Does every cone have ONE right motor?

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Hello all!

I once experimented with a light cone, strong motor driver and for my taste it sounded "stressed" or "overdynamic", so I experimented with series resistors. I found that differences of 0.3 Ohm were clearly audible and at 3.3 Ohm there was a point where I had exacly the relaxed sound I like, neither stressed nor boring (what happened with too large resistors). I am not talking about bass response in a certain enclosure (I used OB and sealed), just about midrange performance, and the effect remained the same when adding a large series capacitor.
Recently I stumled on reports about the 8" Tangbands where (I don't know whether it was the same person) was said the "stronger" one had good transients with percussive sounds and the "weaker" one was more for easy listening.
Are these singular effects, or do they appear with all fragile paper cones?

Oliver
 
Hi Oliver,

did you adjust volume for same voltage across the voice coil when listening ?

Maybe there is an effect when going from voltage towards current drive.

The higher the resistance is, the lower is the frequency dependent influence
of VC inductivity e.g.

Influence of cone resonances on impedance are flattened relatively.

VC velocity vs. frequency may change significantly dependent on the
drivers motor/VC design.

I can imagine that there might be drivers which sound better using a
resistor in series.

Regards
 
The Replikon builders have an interesting idea about optimizing, but it's broader than the motor / series resistance.

They do not use box alignments. Instead, they find the ideal box volume empirically -- the volume that gets the driver / box to sing (with a given amp / room). When the sound "locks in," that's the ideal volume for the driver / amp / room. (They use blocks to vary the volume, just as you're using different amounts of series resistance.)

www.hornlautsprecher.de - solutions in sound

Almost intelligible: Google Translate )
 
I do not know either what that means ... :)

Some wild speculation:

I think it depends on the mode shape of the membrane
resonances under question.

A peak in VC velocity can nevertheless be associated
with a dip in frequency response, in those cases voltage
drive will worsen things.

If the impedance peak is associated with an efficiently
radiating membrane mode however the peak will be less
pronounced using voltage drive.

Constant voltage drive smoothes the sound pressure peaks
for efficiently radiating resonances in VC velocity,
while notches in sound pressure associated with VC velocity
peaks are pronounced.

Constant current drive will act vice versa. Sound pressure
peaks associated with impedance peaks will be pronounced.
Sound pressure notches assotiated with impedance peaks are
smoothed.


Maybe "constant power" is a way of muddeling through at best,
neither voltage drive nor current drive.

The less damped a membrane is - i think you reported mainly
from experience with lightwight paper cones - the more
audible this small changes could be.

With a well damped cone having smooth impedance vs. frequency
a resistor in series might not be audible to that extent.


Regards
 

GM

Member
Joined 2003
Greets!

Qts = ~0.312 gives the maximum bass extension for the minimum box size, so it seems reasonable to me that this yields the most balanced summed (Fs/Vas/Qts) to diaphragm loading/damping through its mass controlled (~flat) BW regardless of box loading type, so cone mass per se is irrelevant, a point that many can't seem to understand, especially when considering horn driver spec requirements.

GM
 
6moons audio reviews: FirstWatt F2

Some seem to praise it ... have no own experience.

But in that article i read that laying a resistor "across" (which means parallel?)
the terminals is needed for optimization when using current drive ...

That would mean "no pure current drive" for optimum result and
would point towards the same direction as your finding.
 
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Thanks for the links, Oliver.

In his article Nelson Pass speaks about overshoots in underdamped systems and reduced bottom end response in overdamped systems.

"Critical damping -- that resistive combination of electrical source impedance, suspension friction and acoustic load -- occurs when you apply a step pulse to the voice coil and the cone's motion doesn't overshoot. Under-damping results in bass notes that hang around a little longer than the amplifier intended. Over-damping has good transient bass control but also suffers a significant loss of bottom end response. Generally, we want something in-between, something closer to critical damping. Whether we slightly over-damp or under-damp seems to be a matter of taste."

He indicates that there are other benefits of not-overdamped systems, too, but neither specifies nor explains them.

"With the low damping factor, the Fostex became a totally different speaker. It suddenly had bottom end response and a better top end. It still had the same annoying upper midrange that had Dick Olsher devise his passive equalization network. The low damping factor didn't cure the upper midrange faults but it seemed to work improvements everywhere else."
 
Low Q high efficiency drivers may benefit from Amplifiers
with low damping factor by having the Q adjusted to a more
practical value for the lower end.

Influence of VC inductance is also reduced when going towards
current drive, so the VC velocity will be higher at the upper end.

More bass, more "sparkle" ...

But i do not know if that is all, what happens.

And since every (fullrange) speaker is different, what is "the right"
damping factor ? And what is the "right" amplifier to choose.

If the Q in a closed box system is adjusted somewhere between
0.5 and 0.7 that may be OK.

But meeting optimum values for the upper end is still difficult.

Another difficulty may be that most drivers are designed
for voltage drive. I can imagine, that the sizing of a whizzer
cone e.g. , its mass and the stiffness of the glues may be
chosen from manufacturers to compensate for rolloff
which may also be caused by VC inductance.

In the end one comes to the conclusion that amplifier and speaker
should be designed together as a whole.

Can equalisation together with a conventional voltage
controled amplifier do the same, to support a given dynamic
fullrange driver ?

Obviously not every speaker can perform with every amplifier.

A speaker with very flat - or ideally pure resistive - impedance
can be assumed to be more interoperable concerning different
amps, than a speaker with highly varying impedance.

Is an amplifier with adjustable dynamic output resistance
possible or useful ?
 
In the article about the F2 they write its output impedance is brought to 15 Ohm by some resistor, and it would have a few hundred without it. Should be a place for adjustment. But sometimes the enclosure doesn't like it even if the cone would. I read about a Fostex BLH where the designer said it doesn't work with valve amps very well because the speaker is simulated with "factory" Qe.
 
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Joined 2009
Calling GM

Greets!

Qts = ~0.312 gives the maximum bass extension for the minimum box size, so it seems reasonable to me that this yields the most balanced summed (Fs/Vas/Qts) to diaphragm loading/damping through its mass controlled (~flat) BW regardless of box loading type, so cone mass per se is irrelevant, a point that many can't seem to understand, especially when considering horn driver spec requirements.

GM

Greetings!

Am I understanding correctly that a driver like the FE167e with a Qts of 0.31 will work perfectly in a horn? (e.g. the eXtra Large Frugel Horn, the Madisound BK-16). Normally I read suggestions to use something like the FE166En (Qts 0.25) or FE168 Sigma (Qts 0.26) and anything higher not very suitable.

Thanks!
 
I'm not GM, & will leave the optimal version to him, but FWIW, basically yes (although the horn should be designed for the driver). Low Q for a back horn is largely myth; essentially if a driver is suited to any other type of vented box load, it's fine for a back horn. Where low Q may (may) come in handy is if it's partnered with a high output impedance amp, since effective system Q will rise.
 
What Scott said, though more like a complete myth if one reverse engineers an early W.E./Lansing/Altec-Lansing BLH, which used drivers either open back or somewhat damped open back chambers and even seen one damped open back where there was no ‘vented’ rear cover, just had a ‘blanket’ cover of felt loosely attached with some wood slats, which possibly [probably?] was due to fine tuning a driver re-cone/replacement.

Regardless, long history lesson kind of short, this misunderstanding of what specs is required for proper horn loading is due to folks measuring early horn drivers, which have a Qts that could be adjusted to as low as 0.1 since until recently only a field coil could generate a strong enough magnetic field AFAIK and it’s my understanding that even then only when the pole was made from Permendur, a material that today would price a driver out of the hands of all but the wealthy.

What they ignorantly and/or conveniently ignored for self serving reasons was the rest of the signal chain, which was driving it with a matching impedance that could have variable damping tone controls that could increase it 2x or more, so the effective speaker system Qt [sysQ] could be 0.7 or more and anyone paying attention to driver specs since ~1929 could not help but notice that driver Qt increased in a delayed lockstep with decreasing amp output impedance over the ensuing decades until PP tube amps finally got down to < 0.125 ohm where it has such a negligible impact on Qts that the driver/box alignment is the determining factor of sysQ, all else equal.

This situation has caused some folks of vintage drivers needing re-cones to be very disappointed with what they actually got since only the last series of re-cone kits are sometimes available, so a driver that came to the re-coner with a 0.2 Qts may return with a 0.4-0.7 Qts and why I always recommend avoiding vintage horn drivers needing re-cones like the plague unless an original repair kit is also available and/or it will be driven with a very low output impedance system.

GM
 

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Scottmoose and GM thank you both for the lengthy explanations.

I am trying to figure oput another item: The FE167e has a xMax of 0.6 mm and I am in the understanding that as soon as the cone moves outside that region non-lineair behaviour raises its ugly head. I've been using google to try to determine how the xMax from the Fonken 167 compares to the xMax of the XL FH (or another BLH like the BK-16) but alas sofar no indication which one would be having the least xMax around 50 / 60 Hz. Perhaps one of you two can shine some light on this? Thanks.
 
Xmax is a driver parameter, not a function of the enclosure. Travel will vary at a given (low) frequency depending on the acoustic load. A reasonably sized back horn should be more efficient in that region, so lower driver travel. The Fonken, as a resistive vent alignment will not however unload to the same extent as the horn will below Fb.


Be that as it may, Xmax is one of the most useless parameters out there at present, since there is no industry standard definition for what it actually is, and thus no standard methodology for putting a number to it. There are quite a few, all of which will give different numbers for the same drive unit. And that's before you start to consider how distortion varies depending on motor design -some drivers overload abruptly, some rather more benignly. The Fostex units generally just tend to sound increasingly compressed.
 
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FF125K may have the most puny Xmax spec out there and goes gracefully out of it - heck, it probably lives out of 0.15mm on anything but recordings of falling leaves or something. :) A full set of Klippel measurements would be more telling if mfg's provided as much.
 
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