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Thread: Ask an Acoustic Engineer (me)

  1. Back To Top    #321
    Noob Jdunk54nl's Avatar
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    Re: Ask an Acoustic Engineer (me)

    If using passive xo, then it can be but it may not work well.

    Passive xo's are designed for those speakers to cross them with appropriate frequencies and slopes for those specific speakers. Putting any other speaker with it will work, but probably not well.
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  2. Back To Top    #322
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by goatpanda View Post
    I understand that there are many different factors that go into a cone driver's design. But I've been wondering, are there any generalizations (ie: pros/cons) that can be made for different cone profiles? I sometimes see mention of straight, curved, parabolic and flat cone profiles. I bet there are tradeoffs to each (like all things in speaker design), it would be cool to have a basic understanding of why a designer would choose one over the other.

    Btw thanks Justin for starting this thread and continuing to respond to it!
    This is related to chithead's question on the first page about cone shapes. Cones need to be stiff/rigid and you can get stiffness either from the material you use or from the shape you make it into, or both. You also want the cone to be lightweight so using as little material as possible is generally the goal.

    The tradeoffs go like this:
    -lightweight means less material
    -less material means less stiffness from material
    -less stiffness from material means more stiffness from geometry
    -more stiffness from geometry means, usually, a deep conical shape

    However:
    -shallow mounting depth means less deep a conical shape
    -less deep conical shape means less stiffness from geometry
    -less stiffness from geometry means more stiffness from material
    -more stiffness from material means more material
    -more material means heavier
    -heavier means less lightweight, see primary goal above

    Then you could:
    -more stiffness from material (and) not more material means exotic material
    -exotic material means more expensive

    So you're left with a "pick any two" problem:
    -shallow mounting depth
    -lightweight cone (higher sensitivity 1w/1m)
    -inexpensive
    (pick any two)

    A good example is Morel's Powerslim 6" woofers.

    Click image for larger version. 

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    The paper cone version (above) has sensitivity at 84dB which means (1) shallow and (3) inexpensive but not (2) lightweight because the sensitivity is pretty poor.

    Click image for larger version. 

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    The carbon cone version (above) has sensitivity at 87dB which means (1) shallow and (2) lightweight since it has double the sensitivity of the paper cone version, but not (3) inexpensive because it is a more exotic material.

    Then you can make it more complex by saying you also want wide bandwidth so your little 3" full-range speaker can play from 300hz to 20khz. Now your material needs to be lightweight, rigid, inexpensive, and also well-damped. If you want to make a shallow-mount one of those then, well, good luck!

    So cone geometry shapes (curvlinear, linear, conical, flat, dome) are usually about tradeoffs in stiffness from the geometry vs mounting depth. At a more complex level, they are also about bending modes (cone breakup) and how it translates into off-axis frequency response and also how smooth the high-frequency rolloff is.

    The stiffness of a profile can, in broad generalization, be ranked like so:
    (lower stiffness) flat - thin mount or shallow cones - straight-wall cone - curved wall cones (higher stiffness)

    Loudsoft makes a program called FINECone that can simulate all of these things and they made a little paper that goes into some details. It's pretty easy to skim through if you want to ignore the jargon. Attachment is below:

    LOUDSOFT_Cones_stiffness_ALMA_2003.pdf
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  3. Back To Top    #323
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by DirtyBumOAK510 View Post
    Can two matching drivers share the same airspace in a closed box? I'd searched all around the home audio forums and there seems to be an ongoing battle between this.
    Let's say I buy to 10 inch subwoofers, they each call for a half cube. I put both subwoofers in a one cube box. Do you need to separate them with a partition? Or can they share the same airspace? this is also assuming that one of the drivers doesn't blow out and end up working as a passive radiator for the other one....

    One thing that is definitely an unknown is whether they share the exact same TS parameters... Which almost certainly they would not.
    I like Jdunk and rton20s answers.

    In theory yes you can play multiple woofers into the same airspace. This is done all the time.

    There are a few small benefits of using separate air chambers though:
    -an additional partition acts as a brace to strengthen the box
    -if one woofer fails, the others can keep playing without issue
    -even with tight quality control, it's possible to get woofers that behave different (especially over time)
    -in the pro-sound world where "the show must go on", woofers are often wired in parallel with separate air chambers for robustness
    -if a shared airspace box gets "large" enough, standing modes inside the box might occur at low enough frequencies for you to care

    If you have two different kinds of woofers though like a 6" and a 3" in a 3-way bookshelf speaker, then you'll want to partition each into separate airspace for sure.
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  4. Back To Top    #324
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by RocketBoots View Post
    Please excuse my ignorance. Can a midrange that is part of a set (mid + passive XO + tweet) be switched out for a different mid? Will anything suffer? Thanks.
    Usually not. A passive crossover is usually a bespoke item that is crafted specifically for the speakers it is intended for.

    It's like asking could you and I swap shoes for the day.
    Technically we could, but there's a good chance they won't fit right.

    However once in a while you might find a solemate where you could swap shoes and it's all good. The more generic the shoes are, the higher the chances of this working. Some really simple sandals have a better chance of working for someone else, whereas custom-fit ice skates never would.

    The same idea is true of crossovers: some are pretty generic and some are super specific.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

  5. Back To Top    #325

    Re: Ask an Acoustic Engineer (me)

    Thread revival!
    I just asked this one on Facebook and I got some answers but not necessarily the facts that I'm hoping Justin and others here can bring.

    So I have heard stuff like "You can't hear distortion in a subwoofer the same you can in a midbass", or that distortion in a subwoofer isn't a big concern due to how we hear those frequencies. I've also heard people say that low distortion subwoofers (such as XBL, Brahmas, C12XL, Ravens etc) suddenly make people get used to what a "low distortion" subwoofer sounds like.

    So how much distortion is audible below 100hz? between 100hz-1000hz? Tweeters?

    Part of where I was getting at is that a lot of amplifiers claim "less than 1% distortion", and we often shoot for .05 or less. With Dacs, these numbers can go into the .001 or lower. I've read on Audio Science Review many articles about the hard numbers of inaudibility for Crosstalk, THD, S/N etc. But how do these apply to subwoofers? Specifically for choosing an amp for a very "low distortion" subwoofer. I've also seen graphs from subwoofer makers that will show at what frequency their subwoofers get localized, which if I remember right was due to distortion where it suddenly becomes localized. So typically we have the rule of thumb that subwoofers become localized above 100hz. S/N ratio of 120db is completely inaudible unless you have "golden ears".

    Where's the data!? What's the number?! What can and can't we hear below 100hz (typical subwoofer duty)

  6. Back To Top    #326
    Noob BenevolentDictator's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Excellent question.
    A man cannot become a hero until he can see the root of his downfall

  7. Back To Top    #327
    Senior Member chithead's Avatar
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    Re: Ask an Acoustic Engineer (me)

    No doubt - was pondering the difference between cone material as well and how it affects the perception of, "sound quality" - seems like your typical SQ subs have an extremely light light cone made of some thin exotic material, whereas your typical SPL sub is compromised of the thickest egg carton material they could find.

    Perhaps the lighter material is because most, "SQ" subs have minimal Xmax, but reproduce sound more naturally, while the ultra tough paper cone is strictly for strength during higher excursion?
    Are you not entertained?!?!


  8. Back To Top    #328
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by DirtyBumOAK510 View Post
    Thread revival!
    I just asked this one on Facebook and I got some answers but not necessarily the facts that I'm hoping Justin and others here can bring.

    So I have heard stuff like "You can't hear distortion in a subwoofer the same you can in a midbass", or that distortion in a subwoofer isn't a big concern due to how we hear those frequencies. I've also heard people say that low distortion subwoofers (such as XBL, Brahmas, C12XL, Ravens etc) suddenly make people get used to what a "low distortion" subwoofer sounds like.

    So how much distortion is audible below 100hz? between 100hz-1000hz? Tweeters?

    Part of where I was getting at is that a lot of amplifiers claim "less than 1% distortion", and we often shoot for .05 or less. With Dacs, these numbers can go into the .001 or lower. I've read on Audio Science Review many articles about the hard numbers of inaudibility for Crosstalk, THD, S/N etc. But how do these apply to subwoofers? Specifically for choosing an amp for a very "low distortion" subwoofer. I've also seen graphs from subwoofer makers that will show at what frequency their subwoofers get localized, which if I remember right was due to distortion where it suddenly becomes localized. So typically we have the rule of thumb that subwoofers become localized above 100hz. S/N ratio of 120db is completely inaudible unless you have "golden ears".

    Where's the data!? What's the number?! What can and can't we hear below 100hz (typical subwoofer duty)
    Hey DirtyBumOAK. Thank you for the question. Very good timing since the class I'm taking now is called psychoacoustics and we are starting to cover things related to distortion and hearing thresholds and so on.

    I don't have an answer for this yet, but I will ask around and see what I can find. I'm really interested too because the more I think about it, the more it sounds backwards from all the mechanisms and studies we have learned about in class. There's something else going on that we haven't covered yet in the class.

    My best guess today is: we know distortion sounds louder, and bass distortion is less objectionable than midrange distortion.
    I'll keep digging though to find a better answer.
    Thank you for being patient!

    If anyone else knows of a study or a paper to read, please share! Even if it's behind a paywall at AES e-library or something.
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
    Updated Justin tuning sheet (Justin and Erica tuning companion for SMAART and REW)
    Do it for them.

  9. Back To Top    #329

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by chithead View Post
    No doubt - was pondering the difference between cone material as well and how it affects the perception of, "sound quality" - seems like your typical SQ subs have an extremely light light cone made of some thin exotic material, whereas your typical SPL sub is compromised of the thickest egg carton material they could find.

    Perhaps the lighter material is because most, "SQ" subs have minimal Xmax, but reproduce sound more naturally, while the ultra tough paper cone is strictly for strength during higher excursion?
    I believe that is a bit backwards.
    At the first order, distortion is largely due to non linearities in the motor force off of the resting position.
    One can have a more linear motor, or they stroke it less to stay in the more linear range.

    A bigger cone needs less stroke than a smaller diameter one.

    (And the bigger stroke subs might need the stronger cone)

  10. Back To Top    #330

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Justin Zazzi View Post
    Hey DirtyBumOAK. Thank you for the question. Very good timing since the class I'm taking now is called psychoacoustics and we are starting to cover things related to distortion and hearing thresholds and so on.

    I don't have an answer for this yet, but I will ask around and see what I can find. I'm really interested too because the more I think about it, the more it sounds backwards from all the mechanisms and studies we have learned about in class. There's something else going on that we haven't covered yet in the class.

    My best guess today is: we know distortion sounds louder, and bass distortion is less objectionable than midrange distortion.
    I'll keep digging though to find a better answer.
    Thank you for being patient!

    If anyone else knows of a study or a paper to read, please share! Even if it's behind a paywall at AES e-library or something.
    That's right up my alley - are you taking a psychoacoustics class in person, or is it available online for anyone to take?

    I have done plenty of reading over the decades but now would be a perfect time, with me starting my install with an imaging-heavy install focus.

    Sent from my LM-G820 using Tapatalk

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