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Author Topic: Bassmaxx's sound awful! Had to return 14 cabinets/ can't get money back!  (Read 19896 times)

Antone Atmarama Bajor

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Re: Why the fuses?
« Reply #20 on: April 23, 2005, 04:20:14 pm »

No it probably wouldn't be a zoeble (Sp).  If an amplifier is clipped, even if it is crossed over the clipping if you analyze it spectrally is a series of harmonics (odd harmonics normally).  Just take the fundamental frequency and multiply it by any odd number and those frequencies will be present (although diminishing in energy with each higher odd multiplication).  

    Basically clipping will turn a sinusoidal wave form into a square wave, Square waves can be analyzed as being rich in odd harmonics.  An infinite, diminishing series of odd harmonics.  MMMM they really clutter up your audio spectrum nice and good.

I would imagine you could use a breaker/relay of a sort and if there is High Frequency energy in the signal from amplifier clipping it could be shunted to a Relay through a capacitor to throw a circuit breaker.  I don't know if the energy would have to be rectified or not but I'm sure it would work well if you have a predetermined cut off frequency.  It might protect the drivers pretty well, prevent them from converting all of those good harmonics into coil warping heat.

    Though Constantly tripping the breaker would probably drive a clip happy DJ MAD!!!  Laughing

Sum
aka Ragnor Raunchy Pants
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Antone Atmarama Bajor

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Re: Excuse me? Would you like to check the facts?
« Reply #21 on: April 23, 2005, 04:37:26 pm »

Once you Hit clipping the "average power" is constant unless your using tubes, you have hit your supply rails.  Once you square off the wave form you have generated tons of harmonics making the previously limited bandwidth much more spectrally rich/broad.  The  sub driver isn't really capable of reacting to the higher frequency harmonics generated by clipping so it gets converted into heat energy instead of mechanical energy Giving the end user a nice toasty voice coil, and eventual failure due to overheating.

    The drivers will probably out live being overpowered by a clean crossed over signal than a clipped underpowered signal.

    Yes the Harmonics can be damaging to professional drivers too  If they are not intended to reproduce those parts of the spectrum.

Sum

 
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John Roberts {JR}

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Re: Excuse me? Would you like to check the facts?
« Reply #22 on: April 23, 2005, 06:32:30 pm »

Nah...

JR
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Antone Atmarama Bajor

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Re: Excuse me? Would you like to check the facts?
« Reply #23 on: April 23, 2005, 09:56:49 pm »

     Here is an old write up by JBL on underpowering although it seems to be intended for Passively crossed over full range cabs rather than Bi/Tri/Quad amped electronicaly crossed over sound systems.  But it still applies to any clipped signal.  All of that high frequency energy energy has do be dissipated.  If its not being converted into mechanical motion than its going to turn into heat.  

http://www.jblpro.com/pub/technote/lowpower.pdf

The Drivers wont "blow up" due to clipping amps but they will go through Thermal Stress and Damage.  Enamel will crack, coils will warp, short, Carbonize, Oxidize, Scrape and scratch, melt.  Its all bad.

Sum  
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Elliot Thompson

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I always found Chuck McGregor's article spot on.
Whereas JBL's....... Rolling Eyes

  http://www.prosoundweb.com/studyhall/studyjump.php?pdf=watts
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Elliot

Antone Atmarama Bajor

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I have no problems with what Chuck saying except one statement is not so clear to me.

"REAL WORLD AUDIO SIGNALS:
Real audio signals usually have peaks at least 10 dB peaks their RMS level."

How does an RMS level have a 10dB peak?

250Watts "RMS" (is power ever rated in peak for periodic signals)
We now have to go to voltage so V=sqr(P*R) V=sqr(250*8)=44.72Vrms
Now peak Voltage Vp=Vrms*sqr(2)  Vp=44.72Vrms*sqr(2)=63.2456Vp
Convert back to Peak Power P=(V^2)/R  P=(63.2456^2)/8)=500Watts Peak.

Call me knuts but thats only a 3dB peak.

I've never heard of anyone getting 2500 Watt peaks out of a 250 WattRMS amplifier?  Or An RMS signal having a 10dB peak.

    Isn't the peak of an RMS signal by definition 3dB more power if we rated things in such a silly way?  Not that a square wave wouldn't give you that magic 3dB in more of a steady state (to a non inductive load at least).

Ahhhhhgghhhhh it makes my brain hurt.  Or is this guy living in peak to peak rating world.

    I don't know I like using my power amps as comparators It gives me a special kinda sound.  That way I can squeeze as much wattage out of my amps as possible, and "all of the sound" gets to my speakers.

Sum
aka Ragnor Raunchy Pants

wants to be a Square Pusher too
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Elliot Thompson

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I'm sorry but, I don't see where he said an amplifier
will put out 10 decibals peak.

Are sure your not mistaken his explaination for input
signal?

Take a look at Bink's Amplifier Shootout spread sheet.

You'll find the older amplifiers offering more power,
the when you go beyond the clip light. They don't back
off. They will distort, but, they will still increase
their output.

However, some of the newer amplifiers, are designed
to limit the output when driven severely into clip.
Some will even shutdown, if you try too exceed the
maximum input signal.

Nowadays, Amplifier companies are making their
amplifiers more aware of the overly abusive customer.






Back To Chuck McGregor.


One of the reasons I recomend Mr. McGregor's notes, is
due to acknowledging, the Thermal & Mechanical limits
of the speaker.

If I fed 25 Hertz to a JBL 2241 @ 300 watts,
and you fed 50 Hertz to a JBL 2241 @ 600 watts,
my speaker will be closer to its mechanical limit
than yours.

By Mr. McGregor mentioning this (Thermal/Mechanical limits)
he's saying, there is no guarantee the speaker will offer
XYZ watts. It all depends on the program material.  

While JBL states low power is no good, they don't
state that too much power is also no good. You can
exceed a speakers mechanical limit way before you reach
the thermal limit.  





Best Regards,
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Elliot

Antone Atmarama Bajor

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Of course.  If you push a driver to do what its not intended to do Its not going to hold up long, (even though I think the 2241 could probably take those levels OK depending on how its loaded)

I know he was talking about line level but +10dB peaks above RMS still violates my brain.  Like wow +10dB transient peaks can happen  if you are giving yourself that much head room but I would never want to think about my line levels in RMS terms.  Maybe hey I'm running +6dB average and I know that when I get my system tuned that I will start clipping my mid bass amps around +XdB, so I have X headroom before I do bad things to my system.

    It is a good thing to illustrate the dynamic nature of sound, and music and how huge the orders of magnitude can be.  But music is sorta hard to put an RMS measurement on.  I'm cool with RMS measurements on an amp because That is normally the edge of what the amp can put out before (heavy) distortion, there is no headroom.  And Peak Power output can be figured for pretty easily.  (I don't know maybe I should start generating steady state tones so I can have an RMS signal to reference my peaks to.  I'm sure bands will love it)

    I haven't heard too many people advocating getting an amp that can produce twice the drivers rms rating (I'm cool with that though seems reasonable).  Most speakers that I see rated have peak power handling capacity's that are exactly 3dB more than RMS (which to me means your already there and the company is just being redundant).  I have seen a couple that state that they can handle short term peak RMS signals great if the amp can deliver it cleanly.

Bla Bla Bla I need to get to sleep.
Sorry what was I rambling about.
I think I'm almost off topic.
Oh yah something to do with clipping a power amp, bassmaxx fuses.

How about those Lab subs
Fun with periodic DC pulses?
Good Night
Sum  
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Liam Flynn

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 ALong with JR's posts on the topic, I have found this article to be very helpful, and it seems to make a lot of sense to me.

It is called "Power Amp Clipping and it's Effects on Loudspeakers" on the Ranenotes page. Just scroll down a few lines.


http://www.rane.com/library.html#rnotes
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Mac Kerr

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Sum, I don't know why you keep insisting that peak level is 3dB above RMS level in all situations. This may be true for a steady state test tone in an amplifier, but it has no relationship to audio signals. An amplifier may be able to deliver a certain voltage at a certain current without maxxing out the power supply and clipping. The same amp may be able to deliver a higher voltage for a short time before the power supply is maxxed out. Those would be the long term/RMS and peak power capabilities of the amp. The 2 levels are determined by the electrical characteristics of the amp. A speaker system is limited by it's thermal characteristics and it's mechanical characteristics. The thermal limits relate to long term power handling, and the mechanical limits relate to short term power handling. The two are not related by any fixed ratio.

Root mean square (RMS) averages are a mathematical method of defining an average for any waveform, I don't know why you seem to imply that they only apply to sine waves.

Since music is full of peaks that can easily be 10dB or more it is up to the system designer to be sure the amplifiers and speakers are capable of delivering enough peak output, and it is up to the operator to be sure that in the use of the system that the long term capabilities are not exceeded. This has become a little easier with the advent of speaker processors that can have separate peak and average limiters, but it is still the responsibility of the operator to use the system within it's long term and short term limits.

Mac.
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