Music modulation with 20Hz effects

[Bazukaz]

Hi,
I have a DIY 3-way speaker system and a "gainclone" DIY amplifier.
The amp has no capacitors at its input.

Today i tried to mudulate a music signal with 20Hz sinewave.I used
spectraPLUS as a generator and Windows Media player as a sound player.The output was set at moderate listening level. The sound changed A LOT when a 20Hz signal was applied.It was quiter and more distorted.
How could this be explained ?
Note that other tones , like 30Hz , does the same effect.


Regards,
Lukas.

 

[angsuman]

What you were hearing is an extreme case of doppler distortion (someone correct me if i'm wrong here). I tried that once when i ran music through a 6in woofer and then modulated with a 20hz tone. At 30hz the cone movement is probably not even to facilliate doppler distortion. The sound is like talking into a fan.

 

[Bazukaz]

Another test i did was to set 1Hz tone ... The cone was moving without sound.Then i played some music ... The music volume was modulated by cone movement.I think it might be caused by loadspeakers , which have non-linear magnetic field and mechanical force ...

 

[maxro]

What you were hearing is an extreme case of doppler distortion (someone correct me if i'm wrong here). I tried that once when i ran music through a 6in woofer and then modulated with a 20hz tone. At 30hz the cone movement is probably not even to facilliate doppler distortion. The sound is like talking into a fan.

Actually, it's intermodular distortion (IMD). Doppler distortion is from a moving sound source, ie a train's whistle sounds higher pitched when approaching than when moving away from you.

Max

 

[pinkmouse]

Personally I would have thought it would be more likely that the PSU can't cope with the demands put on it, or the two superimposed waves are driving the amp into clipping.

 

[darkfenriz]

modulation

You mean you modulated envelope (AM) or multiplied with 20 Hz (DSB-SC)? Or just added and played together?

 

[Bazukaz]

Hi,
I simply played together. PSU cannot be the cause , because volume levels were low.

Regards,
Lukas.

 

[AndrewT]

Hi,
the sound volume level may have been low but the voltage drive to the speaker could be very high.

You just could not hear the 1Hz or 20Hz tone.

The normal music signal would be riding on the low frequency waveform.

I support Pinks thought. Clipping or severe PSU rail droop.

 

[Bazukaz]

Hi,
You were right - at even lower listening levels , the effect does not show up.However , distortion increase can be heard - probably showing that loadspeakers suffer from high IMD.

About the doppler effect - there is an article : http://sound.westhost.com/doppler.htm

 

[soongsc]

Possibly larger cone area with lower travel provides less doppler effects. I also think one should not just consider music effects just by simple signals alone. When we hear bass, we listen in terms of relationship between the initial transient and the continued resonance to determine how realistic sound is produced.

 

[darkfenriz]

Bazukaz
Do you have bass-reflex enclosure with woofer of fs>30Hz?
These enclosures are known to have problems with frequencies below resonance.
Try closing the B-R hole, just for experiment, please.

 

[Bazukaz]

No , it is a sealed 40 litter stuffed box.The woofer is 10".

Regards,
Lukas.

 

[megajocke]

If you push in the cone with your hand while playing music the same thing should happen. It is because the coil is pushed out of the gap, decreasing the magnetic force. It doesn't have anything to do with the doppler effect. It's just that the speaker is driven outside of its xmax.

 

[ManMower]

Are you sure the SpectraPLUS output file was unclipped? (And stayed below 0dBFS the whole time)