Lego loudspeaker project using Dayton ND91-8

[ppataki]

This project is rather for fun but who knows, maybe it will work out well and will do more of these....

I have some spare Dayton ND91-8 full range drivers (leftover from my MCLA and my truncated line array projects) and I will put one of those into a closed cabinet made of Lego bricks
Cabinet is approx. 0.5 liters with a Qtc = 0.707. External dimensions are approx. 13x13x10cm.

3D rendering of the cabinet (made with Bricklink Studio 2.0)

Wall thickness is approx. 16mm (and around 10mm for the bottom and the top)
I am planning to rear-mount the driver with screws. I have tested using screws in Lego bricks and it seems to work pretty well.
Making the cabinet airtight might be a challenge; I am planning to use silicone paste to cover the cabinet walls inside - any other ideas for that would be highly appreciated.
(+ polyester wad filling at the end to 'increase' the volume of the cabinet)

The bricks shall arrive later this week - total cost was about 40 EUR (for just this one box - but think about this: no need for carpentry, no need for paint, literally endless options for colors, decoration, shapes, etc.....)
Will post pictures and also some measurements at the end

 

[mhardy6647]

Waiting with bated breath.

 

[Sashoir]

I follow your posts with great interest and admiration, but I do worry that you are going to perish inside your home after trapping yourself inside by building too many loudspeakers.

Edit: at least if they're hooked up you should be able to call for help.

 

[Berwhale]

Making the cabinet airtight might be a challenge; I am planning to use silicone paste to cover the cabinet walls inside - any other ideas for that would be highly appreciated.

This person used duct tape in their Lego sub...

https://imgur.com/a/vdGrE

 

[mhardy6647]

dang.
Now I'm thinking about doing a Lego transmission line... or a Lego back loaded horn... or maybe a Lego Klipschorn.
dang.

 

[ppataki]

This person used duct tape in their Lego sub...

https://imgur.com/a/vdGrE

Thanks, that is a great idea, I will try that

 

[abdo123]

Lego bricks leak air, you need to glue the whole thing or it will be basically an open baffle.

 

[ppataki]

Lego bricks leak air, you need to glue the whole thing or it will be basically an open baffle.

I hope the duct tape will help
If not, I will try silicone paste too

 

[GXAlan]

Having watched plenty of Lego Masters, using Technic blocks can also be used to enhance the rigidity of your enclosure.

What I would say is that you should take advantage of LEGO to create something nicer than a box and to curve the baffle.

LEGO SNOT Basics: Geometry, Techniques and Pitfalls - BrickNerd - All things LEGO and the LEGO fan community

Take a deep dive into SNOT as we analyze the geometry, look at some basic building techniques and expose some hidden pitfalls of LEGO SNOT.

bricknerd.com

And what would be more ambitious is to try to seal the enclosure without tape or glue. Perhaps if you had cling wrap/plastic wrap that was sandwiched between different Lego layers, it would reduce the leakage sufficiently to work well.

 

[ppataki]

Having watched plenty of Lego Masters, using Technic blocks can also be used to enhance the rigidity of your enclosure.

What I would say is that you should take advantage of LEGO to create something nicer than a box and to curve the baffle.

LEGO SNOT Basics: Geometry, Techniques and Pitfalls - BrickNerd - All things LEGO and the LEGO fan community

Take a deep dive into SNOT as we analyze the geometry, look at some basic building techniques and expose some hidden pitfalls of LEGO SNOT.

bricknerd.com

And what would be more ambitious is to try to seal the enclosure without tape or glue. Perhaps if you had cling wrap/plastic wrap that was sandwiched between different Lego layers, it would reduce the leakage sufficiently to work well.

Good ideas, thanks!
Let's see how this prototype works
If it matches my expectations I will consider building a pair of much bigger boxes for 8" fullrange speakers

 

[ernestcarl]

This might sound like cheating, but if it were my lazy ass doing this I simply would use the bricks as a sort of shell or outer facade layer over the actual speaker enclosure.

 

[mhardy6647]

Lego bricks leak air, you need to glue the whole thing or it will be basically an open baffle.

or... aperiodic loading.
You know -- when loudspeaker alignments give you lemons -- make lemonade.

 

[Berwhale]

Thanks, that is a great idea, I will try that

Or this!

One moment, please...

Do I win a prize?

 

[ppataki]

Finally, the baby is born!

Let me share some photos about the process:

This is how I got started:

I deliberately chose to buy used Lego to be as eco-friendly as possible but it took its toll on the looks as you will see later on

Then started building:

And this is where things started to get messy.......

How to fix the driver in the cabinet?
I tried with screws as I have tested that before but it turned out that where the Lego bricks are joined the screw would tear that apart....
I tried gluing together those parts only where the screws would enter the baffle but still it just did not work:

And I managed to accidentally drill too deep too - twice....

So finally I decided to ditch the screws and just used glue to fix the driver
Also I chose to use silicone paste to make the cabinet airtight at the end of the day:

And this is how it looks:

The bricks (being used) are not equally white and those two holes on the baffle also look a bit messy but anyway, it was good fun and turns out that this whole concept is feasible nevertheless!

Later this week or early next week I will be coming back with measurements and subjective comments too!
Bated breath in the meantime

 

[ppataki]

So here are the measurements!
(1cm away, 0 degrees)

Frequency response with empty box, then felt on the inner walls then felt + wad filling and finally vibrodamping panels + felt + wad filling:

The low frequency ripple I guess is just a measurement glitch - otherwise there are not much a difference anywhere

Let's see the phase for the same:

The empty box stands out, otherwise the rest is pretty much the same

Distortion:

IR:

Step:

I will provide the mdat file at the end of this post so you can check the Waterfalls and the Spectrograms too

Now I think what is much more interesting is to see these same graphs when EQ-d to flat:

Here is a video about how it sounds (EQ-d to flat as shown above + a linear phase 24dB/oct HPF at 40Hz + a high shelf to tame the top)

New video by Peter Pataki

photos.app.goo.gl

Personally I think it sounds awesome! (if EQ-d, obviously)

I will keep it as a souvenir on my shelf but I think the point is that it is totally possible to build a loudspeaker out of Lego and it works perfectly
With a subwoofer crossed around 100Hz to avoid a lot of distortion it would be a great desktop solution and it looks really cool too (when built using brand new bricks and using glue instead of screws - just make sure the cabinet is airtight)
On that note: my box finally is not totally airtight, there is air leakage around the driver itself but that could be resolved by applying an extra layer of gasket - just a word of advice to those who would like to venture into this domain
Probably that is one of the reason for the really high distortion too for the lows (btw at moderate listening levels it is not really audible by ear)

Finally the measurement itself: https://drive.google.com/file/d/1i7osJBhWnwTAoZJfzY0VdAcvdj9WAFd0/view?usp=sharing

Any questions, comments are welcome!