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speaker/cab connecting problem

Discussion in 'Amps and Cabs [BG]' started by W.J., Jan 29, 2001.

  1. W.J.


    Oct 31, 2000
    Hi guys,

    I'm trying to build my own cabs, 1 for a realy low boost
    and 1 for some funky/agressive sound .
    I'll get in the shop 4 x 12' 200W/8 ohm each

    The problem = I want to put in a tweeter (8 ohm) also but how must I connect this guy acc. to the other speakers ?
    If paralell ; should I increase my tweeter power ?
    If serial ; how to connect the crossover filter ?

    my amp is 300W/ 4 ohm minimum

    And how should I build my low cab for some super low/ clean boost?

    any help is welcome, I thank you guys !!
  2. In parallel, with a crossover.

    :mad scientist voice on: Don't even think of connecting a tweeter without a crossover or in series with the woofers. It'll be fried like a chicken!!! :D:D:D :mad scientist voice off:

    You could put the 4 woofers in series/parallel. 2 x 2 woofers in series, and then those 2 lines in parallel. That way you get back at 8 ohms total impedance.

    The tweeter should be crossed over at about 4,000 Hz by at least a 2nd order filter. Use film capacitors and air coils only, i.e. no electrolytic caps and cored coils. Ideally you could also roll off the woofers at the crossover frequency, but it isn't necessary.

    To get a low sound, make the cab really big. I mean, like, 8 cubic feet or so. And tune it accordingly.

    If you need more details, I'd be glad to help.

  3. W.J.


    Oct 31, 2000
    Bedankt Joris,

    I like some more details on that, plz
    I knew this stuff 2x2 etc. but my problem is this tweeter.
    how much power must it have?
    ( 300 w or 100w , I mean : I have 4 woofers , but
    if you seperate high and low do you seperate your impedance
    also ? the tweeter is alone agains 300 w , no?

    and why a second order filter ? must this tweeter have a boost ? ( 12 db/oct )
    should I use a second order filter with the woofers also?
    what do you mean by roll off?

    what do you mean by tuning ? acc. to what?

  4. W.J.


    Oct 31, 2000
    And for the low cab ... can I use a pasive speaker to get the low boosts ? and does measurements make a difference ?
    and how about a bass reflex tube?
  5. Ha die W.J.! Suzanne Vega had misschien wel gelijk:D Bij de Hollanders blijven jullie Belgen toch altijd een interessant onderwerp in grappen (maar andersom is het gelukkig ook zo). Ik heb een collega die in Beerse woont, en hoewel hij Nederlander is, blijft het toch leuk om hem ergens de schuld van te geven en dan te zeggen: "Och ja, voor een Belg is hij zo dom nog niet". Hij kan er zelf altijd mee lachen. :D

    Oh my! Now I have to explain a lot. :D

    The tweeter doesn't have to be as powerful as the woofers. And the impedance is divided by the crossover network. That's what it's partially for. If you cross over a woofer and a tweeter, both 8 ohms, the impedance will be 8 ohms total. You should use at least a 2nd order filter, to make sure the tweeter doesn't get much low frequencies. A 2nd order is made with 1 coil and 1 capacitor. A 3rd order is 2 caps and 1 coil.

    The power rating of the tweeter is important if you play slap, or if you have a small amp. In both cases, the tweeter gets a lot of signal. Slapping means clicking of the strings against the frets, a small amp will distort easily and sound rattling. If you plan on really using all 800 watts for low and mid, I recommend you use at least a 50 W RMS (!) tweeter. The number you gave, 200 watts, isn't an RMS rating, it's measured with a crossover. Meaning that it will sound as loud as a 200 W woofer, but it only gets (the high frequency) part of the test signal, which result in a much lower RMS rating. Professional tweeter manufactorers, like Beyma and RCF (both European) specify an RMS value. You'll see values like 15, 25 or 30 watts. They will match a woofer with 5 to 10 times that power. So 25 watts will be just right for 150-200 watts of woofer power.

    I'll say to you what I say to everyone why wants to build a cab:
    I isn't easy. A bass cabinet is a well-tuned resonator in which bass drivers and bass reflex port interact. If you want low bass, you definitely want a bass reflex (also called "ported") cabinet with a 15 or 18 inch speaker. A ported cab is designed for a specific speaker, of which all data are known: numbers like Fs, Qtc, Xmax, Pth, and so on. Only when you know all these numbers, you can determine if a driver is suitable as a bass guitar speaker. If it is, you can design a cab that suits your needs. I have simulation worksheets for this kind of work, as I desing a lot of cabs. And each time, I spend hours finding the right speaker. Designing the right cab size and tuning to go with it, is the easy part. It takes a few minutes.

    Kort gezegd (in short): Find a speaker, post the specs, and I'll tell you (most of the time just by looking at the specs) if it's a suitable speaker. If it is, I'll give you a cab size and port dimensions. The shape of the cab doesn't matter much, it's the internal volume that counts.

    Tering, wat kan ik langdradig zijn zeg......

  6. W.J.


    Oct 31, 2000
    alvast bedankt Joris ;

    I was thinking about 4 x 10' speakers :
    impedance 8 ohm
    range 24-3000 Hz
    free air resonance : 23 Hz
    Power : 150 w
    power rating : 100 watt rms
    sensivity : 1w/1m 90 db

    I have more information but I hope this will do ...

    So if I use an 8 ohm tweeter .?. rms
    this won't influence the total impedance ( 8 ohm ) if I'm understanding well...

    my amp is 300w rms 8 ohms , sorry .

    How much liters must this cab be ?
  7. W.J.


    Oct 31, 2000
    and for the second cab => I don't know the specs
    because it is used in a combo with this 300w amp.
    So I don't know a thing about this speaker ...
    sorry . I was planning to seperate amp and cab. because
    it is way to heavy ! and to big . ( only goes in my car
    with a special move ) + if I want a new amp I don't have to worry about my cab no more ..

    but how about a passive speaker ? I heard it should
    give you a low boost ?!? is this correct ? or have I been
    drinking to much ?

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