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Where to get 4 off 12 inch speakers in the UK?

Discussion in 'Electronic Repair' started by N Cook, Jan 2, 2007.

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  1. N Cook

    N Cook Guest

    The owner managed to blow all 4 in a cab by overdriving them. 4x 12 inch ,
    16 ohm, 60W , maybe replacements only up to 5KHz and add a tweeter or two
    I have a large useless cab cluttering up the place until he can find
    something to replace. As they're obviously prepared to tolerate nasty noises
    while progressively failing they presumably don't need hi fidelity , just
    cheap enough or I can see this cab going on a bonfire.
    Yes, i've googled ,but 120 quid for 4 would seem to be the breakpoint and
    can find nothing like that.
     
  2. Ron(UK)

    Ron(UK) Guest

    You want four 60 watt 12" speakers for 30 quid each? Chinese junk from
    CPC maybe, the aluminium coned ones aren't too bad for £19 + vat each,
    but you`ll struggle to find 16 ohms off the shelf, so you`ll have to
    wire them in series/parallel for 8 ohms Next up is Eminence Alpha 12 at
    £30 + vat, again you`ll not easily get 16 ohms.

    Celestion do the G12T @ 75 watts in 16 ohms. A natural choice as a 4 x
    12 replacement speaker. but they are £32 plus Gordon Browns bit. CPC
    stock these, tho you might get them cheaper from Thomann in Germany.


    Hth

    Ron(UK)
     
  3. J M Goodey

    J M Goodey Guest

    The message <endbs0$jmq$>




    Rapid Electronics of Colchester (of whom I have no commercial connection)
    sell 12" 200w speakers for about £20:00 plus VAT. I have used several of
    them in situations similar to yours.
    www.rapidelectronics.co.uk
     
  4. Meat Plow

    Meat Plow Guest

    Saw someone on Ebay blowing out 12" OEM Celestion copies supposedly made
    in the USA. These started at $19 US each.
     
  5. N Cook

    N Cook Guest

    I see a rock and a hard place coming up.
    I would replace the 4 16 ohmers with 2 8 ohmer 100 watts and selector switch
    bypassed, but for the same 4 bottle, 120W amp would that be the same oomph,
    as they term it. ?
    Although amp and cab are Crate make they obviously were not made as a
    matched pair as amp has 16/8 ohm output setting and cab is 4 / 16 ohm
    setting. I suspect they'd been running for some time as I received them ,
    amp set at 16 ohm and cab set as 4 ohm , so they certainly won't be getting
    the same oomph as amp at 16ohms and cab at 16 ohms.
    Is there a way of perhaps saving stressing output matching transformer in
    the case of the speaker load going open circuit?
    eg a high watt 50 ohm resistor in parallel with each speaker of the serised
    8 ohm speakers so the load does not go totally o/c and some sound until
    replaced , rather than zero sound . Extra permanent resistor load would be
    un-noticeable I'd have thought.
     
  6. Ron(UK)

    Ron(UK) Guest

    Providing the speaker load matches the amplifier, you should get the
    same output, but the apparent volume depends on the sensitivity of the
    speakers - most of these so called 'high power speakers are notoriously
    insensitive. 'Classic' guitar speakers such as the Celestion G12H etc,
    were/are very sensitive and have corrugated cones designed to 'trash
    out' at high volume without destroying the speaker.
    Some of the Selmer amps had a high wattage resistor across the output
    jacks to help in absorbing some of the energy in the case
    of a loudspeaker cable becoming unplugged. That`s probably the safest
    way to go.

    Before you put too much money into this cabinet, do you realise that you
    can buy a Behringer 400 watt 4x12 for little over £200, or much less if
    you shop around?

    Ron(UK)
     
  7. N Cook

    N Cook Guest

    I'll probably recommend 4x 8 ohms permanently wired as seriese / parallel 8
    ohm and amp switched to 8 ohm with some 50 ohm Rs, at least if they switch
    amp to 16 ohms won't cause problems other than lower output.
    That is 2 seriesed in parallel with 2 seriesed for best failure mode outcome

    Buying new box comes up against sentiment, it won't have a gaudy big "gold"
    logo saying CRATE on the front , the word crate means just shipping crate in
    USA presumably does not have the connotation of "heap of junk" as it does in
    the UK
     
  8. Arfa Daily

    Arfa Daily Guest

    Two things spring to mind here. The first is to just ask the owner what
    exactly he does ( or wants to do ) with the setup. If he is looking to find
    some very high output 'sweet-spot' sound from the rig, then you will need to
    be concerned about output level, impedance matching, and the overall sound
    you are going to get from replacement drivers. It is also important to know
    the instrument that's going to be played through it, and how. It's no good
    having a set of stiffly suspended lead guitar speakers, if it's going to
    have a bass guitar put through it. Likewise, a Yamaha organ at afternoon tea
    dances, is a world away from a synthesiser at a rock concert. I have these
    conversations all the time with musicians, and they can be a fickle lot, so
    best to understand what's needed right from the off.

    The second thing to remember is that speaker impedance is by no means an
    absolute. It is a figure quoted for a particular speaker with a particular
    set of test drive characteristics, and is especially sensitive to frequency.
    If the owner is never intending winding the rig right up to full power, then
    8 ohms of amp into 4 ohms of cab, is not going to be any particularly big
    deal - especially for a valve amp. The output tranny will stand considerable
    overload abuse anyway in my experience, and you've got to work hard to
    damage a set of 4 valves through over-dissipation at their anodes. A 100
    watt amp doesn't come close to delivering an average power of 100 watts to
    the speakers. It might just get there on peaks. Doing it the other way
    around, will also not usually cause a problem in the situations that this
    equipment is normally used in. 8 ohms of amp into 16 ohms of cab, *may*
    appear a little quieter, but even this is not a given. If the owner is not
    going to be trying to squeeze every last dB of sound level out of the rig,
    then he just needs to turn it up a bit to compensate.

    In theory, both conditions will result in a deviation from the 'ideal'
    sound, and I'm sure that there are audiophiles on some of the audio groups,
    who would tell you that such a mis-match is a cardinal sin, and that they
    would be able to hear it, but trust me - you, I or the average modern
    musician, would not hear anything untoward. So the bottom line is yes, by
    all means be aware of the *potential* problems, but don't worry yourself
    into an early grave about them. Equipment mismatches in the rock musician
    world, is the norm rather than exception ( well, perhaps not quite, but you
    take my point ...). Talk to the owner !

    Arfa
     
  9. N Cook

    N Cook Guest

    I'm trying to work through the following , set as a hypothetical

    An amp of 100 watts rating, set for 8 ohms powering one 100 watt , 8 ohm
    speaker in a box..
    Then same amp powering 4 off of same speaker type wired to give 8 ohm
    overall in a cab.
    For the same volume setting of the amp then the same amount of audio out of
    each set up , its just the 4 way one will be able to go into peak overdrives
    much more comfortably, or is there other differences ?
     
  10. Arfa Daily

    Arfa Daily Guest

    For a start, four times the surface area of speaker cone, is going to shift
    four times the volume of air ... I guess this will likely increase the
    perceived volume level, for the same volume control setting in the same
    room. It would make an interesting experiment. I'm not sure that I see where
    you're coming from with the "peak overdrives" comment. Explain more please
    ??

    Arfa
     
  11. N Cook

    N Cook Guest

    assuming 2 series 8 ohm // 2 series 8 ohm and current I ,
    voltage V applied to the single case then 0.5I and 0.5V for each in the 4
    off case so power of .5I x .5V or 1/4 power in each or exactly the same as
    the single case , overall.
    assuming linear 1/x power in leads to 1/x audio power out, which is probably
    not the case, ie non-linear conversion

    I don't know about overdriving as I'm not a muso but I assumed it was what
    many liked doing, taking it to 11 and all that.
     
  12. Arfa Daily

    Arfa Daily Guest

    Ah, OK, I see where you're coming from. 4 x 100 watt speakers, series'd and
    parallel'd to arrive back at 8 ohms makes a 400 watt 8 ohm cabinet, so
    driving in a 100 watts, results in a dissipation of only 25 watts in each
    speaker, right ? Seems a fair point.

    As far as overdrive sound goes, this is normally achieved by deliberately
    overdriving an early stage of the amp, and once you've achieved the degree
    of overdrive sound that you want, it should remain just so over the full
    range of output power of the amp, as controlled by the master gain. So if
    you set up a Canned Heat " Let's Work Together " type sound ( this was
    probably actually done with an external fuzz pedal on the original record,
    but a similarly harsh distorted buzz saw sound can be created by preamp
    overdrive ), then you could take that same sound from a village hall to the
    National Indoor Arena, just by cranking the master. However, some musicians
    believe that there is a particular high power output point on any given
    amplifier, that generates a perfect sound ( for them ). This point is the
    'sweet spot', and may be at a point where the output stage is being driven
    so hard that it is going into hard clipping. This sound cannot easily be
    transported between different sized venues, unless you interpose a power
    absorber between the amp, and the speaker cabinet. Such devices are
    commercially made, and readily available to the professional musician, and
    are usually adjustable, so allowing you to drive the amp at almost full
    output to hit your sweet spot, whilst attenuating the input to the cabinet
    down to village hall amounts. This is why it's important to check with the
    owner just what he wants to do with the rig, before making a decision on how
    to proceed.

    Arfa
     
  13. Ron(UK)

    Ron(UK) Guest

    Something you should know about sound reinforcement speakers is that
    generally speaking it`s prudent, for instrument use, (guitar amps) to
    use speakers which can handle twice the amplifier power. For example, a
    100 watt guitar amp should see 200 watts worth of speakers. This is
    because instrument amplifiers, guitar amps in particular are often
    driven way into distortion where the wave form becomes somewhat squared
    off thus delivering almost twice the RMS power.

    On the other hand, PA speakers should be provided with around twice
    their power handling, ie, a 400 rms watt speaker cab should be driven by
    an 800 rms watt amplifier. The amplifiers used for PA should never be
    driven into clipping, but when they are, that`s when things break!

    In most cases when a speaker burns out, it`s because the amplifier
    driving it wasn't powerful enough to provide adequate volume without
    clipping.


    Ron(UK)

    Not responsible for any ensuing flame wars, as the above is often
    difficult to comprehend, and contentious ;)
     
  14. Arfa Daily

    Arfa Daily Guest

    As someone who is also involved in repairs of this equipment, I would have
    this down as good *practical* advice rather than anything particularly
    contentious - although I can see where you're coming from on that point.
    Basically, it reinforces all that I've said about driving amps to output
    stage clipping, and above all, the need to talk to the owner, to find out
    just what he needs the rig to do.

    Arfa
     
  15. N Cook

    N Cook Guest

    Is it not simply that if you drive an output to clipping then you are
    dumping full rail 60V or whatever DC on the speaker.
    If it stays for more than a few milliseconds driven to full high or low then
    that is enough to burn out the voice coil after its already hot from
    sustained high, but not clipping, normal AC.
     
  16. Ron(UK)

    Ron(UK) Guest

    Well it`s not technically DC, more of a square wave than a sine wave, so
    the peak lasts longer and the waveform contains up to twice the energy,
    but you are correct that it`s voice coil heating that`s the killer.

    There are some handy papers on the Rane site covering what happens when
    amplifiers are driven into distortion btw.

    http://www.rane.com/library.html


    Ron(UK)
     
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