Thank you Mr. Yohn re. subwoofers

[Boomzilla]

DYohn -

It took me a while, but I now have a clear understanding of the effect of current on subwoofer quickness. Cone mass is a relatively minor factor, as is cone size. If one can swing enough current through the voice coil, then the coil can be positioned with precision and speed.

The inductance of the coil itself opposes changes in current - the greater the inductance, the longer it takes for the coil to begin moving on demand and the longer it takes that coil to stop. Also, as inductance rises, impedance also quickly rises with frequency, making the driver non-linear.

So theoretically, a voice coil with nearly vanishing inductance would make the best subwoofer coil (limiting this discussion solely to subwoofers, for the moment). But with lower inductance in the voice coil (all other things being equal), the driver's impedance also drops precipitously. This makes amplifier requirements significantly more restrictive. Only "arc-welder" amps that are stable into virtually dead-short impedances can swing enough current for our theoretical low-inductance voice coil.

This would limit amplification to the following:

1. High-current audio amplifiers stable into 2-ohm or lower impedances (Krell comes to mind)
2. "Pro" audio amplifiers specifically designed for stability into ultra-low impedances (but most often unable to sustain maximum power output into such impedances)
3. Subwoofer plate amplifiers specifically designed for stability into ultra-low impedances (are there any such? I haven't seen any)

The main source of low-inductance subwoofer drivers appears to be a company called "Stereo Integrity," but are there others?

Boomzilla

[DYohn]

Low inductance Le and high BL (motor force) are far more important than mass. Also linear BL across the entire stroke of the woofer , so that system control remains constant at the extremes, reducing distortion. I like Acoustic Elegance woofers. Not the lowest Le on the market but really well designed and very linear Bl with a good balance of all factors.

[Boomzilla]

I'll check them out. Thanks.

[DYohn]

While inductance is of course a component of impedance the impact on woofer transient speed is actually more due to magnetic induction in the coil than to current flow. DCR of the coil is fixed so a low impedance amplifier is not needed if DCR is high enough: indeed at certain frequencies Le might be zero in some voice coils. Higher average Le voice coils create larger EMF effects as the magnetic field changes with current and it is this effect that causes opposition to woofer movement and slows it down. Voltage determines how far the woofer moves, current determines the magnetic field strength and how quickly the movement can happen. So to speak. Plus Le increases with frequency, to the imact tends to be gereater as F increases. This happens in all dynamic drivers but because of the high powers involved is generally more noticeable in woofers.

[Boomzilla]

GLOSSARY - Just for those not familiar with the terms:

Woofer Le = This is the voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1,000 Hz. As frequencies get higher there will be a rise in impedance above Re. This is because the voice coil is acting as an inductor. Consequently, the impedance of a speaker is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs.

Woofer Re = This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This measurement will almost always be less than the driver's nominal impedance. Consumers sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load.

Woofer Fs = Driver free air resonance, in Hz. This is the point at which driver impedance is maximum. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well.

Woofer DCR = Same as woofer RE (DC-Resistance)

(NOTE: all information sourced from www.the12volt.com/caraudio/thiele-small-parameters.asp#_index)

[DYohn]

Using my web site. Cool.

[jackfish]

What about Q?



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[DYohn]

Jan 16, 2020 10:12:20 GMT -5 jackfish said:

What about Q?

What would you like to know? If you just want definitions of the various Q factors, click on the link Boomzilla posted to the 12 volt web site.

[mgbpuff]

Higher voltage can make a big difference too, thus the limitation of car 12v power.

[DYohn]

Jan 16, 2020 12:00:32 GMT -5 mgbpuff said:

Higher voltage can make a big difference too, thus the limitation of car 12v power.

Huh?

[mgbpuff]

Jan 16, 2020 12:12:27 GMT -5 DYohn said:

Jan 16, 2020 12:00:32 GMT -5 mgbpuff said:

Higher voltage can make a big difference too, thus the limitation of car 12v power.

Huh?

You can lower the inductance or you can apply a higher voltage - two ways of getting current to raise faster in an inductive circuit. No?

[DYohn]

Jan 16, 2020 12:24:58 GMT -5 mgbpuff said:

Jan 16, 2020 12:12:27 GMT -5 DYohn said:

Huh?

You can lower the inductance or you can apply a higher voltage - two ways of getting current to raise faster in an inductive circuit. No?

That has nothing to do with the power source to the amplifier (12V vs household voltage.) And to answer your question, no. Higher voltage = higher power, and the power required will be mostly determined by the desired listening level. At a given level, the voltage fluctuates with signal but you can't just increase it without turning up the volume.

[mgbpuff]

Nonsense. Subs can have position feedback, after all sound corresponds to woofer motion doesn't it. The reference voltage represents a position that the wolfer should match. If the reference is very fast or impulse, the woofer has trouble keeping up. One way to make it keep up is to 'over voltage' it, in other words apply a higher voltage to get it moving to its assigned position at any given time. The position feed back can control how much excessive voltage is needed. The voltage does not represent continuous power. But lets face it, position regulated subs are rare but nevertheless possible. I think Bob Carver did something along these lines. Also, Rythmik Audio makes a servo controlled sub. www.rythmikaudio.com/technology.html

[Deleted]

Jan 16, 2020 9:46:51 GMT -5 DYohn said:

Using my web site. Cool.

Well.. what other websites do you author, hmmm?

[DYohn]

Jan 16, 2020 13:09:15 GMT -5 @texzick said:

Jan 16, 2020 9:46:51 GMT -5 DYohn said:

Using my web site. Cool.

Well.. what other websites do you author, hmmm?

Just that one right now. I used to work on several others but no more.

[DYohn]

Jan 16, 2020 13:06:09 GMT -5 mgbpuff said:

Nonsense. Subs can have position feedback, after all sound corresponds to woofer motion doesn't it. The reference voltage represents a position that the wolfer should match. If the reference is very fast or impulse, the woofer has trouble keeping up. One way to make it keep up is to 'over voltage' it, in other words apply a higher voltage to get it moving to its assigned position at any given time. The position feed back can control how much excessive voltage is needed. The voltage does not represent continuous power. But lets face it, position regulated subs are rare but nevertheless possible. I think Bob Carver did something along these lines. Also, Rythmik Audio makes a servo controlled sub. www.rythmikaudio.com/technology.html

You are talking about a completely different theory of woofer control, and again it has absolutely nothing to do with 12 volt systems.

[mgbpuff]

Yep, it's a horse of a different color, but it's still a horse, a faster better horse.

[Boomzilla]

What have I done???!!! This wasn't intended to start another 20-page debate... Oh well, it is what it is.

Thanks again for the info.

[mgbpuff]

Sorry, I thought we were talking sub woofers and I was taking technical, not argumental. Every time I post, someone accuses me of starting some kind of argument.

[Boomzilla]

Jan 16, 2020 14:31:36 GMT -5 mgbpuff said:

Sorry, I thought we were talking sub woofers and I was taking technical, not argumental. Every time I post, someone accuses me of starting some kind of argument.

No worries - I enjoy your posts and don't consider them argumentative at all. Carry on!

And for the record, yes, feedback systems can and do control cone positions quite well. Velodyne, for example, has done so before.