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frequency response

Discussion in 'General DIY' started by c1han, 16 Aug 2004.

This topic originated from the How to page called MDF - Medium Density Fibreboard.

  1. c1han

    c1han

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    I want to make a speaker box from mdf.
    Does anyone knows the frequency response of 18mm mdf board, and the other sizes :?:
     
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  3. loftus75

    loftus75

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    I assume you are referring to the sympathetic harmonics of the material rather than the frequency response, if I've got this wrong than I appologise in advance. It would be very difficult to answer your question based on just the choice of material. The variables include the size of box, the thickness of material, the size and type of speaker, any insulation materials you intend to use, even the mounting, whether its floor standing or fixed to a wall will effect the frequency and quality of sound. Your best bet is to read the speaker specifications which sometimes give a clue as to what is the best materials to use, whether they should be soft as in chipboard or hard as in hard wood. Sorry I couldn't be any more help than this.
     
  4. TexMex

    TexMex

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    BTW. The ideal dimentions for the cabinet should have the ratios of 1:1.6:2.6
    Aparently this Golden ratio gives the flattest frequency response curve. If you make the cabinets too narrow in their response, they will tend to give their own distinct accent to anything that is played on them. (very "Low Fi").

    For the same reason, when you look inside decent speaker cabinets, you'll find that they are lined with anechoic material. It's the speakers that are supposed to supply the sound, not the box they're mounted in.

    I know a lot of people like to have a really resonant base, and achieve it by mounting their speakers in large resonant cabinets. But if you really appreciate music, you should let the musicians (and to a lesser extent your amplifier settings) decide what it sounds like, not your speaker cabinets!

    For the reasons I have just given, it should make very little difference what the resonant frequency of the cabinet material is. A decent speaker cabinet design should, as far as possible, minimise it's influence on the output. (rather than use it to super impose an artificial effect).

    Just a personal opinion. If you like a droning base, make the cabinet ratios 1:1:1 (ie a perfect cube) and as large as possible, with a hard shiny surface inside, (such as laminate).

    To calculate the resonant frequency of the case, take the largest dimention of the enclosure. Multiply this by 2. Divide this figure into 340.29 Metres (distance travelled by sound in a second). The resulting figure will be the resonance frequency (in Hz).

    Hence, to give your cabinet a resonance of concert pitch A (440Hz) you would need to make your cabinet dimentions 38.67cm.
     
  5. AdamW

    AdamW

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    I would put a 99% probability on this being intended for the boot of a car.

    Thicker materials are used in speaker boxes not because of any resonance effects, but because it is less susceptible to flexing. Especially when creating a subwoofer enclosure, where large amounts of air are moved about and instantaneous pressure differentials (get me!) between the air on the inside surface and the air on the outside surface can be great.

    If you want to design your own speaker boxes, it really isn't just a matter of building any old size and shape. There is software to design them, and good quality drivers will come with a datasheet telling you what volume the box should enclose, and what type (ported, sealed etc.) It is often a good idea to buy a box with drivers already in it as they will (hopefully) be matched.

    Designing a thumping subwoofer box is quite easy. Designing great-sounding speakers is NOT easy!
     
  6. TexMex

    TexMex

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    As long as you don't want to hear the subtleties of the tympany section. I wonder how many of these chavs realise that, even drummers tune thier instruments, before a performance. (Not that I'm calling c1han a chav, insufficient data).

    Next time one of these boot thumpers stops and winds down the window, pay attention to that bass thump. It's almost always out of tune! That's because your hearing the resonance of their boot instead of the actual bass percussion, laid down so carefully, in the studio.

    If you're tone deaf, it's probably quite a pleasant experience :LOL:
     
  7. AdamW

    AdamW

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    You are certainly right there Tex! A drummer friend of mine tunes in 4ths, I believe. Seems a bit improbable, tuning an instrument with indefinite pitch. But they do it.

    I have noticed that the boxes in chavmobiles are often "tuned" inadvertently and so in music with a more interesting bassline you have certain notes come out a lot louder... Great if you just want to "impress" people with your windscreen rattling, not so great if you want to enjoy your own system. Then there is the fun you get when you hit the resonant frequency of the car!

    A little tip to anyone who has or is planning to have a chav-bass installation in their car: ALWAYS turn the system off a few minutes before you get where you are going. You might think "Why? I'm installing this so I can pull up at the pub/club/party with my windows buckling and 'impress' people!". Well, the reason is, the only people you impress are the scum who will come and nick it whilst you are in the pub/club/party. This even applies to people who build a quality system: happened to my sister, she had more of an audiophile system in her car, but you could just flick it into a different EQ mode and the rear windscreen would start to flex! One night she drove home in this mode, the next morning the boot was empty.

    N.B: I love bass, I think it is great. I just want to educate the world that a moderate amount of high quality bass is infinitely better than £20 bargain basement subwoofers being overpowered by an underpowered s**te amp. A guy across the street subscribes to the latter, and he was very annoyed when he pulled up once and saw me wincing at the crackling farting rubbishness that is his system. Couldn't understand what I saw wrong with it. Idiot. :LOL:
     
  8. DIYnot Local

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