Continuous vs Programmable watt rating...

[Bob Lee (QSC)]

what i dont understand is why worry about how close to failure gear can be pushed instead of adding more amp/speakers to the rig to allow for less strain on the gear.....surely a second amp/cab would be cheaper long term than melting down ones main rig

Yes, but economic considerations often come into play. It might be more important to determine what you can do with your existing rig than to have to add to it.

 

[bongomania]

Exactly, the rule of thumb is have about 2x what the speakers RMS is for headroom etc. Which is why Peavey says to go by the program rating (a black widow is 350 rms, 700 program.) They do know what they are talking about you see, why people try to always know more than them about everything, I can't figure out...

These same people go only by the rms and send clipping signals to their BW's with underpowered amps, and blow them up (square waves destroy voice coils) and then blame Peavey for poor speakers. Give me a break...

I'm sorry, but that's nonsense from start to finish.

 

[hrgiger]

For most users, amp power of 2× the loudspeaker's continuous rating is a very good match. I would recommend though that inexperienced users who might not be as good at controlling their levels or noticing clipping should use higher-rated loudspeakers, even up to the amp's power rating.

Square waves do not damage voice coils any more than other waveforms do.

Someone said above clipping does not damage speakers too much power does... How are square waves generated? As far as I understand, square waves have 4x the power of sine waves or something...

Straight from my Peavey GPS 1500 manual:

This switch is used to defeat the DDT compression used to protect against signal clipping. It is recommended to leave the DDT compression enabled at all times to protect your speakers from damaging square waves. The DDT function is disabled when the switch is pressed to the “in” position. The DDT LEDs (12) will illuminate when DDT compression is occurring in that particular channel.

 

[Bob Lee (QSC)]

Square waves are probably most often generated by an oscillator. As anyone who's played around with synthesizers and stuff like that can tell you, loudspeakers can handle square waves as well as they do triangle waves, sawtooth waves, pulse waves, etc.

If a clipped signal puts too much power into a loudspeaker, it's as dangerous to the speaker as the same amount of power from an unclipped signal.

 

[hrgiger]

Square waves are probably most often generated by an oscillator. As anyone who's played around with synthesizers and stuff like that can tell you, loudspeakers can handle square waves as well as they do triangle waves, sawtooth waves, pulse waves, etc.

If a clipped signal puts too much power into a loudspeaker, it's as dangerous to the speaker as the same amount of power from an unclipped signal.

I think you are talking like an engineer, I agree with everything you said but in real life when do bass amplifiers create square waves? When they are clipping!

From wikipedia:

http://en.wikipedia.org/wiki/Clipping_(audio)

Overview of clipping

When an amplifier is pushed to create a signal with more power than its power supply can produce, it will amplify the signal only up to its maximum capacity, at which point the signal will be amplified no further. As the signal simply "cuts" or "clips" at the maximum capacity of the amplifier, the signal is said to be "clipping". The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted squarewave type waveform.

 

[Bob Lee (QSC)]

Or when the input signal is a square wave.

Most amps don't produce square waves when they clip, though, because they rarely are pushed that heavily into clipping.

I know that Wikipedia article pretty well because I wrote part of it.

 

[hrgiger]

I know that Wikipedia article pretty well because I wrote part of it.

Then what is meant by this part? "The extra signal which is beyond the capability of the amplifier is simply cut off, resulting in a sine wave becoming a distorted squarewave type waveform."

I'm sure there are full-blown square waves vs. squarewave type waveforms, when Peavey says square waves I think they are not trying to be technical, they are talking about clipping that clips off the sine wave and puts DC into the signal right?

 

[Bob Lee (QSC)]

Yes, there is a difference between square waves and other waves that share some similarities. The takes more than a flat top to actually make a waveform square; it takes a very fast rise and fall time as well, and that's where typical clipped waveforms differe from actual square waves.

Clipping is not DC.

 

[hrgiger]

Clipping is not DC.

I realize that but from other articles I've read, DC is in the signal. I read that "the "flat top" of the signal simulates a DC signal..."

Also for example in this paper : Link Removed, I read that basses produce assymetrical waveforms:

Sources of Asymmetrical Waveforms

Most people probably tend to think that their music signal is relatively symmetrical, and this is usually true when averaged out over a long period (perhaps 30 seconds or more). However, there are a great many sources of asymmetry within the programme material itself, and these include ...

* Human voice (spoken or singing)
* Wind instruments (flute, horns, reed instruments, etc.)
* Plucked and struck stringed instruments (guitar, harp, piano, bass, etc.)

And then I read in this same paper that:

There is no doubt that a clipped asymmetrical waveform will generate a DC component in the output of an amplifier.

So I gathered that a bass guitar signal that is clipping will have some DC in it, which is in other words, a "squarewave type waveform" which can damage the voice coil. Is this incorrect?

 

[hrgiger]

As a rule of thumb IMO connecting a speaker to an amp with double its RMS rating is a recipe for blown speakers.

Well according to JBL (are they any good?) they say:

[Invalid or Expired Link Removed]

How do I choose the right amplifier power for my speaker system?

* Ideally you should pick an amplifier that can deliver power equal to twice the speaker's continuous IEC power rating. This means that a speaker with a "nominal impedance" of 8 ohms and a continuous IEC power rating of 350 watts will require an amplifier that can produce 700 watts into an 8 ohm load. For a stereo pair of speakers, the amplifier should be rated at 700 watts per channel into 8 ohms.
* A quality professional loudspeaker can handle transient peaks in excess of its rated power if the amplifier can deliver those peaks without distortion. Using an amp with some extra "headroom" will help assure that only clean, undistorted power gets to your speakers. Some professional amplifiers are designed so they have additional headroom. These amps can cleanly reproduce transient peaks that exceed the amplifier's rated power. In this case select a model with an output power rating equal to the continuous IEC power rating of the speaker. Consult the amplifier manufacturer or owner's manual to learn more.
* In some applications, such as critical listening in a studio environment, it is important to maintain peak transient capability. For these applications, use an amplifier that can deliver 6db (or four times as much) more power than the continuous IEC power rating.
* If budget restraints or legacy equipment force you to use an amplifier with less power, extreme care should be taken to see that the amplifier is not driven into clipping. It may surprise you to learn that low power can result in damage to your speaker or system. Download our Danger: Low Power tech note for more information.

Hmmm, sounds alot like Peavey... And what I was saying...

 

[hrgiger]

I'm sorry, but that's nonsense from start to finish.

Well I'm sorry you think that, better start studying and read what JBL says in the post above and then add what they say here:

[Invalid or Expired Link Removed]

What is "DC Burn"?
DC (direct-current) burn is a failure mode where the voice coil is burnt only at one end. This is an indication that it has been traveling in one direction more than the other. Since the transfer of heat is from the voice coil to the adjacent magnet and metal parts, the voice coil will be burnt on the end that stays the farthest away from the top plate.

* Woofers: When a DC burn pattern appears on the voice coil of a woofer, the problem will be due to a fault in the associated electronic equipment. Most likely, the power amplifier has leaky or shorted transistors that are allowing its internal power supply voltages to be applied directly to the loudspeaker or loudspeaker system.
* Midrange and Tweeter: When a DC burn pattern is observed on the voice coil of such devices, it DOES NOT always mean that the amplifier is faulty. In systems with passive crossovers, mid and high frequency drivers are protected from DC by the cross-over. The most likely cause of DC-like burns is an overdriven amplifier.
* When an amplifier receives an input signal capable of driving it beyond its power rating, the result is clipping. This means that the negative and positive peaks of the amplifier's output signal are "clipped" off. The amplifier may also clip in an asymmetrical fashion, meaning that the positive side of the signal is clipped more than the negative (or vice versa). When subjected to an asymmetrical clipped waveform, one end of the loudspeaker's voice coil is "on average" spending more time outside of the gap (corresponding to the direction that is clipped) than the other. The end of the coil that is spending more time outside of the gap has poor heat transfer to the magnet structure. As a result, it overheats and burns.

 

[bongomania]

JBL and Peavey both have repeated statements about clipping which are rejected by the majority of pro audio engineers. It is highly likely that whoever wrote that copy for them was just repeating something they were taught by an older tech who was themselves passing along a myth, thinking it truth.

Speaking of "studying", you ought to look at the FAQ.

 

[B-string]

It's "programmable" according to Fender and/or Sam Ash: Invalid Link Removed

Another reason to NOT buy Fender, total nonsense rating they will not have to back up in any way!

I am not allowed to enter this discussion, but I would like to know how many here have been involved in distructive driver (cone speaker) testing? Could someone please give me a definition of DC voltage?

 

[BassmanPaul]

It's "programmable" according to Fender and/or Sam Ash: Invalid Link Removed

Just because some copy editor missed correcting Fender's text and Sam Ash quoted it doesn't make it the correct term.

Paul

 

[BassmanPaul]

Hrgiger, IIRC IEC and RMS are two completely different terms.

Paul

 

[bongomania]

Could someone please give me a definition of DC voltage?

http://en.wikipedia.org/wiki/Direct_current
"Within electrical engineering, the term DC is used to refer to power systems that use only one polarity of voltage or current, and to refer to the constant, zero-frequency, or slowly varying local mean value of a voltage or current."

A square wave is not an example of DC. A square wave has polarity and frequency.

 

[holllowbody]

Anyone know the difference between continuous vs programmable watt rating on a speaker cab? I had the question come up on my message board and can't find a good answer anywhere...

500 programmable, 250 watts continuous...

I have always used the "program" rating to tell me which amp to use with the said speaker cab.

For instance if a speaker cabinet is rated at 250 continuous, 500 program, 1000 peak and the cab has an impedance of 8 ohms I would look for an amp that is rated at 500 watts at 8 ohms or more. 250 watts does not afford much headroom in this case and headroom is a good thing, the more the better as long as you know how to handle it.

 

[B-string]

The question is meant to envoke thought. As in at power up and power down a DC supply with the rise and fall it is no longer DC? At what time constant is a given voltage concidered AC or DC? Automotive applications use a rectified AC generator, when that AC componet exceeds a given point, systems are affected and finally the battery fails to charge. Still concidered a DC system even though properly operating it contains AC ripple of changing frequency and non "constant" voltage. If we are going to split hairs lets have some fun with it?

Or not?

 

[bongomania]

If we are going to split hairs lets have some fun with it?

Oh, I get where you're going there, and in fact I posted the same devil's advocate argument myself a few times when I first joined TB. The engineers on the board gave me a smackdown, saying our amps will never send to our speakers an audio wave long enough to "act like DC", even for a moment.

 

[B-string]

How long was the "moment"? Can they reproduce a flat top wave. Now don't get me wrong. I would say an amp that could maintain it's DC rails at bass freqencies that are flat topped would be a bad thing at max output (I would expect sag and AC component when reserves are depleated). I am wondering at what time period a sustained voltage is not concidered DC? I must have fallen asleep during that lecture? Please no one has to say "our amps won't do that" I trust you know how to design your products!
Just my thought process is hungry?