Crossover question

[billfitzmaurice]

Question for BassmanPaul and billfitzmaurice, why would turning the tweeter level down damage a crossover?
.

Possibly. What's mainly at risk is the LPad itself, as when you turn it down you divert power from the tweeter into the LPad, and too much power can toast it. Not all LPads are as large as they should be to handle the load, especially if the signal is clipped, which raises the high frequency power density and sort of goes hand in hand with why you're turning the tweeter down. Toast the LPad and the rest of the high frequency system, both the crossover and tweeter, also could be damaged.

I was envisioning one very large square cab. With the speakers arranged like the five on the dice, with the 15" in the middle.

Even though the 4x10 is the poster child for how not to build a cab this configuration is even worse, placing the tens even further apart for more severe comb-filtering and narrower midrange dispersion. It seems on the face of it a very good plan for a bass cab if you don't know how speakers work. But if you do know how speakers work, not so much.

 

[walterw]

Doesn't the L-pad present a very high impedance to the circuit, like 50 ohms or something? That would "shunt" basically all the power to the 8 ohm speaker load instead.

The lpad only works because it presents an 8ohm load or close to it throughout the range of the dial, otherwise it would be an attenuator, like a volume knob on your bass, which cuts volume by increasing resistance.

+1 Not all knobs are the same.

oops, you guys are right! L-pads are typically 50 watts, not 50 ohms. they go after the crossover, and (being 8&#937 actually take the load themselves when you turn them down.

i can't believe they would be a failure point in regular production bass cabs if turned all the way down, since being after the crossover, they're not getting a lot of juice, but billF's point about overdriven tones...

Not all LPads are as large as they should be to handle the load, especially if the signal is clipped, which raises the high frequency power density and sort of goes hand in hand with why you're turning the tweeter down.

...makes me nervous.

as somebody who likes mildly grindy ampeg/sansamp tones and hates tweeters, i now have even more reason to dislike them in cabs; turning them all the way down may not be enough!

 

[Joe Louvar]

I think this may be related ~

Here is a message I wrote to Eminence about the following -
-------------------------------
In your “Understanding Loudspeaker Data” under “Power Handling”
[Invalid or Expired Link Removed] it states “Obviously, you need to choose a loudspeaker that is capable of handling the input power you are going to provide. By the same token, you can destroy a loudspeaker by using too little power.”

Question - is this a writers error? If not please explain how “using too little power can destroy a loudspeaker”? Thank you very much. Joe
---------------------------------
Hi Joe,
This is mostly a statement for pro audio applications. The idea is to provide adequate amp headroom so that you avoid clipping the amp and sending a distorted signal to your speaker. Low power doesn't really harm speakers, but distorted signals will.
Regards

Anthony Lucas | Sr. Lab Tech
Eminence Speaker LLC
P.O. Box 360
838 Mulberry Pike
Eminence, KY 40019
----------------------------------------------------------

So, does (clipped) distorted signals really harm speakers - maybe tweeters? BS, told me it’s boloney but what do you say?

 

[walterw]

i can't believe eminence would print the myth like that!

unless they were just lazy in explaining what actually happens, where the amp that's a little too small gets driven to hard clip, whereupon the nearly double amount of power it creates might now be too big.

 

[Joe Louvar]

Huh, I don’t understand?

 

[walterw]

OK, i'll take a crack at it, and you guys check my work:

when an amp clips, it puts out way more power than it's "supposed to", like almost twice as much.

so that "200 watt amp" in full-on square wave clip may be more like "400 watts".

so if you have a "300 watt amp" on your "300 watt speaker", with nothing clipping, you'd be fine. if you put the "200 watt amp" on that "300 watt speaker", with nothing clipping, it would also be fine.

it's when you find that the "200 watt amp" isn't loud enough, and you crank it up to where it starts really clipping, that the problem happens, because now you're putting "400 watts" into that "300 watt speaker". it gets too hot for too long, and eventually dies.

the other thing is that the clipping amp is now compressed too, so it's putting out that "400 watts" all the time, as opposed to a clean amp that puts out big watts on loud hits but a lot less on the spaces in between, so the speaker can cool off between hits.

the compressed sound also makes the speaker get hot and stay hot, killing it if it gets too hot.

(all my watts figures were in quotes because there's still more to it, "RMS", "average power" "peak", and other stuff above my pay grade.)

 

[rpsands]

Distortion can definitely harm some HF devices in some situations

 

[Joe Louvar]

Yea, lets hear it because I'm at a loss.

 

[Windreaper]

I believe they mean that you can exceed the amp's rating (by quite a lot!) by driving it hard. You cannot kill a 300W speaker with a 50W amp, but an amp rated at 300W would be a different case. The distortion is not harmful per se, but the extra power that comes with it. Also the increased high frequency content that comes with high distortion can be fatal to tweeters.

 

[Joe Louvar]

Hold on I'm thinking this out and I think that has some problems.

Distortion can definitely harm some HF devices in some situations

Like if you un-plug the guitar cord out of your bass before you turnoff the amp and the surge/pop takes out the tweeter?

 

[Joe Louvar]

Ok, here is the problem - it’s been posted here over and over again that watts don’t matter but this would mean power does matter because if you overdrive (clip) the speakers you may harm them but if you have speakers with enough headroom you can run your power amp full blast - yes, no?

 

[walterw]

Also the increased high frequency content that comes with high distortion can be fatal to tweeters.

yes, and for the same reason i outlined above; you've now got way more power happening in the high-frequency zone; if it's too much for too long, the horn goes just like a speaker would.

the distortion itself doesn't matter; if it did, no guitar amps would work, and recordings of distorted sounds would blow up sound systems.

 

[Windreaper]

Ok, here is the problem - it’s been posted here over and over again that watts don’t matter but this would mean power does matter because if you overdrive (clip) the speakers you may harm them but if you have speakers with enough headroom you can run your power amp full blast - yes, no?

I believe that is mostly said in context of volume (better improve efficiency by adding speakers). It is also more like that amp ratings can be misleading as they do not tell the full story. One amp can be rated 300W at 1% THD and other 300W at 10% THD (total harmonic distortion). Still, both are technically 300W amps.

EDIT: And not to mention that manufacturers are just as creative at measuring distortion as speaker sensitivity and frequency response. Quoted from [Invalid or Expired Link Removed]

"
Caveat Emptor: THD+N is always going to be a larger number than just plain THD. For this reason, unscrupulous (or clever, depending on your viewpoint) manufacturers choose to spec just THD, instead of the more meaningful and easily compared THD+N.

Correct: THD (5th-order) less than 0.01%, +4 dBu, 20-20 kHz, unity gain

Wrong: THD less than 0.01%"

 

[walterw]

Ok, here is the problem - it’s been posted here over and over again that watts don’t matter but this would mean power does matter because if you overdrive (clip) the speakers you may harm them but if you have speakers with enough headroom you can run your power amp full blast - yes, no?

i think "watts don't matter" was about actual acoustic volume and matching cabs to amps (and was a bit of an exaggeration anyway).

this is where watts do matter, speaker ratings and speaker survival.

i don't think you "overdrive" or "clip" speakers, though; those concepts apply to amps.

you overpower speakers (too much wattage for too long, so they can't cool off);

or you over-excurt them (by giving them lower frequencies than they're meant for, pushing them too far back and forth and breaking them mechanically)

 

[will33]

Distortion carries a lot of hf content/extra power and it can take out tweeters/weak mids. That said, if they're putting out stuff like that, it's wrong. May be in an effort to keep customers from screwing things up, but it's still wrong.

 

[Joe Louvar]

I believe that is mostly said in context of volume (better improve efficiency by adding speakers). It is also more like that amp ratings can be misleading as they do not tell the full story. One amp can be rated 300W at 1% THD and other 300W at 10% THD (total harmonic distortion). Still, both are technically 300W amps.

EDIT: And not to mention that manufacturers are just as creative at measuring distortion as speaker sensitivity and frequency response. Quoted from [Invalid or Expired Link Removed]

"
Caveat Emptor: THD+N is always going to be a larger number than just plain THD. For this reason, unscrupulous (or clever, depending on your viewpoint) manufacturers choose to spec just THD, instead of the more meaningful and easily compared THD+N.

Correct: THD (5th-order) less than 0.01%, +4 dBu, 20-20 kHz, unity gain

Wrong: THD less than 0.01%"

So the only time power doesn’t matter is when we don’t know the spec’s of the power amp? Is the Genz Benz Shuttle 9.0 amp spec’s really that far off?

 

[Joe Louvar]

Cool - thank you Walter, Reaper, and Will.

 

[billfitzmaurice]

i think "watts don't matter" was about actual acoustic volume and matching cabs to amps (and was a bit of an exaggeration anyway).

this is where watts do matter, speaker ratings and speaker survival.

i don't think you "overdrive" or "clip" speakers, though; those concepts apply to amps.

you overpower speakers (too much wattage for too long, so they can't cool off);

or you over-excurt them (by giving them lower frequencies than they're meant for, pushing them too far back and forth and breaking them mechanically)

Watts don't 'matter' because watts aren't what determines either speaker output or over-excursion or over heating of the voice coil. Voltage swing does. You cannot make a direct connection between power and voltage swing either, because that would require that the load be a constant impedance. Speakers are not a constant impedance load. That's why there's no such thing as a limiter that prevents amps from providing too much power to speakers, because the power to a speaker may be 50 watts at one frequency and 500 at another. Limiters do prevent amps from providing more voltage swing than the drivers can safely handle.

i don't think you "overdrive" or "clip" speakers, though; those concepts apply to amps

Pushing a driver with enough voltage to exceed xmax does cause the driver to clip the signal, just as an amp does. Guitar drivers are made with a small xmax to allow them to clip with minimal voltage applied, ostensibly to get good tone without being too loud. Of course that intent gets derailed when guitar'd players use four twelves, if not more, and then they have to crank the bejesus out of the rig "so I can get my tone!".

 

[Windreaper]

So the only time power doesn’t matter is when we don’t know the spec’s of the power amp? Is the Genz Benz Shuttle 9.0 amp spec’s really that far off?

The rating on that amp is meaningless as long as we do not know how it was measured. And far off from what? Depends on what kind of rating the marketing department thought would look good in the brochure. Genz Benz is a reputable company, though, and would not exaggerate amp ratings like other reputable companies such as TC Electronic . But seriously, GB makes good stuff and the amp rating is at least an indicator of overall performance.

 

[walterw]

Watts don't 'matter' because watts aren't what determines either speaker output or over-excursion or over heating of the voice coil. Voltage swing does.

gotcha, the whole "amps as voltage swing producers" and "different impedances at different frequencies" thing for speakers (i'm barely holding on to those concepts by my fingernails).

doesn't "pushing a driver with enough voltage to exceed xmax" mean overexcurting it, though?