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Thread: What happens when one "overstuffs" a cabinet?

  1. #1
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    What happens when one "overstuffs" a cabinet?

    I have an experimental cabinet I had a friend build who is a cabinetmaker/contractor by profession. I did not have any particular design/woofers in mind when we did it a year ago. We just whacked together what looked proportional and what a 4x8 sheet would make per. I ended up with about a 4 cubic foot enclosure (internal). 16"x 20"x 32". I had him make up a series of front plates that could cover the 15" hole, so I could mount other size woofers for experimentation flexibilities. I recently put a Co-AX 15" speaker (Not JBL, sorry guy's) And at first had no stuffing or batting to put in. Sounded super horrible, tubby, and resonant, and the reflected echo came right out through the paper cone. I have not yet put any vents or holes or ports into the box, it is sealed. I don't know what size/type to do? Since I have not chosen a specific woofer/woofers, and it is still a "work in progress" and a test horse. I am not an experienced cabinet maker/designer. Nor do I intend to become one.
    I do enjoy however, playing with speakers though, and learning...and listening for the changes brought by the different properties of design.
    I have a another speaker (Infinity "Monitor" from the mid 70's, given to me free a month ago, with bad surrounds) which has impressive low bass performance, and when I took it apart, it was super-stuffed with batting material, up to the frame of the woofer and filling the entire space. So with that in mind, I obtained a free roll of fiberglass from a friend who was clearing his garage, and overstuffed my cabinet like the other was. What I heard was now a tight sound in the bass, perhaps too restricted? Not much output level in the lows and that is dissapointing, but the tone is fine. no echo blasting out the cone. But can one have too much filler? Should I take some out again? It is up to the speaker frame, filling all space
    Last nite I removed the terminal bracket from the back and now the hole of about 3"x3" seems to relieve the pressure inside and the low output is seemingly greater, now quite nice and balanced. Maybe the stuffing is good all filled up. What might I expect if I were to cut into the front and either put a "slot" or perhaps one or two "tuned" tubular reflex ports? What type of ports are typically most succesful? From the looks of it, JBL finds paired tubes the best most of the time. How close to the woofer frame is advised, what is the theory on placement? What about rear venting? Pros and cons? I can't say what the resonance of the woofer/s are or will be due to not knowing the final Brand or model, I am just asking about average or typical for "most" woofers? I may just copy some typical JBL types, as they seem to know something about the subject. This is a "test horse" cabinet pair, so I don't want to make final conclusions about the design, it is a learning tool.. Thanks for any feedback, You guy's are great. By the way, since you are probably wondering what the CO-AX unit is, I purchased a set of new "on sale" Selenium 15CO1P-SLF 15 inch with 2 inch titanium compression driver blowing through a center dome of acoustically transparent mesh. They were going for $99/each, so I bit. Not up to JBL build quality, but at the price, pretty good, and now with the cabs getting tuned up, starting to sound pretty good...The Fs is 50 Hz. These may not find a final home in these cabs but is fun to play with. Later RE.

  2. #2
    Senior Member Dave G's Avatar
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    link

    http://www.jblpro.com/pub/manuals/enclgde.pdf

    You did see this? Its a start, you can go from there upwards in complexity of theory.

    I am hoping for some comments on my previous thread. This thread concerns what you could do to make a sound good from such a box.

    Overstuffing is possible.

    Dave

  3. #3
    Senior Member duaneage's Avatar
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    Quote Originally Posted by transducergeek
    I ended up with about a 4 cubic foot enclosure (internal). 16"x 20"x 32".

    So with that in mind, I obtained a free roll of fiberglass from a friend who was clearing his garage, and overstuffed my cabinet like the other was. What I heard was now a tight sound in the bass, perhaps too restricted? Not much output level in the lows and that is dissapointing, but the tone is fine. no echo blasting out the cone. But can one have too much filler? Should I take some out again? It is up to the speaker frame, filling all space


    Last nite I removed the terminal bracket from the back and now the hole of about 3"x3" seems to relieve the pressure inside and the low output is seemingly greater, now quite nice and balanced.


    Maybe the stuffing is good all filled up. What might I expect if I were to cut into the front and either put a "slot" or perhaps one or two "tuned" tubular reflex ports?

    What type of ports are typically most succesful?

    How close to the woofer frame is advised, what is the theory on placement?
    What about rear venting? Pros and cons?

    I am just asking about average or typical for "most" woofers? I may just copy some typical JBL types, as they seem to know something about the subject.

    This is a "test horse" cabinet pair, so I don't want to make final conclusions about the design, it is a learning tool..

    I purchased a set of new "on sale" Selenium 15CO1P-SLF 15 inch The Fs is 50 Hz.
    I snipped your post so that I might be able to addres some of your questions. I have built speakers as a hobby for 20 years and I might be able to help

    4.0 Cu feet is a good size for most 15s but unless you have the TS ( Theil Small) parameters you are guessing at what you should use. The 50 Hz FS is one number, you need the Vas and Qts to perform basic box calculations.
    However, since you have a box, try this. Test the Fs in free air and then test it in the box.

    If it is 50 Hz in free air and 65 Hz in the box, the Box has raised the Fs up and it may not sound good with an impedance hump at that high of a frequency. A 15 Inch woofer with that high an Fs indicates a high Qts and very stiff suspension, more suited for large (6cu ft) boxes or open backed applications. The stiff suspension controls the cone, not the sealed box.
    Now for the good news. Empirical data proves that you can increase a cabinet volume (virtually) up to 50% with the right combination of materials. The idea is to suff and test, recording the results to see what works best. You want to tame down the Fs to be closer to the 50Hz number so that it does not boom.
    Try polyester, dacron wool, acoustic foam, Fiberglas ( watch out for home insulation, it sheds fibers that get into voice coils and ejects into the air), and try a combination of more than one. Acousti-stuf is expensive but works good thanks to the random fiber twist and chemical makeup. Fiberglas converts mechanical sound energy into heat, other materials abosrb the mechanical energy and don't give it back.

    ports. There are calculated minimum sizes for ports to prevent wind noise and you will need big ones. Two ports act like one bigger port, two 4" pipes are the same as a 5.6" pipe. Rear porting prevents some problems but requires air behind the speaker. Shelf ports are big and harder to tune than PVC . I would not try to tune this box without TS parameters because of the work involved unless you are looking for a type of "sound" that porting it give you. you may have complex impedance curves your amp will protest about

    One last thing. Stretch some fabric across the rear of the speaker frame fairly tight and test the speaker. This will lower the Qts a bit and make a small box work better, although a slight decrease in efficiency will be noted. But at 96 Db a watt, you can afford to give up some efficency if the speaker sounds better, just add some resistance to the high frequency driver to compensate.

    PM me if you want to go deeper than this into cabinet design and testing.

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Hey, transducergeek...

    We've spun through many of those questions, as recently as the past year. All the experiences of: type of batting, amount of batting, port size, shape and placement - even duct distance from cabinet sides/rear! - duct length and the like. Try some Search strings and evolve your boolean experience as you go - I'm sure you'll find a ton of stuff.

    I've not "heard" of stretching fabric across the back of a frame - dunno about that one, but I've not got the experiences duanage speaks of.
    bo

    "Indeed, not!!"

  5. #5
    Obviously... not a golfer grumpy's Avatar
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    fabric stretching....

    sounds like what used to be popular with the car-audio crowd...
    someone called 'em aperiodic mats (same idea, add acoustic resistance, put
    pro-woofer in smaller-than-designed-for box, lose efficiency...)
    You can probably still get them (usually mounts to front of driver)
    if you wanted to experiment. Haven't kept track of such things for a looong time.
    Have fun.

  6. #6
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    Quote Originally Posted by grumpy
    acoustic resistance
    Flash back 1978 - http://audioheritage.csdco.com/vbull...ead.php?t=4551


  7. #7
    Obviously... not a golfer grumpy's Avatar
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    L50 acoustic shell example

    There you go. What comes around...

  8. #8
    Senior Member duaneage's Avatar
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    Quote Originally Posted by grumpy
    sounds like what used to be popular with the car-audio crowd...
    someone called 'em aperiodic mats (same idea, add acoustic resistance, put
    pro-woofer in smaller-than-designed-for box, lose efficiency...)
    You can probably still get them (usually mounts to front of driver)
    if you wanted to experiment. Haven't kept track of such things for a looong time.
    Have fun.
    I didn't invent it or propose it, I just know it works for drivers with no other choice. Best thing to do is buy the right driver for an application but if you want to make something work, it is an option.

    Your simply adding resistance to the speaker to raise the Qms without adding mass to the cone. Weighing the cone would lower both the FS and reference efficency but that can be hard on the motor and there is a chance the weight could come loose.

  9. #9
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    Aperiodic mats...... shades of 1949! Once upon a time very common practice.


    Cyclotronguy

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