How to change the decay time of a spring reverb tank?

[abbey road d enfer]

Not water, but mineral oil. Nonconductive

The problem for a plate is that adding a fluid changes drastically the moving mass, which results in considerable reduction of displacement.
This is a well-known phenomenon with submarine loudspeakers (hydrophones).
OTOH, the torsional movement of a spring should not be affected too much.

 

[zaldiar]

Very interesting question. What about a counter reaction, either electronic (out-of-phase re-injection with a low pass filter), or electro-mechanical (like in the Fernandes Sustainer guitar= magnetic-feedback system, but out-of-phase)?

 

[abbey road d enfer]

Very interesting question. What about a counter reaction, either electronic (out-of-phase re-injection with a low pass filter), or electro-mechanical (like in the Fernandes Sustainer guitar= magnetic-feedback system, but out-of-phase)?

This has already been answered.
See post #16.
Negative feedback requires a minimum-phase feedback network, which a reverb tank is not.
Positive feedback works only till oscillations occur, but even before the resonances become unmanageable.

 

[U-47]

Back in the day we would take needle nose pliers and twist a few inches in from the end on the reverb spring , effectively shortening the reverb time. While your way is more ingeneous, sometimes the physical way can give good results?

 

[Admiral-dk]

If you look at Fenders Standalone Reverb Unit, you will discover that the *Dwell Time Pot' only changes the Level off the signal going to the Tank - but the result is a change in the Time it takes before the Signal dies out on the Reciever side and therefore the Damping og the Reverb in a sense. Funnylli enough, it does not change the Output Level by much.
It kind of makes sense in the fact, that the harder you 'Excite the Springs' - the longer this Signal bounces forth and Back in the Tank.

Per

 

[abbey road d enfer]

If you look at Fenders Standalone Reverb Unit, you will discover that the *Dwell Time Pot' only changes the Level off the signal going to the Tank - but the result is a change in the Time it takes before the Signal dies out on the Reciever side and therefore the Damping og the Reverb in a sense. Funnylli enough, it does not change the Output Level by much.
It kind of makes sense in the fact, that the harder you 'Excite the Springs' - the longer this Signal bounces forth and Back in the Tank.

Per

From which we can conclude that Dwell is not reverberation time. It's just a control that duplicates more or less the Wet/Dry control.

 

[abbey road d enfer]

If we exclude teh AKG BX series that are impossible to recreate, there are are 3 spring rverbs that are worth studying:

• The Orban 111B, which time is not adjustable
• The MicMix, which was somewhat adjustable via compressor/expanders
• The Fairchild 658b

The latter has a 3 position switch that selects pairs of tanks with different characteritics. I believe there is a better usage with a mixer that would allow soft transition between tanks.
I believe the reason Fairchild chose switches is that they used their standard gain blocks that were quite expensive, but today a 5534 takes very good care of the return signals from the tanks.

 

[sdimond]

It is interesting to me that this discussion has gone on this long with no mention of the identifying characteristic of spring reverb: the dispersion of the audio signal as it travels through the spring. It would be easier to build an alterable dispersion device in DSP.

 

[rock soderstrom]

Back in the day we would take needle nose pliers and twist a few inches in from the end on the reverb spring , effectively shortening the reverb time. While your way is more ingeneous, sometimes the physical way can give good results?

Interesting, especially since the short (decay1) reverb tanks are very hard to come by.
Can you please explain this a bit more?

 

[rock soderstrom]

If we exclude teh AKG BX series that are impossible to recreate, there are are 3 spring rverbs that are worth studying:

• The Orban 111B, which time is not adjustable
• The MicMix, which was somewhat adjustable via compressor/expanders
• The Fairchild 658b

The latter has a 3 position switch that selects pairs of tanks with different characteritics. I believe there is a better usage with a mixer that would allow soft transition between tanks.

Thanks for info! In my current design, I also use a toggle switch for the tanks. In the next one I will integrate a mixer for the different tanks, that is definitely more flexible!

 

[rock soderstrom]

It is interesting to me that this discussion has gone on this long with no mention of the identifying characteristic of spring reverb: the dispersion of the audio signal as it travels through the spring. It would be easier to build an alterable dispersion device in DSP.

Thanks for your post, I don't really understand it though. Do you want to recreate/simulate the whole reverb spring in DSP or would that be meant as an addition for the decay control?

 

[trobbins]

Maybe a wink could be given to how speaker voice coils and magnet assemblies use liquid magnetic damping. Perhaps the magnetic 'gap' would be impractically large, or the liquid characteristics too viscous, or .....

 

[abbey road d enfer]

Maybe a wink could be given to how speaker voice coils and magnet assemblies use liquid magnetic damping. Perhaps the magnetic 'gap' would be impractically large, or the liquid characteristics too viscous, or .....

There is a major difference between loudspeakers and reverb tanks. Loudspeakers produce longitudinal movement when reverb tanks produce torsional movement. Addition of a damping fluid results in significant forces for the former, when the latter is almost unaffected.

 

[abbey road d enfer]

It is interesting to me that this discussion has gone on this long with no mention of the identifying characteristic of spring reverb: the dispersion of the audio signal as it travels through the spring. It would be easier to build an alterable dispersion device in DSP.

Easier to whom?
Not for me certainly.
There are several manufacturers that produce digital emulations of spring reverb, either in hardware or software, even Accutronics, the flag bearer of spring reverb, have DSP-based tanks; but where's the fun?
https://www.tubeampdoctor.com/en/btdr-3-accutronics/belton-digi-log-reverb-horizontal-new?c=62

 

[rock soderstrom]

Easier to whom?
Not for me

Indeed, DSP programming is far away for a tube hobbyist like me.

BTDR-3 sounds good but the real thing is better. This is also true for all the simulations I have heard ITB so far.

but where's the fun?

Exactly

 

[abbey road d enfer]

BTDR-3 sounds good but the real thing is better. This is also true for all the simulations I have heard ITB so far.

I believe the real value in the BTDR3 is in the fact that you don't have to replace the tank after a few weeks on the road.

 

[rock soderstrom]

I believe the real value in the BTDR3 is in the fact that you don't have to replace the tank after a few weeks on the road.

That, the size and the superior price-performance ratio.

My (DIY) tip: Wampler Faux Spring Reverb pedal.

http://effectslayouts.blogspot.com/2016/03/wampler-faux-spring-reverb.html?m=1

 

[alphasnk]

the BTDR3 doesnt sound like a spring to me, it sounds like a cave

 

[JohnRoberts]

[TMI} Not sure why one would want to emulate springs in dsp except for a few specific applications. Modern technology has made mechanical springs the more expensive (size, labor, complexity) solution vs dsp. Even back last century I had managed to substitute DSP for spring reverbs in cheap topbox powered mixers. When we started making cheap guitar amps in China, we had to literally send over US made springs because they couldn't source mechanical springs domestically (that didn't suck). But that was last century and they eventually figured it out. [/TMI]

JR

 

[rock soderstrom]

the BTDR3 doesnt sound like a spring to me, it sounds like a cave

The BTDR 3 also has a strange modulated "pitch shift" when decaying if you listen closely. The chip is based on 3x PT2399 delays.

"[..]the associated patent, US8204240, shows that it uses three PT2399 delay chips, one of which is modulated at a slow rate[..]" Merlin Blencowe

Overall, though, the BTDR-3 is a fine piece for pedals and does a good job there, especially for guitars.