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Thread: Ask an Acoustic Engineer (me)

  1. Back To Top    #171

    Re: Ask an Acoustic Engineer (me)

    As for this thread:
    Quote Originally Posted by Holmz View Post
    ...The reason for the third chamber is also tat the internal volume is relatively precious, so that final port could allow thebox to be in the rear and then the port can pump into the back of the cab.
    and lastly I have a 300/500W (4/2-ohm) sub, so any help in box gain is great... and the truck has a lot of low frequency noise.
    The numerous chambers, extra walls, and all the extra port displacements - that would be the - THE - prime reason for absolutely NOT doing a 6th or 8th order anything... or even a 4th order bandpass, unless you really are loved doing something unusual or had a sub that made chainsaw sounds that you wanted to mask.

    "Small box sub" is what you need, especially in a truck that's probably got plenty of alternator left for a 1000w sub amp.
    Vented or sealed depends on your tastes - it's surprising how much output you can get with a specifically high-excursion sub. Finding a high-excursion sub that has significant powerhandling and is a small box sub... challenging but doable. Of course, in those threads we could play with what you already have, so start those for sure, IMO.

    Quote Originally Posted by Holmz View Post
    Those boxes with resonant chambers and the cones exposed to the air seem to get the resonant gain, but all the IMD and harmonic distortion can jump off the cone into the room. That defeats the concept of scraping away the higher orders of harmonic distortion.
    But is this a real problem? Or are you problem solving a problem that doesn't exist, which could come at great cost - opportunity cost, performance cost, money cost...

    The response of an ABC box - it's NOT flat. That's only OK when you are in a car or closet, and your cabin gain is high enough that it flips that angled response into a flat response.
    It's surprisingly trick in a car.
    In a home where you will just end up with a non-flat response - there's other ways.

    There really are reasons you don't see these often in car audio, and never see them in home audio.

    Quote Originally Posted by Holmz View Post
    And then all I usually hear is, "those need to be exact" and little is evident in describing how they work and tools to design them.

    Plus, like most people do... I got subs, and only now realise I probably got the wrong sub for the application.
    (it is easier to preach, than to practice it)
    That boils down to construction tolerances.
    You can simulate that in the software.
    Take a sealed box and add 10% to the box volume. No biggie. The curve hardly changes. You wouldn't even hear the difference.
    Take a bandpass box and "oops" the port wall so that it's 10% off, making the one chamber 10%-ish bigger and the other chamber 10%-ish smaller. Watch your previously nice, flat response turn into a peaky skateboard ramp.
    Yes - more construction precision is required.

    But also - there's more requirement to actually know your sub's REAL specs.
    Because the flip side is - subs are manufactured to tolerances. That means every sub deviates a bit - and so also the specs deviate a bit.
    If you have a sealed box, or even vented box - again, if the sub specs are off by a bit - no biggie.
    But - if you have your box perfectly modeled using the numbers from the spec sheet, and built that box to absolute precision...
    ...BUT then your specs turned out to be wrong by a bit - it'll impact the actual response just as much.

    So - you can budget DATS, if you want to go exotic into these precision designs:
    https://www.parts-express.com/dayton...ystem--390-807

  2. Back To Top    #172

    Re: Ask an Acoustic Engineer (me)

    Well I have another question then...

    When i I play some podcast on the iPad, why does it sound way better when put the iPad flat in the counter top?

  3. Back To Top    #173

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Cathul View Post
    ...
    Downside is, you need to know the cabin gain before building/designing the box and you need a DSP to really dial in that sub to the target curve.
    Good thing is, above 50Hz in this example you have an excursion well below 3mm at 200Watts of input while with a simple ported box you have at least double that excursion.
    ...
    I can do ^this part^.



    Quote Originally Posted by Cathul View Post
    No idea tbh... in Germany a different approach to bandpass subs is quite popular.
    Here a lot of people purposely tune the bandpass box to a large peak above 60 Hz and cross them low to flatten the curve to achieve a minimum excursion in the midbass area down to about 50 Hz.

    F.e. take a JL 8W3v3 and put it in a 4th order 9 liter for closed, 22 liter for ported and 25cm port length with a diameter of 12cm.
    Magnet inside the ported part of the box.

    ...

    Lots of people like these bandpasses in Germany and recommend them if you got a sedan for it's tight and fast midbass (almost no excursion necessary in the midbass area at all).
    I myself am wondering for some time now if a bandpass would be good in a S550 Mustang, or if i should build a normal ported box.
    If you run across any of these designers, then could you maybe PM me their details, like their email? (Please)
    I am having trouble finding S/W tools and anybody that does it as a service in North America and also in Australia...

  4. Back To Top    #174

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Holmz View Post
    Well I have another question then...

    When i I play some podcast on the iPad, why does it sound way better when put the iPad flat in the counter top?
    You’re focusing the sound instead of letting it go everywhere. Similar to the phone stands that focus the sound but you could try a simple bowl well. Similar concept to corner loading a subwoofer.

    https://www.thisiswhyimbroke.com/min...ker-amplifier/
    https://makeit-loveit.com/diy-passiv...-phone-speaker

  5. Back To Top    #175
    Noob Cathul's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Holmz View Post
    I can do ^this part^.
    If you run across any of these designers, then could you maybe PM me their details, like their email? (Please)
    I am having trouble finding S/W tools and anybody that does it as a service in North America and also in Australia...
    The "inventor" of this bandpass, or should i say the first guy to make this bandpass tuning really popular in Germany is Dietmar Carle.
    He owns a shop in Friedrichshafen Germany. http://www.fortissimo-shop.de

    And you can simulate an approximation of the behavior of such a bandpass with the help of WinISD.
    Take a JL 8w3v3 for example.
    Sealed part of the bandpass about 9 liter, ported part of the bandpass around 22 liter. Basket inside the ported area of the box., square vent with each side about 10cm long, length variying with the tuning frequency, say 65Hz it would be approx 25cm long. 200Watts of power for each box. 1,98meter distance for sealed (measured from drivers seat to the original location in my Mustang, 1,2meter for bandpass if put right behind the back seats in the trunk).
    Simulated response in WinISD would be as follows (shallow line is the same driver in 9 liter sealed):

    Click image for larger version. 

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    And cone excursion for both enclosures:

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    Usually you would say "bah, what a shitty tuning"... fair enough, but now introduce a lowpass crossover in the filters section of WinISD.
    For bandpass i choose 45Hz 4th order LR, and 80Hz for sealed.

    Click image for larger version. 

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    A lot less excursion on the bandpass, less upper bass, stronger in mid and low bass, but still looks peaky, right?
    Now comes the simulation of the cabin gain. Say you got 12db gain with a center frequency of 25Hz in your car. Just add a parametric EQ filter with a Q of 2, gain of 12db and center frequency of 25Hz into the filters section.
    Cone excursion will be meaningless in this case as the cone excursion simulation is fucked up if you add a parametric EQ filter in WinISD.

    Click image for larger version. 

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    Looks better, right? Still a bit peaky around 55Hz, so lower the lowpass on the bandpass to 40Hz.

    Click image for larger version. 

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    Now this looks good, that bit of ripple is of no concern imho. If you need more midbass from the bandpass, tune the port higher. F.e. with a tuning frequency of 75Hz it would look like this.

    Click image for larger version. 

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    Please do note that i also adjusted the lowpass filter to about 45Hz. The only thing that changes in this case is the port length, which gets shorter with higher tuning frequency as expected.
    Please also note that this enclosure is usually only recommended for sedans with a fairly sealed trunk with a small opening to the cabin, unlike my Mustang, that has a big opening behind the rear seats which are no real barrier for the subwoofer waves.
    Dietmar Carle usually recommends ported or sealed boxes in cases where the trunk is not really sealed, like in hatchbacks, just because a 12inch sealed box usually takes around the same volume as a bandpass for a JL 8w3v3.
    See the following picture where i compared a Focal P30F in a 32liter sealed enclosure including cabin gain and a lowpass around 63Hz (1,2 meter distance and 400 Watts of power, but still with 200 Watts of power SPL is still around 6db higher on the Focal sealed sub in the simulation):

    Click image for larger version. 

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    At least in Germany the Focal P30F is less expensive than the JL 8w3v3 f.e. Combine that with a lot simpler enclosure and the case is settled.
    SYNC3 headunit
    Mosconi Pico 8/10 DSP
    Mosconi D2 500.1
    Gladen Zero Pro 165.3 DC
    JL Audio 10w3v3 in custom enclosure (Blueprint by Mark @Caraudiofabrication)

  6. Back To Top    #176

    Re: Ask an Acoustic Engineer (me)

    Ok, I have a few questions that I'm curious to get some input on....


    Speaker Surrounds
    1a. I've noticed that some higher-end speakers like to use an "inverted roll" speaker surround. What is the advantage of an inverted speaker surround, if any?
    1b. Is it true that speakers with a higher Xmax, typically have a "bigger"/"beefier" rubber surround? I'm assuming that the higher Xmax requires the surround to allow for more cone movement? I ask this because I noticed (for example), the 2.5" GS25 wideband speaker has an Xmax of 4mm and the GS690 6x9 speaker has a 5mm Xmax - yet their rubber surrounds are not even close to being the same "size". I honestly can't imagine that the GS25 really has an Xmax difference of only 1mm compared to the GS690. Just doesn't make sense to me.


    Frequency sounds via different speaker materials
    2. Does the same sound frequency sound different depending on speaker material? For example, does 18khz sound different on a metallic tweeter than it does on a paper cone wideband speaker? Or if a speaker produces the same frequency at the same level, will it sound identical regardless of the speaker material used? Another example - will a 200hz signal sound the same on a 6x9 woofer as it will on a 2.5" wideband speaker (again, assuming they are playing the frequency at the same level)? I *have* noticed that 200hz on a 6x9 will *feel* different than 200hz on a 2.5" wideband! I can *feel* the vibrations from the 200hz signal on the 6x9, where I can't on the 200hz signal on a 2.5" wideband speaker.

    Thank you!

  7. Back To Top    #177
    Wave Shepherd - aka Jazzi Justin Zazzi's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by jtrosky View Post
    Ok, I have a few questions that I'm curious to get some input on....


    Speaker Surrounds
    1a. I've noticed that some higher-end speakers like to use an "inverted roll" speaker surround. What is the advantage of an inverted speaker surround, if any?

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    You're talking about this, right?

    I've often wondered about the inverted roll surround too. I haven't found a technical reason why it is superior but it can give you more clearance on the front so your woofer/grille stackup can be thinner to fit into tighter places. We have one at the office right now that is very (very!) tight on space and does this. I think the downside is perhaps less mechanical clearance with the basket so a large inverted roll might be impractical since it cannot have enough room to move on the inward stroke before contacting the basket. Again I havn't found solid technical reasons, these are my best guess.

    Quote Originally Posted by jtrosky View Post
    1b. Is it true that speakers with a higher Xmax, typically have a "bigger"/"beefier" rubber surround? I'm assuming that the higher Xmax requires the surround to allow for more cone movement? I ask this because I noticed (for example), the 2.5" GS25 wideband speaker has an Xmax of 4mm and the GS690 6x9 speaker has a 5mm Xmax - yet their rubber surrounds are not even close to being the same "size". I honestly can't imagine that the GS25 really has an Xmax difference of only 1mm compared to the GS690. Just doesn't make sense to me.
    That does seem a little strange. I would enjoy hearing Andy's response if you ask him.

    In general, the surround needs to be strong enough to withstand the air pressure and the mechanical forces on the cone. A larger cone is usually heavier so it might want a stronger surround (thicker), and a speaker with more travel will want a larger surround so it can move further. I don't think there is any magic there.

    The discrepancy between two surrounds on two speakers with a similar xmax rating like you found could be a number of things. My first guess is the Xmax numbers might be calculated using a method that doesn't account for the performance of the surround such as looking at the voice coil overhang geometry alone. A performance-based Xmax measurement (like the IEC one I can't remember off the top of my head) might give different Xmax numbers. It's hard to say since I'm not sure what method was used.


    Quote Originally Posted by jtrosky View Post
    2. Does the same sound frequency sound different depending on speaker material? For example, does 18khz sound different on a metallic tweeter than it does on a paper cone wideband speaker? Or if a speaker produces the same frequency at the same level, will it sound identical regardless of the speaker material used? Another example - will a 200hz signal sound the same on a 6x9 woofer as it will on a 2.5" wideband speaker (again, assuming they are playing the frequency at the same level)? I *have* noticed that 200hz on a 6x9 will *feel* different than 200hz on a 2.5" wideband! I can *feel* the vibrations from the 200hz signal on the 6x9, where I can't on the 200hz signal on a 2.5" wideband speaker.

    Thank you!
    Below a certain frequency the speaker's cone (or dome) will move up and down as a single uniform shape. If you tap a cone with your finger you can see the whole thing move as one piece with a rigid shape that doesn't change.

    Above a certain frequency, the cone will start to move less as a rigid shape and more like a flexible object, such as in the video below. When this happens the material is flexing and moving and creating sounds of its own as the shape is changing and moving and flexing. This is sometimes called cone breakup and depending on the design it can be gentle and pleasant or it can be rough and sound offensive.



    Below the first bending mode frequency (which is 82.2hz in the video above) the material is not flexing or changing shape and so it will contribute very little extra content to the sound you are playing. For low frequencies such as subwoofers, this is mostly true.

    Above the first bending mode frequency the material will contribute some new acoustic content based on the material it is made of. You can easily hear the effect by picking up a piece of paper and handling it in your fingers and rippling it or bending it rapidly with a whipsaw kind of movement. If someone is behind you and they are shuffling papers in their hands you know exactly what that sound is and you know they are shuffling papers, just like if someone is behind you with a plastic bag you know that sound too.

    To some extent, the material used will contribute to how a speaker sounds but mostly above the first bending mode frequency. One of the holy grails of audio is to get that first bending mode frequency above the audible range of music so that we can never hear the effects of cone breakup and this is one reason why exotic materials are desired like Beryllium and Graphene and Carbon Nanotechnology.

    To make it even more complicated, every material in the speaker has banding modes and will contribute to the sound in one way or another. I've seen the same 2khz peak in frequency response in a number of speakers back at Eminence and it was caused by a very specific kind of voice coil configuration where the former was buzzing and you could hear in through the dust cap. The spider and surround and dust cap and even the basket will also have bending modes that can contribute to the sonic signature too. It's not just all about the cone material, well not always.

    I had a sample thin-ply carbon used for making exotic boats and race cars and it is dead silent when I pick it up and handle it compared to picking up a piece of titanium sheet or aluminum foil or even paper. This is one reason why the new compression driver from Eminence sounds so unique, it is made entirely from the thin-ply carbon diaphragm.

    https://www.eminence.com/speakers/dr...?model=N314X_8

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    So in your example I would say the 18khz tone will sound very different on any two speakers. However, 200hz might sound very similar on many speakers because that is likely below the first bending mode of the cone for many speakers, especially full-range ones like the ones you mention.

    As for why you can feel the 200hz from the larger speaker ... that is likely because it is coupled to the air more directly because it has a larger surface area. I'm guessing if you played 200hz at the same SPL level from 1 meter away you might get a similar experience, but you would have to drive that 2.5" speaker a lot harder than the larger 6x9" speaker.
    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.

  8. Back To Top    #178
    Noob bluedevil1's Avatar
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    Re: Ask an Acoustic Engineer (me)

    Morning Justin,
    I have read this thread twice from start to finish, and it's like taking a Master's level course in acoustics. The level of knowledge displayed by you and other members of CAJ is astounding! With a lot of discussion around reflection inherent in the interior of vehicles and the necessary considerations you must account for in tuning, I am wondering what are some twists that must be considered when designing a system in a vehicle that will lack many of those reflections, such as a Jeep with no top or doors or another convertible type? One of the many features that DSP holds for me is the preset option's; I imagine a scenario where I save one tune for top on/doors on, but create another for summer months. I am reminded of how lighting systems in outdoor arenas (football fields) have gone from a flood effect which used to light up multiple city blocks, to now being so directional that you can stand across the street from a bank of lights at a stadium and it's dark as normal. Any thoughts? Thanks in advance!

  9. Back To Top    #179

    Re: Ask an Acoustic Engineer (me)

    Quote Originally Posted by Justin Zazzi View Post
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    You're talking about this, right?

    I've often wondered about the inverted roll surround too. I haven't found a technical reason why it is superior...
    So theoretically - a speaker is a piston. It moves in and out, not sideways.
    I mention this because there have been thread after thread over the years discussing cone shape, dustcap shape (not counting phase plugs, which don't move) - and surround shape should follow:

    Deep cone, shallow cone, flat piston, dome dustcap, dished dustcap, curved inverted dome cone with no dustcap, dome shape diaphragm... they theoretically all result in the same on-axis sound. And so it follows - the shape of the surround should follow those same points.
    I qualify "theoretically" because Justin's comments on cone breakup cover some changes in sound that could result from both cone material and geometry, so surround could also, although I'm sure much more slightly (although it can also dampen the cone, therefore change the cone breakup modes).
    I qualify "on axis" because I've been deep-diving into the realm of omni-directional loudspeakers lately, which aren't used in cars (though I have an experiment in planning), and off-axis radiation can be different by shape, at least when you are talking about a dome shape that rises above the surround so off-axis sound isn't obstructed - or even inverting a speaker and listening to the back of it...
    ...not to get too off-track with that train of thought, but it makes me wonder if one benefit of the inverted surround would be to allow more of the off-axis sound energy to travel?

    I'd also wonder if a surround could have a horn or edge effect, at higher frequencies anyway? Would a standard surround provide a slight horn effect? Would an inverted surround create a sharp edge that could cause a planned dip in the response (like a sharp edge on a baffle) at some frequency to compensate for over-efficiency somewhere?

    Also, for subwoofers I've seen this used - I have to chalk it up as 100% "gimmick", there... although why not do something that looks cool, if it doesn't matter one way or the other? No harm, no foul there...
    And definitely to your point, then yes, you might be able to fire a subwoofer into a loading panel or under a seat without the surround rubbing. Could be a real clearance advantage for a sub - although I'd have to worry about firing THAT close to a panel to begin with.

    But for that little midrange - off-axis response maybe could be slightly extended? I don't know if you could even tell by looking at the response plots that overlay on-axis with off-axis plots of varying degrees, but it's a theory.

    Quote Originally Posted by Justin Zazzi View Post
    That does seem a little strange. I would enjoy hearing Andy's response if you ask him.

    In general, the surround needs to be strong enough to withstand the air pressure and the mechanical forces on the cone. A larger cone is usually heavier so it might want a stronger surround (thicker), and a speaker with more travel will want a larger surround so it can move further. I don't think there is any magic there.

    The discrepancy between two surrounds on two speakers with a similar xmax rating like you found could be a number of things. My first guess is the Xmax numbers might be calculated using a method that doesn't account for the performance of the surround such as looking at the voice coil overhang geometry alone. A performance-based Xmax measurement (like the IEC one I can't remember off the top of my head) might give different Xmax numbers. It's hard to say since I'm not sure what method was used.
    Well, to be fair, we're talking about a 2.5" speaker compared to a 6x9 speaker here.
    The expected frequency response of the 2.5" speaker - even being a wideband - is likely only going to be as low as like 300hz... 200hz, maybe 150hz if you really push it - and that matters for excursion.

    Also - Xmax is usually going to be limited by the motor, when the voice coil starts exiting the magnetic gap.
    That's of course different than Xmech, which is usually the point the suspension bottoms out physically.

    I mention that because for a midrange, Xmax and Xmech could be very close, without any real risk to the driver - because of the intended use of the driver, not playing low (read: high excursion) frequencies. (explained in the next paragraph)
    On the other hand, for a 6x9 you might even use those as subwoofers. Some companies over the years have even made purpose-built 6x9 subwoofers (was it Infinity who made that crazy cool oval bandpass box with two isobaric pair of 6x9's in the '90s?). Even for regular 6x9's, you will probably want them reaching all the way down to your subwoofers... 80hz, 70hz, if you can. They are pretty comparable to eights, in terms of cone area and motor requirements... so, suspension as well.

    Since for any given speaker, your excursion needs double for every octave lower you ask it to play, that 6x9 playing 80hz will need double the excursion of a 6x9 playing 160hz, and quadruple the excursion of that 6x9 playing 320hz.
    So, since that 2.5" speaker isn't expected to play all that low, it shouldn't need as high-throw of a surround.

    And on the flip side - a 2.5" speaker is a tiny cone. It's limitation to loudness is going to be "small cone area", so the designer may want to give it as large of a cone as possible - which could mean shrinking the surround. And if you don't need it for excursion - why not use a smaller surround to gain a touch more cone area and therefore efficiency?

    In other cases though, where the frequency response of the drivers is more comparable, it could just be a matter of parts availability. A 6x9 likely has fewer parts available on the open market than say, a 6" or 8" round driver.
    In that case, in the parts selection process, a desired cone and basket (two parts you WOULD want to scrutinize from an engineering standpoint) could be found that met the design goals for the 6x9, and a desired cone and basket that met the design goals for the 6" or 8" were found that met the same design goals... open market parts... and so they simply found a surround that worked to bridge the gap that was left, and allowed enough excursion.

    Also, somewhere between 1/2 to 2/3 (depending on who you ask) of the surround counts as actual "cone area", because of the pistonic motion of the speaker, again... So having a wider surround isn't really that much of a penalty. If you could do one of those "all other variables being the same" experiments with an A/B comparison, a slightly wider surround wouldn't even be perceivable, I'm sure.
    That's been discussed to death on all kinds of threads literally going back decades - starting way back when Audiobahn was using ludicrous, laughable "fat" surrounds... then Image Dynamics pioneered the tall/skinny surround alternative for long-throw with the IDmax...
    My point here being that the surround width doesn't matter much until you get to extremes - "so fat" that it's silly, or "so skinny" that you actually are limiting excursion for the desired frequency range.

    Quote Originally Posted by Justin Zazzi View Post
    Below the first bending mode frequency (which is 82.2hz in the video above) the material is not flexing or changing shape and so it will contribute very little extra content to the sound you are playing. For low frequencies such as subwoofers, this is mostly true...

    To some extent, the material used will contribute to how a speaker sounds but mostly above the first bending mode frequency. One of the holy grails of audio is to get that first bending mode frequency above the audible range of music so that we can never hear the effects of cone breakup and this is one reason why exotic materials are desired like Beryllium and Graphene and Carbon Nanotechnology.

    To make it even more complicated, every material in the speaker has banding modes and will contribute to the sound in one way or another. I've seen the same 2khz peak in frequency response in a number of speakers back at Eminence and it was caused by a very specific kind of voice coil configuration where the former was buzzing and you could hear in through the dust cap. The spider and surround and dust cap and even the basket will also have bending modes that can contribute to the sonic signature too. It's not just all about the cone material, well not always.
    So this is a great topic (in my exceptionally geeky technical opinion) for a deep dive... especially since I'm speaker shopping myself, right now - and I always advocate "always listen before buying!", while secretly resenting that there aren't specs and properties to use while shopping to narrow down the list of speakers to give a listen to. Or, in my case - I have several speakers on my list that I simply can't listen to... but man, they'd be great bang-for-the-buck if they sound as good as their specs seem to otherwise imply a perfect fit for my specific needs.

    Is there a general list or study or test result, of cone materials [even understanding there's going to be some variance possible from one vendor to the other - all aluminum cones aren't the same, all paper cones aren't the same, etc] or even a forum thread somewhere... just to at least give a general clue, showing what frequencies that even those first bending modes occur at?

    For example, if aluminum *generally* has a higher first bending mode frequency than paper, and I'm looking to push my tweeter crossover point up higher for some installation design target - it might help to know "you might want to look into aluminum cone mids (along with whatever other materials might have 'higher than paper' bending mode frequencies). Does such a list exist?
    Last edited by geolemon; 06-04-2020 at 04:06 PM.

  10. Back To Top    #180

    Re: Ask an Acoustic Engineer (me)

    One more thought on that specific Peerless speaker there... and maybe it specifically relates to it being a wideband (where again... to play lower, using the same speaker, you need more excursion capability)...

    Looking closer at the picture now that I'm on my PC with the big monitor, it looks to me like THAT particular suspension is different than the standard inverted surround.
    So, my comments above relate to the standard inverted surround.

    THAT Peerless speaker there, it looks like the surround is attached on the front side of the cone, but then rolls around and follows the back side of the cone.
    So instead of a half-roll, there's more like a 3/4 roll. Here's what I think I'm seeing:
    (anyone know why I can't share a JPG I drew? Clicking picture, upload from computer, selecting it... clicked upload file...? Just disappears, no image here...)

    And maybe that gives it a bit more surround material, to help give it a bit more excursion before the surround is fully extended?

    If so, I'd think Peerless would advertise or market that feature - that's a unique surround approach.

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