Fast bass, slow bass...

Interesting read and nice find, John.

Although imo some of that characteristic of the lighter, pro-style woofers compared to the heavier cones 'subs' does strike me as common sense. It's nice to see a good writeup on something like this. I'll check out the link when I'm not at work but good stuff.

I've read this before, and it seemed to agree with my intuition. I've often looked at mass, compliance, and BL when considering drivers. I have wondered if it also applies to higher frequencies. You hear the word detail thrown around. Perhaps a heavy stiff suspension doesn't reveal the details like a light compliant one would. Because it doesn't get moving with such small signal inputs. Not quite what the article is about, but something it makes me think about. I've heard people say they have to turn up certain systems quite loud to get detail. Possibly to get those signals high enough for the heavy driver to react well enough.

Aaaack! Is even the DIY community still confused on this one?

While the signals do have different rise and settling behavior, the above author completely missed the WHY. The common error made here in comparing to the electrical input signal greatly confuses the issue. While the comparison does make a case for differing bandwidth and order designs, there is zero info that should infer mass/inertia or motor strength are to blame. This is simply bandwidth and roll off qualities seen in any Fourier decomposition.

The blue reference signal is not what we should compare to. We should look at the input signal with at least a comparable low pass filter that mimics the high frequency response of the woofer. Even better is to electronically low pass the driver under test within its pass band as it might be used in practice so the roll off and associated behavior is known. The woofer is not a full range speaker, and is not supposed to perfectly match the displayed waveform unless it extends past 10kHz and is used that high.

FACT: You cannot create the sharp start/stop shape at each end of the blue waveform without extended high frequency content. Right off the top, part of the softening of each end is the lack of high frequency content.

This is why the tone bursts used by Keele, Linkwitz and the CEA measurements ramp up and down over 5-6 cycles to keep the required bandwidth of the signal within the range of interest (ie ~1/3rd octave wide).

Quite to the contrary of what is asserted, you could add some mass to the RS225 woofer, use a larger sealed box resulting in the same Qb, and you would BETTER follow the input signal.

All one in the same. The ramping up of the signal and tailing down happen with different shapes due to the bandwidth of the playback device and the relative phase shift through the spectrum. Any driver with the exact same frequency response and phase response will have the same behavior, even if it's 10x heavier or 10x lighter.

It is a nice graph. But, these are differences that most people will never really get to evaluate. There are more variables than simply moving mass at play. Motor Strength, inductance, suspension compliance, air spring (or not), etc.

Comparing a light moving mass, higher Fs, high sensitivity driver to a heavier moving mass, lower Fs, lower sensitivity driver is just not a good apples/apples. They are designed for different things. One is designed for more output at higher frequencies for a given input signal. The other is designed to be able to generate more output for a given inout signal at lower frequencies. Even this comparison is waayy too simplified.

For more info on the subject, you need to pick through some of this:

http://www.baudline.com/erik/bass/thomas_danley.html

Or read what Mark said above.

I tell folks the following:

If you do not have near identical clean (read: low distortion, however you want to measure it, but a baseline must be set, whatever it is) output and extension with flat frequency response, you cannot really compare two alignments with regards to group delay, transient response, etc. without significant bias. This means that in a small room, the 2 compared speakers must be in the exact same location when being compared, as differing locations could lead to differing freq responses. Especially in small rooms. Outdoors, not so much.

I don't know of too many folks who have compared 2 LF (or fullrange, or whatever) units that have fulfilled the above criteria.

Also, there's what I call the 'paraxial criteria' of audio. The less the driver has to move, the more accurate the reproduction of the signal, just like in optics, the closer you are to the optical axis, the lower the aberrations. Very large Xmax drivers may be great for spl, but not necessarily for 'starting and stopping on a dime' like a 2226H.... Then again, not apples/apples, and different freq ranges with differing excursion needs, and......you can go round and round on this topic. Just too many variables. In general, spread the load (be it with a horn/waveguide or multiples) and don't make a driver work too hard...


JSS

^^^^^^^

And this is what I absolutely LOVE about audio.

Thanks for the graphs, that's 1/4 of the way there. Now include the stop of the waveform (sine wave x step function of t=3 periods) and we're 1/2 way there.

Next add a 30Hz 2nd order high pass with Q=0.7 and then overlay that with a 30Hz 4th order Butterworth high pass. Now shift the Fc of the high pass to 15Hz and compare...

If you keep playing and compare different Q values at the same frequency, you can create various behaviors, and they all follow the response shape of the driver and box tuning. Any driver with a Q of 0.7 and Fb of 30Hz and the same high frequency extension will give the same waveform for this test, no matter how heavy/light, weak/strong the driver is. What changes with those variables is box size to achieve the alignment and the Voltage required to produce the same level.

I agree wholeheartedly. IF the objective was the attempt at tracing the input signal you would need a single loudspeaker capable of a huge bandwidth (super low, maybe even negative, inductance) in order to do so. Well put Mark.

The main problem with quantifying 'fast' versus 'slow' bass is that the cues that our ear/brain use to make that determination don't come from the frequencies below 80 Hz, they come from the frequencies from roughly 80 to 500Hz. So yes, transient response is very important, but not the transient response of the subs, but rather the transient response of the midbasses. Earl Geddes would have a field day over this one.

Somewhere in the archives is a thread that examined this verycomprehensively; I wondered how a vented box good work very well, as it's a spring/mass system that takes a number of cycles to pump up to full amplitude.

Illka provided some very interesting analyses and plots that showed the acoustic outputs for the first few cycles of sealed and vented systems.

Fascinating stuff, i learned something new today Once again what seems logical is not necessarily the truth.

One error to avoid in stuff like this. "A sine wave that starts at..." is most definitely NOT a sine wave. Sine waves don't start or end. Don't be fooled into thinking that using a sinusoid shape in a part of the waveshape limits you to effects near the sinusoid's frequency or period. This is maybe a gated sinewave, which contains energy over a much wider bandwidth than a sinewave (which has ideally, none), so you can't make conclusions about characteristics of just the highpass natures of the types of boxes.

Great posts Mark.






I seem to remember that one. No idea what it was called or when though. It's been a few years at least.

What Mark said.

Hate to be a repetitive pedant, but people really should read up on linear systems, particularly the fundamental frequency-time duality, if they really care to understand this stuff. Largely, if you know the FR, you can infer the time-domain response, and vice versa. Raw intuition can be misleading, sometimes grossly so. And what's commonly "known" can be wrong.

And one other thing. Practically, all of this is likely swamped out by what the system does in the room at the listening position, which is what really matters. As long as a given woofer can be cleanly driven to excursion and in-room response properly eq'd, alignment doesn't really play. Many ways to skin the cat: cubic inches, cubic dollars, cubic sweat...

Once again Mark's knowledge never ceases to amaze me!

^^^
this.

JSS

This^^^

Bosso

I can comment more later, the subject of the original post is at least one that is consitent and can be predicted. It's a known factor.

People often ignore eddy currents and their effect on the position of the driver. As current flows through the VC it becomes an electromagnet. The more current, the stronger the magnet. This magnet is then moved up and down in the gap many times per second. As it does this, the magnetic field created by the VC pushes the permanent magnetic field around which is called modulation. The permanent magnetic field that propels the VC is continually moving and changing. As this happens the VC is no longer able to be positioned where it should be.





This is something that cannot be corrected for other than to eliminate the eddy currents. Will post more later on this as I find my other FEA info.

I disagree with your last statement here. I don't think it's possible for a ported subwoofer to have better transient response than a (well made) sealed subwoofer, regardless of driver. I could be wrong, and would love to be educated on this. Perhaps it's related to EBP or Qts.. ?

+1. The statement also implies that there's an inherent benefit to better transient response in a sub. Just because it looks better on a chart doesn't mean it sounds better.

I'm sorry, but I don't need you to interpret Mark's thoughts for me. What he was implying, and we know this because he went on to explain it, is that this sort of nonsense belongs in a forum where the subject hasn't been beaten to death for a decade.

Try searching the archives.

I don't have to present anything. If you want to continue to muddy the waters and confuse everyone who reads your thought-for-the-day posts, then take responsibility and follow up when you realize you were just rambling.

You can start by getting the term 'transient response' correct and stop referring to it when you actually mean dynamic tracking. That would have saved Mark a lot of typing.

Bosso