Speaker Modification
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  1. #1
    Tech Mentor sparkbro's Avatar
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    Default Speaker Modification

    Ok, so i bought 2 x 12" speakers + amp. Now, i lent them to my friend, and he blew the voice coil in both of the woofers in each box. I then replaced these (With his financial help for breaking them) and now all good. But - So i can run these LOUD (distortion free) for long periods - would it be a bad idea to put a heatsinc on the big metal bit at the back of the driver? (I'm not into the whole speaker lingo so you will have to forgive me if there is a proper name for it).

    Anyway yes - Would this be a bad idea? because since the first lot blew, i have been stopping the music, and checking the temperature of the cone -and it heats up alot (when played as loud as possible without distortion).
    They are wooden boxes, so i could put a heat sink on the back bit of each speaker, and then possibly drill holes and put a fan or two on the back of the speakers to help cool it down more.

    This may be overkill - but i want to make sure they don't blow again.

    Ideas on this?

    Thanks.
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  2. #2
    Tech Mentor JSM's Avatar
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    you are blowing them due to an amp/speaker mismatch. Google the subject and it will explain all.

    Adding anything to a speaker will affect it's sound, cabinets are designed to allow a particular airflow which affects bass response.

    I always have speakers power rating that are TWICE my amps power rating. I make sure I never clip the signal, this just causes distortion of the signal and some amps don't like that and end up sending far too much signal to the speakers.

    You will also need to make sure that the speaker crossover units are matched correctly, just uprating them without adjusting their frequencies is a bad idea (I've killed a couple of amps doing that !).

    There are a couple of sound engineers on this forum and I am sure there will be a few cabinet builders out there to help.

    remember google is your friend.
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  3. #3
    Tech Mentor sparkbro's Avatar
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    So you're saying that the output of the amp (in ohms) is less or more than that of the speakers.

    I just checked, the amp is rated to 2x8ohms at 200watts and the new cones are 250rms with 8ohms.

    I'm not sure what the original ones were - but i bought the amp+speakers as a package, so i think my friend was just running the volume too high for too long and they just got really hot and burnt.

    I'm not sure if this will happen again, but what can i do to make sure this doesn't happen again?

    Thanks

    T
    “Getting information off the Internet is like taking a drink from a fire hydrant." Mitchell Kapor
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  4. #4
    Tech Mentor JSM's Avatar
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    you need to read about RMS, PMPO etc. these are usually there to make customers think they are getting more than they thought. What you need to know is the real power output at a specific impedance.

    Then the speakers should be roughly double that of the amp and avoid clipping at all costs (it's your enemy).

    Remember there's a crossover inside the speaker cabinets, and that also needs to be matched, I've modified many of them myself, upgrading then with audiophile class caps and huge wattage resistors (these are both very expensive additions).

    Modifying speakers is an art on it's own, check your real impedance with a meter (when everything is on the cabinet), every bit of wire and connection will change the value slightly.

    Don't worry too much about it though, i've seen Mackie and Alesis self powered speakers set on fire due to user error ... so even top manufactures can't foresee every thing.

    Just avoid clipping and overloading things ... or buy everyone headphones !
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  5. #5
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    The natural movement of the driver without clipping should keep the coil cool enough, when clipping occurs it makes the driver movement shorten and hence the airflow is not enough to keep it cool.

    The way pro audio equipment is used is usually you spec the wattage of the amp over the speaker and limit/set levels so the amp has headroom as most of the time its the amp clipping what takes out the coil.

  6. #6
    Tech Mentor sparkbro's Avatar
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    Hmm... So it's not normal for the actual drivers to heat up a bit without clipping? Or do they normally heat up- but not too hot. I'm just not sure where I should be cutting the volume line at for house parties etc.

    Thanks
    “Getting information off the Internet is like taking a drink from a fire hydrant." Mitchell Kapor
    Setup: TP2 - Vestax Typhoon - Korg NanoPad - Windows 7 x64 - Sony Vaio (Deceased) - Acer Aspire Timeline.
    House Parties - 2x12" Titan Audio PA's, 1xBehringer B1500D Sub

  7. #7
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    drivers fail from being overdriven. and in almost all cases, you CAN hear it. either distortion, or the clicking of the driver bottoming out.
    If your driving a system and it sounds as clean as driven snow, the drivers should not fail.
    the problem is, when your talking about the decibals most DJ systems are operating at, your ears can't tell the difference between driver distortion and ear distortion. you think it sounds good for a club system but you may be killing it.
    for the layman, the easiest answer is, don't push it. be very very conservative. you can get a lot of impact by nudging up the fader and then the gain, but eventually your gonna kill gear.

  8. #8
    Tech Mentor JSM's Avatar
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    you can also "smell" the heat if things are run to hot for too long, you can sometimes smell the coils going before they have actually caused any damage.

    200Watts of power is enough to run a small party outdoors if you have very efficient speakers. You often see SPF level on them. This is basically the pressure the give at 1m. The bigger the number the louder they are, if you have no-name or cheaper branded units they will require more power to drive them.

    As i said before, it's a bit of an art getting PA equipment right, some people spend their entire lives in search of perfection.


    Have you thought of a different solution? Add a powered subwoofer (or sub and sub amp). If your mixer has a sub-output you can use that, if not you may need a external crossover unit or speaker management box ...

    That way you won't be killing your speakers ... the bass makes the cones move furthest, the highs make them move the fastest .... all in one speakers have to do a lot these days, more frequencies to deliver cleanly. Adding a subwoofer take can some of the stress of producing bass, whilst still getting clean mids and tops.

    Rule of thumb - Red means danger ....not louder
    XPS L701x i7 16GbRAM 2x 500Gb SSD RAID HD (Windows 7 Ultimate x64) 1 x 1Tb 7200 int.
    TSP 2.6.1 ¦ Audio 8 ¦ Audio 4 ¦ 4 x Denon SC-2000 ¦ 2 x DX2 ¦ EMU shortboard ¦ MIDI_FIGHTER_PRO_PLUS
    SL1210Mk5 x 2 ¦ Numark TTX x2 ¦ DJM-T1 ¦ DDM4000 MIDI Mixer ¦ Numark 4TRAK ¦ neoD+ cables
    8000+ 45's & 2500+ 12's ¦ 2 x Traktor Kontrol S4 ¦ X1 & F1

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