Simulation Analysis - Screws in Waveguide

[fluid]

I ran a few similar simulations (these are the ones I mentioned before where the woofer was modelled as a rigid boundary below the waveguide and is responsible for most of the diffraction seen in the simulation). When I ran a lower resolution mesh for the fully rounded corners the results had less obvious mesh issues at the highest frequencies than when I upped the resolution in the corners. I put this down to the mesh vertices not being aligned completely together as this has resolved similar differences before. The mitred corners suffered some of the same issue where it becomes difficult to rely on the simulation results as the frequency goes up. I hoped that if you could model them all at high enough resolution it might give a more confident result.

 

[AnalogSteph]

Regarding speaker grills I could simulate that too. The easiest case would be perforated metal and if someone has a particular geometry or loudspeaker model to be inspired by, I might find time to do that too.

If so, the effect of a grille / diffuser delete on a Behringer B2031A would seem an interesting case to investigate.

Awesome thread btw.

 

[Spocko]

Sounds like a good plan, but unless the manufacturer can provide trustworthy proof, you would still need to be able to do test it yourself.

Too many claim transparent grilles today and testing has shown that they are not.

Or like you said, the grills are not "transparent" but the speaker has been designed with a frequency curve that requires the grill to be otherwise it sounds worse with the grills off?

 

[René - Acculution.com]

Or like you said, the grills are not "transparent" but the speaker has been designed with a frequency curve that requires the grill to be otherwise it sounds worse with the grills off?

Yes, but we can calculate the influence. If I either know the porosity or get the geometry it is doable.

 

[Rick Sykora]

Or like you said, the grills are not "transparent" but the speaker has been designed with a frequency curve that requires the grill to be otherwise it sounds worse with the grills off?

Have not seen that in any testing I have done or seen. In every case, the measurements were worse with the grilles on.

So, while it may be possible that the grille improves the speaker, it has not been my experience. While there may be some benefit to simulation, there are plenty of ways to counter diffraction. Many have been measured extensively (as with the grille case), so there is no major controversy, but may be useful in CAD to help produce a new design more productively. I rely on @ctrl for this stuff as he has much more experience than I. Even if the general results are well kniwn, it may be that the sim is compute-intensive. So, if @René - Acculution.com is willing and it improves productivity for others, am good with it.

 

[eddy555]

what software is this btw? Can it do compression driver and waveguide simulation aswell?

 

[Francis Vaughan]

what software is this btw? Can it do compression driver and waveguide simulation aswell?

COMSOL Multiphysics
It would appear it can do almost anything you can throw at it. However the price starts at your first born child and goes up from there.

 

[DualTriode]

So what have we learned?

We knew going in the waveguide screws were too small to be significant. Nothing new.

Speaker issues are more problematic to the perceived sound. Also known.

Sound interaction with the room is more complex and potentially more problematic than the speakers and electronics combined.

Not much added here by the modeling software.

A couple color graphics would be nice.

Thanks DT

On my bench are a a couple calibrated GRAS microphones cut from the same cloth as the 45CA fixture microphones. Put the microphones up close to a speaker real-time and you can get some meaningful measurements like Frequency Response and distortion products.

Place the microphones out into the room, things get a lot more complicated real fast. Use time-gating and you can pretend that the walls, floor and ceiling are not there. This is a topic where everyone is an expert, just ask.

Or perhaps people do not have a clue.

 

[NTK]

When you get a new piece of simulation software, or introduce simulations to people new to the technology, the first thing you usually do is to replicate some already well understood phenomena. I think this is basically René's purpose.

When comparing simulations to prototyping and test, asking how many tests you can do in a day is not the important question. The important question is how many new prototypes you can design and build in a day.

To illustrate what simulations can do/have done, I'll use aircraft engines as the example. This is the engine on the original Boeing 747-100.

This is the engine on the Airbus A350.

See the much more intricated shape of the inlet fan? Without 3D computational fluid dynamics (CFD) simulations, it is impossible to come up with and optimize the complex 3D geometry of this fan. Together with all the other efficiency improvements, the A350 has a per passenger-mile fuel burn about 60% of the 747-100.

 

[DualTriode]

When you get a new piece of simulation software, or introduce simulations to people new to the technology, the first thing you usually do is to replicate some already well understood phenomena. I think this is basically René's purpose.

When comparing simulations to prototyping and test, asking how many tests you can do in a day is not the important question. The important question is how many new prototypes you can design and build in a day.

To illustrate what simulations can do/have done, I'll use aircraft engines as the example. This is the engine on the original Boeing 747-100.

View attachment 133222

This is the engine on the Airbus A350.

View attachment 133223

See the much more intricated shape of the inlet fan? Without 3D computational fluid dynamics (CFD) simulations, it is impossible to come up with and optimize the complex 3D geometry of this fan. Together with all the other efficiency improvements, the A350 has a per passenger-mile fuel burn about 60% of the 747-100.

I am sorry. Look at the dates of manufacture for the two items in your example.

Engineering is an iterative process, it is not finished until you run out of time and or money. In other words engineering is a trial and error process with improvements at each step along the way.

Yes there were a few CAD work stations along the way.

 

[fluid]

So what have we learned?
We knew going in the waveguide screws were too small to be significant. Nothing new.

While this is true it does highlight the power of this type of simulation software to allow an analysis of things that are hard to measure in the real world. It could be argued that if it is hard to measure it is of little consequence, and in the overall hierarchy of issues things like this would not rise out of the noise.

But in terms of advancing the state of the art a bunch of these small changes could result in a worthwhile improvement that would have been difficult to realise without this sort of simulation.

 

[DualTriode]

While this is true it does highlight the power of this type of simulation software to allow an analysis of things that are hard to measure in the real world. It could be argued that if it is hard to measure it is of little consequence, and in the overall hierarchy of issues things like this would not rise out of the noise.

But in terms of advancing the state of the art a bunch of these small changes could result in a worthwhile improvement that would have been difficult to realise without this sort of simulation.

Still waiting for something new!

The screws in the waveguide were not new!

If the screws in the waveguide were to get our attention, Where is the rest of it?

 

[Head_Unit]

I did a quick series of test of Revel Grill versus a couple of projection screen material that were supposed to be "transparent." Here are the in-room measurements:

Revel grill in black did the best.

Cool test! Those effects don't look so bad. But how about in the time domain? Any weird effect?

 

[René - Acculution.com]

Cool test! Those effects don't look so bad. But how about in the time domain? Any weird effect?

Grills are probably in general worse than screws.