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Thread: Ask an Acoustic Engineer (me)

  1. Back To Top    #11
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by JCsAudio View Post
    Do you know anything about power supplies of amplifiers and the pros and cons of regulated vs non regulated power supplies in car audio amplifiers. An example of a regulated power supply would be JL Audio RIPS (regulated, intelligent power supply) or I think Rockford Fosgate constant power. Most car audio amplifiers have non regulated power supplies and their power changes with voltage and impedance as well as the inductance of a speaker has a great affect on power output, but dynamic power output can also be better with a non regulated power supply vs regulated. Will you hear the difference, I don’t know.
    I know a little bit, but not as much as I'd like. I have to pass on this one.

    Quote Originally Posted by JCsAudio View Post
    How about some commentary on speaker cone material and the certain attributes or pros and cons of each type. I have experience with some and have done a lot of research on this. I experienced the odd order distortion or breakup of aluminum cones as listening fatigue myself. Here is what I understand as sort of generalizations:


    1. Paper, the most popular which is light weight, strong, and doesn’t have nasty breakup nodes or odd order distortion like metal cones but isn’t as moisture resistant. Can be used in both three ways and two ways.
    2. Aluminum, has great detail, is very rigid and strong and has good pistonic action but can suffer from ringing and nasty cone breakup in higher octaves. Best used for three ways.
    3. Poly, exhibits a smooth response and breaks up gradually for a smooth extended response but can lack detail, is heavier, and temperature can have a great affect on performance. Good for car audio and can be used in both three ways and two ways. Great for two ways.
    4. Fiberglass and Carbon Fiber. I have a pair of Focal poly glass midwoofers that seem to sound very similar to how my paper cone mids do. Not much is known really. Can be expensive and possibly heavier than paper.
    Speaker cone and compression driver diaphragms and tweeter dome materials all have the same goal:
    -be lightweight
    -be rigid
    -be damped
    -be durable
    -be sexy
    -be affordable

    Paper is an amazingly good balance of these things with a little weakness on durability, and less sexy factor. Thankfully paper cones can be coated with water-resistant treatments that make them very durable. I am still absolutely amazed that one of the least expensive cone materials is also one of most well-rounded performers too (paper).

    All the other materials are basically a mixture of those five qualities above. There are too many materials to analyze here but I think some of the the more exotic materials like beryllium and graphene have higher performance because they have the trifecta: lightweight, rigid, damped. The high price and exotic nature makes them sexy too.

    Synthetic materials are great for mobile audio and marine and motorcycles where the environments are harsh. All kinds of plastics and polymers and composites are used because of their chemical and ultraviolet resistance. They don't always have the lightest weight, but they are generally affordable and very durable.

    I'm not sure what you mean about odd order harmonic distortion though. When a cone is playing a high enough frequency it starts to distort in shape and has standing waves and bending modes but I don't think they add harmonic distortion to the mix. All the cone breakup and bending modes are the same frequency so you will get some off-axis response changes and some higher frequency roll-off, but I'm not sure there will be extra energy at other frequencies. See my post above with Dr. Russell's website and his animated gifs. They are sensational!

    I think the thing you are hearing that is undesirable is the different damping coefficients. Better damping means the breakup modes are more controlled. Also certain material and geometry combinations can lead to dramatic or less dramatic breakup mode shapes. Scanspeak for example does a lot with geometry to control the way the breakup modes form and which standing waves are supressed. I'm going to borrow a picture from Erin's site below.

    Attachment 9807
    https://www.erinsaudiocorner.com/dri..._4.5_midrange/

    Something else to consider: every cone or diaphragm will have a breakup mode at a high enough frequency. The clever speaker designers will either make those breakup behaviors gentle and polite such as the Scanspeak speaker above, or the designers will try to push those breakup behaviors well above the intended frequency range of the speaker.

    The Audiofrog GB60 is a great example of this because it is intended to be crossed over at 2khz but the spike in frequency response from bending modes occurs at about twice that frequency.

    The Peerless SLS 6" is one of my favorite midbass speakers. The frequency response falls apart above 500hz'ish due to bending modes. I'm guessing the manufacturer didn't worry about that because the specs on that driver scream "strong midbass for a 3-way system". It's all about the intended use in the end!

    Click image for larger version. 

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    edit: this is fun! thank you for the questions
    Measure with mics, mark with chalk, cut with torch, grind to fit, sand to finish, paint to match.
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  2. Back To Top    #12
    DIYMA Janitor SkizeR's Avatar
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    Re: Ask an Acoustic Engineer (me)

    So we know the advantages of XBL2 motor designs (flat BL curve until the very end). But like everything, there is a con to each pro. What are the cons of an XBL2 motor topology

  3. Back To Top    #13
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by SkizeR View Post
    So we know the advantages of XBL2 motor designs (flat BL curve until the very end). But like everything, there is a con to each pro. What are the cons of an XBL2 motor topology
    The XBL² motor geometry is patented by Dan Wiggins. He is perhaps the most energetic guy I've ever met haha. The design calls for a very short voice coil similar to an underhung design, and a unique top plate geometry. We had a fun discussion about it over on diyma in the thread below. Dan and I both talk about the XBL2 design, distortion measurements with the Klippel analyzer, and especially a lot of talk about the report I created that Adire Audio posted on their website that showed all the performance specs and Klippel measurements. It's a fun read.
    https://www.diymobileaudio.com/threads/industry-standard-for-distortion-iec-62458.415015/

    Downsides of the XBL2 design are:

    The voice coil must be fairly short so you are limited by how much wire you can use in the voice coil, which can result in a lower BL strength at the rest position. Since BL strength affects many of the other Small Signal parameters like Qts, this can make the enclosure design different.

    A lower BL at rest also influences the 1w/1m voltage sensitivity rating. If you are trying to design a speaker for use in pro audio like stadiums and concerts, one of the few spec numbers that are critical is the SPL sensitivity. If you have a lower than average sensitivity, that speaker will not sell well in the pro audio world.

    You can see both of the above trends in a comparison I made of the Stereo Integrity TM65mkII vs the Audiofrog GB60. The TM65mkII has an XBL2 motor and it is very interesting to see the design tradeoffs. You can grab that report off my dropbox here:
    https://www.dropbox.com/s/x151rliohp...02.11.pdf?dl=0

    Simulation and design software for the XBL2 geometry is rare. The only program I've seen that does it is the one Dan Wiggins programmed however that business venture fell through so you have to get his attention and ask him for a copy. He was happy to let us have a copy at Eminence when I worked there and he even gave us a little training so that was nice.

    Since it is a patented technology, it requires a fee to use. The fee might be small at the manufacturing level, but it gets multiplied by the time the product reaches the customer. This makes the product more expensive, but the cost is hopefully worth the cool factor and the performance boost.

    The motor geometry is very non-standard so a typical speaker manufacturing house might not have experience with it. This could add to design and development costs when getting the first production batch up and going.

    The motor also leaves a perfect gap inside the center of the voice coil to place a copper or aluminum shorting ring. The shorting ring is not a requirement of the XBL2 design but the opportunity is so perfect that it is tempting to add one which would increase the speaker cost. I think the ability to add a shorting ring in such a perfect spot is my favorite attribute of the design.

    Here is a picture that I borrowed from the May 2009 Voice Coil magazine.
    http://audience-av.com/wp-content/uploads/pdf/VC509_TB_Audience.pdf

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    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.

  4. Back To Top    #14

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Justin Zazzi View Post
    I know a little bit, but not as much as I'd like. I have to pass on this one.
    ...
    Let's slow up there young bull...

    This is is a perfect topic.
    Here is what I propose.
    1) see if anyone near you has a regulated amp that you could test.
    (I'll assume you have a non regulated amp)
    2) Get a variac and use it to set the voltage and few capacitors behind a full bridge rectifier to feed DC to a battery.

    Then put a current measuring device between then... probably something outputting to a datalogger.

    Then get the test speaker producing the same SPL with both amp by adjusting their gains.

    Then if one was to run something like 1/2 second of 40-Hz bursts out we can see what the input current is like in each case... both as an impulse and in a steady state sense.

    One can also start turning down the variac to do the same test at 13, 12, 11 and 10V.
    it is likely that that output SPL, in the non regulated amp, will vary as the voltage decreases.


    Of course it is is a lot of hours of work, so it is easy for me to propose. But that is how I would likely start... and change it when I found some problem. At least knowing how to assess the problem would be a great thing to outline.
    Last edited by Holmz; 03-21-2020 at 03:18 AM.

  5. Back To Top    #15
    Noob JCsAudio's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Thank you Justin for sharing your expertise. This is a rare thing for someone like this to come on here and offer this kind of knowledge so everyone should take advantage and ask but please ask nicely. I’ll try to come up with a few more good relevant questions and post them later.

    Holmz, I think what would be most helpful in terms of my question about regulated power supplies vs non regulated would be how these technologies actually matter when used as intended in the automotive environment. Having sagging voltages isn’t really typical unless you have inadequate power supply from the car. I’d like to know how do these technologies affect the sound when used as intended comparatively? Does the greater dynamic capability and faster response of a non regulated power supply make an audible difference comparatively? I think it does somewhat.

    Reading a little bit about inductance from the XBL talk above from Justin and Dan Wiggins I realize that subwoofer inductance plays a huge roll in how a subwoofer sounds (please correct me if wrong) so an amplifier with a regulated power supply might be able to compensate somewhat for this, but is it audible? When I had my RF Power ti1500 I ran some basic tests and it made about a 1 db difference compared to my non regulated Infinity K-1000. The Infinity seemed to sound as if it had a little more dynamic headroom, which seemed to manifest itself as more boom in those quick low bass hits. I had to do a long A vs B session to determine this and it was just me doing it so the test isn’t really reliable or very scientific.

    Thank you again Justin for sharing your knowledge.
    Mazda CX5 AF GB10, AF GB25, AF GB60, JL VX800/8i, AF GB12 sealed, Mmats M1400.1

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  6. Back To Top    #16

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by JCsAudio View Post
    Thank you Justin for sharing your expertise. This is a rare thing for someone like this to come on here and offer this kind of knowledge so everyone should take advantage and ask but please ask nicely. I’ll try to come up with a few more good relevant questions and post them later.

    Holmz, I think what would be most helpful in terms of my question about regulated power supplies vs non regulated would be how these technologies actually matter when used as intended in the automotive environment. Having sagging voltages isn’t really typical unless you have inadequate power supply from the car. I’d like to know how do these technologies affect the sound when used as intended comparatively? Does the greater dynamic capability and faster response of a non regulated power supply make an audible difference comparatively? I think it does somewhat.

    Reading a little bit about inductance from the XBL talk above from Justin and Dan Wiggins I realize that subwoofer inductance plays a huge roll in how a subwoofer sounds (please correct me if wrong) so an amplifier with a regulated power supply might be able to compensate somewhat for this, but is it audible? When I had my RF Power ti1500 I ran some basic tests and it made about a 1 db difference compared to my non regulated Infinity K-1000. The Infinity seemed to sound as if it had a little more dynamic headroom, which seemed to manifest itself as more boom in those quick low bass hits. I had to do a long A vs B session to determine this and it was just me doing it so the test isn’t really reliable or very scientific.

    Thank you again Justin for sharing your knowledge.
    Well I took a shot at what I thought might be what one would want.
    So in my mind, it would be SPL versus input voltage, and/or output waveform/voltage versus input DC supply voltage... and whether they diminish at the onset of the musical attack, or later in the steady state.

    I think it would need need to be something we could measure and quantified(?). If we knew what it was, then we could test it in a calculus f(x) sense...

  7. Back To Top    #17
    Noob JCsAudio's Avatar
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    Re: Ask an Acoustic Engineer (me)

    True Holmz but that someone isn’t going to be me and math isn’t my forte.
    Mazda CX5 AF GB10, AF GB25, AF GB60, JL VX800/8i, AF GB12 sealed, Mmats M1400.1

    Ford F150
    AF GB10, AF GB25, JLC5, JL twk88/Pioneer D8604, Mosconi Pico, JBL Club 5501, Sundown SD3-10 ported @ 30 Hz

    Sienna
    AF GB15, Audiofrog GS690, JL twk88/Pioneer D9500F, JBL GTX500, Alpine SWS10 ported @ 31 Hz

    https://www.diymobileaudio.com/threa.../#post-5608901






  8. Back To Top    #18

    Re: Ask an Acoustic Engineer (me)

    Ok Justin I have a question.

    how do I compute the x position at DC for a given voltage or current for an IB configuration?

    i am thinking of putting together one of the subwoofer boxes as a small sealed box with a 1-way inlet and outlet, and making a respirator in a McGyver fashion.
    So I either to pump the sub in a stoke near DC (like 1/2-Hz)
    or
    I run a small signal at ~30-Hz for ~1-2 seconds and then have it rest for a few seconds.

    Thoughts?

  9. Back To Top    #19
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    This sounds like fun, but I don't understand the question.

    Are you asking what the displacement will be for a given voltage in a certain speaker so you can create a resperator and save the world?
    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.

  10. Back To Top    #20

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Justin Zazzi View Post
    This sounds like fun, but I don't understand the question.

    Are you asking what the displacement will be for a given voltage in a certain speaker so you can create a resperator and save the world?
    I'll start out small, so just a person or two...

    i have enough subwoofers for 4 of them, which equals what I hear if the sad number that the hospital has.

    I think I'll just slap together a seal box with an inlet and outlet, and use a 30-Hz tone and see what it pumps.

    It would be nice to if I could send in something around 10-Hz without smoking coils, and the math behind working of the displacement versus current/watts.

    But I just do not know how the parameters translate into displacement... hence the question.

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