Quack tamed by proper impedance matching - why?

[Cuki79]

Originally Posted by martingitdave

I might suggest that no pickup will sound like a mic without processing. It’s inside the guitar and only picking up vibrations on the bridge. Regardless if the pickup is brass, plastic, or an exotic material, it will never capture the sound of the air leaving the instrument, no?

Honestly my DIY pickup v5 in the Eastman sounds pretty much like a mic... IR does not improve it significantly in my opinion, and the IR I made ended super flat.

The only problem is that I could not get the same result in the D-18. So it is just a good match between the pickup and the guitar.

I think position & mass are the keys.

my 2 cents (right now 04/2020)
Cuki

[martingitdave]

Originally Posted by Cuki79

Honestly my DIY pickup v5 in the Eastman sounds pretty much like a mic... IR does not improve it significantly in my opinion, and the IR I made ended super flat.



The only problem is that I could not get the same result in the D-18. So it is just a good match between the pickup and the guitar.



I think position & mass are the keys.



my 2 cents (right now 04/2020)

Cuki

Based what I heard from your Eastman last week on the recording I would agree. It sounds like a mic. But my question is more to the point that it would not sound like a mic in front of a guitar. However, your IR suggests that it might not matter from a practical standpoint.

[jonfields45]

Originally Posted by martingitdave

Based what I heard from your Eastman last week on the recording I would agree. It sounds like a mic. But my question is more to the point that it would not sound like a mic in front of a guitar. However, your IR suggests that it might not matter from a practical standpoint.

With a little sleuthing I am prepared to point out its been 21 days that the HFN has had continued residence is your Sable!

Could it be that something that is perceived as mic-like at one point in time loses that perception later for many?

[martingitdave]

Originally Posted by jonfields45

With a little sleuthing I am prepared to point out its been 21 days that the HFN has had continued residence is your Sable!



Could it be that something that is perceived as mic-like at one point in time loses that perception later for many?

Good question! I’m happy with the HFN because is does have a mic like quality and matches that guitar really well. It also misses whatever “actual” mic qualities that the Anthem tru mic has that I didn’t like. Lol

[Cuki79]

Originally Posted by jonfields45

With a little sleuthing I am prepared to point out its been 21 days that the HFN has had continued residence is your Sable!

Jon, it is just because Dave is locked in his house without being able to hide from his wife

[James May]

Originally Posted by Cuki79

...

However James, and I know we disagree on this, I feel somehow the piezo disc keeps a bit of the brass disc resonance once installed. I once computed with finite element method those resonances and the main mode was exactly in the 3-5 kHz range. Of course your argument about the glue making a perfect coupling to the top makes sens. But I feel that the velocity mismatch between the top (wood) and the disc (brass) would still be strong enough to maintain a bit of brass disc resonance. I have no measurement to prove it thought. So my question is: Since you think the piezo quack is only due to position of the sensor, and since the Ultratonic pickup can avoid feedback by destructive interference, why don't you elaborate a method to locate the optimal position of the piezo discs and avoid the necessity of Tonedexter?
Thanks James,
Cuki

Cuki, as always your comments are appreciated.

Regarding the resonance inherent in a piezo disc consisting of a PZT (lead zirconate) crystal glued onto a brass substrate with conductive glue: It does have an inherent resonance, as you point out. The published resonance figures are typically from 5KHz to more than 15KHz. It depends on how thick the brass is. However, a most important point is that THESE ONLY APPLY WHEN THE DISC IS SUPPORTED ONLY AT THE EDGES. Then and only then does it behave in a manner consistent with the finite element analysis methods typically used.

If you glue (or tape) it to a bridge plate or soundboard and it is securely attached along its whole surface area, then those published resonance peaks essentially disappear. They may still exist in very small magnitudes way above the audio range. I know this because I've verified this phenomenon with a network analyzer.

A quick google search for the speed of sound in various materials yields:
air - 343 m/s
wood - 3960 m/s
brass - 4700 m/s

It may be that the mismatch between wood and brass can still result in some resonance, but I maintain it is way above audio frequencies if it exists at all.

Regarding your last point, the answer is easy. Even with a SBT located quite far from the strings, you will get a good representation of the wood vibrations at that particular point, essentially no quack, but still not have anything close to the complexity of the real acoustic instrument sound. This is because you don't have the air vibrations manifesting out front caused by the sum of a lot of different locations of wood vibrating plus the helmholtz chamber resonance. Hence the need for a ToneDexter (or other high quality IR) if you want it to sound really natural.

[Cuki79]

Originally Posted by James May

Cuki, as always your comments are appreciated.

Regarding the resonance inherent in a piezo disc consisting of a PZT (lead zirconate) crystal glued onto a brass substrate with conductive glue: It does have an inherent resonance, as you point out. The published resonance figures are typically from 5KHz to more than 15KHz. It depends on how thick the brass is. However, a most important point is that THESE ONLY APPLY WHEN THE DISC IS SUPPORTED ONLY AT THE EDGES. Then and only then does it behave in a manner consistent with the finite element analysis methods typically used.

If you glue (or tape) it to a bridge plate or soundboard and it is securely attached along its whole surface area, then those published resonance peaks essentially disappear. They may still exist in very small magnitudes way above the audio range. I know this because I've verified this phenomenon with a network analyzer.

A quick google search for the speed of sound in various materials yields:
air - 343 m/s
wood - 3960 m/s
brass - 4700 m/s

It may be that the mismatch between wood and brass can still result in some resonance, but I maintain it is way above audio frequencies if it exists at all.

Regarding your last point, the answer is easy. Even with a SBT located quite far from the strings, you will get a good representation of the wood vibrations at that particular point, essentially no quack, but still not have anything close to the complexity of the real acoustic instrument sound. This is because you don't have the air vibrations manifesting out front caused by the sum of a lot of different locations of wood vibrating plus the helmholtz chamber resonance. Hence the need for a ToneDexter (or other high quality IR) if you want it to sound really natural.

Thanks James for this detailed answer! If you measured it with the network analyser then for sure it is true!

I agree with all you wrote. I agree the «air» is the hardest to capture.

[Gorquin]

I've had two K+K 's in different guitars and was not satisfied with the sound. It seemed a bit dull and woofy to me and although a bit too close to an electric guitar I thought the Baggs M1 through the Baggs Venue sounded better overall.

I recently purchased a Pono OM-20C that I'm looking to install a pick into.

Any opinions on the Barbera Soloist vs Dazzo or other pickups to be used into the Baggs Venue?

Thanks!

[agedhorse]

Originally Posted by jonfields45

Both magnetic and piezo pickups have a series parasitic, inductance for a magnetic, and capacitance for a piezo. To sound good you want your load to be much higher than the parasitic's impedance. 1M ohm is a great choice for both types of passive pickups (irrelevant if already buffered with a preamp). As maybe the only person who's RainSong CO-DR1100N2 with a K&K sounded bad into 10M ohm, maybe that might not be a good choice for some. In any case too low an input impedance rolls off the highs for a mag and the lows for a piezo. Plug a passive pickup into a mixer mic input to hear it first hand.

IME, the thinner tone is generally due to a very small (low capacitance) piezo crystal. The lower the source capacitance, the greater the output impedance becomes as frequency falls. This combines with the input impedance (resistance generally) of the amp to create a first order high pass filter. Having tested a lot of pickups in my day, I have found that the sweet spot is generally somewhere between 750k and 1M, though a very few might benefit from higher than 1M. Why not make the input impedance 10M? Because with a long (20') cable from a passive pickup to the amp, there will be an increase in noise floor, RF intrusion and tribo-electric noise from the cable. It's very much a balancing act.

The quack is caused by a different mechanism (or mechanisms), one of which is the combination of mechanical and electrical resonances. In a pickup, there are L, R and C components to the impedance of the pickup and the cable. The combination of these can create some electronic resonances which show up as ringing in the signal. There are also mechanical resonances from the pickup itself, the pickup/guitar interface, the pick-up/bridge interface, and even locations on the guitar itself where portions of the instrument might resonate within a narrow frequency band. If you were to map the surface of the guitar, each point on the guitar will resonate (or excite) at a different frequency based on the relative dimensions of the guitar body, the stiffness and the mass in that area. This is why moving a pickup even an inch can result in a significant change. Placing a very thin damping material (like 0.010" rubber) between the element mounting surface and the guitar surface is one way to alter the resonance of the interface. another way is to mount the pickup under bending load like a cantilever, this is done in some (typically) bowed electronic instruments like violin, cello and bass for this reason.