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Morten,  Brought this over from Singer forum.


I've been out've this stuff far to long to remember any of it.


Clipping vs distorting.

Wouldn't "clipping" just suddenly stop all sound ?


  I'll ask you about this over in the tech board.   It's been ages since I knew what this stuff meant, so I'm confused as to the differences between distorting with a high output instrument such as electric piano, and clipping.


IE  100 watt Soundtech quik-mix mixer turned up around halfway. Cones of Speakers (rated at being able to handle 300 watts peak each) start to crackle.
(15 inch 3 way speakers)  Checking cones and speakers I see that nothing is ripped, or blown.



Is this clipping ?  or normal distortion from the high output of a piano ?

How would I know if I am distorting the mixer.  or the speakers ?

(reposting to tech board)

Clipping is the cause of distortion.

Typically sound engineers will get an amp rated double the RMS power handling of the speaker.  When you get an under powered amp - the 100 watt amp in question & your speaker handles 300 watts, you may be pushing that 100 watts, but find that isn't enough now you turn it up even more (yes most amps will turn up higher than there rated output but it will be in the form of distortion), so now you are sending a clipped - distorted signal to the speaker because the amp is giving all the "clean" signal it can.  Not saying an amp double the power of a speakers handling capacity won't blow it, it most definately can, however, the chance you will be turning it up higher than the rated output is less because you are sending more "clean" signal to the speaker.  So say your speakers handle 300 watts RMS, you get an amp that pushes 600 watts per side.  When you are running it (say you replaced the 100 watt amp), you get to the same volume level as with the smaller amp.  Now you find you need to turn it up, well now you have some room before that dirty signal gets to your speaker & you CAN turn it up higher without any problems.

You aren't going to distort the mixer - unless you are clipping any of the individual channels.  If that's the case, then it won't matter what kind of amp your are running, you are already amplifying a dirty signal.

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Lonman,

   Thanks,  yet I'm abit confused.  As you know, the beauty of tube amps is that we go for the warm distortion.  The smoother sound of the distortion of tube amp vs the harsher sounding dist. of tranny is often a discussed issue.

   Is the warmth and mild distortion that makes blues sound so nice on a tube rig in essence "clipping" ?   or can distortion also take place without clipping ?

   In the tube days double the RMS power was roughly the peak handling power as I recall.   Yet tranny came along,  and I recall peak was replaced by (something like CPI) which didn't break down the same. Is the smoother tube distortion still clipping the sine wave ?

Is the rule of thumb still to get an amp rating, that matches the speakers peak handling rating ?   IE......... Cabs can handle 150 watts each  (supposedly), so do you go with a powered mixer rated at 300 watts peak  per speaker ?   or because there are two speakers in a PA  600 watts  peak.  The combined peak rating of the cabs?

Tube amps are a completely different scenerio completely.  I don't use them much except for my guitar amp.  But I know the manufacturer matched a 30 watt Celestian guitar speaker to a 100 watt head!  For PA, i'm not real sure how a tube amp would come into play.

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Realisticly if a speaker is stating they handle 150 watts, you may want to really consider a better speaker.  But yes if your speakers state they handle 150 watts RMS each, get an amp that pushes 300 watts per channel & you should be fine.    When combining the speakers to 1 output, well now you have changed the equation again - in ohms & power handling.

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That's interesting,   My Marshall Cab has 4 celestian vintage 30 watt 12's.  For the JCM 100 watt head, I guess that sounds about right.

Yet if I were to put 100 watt tube into one 12, I'd be afraid to go anything less than the celestian 75 watt rated speakers.   Would seem that the 30 watt rated speaker couldn't take that head cranked.

The cabs are rated at being able to handle 300 peak each.   I made the assumption that that means something comparable to 150 RMS each.   The specs don't state that.  These are cross-over cabs. 15's with horns.


I understand what you are saying.   Matching the peak rating of each speaker cab. to the output rating of that speaker cabs amp channel.... Thanks.   I just hear about 600 watt heads thru 300 watt rated cabs,  and The first thing that comes to my head, is costly speaker replacements.  I don't know anything about todays specs, and rules of thumb.  Speakers today are so much more efficient than the old days, where putting anything more than 40 watts RMS into a single 10 inch speaker, would rip the thing to shreds.


As always,  appreciate the help

If those speakers state 300 watts peak then the RMS/program power is probably close to 150 watts, which also means it's continuous power handling may be even less.  Many manufacturers now list 3 ratings on their cabinets.  The continuous, the RMS/program & peak.  Each rating is usually doubled from the first.  Peavey & JBL are perfect examples.  If they state a cab handles 300 watts continuous, the RMS rating is 600 & the peak rating is 1200.

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Just a thought........ but the poping and distorting you might be getting may be caused in part from overdriving the preamp input... this could be sending your amp into clip and making the distortion worse. Add that to mismatching wattage with handling capability its a recipe for a nightmare. Not sure of your exact setup item for item but some keyboars /mic's Ect..... can put out a hot signal you just have to be aware of this when bringing up your levels. I'm trying to explain it and its confusing for me. I know Its alot to check adjust just to get some sound.
Djpauly

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Steven,

I didn't carefully read the exchange with lonman, so perhaps I duplicate some of his responses...

As Lonman states: clipping is the source of distortion. Clipping just means that instead of ex. a perfect sine tone going to your speakers the tops and bottoms are flattened. Spectrally that means that a lot of new frequencies are added. These frequencies were not in the original signal and thus creates the distorted sound.

Clipping occurs whenever the demands of a gain circuit exceeds its capabilities. Your mixer can clip, your amplifiers etc. Ex. your high output instrument into a mic input designed for high gain and low input will clip the input stage. Once you have clipped a gain stage it doesn't matter that the subsequent stages are not clipping. They will faithfully reproduce the distorted signal.

Clipping can be desired in the process of generating music. The best example is a tube guitar amplifier where the clipping actually adds to the sound. Clipping should be avoided at all costs when reproducing music since the clipping adds frequencies that were not in the original material that you are trying to reproduce. For this reason tubes are used in guitar amplifiers but seldom in PA systems.

A tube amplifier can also be operated in clean mode with no or little clipping. That is only a question of not cranking it up too much. The reason a tube amplifier is preferred for guitars is that the clipping in a tube amp happens more gradually and therefore produces a more pleasant sound than a clipped solid state amp. However, even a tube amp, if overdriven too much will result in an unpleasant sound. Furthermore, clipping a single instrument can sound pleasant with moderation - clipping the whole band at once does not.

First I just wanted to describe clipping. My next post will discuss how all this relates to socalled "underdriven" speakers.

Morten

Now on to socalled "underpowered speakers".

First off, let me say that I really hate that term! There is no such thing as an underpowered speaker - only underpowered amplifiers!!!!!

Before we get more technical let me first give a few simple examples. You are playing music in your bedroom and your spouse (or mother depending on age) enters and asks you to turn the volume down. You respond back: "I can't, I would be underpowering the speakers and that ruins them". This is of course incorrect. Second example. You buy a new speaker cabinet and you are trying to decide between which 15" woofer to mount in the cabinet. You intend to use the speakers with a 300 W amplifier. You have a choice of either a woofer with a 2" voice coil and a power handling of 200 W or a woofer with a 3" voice coil and a power handling of 400 W. You choose the woofer with the lower power handling since you would be underpowering the other one. This of course also incorrect.

Let me just make this clear speakers only die if overpowered. The two most common failure modes are:

1) the excursion limit of the speaker is exceeded.

Ex. you mic the bass drum. Your amplifier can provide plenty of power. The drummer kicks especially hard and your woofers start flying.

2) the voice coil is burnt.

Ex. your amplifier is not powerful enough and you are having a party. You crank the amp and start clipping. When clipping too much power is send to the tweeter and you exceed the power dissipation limit of the tweeter.

In both cases the speaker/driver was overpowered. This can happen even if the amplifier is rated below the maximum rating of the speaker. When an amplifier clips (in the limit) a square wave is send to the speakers. The power of that square wave is twice the power of the rated output power from the amp. Thus, any amp when severely clipped can provide an output power twice the rating. Secondly, music has most of the energy at lower frequencies. Thus, the woofer has the largest power handling capability and the tweeter the smallest. The moment the amplifier clips a disproportionate amount of power is now transferred to the trebble fequencies. That is why the tweeter is the first thing to go.

to be continued...

continued...

Before we continue the discussion I would just like to add that the speaker power handling can be specified in several ways: RMS, program, and peak.

- RMS: this is a measurement of how much power in a single tone (sine wave) each driver can handle over long periods of time. This is mainly a thermal limit, i.e. how much power is needed to burn the voice coil. For the speaker as a whole the RMS rating is often equal to that of the bass woofer since most of the power occupies the low frequencies.

- Program: The program rating takes into account that we don't like to listen to pure tones, but prefer some dynamic content and complex harmonies. Thus the voice coils have time to cool down between the loud passages. This program rating takes into account properbilities of different frequencies on most music. Often the program rating is twice as big as the RMS rating.

- Peak: takes into account that for a short period of time voice coil can accept larger currents than continous. This rating is also affected by the maximum excursion of the drivers.

Back the underpowering discussion.

The crux of the underpowering argument goes that in essence you buy your speaker to be able to achieve a certain loudness. In an attempt to reach that loudness you would be more likely to crank the amp into clipping if the amp is not at least 1.5-2 the RMS handling capability of the speaker (which is equal to the program power).  This is not an unreasonable argument especially for pro use where it is not cost efficient to buy more power handling than needed.

However, that argument can also be turned around: you buy your amplifier so that (taken into account the efficiency of your prospective speakers) you can reach the desired loudness with some desired amount of headroom. As long as the speaker power handling exceeds that needed to achieve the desired loudness there is no issue. If you can get even better power handling from your speaker that just means that the system in the future can be upgraded by buying bigger amps.

Also remember that even a doubling of amplifier power only adds 3 dB to the sound preassure level. This is barely discernable. A 10 dB increase in amplifier power (i.e. 100 W vs. 1000 W) is needed to double the perceived loudness!!!

So, the basic issue is really just to never clip any amplification stages in your stereo/PA system. If clipping is avoided no distortion will be created and as long as your speaker can handle the power of your amps you are good. The way to avoid clipping is to operate with correct gain structure throughout your system. I will detail gain structure in a future post.

Steven, I hope this tells you more about clipping, underpowering etc. than you ever wanted to know. If anything is unclear please point it out and I will try to clarify.

Morten

I cant add much as Lonman and mortenN had some exellent responses As an old old engineer I will try to simplify it a bit.  Audio clipping occurs when the amp can not handle the input. For example an amp with a gain of 10 with a 1 volt input and and a power supply of 9 volts will clip at 9 volts  (cant go to 10 p/p) (actually less)  At audio frequencies a high frequency component is added with harmonics at lower audio frequencies  At the time the Ac signal is clipped the over all level is a Dc component.. which forces the cone in one direction and if clipping is high enuff or long enough in the cycle (heavy clipping ) blows the coil in the speaker and is easy to tell when the speaker pops on heavy bass,..
When an amp tries to produce the peak to peak that the speaker is capable of and clips, a dc  component  is added and the speaker coil is fried It is simple as that....That  is underpowring  however if you are running an avererage level througout your system and not clipping, the load match between amp and speaker is not exceeded, there is no problem (do not run anything at unity) The simple fact is if ur speakers are poppin u got a problem.....

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Here is a fun little calculator.  Perceived volume in going from a 100-200 watt amp is no different than going from 10,000 watts to 20,000 watts.

http://www.trinitysoundcompany.com/dbvspower.html

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Thanks all,

   This stuff get's tricky. An 8 ohm speaker rating of 100W peak means at 8 ohms  the speaker can handle a max of a little over 28V RMS for short times. I tend to forget that the classic companies such as Celestion Fender Marshall and Vox put out their specs in RMS. The Vox AC-30 has two speakers rated at only 15 watts each. At 8 ohms given the use of most guitarists, an efficient speaker combo capable of handling 30 watts RMS is fine for the 100 watt MAX head. Yet it even get's tougher to understand  because the needs of the audiophiles and guitarists and even synth/electric piano players (who put a very low frequency flattened sine wave into a speaker) have very different needs.  This is where It's tough for me to know if I'm clipping the preamp stage, or the speaker itself, or if the high output that has been known to fry speakers (Harsh sudden output of electric piano and synth lower freq) at even a proper amp/speaking match for most apps just needs to always go through a VERY good powerful amp/speaker comb (such as a bass reflex, or folded horn cab)

Steven,

I think most guitar heads are rated as RMS. However, when you add two 8 ohm speakers you can either add them in series and the impedance is now 16 ohm or in parallel in which case the impedance is 4 ohm. For a tube amp it doesn't matter since most tube amps have an impedance switch to match the output transformer to the load. However, for heavily overdriven guitar I think I would want the speaker rating to at least match the amplifier rating. Remember when you severely overdrive the head can provide twice the power of the rating.

Regarding the synth/keyboard I think you have it wrong. Neither should be clipping any waveforms (unless they are simulating an overdriven guitar).

The key to not clipping anything in a PA is to use the correct gain structure.  Hopefully, your mixer has a vu meter, peak light, row of LED's, or something similar. When you connect the instrumment/source into the mixer you should set the channel gain so that it is as large as possible, but do not light the peak light. In this way you should not clip the pre-amp. When you do this test it might be a good idea to disconnect the speakers. To set the gain structure of the rest of the system it is advisable to use pink noise. The main idea is that everything following and including the mixer should clip at the same time to minimize noise and maximize headroom. I will post later a more thorough description of setting the gain structure, but that is the crux.

Did the rest of my posts make sense to you?

Morten

MortenN,


I'd challenge you on this, yet please keep in mind that I pride myself in being a technical moron, My criteria for a girlfriend is that she knows how to gap spark plugs, and change oil. Oh yeah, and clean my caps as well as bias my tube amps !  LOL

Yet here goes !



First off, not all companies used RMS rating. Of course they should. Yet some "hoodwinked" the customer and used peak power and some even went as far as using instantaneous peak power which can result in wattage figures in excess of 4 times the RMS value. I think this somewhat subjective rating of wattage is always used in SPL however. IF that's changed today, I don't know.  This is how it was when I was more into the tech aspects of the equip I own.

Musical instruments into a speaker, (as I recall) don't put out the smoother more even distribution of sound level as say the orchestral tape the audiophile will play. The signals are different, especially guitar, which only has a limited range of about 80Hz to around 6kHz. Even-so when I play the guitar two types of signal are generated; If I play chords, there's a smoother distribution over the speaker as when I play single note solos. Wattage ratings of speakers generally work well because they take into consideration MOST conditions. Yet they are still a compromise.

For chord type guitar playing (I thinK...don't recall this as fact) usually the RMS rating works fine, but one note at a time solos, ESPECIALLY the lower bass frequencies, can usually go twice that power rating or even more.  There is more wear and tear on a standard speaker from this type of input.

A synth or hammond organ playing a very low square wave, or the hammer action harsh signal of a low note on my Yamaha CP-25 EP can EASILY destroy a speaker at well below it's nominal power rating.

Two additional notes:  First I'm sorry about the initial placement of the smiley, I wasn't laughing at anything you said.  Secondly NO,  My current PA head has no meters, it's a pretty cheap model.  I DO need a better PA head.  Even though my equipment is only used for small room, home conditions,  It shouldn't be distorting at the levels I am capable into it.

I put an old 6 channel Boss KM-600 6 channel keyboard mixer (low power), into two channels of a Soundtech Quikmix 6 (perhaps 60-150 watts?)  Left channel into one input, right channel into a second.  Volumes of Keyboard mixer are turned up about 50%,  Soundtech mixer (which has outputs going to PA cabs) also stay at around 50%.  Do you think this might be overloading the preamp stage of the Soundtech mixer ?  I'm not sure about this stuff.

Morten, "headroom" get's into another fascinating area. ANOTHER aspect of sound physics I completely forgot EVERYTHING I ever learned.

Yet the fascinating thing about this interesting area of sound physics really came into play when I used my marshall JCM 800 100 watt tube head outdoors thru a 2x12 speaker config, VS the full stack  (8x12).

Sure the measured output might've been around 30 watts on average if measured during rock playing.  Yet that 30 watts sounds MUCH louder thru the stack, than thru a single 12 inch speaker, or a 2x12 speaker config ~

I think headroom is where you notice the real difference in the slight DB discernible rating when doing the head to head rating between the 3 DB sound difference of 50 vs 100 watt RMS rated tube head... apples to apples comparison in brand of course.

In essence you can FILL OUT a much larger area with the 100 watts given a proper speaker config.  Outdoor venues this is crucial

That goes without saying.  You can effectively double the perception of loudness by doubling the amount of speakers - hence your 4x12" vs 1 or 2x12".  Same goes with PA systems as well.

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