Bad Clipping vs Good Clipping (in bass amps)

[Drummer4gc]

Hi all, I'm sort of new to bass and bass amps, and I'm hoping to better understand why amplifier clipping can be bad for bass speakers and in what contexts. There is a lot of talk out there on forums about clipping and speakers, but much of it seems to be opinion, unclear, or incorrect.

So - general consensus seems to be "pre-amp clipping good, power amp clipping bad". If there is accuracy in this statement, can someone help me understand why? It seems to me that a preamp clipped to square wave and then cleanly amplified is pretty much the same as a square wave caused by the power amp hitting it's limit.

Then, there is again this understanding that this applies to solid state amplification, but it's cool to run tubes into clipping. Again, what's the reason? an overdrive pedal in front of the amp is solid state clipping, so I don't see a difference between that and overdriving the preamp.

For a specific example: I've got an Acoustic 270 which I play guitar and bass through. It starts clipping pretty early with a guitar or bass with modern "hotter" pickups. As there is a single volume knob, not a gain/master volume setup or any modern clipping LEDs or any of that, it's tough for me to tell what's preamp clipping and what's clipping the power amp. With guitar, I don't really care - I think it sounds pretty good as the whole thing gets loud and distorts. With bass, where is the line between oldschool overdrive and something that is going to damage my speakers?


Thanks!

[J M Fahey]

Hi all, I'm sort of new to bass and bass amps, and I'm hoping to better understand why amplifier clipping can be bad for bass speakers and in what contexts.

Amplifier clipping puts out *a lot* of power into the speakers.
Not only a squarewave has up to double RMS power than same peak value sinewave, but clipping kills dynamic range, output level becomes closer to a "continuous tone" , not leaving gaps or pauses for the voice coils to cool a little, result is thermally devastating to speakers.

You end up with voice coils looking such as these:



with the one on the left being "not that bad"
compared to what I often find when reconing speakers

now thatīs a crispier one:


which after being subject to wild slapping and thumping becomes:


and a couple minutes later:

There is a lot of talk out there on forums about clipping and speakers, but much of it seems to be opinion, unclear, or incorrect.

you bet, lots of people "must" write something, even if little or no clue.

So - general consensus seems to be "pre-amp clipping good, power amp clipping bad". If there is accuracy in this statement, can someone help me understand why?

Not too sure about that very wide blanket statement.
All I can think is that power amp clipping can destroy voice coils as I showed above, because it guarantees maximum thermal output , while pedal/preamp distortion used as an effect, does not necessarily imply maximum punishment.
But not sure they go that deep, sounds more like "I read it somewhere" or "it happened to a friend of a friend" type knowledge.

It seems to me that a preamp clipped to square wave and then cleanly amplified is pretty much the same as a square wave caused by the power amp hitting it's limit.

Maybe, it depends on where is that clipping happening.
If at preamp end and then straight to speaker, yes; if earlier or even in a pedal, it goes through a lot of stages, none really flat, and squarewave can turn into "anything".
So it depends on each particular case.

Then, there is again this understanding that this applies to solid state amplification, but it's cool to run tubes into clipping.

In general SS amps are quite more damaging speakers for a couple reasons, which are easy to understand:
1) SS amps can be way more powerful.
Notice what it takes to get 300W RMS out of a tube amp (which is usually closer to 250W RMS or so): an old air conditioner size and weight head, only one in wide use (Ampeg SVT) and only a couple competitors, way less popular.
Even if full clipped, it wonīt put much more than 400/450W squarewave into speakers.
Couple that to being used with 8 speakers sharing the load, they can be relatively safe even under constant Tour duty.

Now 300W RMS are a piece of cake for an SS amplifier, with many 400/500/700 and even 1000W RMS being available.
And often driving just a couple 15" speakers, or one or 2 4 x 10" ones, best case.
Now the battlefield is full of casualties.

2) Tube amplifiers use Output Transformers which never ever pass DC through and sweat a lot just reaching down to 40Hz , while SS amps can happily deliver **deep** lows if pushed ... and straight DC when they are damaged.

A particularly deadly combination are the new brick sized Class D amplifiers: 300 to 500W seems to be the norm, their diminutive size makes them look harmless, and worst of all; users have a "now I have conquered size" mentality and want 500W RMS 2 x 10" speakers.
I am *flooded* with such requests, always suggest at least a 4 x 10" ... or two .... , but Musicians want matchbox sized speakers.
I have a batch of 100 new speakers being zinc plated by now, so in a couple weeks Iīll be offering new high power cabinets ... lots of doubts about that.
Fear a tsunami of sales ... followed by "I burnt my Fahey cabinet" a few Months later.
Oh well.

Again, what's the reason? an overdrive pedal in front of the amp is solid state clipping, so I don't see a difference between that and overdriving the preamp.

Both are basically the same, "an effect", but lighter than power amp clipping.

For a specific example: I've got an Acoustic 270 which I play guitar and bass through. It starts clipping pretty early with a guitar or bass with modern "hotter" pickups. As there is a single volume knob, not a gain/master volume setup or any modern clipping LEDs or any of that, it's tough for me to tell what's preamp clipping and what's clipping the power amp.

You are certainly clipping the power amp.
But itīs not *that* powerful amp compared to modern ones.

With guitar, I don't really care - I think it sounds pretty good as the whole thing gets loud and distorts. With bass, where is the line between oldschool overdrive and something that is going to damage my speakers?

In your case, speakers suffer "thermally" as much with a clipped Guitar as with a clipped Bass, so if they stand one, they stand the other.
And you do not tell us which cabinet you are using, or speakers inside it

EDIT: some images from the excellent Rodd Elliott site which I suggest you visit.
Chock full of no nonsense information there: http://sound.whsites.net/articles/speaker-failure.html

[Justin Thomas]

I was hoping you'd chime in, Juan...
The answer? Well, <MY> answer is a low-powered tube amp with "real" speakers (paper, glue, and EFFICIENT) for my bass... I get WAY more complaints about my 50W Bassman being too loud through a 68 Fender 2x15" than I ever got with a megawatt bass amp with "bass" speakers.

<Rant-Mode ON>
Dear bass players: we're going the wrong way! When did anyone ever need more than an SVT pushing a fridge cab or two, anyway? Besides - your apeakers will thank you. I'll keep toting around my Bassmans (50 &100W) and getting whiny complaints from "sound guys" about being too loud & compliments from audiences about sounding "clear, defined, & phenomenal." Tubes rule, even for bass, keys, & vocals. When people stop complimenting, maybe I'll change my mind.

<Rant-Mode OFF>

Justin & Jusrin

[Enzo]

I think "starts to clip" is worth thinking about too. When an amp starts to clip, it doesn't automatically turn everything into square waves. Clipping the tops off waveforms still leaves plenty of waveform.

And the whole clipped preamp into clean power amp versus clean preamp into clipping power amp being equivalent, well, they are not. I can hard clip a preamp, and then set the power amp master for oh half a watt. That stresses nothing. Not at all the same as cranking the power amp into oblivion.

[Helmholtz]

Chock full of no nonsense information there: http://sound.whsites.net/articles/speaker-failure.html

Thanks a lot for this excellent piece of serious information!