October 23, 2020 at 8:49 am #12045d2uMember
I’ve stumbled on a problem when I was designing a speaker. I use the winisd software for modelling the speaker. Once one has finished modelling, the program gives a box-volume(v) and port size. In my case the box volume was 50 liters and the port had a diameter of 7,6 cm and a length of 16.6 cm.
In my design the port will be inside the box. Correct me if I’m wrong, but that means that the internal volume of the box should be the volume given by winisd + the volume of said port that will be inside of the box, right? If so, should I also take the driver volume into account? If so, is there any easy trick to find out what volume your driver is?
In my case I’m planning on using 18mm mdf as base material. So the internal volume should be equal to 50L + (Pi*8cm^2(ie. outer diameter of port)* (16.6cm-1.8cm) )/1000(in order to go to liters) + driver volume
≈ 50L + 2.98L + driver volume = 52.98L + driver volume.
Lastly, once I had my volume I was planning on getting the box dimensions by taking the third root of the volume converted to cm. Is this a proper way of getting the box dimensions? I’m kinda newbie to this so if there are certain design rules for converting your enclosure volume to dimensions plz share :).
Thanks a lot for the help.
October 23, 2020 at 1:33 pm #12048tvor-ceasarModerator
“50L” is the optimum internal volume that would make the driver(s) perform correctly. And yes, you Should take into account for things like driver displacement (considering mounting type – inside or outside baffle and adjust accordingly), port volume (outside dimensions), and other “large-ish” objects, such as bracing and X-over components. Small stuff, like wires etc. can effectively be ignored since box size is actually somewhat forgiving. My personal number is +-10%.
Once you have that done take the total and get the Cube Root, then use the correct multiplier to get to your unit of choice. That will give you your internal base “Width” (of the face plate), which you can use to get the rest.
(this classically is the most pleasing to the eye)
(this is designed to reduce standing waves inside the box)
Of course, these are just guidelines. You can play with the numbers to get your own unique box, as long as you end up with the correct volume.
October 23, 2020 at 2:11 pm #12050d2uMember
Thanks a lot for your feedback! I’m going to build a few test-boxes very soon. I plan on 3d printing the final enclosure, but I first wanna be absolutely sure I have the right dimensions. Thus, I’m gonna make a few prototypes first. About the standing waves, is it possible to correct them by using a simple dsp? Or would the effect be negligible compared to a box design with your acoustic ratio? Also, would it help if the corners inside the box would be round instead of hard 90 degree angles?
Lastly, does the placement of the driver on the front baffle have any influence on the occurrence of standing waves? Should it be centered or have a small offset to the bottom or is the effect negligible?
Again, thanks a lot for the feedback 😀
October 23, 2020 at 9:17 pm #12052
February 14, 2021 at 5:18 pm #12655tvor-ceasarModerator
Sorry for the delay, a lot has happened since your post, mainly health and work issues, and I completely missed it.
Standing waves are at a frequency that will resonate within a box, usually at a frequency of a box panel. That’s why so many more expensive speakers use heavy panels, bracing, and other schemes to deaden the box. And this is more to take care of low(er) frequency resonance.
One of the things you see often is a brace that couples 4 sides together. Yes, it makes those panels more stiff, but the question is why? It’s a a simple matter of making a large panel seem like 2 smaller panels. The smaller a panel of X thickness, the stiffer and more resistant to low frequency resonance (makes the resonant frequency higher). Thus, if you make the apparent panels different sizes, you spread that reduction across a band of frequencies, each one less apt to react than if they were all the same.
You can achieve similar results on smaller, less bass heavy units by adding stiffening braces across individual panels in an asymmetric way. For example, using a relatively hard wood square stock, 1/2″ or 3/4″, on a side panel, running from 1/3 the distance top to bottom to 1/2 the distance top to bottom, will asymmetrically split that panel into 2, thereby stiffening them each, raising their resonant frequency above the main energy of the low frequency driver.
So, since this is really a pressure related topic, it won’t make much difference where you place the driver on the face. Where that makes a difference is in baffle step. When you have asymmetric placement, it reduces the cancellation effects of baffle step due to differing distances from edge of driver to edge of box.
Hope this helps at such a late date.
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