About subsonic?

[blakey72]

So, the subsonic button on my Pro-ject Phono Box DS3 B. I know it stops the woofers silently moving when you turn it up but what is it actually doing? Why do the woofers do this? Does it subtract or affect the bass response? Something I haven't used much or really thought about.  

[blakey72]

Seems like no one knows much about it. I'll have to investigate....

[wartman]

Could it be a rumble filter?

[andyr]

On 17/10/2024 at 11:48 AM, blakey72 said:

So, the subsonic button on my Pro-ject Phono Box DS3 B. I know it stops the woofers silently moving when you turn it up but what is it actually doing? Why do the woofers do this? Does it subtract or affect the bass response? Something I haven't used much or really thought about.  

 

I believe as in the above post:

 

43 minutes ago, wartman said:

Could it be a rumble filter?

 

... yes, it's a rumble filter - ie. it cuts off very low frequencies.

 

But the filter is not a "vertical line" - iow, it starts to cut off bass frequencies much higher.

 

Why do you see your woofers 'silently moving'?  I don't - so I suggest it might be the type of TT you have?  (I have a belt-drive - and my woofers don't "silently move".

 

 

[wartman]

I have seen several systems with woofers silently moving.

All had a turntable and amplifier switched to phono 

Seems to be room interactions.

Moving the TT to a different location helps.

Otherwise, a rumble filter sorts it out.

 

 

[peterjschmidt]

3 hours ago, wartman said:

I have seen several systems with woofers silently moving.

All had a turntable and amplifier switched to phono 

Seems to be room interactions.

Moving the TT to a different location helps.

Otherwise, a rumble filter sorts it out.

 

 

I believe you are correct.  It's usually a feedback look between the woofers and the stylus, much like having a microphone in front of a speaker instead of behind it.  Some say it's not really a problem that the woofers fluttering won't hurt them.

 

Mine were doing it, and because I couldn't really put my turntable out of harm's way, I installed a KAB rumble filter. It solved the problem with no audible effect on the sound.

[wartman]

25 minutes ago, peterjschmidt said:

25 minutes ago, peterjschmidt said:

I believe you are correct.  It's usually a feedback look between the woofers and the stylus, much like having a microphone in front of a speaker instead of behind it.  Some say it's not really a problem that the woofers fluttering won't hurt them.

 

Mine were doing it, and because I couldn't really put my turntable out of harm's way, I installed a KAB rumble filter. It solved the problem with no audible effect on the sound.

 

KAB rumble filters work really well.

Edited October 19, 2024 by wartman
Poor spelling.

[SonicArt]

15 hours ago, andyr said:

 my woofers don't "silently move".

My woofers move with much vigor and mumbo

[audiofeline]

My understanding is that the subsonic filter will cut very low frequencies.  If your room has sonic problems and feedback from a turntable, these low frequencies can cause excessive movement from the woofers which can contribute to less clear bass, and (I think) when extreme could risk blowing the woofers. 

 

If you don't have a turntable you probably don't need it.  If you have a turntable and your woofer's don't show this movement, you probably don't need to use it.  If you do need to use it, it's good to have! 

[BioBrian]

I remember being fascinated to see my 91 dB, 10" woofers moving in and out very slowly (in the days of using a TT).

 

If the TT revolves at 33 RPM, then that would equate with the speed of the moving woofers - ie approx 0.5 Hz (one second in, one second out). It's obviously way too slow to be a resonance, or feedback, in this case. Decades later, I put it down to warped records - makes sense to me anyway. I've never heard anyone mention it until now, if it's indeed the same phenomenon.

[audiofeline]

Yes, I believe that a warped record with a resonant arm can increase these low freq's making them dangerous for a woofer.

[almikel]

 

On 19/10/2024 at 3:25 PM, BioBrian said:

Decades later, I put it down to warped records - makes sense to me anyway. I've never heard anyone mention it until now, if it's indeed the same phenomenon.

^this

Warped records create unwanted infrasonic signals (by "infrasonic" I mean signals lower than 20Hz) that get reproduced by the stylus/tonearm/phono/amp through to the woofers.

A warped section on a record will generate a signal at 33.3 rpm / 60 = 0.55Hz - not something you want being amplified and going to your woofers!...

...especially ported woofers where below the tuning frequency of the port, woofer excursion increases dramatically.

 

Rumble filters (typically part of the phono pre-amp, but usually able to switch them on/off), stop this by providing a steep high pass filter - usually set around 20Hz or so, at least 24dB/octave or steeper roll-off.

 

An example of a rumble filter in the DIY world is Rod Elliot's - an analog high pass rumble filter at 18Hz and 36dB/octave slope (6th order).

https://sound-au.com/project99.htm

 

On 18/10/2024 at 8:48 PM, andyr said:

But the filter is not a "vertical line" - iow, it starts to cut off bass frequencies much higher.

Sure no filter is a vertical line, but I don't necessarily agree with this - an appropriately designed rumble filter - let's use Rod Elliot's design as the example - Xover frequency at 18Hz, a Q of 0.707, and 36dB/octave (6th order) - this rumble filter will be essentially flat to 36Hz, only 3dB down at 18Hz, but 36dB down at 9Hz.

This is a reasonable compromise.

 

Mike

[andyr]

5 hours ago, almikel said:

Warped records create unwanted infrasonic signals (by "infrasonic" I mean signals lower than 20Hz) that get reproduced by the stylus/tonearm/phono/amp through to the woofers.

A warped section on a record will generate a signal at 33.3 rpm / 60 = 0.55Hz - not something you want being amplified and going to your woofers!...

 

Agreed!    However, 0.5Hz is not a frequency that can be delivered by my phono stage / amplifier chain!  

 

I have a test LP which has tracks of 8Hz, 12Hz and 16Hz.  A 16Hz tone is delivered by an organ with a 32 ft pipe ... 8Hz needs a 64 ft pipe!

 

I can hear/feel the 16Hz tone ... but all I see with the 12Hz and 8Hz tones is the cantilever frantically moving from side to side ... with no sound coming from the spkrs.

 

5 hours ago, almikel said:

...especially ported woofers where below the tuning frequency of the port, woofer excursion increases dramatically.

 

Hence one shouldn't use ported spkrs!  

 

5 hours ago, almikel said:

 

Rumble filters (typically part of the phono pre-amp, but usually able to switch them on/off), stop this by providing a steep high pass filter - usually set around 20Hz or so, at least 24dB/octave or steeper roll-off.

 

An example of a rumble filter in the DIY world is Rod Elliot's - an analog high pass rumble filter at 18Hz and 36dB/octave slope (6th order).

https://sound-au.com/project99.htm

 

Sure no filter is a vertical line, but I don't necessarily agree with this - an appropriately designed rumble filter - let's use Rod Elliot's design as the example - Xover frequency at 18Hz, a Q of 0.707, and 36dB/octave (6th order) - this rumble filter will be essentially flat to 36Hz, only 3dB down at 18Hz, but 36dB down at 9Hz.

This is a reasonable compromise.

 

I'm not prepared to accept this compromise!  Luckily, my TT does not cause my subs to flap, un-necessarily.

 

[almikel]

On 22/10/2024 at 8:46 PM, andyr said:

but all I see with the 12Hz and 8Hz tones is the cantilever frantically moving from side to side ... with no sound coming from the spkrs.

I wouldn't expect to hear sound, but do you see your sub drivers moving with the 12Hz and 8Hz tones?...I would expect you should, unless high pass filtering is happening somewhere in the chain.

 

On 22/10/2024 at 8:46 PM, andyr said:

I'm not prepared to accept this compromise!  Luckily, my TT does not cause my subs to flap, un-necessarily.

possibly you have accepted the compromise without realizing if your cantilever frantically moves on 12Hz and 8Hz tones but your sub drivers don't move?

 

cheers,

Mike

[andyr]

2 hours ago, almikel said:

I wouldn't expect to hear sound, but do you see your sub drivers moving with the 12Hz and 8Hz tones?...I would expect you should, unless high pass filtering is happening somewhere in the chain.

 

Well, yes - as my phono stage and power amps are not DC-coupled ... they have an intrinsic VLF roll-off!  And the digital items in my signal chain (A2D converter and DACs) are also specced for a 20Hz lower limit, right?

 

I believe it is this that is making the 12Hz and 8Hz organ tones inaudible, in my system.

 

[almikel]

@blakey72 - apologies this is going a little off topic - but it has some relevance, as I've just got a TT running in my system connected to the analog input on my DEQX.

 

On 26/10/2024 at 5:34 PM, andyr said:

And the digital items in my signal chain (A2D converter and DACs) are also specced for a 20Hz lower limit, right?

 

That's a really good question I can't answer - @Keith_W is far more knowledgeable than myself in this space.

 

I know with digital you can lose resolution at lower frequencies, and for digital filtering you need more taps and computing power at lower frequencies for the same "steepness" of filter compared to higher frequencies.

 

I'm unsure what happens for ADCs and DACs if an audio signal lower than 20Hz is attempted to be processed?

@Keith_W - can you shed any light?

 

cheers,

Mike

[Addicted to music]

The reason why most electronics are spec out to 20hz is that you are unable to hear below 20Hz,  not that you won’t feel it!   
Usually electronics are DC decoupled  is to prevent DC getting from one stage to another that requires a very different DC level,  especially between amplifier stages as you do not want DC to be effected between the stages and also be amplified,  and I’m sure you do not want any DC downstream to your speakers that can do severe heat damage 
With digital,  the higher analog frequencies the higher the sampling rate to reduce sampling errors.  

[Keith_W]

21 hours ago, almikel said:

I'm unsure what happens for ADCs and DACs if an audio signal lower than 20Hz is attempted to be processed?

@Keith_W - can you shed any light?

 

Hi Mike, the answer is pretty simple. 44.1kHz PCM is capable of sampling and reproducing any frequency below half the Nyquist frequency, or 0Hz - 22.05Hz. The reason we have 20Hz - 20kHz is because of the RBCD (red book CD) specification. I believe that the 20Hz limit is only there to protect woofers from subsonic frequencies. Test this yourself - use REW to generate a 0.5Hz sine wave and send it to your DAC (with amp and speakers disconnected!). Measure the output on an oscilloscope or voltmeter and you will see output. Maybe a 0.1Hz output if your voltmeter is too slow. DAC's should handle it just fine. 

[almikel]

On 02/11/2024 at 5:28 PM, Addicted to music said:

Usually electronics are DC decoupled  is to prevent DC getting from one stage to another

This is AC coupled - ie so DC doesn't get through.

DC coupled means the dc does get through to the next component - which is avoided in audio

 

On 26/10/2024 at 5:34 PM, andyr said:

And the digital items in my signal chain (A2D converter and DACs) are also specced for a 20Hz lower limit, right?

not the case according to Keith - your ADCs and DACs will process very low frequencies...but given they're likely to be AC coupled also, AIUI there will be rolloff similar to your phono and power amps (much lower then 20Hz).

 

cheers,

Mike

[almikel]

On 03/11/2024 at 11:05 AM, Keith_W said:

0Hz - 22.05Hz.

you left out a "k"...22.05kHz 

Edited November 4, 2024 by almikel

[andyr]

1 minute ago, almikel said:

DC coupled means the dc does get through to the next component - which is avoided in audio

 

Correct!  

 

1 minute ago, almikel said:

not the case according to Keith - your ADCs and DACs will process very low frequencies...but given they're likely to be AC coupled also, AIUI there will be rolloff similar to your phono and power amps (much lower then 20Hz).

 

Agreed - Keith is correct.

 

But, as I said ... I think the intrinsic roll-off of my AC-coupled phono stage - plus the fact that:

• I have a belt-drive TT
• with a quality bearing
• and I don't have warped LPs

 

... means I don't experience spurious woofer movement.