3D printed classic 3-way budget speaker project using SB and Dayton drivers

[ppataki]

After having a lot of fun and success with my first 3D printed project I decided to continue on this path

I will not have time to actually start this project until Q4 this year (it might even slip to Q1 next year) but I thought I would share my design ideas upfront for some comments and suggestions since I have never designed/built a classic 3-way speaker before

The project goals are:
- fully 3D printed classic cuboid cabinet with separate chambers for all three drivers
- slanted internal walls to have zero pair of parallel planes inside the cabinet to reduce internal standing waves
- sealed design
- fully active crossover (all LR 24dB/octave) and EQ using DSP (PC-based: using Jriver, various VST plugins and Dirac Live as DRC)
- budget friendly drivers

Let's start with the drivers and the planned crossover settings:

Woofer:
SB Acoustics SB17NRX2C35-4 (106 EUR/pair from TLHP)
6.5"

I will use a sub (actually two) so I will apply a HPF at 80Hz and a LPF at 300Hz
In a 4 liter sealed cabinet it will have -4.3dB at 80Hz so some slight EQ compensation might be necessary, also depending on the room gain

At 80Hz the max SPL (xmax limited) will be 104dB for mono and 110dB for stereo at 1 meter

Midrange:
SB Acoustics SB12MNRX2-25-4 (90 EUR/pair from TLHP)
4"

Planned HPF at 300Hz, planned LPF at 2200-2500Hz since that is where the off-axis curves start to fall but please correct me if I am wrong with this notion

In a 1.5 liter sealed cabinet it will produce -0.9dB at 300Hz - a very slight compensation might be needed

Tweeter:
Dayton Audio ND25FW-4 (38 EUR/pair)
1" soft dome with waveguide

HPF at 2200-2500Hz as per the above


Now let's see the cabinet!

Rounded edges, separated chambers for all drivers, drivers flushed, sealed design
Outer dimensions: 185 x 248 x 425 mm
Cross-braces will be added to the design too

The internal slanted walls can be seen here:

It will be printed in two parts, printing will take approx. 6 days per speaker

Total cost will be: 234 EUR for all the drivers + 130 EUR for all the filament = 364 EUR (+ some electricity costs + the internal treatment of the cabinets using vibrodamping sheets and melamine foam)

I would appreciate any comments/suggestions
Thank you

 

[RickS]

Given the resources required and fairly boxy shape , why not build a wood prototype first?

 

[ppataki]

Given the resources required and fairly boxy shape , why not build a wood prototype first?

I will print only one speaker first and then see how that works out but to be honest I have (very) high confidence in the printed design after venturing into this domain with my previous 3D printed speaker project (printed quite a few prototypes there during the process)

 

[Francis Vaughan]

Given the freedom of form 3D printing provides, it seems something of a waste to essentially reproduce a basic rectangular wooden box. The only good reason we use rectangular boxes is that wood sheets are flat. You are pretty satisfied with your spherical design, so why the regression? The slight asymmetry of internal shape is likely going to provide only a very small effect on internal acoustic resonances. Flat panels are going to require a lot more than adhesive damping to tame the mechanical resonances. Compared to the sphere, flat is about about the worst.

The obvious speakers to drawn inspiration from would be modern Genelecs. The cabinet shape incorporates a huge amount of smart engineering to good effect. The shape performs multiple duties with mechanical, internal acoustic and external acoustic behaviour all benefiting.

I love melamine foam for taming upper frequency behaviour. However you may find that the bass response isn't as fabulous if you fill the bass volume with it. It can be too resistive, and you end up with an alignment with less bass extension that you hoped for. 300 Hz has a wavelength of roughly a metre. The regime inside the bass enclosure versus the mid enclosure is very different. Which is also why the slanted walls are essentially useless in the bass enclosure. You need the path length differences to be of a similar order to the wavelength to have any effect.

Have you considered making the mid enclosure a short cylinder with a hemispherical cap? Lots of reasons that might work well.

 

[TurtlePaul]

I would make the boxes look like Blueroom Minipods.

 

[ppataki]

Given the freedom of form 3D printing provides, it seems something of a waste to essentially reproduce a basic rectangular wooden box. The only good reason we use rectangular boxes is that wood sheets are flat. You are pretty satisfied with your spherical design, so why the regression? The slight asymmetry of internal shape is likely going to provide only a very small effect on internal acoustic resonances. Flat panels are going to require a lot more than adhesive damping to tame the mechanical resonances. Compared to the sphere, flat is about about the worst.

The obvious speakers to drawn inspiration from would be modern Genelecs. The cabinet shape incorporates a huge amount of smart engineering to good effect. The shape performs multiple duties with mechanical, internal acoustic and external acoustic behaviour all benefiting.

I love melamine foam for taming upper frequency behaviour. However you may find that the bass response isn't as fabulous if you fill the bass volume with it. It can be too resistive, and you end up with an alignment with less bass extension that you hoped for. 300 Hz has a wavelength of roughly a metre. The regime inside the bass enclosure versus the mid enclosure is very different. Which is also why the slanted walls are essentially useless in the bass enclosure. You need the path length differences to be of a similar order to the wavelength to have any effect.

Have you considered making the mid enclosure a short cylinder with a hemispherical cap? Lots of reasons that might work well.

I guess I was just way too convenient with the cuboid design - the spheres are indeed awesome!
You are totally right, thinking 'outside the box' in this case is well justified

Have you considered making the mid enclosure a short cylinder with a hemispherical cap? Lots of reasons that might work well.

That is a very good idea! But why just the midrange? I was thinking that I could print three 'tubes' with hemispherical caps and stick them under each other so it would look something like this from the side (speaker drivers would sit on the left side of course):

I would make the boxes look like Blueroom Minipods.

To be honest I really don't fancy their looks

 

[ppataki]

Something like this:

 

[Francis Vaughan]

Hmm maybe.
The diffraction effects off the other enclosures isn’t going to be pretty. I actually meant to make the interior enclosure for the mid like that. But I would be still thinking in terms of a single enclosure. Modern speaker design places a lot of emphasis on controlling diffraction and its effects on directivity.
A 3D printed enclosure allows you to manage this in a way that is difficult and expensive for more traditional techniques.
Genelec’s tooling costs must be extraordinary to get the same effect in die cast aluminium.

 

[ppataki]

It looks soooo cool (at least in my opinion) that I will have to give it a try anyway

 

[Heinrich]

That is a very good idea! But why just the midrange? I was thinking that I could print three 'tubes' ...

Tube resonances? Tried once, never again - they are so tenacious.
In case I would investigate technologies used for combustion engines' exhaust pipes to at least mitigate the problem a bit, in using the merits of a free-forming 3D print. KEF's "meta" design comes into mind.

 

[Audionaut]

Why three ways? You are using a 6-inch driver that works perfectly well in two-way designs and reproduces a very nice midrange.

If three ways, then I would use a 10 inch or 12 inch woofer.

 

[ppataki]

Tube resonances? Tried once, never again - they are so tenacious.
In case I would investigate technologies used for combustion engines' exhaust pipes to at least mitigate the problem a bit, in using the merits of a free-forming 3D print. KEF's "meta" design comes into mind.

I totally get the point but to be honest I (subjectively) love this design so much that I will give it a try nevertheless
At least we will see some measurements about such a design too

 

[ppataki]

Why three ways? You are using a 6-inch driver that works perfectly well in two-way designs and reproduces a very nice midrange.

If three ways, then I would use a 10 inch or 12 inch woofer.

Fair point. The reasons why I would like to try a 3-way design are the following:
- I have never done it before and love to get some experience
- More ways are supposed to yield lower IMD (happy to stand corrected though)
- Probably THD shall be lower too
- I am curious to hear how the sound stage will 'look like' compared to my previous projects using fullrange and coax drivers and traditional 2-way designs

Edit: and I have two subwoofers so probably no need for big front speakers

 

[Audionaut]

The reasons why I would like to try a 3-way design are the following:

Don't let me stop you, you always do cool things.
Good luck

 

[ppataki]

A small update:

The tweeters have arrived!

The schedule of the project is a bit unclear at this moment: I might start it in October or I might postpone it to early next year
It all depends on the timing of the move to my future new apartment

I will order the other components based on how the above things evolve - but anyway I can't wait to kick this off!!

 

[kemmler3D]

Late to this thread but love the way it's shaping up. I do tend to agree that if you're going 3 ways the woofer should be beefier, but I am stoked to see the unconventional design taking shape.

Since you're doing a cylinder I think it might be a good idea to add extra space for extra stuffing in the midrange chamber, and/or some internal structure to break up standing waves?

 

[ppataki]

I do tend to agree that if you're going 3 ways the woofer should be beefier,

What is the reason for that? I mean I will have 2 subs helping these speakers, hence I thought a pair of 6.5" would be OK - 110dB at 1 meter at 80Hz would be more than enough for me (at 3 meters that is still 98dB). And I could keep the cabinet pretty small.

But I am way open to changing the plan still, hence I am asking for the reason

to add extra space for extra stuffing in the midrange chamber, and/or some internal structure to break up standing waves?

I am planning to add 4mm of vibrodamping sheets + 10mm of felt + wad stuffing
Would that be OK?

 

[Salt]

Stuffing would increase the virtual volume of the enclosure. Would do no harm in midrange.

 

[kemmler3D]

What is the reason for that? I mean I will have 2 subs helping these speakers, hence I thought a pair of 6.5" would be OK - 110dB at 1 meter at 80Hz would be more than enough for me (at 3 meters that is still 98dB). And I could keep the cabinet pretty small.

But I am way open to changing the plan still, hence I am asking for the reason



I am planning to add 4mm of vibrodamping sheets + 10mm of felt + wad stuffing
Would that be OK?

Nothing wrong with doing it this way but if you are adding an entire 3rd way I personally feel like doing 8" or 10" makes more sense to extend the lows and reduce distortion from 80-200hz more.

I am not sure but 15mm of damping material doesn't sound like a lot?

 

[ppataki]

Nothing wrong with doing it this way but if you are adding an entire 3rd way I personally feel like doing 8" or 10" makes more sense to extend the lows and reduce distortion from 80-200hz more.

OK, I got your point and I concur. It is just that with a 6.5" I can keep the cabinet small....I will take a look at some 8" options though; maybe I can find a suitable one

I am not sure but 15mm of damping material doesn't sound like a lot?

I have always done it like this with all my previous projects and worked fine (it might still be a lot though)
The butyl sheets help with vibration reduction (a lot!) and felt helps with the damping + wad for increasing the virtual volume as mentioned by @Salt
This has been my 'recipe" so far..... (although once I run out of felt I might replace that with melamine foam)