Calculations for determining volume of speaker enclosure. - Page 1
Forum section: electronics / general

author: tpowell1830
author_rank: Frequent Contributor
timestamp: December 14, 2018, 10:54:02 pm
content: Back in the nineties I had found some general rules of thumb and calculations for the volume of a speaker enclosure and port size for various size speakers (woofers). I then wrote a small application in BASIC that enabled me to input the size and throw of a woofer and then the program would automatically calculate the estimated required volume for me. I have since lost those formulas and the BASIC program.Could someobe here give me some basic calculations that I can use for re-writing this. I will write this in C# and share it with everyone if I can get the info. I did a search on Google, and as usual found too many sources. I am looking for the right information from an experienced source, in other words from someone who has successfully built speaker enclosures.Thanks in advance.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 15, 2018, 12:59:38 am
content: I think this is what you're looking for.https://en.wikipedia.org/wiki/Thiele/Small_parametersEd

author: tpowell1830
author_rank: Frequent Contributor
timestamp: December 15, 2018, 01:13:30 am
content: Quote from: edpalmer42 on December 15, 2018, 12:59:38 amThanks for the Wikipedia source, found it myself. But do you verify that it is a good source from your own experience?In all honesty, I trust Wikipedia as much as I trust the guy on the corner on the freeway with a sign.

author: cdev
author_rank: Super Contributor
timestamp: December 15, 2018, 01:43:04 am
content: There is some good info here on speaker construction:https://www.parts-express.com/resources-build-a-speaker

author: floobydust
author_rank: Super Contributor
timestamp: December 15, 2018, 01:50:27 am
content: I did a lot of work with the Thiele-Small parameters in the 90's and learned the hard way that the math always gives you a box too small. It provides a theoretical Vbox, and due to losses you must add some fat.I was doing ported designs, comparing the predicted verses actual low end freq. response in an anechoic chamber.It gets a bit complicated because the port is also theoretical and can be tuned to try correct for a (too small) box.The driver's TS parameters change with temperature, age, batch and humidity, so understand it's a guideline only.Now, you can even do the calcs in an Excel spreadsheet or somewebpages.'The Loudspeaker Design Cookbook' by Vance Dickason is very good if you don't have a lot of time.Highly recommended.

author: edpalmer42
author_rank: Super Contributor
timestamp: December 15, 2018, 03:34:29 am
content: Quote from: tpowell1830 on December 15, 2018, 01:13:30 amNo, I can't confirm that it's a good source. You caught me on that one!However, when I look at the history page, it looks like the article has been edited multiple times since it was first posted back in 2004. I would be surprised if any significant errors remained. An article that's posted and then ignored is quite suspicious. One that's been reviewed and/or edited by multiple people seems much more trustworthy to me.Ed

author: tpowell1830
author_rank: Frequent Contributor
timestamp: December 15, 2018, 04:20:50 am
content: Quote from: floobydust on December 15, 2018, 01:50:27 amThanks.Yes, I built several speakers of my own design back in the '90s, and as I said in my original post, using some formula as well and got pretty good results with some $7 8" speakers that I picked up at a surplus store. I still have those speaker boxes with original speakers and they are still doing very nicely for me. This has proven to me that the secret sauce is in the construction of the boxes. I recently picked up a pair if 10" JBC speakers, complete with built in crossover and I want to build boxes for these. The boxes need to be of the correct volume if I expect them to sound decent.But you are saying that the Thiele-Small parameters are not correct, what formula do you use? As far as time, as I said, I intend on writing a C# application that will allow me to enter the parameters and then calculate the correct volume and save any parameters for that box design, such as height, width, construction notes, etc. I am semi-retired and I will take adequate time to do this right.

author: floobydust
author_rank: Super Contributor
timestamp: December 17, 2018, 07:52:27 pm
content: Modeling and simulation of a loudspeaker system is limited. Modelling moving air molecules, plastic, rubber, magnetics is very difficult.Equations are simplified, assumptions made, terms crossed out etc. to take the math out of academia and make it practical.My understanding is theThiele/Small parametersare not "wrong" per se but in being simplified, the assumptions made around losses in the driver, enclosure and filling material show up as unpredictable results and give a lower system Q than expected.I'm not sure if your project is a vented or sealed box design. Ported systems are much more sensitive to losses.Pro's design the box 20-25% overvolume and then bring it down (add bulk inside) and re-measure and adjust to determine a final size. I'd suggest building more than one size box and experimenting. The model only provides a ballpark value.See here the filling is a big part of the design:https://www.scan-speak.dk/toolbox/