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building cabs

Discussion in 'Amps and Cabs [BG]' started by Stingray, Apr 22, 2002.


  1. Lovin Bass

    Lovin Bass

    Feb 8, 2002
    Los Angeles
    FWIW:
    The avatar site has a logo that flys in from the lower right corner. If I try to hit any links before the logo has "flown in" then this seems to cause problems and occasionally will lock up the page. I don't know what you have tried....try letting the page fully load before doing anything. If you have any anti-virus programs or firewalls on your computer then sometimes disabling them temporarily may cure the problem and let the page load properly. The firewall has to scan every piece of the webpage as it is downloaded and occasionally will cause similar problems of the page not loading properly.

    This may or may not cure your problems. Just in case, here is some info from the Avatar site that you can use to contact them:

    AvatarĀ® Speakers
    5840 Government Way UNIT E
    Dalton Gardens, ID 83815
    208.762.5251

    EMAIL: sales@avatarspeakers.com

    Try doing a search here on Talkbass for subject "Avatar" and user "quadzilla" He is a member who has made a previous thread with pictures of his cabs so you can see the cabs there if you can't get into the website. The website works fine for me so it must be your computer with some renegade electrons in it!:D
     
  2. bben

    bben

    Feb 28, 2002
    Santa Fe, NM
    Taking a stock cab and putting a speaker in it is a good way to get bad sound. Buying an empty cab from Avatar or anybody else isn't a very good way to go unless you are going to put the exact same speakers in it that they do. And they can buy the speakers a lot cheaper than you can.

    If you already have speakers, you need to know the Thiele/Small parameters to figure out box volume and tuning for a good response.

    If you don't know what T/S parameters are, and you want to build speakers, you need to do your homework and find out. Vance Dickason's "Loudspeaker Design Cookbook" is a good place to start.
     
  3. steve-o

    steve-o Guest

    Apr 17, 2002
    yep you all have done it. now i am going to build a cab.
    what is the differnece in porting.
    all the cabs i like have the bottom vent. you know the window port.
    what about where the ports are?
    what about sealed speakers?

    thanks steve
     
  4. Tom Crofts

    Tom Crofts

    Mar 15, 2001
    I don't think the port shape matters as long as the volume of air within it is the same. I was told by Doctor Decibel (clever Celestion bloke) to keep the ports away from the edges and between the speakers as much as possible. So mine are right in the middle.

    Here's what I wrote about reflex enclosures for my tech project (the reason why I made my cab):

    The reflex enclosure is airtight, like the infinite baffle design, except for a small vent (known as a port) at the front of the cabinet with a small inlet pipe penetrating the enclosure. This means that at low frequencies the rear wave is delayed and so emerges later in phase with the front wave, thereby reinforcing it instead of cancelling it out. The air in the inlet pipe is isolated from the rest of the air in the enclosure except at its inside end. The air in the port has a mass and inertia and so has a resonant frequency of its own which is largely independent of that in the enclosure. The pipe is proportioned so that its resonant frequency is the same as that of the cone and enclosure air combined.

    At high frequencies the inertia of the air in the pipe is too great for it to respond so at these frequencies the cabinet acts as if it was a sealed enclosure but at lower frequencies when it is at its resonant frequency the air mass in the pipe reacts against the springiness of the enclosure air mass and vibrates in opposite phase to it. This increase in the percentage of waves leaving the cabinet provides nearly twice the output for each cone movement than an infinite baffle cabinet of the same size.

    With the air in the pipe moving outward at resonance at the same time as the cone, the decompression inside the enclosure is greater than with an infinite baffle design and when the air moves backwards it does so at the same time as the cone thereby increasing compression inside the enclosure. Thus the movement of the cone is highly damped at resonance and its excursion is no greater than at other frequencies. This is opposite to its normal behaviour by which cone excursion is greater at resonance. This means it can handle a larger signal without distorting.

    However the cancellation effects below resonance produce a large drop in output, about 24dB per octave. This is partly due to the high efficiency above resonance, about 5dB higher than an infinite battle enclosure. Also only a small amount of lagging can be used inside the enclosure because lagging would stop the out of phase waves from being reflected back out of the port. This means that unless the cabinet is built absolutely perfectly there will be vibrations when it is at its resonant frequency.

    (Adapted from Loudspeakers from Musicians and some book on guitars)
     
  5. Stingray

    Stingray

    May 12, 2000
    ok if i buy a speaker cab how do i test the parameters to know what speakers will work im mean ill do my homework to find the best possible match. but i cant do anything if can figure out the parameters so how do you test them .and how if i built my own cab how would i test it before it was built i dont think you can, can you? would i have to start over if i built it wrong. anyways also what is the best type of would to use in building a cab and is cheaper to over it in carpet of that weird synthetic leaher stuff( idontknow what its called.)
    hlp me i need to know everything before i make my descision.
     
  6. Tom Crofts

    Tom Crofts

    Mar 15, 2001
    I used 18mm MDF, inert and heavy so won't alter the tone too much. The best is apparently Birch Marine Ply, but I think that's pretty expensive. Try getting in touch with Celestion or somone at your company of choice and see if they can help you. They'll be able to use expensive computer programs to work out exactly how big the ports should be. That's what I did anyway. Hope I've helped.
     
  7. Stingray

    Stingray

    May 12, 2000
    could somebody cick the link on avatar that takes you to the basss page and tell me what the address bar reads that why i can get a direc link to that page
     
  8. steve-o

    steve-o Guest

    Apr 17, 2002
  9. Those of you asking basic questions about ports, etc... please consider buying a cab instead. This is not dissing anybody or being a snob. If you don't have a solid understanding of speaker and cabinet design, please spare yourself the grief and expense.

    Vented boxes are DIFFICULT to design properly. Those that are poorly implemented sound like crap, look like crap, cost a lot of money and waste a lot of time. This is very demoralizing. There is no instant gratification, and it takes a LONG time to get one completed.

    Unless you a building for a specifc need that cannot be found in a commercial offering, there is no cost savings or advantage in building your own. You are much better off auditioning and buying a ready-made cab.

    [ edited for grammar ]
     
  10. Bgavin, how shall I put it?

    Ditto :D
     

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