"Fast" woofers.

[Kip]

"Fast" subwoofers are not a thing, bass wavelengths are long and therefore take time to propagate, 12.5ms at 80Hz, 25ms at 40Hz, etc. All subwoofers are slow by nature. Ported vs sealed vs infinite baffles are not changing the speed of the driver, but rather how it interacts with the room.

The primary performance factors of a subwoofer are smooth frequency response and low distortion. If you can achieve those 2 things, it will sound good. Infinite baffle subs are a good solution for someone with power to spare and EQ. Group delay and resonances cannot be entirely discounted, but those are easy things to get right simply by designing the correct enclosure.

I assume you have seen the ASR review of your Magnepan LSR? You probably want to crossover at 80 or 100Hz, distortion rises quickly in the bass region.

There exists no woofer, sub or otherwise that is exempt from the physical characteristics that produce measurable differences in a spectral decay.

 

[NTK]

There exists no woofer, sub or otherwise that is exempt from the physical characteristics that produce measurable differences in a spectral decay.

... which is completely described by its frequency response.

 

[Kip]

... which is completely described by its frequency response.

How do you suggest the frequency response is relevant at all when the decay is how fast the sound production stops after the signal has stopped ?

 

[NTK]

How do you suggest the frequency response is relevant at all when the decay is how fast the sound production stops after the signal has stopped ?

Go back to my second question in post #46: Do you know how waterfall plots (or "spectral decay" plots) are generated?

If you don't, may be those who do may know something you don't (in addition to how waterfall plots are generated).

 

[Kip]

Because of other attributes like cone breakup and resonances.

What is your understanding of a spectral decay plot ? Do you know why Speaker Engineers use it ?

Go back to my second question in post #46: Do you know how waterfall plots (or "spectral decay" plots) are generated?

If you don't, may be those who do may know something you don't (in addition to how waterfall plots are generated).

If you think you know, please, do free to tell me.

 

[NTK]

What is your understanding of a spectral decay plot ? Do you know why Speaker Engineers use it ?

If you think you know, please, to free to tell me.

This has gotten pointless. Bye.

 

[rdenney]

How do you suggest the frequency response is relevant at all when the decay is how fast the sound production stops after the signal has stopped ?

Think about it physically. The driver can’t stop instantly, but if it was asked to, it’s because a high-frequency component asked it to. A sudden stop of motion is a high-frequency component. That’s the point of looking at the spectrum plot and not just the impulse plot.

No low frequencies would ever ask the cone to engage such sudden motions, because such sudden motions simply don’t exist in low-frequency signals. The frequency determines the steepness of the impulse, even if it’s a step function that presumably contains only one half of a cycle.

That’s why cone inertia is fully described by its frequency response and resonance (that is, both system and electrical resonance) characteristics.

All signals are the sums of sine waves.

Rick “avoiding a sub that produces frequency content not sent to it” Denney

 

[BDWoody]

Fast woofer is a real thing.

This has been explained to you, but it can't be understood for you. You are just trolling now, so you are done in this thread.

 

[Geert]

What is your understanding of a spectral decay plot ? Do you know why Speaker Engineers use it ?

Seems your understanding of this topic is so minimal that you didn't notice you're in discussion with experienced engineers with relevant knowledge.

 

[fpitas]

Seems your understanding of this topic is so minimal that you didn't notice you're in discussion with experienced engineers with relevant knowledge.

If he's serious (which I doubt) perhaps he'll go study the subject.

 

[kemmler3D]

The decay is measure after the signal has stopped, correct ??

The main thing to understand is this:

If a cone can stop fast, it can also produce a high frequency. This is because frequency and acceleration (i.e. stopping fast) describe the same thing, but in different ways.

A steep line on the oscilloscope (i.e. "fast") has high frequency components. The steeper the line, the more high frequencies.

This is why people say there is no such thing as a "fast" woofer apart from its frequency response, since the frequency response tells you how fast the cone can (or can't) accelerate/decelerate. There are definitely fast or slow drivers, but this isn't a quality that ought to be measurable apart from FR.

What else might produce a longer-than-wanted decay time?

Resonance: This should show up in the frequency response plot, but to your point, is easier to see in the CSD plot.

Group delay: This shows up in the phase response plot.

If you're thinking about transient response, you're thinking about the impulse response or step response plot, right? These are actually just different ways to visualize the frequency + phase response plots, same with CSD - they actually all show the same thing, but presented in different ways.

Another way to think about it: How can you have a pure 20hz signal that lasts for less than 1/20 of a second? (hint: you can't, that's what 20hz means)

I think high THD might also create the impression of a slow woofer, because if you have resonances in the same system, you might end up exciting a resonance with a harmonic of the bass note you're actually trying to play, causing the note to ring longer than it should. All this stuff put together probably creates the impression of "slowness" in cheap / badly designed subs.

 

[Geert]

If he's serious (which I doubt) perhaps he'll go study the subject.

The problem is that this topic is counterintuitive. Basic logic is inadequate. Studying it is.

 

[fpitas]

The problem is that this topic is counterintuitive. Basic logic is inadequate. Studying it is.

Well, I linked a good starter book. And there are plenty more, as well as lots of good stuff for free on the internet.

 

[Deleted member 48726]

Think about it physically. The driver can’t stop instantly, but if it was asked to, it’s because a high-frequency component asked it to. A sudden stop of motion is a high-frequency component. That’s the point of looking at the spectrum plot and not just the impulse plot.

No low frequencies would ever ask the cone to engage such sudden motions, because such sudden motions simply don’t exist in low-frequency signals. The frequency determines the steepness of the impulse, even if it’s a step function that presumably contains only one half of a cycle.

That’s why cone inertia is fully described by its frequency response and resonance (that is, both system and electrical resonance) characteristics.

All signals are the sums of sine waves.

Rick “avoiding a sub that produces frequency content not sent to it” Denney

Rick "with many aliases" Denney.

 

[Zapper]

Seems your understanding of this topic is so minimal that you didn't notice you're in discussion with experienced engineers with relevant knowledge.

Another case of the Dunning-Kruger effect.

 

[ebslo]

Rick "with many aliases" Denney.

He's using an apodizing filter.

 

[jsilvela]

I find physics and audio over-kill for understanding the frequency-time linkage.
It's purely math.
The Gibbs phenomenon which is "seen" as ringing in the time domain, is due to frequency limitation.
Won't insult anyone by linking the wikipedia article.

You get the same frequency-time issues in image processing, with no moving parts.

 

[audiofooled]

I'm sorry but I just can't help it

Make what you will of this, but this is to illustrate my level of frustration when people with knowledge spend their time on and on and yet we still have it. Fast bass. Also to illustrate the superiority of transients at the signal, amplifier and transducer level over room interaction and ultimately our perception.

Since there's no need for any more science around this subject, I wish to thank you all who shared their knowledge.

 

[witwald]

I agree that Damping Factor may be a misleading, perhaps worthless metric but wouldn't you agree that amplifier/speaker interaction issues with high output impedance amplifiers are real?

Most definitely.

The dummy load used by JA when testing amplifiers seems to indicate that the combined amplifier/speaker response can be greatly affected depending on the output impedance of the amplifier.

The above plot very clearly illustrates the point that you were making. It indicates that amplifiers with a high output impedance (low damping factor) should be avoided in order to minimize the frequency-dependent equalization of the loudspeaker's output that otherwise occurs. The above seems to be a particularly good (bad?) example of the harmful effects.

The figure below shows the effects of various damping factors (amplifier output impedances) when connected to the Stereophile simulated loudspeaker load. By the time the amplifier has a damping factor of 64, the effects on frequency response are relatively minor, being in the range ±0.1dB or so.

 

[egellings]

"Fast" when used to describe a subwoofer makes no sense to me, since bass frequencies are long in wavelength, and you don't need to move quickly to track them. Shoot, I can jump up and down that fast while holding a beer in my hand. It's not speed but timing that is important. The bass should arrive such that it meshes well with its accompanying HF content.