# Ported Enclosures - Group Delay, Transient Response, Goals of Modeling?



## Sleepy122CID (Aug 26, 2007)

I've never messed with ported enclosures, but my next two installs will definitely include ported enclosures. I've been searching and reading seemingly endless amounts of info over the past few days, but I seem to just develop more questions.

I've been messing with Unibox and WinISD a lot as well. My main goals of modeling were frequency response (particularly a flat curve and low-end extension) and SPL with a given amount of power while keeping cone excursion within limit.

Today something struck me like a bare, hairy chest to the face in a shirts vs. skins basketball game (yeah that is a reference to that movie you saw). How am I supposed to know how the transient response of a ported driver will be? For sealed enclosures, Qtc will pretty much tell you how "tight" the sub-bass should be reproduced. But what do you turn to when designing a ported enclosure?

Group delay? What is actually audible in the <80hz regions? 20ms? 30ms? More? There seem to be too many different answers out there which actually seem to be more like opinions or estimations considering how little research there actually is. I'm not sure that group delay is exactly what could be attributable to transient response though. 

Am I looking for something else? Or should I assume the transient response will always sound good as long as the frequency response curve isn't too peaky?

I'm not sure that I'm looking for hard answers, for there may not be any. Perhaps this could be more of a discussion...


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## bassfromspace (Jun 28, 2016)

You asked a ton of questions.

If I'm getting the general jist of what you're saying, I'd tune the box to the flattest point I possibly could without sacrificing the ported box benefits. You can typically tune out any unnecessary peaks from that point forward.

As far as transient response is concerned, I'd again shoot for a box devoid of any major peaks and made sure I had adequate midbass up front to keep the sound in the front of the car.


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## Sleepy122CID (Aug 26, 2007)

Basically all I was asking is how do you determine how the transient response will be of a ported enclosure (ie tightness/looseness/sloppiness; accurate control of the cone)?


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## Guest (Sep 5, 2007)

I'm not familiar with WinISD ... can it show you the time-domain impulse response? It should ... it has all the info it needs. Mathematically, the time-domain impulse response is nothing but the Inverse Fourier Transform of the complete Frequency Response (amplitude vs. freq and phase vs. freq ... and group delay is nothing but the derivative of phase wrt freq, so the program has already computed the necessary info).

Or maybe it can show you the time-domain step response ... also a member of the "transient response" family. The step response is nothing but the integral of the impulse response, so from one the other is easily computed.

Finally, does WinISD allow an approximation of cabin gain to be included in the analysis?


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## bassfromspace (Jun 28, 2016)

Sleepy122CID said:


> Basically all I was asking is how do you determine how the transient response will be of a ported enclosure (ie tightness/looseness/sloppiness; accurate control of the cone)?


What you've listed are ported box misnomers. A properly tuned ported box can be as good or better sounding than a sealed box. Again, midbass is key to the entire setup as it integrates the sound front-to-back and eliminates the gremlins you just listed.


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## Sleepy122CID (Aug 26, 2007)

I have the Pro version of WinISD, and I cannot seem to find where either of those functions can be performed (if they can).

Unibox does show step response though, but I have no idea what I'm looking at. Perhaps I can get a picture of an example posted up in a couple minutes so you could describe the graph for me (us)?


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## Sleepy122CID (Aug 26, 2007)

bassfromspace said:


> What you've listed are ported box misnomers. A properly tuned ported box can be as good or better sounding than a sealed box. Again, midbass is key to the entire setup as it integrates the sound front-to-back and eliminates the gremlins you just listed.


I know that a properly tuned ported box can be as good or better sounding than a sealed box; I read that all the time. What I'm asking is how do I design a good or better sounding ported box. So you are saying that there is no such thing as transient response in a ported enclosure? It is not possible for the driver cone to do anything but exactly what the signal is telling it to do? I'm not referring to blending the subwoofer bass with the entire system. I'm just talking about accurate signal reproduction of only sub-bass frequencies...???


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## Guest (Sep 5, 2007)

First thing you should do, if you would be so kind as to indulge me, is plot the time-domain step response of a _sealed_ alignment, with a couple values of Qtc ... say, from 0.5 to 1.0 in 0.1 increments.

What you are observing is identically ... The Transient Response.

This is simply the complete, time-domain response to a transient input ... such as a step function, or impulse function.


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## npdang (Jul 29, 2005)

werewolf said:


> I'm not familiar with WinISD ... can it show you the time-domain impulse response? It should ... it has all the info it needs. Mathematically, the time-domain impulse response is nothing but the Inverse Fourier Transform of the complete Frequency Response (amplitude vs. freq and phase vs. freq ... and group delay is nothing but the derivative of phase wrt freq, so the program has already computed the necessary info).
> 
> Or maybe it can show you the time-domain step response ... also a member of the "transient response" family. The step response is nothing but the integral of the impulse response, so from one the other is easily computed.
> 
> Finally, does WinISD allow an approximation of cabin gain to be included in the analysis?


I wish  Would sure be alot cheaper than paying for LEAP...


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## Sleepy122CID (Aug 26, 2007)

Example step response graphs for Dayton 10" HO sealed enclosures with 350W

.5 Qtc









.6 Qtc









.7 Qtc









.8 Qtc









.9 Qtc









1.0 Qtc


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## Guest (Sep 5, 2007)

Sleepy122CID said:


> I know that a properly tuned ported box can be as good or better sounding than a sealed box; I read that all the time. What I'm asking is how do I design a good or better sounding ported box. So you are saying that there is no such thing as transient response in a ported enclosure? It is not possible for the driver cone to do anything but exactly what the signal is telling it to do? I'm not referring to blending the subwoofer bass with the entire system. I'm just talking about accurate signal reproduction of only sub-bass frequencies...???


no no no !!!

EVERY system has a transient response ... this is simply the way the system will respond to a transient input.

In electrical engineering, we often analyze systems according to 2 categories of response : the so-called "forced response", which is simply how the system responds to a fixed input, like a sinewave, and the "natural response", which is how the system responds to a quick, transient input like a step or impulse (I've used these terms a bit loosely). The natural response will show you, for example, how the dynamics of the system release energy by decaying, overshooting, ringing, etc.

ALL systems have transient responses. Speakers, amplifiers, airplane wings and kitchen tables


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## bassfromspace (Jun 28, 2016)

Sleepy122CID said:


> I know that a properly tuned ported box can be as good or better sounding than a sealed box; I read that all the time. What I'm asking is how do I design a good or better sounding ported box. So you are saying that there is no such thing as transient response in a ported enclosure? It is not possible for the driver cone to do anything but exactly what the signal is telling it to do? I'm not referring to blending the subwoofer bass with the entire system. I'm just talking about accurate signal reproduction of only sub-bass frequencies...???


The reason why I stated that a properly designed ported box can sound as good as a sealed box because you gave all the typical responses that people give as to why a sealed box is better.

You are, in fact, referring to blending the entire system together. "Tightness", "Sloppiness", "Looseness" are all analogies that refer to an improperly tuned "SYSTEM". Notice I said "system" and not box. 99% of the time, a system lacks tightness or sounds sloppy or loose because the system lacks proper midbass integration and the user must turn the volume of the sub up and/or compensate by adjusting the xover and forcing the sub to operate outside of it's operating range.

You're making this harder than it has to be.


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## Sleepy122CID (Aug 26, 2007)

Sorry, I was responding to Bassfromspace. He said what I was describing were ported box misnomers. I was trying to communicate what you said - to him, except not in a technical way (not because I didn't want to be technical, just because I don't know all the technical stuff heh)


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## bassfromspace (Jun 28, 2016)

Sleepy122CID said:


> Sorry, I was responding to Bassfromspace. He said what I was describing were ported box misnomers. I was trying to communicate what you said - to him, except not in a technical way (not because I didn't want to be technical, just because I don't know all the technical stuff heh)


I'm not disputing the existence of transient response. I'm just pointing out some practical ways to deal with it.


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## Sleepy122CID (Aug 26, 2007)

bassfromspace said:


> The reason why I stated that a properly designed ported box can sound as good as a sealed box because you gave all the typical responses that people give as to why a sealed box is better.
> 
> You are, in fact, referring to blending the entire system together. "Tightness", "Sloppiness", "Looseness" are all analogies that refer to an improperly tuned "SYSTEM". Notice I said "system" and not box. 99% of the time, a system lacks tightness or sounds sloppy or loose because the system lacks proper midbass integration and the user must turn the volume of the sub up and/or compensate by adjusting the xover and forcing the sub to operate outside of it's operating range.
> 
> You're making this harder than it has to be.


Read the thread above yours. That is exactly what I am trying to say. Not to be rude, but you are making this harder than it has to be. I am not at all describing a system. 

I am describing a specific part of a system. Take away every other part of the system and imagine yourself sitting in a chair in front of a subwoofer in a box. There is music playing, but you can't really tell because the only thing there to play the music is the subwoofer and the box. Nothing else is in the room. All you hear are random sounds below 80hz. You are saying that no matter what kind of box (ported or otherwise) you have the given subwoofer in it is going to respond the same? No, of course not. And all I am trying to do in this thread is figure out how to optimize that one small part of an entire audio system.


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## Guest (Sep 6, 2007)

Just saw your step response plots ... very nice, thanks for indulging me 

What you have plotted is exactly and precisely "The Transient Response" ... nothing more, nothing less.

And you can see how, as Qtc _increases_ in a sealed enclosure ... in other words, as damping _decreases_ from overdamped to underdamped ... the subwoofer output starts to overshoot and ring.

Excessive time-domain overshooting and ringing is considered to be poor transient response. Basically, the sub doesn't stop when it's supposed to ... translating to "sloppy" bass that tends to "overhang." Also makes it difficult to integrate well with a well-damped front stage.

The value of Qtc=0.707 is considered by some to be "optimal" (at least in the absence of cabin gain), because it equates to a "maximally flat" magnitude response in the frequency domain, achieves the lowest possible -3dB frequency, and the transient response doesn't overshoot or ring too badly. Others prefer Qtc closer to 0.5, focusing purely on time-domain transient response and arguing ... quite convincingly, in my opinion ... that you've got cabin gain helping you in a vehicle anyway, so maximally-flat magnitude from the enclosure alone is not a meaningful goal.

Edit : the "transient-perfect" value of Qtc is closer to 0.6, i think (gotta blow the dust off), and we can see why. The value of Qtc=0.6 really has no ringing, and "stops" about as quickly as possible. Too low a vlaue of Qtc leads to a long "tail" in the response ... no ringing, but not exaclty a "quick" elimination of energy either. Too high a value of Qtc leads to excessive overshoot and ringing.


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## Guest (Sep 6, 2007)

And perhaps now we can repeat the same exercise for ported enclosures ...

... but be prepared, it may not be pretty  And we may quickly discover why many believe that sealed enclosures (including infinite baffle) are the _only_ choice for SQ.


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## Sleepy122CID (Aug 26, 2007)

I'm sorry, but if you could now indulge me just a little bit more about those graphs. At this point my new goal for modeling up a ported enclosure is to make sure it looks very similar to the step response graph with a .6 (I think isn't .588 supposed to be the optimal, but .707 is the best compromise?) Qtc, but I don't really understand what the x or y axis represent. I'm assuming the x axis is how long the driver takes to return to rest after the signal ends? But I don't really understand what the y axis is actually representing...


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## Sleepy122CID (Aug 26, 2007)

werewolf said:


> And perhaps now we can repeat the same exercise for ported enclosures ...
> 
> ... but be prepared, it may not be pretty  And we may quickly discover why many believe that sealed enclosures (including infinite baffle) are the _only_ choice for SQ.


Well, since I can't enter a desired Qtc for ported enclosures, how would you recommend I adjust from graph to graph? Tuning frequency? Just a few random boxes?

You say it may not be pretty... although I see what the optimum sealed ~.6 Qtc step response graph should look like, what would an acceptable ported box look like? What is actually audible?


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## Sleepy122CID (Aug 26, 2007)

Ok, here we go. This is an eD SQ10 with different ported enclosures and then the respective step response graphs for each box.

First, the frequency response curves overlayed:









1.0 cf - 30 hz









.8 cf - 32 hz









1.5 cf - 25 hz









And just for fun, a 6db peaker - 1.0 cf - 47 hz


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## Guest (Sep 6, 2007)

Sleepy122CID said:


> I'm sorry, but if you could now indulge me just a little bit more about those graphs. At this point my new goal for modeling up a ported enclosure is to make sure it looks very similar to the step response graph with a .6 (I think isn't .588 supposed to be the optimal, but .707 is the best compromise?) Qtc, but I don't really understand what the x or y axis represent. I'm assuming the x axis is how long the driver takes to return to rest after the signal ends? But I don't really understand what the y axis is actually representing...


Basically, yes 

The x-axis represents time. And we know that the step "input" actually stopped at t=0 ... this is the precise instant when the step input transitioned form 0 to +1 in amplitude. So it's completely fair to say that the input "stopped" at t=0.

The y-axis represents acoustic output from the subwoofer, according to some scale factor. Yes ... the good modelling programs actually model the electrical, mechanical and acoustical elements of the subwoofer to determine it's acoustical output for the given electrical input (thank you, Dr. Beranek!).

Allow me to also address the comments above, concerning complete system response versus a single driver by itself. And I'll use two examples :

1. A midrange driver, crossed over to a tweeter. It is VERY true, that either driver by itself may exhibit transient issues that are somewhat compensated by the other driver ... in much the same way that the frequency responses compensate each other : each may be down -3dB at crossover, for example, or -6dB at crossover, but when summed are reasonably flat. Well, the transient responses in the time domain also "sum" ... so we may be a bit misled by either single driver.

2. A subwoofer. The transient response issues we are seeing are a result of the subwoofer's high-pass response. What? When did we put a high-pass filter on the subwoofer? We didn't ... it just so happens that _any_ driver in _any_ enclosure will exhibit a high-pass response. The speaker itself, you see, is a high-pass filter  And unfortunately, for subwoofers, there's no other driver in the system to "compensate" for this high-pass response. So it is quite accurate, and meaningful, to examine the sub's transient response in isolation.

Make sense?


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## Guest (Sep 6, 2007)

I now see your ported transient responses 

First thing, with the ported enclosure ... you are definitely getting more "low frequency" output from your driver. So i think it's fair to say, that all activity will naturally be "stretched out" in time compared to the sealed enclosure ... this is not, in itself, the concern.

However, what is of concern is the overshoot and ringing. There's no free lunch  You won't get more low frequency output from any given driver without paying the price somewhere 

How much is audible? No simple answer as far as i know. But do remember that we've got cabin gain in a vehicle. Many will argue ... again, quite convincingly ... that sealed is the way to go for SQ, because the cabin gain nicley compensates the 12dB rolloff of the driver+enclosure, giving you all the "low-end" you want or need ... no need to "enchance" with ports or passive radiators ... plus, you get to keep the reasonably nice transient response the sealed enclosure gives you.

I'm not dumping on ported or PR enclosures, by the way. Just offering the tradeoffs as I see them


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## Sleepy122CID (Aug 26, 2007)

Yessir, so would it be accurate to say the peaks of the waveform represent the driver's cone's forward (outward, I dunno) excursion and the troughs represent the backward (inward) excursion? Is there any standard on what is considered acceptable considering anything we may experience in general musical programs? For example, the cone should come to rest within .05 seconds and/or the driver output should not be more than .2 (of whatever increments those are) in either direction?

Edit: Just read your comment about what is audible. I knew it couldn't be that simple =P


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## Guest (Sep 6, 2007)

Now, just for kicks ....

I have said that what we are looking at is the Transient Response of the driver in different enclosures. This is, without question, absolutely TRUE. The time-domain transient response is the COMPLETE time-domain response of the driver to a transient input ... like, a step-function input.

I want to introduce the concept of subwoofer inductance. Please note ... inductance is probably not included in the results so far. It may be, but the point is that the responses we are viewing are most definitely NOT "dominated" ... in any sense of the word ... by inductance. These responses are controlled by the classic T/S parameters : Fs, Qts, Vas. So yes, we definitely have substantial, and sometimes very different, transient responses ... even in the complete _absence_ of voicecoil inductance.

Here's the million dollar question : If we introduce some voicecoil inductance into these responses ... or, if some small values are already included, let's start increasing the inductance ... how will this increasing inductance show up in the transient responses? What about the responses will start to change, as we increase voicecoil inductance?

I will literally ship a prize of some value to the first response that's correct !!!


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## Sleepy122CID (Aug 26, 2007)

Just from looking at my few ported response graphs, I would generally think that a peaky box like the last graph represents (1cf tuned to 47hz) would not be nearly as clean, but I could be wrong.

If that thinking is correct, perhaps the driver output, y-axis, should be the one we should be more concerned with. This would carry some logic in my mind, for more output after the signal ends would make the bass sound "loose" or "muddy," while the time it takes the cone to stop moving wouldn't matter as much - especially if a new signal was sent within the time it takes for the cone to stop - assuming there wasn't audible output within that time...


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## danez_yoda (Sep 6, 2007)

May I suggest you buy the "Loudspeaker Design Cook Book" by Vance Dickason

Check Amazon or Parts Express.

He has a chapter in there that goes into different allignments for a sub enclosure. I believe the QB3 (Quick box) allignment had the best tradeoff between lowest F3, smallest volume, and decent transient response. There were other allignment like Chebychef (SP?) Super boombox (SBB) and a few others.

Basically the sharpness of the "knee" at the cutoff frequency effects the phase repsonse which is linked ot the group delay (phase shift/frequency)

If the knee is a soft gentile curve, you will get a better group delay than if the knee had sharp and abrupt or if it had a hump before rolling off.

To get a softer knee you need to increase the box size and lower the tuning frequency (longer port). Sofening the knee to get SQ will cost you some in power handling above the F3.

Put the F3 will be higher the F10 may be lower with a softer knee and it may tune out better in a car with the low frequency response gain.... you have to tune and see.

As you can see ported boxes have a lot more tradeoffs than a sealed box but the results can be very rewarding depending on ehay you're looking for.

Like Warewolf I'm a EE that got his degree to learn how to design Crossover networks!  Been doing this for a LOONNNNGGG time. Not much has changed

Other tips, Look closely at the port size or all you tuning will fruitless. For large excersion woofers you need a large port area or they will "huff" and ruin any gains you get from the ported design. Multiple parts or shelf ports are good for this. Make sure you round off the corners on either end of the ports also. WinISD should have something that tells you the airspeed in the ports you want to keep this as low as reasonably possible. If you have a small/shallow box, consider a passive radiator to get low tuning frequency. Tuning will be by trial and error but you just keepd adding weights to the PR until it sound good and leave it there.  

Have fun


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## Guest (Sep 6, 2007)

Sleepy122CID said:


> Yessir, so would it be accurate to say the peaks of the waveform represent the driver's cone's forward (outward, I dunno) excursion and the troughs represent the backward (inward) excursion? Is there any standard on what is considered acceptable considering anything we may experience in general musical programs? For example, the cone should come to rest within .05 seconds and/or the driver output should not be more than .2 (of whatever increments those are) in either direction?
> 
> Edit: Just read your comment about what is audible. I knew it couldn't be that simple =P


not quite ... the peaks and valleys do not represent cone _position_. The acoustic output of the driver is proportional to cone acceleration ... the peaks and valleys represent peaks and valleys in the driver's _acceleration_, rather than the cone's _position_. They are, of course, related ... anybody remember Newton's Laws of motion? 

There's a clue, in the graphs, that tells you it's IMPOSSIBLE for the responses to be showing you cone _position_ ... or, for that matter, cone _velocity_  But i won't give up this clue, until my quiz question gets answered


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## Sleepy122CID (Aug 26, 2007)

werewolf said:


> Here's the million dollar question : If we introduce some voicecoil inductance into these responses ... or, if some small values are already included, let's start increasing the inductance ... how will this increasing inductance show up in the transient responses? What about the responses will start to change, as we increase voicecoil inductance?
> 
> I will literally ship a prize of some value to the first response that's correct !!!


I dunno, I could only guess, for it doesn't seem to affect the step response in the program no matter how I change it =(


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## Sleepy122CID (Aug 26, 2007)

danez, it has all those boxes in winisd =)


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## unpredictableacts (Aug 16, 2006)

Thanks Guys I now have a headache......I have done several boxes and custom set ups and have never thought this hard into to it.


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## SSSnake (Mar 8, 2007)

An inductor is an energy storage device. Increase the inductance and the ringing should get worse or at least take longer to settle out.


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## Sleepy122CID (Aug 26, 2007)

So I added the aforementioned supposedly best transient response box model to the response graph and also a step response graph for that alignment:


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## Guest (Sep 6, 2007)

SSSnake said:


> An inductor is an energy storage device. Increase the inductance and the ringing should get worse.


yes, an inductor is an energy storage device ... but worse ringing is not the first place you'll see it.

quiz still open


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## SSSnake (Mar 8, 2007)

OK the low pass filtering provided by the inductor would decrease the freq response and therefore adversely affect the transient response. The question is where does this become the dominant factor in the transient response?


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## solacedagony (May 18, 2006)

Inductors oppose changes in current?


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## Guest (Sep 6, 2007)

SSSnake said:


> OK the low pass filtering provided by the inductor would decrease the freq response and therefore adversely affect the transient response. The question is where does this become the dominant factor in the transient response?


dude you are SO CLOSE ... i can immediately tell you that the responses shown are pure high-pass ... they have NO low-pass function at all. How can I tell?

Clue : same way i can tell the responses can NOT be cone position or velocity. It's immediately obvious


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## Guest (Sep 6, 2007)

solacedagony said:


> Inductors oppose changes in current?


yes they do ... and current supplies the FORCE for the driver ...

quiz still open


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## solacedagony (May 18, 2006)

werewolf said:


> yes they do ... and current supplies the FORCE for the driver ...
> 
> quiz still open


Based on that, the force applied isn't going to disappear instantly (it will continue acting on the cone), causing your overshoot. I'm not sure if that answers the question though.


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## Guest (Sep 6, 2007)

solacedagony said:


> Based on that, the force applied isn't going to disappear instantly (it will continue acting on the cone), causing your overshoot. I'm not sure if that answers the question though.


it doesn't answer it ...

what happens when i start to add coil inductance? What happens when we introduce a low-pass function, at some _higher_ frequency, into the response? Where will i immediately notice it in the time-domain response graphs?

And how do i know these responses cannot possibly represent the position or velocity of ANY physical system? BUT ... they CAN represent acceleration, providing that the FORCE is not impeded ... by an inductance, for example ???

These questions are INTIMATELY related 

This is important stuff dudes ... I'm not being cute-sy. I'll request this thread be moved into the tutorials section.


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## SSSnake (Mar 8, 2007)

Not sure if this is what you are looking for but the rise time looks to be zero on the graphs. Inductors oppose changes in current flow. You can't have a zero rise time with an inductor present. Also position cannot change instantaneously.


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## Guest (Sep 6, 2007)

SSSnake said:


> Not sure if this is what you are looking for but the rise time looks to be zero on the graphs. Inductors oppose changes in current flow. You can't have a zero rise time with an inductor present. Also position cannot change instantaneously.


BINGO !!!!!

WE HAVE OUR WINNER !!!!!!!!!!!!!!!

WELL DONE !!!!!!!!!

I'll post more, and tie it all together in another post or two ....  

THIS IS SO IMPORTANT, because there's been so much mis-info on "transient response" floating around ... this thread can clear it all up, for anyone willing to read and digest 

Send me your mailing address by PM dude


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## solacedagony (May 18, 2006)

SSSnake said:


> Not sure if this is what you are looking for but the rise time looks to be zero on the graphs. Inductors oppose changes in current flow. You can't have a zero rise time with an inductor present. Also position cannot change instantaneously.


How is "rise time" depicted on the graphs? Meaning that the plotting starts at that top position at 0.0 seconds instead of ramping up to it?


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## Guest (Sep 6, 2007)

First, the physics/dynamics part.

Yes ... i can immediately tell that the responses shown can not possibly represent a physical position or velocity, because there is ZERO risetime in the step response. 

Velocity can NOT change instantly, because that would require infinite acceleration (since acceleration is the first derivative of velocity). And infinite acceleration would mean infinite force, since force and acceleration are simply proportional by F=ma.

Position can NOT change instantly, because that would require infinite velocity (since velocity is the first derivative of position). And infinite velocity would require doubly-infinite acceleration  which can't happen (see above).

However, acceleration CAN change abruptly. This only requires an abrupt change in force, which is not only physically possible ... it happens all the time. No "infinities" required!  So zero risetime in acceleration is quite OK ... as all of these modelling programs (at least, those that ignore inductance) clearly demonstrate.

More in a bit ...


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## SSSnake (Mar 8, 2007)

Werewolf,

Thanks for the offer but I USED to be an EE (15 years removed from school with not a lot of analog circuit design work since...). I am a Modeling and Simulation SME/Program Manager for a local defense contracting firm. Thanks for the prize offer but just keep contributing to the forums. I track your posts in multiple forums and you are doing quite a bit to dispel myth and misinformation in audio circles. 

My current frustration is that I get lots of people arguing against scientific method based off of anecdotal evidence.

Charles


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## Guest (Sep 6, 2007)

SSSnake said:


> Werewolf,
> 
> Thanks for the offer but I USED to be an EE (15 years removed from school with not a lot of analog circuit design work since...). I am a Modeling and Simulation SME/Program Manager for a local defense contracting firm. Thanks for the prize offer but just keep contributing to the forums. I track your posts in multiple forums and you are doing quite a bit to dispel myth and misinformation in audio circles.
> 
> ...


as you wish


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## Guest (Sep 6, 2007)

solacedagony said:


> How is "rise time" depicted on the graphs? Meaning that the plotting starts at that top position at 0.0 seconds instead of ramping up to it?


risetime is depicted thusly (always wanted to use that word):

the step INPUT transitions from 0 to 1 at t=0. Before t=0, the input was zero. And this necessarily means that the output was also zero before t=0 (assuming the system is causal and stable, but i digress).

So we know that the ouptut was zero before t=0. But exactly at t=0, when the input jumps, the output INSTANTLY jumps.

As explained, any physical object's position or velocity can NOT behave this way. But it's acceleration can ... only thing that's required is an abrupt change in FORCE 

If our voicecoil has zero inductance, a step change in VOLTAGE across the loudspeaker terminals will result in a step change in CURRENT. That step change in current will cause a step change in magnetic force. That step change in force will cause a step change in acceleration, which ultimately means a step change in acoustic output ... AS SHOWN IN THESE GRPAHS 

Once we introduce voicecoil inductance, we can STILL apply a step change in voltage to the loudspeaker terminals. But that step change in voltage will NOT cause a step change in current, with inductance present. Hence, the current, force, and acoustic output will have a non-zero rise time.

How are we doing? Making sense so far?

By the way ... all of the Transient Responses analyzed by the classic Small papers did NOT include inductance. Hence, they all had zero risetimes.

However ... and this is IMPORTANT ... even in the complete ABSENCE of inductance, we still have very dynamic transient reponses, with qualities like overshoot and ringing, that are controlled by the classic T/S parameters Fs, Qts, Vas.


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## solacedagony (May 18, 2006)

Ok, let me see if I've got this right...

That graph WITH inductance would show the plotting starting at 0, 0. The plot would show the cone acceleration over time going up and coming back down. In a perfect transient world, should the plotted curve go up and back down to the line without going below at all?

Also, as inductance increases, rise time (and equally, "fall" time) will increase. Meaning that acceleration/deceleration decrease.


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## Guest (Sep 6, 2007)

solacedagony said:


> Ok, let me see if I've got this right...
> 
> That graph WITH inductance would show the plotting starting at 0, 0. The plot would show the cone acceleration over time going up and coming back down. In a perfect transient world, should the plotted curve go up and back down to the line without going below at all?
> 
> Also, as inductance increases, rise time (and equally, "fall" time) will increase. Meaning that acceleration/deceleration decrease.


Let's be clear what zero ristime means 

The reponses shown actually have a component .. a "vertical line" if you will ... that starts at the origin (0,0) and goes straight up. You know it's there, because the response starts "falling" from a point that's NOT the origin as soon as time gets away from t=0. As time starts increasing, the response "gradually" falls ... gradually, compared to how _abruptly_ it _rises_. Make sense?

The response graphs do not show a zero fall time ... the fall time is gradual, and laden with overshoot and rigning, compared to what happens at t=0.

Make sense? Let's get this point completely clear first ... namely, what the graphs shown actually indicate.

Edit : In other words, the responses actually "seem" to start at the point t=0, y=1. See what I mean? But they DON'T ... they start at t=0, y=0 and immediately JUMP, vertically, to (0,1). I know this is true ... because I know that before t=0, the output HAD to be zero.

It's imperative that this point is crystal clear.


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## Guest (Sep 6, 2007)

I will belabor this point as much as necessary  What would the graph look like, if i removed all "graph lines" ... just leaving the response without any tics or marks or lines ... and i started plotting at t=-0.01, instead of t=0?

by the way, to the original poster, please don't edit those graphs! Make new ones, if necessary


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## solacedagony (May 18, 2006)

werewolf said:


> I will belabor this point as much as necessary  What would the graph look like, if i removed all "graph lines" ... just leaving the response without any tics or marks or lines ... and i started plotting at t=-0.01, instead of t=0?
> 
> by the way, to the original poster, please don't edit those graphs! Make new ones, if necessary


I understand what you mean, I wasn't thinking about it in that context.

If you started t at -0.01, on the previous graphs with NO inductance added in, y would be 0. y should be 0 to -infinity because we didn't start measuring or simulating yet.


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## Guest (Sep 6, 2007)

solacedagony said:


> I understand what you mean, I wasn't thinking about it in that context.
> 
> If you started t at -0.01, on the previous graphs with NO inductance added in, y would be 0. y should be 0 to -infinity because we didn't start measuring or simulating yet.


Yes ... "y" would be zero from t = -infinity, just up until t=0. But the reason this is so, is because the step _input_ was exactly zero over that whole time period as well. I know this, because this is the very definition of a step input 

Then, exactly at t=0, the input immediately changes to +1.

And in the absence of inductance, the output also immediately changes to +1 ... just as the graphs show


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## Guest (Sep 6, 2007)

So we know that, in the absence of inductance, we have infinitely fast risetime in the sub's transient response. However, we still have overshoot and ringing in the transient response ... these are controlled by Fs, Qts and Vas.

Another way of saying this, is that Fs, Qts and Vas control the subwoofer's HIGH-PASS frequency response, in the frequency domain. These parameters describe the characteristics of our high-pass "filter" ... cutoff frequency, and possible "peaking" in the frequency response associated with Qtc. And remember ... we've added no electrical high-pass filter, but the sub's acoustical output itself must be a high-pass version of it's electrical input. This "high-pass" response is clearly shown in the frequency response graphs that accompany some of the transient plots shown 

Furthermore, these high-pass "dynamics" ... the cutoff frequency, possible peaking ... occur at realtively LOW freqeuncies. Remember ... a HIGH-pass cutoff will actually be at a LOW frequency  And we see that, in the time domain, the "artifacts" of the peaking actually extend out over a LONG period of time. This is because of a duality between time and frequency : LOW frequency artifacts correlate to LONG time periods.

*BOTTOM LINE, for now : The classic T/S parameters of Fs, Qts and Vas control the sub's HIGH-PASS behavior, at relatively LOW frequencies. These parameters directly effect the overshoot and ringing of the transient response ... transient artifacts that tend to be stretched out over a relatively LONG period of time.*


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## Guest (Sep 6, 2007)

We're almost done ...

Now we add some voicecoil inductance. We've already argued what happens in the time domain ... the risetime will no longer be zero. That striaght line "up" in our output response at t=0 will no longer be a srtaight line "up" ... it will have a finite slope. Sure ... the ringing and overshoot will be effected a little bit, but you would have a hard time noticing ... as long as the inductance is not crazy big.

What does the inductance do in the frequency domain? Think about what a series inductor does in a first-order crossover network ... it adds a first-order LOW-PASS filter  And so it is with voicecoil inductance. Those frequency response plots shown with some of the transient responses will have a low-pass characterisitc introduced at some higher frequency ... preferably, out past 100 or 200 Hz. The exact cutoff will be determined by the voiceoil resistance divided by voicecoil inductance (divided by 2pi).

*BOTTOM LINE, for now: Voicecoil inductance adds a first-order low-pass filter, much like a first-order crossover, to the subwoofer's frequency response ... at a relatively high frequency, compared to the high-pass part controlled by Fs, Qts and Vas. And inductance shows up in the transient response by limiting the risetime. This is all consistent with inductance limiting the applied force, and consequently acceleration and acoustic output, of the cone. *


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## Guest (Sep 6, 2007)

hee hee ... if anyone is still reading, this is it ... the summary 

The sub's time-domain transient response is related to the frequency-domain response through the unique Fourier Transform. 

In the *frequency domain*, we have a two "regimes" :

1. The _high-pass_ regime, with dynamics like Fc and peaking, at relatively _low_ frequencies. This regime is controlled by Fs, Qts and Vas.

2. The _low-pass_ regime, at relatively _high_ frequencies. This regime is controlled by voicecoil inductance (in relation to resistance, like any first-order low-pass filter).

Likewise, we tend to have two regimes (not quite as easy to separate, but still approximately accurate) in the time-domain transient response :

1. The _longer-time_ regime where overshoot and ringing are apparent. This corresponds to the first, _low-frequency_ regime above.

2. The _short-time_ (or quick) regime, where we observe finite, non-zero risetime. This corresponds to the second, _high-frequency_ regime above.

The quickest possible summary, while still maintaining a good degree of accuracy, is this :

*Inductance controls the transient attack, while the classic T/S parameters of Fs, Qts and Vas control the transient decay (including possible overshoot and ringing).*

That's it!

me = done


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## forty5cal1911 (Sep 11, 2006)

Man what a great thread! 
I knew Werewolf got tight, but this thread explains a lot. 
Is the only way to accurately measure inductance of a voicecoil to have some type of speaker tester either hardware that goes into a computer or something like dayton woofer tester? Is there a way to calculate this without knowing the gauge of wire used in the voicecoil wrapping, the diameter, and how many windings it had?


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## mvw2 (Oct 2, 2005)

A good read.

I've always associated low inductance drivers with improved high frequency extention, but this is the first time I've thought of a speaker as its own low pass filter. I always wondered how programs like Bassbox guesses the high frequency roll-off of a driver.

I do have one question about inductance. In terms of loud speakers, is it generally preferred to have a low inductance driver over a high inductance version? Is there a case where we would actually prefer a high inductance driver? Would this just come down to a matter of taste in sound?

As well in terms of transient response and attack, I've seen mention of qms as an indicator for such characteristics as well. A high qms indicates an efficient driver/suspension design, light weight parts, hopefully not so much so that rigidity is compromised. In essence, a high qms low Le driver will be quick to move with little mechanical or electrical resistance. I'm curious if one aspect is dominant over another or at perhaps what frequencies should a person be concerned about one or the other.


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## c0mpl3x (Nov 30, 2005)

Whew! I finally got around to reading the entire thread and I'm really glad I did. 

I must say Werewolf, it's a pleasure to have you a part of this forum.


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## Genxx (Mar 18, 2007)

Just got done reading the entire thread and now my head hurts. I am sure after I read this another 10 times it will start to sink in. My BA in History sure does help me out in understanding all this.LOL

Damn its nice to have all you smart guys around to learn something new every day.


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## Medicineman (Apr 9, 2007)

I have some plots from SoundEasy that may be helpful. I do not claim to know what they are telling us. :blush: Just hoping it helps keep the discussion going. This thread has been very informative so far!

These are for a 0.55 Qtc sealed enclosure.

First, a quick look at the settings. Pulse frequency is set at 60 Hz. Notice I used a square wave type pulse here. Impulse duration does not alter the plot. The square wave type pulse seemed to best demonstrate the effects of added inductance.











This plot is for the driver *without* any low pass network. The inductance from the coil was measured as 1.61 mH (if that matters to anyone) but does not seem to be included in the step plot. It is very evident in the spl plot.











This plot has a first order Butterworth type passive xo centered at 60 Hz. (basically one inductor and a couple of resistors)


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## tard (Jul 13, 2006)

while werewolf can feed you all the technical nourishment... i can throw some things in layman's terms and some tricks to get it perfected.

there are factors that won't show in your simulation plots. or at least are best dialed out by ear and not relying on the simulation. suspension compliance is another major factor to look at.

ported box's can tend to have less restorative force, especially as you start going bigger in port size. this will attribute to overshooting. and as was stated, inductance will also degrade transient times. so if you go for a sub that maintains a stiff suspension after break in, it will help fight the sluggishness in cone direction change caused by inductance and also from the decreased box restorative force.

there's a trade off in anything, like werewolf said. up to a point, a bigger port = bigger radiating area = increased output = better efficiency. but also can = degraded transience and sloppy cone control making everything but a low note sine tone sound like poo.

you also don't want to go overly long with the port in attempts to get low tuning. you'd be better off building a TL instead of a 36" long port for a musical box imo.

medium to smaller ported box tend to have better impact. if you want a superb ported box, first play the crap out of your sub and get it broke in. build the box on the big side with one of the designs you came up with in your simulation program. do all tests in your vehicle how it will be normally listened to. rolling down windows or opening doors can have a big effect in performance/ response.

play all sorts of music. add some bricks or jugs of water to the box to shrink the net volume. play your music. try changing port length. keep jumbling all that around until it is tuned and dialed to your liking. even vance dickasons book should tell you to do that. all these box alignment formula's basicly just get you close. can be close enough for many, but if you want perfection... dynamically tune it. it shouldn't take long before you get a feel for what changes will have what general effect to the sound.

that was just your test box. calculate what your final net volume is and port specs. then build your final box to those specs. you should also take into consideration cabin loading/sub-port placement in the vehicle. this can also have an effect to the sound. the trick to get better transience from a bigger size ported box is to load the sub close off of a wall or add in a "loading shelf" in front of the sub.


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## tard (Jul 13, 2006)

you also want to pay close attention to port specs. you don't want a "leaky" port. that is one where the gross vol displacement of the cone travel will move more air than what is contained in the port.

you also don't want too small an area of port or else port velocity will increase and cause noise. flare or round any edge that air will flow over.


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## Oliver (Jun 25, 2007)

"BRAVO, WereWolf !!! Bravisimo  

What a tour de force


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## solacedagony (May 18, 2006)

Thanks, Werewolf, for taking your time to explain the more technical info!


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## forty5cal1911 (Sep 11, 2006)

I have attached a good read on transmission line enclosure design. I know most people don't have access to the LEAP software but it still has some great information for those wanting to tackle an enclosure of this difficulty.


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## Oliver (Jun 25, 2007)

Nice corresponding information relating to QTS.

Just read the whole article!!

http://www.infinitysystems.com/car/products/10946_eprint.pdf


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