Have a look for a book by David Weems - Designing Building and Testing Speaker Systems, I think he might go over it in more detail for a beginner. But TBH I can't be sure as I've read so much since and it was so long ago...
Vaughan, the ported sub will have low (relatively speaking) harmonic distortion around the tuning frequency due to the driver moving so little. Here is the THD of a subwoofer tuned to ~25hz - notive the decrease in THD at that point.
Were that a sealed sub instead, that THD would have just kept rising exponentially - here is an example of a different brand sealed sub.
However, while the ported sub will have low THD (relatively speaking) around tuning, it is at risk to have high noise distortion - one of the reasons is because air is moving fastest in the port around tuning. You can eliminate that as a concern with a large enough diameter port and a large enough flare though.
An externally hosted image should be here but it was not working when we last tested it.
Were that a sealed sub instead, that THD would have just kept rising exponentially - here is an example of a different brand sealed sub.
An externally hosted image should be here but it was not working when we last tested it.
However, while the ported sub will have low THD (relatively speaking) around tuning, it is at risk to have high noise distortion - one of the reasons is because air is moving fastest in the port around tuning. You can eliminate that as a concern with a large enough diameter port and a large enough flare though.
Noah, do you have any good recommendations on books that really go indepth on this kind of stuff ? I'm hungry for knowledge here.
Just remember that I'm not a math geek. If I see equations I'll fall over and knock myself out. 🙂 But seriously, I am someone who wants more intuitive, practical explanations on these kinds of phenomena.
Thanks.
--Sincerely,
Just remember that I'm not a math geek. If I see equations I'll fall over and knock myself out. 🙂 But seriously, I am someone who wants more intuitive, practical explanations on these kinds of phenomena.
Thanks.
--Sincerely,
SteveCallas, thank you for posting those graphs. So I was right in thinking that the drivers cone excursion is minimized because of the sucking of energy of the port "off the driver".
Could you also please recommend me a few good books on the mechanics of ported design, on resonance, etc. As I said, I have the Vance Dickason book which I think is great but it explains the "how" but not the "why".
I also have the Master Handbook of Acoustics. Great book. But looking at those graphs you posted makes things a bit easy to understand.
Thanks a lot.
--Sincerely,
Could you also please recommend me a few good books on the mechanics of ported design, on resonance, etc. As I said, I have the Vance Dickason book which I think is great but it explains the "how" but not the "why".
I also have the Master Handbook of Acoustics. Great book. But looking at those graphs you posted makes things a bit easy to understand.
Thanks a lot.
--Sincerely,
I'm not familiar with any such books - while I'm not nearly as knowledgeable in the technical aspects as someone like Noah, I picked up what I do know from experimenting with simulation programs and correlating them to real world measurements.
That Secrets article you linked to a page or two back is very informative and should be able to answer most of your questions. It even has diagrams of models showing how the motion of the cone at generic frequencies (above tuning, at tuning, below tuning) affects the air mass in the port.
Whatever questions you have left should be answered in that AVS thread - the measurements Ilkka conducted tell a whole lot.
That Secrets article you linked to a page or two back is very informative and should be able to answer most of your questions. It even has diagrams of models showing how the motion of the cone at generic frequencies (above tuning, at tuning, below tuning) affects the air mass in the port.
Whatever questions you have left should be answered in that AVS thread - the measurements Ilkka conducted tell a whole lot.
“I have the Vance Dickasons book which I've read three times and I understand the mechanics of speaker design and operation very well. But the book does not go into detail how ported subwoofers work.”
If you got any intuitive grasp on things from LDC my hat’s off to you. I found it frustratingly sparse of explanations of how things work to go along with the cookbook recipes.
“I understand that the driver is working in order for the air to be sucked through the port. Understand that. But if the sucked air is reducing the cones motion then surely there is less distortion from the driver ?
Correct ? According to the article I posted, the driver will hardly be moving at resonance and so I assume that distortion is very low at this point. Otherwise where would this llow distortion come into play with a ported design ?”
Yes it is, as it says in every description of vented system operation I’ve seen. I don’t understand why that’s still a question in your mind.
“I need to read more books on resonance and as MJK said, vibrational theory. Now I'm not a big math guy, I prefer to understand more empirical (and practical) explanations of things.
I know that math and theory are intertwined, but I would like to understand the theory well. Are there any books which really go in depth on this (and are math-less )?”
I’ve given you my best recommendation for understanding what’s going on w/o math several times.
The key will be to notice the phase of your hand's motin relative to the ball, and the forces you're feeling in your hand.
You're hand is the driver, the elastic band is the box air, and the ball is the port air mass.
”So I was right in thinking that the drivers cone excursion is minimized because of the sucking of energy of the port "off the driver".
Can’t quite make sense of this, but I think you have an over-fascination with the port sucking.
“Minimum phase would refer to crossover schemes where the aim is to achieve minimum phase shift/difference between drivers. Nothing whatsover to do with vented systems.”
AFAIK minimum phase is every bit as relevant to ported as to vented systems.
I admit though that my intuitive grasp on these things does not extend to this arena.
If you got any intuitive grasp on things from LDC my hat’s off to you. I found it frustratingly sparse of explanations of how things work to go along with the cookbook recipes.
“I understand that the driver is working in order for the air to be sucked through the port. Understand that. But if the sucked air is reducing the cones motion then surely there is less distortion from the driver ?
Correct ? According to the article I posted, the driver will hardly be moving at resonance and so I assume that distortion is very low at this point. Otherwise where would this llow distortion come into play with a ported design ?”
Yes it is, as it says in every description of vented system operation I’ve seen. I don’t understand why that’s still a question in your mind.
“I need to read more books on resonance and as MJK said, vibrational theory. Now I'm not a big math guy, I prefer to understand more empirical (and practical) explanations of things.
I know that math and theory are intertwined, but I would like to understand the theory well. Are there any books which really go in depth on this (and are math-less )?”
I’ve given you my best recommendation for understanding what’s going on w/o math several times.
The key will be to notice the phase of your hand's motin relative to the ball, and the forces you're feeling in your hand.
You're hand is the driver, the elastic band is the box air, and the ball is the port air mass.
”So I was right in thinking that the drivers cone excursion is minimized because of the sucking of energy of the port "off the driver".
Can’t quite make sense of this, but I think you have an over-fascination with the port sucking.
“Minimum phase would refer to crossover schemes where the aim is to achieve minimum phase shift/difference between drivers. Nothing whatsover to do with vented systems.”
AFAIK minimum phase is every bit as relevant to ported as to vented systems.
I admit though that my intuitive grasp on these things does not extend to this arena.
Noah, I just wanted reassurance that my understanding was correct on the issues I raised. Rereading it through, it seems like I was just repeating what I said before but I guess it's a bad habit of mine.
Thank you for all your contributions to this thread. I think without a doubt my understanding of ported subwoofers has improved quite a bit. Thanks to all for their advise and explanations.
Really, really appreciate it. Thanks.
--Sincerely,
Thank you for all your contributions to this thread. I think without a doubt my understanding of ported subwoofers has improved quite a bit. Thanks to all for their advise and explanations.
Really, really appreciate it. Thanks.
--Sincerely,
Maybe you should restate your understanding and someone else might take a crack at helping you out. Be aware that it is very difficult to understand this without ~3-4+ years of engineering or physics education - and many who have that still don't really understand the mechanical system anyway. Among those that do, there are few that can boil it down to laymans terms... So no promises 😉
Well, my manager has been in the audio field for almost 35 years, he has an engineering degree, has worked in several music studios with all the credentials you could want.
But, well, he tells me that it's physical impossible for an 18" driver to be as "fast" as an 8" driver. Now if someone with all that experience and technical qualifications can't understand why that is wrong then I don't know.
Whatever.😀
--Sincerely,
But, well, he tells me that it's physical impossible for an 18" driver to be as "fast" as an 8" driver. Now if someone with all that experience and technical qualifications can't understand why that is wrong then I don't know.
Whatever.😀
--Sincerely,
LOL your manager is letting audio BS accumulated over the years of working in studios, to cloud his engineering judgement 😉
Steve, I know, I know, I just wanted to make a point. 😀 I definitely will not go through that again.
Promise. Heh.
--Sincerely,
Promise. Heh.
--Sincerely,
Vaughan said:
Perhaps we have different connotations for the term "understand". Just because one fulfils a prerequisite doesn't mean they automatically pass the class 😉 It is a necessary but not sufficient condition.
What you can seek without the math/theory background is an intuitive grasp. AFAIK, that is what you want. Some of the answers in this thread are helpful, some are misleading. Rather than replying to each post individually or spending my time finding these, I suggested you roll up what you have taken away from this discussion so far so it would be easier for people (not necessarily, or even likely, including myself) to respond to any potentially interesting questions.
One definition for minimum phase is "a transfer function having no poles in the right half plane" which probably means a LOT to you now, doesn't it 😉 BTW, the responses of all typical passive RLC circuits (and loudspeaker frequency responses) are more or less minimum phase. So why do you ask?
I asked about minimum phase because I've heard about it in a lot of acoustic threads and I had no idea what it is.
Still don't. 🙂
I feel like I've learned something from this thread. But you say that some of the "advice" in this thread was also misleading ? That is a bit disparaging.
I wish you could have been a little more specific though.
--Sincerely,
Still don't. 🙂
I feel like I've learned something from this thread. But you say that some of the "advice" in this thread was also misleading ? That is a bit disparaging.
I wish you could have been a little more specific though.
--Sincerely,
One definition for minimum phase is "a transfer function having no poles in the right half plane" which probably means a LOT to you now, doesn't it
Did you read that off a site ? 😀 Seriously, I don't understand what that means. Could you please give me an intuitive explanation on what minimum phase is ?
Thanks.
--Sincerely,
Did you read that off a site ? 😀 Seriously, I don't understand what that means. Could you please give me an intuitive explanation on what minimum phase is ?
Thanks.
--Sincerely,
Vaughan said:
Yeah, everything I know about everything I learned on the internet...you can believe that if it makes you feel better, I don't give a rip. These concepts are from control theory - causality (order of numerator less than or equal to denominator - or the ability to derive input from output) and stability, (no positive real poles or zeroes).
If you want a webpage do a search.
Minimum phase essentially means that the phase is derivable from the frequency response. This means jack squat for most audio circuits or systems because passive filters (at least planar and passive ones) are all minimum phase and loudspeaker response is "effectively" minimum phase. That is, a speaker designed with derived (hilbert) phase will perform the same as one designed with measured phase.
I told you quite clearly it is asking too much to read every post and argue point for point. If you roll it up, it will be easier for everyone involved. Noah, Steve, whoever....
Good luck.
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