squaring a rectangle

[rokr]

I've built a classic shape rectangular (w=20cm h=30cm d=30cm) bookshelf kit speaker and it's great!
A friend of mine heard it and really liked it, so he asked me to build a set for him, but he wanted his to be square (w=30cm h=30cm d=30cm) …
I tried to explain to him that a lot of measurements and experiments were made in order to achieve the performance of this speaker and changing the size will probably hurt the performance. He was sure I'll find a way, and let's face it, he is the client.

So, I thought about keeping the original sizes enclosed in the larger cabinet. I can fill the side voids with polyfil or even wood.
The image attached will show what I'm talking about (red-original | green-enlarged | blue-enclosed).
I'm new to speaker building and I still don’t have measuring equipment.

How would you go about this?

 

[Deleted member 21219]

From whom did you purchase the original kit? Can you contact them and ask them? It may make a big difference, and then again it may not.

Jim

 

[fpitas]

The wider front baffle will affect (lower) the baffle step transition frequency. Unless you want to wade into that, probably best to do as Jim suggested.

 

[kemmler3D]

If you keep the internal volume (bracing, damping, fill) the same, then output at the cone should be the same. However, as others have noted, changing the shape and size of the baffle will have an effect on frequency response and directivity, which might even indicate changes in the crossover. It's not a consequence-free alteration. I would expect okay results but without dealing with all these effects the sound will probably get a little worse.

 

[rokr]

From whom did you purchase the original kit? Can you contact them and ask them? It may make a big difference, and then again it may not.

Jim

Thanks. That's a good idea.

 

[rokr]

If you keep the internal volume (bracing, damping, fill) the same, then output at the cone should be the same. However, as others have noted, changing the shape and size of the baffle will have an effect on frequency response and directivity, which might even indicate changes in the crossover. It's not a consequence-free alteration. I would expect okay results but without dealing with all these effects the sound will probably get a little worse.

The way i looked at is that I'm getting some extra bracing, more dampening and a bigger front baffle (which I thought is a good thing).

 

[Killingbeans]

Isn't a cubic internal volume one of the worst choices for a speaker, only surpassed by a sphere? Or is that a myth?

 

[Deleted member 21219]

Isn't a cubic internal volume one of the worst choices for a speaker, only surpassed by a sphere? Or is that a myth?

A true cube is supposedly bad. A square shape with one dimension shorter or longer is generally considered not nearly as bad. But a true cube and a sphere can both be accommodated with the correct engineering.

https://webstore.hificinema.co.uk/product/gallo-acoustics-adiva-spherical-speaker/

Jim

 

[kemmler3D]

The way i looked at is that I'm getting some extra bracing, more dampening and a bigger front baffle (which I thought is a good thing).

Bigger front baffle can be good, but it's in terms of the lowest frequency you get directivity at. 1143hz has a wavelength of 30cm so it's not big enough to get you really low, and in fact it might be a relevant frequency for the crossover, which makes things a bit complicated.

As far as bracing and damping, I think it's probably a win if you build it right, but you'll want to think through whether your crossover is going to get screwed up in the process.

 

[fpitas]

I think he would simply build out around the rectangular box to get a cube. So, the main thing affected is the front baffle shape.

 

[fpitas]

Isn't a cubic internal volume one of the worst choices for a speaker, only surpassed by a sphere? Or is that a myth?

I think he would simply build out around the rectangular box to get a cube. So, the main thing affected is the front baffle shape.

 

[Zapper]

A true cube is supposedly bad. A square shape with one dimension shorter or longer is generally considered not nearly as bad. But a true cube and a sphere can both be accommodated with the correct engineering.

https://webstore.hificinema.co.uk/product/gallo-acoustics-adiva-spherical-speaker/

Jim

His friend asked for a true cube: "but he wanted his to be square (w=30cm h=30cm d=30cm)"

 

[rokr]

His friend asked for a true cube: "but he wanted his to be square (w=30cm h=30cm d=30cm)"

The actual request was for a square front baffle. I didn't want to change the depth because it would mean that the rear port will need a size adjustment.
If a square is so bad, i can do two things, fake a square, lets say w=29cm h=30 (he will never know .
Another thing i can do is move the "internal speaker" slightly to one side, and by doing so desquaring it in a way.

 

[Killingbeans]

If a square is so bad, i can do two things, fake a square, lets say w=29cm h=30 (he will never know .
Another thing i can do is move the "internal speaker" slightly to one side, and by doing so desquaring it in a way.

I don't think that will do much. I normally see people recommending getting as close to the golden ratio as you can.

The "blue" solution is probably your best bet. But depending on what you choose to fill the voids with, you could start seeing the effects of mass loading and possibly some shifting of resonance frequencies. The new baffle shape might also require changes to the crossover.

EDIT: Speaker design is not one of my biggest areas of expertise, so there's a high risk I'm simply talking out of my a$$ and/or focusing on non-important issues. Honestly, if I were in your shoes, I'd build the original design and tell my friend to get creative with some styrofoam and glue if he absolutely wants a square shape

 

[kemmler3D]

I guess my real advice here is to do some sims with the rectangular vs. square baffle and see if you need to do anything with the XO. If not, just having some sealed chambers adjacent to the "real" speaker chamber should not have any serious effects. Vituix should be able to give you some pretty reliable direction here.

 

[RayDunzl]

A friend of mine heard it and really liked it, so he asked me to build a set for him, but he wanted his to be square (w=30cm h=30cm d=30cm) …

Why does he want what he wants?

 

[rokr]

Why does he want what he wants?

It has do with his shelving and interior-design...

 

[voodooless]

You can really test the square baffle really simple and fast: just add some cardboard boxes to the sides of the kit in the right size and listen if it sounds. If the guy is happy with that, make the square box like your blue drawing.

 

[rokr]

I don't think that will do much. I normally see people recommending getting as close to the golden ratio as you can.

The "blue" solution is probably your best bet. But depending on what you choose to fill the voids with, you could start seeing the effects of mass loading and possibly some shifting of resonance frequencies. The new baffle shape might also require changes to the crossover.

EDIT: Speaker design is not one of my biggest areas of expertise, so there's a high risk I'm simply talking out of my a$$ and/or focusing on non-important issues. Honestly, if I were in your shoes, I'd build the original design and tell my friend to get creative with some styrofoam and glue if he absolutely wants a square shape

About that golden ratio, it actually means that all floor-standers are completely out of proportion and a good ratio speaker will be ~ 35cm, 17cm, 25cm. let's say the baffle width is 35cm, it means that either the height or the depth should be 17cm which both are a big (small) problem. I don't remember seeing such a speaker.

 

[voodooless]

About that golden ratio, it actually means that all floor-standers are completely out of proportion and a good ratio speaker will be ~ 35cm, 17cm, 25cm. let's say the baffle width is 35cm, it means that either the height or the depth should be 17cm which both are a big (small) problem. I don't remember seeing such a speaker.

These are close to the golden ratio. JBL Classic L100 the depth isn’t very important for ascetic’s generally. Your kit is also just 2cm short. Close enough.