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Sub Vibrations and PJ position?

Discussion in 'Projectors, Screens & Video Processors' started by Chipster, Dec 23, 2003.

  1. Chipster

    Chipster
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    Should I take account of sub vibrations when positioning my new Z2.

    I have a Rel storm which kicks out some serious bass and would not like to think any damage to the lamp would occur if the PJ is placed too close to it. (For the moment, my short term placment is on a coffee table about 1.5 mtrs from the sub)

    Sounds like a silly question I know, but everything else (including the floor) shakes in the room so I guess my PJ will too.

    Where is your sub in relation to your PJ?

    Thanks.

    Chipster.

    PS Dont tell me to turn it down :(
     
  2. Chris Frost

    Chris Frost
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    This is a very intelligent question. I have seen the effects deep loud bass can have on projectors. Circuit boards can get rattled loose over time :eek:

    Bass frequency sound levels are boosted at even fractions of the room dimensions - 1/2, 1/4, 1/8 etc. These are called bass peaks. There can also be spots where the bass is diminished. These are called nulls. If you've ever found that the bass sounds louder in certain areas of the room than others then you will have experienced this effect. Some home cinema designers plan the seating layout to be at odd room fractions - 1/3rds, 1/5ths etc to counter this effect. It all gets quite complex because you have to consider the effects in three dimensions - room length, width and height.

    Projector position is a bit more restricted than seating layout, but you do have zoom so it is possible to try slightly different locations in the room.

    There is a theory that you can affect the bass peaks in a room by changing the position of the sub. The idea is that you put the sub where you would normally sit to listen, then play a bass heavy soundtrack and walk around the room listening for an area where the bass seems weaker. Mark that spot and try the sub there instead. The idea is simple enough for a listening position, but it's going to be a bit harder to put into practise for a ceiling mounted projector ;)

    good luck
     
  3. Chipster

    Chipster
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    Thank you Chris for your detailed and interesting reply. I have allready done what you have suggested and have found a 'sweet spot' for the sub but it is very close to the projector. The room is not a 'normal shaped' room, it has straight and curved walls with a spiral staircase as well, making acoustic placement of all my equipment (including the sub) very difficult. I have noticed the effect you speak of all over the house when doors are left open so I understand what you mean.

    Not wanting to dislodge my PJs circuit boards :eek: I'm now wondering if some kind of isolation platform would help stop physical vibration. As far as sub air movement well I guess theres nothing I can do about that.

    Sadly for the time being, the PJ will have to stay where it is on the table due to lack of options.

    Cheers

    Chipster.
     
  4. Kramer

    Kramer
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    I wouldn't be too concerned TBH.

    PJs are meant to be used, not wrapped in cotton wool. Understandable how owners want to protect their "pride & joy" but no need to get carried away.

    "Should I unplug my PJ when not in use? How long is too long (running time)? Should I filter the air? Should I put a hot water bottle on it?"

    Sit back, relax. Enjoy the movie. If it breaks under warranty, it'll be repaired/replaced. You'll probably be looking at an upgrade long before a new lamp is required anyway.

    :zonked:
     
  5. buns

    buns
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    Amen to that!

    If you are particularly worried, mount the projector on something absorbent, half a squash ball will do the trick will do the trick as well as most things more exotic

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  6. Kramer

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    Won't really help with bass/sub-bass frequencies. Even an object suspended by elastic will resonate/vibrate - low frequency air movement.

    :)
     
  7. Chipster

    Chipster
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    Yeah, your right of course Kramer... It just made me wonder after a glass containing my favouite wine toppled off the coffee table in time with a U571 depth charge scene. Might try some sqaush balls though buns, As far as exotic, I've really no idea what you mean :eek:. Makes you wonder though :laugh:

    Cheers

    Chipster.
     
  8. buns

    buns
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    In using the damped absorber, the resonance will still exist though may be shifted and should be somewhat....... errrr...... well...... damped! I'll scrawl you some apparatus to go test it if you like :D

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  9. Chipster

    Chipster
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    Thanks buns

    Would be interseted to see what you have.

    Chipster
     
  10. buns

    buns
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    sorry..... that was a bit tongue in cheek.....

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  11. Chipster

    Chipster
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    Hey, I thought as much.

    Was expecting a graphic diagram of a huge pair of mellons :laugh: :laugh:

    Now theres a thought!!
     
  12. buns

    buns
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    lol..... that is actually a thought..... get a cast of helful females of differing sizes...... modify a bra each to couple the 'huge pair of mellons'. get them to lie down and one at a time you play test tones at them and plot the frequency of their vibration against the driving frequency...... hehe, this is a really fun way to show damped oscillation..... with any luck, that wouldnt be the only oscillation you would get ;) :D

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  13. Paul D

    Paul D
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    Just put the sub on the ceiling, and you will be fine!:devil: :p :devil:

    I couldn't find a suitable place due to the layout of my room. I found the only place we couild fit the sub, left a "bass hole" ( weak bass) where we sat, yet it sounded great in the bathroom!:rolleyes:

    The sound is now so direct and warm. Maybe because no furniture gets in the way. Just hope it doesn't land on the plasma if it ever falls down:rolleyes:
     

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  14. Chipster

    Chipster
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    Hi fulabeer

    I'm glad you came along and cleaned up this thread, it could have got out of hand

    :D

    Thats a very good idea you have, but I cant imagine bolting a Rel storm to the ceiling. What type of sub do you have and is it actually mounted in or on the ceiling?

    Absorbing melons still rank highly I have to say. :laugh:

    Cheers

    Chipster.
     
  15. buns

    buns
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    its a valid arguement....... women have use in your cinema ad sound absorbers and diffusers...... maybe i need a dedicated Xmas special thread about this!

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