~20 years ago when Manhattan still had several audiophile stereo equipment stores, I got kicked out of one for playing my own score (I'm a sound designer for contemporary dance and back then mostly made mixes of recorded natural sound). The owner yelled at me for playing "warble tones". Not sure why I'm thinking about it today, but I finally looked up what a warble tone is and I can't figure out how that kind of sound could possibly damage any equipment, certainly not any more than another sound of equivalent energy. Also not finding any stories of blown speakers attributed to warble tones. I've always thought the owner's reaction was ignorant, but maybe someone has some insight?

Edit: I mean, if he had said "dude, get out of here, your music is awful and driving away customers" that would've made more sense.

Sounds BS to me. DC would damage speakers but you can't detect DC by ear (for obvious reasons).

Interestingly, though, FM easily suffers from DC while phase modulation seems not to, at least for ratio >= 1.

23-0515-fm-pm.pd

hjh

@ddw_music Definitely interesting. It's too late for me to think clearly about this, but if we stipulate that people can't hear the relative phases of harmonics, then shouldn't there be some arrangement of a given tone's harmonic's phases such that the DC component is maximal (I'm thinking of all the times I got the ramp wave wrong using additive synthesis)? And that that tone would be indistinguishable from the original? And so any sound could potentially have dangerous gear-eating DC components lurking within it? And so the best course of action if you own precious audiophile components is to never listen to anything?

@jameslo From what I understand a warble tone is a beat frequency and an amplifier which does not limit low frequencies can kill speakers because outside of sub woofers most speakers can not deal with the sort of extension required by those frequencies for very long. A midrange or fullrange speaker can not reproduce a 4hz waveform directly but can reproduce it as a beat frequency, in most music a beat frequency is a fairly brief thing and causes little grief to a speaker but when they are maintained or exploited they quickly cause either over extension or heat build up in the coil (depends on the speaker) which are not good things for speakers. It is really easy to kill a speaker if you know how, even if it is rated for 120 watts and is only being driven by 10.

@jameslo said:

if we stipulate that people can't hear the relative phases of harmonics, then shouldn't there be some arrangement of a given tone's harmonic's phases such that the DC component is maximal

This actually isn't true. The integral of a sine wave is always 0. The sum of the integrals of multiple sinusoidal components, then, must also be zero.

If you have extremely low frequency components, like 1/10 Hz, then at any given moment, that component's contribution in the short term may resemble DC and may be just as harmful to speakers as DC. But this isn't a harmonic component of a tone whose fundamental is audible, so it's not properly part of the "tone" that you mentioned.

True DC must have frequency = 0, which isn't a harmonic of anything (but which is necessary in Fourier analysis to account for an average offset away from the zero line).

That's interesting about the warble tones as beating, like an amplitude modulation artefact. EDIT: I'm having trouble, actually, finding a consistent definition of "warble tones." Some sources refer to frequency modulation, while others say it's amplitude modulation consistent with oid's post. That's not making it easier to evaluate the claims.

hjh

@jameslo All equipment manufacturers state " Maximmum RMS, or maximum peak music power (4x RMS), and no warble tones".... we rarely read the small print though....
Few include DC protection. I recently destroyed an old pair of powered studio speakers by "mis-connecting" a DI box..... 48V on just one leg of the balanced mic input (modern...? transformerless) produced a lovely acrid whiff of melting coil and a very pretty cloud of smoke. Even subs are destroyed in seconds without cooling movement..... the glue and varnish melt.
When I had my own sound reinforcement company we added very large electrolytic capacitors to the inputs of all our loudspeakers..... the only place where DC protection would always be effective, as when sub-renting we could not know what amplifiers would be used..... and many were prone to output stage shorting in the early mosfet era.
In Pd..... almost all of the help-files with a [dac~] output include a [hip~].
David.

I admit to some ignorance here.

Beating is the result of producing sine waves at near frequencies. It's the same as amplitude modulation: mixing two sine waves at 1000 and 1100 Hz has the same spectrum as a sine wave at 1050 Hz times a sine at 50 Hz. The amplitude is beating at 100 Hz, but, conspicuously, 100 Hz is absent from the FFT. If sub frequencies aren't seen in the Fourier transform, then they just aren't there -- there is no energy present in that range.

You could do 1000 Hz * 996 Hz and this would produce 4 Hz + 1996 Hz... but this won't sound like a warble. One of the sines is too low to be audible; the other will be steady at a much higher frequency.

Also that conflicts with the definition: "A tone whose frequency varies periodically several times per second over a small range" -- slow FM likewise doesn't produce sub-audio frequencies. Even with the modulator at, say, 30 Hz -- to get sidebands extending down to 4 Hz would require a very high modulation index.

So a speaker-destroying warble tone is not simple beating / amplitude modulation, and it isn't simple frequency modulation at a slow rate.

The only technical specifications of a warble tone that I can find are circuit diagrams, but I'm afraid I'm quite unfamiliar with those.

So at present, I've been unable to find any digital technique that warbles and produces massive low-frequency energy. It seems there's a legit thing here but surprisingly I'm finding it hard even to find BS online. There's just... no technical detail at all, not even wrong tech.

hjh

@ddw_music said:

The integral of a sine wave is always 0. The sum of the integrals of multiple sinusoidal components, then, must also be zero.

Oh duh. I guess I was hell bent on making that joke

@whale-av

All equipment manufacturers state " Maximmum RMS, or maximum peak music power (4x RMS), and no warble tones"

I can't tell if that was a joke...I've never seen that statement.

@ddw_music said:

I also admit some ignorance here and I suspect we are going to enter the clashing worlds of digital and analog, the brutal absolutes of the digital world are alien to my analog sensibilities where we can just ballpark it and generally get closer to the real world result than the math would get us and get there in a fraction of the time (talking circuit design and the like here, not physics). And like you I am not 100% certain what is meant by warble tone, I based my answer on what was likely to kill a speaker which assumes the salesman that scolded jameslo had a clue.

One of the sines is too low to be audible

How does the amplifier and speaker know what is audible? We can hear the tremolo effect of this beating so the speaker has to be moving at that rate and those tones we hear as tones are moving on top of that beating, the 4hz looks sort of like a carrier frequency as far as the speaker is concerned. Beat frequencies can cause large extension to the point of over extension (voice coil pops out of the gap) and sustained beat frequencies of these low frequency sorts can cause heat to build up in coil faster than it can dissipate it leading to warping. Getting a good strong beat frequency going and feeding it into a speaker with decent extension will let you see that beat frequency, change one oscillator to half or double the frequency of the other so there is no beating and it will barely move, just a nice even tremble. This of course is dependent on the frequency characteristics of the entire setup but generally if you get one of those beat frequencies going that you can feel than you will be able to see it in the speakers movement.

Beating can be produced from any waves, not just sines.

@oid said:

@ddw_music said:

One of the sines is too low to be audible

How does the amplifier and speaker know what is audible? We can hear the tremolo effect of this beating so the speaker has to be moving at that rate and those tones we hear as tones are moving on top of that beating...

Perhaps, but when I checked standard sine vs sine amplitude modulation (ring modulation), any subaudio energy was too low to be detected, nowhere near loud enough to burn anything. There might have been some subaudio energy but it must have been at least 70-80 dB below the upper frequencies.

EDIT: SuperCollider's freqScope shows a peak up to 0 dB around 440 Hz, and low-frequency energy hovering around -80 or -90 dB for SinOsc.ar(440) * SinOsc.ar(4):

That's some subaudio but still much quieter than the sine waves.

hjh