"Fast" woofers.

[Kip]

Welcome

If you read the rest of the thread (it's not particularly long) and ask specific questions on points that need clarification, you will come to see how no violation of physics is required.

That said, I'll try a simple appeal to intuition. Consider a subwoofer playing a 100Hz tone. The driver decelerates, stops, and accelerates in the other direction 200 times every second, or once every 5 milliseconds. Any subwoofer can do this just fine, and play at frequencies much higher than 100Hz. We often model a driver as a piston, but it's very much not like the piston in a car as there is no drive shaft or flywheel that would store angular momentum. The motor directly decelerates and accelerates the cone every cycle.

ps. In an interesting twist, it turns out the motor's max power, or its ability to accelerate the cone, has nothing to do with what frequency a driver can play, only the SPL it can generate.

Doesn't a spectral decay plot show how fast the driver, or overall system goes silent after the tone(s) have stoppped.
If so, I still see no reason to attempt exempting subwoofers from what is considered "fast".

That said, I'll try a simple appeal to intuition.
Are engineers designing speakers wasting their time collecting the data to make the spectral decay chart ?

 

[NTK]

Doesn't a spectral decay plot show how fast the driver, or overall system goes silent after the tone(s) have stoppped.
If so, I still see no reason to attempt exempting subwoofers from what is considered "fast".

That said, I'll try a simple appeal to intuition.
Are engineers designing speakers wasting their time collecting the data to make the spectral decay chart ?

Dr. Toole's AVSForum post.

 

[Kip]

Dr. Toole's AVSForum po

Dr. Toole's AVSForum post.

View attachment 274266

Well I guess everyone has it wrong. Maybe selling speakers is a better idea than selling books. While I agree there is a huge can of worms containing contention about how much is perceived by one's ears, the laws of inertial are not meaningless.

 

[Kip]

Well I guess everyone has it wrong. Maybe selling speakers is a better idea than selling books ? While I agree there is a huge can of worms containing contention about how much is perceived by one's ears, the laws of inertial are not meaningless.
If there is no information to be obtained, wouldn't all the plots look the same ?
Is there a website called APR Audio Perception Review ??

 

[NTK]

Well I guess everyone has it wrong. Maybe selling speakers is a better idea than selling books. While I agree there is a huge can of worms containing contention about how much is perceived by one's ears, the laws of inertial are not meaningless.

So you think you are right and everyone else is wrong?

If there is no information to be obtained, wouldn't all the plots look the same ?

Do you know how waterfall plots (or "spectral decay" plots) are generated?

Is there a website called APR Audio Perception Review ??

You are welcome to start your own

 

[BDWoody]

Well I guess everyone has it wrong.

No, not everyone.

the laws of inertial are not meaningless.

No, but often misunderstood for sure.

 

[Geert]

the laws of inertial are not meaningless

Is there a reason to believe we can't manage inertia by applying the required force to keep things under control?

 

[fpitas]

Doesn't a spectral decay plot show how fast the driver, or overall system goes silent after the tone(s) have stoppped.
If so, I still see no reason to attempt exempting subwoofers from what is considered "fast".

That said, I'll try a simple appeal to intuition.
Are engineers designing speakers wasting their time collecting the data to make the spectral decay chart ?

No, but the crossover makes a huge impact on spectral decay, too. As will the room.

 

[gamerpaddy]

Is there a reason to believe we can't manage inertia by applying the required force to keep things under control?

View attachment 274270

Isnt this what servo-woofers do?

 

[fpitas]

Isnt this what servo-woofers do?

Well...not exactly. Servo woofers use some form of negative feedback to linearize the cone motion. I'm not sure how we got to inertia, that's covered in the driver frequency response.

 

[Kip]

So you think you are right and everyone else is wrong?


Do you know how waterfall plots (or "spectral decay" plots) are generated?


You are welcome to start your own

Laws of inertia are not a matter of opinion. Why do you think there is considerable analysis of the tradeoffs of different cone material construction ?

 

[fpitas]

https://www.amazon.com/Introduction-Loudspeaker-Design-John-Murphy/dp/0966377346/ref=sr_1_5?crid=3KPO40ASMCAV3&keywords=loudspeakers+books&qid=1679668288&sprefix=loudspeakers+book%2Caps%2C143&sr=8-5

 

[NTK]

Laws of inertia are not a matter of opinion. Why do you think there is considerable analysis of the tradeoffs of different cone material construction ?

I'll give you the benefit of the doubt that you want to be here to learn something instead of in a crusade to telling everyone here that they are all wrong.

I am assuming you don't full understand what I wrote in post #39. The graphs below is a slightly different version of it. I'll explain it in detail this time.

In this case again I have a single cycle sine burst (blue curve). It starts abruptly and stops abruptly. This sine burst signal is split into two components -- the low and high frequency components. The crossover filter used is linear phase to simplify things. The crossover frequency is 2.5X the fundamental frequency of the sine burst.

In the top plot, the orange curve is the low frequency (low passed) components, and the green curve is the high frequency components. Because the xo frequency is 2.5x that of the fundamental, the majority of the signal energy is in the low passed components. You can see that there is no abrupt changes in the orange curve. That is the portion of the signal handled by the woofer. The green curve is the portion of the signal handled by the mid-range/tweeter, which can reproduce higher frequencies and therefore is much better at reproducing the abrupt changes.

You can see that the sum of the orange curve and the green curve equals to the blue curve, which is the original signal. The woofer doesn't need to be "fast". It only needs to faithfully reproduce the low passed components, which is "slow". The bottom plot is the signals represented in the frequency domain. The vertical dotted line is where the crossover is.

No law of physics is harmed in the production of this simulation.

"A fast driver needs a light cone" is another audio myth. See Purifi's blog post.

A fast driver needs a light cone. Or does it? - PURIFI

Intuition can play us tricks. Take this simple example: how does a speaker cone move when you try to make it produce a “pulse”? I’m willing to bet quite a few of you will guess it will rapidly move forward and then equally rapidly return to its rest position. And from that it’d be quite... View...

purifi-audio.com

 

[Geert]

Laws of inertia are not a matter of opinion. Why do you think there is considerable analysis of the tradeoffs of different cone material construction ?

Because of other attributes like cone breakup and resonances.

 

[fpitas]

Because of other attributes like cone breakup and resonances.

Polar patter, too. The stiff cones act more like a true piston below the first breakup frequency. Of course, they also tend to have a spectacular resonance at a few kHz.

 

[mhardy6647]

"Laws" of physics, you say?

Oh, my mistake! I was thinkin' I was on one of those audiophile websites!

 

[fpitas]

"Laws" of physics, you say?

Oh, my mistake! I was thinkin' I was on one of those audiophile websites!

Not even guidelines. Part of my job as an engineer is to convince people that physics has actual laws. It's surprising how many are completely gulled.

 

[mhardy6647]

Not even guidelines. Part of my job as an engineer is to convince people that physics has actual laws. It's surprising how many are completely gulled.

I wish the "battery technology" industry would be honest with itself -- and its investors -- about those pesky law things.
... but I digress.

My point (of course) -- some designers treat the laws as nice to haves.
Bless their hearts.

 

[Geert]

Part of my job as an engineer is to convince people that physics has actual laws.

You're misguided, it's only our current and very limited understanding of things. You need to be more open minded

 

[ex audiophile]

Welcome

If you read the rest of the thread (it's not particularly long) and ask specific questions on points that need clarification, you will come to see how no violation of physics is required.

That said, I'll try a simple appeal to intuition. Consider a subwoofer playing a 100Hz tone. The driver decelerates, stops, and accelerates in the other direction 200 times every second, or once every 5 milliseconds. Any subwoofer can do this just fine, and play at frequencies much higher than 100Hz. We often model a driver as a piston, but it's very much not like the piston in a car as there is no drive shaft or flywheel that would store angular momentum. The motor directly decelerates and accelerates the cone every cycle.

ps. In an interesting twist, it turns out the motor's max power, or its ability to accelerate the cone, has nothing to do with what frequency a driver can play, only the SPL it can generate.

At first glance it seems intuitive that smaller cones are able to move "faster" than larger ones, however given that the primary purpose of the driver is to move air, I've read and talked with knowledgable folks (Randy at JL Audio for instance) that larger cones can move more air with less excursion and hence would have an advantage over smaller cones that have to move a longer distance to move as much air. Does this play a role in this discussion (I am just an enthusiastic reader, no engineering knowledge).