Low resonances create IM products that no filter can ever remove.
The lower Fres, the stronger these IM products, where 10Hz should be seen as an optimum according to several studies, amongst them B&K.
Hans
I have a badly warped Manhattan Transfer LP. I used it as a demo on my commercial pre that has a 25 Hz switchable rumple filter. Amazingly, the arm/cart combo can play it perfectly. If the filter is switched out, the cone flap is astounding. With the filter in, perfect sound. I’ll have to post a video up sometime.
Indeed, using a good filter to eliminate feedback and rumble lets you enjoy your music and system a lot more.
No one needs a system to respond to sub-sonic noise anyhow.
And as I previously mentioned, the amp can then concentrate all its power on what you can hear.... the music.
We are discussing two completely different things:
1:rumble caused by warp, which can be removed with a rumble filter
2:IM products caused by Fres of arm/cart combination, which can never be filtered.
But the more below Fres below 10Hz, the stronger these IM products become.
In the image below, a 1Khz test tone is recorded with my PU, clearly showing all multiples of +/- Fres.
Hans
.
1:rumble caused by warp, which can be removed with a rumble filter
2:IM products caused by Fres of arm/cart combination, which can never be filtered.
But the more below Fres below 10Hz, the stronger these IM products become.
In the image below, a 1Khz test tone is recorded with my PU, clearly showing all multiples of +/- Fres.
Hans
.
Attachments
The various subsonic interfererences, while being born due to different specific conditions, all can be be reduced to levels that do not interfere with musical enjoyment.
Warp record frequency causes woofer pumping, we all know that.
Feedback howling due to spring suspension type turntables and/or cabinet vibrations also eat up amplifier power.
And any resonances of subsonic nature due to tonearm/cartridge interaction also can interfere with listenable music.
The Sallen-Key sub filter that I discussed earlier effectively deals with all these nasty products that live below hearable frequencies - the lower the frequency, the deeper it's buried into oblivion.
The 4 devices that I've built so far have proven that fact in their specific situations.
Dimitri,
I have never really tried to find an explanation, but it may have to do with the fact that the lower the frequency, the larger the excursion.
I read this for the first time in a B&K test that was performed many years ago, and came across several times after that.
If you want I can retrieve the original B&K paper and post it here.
Hans
I have never really tried to find an explanation, but it may have to do with the fact that the lower the frequency, the larger the excursion.
I read this for the first time in a B&K test that was performed many years ago, and came across several times after that.
If you want I can retrieve the original B&K paper and post it here.
Hans
The reason for this is that the rumble filter almost always comes after the EQ amp - by that time the damage is done and the Fres components have been folded up into the audio band. There are some clever (but probably not too quiet) circuits that incorporate the rumble filter into the RIAA that may address this issue.
The original breakpoints (3180us, 318us and 75us) were set out in IEC 98 (1964). The 7950us breakpoint (20 Hz roll off to suppress arm/cart resonance and other LF anomalies) was only introduced as an amendment in 1976. I don't know when the B&K paper was published, but it may have been before this so this is why they say it is worse the lower Fres
However, the IMD components are very low level, and probably well buried in the noise floor once the stylus hits the vinyl.
There is a lot of material out there supporting the c. 10Hz Fres frequency - this was discussed in the thread with LuckyDog, George, Bill Shurv et al. I only use the rumble filter for cone flap and, when switched to 45 Hz (40 dB/decade) to suppress the acoustic rumble on classical recordings. It will not for example fix off-centre record introduced LF anomalies because those come through as frequency modulation of the music signal (maybe this was also covered in the B&K paper?)
The original breakpoints (3180us, 318us and 75us) were set out in IEC 98 (1964). The 7950us breakpoint (20 Hz roll off to suppress arm/cart resonance and other LF anomalies) was only introduced as an amendment in 1976. I don't know when the B&K paper was published, but it may have been before this so this is why they say it is worse the lower Fres
However, the IMD components are very low level, and probably well buried in the noise floor once the stylus hits the vinyl.
There is a lot of material out there supporting the c. 10Hz Fres frequency - this was discussed in the thread with LuckyDog, George, Bill Shurv et al. I only use the rumble filter for cone flap and, when switched to 45 Hz (40 dB/decade) to suppress the acoustic rumble on classical recordings. It will not for example fix off-centre record introduced LF anomalies because those come through as frequency modulation of the music signal (maybe this was also covered in the B&K paper?)
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Typical record warp frequencies peak around 5-8 Hz, so a cartridge - arm resonance near that range is pretty much a worst case scenario.
Actually, this IM is a mechanical phenomenon. Once the record groove modulation has been modulated by the warp frequency, that’s it. The location of the rumble filter doesn’t matter.
Shure recommended an arm resonance above 10 Hz , 10-12 Hz. B&K, even higher.
Here’s a link to Landegaarde’s paper:
https://www.theanalogdept.com/images/spp6_pics/TT_Design/MechanicalResonances.pdf
Anyone interested in an arm - cartridge interface done right should look up Ben Bauer’s integrated arm cartridge designed for Shure back in the 1959s.
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ok, from attached article:
"An unfavorable tonearm cartridge combination can also unfold in an adver-
se bass resonance, which results from the compliance of the cartridge (spring) and the effective mass of the tonearm.
The bass resonance should ideally be 10 Hz, but any value between 8 and 12 Hz is considered acceptable. If the resonance is too deep, for example when combining a magnetic systems with soft suspension with a heavy tonearm, the cartridge will attempt to track the record warps at 1.8 to 5.4 Hz. This leads to periodic distortions, due to the large cantilever deflections when the diamond tip immerses into the cartridge body and
emerges out again. In contrast, an exceedingly high resonance frequency – such as when a stiff suspension MC system operates in a light tonearm – results in a raising response towards the lowest frequencies. The result will be a boomy, uncontrolled bass."
However Fig.8 shows resonance at 22Hz. Also I don't think that AP can measure from 1Hz
"An unfavorable tonearm cartridge combination can also unfold in an adver-
se bass resonance, which results from the compliance of the cartridge (spring) and the effective mass of the tonearm.
The bass resonance should ideally be 10 Hz, but any value between 8 and 12 Hz is considered acceptable. If the resonance is too deep, for example when combining a magnetic systems with soft suspension with a heavy tonearm, the cartridge will attempt to track the record warps at 1.8 to 5.4 Hz. This leads to periodic distortions, due to the large cantilever deflections when the diamond tip immerses into the cartridge body and
emerges out again. In contrast, an exceedingly high resonance frequency – such as when a stiff suspension MC system operates in a light tonearm – results in a raising response towards the lowest frequencies. The result will be a boomy, uncontrolled bass."
However Fig.8 shows resonance at 22Hz. Also I don't think that AP can measure from 1Hz
ok got it - so once its happened it's game over from the IMD perspective. There's nothing you can do about that in the electronics if the source signal is already corrupted.
In my opinion that is absolutely wrong.
If you ask me I would say that the rumble filter should be placed as soon as possible in the chain.
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Hans
Pretends to be German, but:
Fone number is outside Germany or not existent.
No impressum found.
edit: too late!
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Two different topics.
I was addressing the effect that location of the rumble filter will have on IM sidebands. Clearly, it doesn’t matter.
With respect to headroom it would be helpful to filter out LF below the audible range, but it’s not clear to me how that could be done in the front end without comprising noise, especially in an MC pre-preamp.
The best solution is, of course, to use an arm cartridge combo with a sensibly high resonance.
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