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Thread: Building my dream system, need lots of advise!

  1. #121
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    Quote Originally Posted by jmpsmash View Post

    the downside is i prefer the Fostex to sit up front near the lip of the 2397. purely aesthetic, but hey...
    This is what I did with a 2397 and 2405 tweeter, maybe you like the idea.

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  2. #122
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    Quote Originally Posted by jmpsmash View Post
    with a cabinet this large, is it realistic for it to be completely inert when the driver is pumped way high in volume? from touch alone, mine is not, there is some vibration, but at the same time, it is not resonating like crazy either. quite dull, but still there.
    No, some kind of vibrations will always remain.
    Of course you can reduce these vibrations by 90% or more, but not completly.
    I had build concret enclosures with 1,5" panel thickness, even those vibrated a little.

    A couple of years ago I did build these enclosures.
    1,2" plywood with extensive bracing. These cabinets had 8 cubic feet internal volume.
    Even with the bass playing at maximum the vibrations are barely noticeable! I wouldnīt put that much effort into enclosures again, but it really worked out great!

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  3. #123
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by jmpsmash View Post
    with a cabinet this large, is it realistic for it to be completely inert when the driver is pumped way high in volume? from touch alone, mine is not, there is some vibration, but at the same time, it is not resonating like crazy either. quite dull, but still there.
    Cabinet vibrations can be reduced significantly with rigid construction and added mass to absorb the excess energy. Westlake uses massive amounts of acoustic damping goop and their very large cabinets are very inert.

    In my larger projects I have used a 3/4” MDF inner box or panel constrained by an outer layer of 3/4” birch plywood since it is much stiffer. I use massive internal bracing as well. I have not subjected this construction to any advanced analysis which would be beyond my rudimentary math skills, but subjectively it has been very successful.

    Even at extreme SPLs the twin 2242 subs I built for Scott Fitlin for his disco system were non-resonant. My Project Widget speakers use this same construction except on the curved sides. There I have 4 layers of 3/4” MDF in the center of each panel. Running my hand on these panels at extreme SPLs, there is an extremely slight sense of vibration. The floor of the room and every other surface in the listening room is far more excited... is taking that on the next project?


    Widget

  4. #124
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    Dr.db & Mr.Widget,

    those are some serious bracing you guys have done. And now that I have mine built, I understand why! In mine, I have mostly done bracing on each of the surface, sides and back have 4-5 2" brace, bottom and top have 3. front has corner and braces along the available spaces around the driver/port. I also have corner brace for the side/top/front. I don't have that many cross braces though.

    anyhow, the box is pretty solid when knocked. But playing loud there are still vibration.

    Next I need to figure out the padding inside. Right now I only have a cushion covering the back wall. I noticed the sound is more dull with it. Obviously not the correct implementation.

    Previously I was also tweaking the 2397. I put some foam on the side channels. they do help the imaging, in fact, imaging is quite good. but it killed the broad sound stage and worse is that it killed the liveliness of the sound. So out the foam goes.

    More work definitely need to be done there at the top end. If i take out the Fostex, it sounds even more natural. instrument timbre is more coherent, despite falling off above 10kHz. Adding the Fostex fills in the missing sound, but soften the texture. Maybe the Fostex is too smooth.

  5. #125
    Senior Member Ian Mackenzie's Avatar
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    Standard practice is to start with 1 inch fibre glass insulation on all surfaces except the front baffle.
    The fibreglass actually absorbs sound.

    Do not use other materials such as carpet under felt.

    Adding fibre glass will alter volume of air seen by the driver in the enclosure.
    Adding 1 inch fibreglass adds approximately 10% volume to the enclosure. Too much fibreglass can create an over damped sound.

    Attempting to make the enclosure completely inert acoustically is very difficult and may create more problems than it solves. For the purpose of identifying sound from the enclosure the way to think about it is to imagine your enclosure is mounted into a wall in a room. Your in the room behind the loudspeaker. How much sound can you hear coming from the enclosure? Assuming the wall is completely sound proof you will hear something. The sound from the box will ideally be Zero. Sounds are not always continuous tones. So you donít want the box to resonate with a long decay time after exciting with enclosure with a short bursts of sound. Assuming the driver has an output of 100 dB you need to figure out an acceptable target for the enclosure? In the above scenario you could measure the difference. It might be 100 dB - 65 dB = 35 dB. It might be less or it might be more in total across all frequencies. You also have sound from inside the enclosure coming back out through the woofer cone. How do you stop that? You canít. The fibreglass does however play a key role in absorbing sound at frequencies where this could become a problem. You can work towards a best case scenario by constructing the enclosure with golden ratio proportions, minimising panel resonances and other problems such as standing waves which focus at one particular frequency or set of frequencies. (See Golden Ratio). There is also sound other than bass frequencies from the port to consider.

    My suggestion is donít loose sleep over it.

    My suggestion as discussed earlier is to create a 3rd order low pass filter on the 2397 and the Fostex at 8000-10000 hertz.

  6. #126
    Member jmpsmash's Avatar
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    do you just use the fiber glass insulation from the hardware store? is there a risk of the fiber getting airborne with all the vibration? The acoustic panel people are talking about how they are carcinogenic.

  7. #127
    Member jmpsmash's Avatar
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    Quote Originally Posted by Ian Mackenzie View Post
    Do not use other materials such as carpet under felt.
    any reason why?

    I have opened up a pair of former pretty top end speakers from a certain famous French speaker manufacturer and that's what they have inside.

  8. #128
    Member jmpsmash's Avatar
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    despite still some stuff to be done before I can call the speakers done (or will it ever be "done"? ) , the speakers are very very listenable and very enjoyable. great sound stage, great texture, incredible bass.

    in fact, for the past few days, I have been spending a lot more time actually listening and enjoying music instead of busting my ass cutting wood, gluing, etc.

    not losing track of what still need to be done. here is the list...

    internal sound absorption
    tune crossover points
    finish - right now it is bare - it doesn't look bad at all but need to be more refined.

    and something not directly the speakers, but to put in more acoustic treatment into the room.

  9. #129
    Senior Member Ian Mackenzie's Avatar
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    Quote Originally Posted by jmpsmash View Post
    any reason why?

    I have opened up a pair of former pretty top end speakers from a certain famous French speaker manufacturer and that's what they have inside.
    You can use other materials but they wonít have the same sound absorption coefficient as fibre glass. Fibreglass is a known quantity and itís properties are predictable. Other materials may also reduce the volume of the internal enclosure. There are different sheet thicknesses and densities of fibre glass. Look at the Jbl enclosure guide in the Library to familiarise yourself with these recommendations. You can then decide on your options. Google is your friend.

  10. #130
    Senior Member srm51555's Avatar
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    Awesome project. What was the final internal dimension? After reading your thread I finally got the ambition to try my 2397's with the 2216 and I will say they didn't disappoint, especially considering it was your standard Q&D horn on top of other cabinet. I was quite surprised on how the L300 charged coupled crossover on the 2440/2405's integrated with the standard M2 settings for the 2216. It wasn't absolutely perfect but pretty dang good. As Ian suggested run I'd the fostex in at 8-10K, no sense on waisting that sweet 4" JBL diaphragm's midrange. Keep up the good work, these will be keeper speakers.

    Thanks,
    Scott

  11. #131
    Member jmpsmash's Avatar
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    The internal dimension is 22.5x19x30.5. which bring it to 7.5 cu ft gross. net is approx 6.5 cu ft given all the bracing and the driver/port.

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