Can somebody explain the pros/cons of adding cone mass?

[Tom Danley]

Hi

This is a “rule of thumb” if one does so by gauging the R/L corner.
The lower in frequency it is, the “slower” in response the driver is to a transient so far as the motor goes.
What one could also do is to compare impedance curves as the Rmin point IS the conjugate of the C of the moving mass and series Le, at that point the R and C are equal but opposite and cancel out leaving the resistive impedance (made of Rdc + radiation resistance + mechanical losses) at Rmin.
The lower the Frequency where this happens one can also assume the slower the driver is.
In Pro-sound, the coil diameters are large but the Xmax is not usually, where one is more likely to see a problem is on drivers with larger motors (large coil AND large Xmax) such as those used more often in Car audio.

There is a thread dedicated to this already and every one is entitled to there own opinion, but from my perspective here is the situation.
“Slow bass”, a subjective judgement, it can also be unrelated to the HF response of the driver. In Pro audio, it is normal (and totally wrong) to judge a subwoofer according to how well it produces a kick drum.
On the surface, this seems reasonable.
Normally, when comparing two subs with equal low cutoffs, it will be the one that produces more harmonic distortion that is judged to be a better reproduction of a kick drum. This is because subs are limited bw devices and have a low pass filter (crossover) which further removes the hf signals.
Hence, when evaluated alone, the sub that produces more of the missing upper spectrum is judged to be “faster” and more like a kick drum.
The problem is that the “bonus sound” the “better” sub produces, that makes it more “real” sounding, is produced by the driver nonlinearity and is not part of the input signal.
When the “faster” sub is compared in the system with the upper bass and mid bass speakers operating, the “bonus sound” now makes the total sound muddy (why many believed for a long time that having low frequency’s was actually detrimental, it was, but due to the speakers). When part of a system where the upper frequencies are produced by other drivers, then the reverse is the case, the lower distortion sub sounds the best.

For two subs of equal distortion but different low cutoff’s, the one with the higher cutoff will sound “better”, more like a lick drum.
Added to a system, the one with the lower cutoff makes the system sound better.

For two subs of equal cutoff, distortion, loudness capacity etc, the one with the more gradual roll off will sound faster and sound like its deeper and in both cases it is.
Vented boxes (with a sharper rolloff) have much more group delay at the low corner and any method you choose to make a steeper corner, does so also. Raising the “Q” of the low corner makes it sound (and is) slower in that it spreads the signal out in time more.

For two subs of equal frequency response, distortion, roll-off slope and so on BUT one being a proper horn and the other a direct radiator, the horn will sound faster and is faster.
In this case, it is because the generally lagging and variable acoustic phase spreads any broad band signal out in time compared to a proper horn which has an acoustic phase closer to zero degrees.
If one were being real picky and say that a loudspeakers job was to actually re-produce the waveshape of the input signal, then the zero degree acoustic phase is a requirement, making a proper horn even closer to the ideal.

It sounds like your in Pro-Audio, I designed a DIY bass horn a couple years ago which has proven its salt, you might want to see who has them in your part of the world and give them a listen. Go to http://srforums.prosoundweb.com/index.php/f/3/0 and check out the LAB Sub project.
Some one (don’t know who) had collected all my relevant posts in the design process.

http://64.233.167.104/search?q=cache...speakers&hl=en

Anyway, these go down low, go very loud and have very low distortion (so far they have won at the shoot outs over everything else tested so far) and sound good.
Oh, the plans etc are free too.
Hope this helps things clearer by bring out more of the “factors”.
Best Regards,

Tom Danley

[AndrewT]

Thanks Tom,

[DanWiggins]

Originally posted by Rademakers
Could this be applied as a rule of thumb and is there a way around this? Since almost all otherwise good PA woofers have big voicecoils (4" and up).

Mvg Johan

It is actually the voice coil dimensions - remember, most prosound drivers have very little overhang of the gap, and have little amounts of stroke. The longer the voice coil, the more stroke, the more bass output.

Inductance is linear with the diameter of the voice coil; going from a 2" to a 4" voice coil will double the inductance. Of course, Re is also linear with diameter, meaning going from a 2" to a 4" diameter voice coil the DCR will double, and thus the inductive roll-off corner stays the same.

HOWEVER, inductance goes as the square of the number of turns. Double the length of the voice coil (for more stroke, for example) or double the number of layers (for more power handling or total BL), and you quadruple the inductance, while DCR (which is linear with the total length of wire) only doubles. So you halve the frequency at which you start rolling off.

So, for higher stroke, high power handling drivers, you typically have 4 layer long voice coils, which an yield a high inductance. Most prosound drivers are big diameter to help with power handling, but have very short voice coils (gaps typically around 8mm tall, with a voice coil length around 20mm). Low inductance, low mass means wide bandwidth and high efficiency but the downside is reduced low frequency output, because of the lower stroke.

Dan Wiggins
Adire Audio

[Rademakers]

Thanks for the very long aswer,

I don't understand the 5 first rules (lines?) of your post (lack of knowledge) but the rest makes things very clear, thanks again.

It sounds like your in Pro-Audio, I designed a DIY bass horn a couple years ago which has proven its salt, you might want to see who has them in your part of the world and give them a listen.

I wouldn't mind having two cabs (one each side), the size of a Labhorn, but 6 well....I only do parties up to about 80..150 people so it would be the wrong tool for the job I guess. Also I'm just a hobbyist.

Since I like low end that much, I use (unussual I know) a 500 ltr 18" Transmission Line on each side (with 18sounds, 18LW1400). With an f3 of about 30 Hz and 126,5 dB at 1m at full power (theoretical) it sounds great with slow music but sounds slow with faster music.

I already came to the conclusion that I probably need a frontloaded horn and since I like to design and build loudspeakers, it will be fun too Guess I'll try the 18LW1400 again (unless it turns out to be the wrong speaker for the job).

Some one (don’t know who) had collected all my relevant posts in the design process.

Thanks to both of you, it seems to be a very helpfull guide in designing horns.

Mvg Johan

[Leslie Horn]

I am coming form a more practical and less theoretical standpoint, so please bear with me here.

Ok, it may work satisfactorily.

To get a lower Fs, maybe.
This can 'effectively' lower Vas, but it's cheating.

It might work better for acoustic suspension systems.

Note that rings or weights added by the manufacturer are not necessarily an afterthought; they may well be employed to offset the lower density of the cone material, and bring Mms up to design specs without using a 'heavier' cone material. This is seen with metal and plastic cones alot..

Artificially increasing Mms or Mmd beyond manufacturer's specs may adversely affect damping at lower frequencies and longer excursions, leading to overshoot, which can cause mechanical bottoming out, and therefore, severe distortion. But I think this effect may be minimized in acoustic suspension designs, especially if the driver was originally designed for use in a ported reflex or vented box.

'Effective compliance' may increase, too. Note, not physical compliance, per se. It is analogous to photography, in a sense, where a longer focal length, for purposes of camera shake/motion blur, will reduce the 'effective shutter speed', even though the shutter doesn't physically operate any slower. In other words, when externally extending a paramater, you run the risk of increased distortion.

Just my two cent's worth.

[Leslie Horn]

Originally posted by Stocker







Guys, don't overlook the purpose of the excercise here.

Abs, so lewdly.