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Simulation Analysis - Screws in Waveguide

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René - Acculution.com

René - Acculution.com

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The modelling I was interested by was calculating enclosure vibration and radiation as a proportion of the whole output.
AFAIK this can only be calculated since something like the Klippel measurements have no way of separating any output from the enclosure from that from the drivers.
I have been told the effect is important but never seen it quantified.
You hit the nail on the head as to why simulations are often superior to measurements: When you measure you get one scalar, complex value for each point, which is an amalgamation of all vectorial contributions from the actual physical object; here the loudspeaker. What can easily be dissected in a simulation is often impossible to separate in a measurement; the loudspeaker either plays or it does not, whereas in a simulation you can decouple things, apply vacuums and isolate the structure, and on and on. I have done a simulation once in a loudspeaker company showing that the cabinet vibration was not as important as the engineers thought, but this must be evaluated on a case by case basis.
 
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Rottmannash

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Silly question, but what speakers do you own/listen to? And do you listen with the grills on or off? Inquiring minds want to know;)
 
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René - Acculution.com

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Silly question, but what speakers do you own/listen to? And do you listen with the grills on or off? Inquiring minds want to know;)
So maybe I should preface this a bit: I am not the one to ask advice about when it comes to which speakers to buy. If you like a speaker that measures bad, I am fine with that, preference is preference. For me, I would try and go for something that measures well, but looks are also very important. I am probably more fascinated by the technical and physical aspects of loudspeakers (and other products that I work with) than the music itself, and would think my speakers are more used for movies than music, as I tend to listen to music on headphones or smaller speakers, while working.

So, the speakers I have are the Avance Dana 980:
Untitled.png

They were half off many years ago, Danish designed, well tested at the time, and I like how they look and sound. I have later gotten the matching sub and rear speakers. I don't see myself buying anything new, unless these crap out. I recently borrowed a Purifi power amp from my Purifi friends which connected to my surround receiver really lifted things, so that could be the next buy I do. I have the grills on, but if they could sit on the rear of the speaker (as you can do with some speakers now), I would probably do that, but probably mostly because sun light changes the color ever so slightly where the grill is not blocking it.

So don't copy anything I do HiFi-wise; I am not a help there ;-)
 
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puppet

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I have done a simulation once in a loudspeaker company showing that the cabinet vibration was not as important as the engineers thought, but this must be evaluated on a case by case basis.
This is also a very interesting topic. Are you able to expand on this as well?
 
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René - Acculution.com

René - Acculution.com

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This is also a very interesting topic. Are you able to expand on this as well?
Sure, it is somewhere down the line after edge diffraction. For the mentioned case a protype was made for a small two-way speaker that sounded 'too good' as it was believed to vibrate more than the wood that would later be used. As I had already simulated the mid-woofer I could extract the reaction forces and apply to the cabinet using the two different material, and from the resulting vibration extract the sound field from the cabinet alone (probably via the Rayleigh integral), and it was quite below the sound field from the drivers for both, although wood was 'better'. A lot of these audio myths can be resolved over a weekend, but I don't see anyone doing it, so why not me ;-)
 
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Jim Matthews

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DualTriode

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I don't understand the context of this comment. Are you questioning the value of simulation tools? Just curious.

“For this particular case the influence of the screws in fairly minimal, yet it is there. The wavelength even at 20 kHz is 1.7 cm, which is larger than the screws themselves, and so it is to be expected that the sound field will not be affected much.” Says Dr. /René



In this case before the simulation software was booted the answer was known.
 
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René - Acculution.com

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“For this particular case the influence of the screws in fairly minimal, yet it is there. The wavelength even at 20 kHz is 1.7 cm, which is larger than the screws themselves, and so it is to be expected that the sound field will not be affected much.” Says Dr. /René



In this case before the simulation software was booted the answer was known.
Any constructive suggestion for other simulation cases to explore?
 

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maxxevv

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Any constructive suggestion for other simulation cases to explore?


Would be interesting to see how alternative speaker envelopes like those of Genelac can affect the overall directivity / performance of a given speaker configuration versus a traditional flat sided box.
 
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René - Acculution.com

René - Acculution.com

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Sure, Dr. /René,

What does the simulation show us for the comb filtering at the crossover between the woofer and tweeter of the JBL 4349?

For best listening and measuring what elevation should my ear and GRAS calibrated microphone be placed relative to the center line of the tweeter.

https://www.audiosciencereview.com/...jbl-4349-review-studio-monitor-speaker.22686/

Thanks DT
Hi. I would need the horn geometry and crossover information to say anything more than what the measurements show. But I am planning a post about sound radiation from sources that are crossed over with different filter topologies, so maybe that can shine a little light on this topic.
 
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René - Acculution.com

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Would be interesting to see how alternative speaker envelopes like those of Genelac can affect the overall directivity / performance of a given speaker configuration versus a traditional flat sided box.
If someone can draw an approximate geometry that would certainly be interesting (as long as Genelec does not mind).
 

Frank Dernie

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Sure, it is somewhere down the line after edge diffraction. For the mentioned case a protype was made for a small two-way speaker that sounded 'too good' as it was believed to vibrate more than the wood that would later be used. As I had already simulated the mid-woofer I could extract the reaction forces and apply to the cabinet using the two different material, and from the resulting vibration extract the sound field from the cabinet alone (probably via the Rayleigh integral), and it was quite below the sound field from the drivers for both, although wood was 'better'. A lot of these audio myths can be resolved over a weekend, but I don't see anyone doing it, so why not me ;-)
I would imagine the effect would be both dynamic behaviour of the panels (to the mechanical and acoustic excitation) and size (ie surface area of cabinet) dependant so probably very much more important in large speakers.
I built a large 3-way pair of speakers (around 80 litres) when I was an impecunious student in 1970. I used chipboard because it was cheap and not that thick either, ⅜", around 10mm since I had to carry it home from the DIY shop.
The "feel" of the vibration on the panel surfaces didn't seem much less than the "feel" of the KEF B110 mid driver vibration given the much bigger surface area. I went on to do noise and vibration research for work and spent the next few years trying different ways to make the cabinets more inert as a hobby!
Each reduction sounded better to me, of course, but that could easily be expectation bias!
Back then I did have access to a computer (Imperial College had two and I was on a computing course which gave me access) but it is amusing, looking back, how far both hardware and software (and their price) have changed since then!
OTOH I did start writing my first software that earned me money then. There was no software one could buy, you wrote it yourself :)
 

voodooless

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Would be interesting to see how alternative speaker envelopes like those of Genelac can affect the overall directivity / performance of a given speaker configuration versus a traditional flat sided box.

Why don't we explore configurations that have not actually been made and measured? What would be the point to recreate the Genelec design other than verifying the simulation's validity?
 
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René - Acculution.com

René - Acculution.com

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I would imagine the effect would be both dynamic behaviour of the panels (to the mechanical and acoustic excitation) and size (ie surface area of cabinet) dependant so probably very much more important in large speakers.
I built a large 3-way pair of speakers (around 80 litres) when I was an impecunious student in 1970. I used chipboard because it was cheap and not that thick either, ⅜", around 10mm since I had to carry it home from the DIY shop.
The "feel" of the vibration on the panel surfaces didn't seem much less than the "feel" of the KEF B110 mid driver vibration given the much bigger surface area. I went on to do noise and vibration research for work and spent the next few years trying different ways to make the cabinets more inert as a hobby!
Each reduction sounded better to me, of course, but that could easily be expectation bias!
Back then I did have access to a computer (Imperial College had two and I was on a computing course which gave me access) but it is amusing, looking back, how far both hardware and software (and their price) have changed since then!
OTOH I did start writing my first software that earned me money then. There was no software one could buy, you wrote it yourself :)
Yep, this was a very small two-way. Some manufactures use thin cabinets and 'tune' their sound. Don't quite know what to think of that approach, but to each their own. Software has come a long way, but the best way to understand the expensive software is to have programmed it yourself, as I have with both FEM and BEM code. Thanks for your input :)
 
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René - Acculution.com

René - Acculution.com

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Why don't we explore configurations that have not actually been made and measured? What would be the point to recreate the Genelec design other than verifying the simulation's validity?
Sure. I think for this forum it is a good idea to look at general topics: "Does it matter if you round cabinet edges?", "Do screws matter or not?", "Does cabinet vibration matter?" and so on. Anything where there are myth about general topics can often be closed down fairly quickly with simulations.
 

DualTriode

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Hi. I would need the horn geometry and crossover information to say anything more than what the measurements show. But I am planning a post about sound radiation from sources that are crossed over with different filter topologies, so maybe that can shine a little light on this topic.

Hello Dr. /René,


It is likely best not to reverse engineer the monitor, we do not want to give away any secrets.


Some educated reasonable assumptions would be a good place to start:


The woofer is 12 inch that begins to lobe or some would say beam as the frequency increases. A reasonable assumption that the -6dB lobe is somewhere in the +- 50 degrees range at 1.5kHz.


The horn / waveguide from the data sheet looks to be -6dB in the +- 50 degrees range at 1.5kHz.


The crossover is likely patterned from the old tried and true crossover used in the original 100 X 100 Butt Cheeks Bi-Radial monitor from the 1980’s. You know with the capacitor bypassed L-pad used to compensate for the compression driver mass-break roll off.



A comb filter simulation at varying crossover frequency and or varying distance between the woofer and tweeter centerlines would be interesting to see.



Thanks DT

Somewhere in the speaker review thread there is a dimensioned drawing of the monitor.
 
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