Infinite Baffle Subwoofer - Wow!!!

Discussion in 'Home Theater Projects' started by Kevin Deacon, Feb 3, 2004.

  1. Kevin Deacon

    Kevin Deacon Second Unit

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    I just recently installed a IB sub in my attic using 2 15" Dayton DVC IB drivers, PE 250 watt plate amp, and a Behringer Feedback Destroyer. Not to brag or anything, but this is the best bass I think I've ever heard. Very tight and accurate and can be very loud with little amplication. Seems effortless and enveloping. The BFD was mandatory with my room. When I first fired up the sub it sounded real bad as there was such a ragged freq response. Once I figured out how to use the BFD I was able to get a ruler flat response at 90db's from 18hz to 125hz using the RS meter with corrections. Can you say "No rolloff until 18hz"? I need to play with the equalizer more as a flat response doesn't necessarily sound the best. I also need to deal with a couple vibrating recessed lights in the ceiling.

    Here's the beauty part:
    The total cost of my system was around $500.00.
    The only thing necessary for aesthetics was the cover for the hole in the ceiling.
    No huge box or sonotubes in the corner.
     
  2. ThomasW

    ThomasW Cinematographer

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    Gees Kevin,

    Don't you know this is supposed to be a secret?
    After all, we are a 'cult' ya know..... :wink:
     
  3. Chris Brock

    Chris Brock Second Unit

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    reading these types of comments about IB setups has realyl gotten me interested. I am in the middle of building a new home. the room for my HT is right at 3200 cubic feet. what would it take to get reference levels from an IB setup in that size room? I am currently waiting on 1 tempest to get here. so how many more would i need to produce true reference levels?
     
  4. ThomasW

    ThomasW Cinematographer

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    Usual recommendation is build a 18"-20" cube. Start with a pair of 15"s. If you find that's not enough to suit your needs/wants, add a second pair.

    BTW: there's lots of info on the "Cult" FAQ page.
     
  5. Rich Kraus

    Rich Kraus Stunt Coordinator

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    see thomas, we keep tellin these guys- and yet their supprised when it performs. [​IMG]

    i dont think ive heard an IB gone bad. its simple to build, inexpensive; and for those with the guts to cut "the hole", a path to bass nirvana.
     
  6. Zack_R

    Zack_R Stunt Coordinator

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    Wouldn't the back wave of an IB affect the sound you are hearing?

    I contemplated an IB a while back but I was unsure what effects the back wave of the drivers has on what you hear in the room. Many of the installations I've seen and the kind I would have done would only have sheet rock between the storage / attic room enclosure and the listening area.

    In a former home, I had a pair of cheap 10" rat shack patio speakers installed and mounted in the attic. The sound was played in the soffit over the patio but the speaker box was the attic. When standing in the interior room of which was adjacent to the outside patio the bass coming through was pretty significant. Way more than if you were outside with the door open. When I stood in-between the patio door or just outside with the patio door open you could still hear the bass.

    So in my limited experience and knowledge with this kind of install, it seems that the bass could be over emphasized on the low end. If this is the case wouldn't the actual lower frequency bass sound be less accurate or unnatural due to the potential of overemphasized back waves rebounding and coming through the sheetrock?

    I'm thinking this could be similar to the phenomenom with a portable sub when you go in another room and you hear lower bass frequencies at a louder level than you do when you are in the room itself.
     
  7. Chris Brock

    Chris Brock Second Unit

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    how would the output compare toa typical ported setup? I have been reading alot of the info on "the cult" page and i am getting more and more interested. I guess it comes down to the fact that I have never saw or heard a IB in a HT before. it is just hard for me to fathom that i could make a hole in my wall and throw a couple subs in and be done.:b
     
  8. Richard Little

    Richard Little Stunt Coordinator

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    Using UniBox to do a quick model, it would take at least 8 Stryke AV15's (behind only the, $500 Tumult, in volume dislaced per stroke). That is figured with a 15hz low end and the drivers being pushed to max excursion to get to refrence level at 20hz.
     
  9. ThomasW

    ThomasW Cinematographer

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    One more time, here's the deal with IBs. No 'box', so no box induced colorations.

    Unknown to most listeners is that there are subtle details recorded on the most bass tracks. With a good quality main speaker, if you listen to a 6-string guitar, you hear the 'pluck' of the pick. With an IB you hear the same 'pluck' from a stand-up bass. You hear the 'transient attack' of the foot pedal on a bass drumhead.

    Every standard 'box', ported/sealed/PR/isobaric/whatever, tends to "smear" the details of the bass tracks. So people aren't able to hear what they paid good money for in the recordings. Now if your idea of 'great' bass is a low-rider booming down the road, please go elsewhere. However if you want high quality, very LOW frequencies, with amazing amounts of detail. Then IB bass is the ticket.

    Don't have the ability to cut that hole in the wall/ceiling/floor? Then dipole bass is your salvation. Same great quality, same great detail, in a portable cabinet. Here are some links where to Seigfried Linkwitz (yes he's the "L" in L/R crossovers) talks about "H" baffle and "W" baffle dipole bass designs. These are a little more tricky than a 'box' sub because they require specialized EQ. But they easily deliver the same great bass quality as IB subs

    Zack_R

    Not to worry. Comparing an IB sub to the soffit mounted RS speaker, is something like comparing a tricycle to a Vette.
     
  10. Chris Brock

    Chris Brock Second Unit

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    this is sounding more and more liek th route i want to take. i am basically to the point in my stereo hobby that i am after a bass system with no compromise in sq, the ability to play sub-sonic freq and play at reference levels. it sounds like to much to ask but i am begining to think that IB could provide this type of bass for me.

    here is my setup.......
    when my home is finsihed my HT room will 19 x 21 x 8. and here are my initial thoughts for an IB setup, 4 tempests total and running a pair off of each channel of my Nady XA900 pro amp. it produces 200wrms per channel at 8ohms. so i would have 100wrms per driver. could someone give me some opinions on this setup?
     
  11. Rick Guynn

    Rick Guynn Second Unit

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    I get better than reference with just my two Tempests and a PE250 amp at 20Hz.

    RG
     
  12. Kevin Deacon

    Kevin Deacon Second Unit

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    Is reference level 120db???

    I went back in last night and ran the test tones again at a louder volume and here are the results. Remember, this IB uses two lowly Dayton 15"DVC IB drivers and a lowly PE 250 watt plate amp. I'm sure I had room to go much louder before bottoming the drivers, but the whole house was violently shaking at the lower freqs. I would love to know the lowest freq at which this thing rolls off. My head was starting to compress after two cycles through the test tones.

    16' x 26' x 9' - Room size with a 8' opening into the rest of house.

    16hz 99.5db Incredible vibration
    18hz 99db Incredible vibration
    20hz 93.5db Incredible vibration
    22hz 91db Starting to hear sound
    25hz 91db
    28hz 91db
    31.5hz 90.5db Ceiling fixtures doing a dance
    36hz 90.5db
    40hz 90.5db
    45hz 92db
    50hz 92.5db
    56hz 91.5db
    63hz 90.5db Starting to get very loud
    71hz 90.5db
    80hz 90.5db
    89hz 90.5db
    100hz 90db
    111hz 90db
    125hz 99db above xover point and not equalized
    142.5hz 82.5db above xover point and not equalized
    160hz 81.5db above xover point and not equalized

    Oh, BTW, I was able to get this thing built, in the ceiling, and producing sound in about 6 total hours over two days. Using the BFD to equalize took, well, lets just say it took 'me' a lonnngg time.

    Kevin
     
  13. Chris Brock

    Chris Brock Second Unit

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    so you dont feel that you even maxed the woofers out that level either? that is pretty amazing output below 20hz:b [​IMG]
     
  14. Kevin Deacon

    Kevin Deacon Second Unit

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    The plate amp level is set at 1/3 of max. I was definately not at max driver excursion with those measurements. I did run the test tones at a louder volume, probably averaging 100db, but the banging and violent rattling of the house was incredibly loud and may have skewed the RS meter levels. I was truly scared that the drywall was going to crack or something was going to break. The second floor of my home, where the theater room resides, is about 2300sq. ft. and the whole thing was vibrating. I can't imagine what 4 drivers would do and IMHO is unnecesasary as I don't intend to listen to anything at reference level.

    I was getting 108db at 16hz and 18hz. I want to get some tones below 16hz to see where this bad boy drops off.
     
  15. Chris Brock

    Chris Brock Second Unit

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    so you were able to produce 108db at 16hz with only 250wrms and no visual sign of a sub in sight? i am simply speechless. this is exactly the type of reassurance i was looking for. thank you very much!
     
  16. ThomasW

    ThomasW Cinematographer

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    This must be an example of that "new math" they're teaching in schools these days.......... [​IMG]
    With IB mounting, 8 AV15"s driven to full excursion @20Hz would break the drywall, and blow out the windows of most HT's.
     
  17. Richard Little

    Richard Little Stunt Coordinator

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    It was my understanding that THX specs for the LFE channel was 115db, but as a rule of thumb, because most HT setups set the mains and other surrounds to small, all there bass is redirected to the LFE channel requiring the sub to play both the dedicated LFE material + (notice: same old arithmetic symbol we've used for many years[​IMG]) all the bass below the crossover point for the surrounds. I've thought that this additional material was supposed to account for and extra 6dB, so total required workload on the sub would be 115+6 or 121dB. I may be wrong, tell me if I am.

    Kevin, that’s awesome! I hope to get an IB set up some day.
     
  18. Brian Corr

    Brian Corr Supporting Actor

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    I'm intrigued and have a couple questions.

    1. Do the dimensions of the box matter all that much? If making a 20" cube, does it matter if it's 20" on the inside or the outside?

    2. Does the hole in the wall need to match the opening in the 20" cube (around 20" square) or is there a formula I missed for the manifold opening?

    3. From what little I've read, 2 tempests in a 20" cube with the 250 watt PE amp is an ideal start to an IB. Would one of the more powerful amps from PE make a difference?
     
  19. ThomasW

    ThomasW Cinematographer

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    Like Bose, we're selling 'image' not performance...... [​IMG]

    'Room gain' needs to be included in the calculations. And as one can see from Kevin's example, it plays a BIG role in the performance of any sub.......... If someone want's to accurately model an IB, they need to use a program like LspCAD. Then the specifics regarding the placement of the IB, boundry loading, and all the other acoustical characteristics of the room can be entered.

    Brian,

    If you're a 'by the numbers' kind of guy.......

    The formula for calculating the "perfect" box opening is the square root of the total air volume divided by the specified cone velocity.

    Or.............

    Don't go all crazy regarding the 'box'. The 20" dimensions aren't critical. The idea is to have a box sized so that it's easy to mount the drivers. So 18", 19", 20" cube, whatever trips your trigger. Don't want a 18"-20" hole in the ceiling? Then make a rectangle that's the width between the ceiling joists and long enough to mount 2 driver/side... Just don't have an opening that's smaller than the cross section of the box itself. If you do you'll create a bandpass filter.

    Monster amps aren't a requirement for IB subs. The reason for this, is that IB's are limited by the amount of power needed to drive them to full excursion. Drivers in a standard 'box' sub are primarily thermal limited by heating of the voice coil. As a result they can tolerate power levels 3-4-5 times higher than an IB. An example of this is the Tempest. Rated Pmax is 750 watts. In an IB it takes about 130 watts to drive them to the limits of the excursion.

    Wander around the "Cult" FAQ and gallery pages for more info and examples.....
     
  20. Chris Brock

    Chris Brock Second Unit

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    but think about what you have with the original 4 av15 sceniero you modeled for a sec. you say that you modeled it at 115db at 15hz? that kinda of output at 15hz alone is pretty incredable. you factor in even a conservative room gain value of 3 - 4db and you are knocking on the magic 120db door.....at 15hz!! and anything @ 20hz and over with that set up would likly bring the house down...... literally. all this with no enclosure and actually no visible sign of a sub at all except for a hole that could be covered with cloth to match the color of the room and a very modest amp. i just really do not see a downside here.
     

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