advice regarding the project of 2 definitive speakers

[Ema79]

Good morning. I'm building some fairly large speakers that should be permanent. I need advice on the construction of the wooden cabinet. I'm thinking of using oak. But if there are cheaper but equally acoustically sound solutions, I'd appreciate it.
The towers will be approximately 70cm tall, 48cm wide, and 35cm deep. The crossover will be a DSP Xilica XP 8080. For subsonic frequencies, I have a FaitalPRO 18XL1800 subwoofer tuned to 15/65Hz.
The towers will be designed as a sealed box and will house a 12-inch woofer, specifically the Eighteensound 12NW350 model, and an Eighteensound 6ND430 medium, which will be cut as follows: 12NW350 65/250, 6ND430: 250/2500 24/dB, or a B&W LF26727 medium. This will depend on the availability of the B&W driver and the feasibility of the project. I think the B&W should offer me much more than the 6ND430, but it's just an impression. (I'm open to suggestions.) And finally, for the mid-high range, there will be a Beyma TPL 150 (I'm still not sure whether to use it in a dipole or a sealed enclosure (I'm open to suggestions).
The speaker will have two horizontal reinforcement shelves, plus one vertical one.
The volume will be approximately 65 liters, of which 40 liters net are for the woofer and 5 liters for the midrange.
This is my first and hopefully last DIY speaker. I'd first need to know how far apart the drivers should be from each other for maximum dynamics and quality, and whether the cabinet geometry is appropriate or whether it's better to have a separate cabinet for each driver. Whether the choice of wood is a good one or whether there are better options at a lower price, or anything else you can think of to improve the design. Because I'm absolutely not an expert. And I don't want to fail miserably. Thanks.
The distance between the 2 speakers is 2.70 meters. The listening distance is 3.50 meters, and the room is 5x5 meters.

 

[staticV3]

But if there are cheaper but equally acoustically sound solutions, I'd appreciate it.

Natural woods, unless specially treated, do not handle changes in temperature and humidity very well and cabinets made thereof tend to crack over time.

Some owners of D&D 8C and March Sointuva systems had that unfortunate experience.

The general recommendation is to use MDF or plywood instead.

The towers will be designed as a sealed box

Sealed design raises internal pressures and makes building a stable cabinet that much more important. Don't forget to add some bracing to the woofer section.

 

[kemmler3D]

@staticV3 gives good advice on construction here, solid wood is not a good idea. Baltic birch ply is popular when MDF is not used. MDF is a surprisingly effective material given how un-glamorous and cheap it is.

I would further say - if you want this to be your last DIY speaker, you need to do it right, but you've got some 101-level-ish questions in this post that make me concerned for that prospect.

Have you read or at least perused the Loudspeaker Design Cookbook by Dickason? That should clear up all the questions you have here, raise others that you should be asking, and answer those as well.

You can also get a lot of mileage by reading threads at DIYAudio.com if you aren't already. There's a bit of crackpottery over there, but IMO it's far outweighed by discussion and measurement of real-world examples.

What software are you using to design the speaker? WinISD is a minimum, VituixCAD is recommended these days.

How did you select these drivers? Do you have a DATS to measure the drivers once you have them?

An endgame DIY speaker is certainly achievable if you have the tools, budget, and will, but there is no substitute for proper planning and careful measurement!

 

[Ema79]

Hi, thanks for the advice.
I also use Vituix CAD, but only for box calculations. I don't know how to get my hands on the other functions yet. I have an Umik 1 microphone and Rew for measurements. As for tuning, I use Xilica XP 8080.
But aside from leveling the frequency response, I can't do anything else. Also because I've only had these tools for a short time. But in reality, I don't understand much about them. I read and reread, but if I don't see it on a practical level, I can't do it.
But from what I understand, the microphone and the Rew program can also align the response in time and amplitude, as well as the dispersion between drivers. But I absolutely don't know how to do that. It's also something I'd have to do with the drivers at home in a test box. Unfortunately, I don't have the means to do all this.
The components were chosen based on their quality. The TPL is a heil and I like it to death.
The midrange was chosen more to connect well to the Beyma TPL at 2500kHz. While the bass isn't ideal for a closed cabinet, it was chosen because I don't want full, overflowing bass. Instead, I want fast, precise, and very controlled bass. The subwoofer provides plenty of bass. I can also play with the DSP.

Anyway, the volumes were calculated with Vituix cad. They should be correct. I'm not sure they should be, because as you may have guessed, I'm a total loser.

 

[Sokel]

because as you may have guessed, I'm a total loser.

A loser is one that does not ask and learn.
Since you do, you're not.

Other that reading left and right you can get a sense of what it needs here:

N

'How to make quasi-anechoic speaker measurements/spinoramas with REW and VituixCAD'

Mar 29, 2021

NOTE from ASR staff: The following content has useful tips and details, but as REW and VituixCAD continue to be actively upgraded, some parts of this thread may be obsolete. Be sure to consult the respective software sites for the latest updates.


Quasi-anechoic measurements are a way to capture the 'real' frequency response of a speaker without the influence of a room. They are called 'quasi-anechoic' because they have the potential to get you really close to the results one might achieve with a non-reflective environment like an anechoic chamber or using a device like the...

• napilopez
• Replies: 354
• Forum: Speaker Reviews, Measurements and Discussion

• 

 

[Ema79]

A loser is one that does not ask and learn.
Since you do, you're not.

Other that reading left and right you can get a sense of what it needs here:

N

'How to make quasi-anechoic speaker measurements/spinoramas with REW and VituixCAD'

Mar 29, 2021

NOTE from ASR staff: The following content has useful tips and details, but as REW and VituixCAD continue to be actively upgraded, some parts of this thread may be obsolete. Be sure to consult the respective software sites for the latest updates.


Quasi-anechoic measurements are a way to capture the 'real' frequency response of a speaker without the influence of a room. They are called 'quasi-anechoic' because they have the potential to get you really close to the results one might achieve with a non-reflective environment like an anechoic chamber or using a device like the...

• napilopez
• Replies: 354
• Forum: Speaker Reviews, Measurements and Discussion

• 

If I understand correctly, this would be the near-field measurement. Right? That is, the measurement with the microphone at the center of the driver and 5 centimeters away.
This way, you get a mapping of the overall frequency response. So far, so good. But if I understand correctly, this is to get the actual data from the speakers and their frequency response. But how do I determine if that driver needs a minimum distance from the next driver? How do I tell if it has a narrow or wide-field radiation pattern? And how do I tell if one speaker is out of phase with the other?

 

[Sokel]

If I understand correctly, this would be the near-field measurement. Right? That is, the measurement with the microphone at the center of the driver and 5 centimeters away.
This way, you get a mapping of the overall frequency response. So far, so good. But if I understand correctly, this is to get the actual data from the speakers and their frequency response. But how do I determine if that driver needs a minimum distance from the next driver? How do I tell if it has a narrow or wide-field radiation pattern? And how do I tell if one speaker is out of phase with the other?

No, that's not it.
The idea is to get the response without the room influence. That's what gating does.
A meter from the speaker is ok.
If you can do it outside without boundaries is way better, and finally if you can do it outside on a turntable high enough where you can do a spin (response pet angles) you will be approaching the true response of your speaker on and off-axis.

 

[Ema79]

What's the point of taking this measurement? I say this because the speaker will then be placed in the room. And this will affect the sound. It might be useful if you plan to modify the room where the speakers will be placed. Which is a good thing. But it's still useful once you have a finished speaker. Now I should be able to build it. Then I can take this data and do the rest.

For example, I need to know how to space the drivers. For example, I know that each frequency has a wavelength. And since I can't calculate this length, I can't space the drivers for proper sound diffusion without them overlapping. Or is it better to have a cabinet narrower than the woofer, or can I leave it unchanged? Should the edges be rounded? Is a horn tweeter necessary? Is a dipole or a sealed cabinet better for the tweeter? I'm not sure I've explained exactly what I need now...

 

[kemmler3D]

For example, I need to know how to space the drivers. For example, I know that each frequency has a wavelength. And since I can't calculate this length, I can't space the drivers for proper sound diffusion without them overlapping. Or is it better to have a cabinet narrower than the woofer, or can I leave it unchanged? Should the edges be rounded? Is a horn tweeter necessary? Is a dipole or a sealed cabinet better for the tweeter? I'm not sure I've explained exactly what I need now...

These are all things that are explained in the book and I'm sure you can grasp them if you take some time on it.

For example, calculating the wavelength at any given frequency is not hard... There are calculators online but it's a pretty simple equation based on the speed of sound.

The distance between drivers should ideally be (iirc) less than 1/4 the wavelength at the crossover frequency to avoid cancellation.

Edges should be rounded in most cases due to diffraction.

Horns come with their own significant pros and cons.

Likewise dipole or sealed is a major choice about how the speaker sounds, and you simply need to form your own opinion on that, one isn't strictly better than the other, but the outcomes will be very different.

This is why I say you should probably spend more time reading. If this is going to be your first and last DIY speaker, you really need to be confident about choices like dipole vs. closed or horn vs. direct radiating. They are big decisions that other people can't really make for you, they are a matter of taste / opinion.

as you may have guessed, I'm a total loser.

No way! If you are even considering DIY you are already beyond 99% of people. I spent a lot of time reading about DIY with a similar thought to you... One and done... Eventually I realised it was not practical for my space and left it alone. Early on, I found out that it was more complicated than I realized. After close to a year I felt ready to start spending big money on drivers, but I moved to a new house where there was no place for such a speaker. Oh well, someday...