In-Wall SVS? I need advice

Discussion in 'Archived Threads 2001-2004' started by Robert George, Mar 25, 2002.

  1. Robert George

    Robert George Screenwriter

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    Okay, my mind has been wandering again. That usually means I'm about to make another mess, but before I do this time, I need some advice from those that know a few things about how a sub will react in an unusual placement configuration.
    Here's the setup....
    [​IMG]
    The ideal situation is to get the SV Subs out of the corner and still be unobtrusive. Not an easy task, I know, but here is what I am thinking.
    Looking at the above picture, the area on either side of the TV and behind the main speakers can be rebuilt to have a recessed compartment similar to the way the audio rack on the left side is built-in. I am thinking an 18" wide 49" high "box" recessed into the wall on either side of the TV with a 12" front opening covered with speaker grill cloth. The sub would be placed into the "box" from behind with a solid back screwed on. The entire box would be sealed all around with only the front open. There would be about 3" between the inside wall of the sub box and the outside of the TV. I figure somewhere around 24", perhaps a bit less, from the driver magnet and the closest CRT in the TV.
    Three concerns....
    1) Any possible magnetic interference with the TV?
    2) Any physical interaction with the TV (ie, will the sub cause excessive vibration of the TV screen through the sealed box)?
    3) Will the performance of the two subs be compromised being placed in an enclosure with an opeing only in the front?
    Thanks for any help and advice.
     
  2. Joe-T

    Joe-T Stunt Coordinator

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    I really can't answer the questions on acoustical outcomes of such a setup, but regarding the magnetic interference, have you tried moving the subs to a roughly equivalent distance from the CRT and viewed the results? I know that on my Sony RPTV, the subs placed that close did cause an immediately noticeable distortion in the picture.
     
  3. TerryC

    TerryC Stunt Coordinator

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    If you are going that far to hide the SVS, I'd just sell them and implemnent a custom DIY configuration. Would you be willing to try that? Can you build it directly behind the SVS's? I'm sure you know the sub is better off in the corner.
     
  4. Robert George

    Robert George Screenwriter

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    I have a raw driver out of an enclosure so I tried placing it on the side of the TV approx. where it would be if installed the way I am describing. There was no distortion on the TV. I suppose my question at this point is, is the magnetic field of the driver much stronger when it is operating?

    Terry:

    No, I don't want to try a DIY as I am not a speaker designer and I'd rather leave that to the people that make a living at it.

    The wall where the subs are sitting is a no-go. Not only would that section of wall be much more difficult to go through, but there is something on the other side that can't be moved. The only space available is about 24" on either side of the TV.

    I understand the acoustical properties of corner loading a sub. I also know this is not always desirable. With dual SVS Ultras, the amount of output in my room does not require corner loading for satisfactory levels. In fact, getting the one sub out of the corner tends to tighten up the low bass noticably. That's one reason I have been looking for a way to get them out of the corner.

    Wouldn't placing the subs in an enclosure that is open only on one side do something similar to corner loading? Increase in-room response? No?
     
  5. Joe-T

    Joe-T Stunt Coordinator

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    From what I recall when I tried placing them next to the TV, the subs were "on" in that the S1000 amp was switched on, but no music was playing through them. It still distorted the picture.

    If you don't like corner loading, have you tried placing a sub on either side of the TV behind and to the outside of the main speakers? This might not be the most aesthetically pleasing to you, but it would take them out of the corner. Also, it looks as though a sub would nicely fit between your equipment rack and your left main speaker. This would be an easy "tweak" to your system.

    I would think that if you were to place the subs within a wall, the enclosing space formed by the three walls would have to be rather large in order to give a good response. Also, being enlosed by two tight corners and three walls would seem to make it even more boomy. This is of course speculation on my part, hopefully Tom V. or someone else with good knowledge will chime in.
     
  6. jeff peterson

    jeff peterson Supporting Actor

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    Obi, I now it's not much help; but I seem to recall reading here (maybe in the display devices topic) that the CRTs in RPTVs aren't inherently susceptible to magnetic interferance due to the electrons not being "shot"to a phosphor screen.

    I have no idea of the validity of the above; just adding it for discussion's sake. Has anyone ever gotten magnetic induced RPTV distortion? I just went from a 27" direct view (Tosh) to a 50" RPTV (also Tosh). Formerly, my Klipsch floorstanders caused severe distortion unless very carefully placed next to the direct view...now, none.
     
  7. Wes

    Wes Screenwriter

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    How about trying your SVS's behind the wall in your service area. Try it and see what it does to the bass! My guess it will as well as doing what your suggesting will change your bass and most likely not in a good way.

    And Magnetic fields do effect CRT's, but as you have stated the distance is the factor! On my 50" Ultravision I upgraded my TV's speakers and now use it as the center channel and I had to readjust the convergence to work with the newer stronger magnets of the new 5 1/4" speakers!

    Wes
     
  8. Mike Knapp

    Mike Knapp Supporting Actor

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    No speaker, including a sub should be placed inside a box. Unless the box is big enough to fit you and your sofa inside as well. Wait, they call a box that size a "room". [​IMG]
    You will have boomy, muddy, thumping bass if you do this.
    The answer to your problem is a DIY built in sub with a large cabinet to the right of the TV. Get the SVS drivers (since you like the sound of your SVS subs now) and ask Tom V to work out the cabinet dimensions. I have even considered doing something similar in my room with an un-used closet and some Shiva drivers. With your handyman skills you can build a hefty box that will sound great.
    Or...perhaps you should consider an IB design in your attic (this would be your best and cheapest choice in my opinion) I would have an IB in a minute if I had an attic in my room.
    Mike
     
  9. TerryC

    TerryC Stunt Coordinator

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    Obi, there is nothing magical about sub building once you learn a little. I aggree with Mike, I don't think a boxed in cubby hole will sound good. I'm sure Tom V. will help accommodate you since you are already such a great customer, maybe he can hook you up with some CS Ultra drivers to use too at a special price. I'm sure you know there are many competent sub designs at your disposal on this forum too.

    Literally, if you use the same Driver and same internal volume along with the same porting with solid construction there is no reason you won't end up with a similar if not identical sound compared to a SVS Ultra sub. Likely Tom will even suggest using more internal volume too for added performance but I don't know the drivers specs so can't be sure of that.
     
  10. Dustin B

    Dustin B Producer

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    Here is what is meant by an IB (infinite baffel):
    http://home.tampabay.rr.com/kraushome/IB.html
    Two Tempests (what's used in the above link) will run you about $300. In an IB config 100-120Wx2 at 4ohms would be lots of power for them (IB can be very effiecient so $200-$400 for an amp will do). Then add an EQ to tame any peaks and you're set (BFD about $140). I wouldn't pull the Ultra's appart, I'd sell them whole and buy a comparible raw driver. The Tempest is capable of the same or greater output than a CS Ultra.
    Sub design is really quite easy. Crossover design is really really hard (you don't have to design a crossover for the sub). Also by all accounts (from some very well respected members of this forum, Mike Knapp, ThomasW, JackG, Rich Kraus etc) an IB is the ultimate in bass quality when the correct driver is used. The Tempest is one of those drivers.
    Mind you this entirely assumes you have an attic in that room to use that can completely seperate the back wave from the front wave and has a minimum of 7000L of space.
     
  11. Robert George

    Robert George Screenwriter

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    No attic space over my living room (vaulted ceiling).
    I have talked to Tom V. this morning and have discarded the idea of placing an SVS tube in a recessed compartment. Too many compromises.
    Tom has agreed to do some calculation on appropriate volume of a "standard" box with a front-firing Ultra driver and a 4" port. I will attempt to construct a custom cabinet for a "flush" installation on both sides of the TV (two subs).
    We'll see how it comes out. I'll post pictures when the project gets started.
    Wish me luck...[​IMG]
     
  12. Dennis Reno

    Dennis Reno Supporting Actor

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    Joe-T

    Just FYI, speakers use permanent magnets. Even if the amp is off they can still distort the picture. Be careful, unless you prefer your TV to have blue and green blobs!
     
  13. Joe-T

    Joe-T Stunt Coordinator

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    Dennis,

    I don't have them next the the TV any more. I placed them there for a few minutes, found the distortion, then moved the back. I do have one CS+ about 3' from the CRT and it doesn't cause any distortion.
     
  14. Mike Knapp

    Mike Knapp Supporting Actor

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    You dont need attic over the room. Yo have attic in the back of your house, the IB just needs to vent into the room.

    Mike
     
  15. Robert George

    Robert George Screenwriter

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    Okay, here's where I am right now. The infinite baffle sounds liek something that might work after all. Now I need some placement advice for two drivers in what I am reading is called a "traditional" IB design. I plan to do something along the lines of this...
    [​IMG]
    The area behind the wall with the TV (look above) is a room that is 15' wide, 3' deep, 9' high. I believe this should be adequate space for two 12" drivers. I would prefer mounting the drivers low and to the sides of the TV. The question is, is it better to put both drivers together on one side or put one on each side?
    Also, how much dynamic pressure is created on the back side of the drivers? I am concerned about pressure interaction with the TV (screen "flapping"). With the open back, is that problem eliminated?
     
  16. TerryC

    TerryC Stunt Coordinator

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    Robert,
    You will be a convert to DIY after this! [​IMG]
    I haven't tried IB myself but hear they work great. If you don't like the sound just enclose them from behind and add a port.
    Not sure what drivers you plan to use but hopefully Tom can tell you if the SVS drivers work for IB?
    As far as placement. I'd try experimenting with your SVS's on either side of your TV and then both on that one side to see which way you like more.
     

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