More speaker design questions...

[im_gumby]

Hi, I didn't see this being discussed ... apologies if I missed earlier discussions.
In my other thread I talked about doing a Fyne F1-8 or F1-5 tribute speaker. Also looked at the Focal Diablo.
I'm more in to reverse engineering their designs to see what can be done.

Fyne Questions:

The speaker is ported down. I get how they do that... but inside the box... does the shape matter, or does just the volume matter?
Also what about adding acoustic paint? (I saw one craftsman do this to his box) And what about other material like specialized acoustic material in combination w something like carpet padding /rockwool, etc ...?

If I build the Fyne tribute, I'd CNC or Laser cut the MDF and then stack it. Since I can control the thickness and shape of the walls, Not sure how much bracing is needed. I also thought of a way to make it easy to vary the height by sections using 3D printed spline connector pieces that when completed could be glued into place.

The other speaker I saw that looked interesting was the Focal Diablo.

The bass/mid is tilted slightly back and then the tweeted is in its own separate box.
Is the tweeter always sealed? Even in a more traditional box design? (Sealed, treated and filled w dampening material? )
I've watched YouTube vids and read about timing... In the focals, is the tweeter set back since the woofer is tilted back and it looks like the dome tweeter is behind the baffle?

Of course all of this is still just a thought process. If I am going to do this, I'll need to convince my wife to let me get a Snapmaker artisan, and then bribe my nephew (A mech e ) to help w the design and cad drawings.

 

[kemmler3D]

but inside the box... does the shape matter, or does just the volume matter?

Shape can matter but typically volume is way more important, especially for low frequencies.

what about other material like specialized acoustic material in combination w something like carpet padding /rockwool, etc ...?

Depends on what the material is and what you intend to accomplish with it.

Since I can control the thickness and shape of the walls, Not sure how much bracing is needed.

You will still want bracing. Since you are doing it with CNC, maybe just design some of the layers to be braced.

Is the tweeter always sealed? Even in a more traditional box design?

Typically yes, in fact a lot of tweeters have sealed backs of their own, off the shelf.

I've watched YouTube vids and read about timing... In the focals, is the tweeter set back since the woofer is tilted back and it looks like the dome tweeter is behind the baffle?

The tweeter setback is for timing/phase alignment. This is tricky to do well, generally people will tell you to do it with DSP and don't worry about physically aligning the drivers like that.

 

[im_gumby]

Shape can matter but typically volume is way more important, especially for low frequencies.


Depends on what the material is and what you intend to accomplish with it.


You will still want bracing. Since you are doing it with CNC, maybe just design some of the layers to be braced.


Typically yes, in fact a lot of tweeters have sealed backs of their own, off the shelf.


The tweeter setback is for timing/phase alignment. This is tricky to do well, generally people will tell you to do it with DSP and don't worry about physically aligning the drivers like that.

Thanks for the quick response.
I saw vids on shape in terms of depth but w a CNC, you can create curved walls, not just rounded corners. Think of a trailing edge of an airfoil of sorts.
And yes I thought about creating layers w cross bracing in it. I guess simplest thing is to sand the edges round along the brace.

In terms of dampening material... I saw one using a material you cut into shape and then heated it and used a roller to get it to stick. Others just used foam or carpet padding.
And in sealed they added batons of fluffy material to help break up the waves. Since the Fyne is ported... do you want to do this? Does it impact the volume requirements? Also saw the port filled w material in some cases.

In my design, for the Fyne use the coaxial speaker and go with the recommended crossover board (sold separately) as a start. I wanted to avoid using a DSP since it meant bringing in power to the speaker.

Thx again.

 

[kemmler3D]

Since the Fyne is ported... do you want to do this?

Probably yes. It helps tame mid and high frequencies. In fact, you especially want to do this with ported designs because you can get those frequencies leaking out of the port if you don't.

Does it impact the volume requirements?

It does, there are ways to calculate it but I couldn't tell you off the top of my head. Check DIYaudio for that.

I saw one using a material you cut into shape and then heated it and used a roller to get it to stick. Others just used foam or carpet padding.

So there are types of material you can put on the walls to dampen vibrations or add mass. In general those are considered possibly a waste of time since adding mass does a bit to stop transmission, but also lowers the resonant frequency, so you end up with more energy to drive the resonances and therefore louder resonances. In terms of damping vibrations - you should have enough wall thickness and bracing to avoid them / push them up in frequency anyway. So adding heavy layers to the walls probably won't help there either.

Foam and carpet padding are good for absorbing higher frequencies inside the box and most people will tell you to use rockwool, actual wool, cotton, basotect (melamine foam), etc.

I thought about creating layers w cross bracing in it. I guess simplest thing is to sand the edges round along the brace.

Probably don't need to do that, even. Having sharp corners inside the box won't hurt anything. That only matters for high frequencies and you don't want those escaping the box anyway.

 

[tmuikku]

And to be able to figure the stuff out yourself, what matters is sound wavelength.

1kHz is about one foot or 34cm long. When physical object or shape is about similar in size, or larger, as wavelength it has very strong effect to it. When object is much smaller than wavelength it has very little effect until at some point it's basically invisible.

So, for example if you have irregular shape inside the box, like a pyramid for example, sized about 10cm, it would reflect and diffract sound inside the box with wavelengths roughly 10cm and shorter, ~3kHz and up, while being invisible and irrelevant for sound whose wavelength is for example 10x longer, 300Hz and down. Even few times longer wavelength than size of the feature and effects are already reducing so such pyramid might have some effect say 1kHz and up.

100Hz is 3.4meters long, or about 11ft, 34Hz would be 10m long, about 30ft so you can imagine anything you can fit inside small box has very little effect to it. Your room however, has strong influence on it.

Also, if you have say one inch thick acoustic insulation/damping material, it is most effective when it is thick enough compared to wavelength, and less so the longer the wavelength. As you can imagine, such thin acoustic material has very little effect on low bass whose wavelength is much longer than thickness of the material. It might have some effect on low mids and be fully effective somewhere higher up. Some materials are better, some worse, positioning and all kinds of things matter.

Thus, you could quickly reason any issues within the box are on low frequencies, which the acoustic damping inside the box has effect on but where the wavelength is long enough to form standing wave for example, twice the size of longest dimension inside the box. longer wavelength than this is just relatively uniform pressure inside the box, which changes as cone accelerates. Sound whose wavelength is smaller than the box dimensions however, has a chance to bounce inside until dissipated either transmitting into the panels or absorbed by damping material.

All this is simplified and rough to help guide thinking. You can check closer to details when ever need to. For example effectiveness of thin layer of damping material in box might be just fine due to sound passing through it multiple times, incident angle matters and so on. To help get imagination into right track, inside a 34cm or 1ft sized speaker with speed of sound of 343m/s sound will hit walls every 1000th of a second. Blink of an eye is about tenth of a second so you've got already 100 bounces inside, 100 chances of acoustic material to reduce level within blink of an eye. Also, room being roughly 10 times the size of the box, sound would have already bounced inside your room about 100 times as well. It takes some practice to get all of it into intuition, but basically wavelength is how sound relates to physical world and thinking this stuff with wavelength is key to understanding.

Have fun!