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  1. #1
    Forum Regular audio amateur's Avatar
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    bookshelf port problem

    hello all,
    Haven't been here in a while. I see things are still moving on, I don't get to come that often anymore... eh florian? haha
    Anyway, a buddy of mine lives in a uni dorm, and has rear ported 'Tonsil' (polish) loudspeakers.
    They are close to the wall, and he is wondering how to get less bass/resonance without having to move them away from the wall. Is there anyway he can plug the ports? or do something to that matter (apart from turning the bass down, which he can do on the amp).
    Just looking for a quick answer. Thanks

  2. #2
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    Hmmmm.... dorm room...... try a pair of gym socks. Most anything like that, that will stop the flow of air through the port will work alright. Depending on the size of the port you may be able to find a rubber ball to fit. Just use your imagination there's no specific object unless it comes with the speaker.

  3. #3
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    This is mean't in the most loving way!!

    While I know nothing about those speakers, they will sound sooo much better on nice weighted stands and a bit back from the walls. ported small speakers need air to sound their best, if you cant't give them air get different speakers, socks balls heck even steel plates will work for now!! They were designed that way for a reasone, since it's dorm I assume there are party's?? Get some nice stands, or make some, listen to them out in the room when ya'll are serious about the sound, when ya'll are partyin' stuff a sock in the ports and push them back!!

    I'm a 44year old rock n roller and when you party everyone should respect the tunes and the equiptment it comes from!!!!!!

    Peace Craig

  4. #4
    rockin' the mid-fi audio_dude's Avatar
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    try some foam or styrofoam, cut it to size and it should work fine! oh ya, get some thick foam, thin stuff won't do squat...

  5. #5
    Do What? jrhymeammo's Avatar
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    Living in a dorm and wants less bass? Is he worried about others? Whatta?Your friend is a wuss.... Just kidding.
    Your friend sounds very sincire.

    You shouldnt mess with plugging ports. Speakers werent designed for to be sealed. Can't he just mess with EQ setting? If he's worried that differnt settings will compromise the SQ, then he shouldnt plug the ports either,
    One way to do it is to place the speakers high. If possible wall-mount them high near the ceiling and have'em face downwards. People living below are more likely to be bothered by noise than folks above.

    Maybe stick more stuffings inside of speakers.

    I'm still very confused about this.

  6. #6
    Loving This kexodusc's Avatar
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    jrhymeammo is right - plugging ports unless the design specifically allows for it is usually not a good idea, and can lead to damage. You're changing the complete system, and affecting the relationship between woofers and enclosure - the last thing you want is to damage the woofer. The port tuning frequency offers protection to the woofer over an octave or so of bass frequencies that you're just removing - the result is increased excursion (which could lead to "bottoming out"), poorer transient response, and increased distortion. Not a great trade-off for less bass. Plugging will work as a last resort, but keep the volume down, a sharp bass transient that sucks some power could smite the woofer.

    Sticking more stuffing inside the speakers may acually make the problem worse, but if you stuffed it enough you would choke the woofer. Again, not a great thing IMO, but it would reduce the bass.

    Sounds like the small room is providing ample room gain - his best bet is to cut the bass through equalization -that's why they provide those features on amps anyway. If it's a digital receiver, he could try setting the speakers to small and playing with the LFE crossover point.

  7. #7
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    Quote Originally Posted by kexodusc
    jrhymeammo is right - plugging ports unless the design specifically allows for it is usually not a good idea, and can lead to damage. You're changing the complete system, and affecting the relationship between woofers and enclosure - the last thing you want is to damage the woofer. The port tuning frequency offers protection to the woofer over an octave or so of bass frequencies that you're just removing - the result is increased excursion (which could lead to "bottoming out"), poorer transient response, and increased distortion. Not a great trade-off for less bass. Plugging will work as a last resort, but keep the volume down, a sharp bass transient that sucks some power could smite the woofer.

    Sticking more stuffing inside the speakers may acually make the problem worse, but if you stuffed it enough you would choke the woofer. Again, not a great thing IMO, but it would reduce the bass.

    Sounds like the small room is providing ample room gain - his best bet is to cut the bass through equalization -that's why they provide those features on amps anyway. If it's a digital receiver, he could try setting the speakers to small and playing with the LFE crossover point.
    I'm not sure I understand the physics of your statement. There has to be something I'm not seeing. How does closing, or partial closing of the port increase excursion. It seems closing the port would increase the physical resistance by either not letting air into the box during outward cone excursion, or letting air out of the box for inward excursion. I can believe the poor transient response, increased distortion, less bass and less efficiency, (all due to increased physical resistance) but can't see why there would be more woofer travel. Unless, of course the user would increase the power/volume to compensate for all the above, which he wouldn't because decreased bass is the goal. How does more resistance equate to increased excursion? I don't pretend to know all there is about speaker design, but on the surface, increased excursion just doesn't sound right.

  8. #8
    I took a headstart... basite's Avatar
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    move them away from the wall or do something with the eq, stuffing them doesn't look like a good idea, i've seen pictures of those tonsil speakers and they look like the woofer/mid is made to move alot, so if you stuff them you will cause problems, maybe even damage and get a different badder sound.

    peace
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  9. #9
    Loving This kexodusc's Avatar
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    Quote Originally Posted by bfalls
    I'm not sure I understand the physics of your statement. There has to be something I'm not seeing. How does closing, or partial closing of the port increase excursion. It seems closing the port would increase the physical resistance by either not letting air into the box during outward cone excursion, or letting air out of the box for inward excursion. I can believe the poor transient response, increased distortion, less bass and less efficiency, (all due to increased physical resistance) but can't see why there would be more woofer travel. Unless, of course the user would increase the power/volume to compensate for all the above, which he wouldn't because decreased bass is the goal. How does more resistance equate to increased excursion? I don't pretend to know all there is about speaker design, but on the surface, increased excursion just doesn't sound right.
    It's not so much that the excursion is being "increased" by closing the box, but rather the excursion is "decreased" by porting the box.
    The air inside the box is resonating, as the frequency approaches the tuning frequency of the ported box, what actually happens is the woofer excursion approaches minimum and the air does all the movement - the air is a secondary resonant device, and literally "sucks" energy from the woofer, and is said to "load" the driver. In a perfect system at the ported box frequency the woofer's movement is 0. But in practice it's just greatly reduced.

    Here's a graph of excursion for a 6.5" woofer in a typical bookshelf size, ported enclosure...

    You see that dip at around 55 Hz? That's the tuning frequency, and excursion is at a minimum. You could pretty much draw a straight line in a sealed enclosure that would run over that dip - granted, it'll be slightly lower at 30 Hz and below than the ported equivalent, but that's beyond the musical range of most sources and this driver - you see the general trend. As you increase the power output (like in a strong bass drum transient), that excursion is going to jump over the red line and runs the risk of exceeding it's mechanical limitation. Some woofers can do just fine in either enclosure (though usually a sealed enclosure is considerably smaller -50% or more is common) some can't.
    Attached Thumbnails Attached Thumbnails bookshelf port problem-ported.gif  
    Last edited by kexodusc; 10-10-2006 at 06:56 AM.

  10. #10
    Loving This kexodusc's Avatar
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    Quote Originally Posted by bfalls
    I can believe the poor transient response, increased distortion, less bass and less efficiency, (all due to increased physical resistance) but can't see why there would be more woofer travel.
    Actually, the increased air resistance acts as a braking force in a sealed enclosure compared to ported enclosure. This actually improves the transient response, distortion, etc. This is one of the big reasons why sealed subwoofers are said to be better for music than ported subs. Transient response can be up to 4 times as fast. But keep in mind, that an optimal sealed enclosure is much, much smaller than an optimal ported enclosure. Just plugging the port turns the ported speaker into an oversized sealed enclosue, which provides relatively less braking force (resistance) than the optimal smaller sized sealed box would. Like I said earlier, some drivers will let you get away with it, some won't.

  11. #11
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    Thanks a crap load to all of you you've always been there for me
    Basicaly I told him he didn't really have any option other than turning the bass down on the pre.. but then I told him I would ask you guys if he could maybe play with the port. He isn't really a party dude, he is more into classical etc etc (well polish really) haha na just kidding.

    Yeah I met him on my course (audio media engineering) here in the university of surrey in england, (I was living near geneva before though). I have a crappy 'mitsui' compact hifi that someone here kindly gave me. it sounds like absolute sh** but it's nice to have a couple tunes here and there.

    Wish I had a little money but I dont have any to spare. Once again thanks for the kind words, I did think blocking the port would effect excursion etc etc. Thanks to you kexo for explaining it all.

    PS: finished my sub kex, never sent ya photos sorry.. but it's working alright!! left it home in Geneva though..!!!! it hits 25Hz fairly well. bigger box means less gain=less amp clipping=no overheat!!!! so that's nice. But can't use it right now so that's not any good....
    Last edited by audio amateur; 10-10-2006 at 12:48 PM.

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