How do you guys calculate all this?

[FNG212]

I have a math and physics background but only briefly studying electrical engineering. I am confident in working the problems but I haven't found too many resources that explain how to calculate box volume (required for the driver, not just HxWxL), tuning freq (i still dont quite understand what that is or how you figure it out), port length/size. I really want to nerd out on this stuff but don't know where to start studying.

Any direction would be greatly appreciated.

 

[nibhaz]

Most people are using software based modeling to do the calculations for them. I’m not builder, so I don’t know the names of the programs. I think one might be WinI Sd or something close to that. I’m quite sure those who build will chime in shortly.

 

[Warpdrv]

Here is a great place to get some help on all this....

http://www.hometheatershack.com/forums/enclosure-volume-calculator/

For someone that has a good deal of engineering it may not really be necessary, but I found alot of useful info over there.

Should be more then a good start for those in need of some help.

 

[Swerd]

I have a math and physics background but only briefly studying electrical engineering. I am confident in working the problems but I haven't found too many resources that explain how to calculate box volume (required for the driver, not just HxWxL), tuning freq (i still dont quite understand what that is or how you figure it out), port length/size. I really want to nerd out on this stuff but don't know where to start studying.

Any direction would be greatly appreciated.

If you want to nerd out on this stuff, read the first few chapters in Speaker Building 201 by Ray Alden. It explains most of the concepts in box design and does simple derivations of the math involved.

As others have already said it is easiest to use online or downloadable calculators for this.

 

[lsiberian]

I use WinISD Alpha to model volumes and ports. Then I use box notes to generate a cut list.See my MBM thread for more information.

 

[FNG212]

Is there a way to generate necessary driver specs and box config to achieve a specific result?

A lot of these calculators go the direction of "input driver specs, output box volume/config"

Is there a program that inputs desired results of say "input: -3dB @ 15Hz, output: 15" driver, specs XYZ, box config ABC"?

I guess my question revolves around the fact that there are so many variables, is there a way to start at the end and work backwards or is it sheer trial and error of changing one or two variables at a time to achieve the desired results?

 

[lsiberian]

Is there a way to generate necessary driver specs and box config to achieve a specific result?

A lot of these calculators go the direction of "input driver specs, output box volume/config"

Is there a program that inputs desired results of say "input: -3dB @ 15Hz, output: 15" driver, specs XYZ, box config ABC"?

I guess my question revolves around the fact that there are so many variables, is there a way to start at the end and work backwards or is it sheer trial and error of changing one or two variables at a time to achieve the desired results?

Not that I'm aware of. But I'm sure if you dig enough you can find out.

 

[TLS Guy]

Is there a way to generate necessary driver specs and box config to achieve a specific result?

A lot of these calculators go the direction of "input driver specs, output box volume/config"

Is there a program that inputs desired results of say "input: -3dB @ 15Hz, output: 15" driver, specs XYZ, box config ABC"?

I guess my question revolves around the fact that there are so many variables, is there a way to start at the end and work backwards or is it sheer trial and error of changing one or two variables at a time to achieve the desired results?

No and with good reason. You can't pull an F3 out of the air. More often than not the lowest F3 possible is not the best alignment. The reason being you often sacrifice efficiency, power response and increase distortion. Good modeling programs steer you to the optimal alignment, which is usually not the lowest F3 possible. In any event the F3 if picked out of the air, may well not be possible for that driver.

 

[FNG212]

Got it. Thanks!

I guess I'll start messing around with different drivers.

Does anyone have recommendations on drivers for the lowest response? Once I have the funds I am going to do the Kappa build to get my feet wet but I want the start of a plan on a ~15Hz sub if possible. I think I can convince my wife on size if its necessary. I have this silly idea in mind for like dual 18s or something.

I have been poking around on hometheatershack.com and they have some good build threads.

Can round ports be converted to square? I don't really like the look of round ports.

Thanks again.

 

[TLS Guy]

Got it. Thanks!

I guess I'll start messing around with different drivers.

Does anyone have recommendations on drivers for the lowest response? Once I have the funds I am going to do the Kappa build to get my feet wet but I want the start of a plan on a ~15Hz sub if possible. I think I can convince my wife on size if its necessary. I have this silly idea in mind for like dual 18s or something.

I have been poking around on hometheatershack.com and they have some good build threads.

Can round ports be converted to square? I don't really like the look of round ports.

Thanks again.

The best ports are slot vents which are usually rectangular. They can be made with a large enough cross sectional area to avoid high air velocities and port compression. Do not get hung up on a low F3. This is one of the most common mistakes a beginner makes, and is one of the chief ways designs get compromised.

The Fs of a driver pretty much determines the F3 point of the design, in fact the optimal box usually has an F3 a little above Fs. Trying to tune a system below Fs is fools gold and will compromise the design.

Here are bunch of drivers I have doodled with.

In the last alignment we had a member trying to tune for too low an F3 and you can see how this made for a worse sub than one tuned for a higher F3.

 

[lsiberian]

The best ports are slot vents which are usually rectangular. They can be made with a large enough cross sectional area to avoid high air velocities and port compression. Do not get hung up on a low F3. This is one of the most common mistakes a beginner makes, and is one of the chief ways designs get compromised.

The Fs of a driver pretty much determines the F3 point of the design, in fact the optimal box usually has an F3 a little above Fs. Trying to tune a system below Fs is fools gold and will compromise the design.

Here are bunch of drivers I have doodled with.

In the last alignment we had a member trying to tune for too low an F3 and you can see how this made for a worse sub than one tuned for a higher F3.

What about the JL Audio 12w7 it's Fs is 27 hz, yet it models best in a 21hz tune in a 5 cuft box?

Seems this is only one factor. Of course the 12w7 is by no means a typical driver so I'm guessing it's a result of excellent engineering that it works so well with a lower tune. You get a truly flat response to 20hz with that beauty.

That being said chasing the sub 20hz range is foolish IMO. The Kappa is probably the biggest sub most people need and that is still stretching it. Your best bet is to stick to that IMO. It's a great sub and hard to beat without significantly more power and cash. I will be building my own sub in a similar box. I've found many drivers that model well in the Kappa box so your certainly not limited to that driver. The TC Sounds TC-1000 is what I will be using in it. Of course I will only build one for sub 50 work. I'm going with the MBM method for my 50 to 150hz range.

 

[highfigh]

I have a math and physics background but only briefly studying electrical engineering. I am confident in working the problems but I haven't found too many resources that explain how to calculate box volume (required for the driver, not just HxWxL), tuning freq (i still dont quite understand what that is or how you figure it out), port length/size. I really want to nerd out on this stuff but don't know where to start studying.

Any direction would be greatly appreciated.

I have an old copy of The Loudspwaker Design Cookbook, by Vance Dickason and I have to assume the new edition has all of the formulae, too, with updates. If you want info on this, google is your friend- In that book, the bibliography is very complete and full of the names of people who did all of the heavy lifting in this.

Doing the calcs for box design is a boring, tedious process, although you could do your own Excel sheet for it. Still not as fast as using one of the existing programs.