Forums > MaxMSP

constant amplitude: advices needed


f.e
September 24, 2008 | 7:50 am

Dears,

I use a basic loudspeaker (mid-range) as a mechanical device acting like
a piston engine. A sine at low frequencies (from 0. to 6. max) does the
job.

have a problem keeping a constant amplitude. The higher the frequency,
the higher the amplitude on the loudspeaker. Is it normal (because i
play LFOs in a mid-range speaker) ? If not, how does it happend that
normalize~ doesn’t do the job ? What is the smart way to keep a constant
amplitude on my speaker ?

Best wishes

f.e


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kjg
September 24, 2008 | 11:17 am

I wouldn’t expect a smallish (or any) loudspeaker to have a somewhat "flat" response to frequencies that low (and/or frequencies out of its designed range).
In such case I expect "efficiency" to get lower and lower the closer you get to DC. Normalizing the signal won’t help you much either because the problem lies more in how the speaker/coil/magnet assembly translate that signal (normalized or not) into movement, and it not doing it at the same efficiency at different frequencies.

Could you just scale the amplitude of the signal down with higher frequencies, so the movement of the speaker (instead of the signal sent) to the speaker remains constant?

I guess you could manually create a lookup for the amplitude scaling factor after testing at different frequencies, and then tweak it a bit for perceived "smoothness" when sweeping to the range, right?

Hope this helps.
Klaas-Jan


September 24, 2008 | 2:59 pm

>Dears,
>
>I use a basic loudspeaker (mid-range) as a mechanical device acting
>like a piston engine. A sine at low frequencies (from 0. to 6. max)
>does the job.
>
>have a problem keeping a constant amplitude. The higher the
>frequency, the higher the amplitude on the loudspeaker. Is it normal
>(because i play LFOs in a mid-range speaker) ? If not, how does it
>happend that normalize~ doesn’t do the job ? What is the smart way
>to keep a constant amplitude on my speaker ?
>
>

not sure at all but what if you over-amplify your signal in max, and
then appply a "brickwall" limiter at the last stage????

you would always have the same level (or so it seems to me)

best

kasper



kjg
September 24, 2008 | 3:03 pm

Quote: Kasper T Toeplitz wrote on Wed, 24 September 2008 16:59

> not sure at all but what if you over-amplify your signal in max, and
> then appply a "brickwall" limiter at the last stage????

Wouldn’t this present an even heavier load to the speaker which is already suffering "abuse"? It seems to me like a great way to burn the voicecoil.. Also, what about the harmonics generated?

regards
kjg



f.e
September 24, 2008 | 3:31 pm


September 24, 2008 | 4:27 pm

>Quote: Kasper T Toeplitz wrote on Wed, 24 September 2008 16:59
>
>> not sure at all but what if you over-amplify your signal in max, and
>> then appply a "brickwall" limiter at the last stage????
>
>Wouldn’t this present an even heavier load to the speaker which is
>already suffering "abuse"? It seems to me like a great way to burn
>the voicecoil.. Also, what about the harmonics generated?
>

maybe maybe… but then what i said was to limit eh max output – not
to send an hyper-amplified signal (basically to do what is often done
in dance CD’s – overcompress)

well, that was just an idea……

kasper



kjg
September 25, 2008 | 2:35 am

yes i see. but that would compare to just sending a square wave, right? the speaker would "pulse" x times per second with every zero crossing. lots of loud harmonics. could be cool, actually. but noisy for sure.

and i’d be woried bout the life of the speaker. i suspect that the speaker might give in soon though, but maybe if only in short bursts… so the voice coil can cool down in between?


September 25, 2008 | 4:26 pm

f.e schrieb:
> I use a basic loudspeaker (mid-range) as a mechanical device acting like
> a piston engine. A sine at low frequencies (from 0. to 6. max) does the
> job.
>
> have a problem keeping a constant amplitude. The higher the frequency,
> the higher the amplitude on the loudspeaker. Is it normal (because i
> play LFOs in a mid-range speaker) ? If not, how does it happend that
> normalize~ doesn’t do the job ? What is the smart way to keep a constant
> amplitude on my speaker ?

First you need an audio interface capable of putting out DC.
Second, speakers form a physical object with their environment, and
normalize~ doesn’t know anything about it, it just pulls out the correct
voltage and assumes it will be translated precise…
As a speaker is a swinging resonating object, you need much less effort
for a specific amplitude, when the speaker is "swinging". To get the
same amplitude with DC might burn the coil of the speaker, its not
really made for that, be careful…

Stefan


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