Ideally damped speaker cone

[Shefffield]

I'm still in the process of reading Floyd Toole's excellent book. In chapter 4.6.2 Resonances Viewed in Frequency and Time he explains that low Q resonances are far more audible than high Q resonances. Quite the opposite of what one would expect. One reason being, that the sharp, narrow high Q issue needs to get hit precisely by the music signal, whereas the broad low Q issue has a much, much higher chance of being hit. Also, music is not a steady state signal, so the large footprint in the time domain that a high Q resonance has seems to be less problematic than expected. It just doesn't get excited long enough to fully build up the resonance.

I might need more time to digest the densely packed information in the book. Also recommend you get it yourself, it's pure gold!

Out of curiousity: Why tube amps?

 

[KSTR]

I strongly believe that overdamped woofers are preferrable! That's how I understand the remarks about electrical control in the 'woofers are not flat' video. Maybe the 'over' is misleading and we should just call them 'tightly controlled'?

Exactly.

The larger the "Back-EMF" (better named microphonic voltage) in comparison to the static voltage drop accross Re(+Le), the higher the inherent motional feedback in the driver (when driven with standard voltage drive). And this is velocity feedback at work, hence a section of 6dB/oct slope forms around resonance where the driver input is basically the velocity. But flat SPL until cutoff requires a falling velocity and that has to be dialed in via EQ to get to your system target response.

Linearity is only bettered to the extent the voice coil operates in linear fashion as a sensor which it does not at higher excursions. As ususal, applying some limited feedback to a nonlinearity does not really make things better.

The driver motor itself still operates overdamped, though. This is reflected in the error recovery behavior (like from dynamic DC offset from nonlinearities or simple overdrive) which is slower than with aperiodic damping but it does not overshoot, so bascially very acceptable. Whereas an way underdamped ringing response cannot be EQ out for the nonlinear/error part of the signal.

The price to be paid is that the amp and upstream signaling need some significant headroom for the EQ so that the amp can overcome the large'ish back-EMF voltage at low frequencies. Best used with efficient class-D.

 

[Head_Unit]

It covers three Eminence drivers with Qts of 1.2, 0.5 and 0.3. They all overshoot, but the overdamped has the shortest settling time.

Now I am remembering one of my electrical engineering professors telling me it was impossible to have a Q less than 0.5. He had gone straight from Bachelors to Masters to PhD, never had an actual job. As for the overshoot, Q of 0.5 or 0.3 should in theory not overshoot, so I wonder what was up with that. Although all these behaviors are assuming like some impulse or step input, not actual bass transient waveforms. And much of the thinking/statements around these issues are generalized, whereas my belief is that the relation of resonance frequency versus the frequencies playing probably matters. Some folks preference for low Q alignments may have more to do with keeping the resonance frequency lower than the nonhumongous changes in frequency response.

 

[Head_Unit]

The beauty of DSP is that we can easily roll over the high Qtb and equalize the frequency response to our desire. All we need is an amplifier that can put out enough volts and a driver that can take the pressure.

There was a subwoofer like that...Bag End, essentially operating entirely BELOW resonance. The relatively small box provides a linear air spring. The downside is yeah you need a lot of amplifier power. chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/https://bagend.com/wp-content/uploads/2014/09/ELF-GUIDE-COMPLETE-V-1.3.pdf

 

[Shefffield]

There was a subwoofer like that...Bag End, essentially operating entirely BELOW resonance. The relatively small box provides a linear air spring. The downside is yeah you need a lot of amplifier power. chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/https://bagend.com/wp-content/uploads/2014/09/ELF-GUIDE-COMPLETE-V-1.3.pdf

I think this gets blown out of proportion way too often. I use hefty EQ on a 15" woofer with a massive 4,5" VC (so the driver can take a lot), but it's currently only driven by a cheap no-name PA class AB amp. At best 300 W per channel into 8 ohms, if that much. No problem whatsoever.

I only pushed the amp into shutdown when I loosened up the woofers with a 10 Hz signal after a longer hibernation period.

Room gain seems to be so powerful that even with my EQ settings the power demand is way lower than most people would think. And I listen in an attic-like living room with open kitchen and corridor areas (50+ m²) with a ceiling height of 5 m at the highest point. Plenty of volume to fill, no overly problematic bass modes.

1 kW class D amp modules are waiting to replace the bass amp, but there's no rush.

 

[JRS]

Now I am remembering one of my electrical engineering professors telling me it was impossible to have a Q less than 0.5. He had gone straight from Bachelors to Masters to PhD, never had an actual job. As for the overshoot, Q of 0.5 or 0.3 should in theory not overshoot, so I wonder what was up with that. Although all these behaviors are assuming like some impulse or step input, not actual bass transient waveforms. And much of the thinking/statements around these issues are generalized, whereas my belief is that the relation of resonance frequency versus the frequencies playing probably matters. Some folks preference for low Q alignments may have more to do with keeping the resonance frequency lower than the nonhumongous changes in frequency response.

That's odd, as in physics 101 material for a damped harmonic oscillator: think of a mass attached to spring on surface with variable friction. There are different definitions of Q, but none to my knowledge say that q>1. What happens for harmonic oscillator as q<=0.5 the system will never overshoot (overdamped) when displaced from equilibrium position, and at exactly Q is 0.5 return to equilibrium in least time (think very coarse sandpaper tabletop). After that its a matter of best transient response so overshoot present (Bessel alignment where Q=1/sqrt 3 and than maximally flat bandwidth (Butterworth) Q is 1/sqrt 2 and after that as Q exceeds 1.0 becomes more and more of a twanger, think air hockey table, and yanking on the chain.

 

[dennnic]

1 kW class D amp modules are waiting to replace the bass amp, but there's no rush.

I think that 1 kW would suffice the heating needs of most of my apartment. That said, a tube amp seems to be doing just fine in that department as well.

Out of curiousity: Why tube amps?

I compared several tube amps to SS amps (Naim mostly) and always got similar results. When tubes are used you get some strange 3d effect of the sound, as if sound is not radiating from speakers. Vocals do not seem to have the same high extension, they seem more more pleasant to listen. It's especially obvious if you immediately switch to a solid state amp.
You might call this second harmonics and a distortion, but it's interesting, none the less. I even got the same effect by putting a tube preamp before a Naim amp. However, with absence of tube wolly bass.

Offtopic:
I even run Audiovectors passively biamped with a Naim (bass drivers, up to 600 Hz) and a tube amp (600 Hz upward), in hoping of getting best of both worlds. I did get a very strange representation - if you play some 'modern' jazz, it almost sounds as if a saxophone player was high on THC, with drummer being hard on LSD. It was less hearable with different genres.

I plan to use the same amp (ss & tube) combination on the present project (two way open baffle), however with a lower crossover frequency of around 300 Hz. I hope to get less difference in rhythm by forcing one driver to cover a broader frequency range. Anyone experimented with this?

 

[Lambda]

- if you play some 'modern' jazz, it almost sounds as if a saxophone player was high on THC, with drummer being hard on LSD. It was less hearable with different genres.

Not sore if this is a bad thing

 

[dennnic]

Not sore if this is a bad thing

It is. You shouldn't mix active substances.

 

[dennnic]

I run Audiovectors passively biamped with a Naim (bass drivers, up to 600 Hz) and a tube amp (600 Hz upward), in hoping of getting best of both worlds. I did get a very strange representation - if you play some 'modern' jazz, it almost sounds as if a saxophone player was high on THC, with drummer being hard on LSD.

Sort of a continuation of the previous post:

Is it possible that such a dramatic change in rhythm and dynamics between a solid state and a tube amp is a result of a difference of their damping factor and transient response time?

 

[KSTR]

Is it possible that such a dramatic change in rhythm and dynamics between a solid state and a tube amp is a result of a difference of their damping factor and transient response time?

Damping factor? No, typically. You can reduce the damping factor with a series resistor for the SS amp and it still will sound the same (apart from the slight frequency response difference created by non-constant speaker impedance). Unless you go extreme, of course.