excellent points.) The resistance provided by the sealed enclosure helps resist excessive cone motion at freq below that, but it is still easy to over-drive things using bass test tones.

Either way, use common sense when sending bass test tones to small-ish speakers. I'd hate to see you break something.

 

[Dan]

Thanks, you are correct. Perhaps it would be safer and more realistic if the speaker were set to "small" since that is how it would be set up with a sub, whether it is ported or not. That way there will not be undue low frequencies passing into the speaker,they'll be routed to the sub.