Looking for help with speaker box size calculation and cross-over build

Onebean

AK Subscriber
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On cyber Monday I made an impulse buy and grabbed a pair of these Seismic Audio Co-Ax divers.

https://www.seismicaudiospeakers.co...rs/products/12-inch-coaxial-speaker-pair-each

I emailed them for the T/S parameters, and here's what they sent me.

CoAx-12:
T/S Parameters:
Resonant Frequency (fs): 52 Hz
DC Resistance (Re): 5.8 Ohm
Mechanical Q (Qms): 7.42
Electromagnetic Q (Qes): 0.5
Total Q (Qts): 0.5
Compliance Equivalent Volume (Vas): 57.16 Ltr
Mechanical Compliance of Suspension (Cms): 0.184 mm/N
BL Product (BL): 17.35 Tm
Diaphragm Mass Airload (Mms): 65.7g
Surface Area of Cone (Sd): 547.4 cm2

My goal for these speakers is to build a set of main speakers for a PA rig for jamming with my buddies. I'd like them to be as full range as possible, while keeping the box a reasonable size. I used a box calculator on DIY Audio and Video, and it says the box needs to be 4 cubic feet and ported. That's way bigger than I can tolerate for the space we have available. I'd like them to be full range, and play as deep as possible, but I'd trade low end for a smaller box size. For band use, we would only run vocals through these, but it would be nice to use them for party's and other events that require full range music.

How do I design a speaker box and estimate the bass roll off as it relates to the to the box size?

I also need to design and build a cross over. Can you point me to an online resource that can help me calculate and design a cross over? Should i buy a MiniDSP and use that to develop the cross over, then build a passive cross over for each speaker based off that?

Did a get ripped off for $99 per pair on these speakers?

Onebean
 
Here's one that I use quite a bit www.mh-audio.nl click on the calculators bar ... all kinds of plug-in calculations for boxes, crossovers, attenuation circuits, contour circuits, etc.
 
I use winISD found here:
http://www.hometheatershack.com/for...wnload-detailed-guide-how-use-winisd-pro.html

I also learned a lot of useful theory from this book:

https://www.parts-express.com/speaker-building-201-book--500-044

It will allow you to play with port size, volume and ported vs sealed to compare response.

One of the things I leared from that book is that as you vary the size and tuning of a box two things happen, the bass extention changes and the overall Q does as well. That has an impact on the transient response of the woofer. The closer to .5 final Q the better the tranient response will be. That is important for the human voice to be clear and understandable. The best speakers for movie dialog will be at or close to an overall Q of 5.0. In fact I recently replaced my woofers in my home system with ones selected to give me an final Q of .5 to improve the sound of the tranients. I then used my equalizer and the software REW to get back the low bass by boosting the low frequencies that I lost doing that.

Good luck with your project.

Shelly_D
 
My favorite speaker design program is Unibox. It's available here: http://audio.claub.net/software/kougaard/ubdwnld.html

You need Excel to use it... which you hopefully already have somewhere. It should also run fine with LibreOffice (which is free, as the name implies).

In Unibox you just enter your drivers parameters, and then you can simply click the buttons that calculate the "optimum" enclosure for sealed, vented, or band-pass. If you want a smaller box, simply enter the size (in liters) that you want and refresh the graph; then you can see where the bass roll-off will be. Tweak a few other parameters until you're happy with the predicted response. Always remember that the room will have a big influence on your final frequency response as well.

Unibox has many other features, including graphs that can show you how much output you can get out of your speaker before reaching xmax (e.g. the driver starting to make funny noises...).

Great program, and doesn't cost anything at all.

Further I recommend all of Jeff Bagby's software. It really works, especially the "Baffle Diffraction and Boundary Simulator":
http://audio.claub.net/software/jbabgy/jbagby.html

Again, Excel-based.
The more you dig into DIY speaker building, the more Excel-based programs you will find... most are free.
 
Thank you for all the links. I've been playing with the MH-audio software a bit, and hope to have some free time this weekend to really dive into it.
 
It really only takes a minute to test this driver with Unibox... so I tried it out.

The "standard design" recommendation is a 126.8 liter vented box. But it looks like a 3 cubic feet box will still give pretty decent results. The graph below shows you the predicted response. You could now just lower the volume (85 liter in the graph, which is approximately 3 cubic feet) and click "start" under "Optimize for Fb for wanted peak", and it would recalculate the response graph etc. Also pay attention to the port length and diameter, sometimes certain diameters would require very long ports etc. or simply don't work.
 

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