how to determine optimum box size

[apilon]

Good afternoon

I am trying to find out how to determine the optimum box size in regard to the size of the driver being used.

Let me explain....I want to build a sub using a 15 inch driver i know that i can use software like winisd but what criteria do i use to find out the optimum box size

Alain

[---k---]

There is no one optimum size. (are you talking sealed or ported?) It is a balancing act. I suggest using Unibox and setting the Q=0.7 and then adjust the box size, tuning and port size to see what happens. You're looking for a reasonably flat response, with port speed generally under red line. Play with Unibox for an hour and you'll start to see how it works. Post the screen shot of your model inputs and results and we'll offer up comments.

[atx_hometheater]

i know that i can use software like winisd but what criteria do i use to find out the optimum box size

Depends on a lot of variables. What size is your room? Is it sealed off from other rooms or open floor plan? What TYPE of subwoofer enclosure do you want (sealed, vented, huge, small, rock music or home theater, etc).

If looking for a sealed subwoofer, then just tell WinISD you want a -3db Sealed subwoofer and it'll automatically calculate the optimum enclosure size for you. Same for -6db. And same for a few of the most popular vented enclosures.

So if you're willing to accept the default optimum enclosure sizes that WinISD suggests, then you're golden.

If not, THEN you need to start worrying about criteria for designing an enclosure.

Once you get the enclosure volume & port size (if used) squared away, the next step is to design the enclosure itself. I like to use "boxnotes" for this. It's freeware that can be found with a Yahoo search.

[apilon]

Depends on a lot of variables. What size is your room? Is it sealed off from other rooms or open floor plan? What TYPE of subwoofer enclosure do you want (sealed, vented, huge, small, rock music or home theater, etc).

If looking for a sealed subwoofer, then just tell WinISD you want a -3db Sealed subwoofer and it'll automatically calculate the optimum enclosure size for you. Same for -6db. And same for a few of the most popular vented enclosures.

So if you're willing to accept the default optimum enclosure sizes that WinISD suggests, then you're golden.

If not, THEN you need to start worrying about criteria for designing an enclosure.

Once you get the enclosure volume & port size (if used) squared away, the next step is to design the enclosure itself. I like to use "boxnotes" for this. It's freeware that can be found with a Yahoo search.

Thanks a lot for these explanation

[fatmarley]

I've used THIS calculator to decide whether to go sealed or ported.

And THIS one to determine box size.

[cjd]

The software all works well. Understanding just how to use it for best accuracy... that's where it gets tougher.

None of the software will deliver without good data up front. T/S parameters in this case.

[fatmarley]

The software all works well. Understanding just how to use it for best accuracy... that's where it gets tougher.

None of the software will deliver without good data up front. T/S parameters in this case.

I'm a novice when it comes to all this, but aren't the manufacturers published T/S parameters good enough to design the enclosure ?

[cjd]

I'm a novice when it comes to all this, but aren't the manufacturers published T/S parameters good enough to design the enclosure ?

Assuming they are accurate, yes.

[apilon]

I've used THIS calculator to decide whether to go sealed or ported.

And THIS one to determine box size.

Hi i used both your recommendation to figure a box using the tc sound lms-r15 driver

This is what i got as a result

Vb = 2.95 ft3 = 83.5 lts
= L x W x H
f3 = 37.08 Hz
fb = 37.08 Hz

Now i know that i need 2,95 CU Feet for internal size but how do i figure out the lenght width and height of the box that i need to build?

Also if i stuff the box with polyfill will that bring down the f3 and fb ?


Alain

[peepaj]

You could try boxycad2. link is right above beer can speakers.

http://members.cox.net/pjay99/speakerhome.htm

[fbov]

Good afternoon

I am trying to find out how to determine the optimum box size in regard to the size of the driver being used. ...

One of the values of simulators is the ability to get a lot of data on the cheap - without building boxes. This allows for a quantitative optimization.

Simulators like WinISD and Unibox turn driver T/S parameters and box geometry you specify into a simulation of the system frequency response. You'll typically pull several critical parameters from the system response like F3, F10, port air velocity, driver excursion, FR peak frequency and amplitude, etc.

Please note that each simulation is an optimization, in a sense. The port length is optimized to achieve a specific resonance frequency at a specific box volume and port diameter. Adjusting port diameter to control peak port air velocity is another optimization, but one that has very little effect on driver performance below the point of port audibility.

So simulators get you data, but you also need criteria; what combination gives the "best" result? Goodness depends on application - what you want it to do. Room size and furnishing, program material, personal preference, speaker capabilities (since we're talking about subs), sound level requirements, etc. play a part, as well as WAF, allowable box size, box location and orientation, port location, etc.

Some of this is mutually exclusive, so you'll be making tradeoffs based on the data. Let me give you an example. Assume amp power and box size is fixed, you can change box tune using the port. Plot F3, F10, cone excursion and port air velocity vs. tuning frequency.
- F3 will track down with tuning, and then rise sharply
- F10 will continue to track down
- cone excursion will increase as tuning drops
- port air velocity will rise as tuning drops
- any FR response peaks will disappear as tuning drops

Then change box size and replot outputs vs. port tuning frequency to see box size effects. In most cases, you can find a design where F3 and F10 predict the bass extension you want, the driver won't self-destruct, and you'll never hear the port. That the optimum for your application.

Have fun,
Frank