Confused about the math

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Ponwan

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Joined 2018
#1
Hello,

Sorry if I'm in the wrong area but this was the closest I could find...

I'm in the process of writing a software designed for calculating and constructing molds for spherical speakers (taking account for speaker displacement, the caps that get lost when mounting a flat surface to sphere, the thickness of the material and so on..) but I have a problem I can't wrap my head round, when implementing support for volume calculations I have encountered more than one formula both for vented and sealed systems, using my reference parameters (for EAD E100HD MKII and Dayton RS100-4) mainly two formulas (for sealed boxes, that seems to be accepted through out the community) give me volumes and frequency tuning-values that doesn't match up to the manufacturerers recommended values. The same problem arose when trying to do the math for vented boxes. In my trial builds (only tried closed box designs so far) all of the tested formulas have sounded good with the main difference being the depth of the base and how well they play with more load. I guess I'll have the same behaviour with vented boxes, also all frequency curve calculators I've found and tested are far of from the real deal and that makes me even more confused.

When trying to calculate a Transmission line or a quarter wave horn I end up basically spot on the manufacturers recommended designs for the EAD-speaker so I guess it isn't my math trolling me but rather different design ideas.

Is there any widely accepted formulas to use (primarily for vented boxes)?

I'd love your input here, in worse case I have to use the formulas I've got but anything that points to several different formulas and the characteristics I could expect would be very helpful.
 
#3
Ponwan said:
I have encountered more than one formula both for vented and sealed systems

....give me volumes and frequency tuning-values that doesn't match up to the manufacturerers recommended values.

...also all frequency curve calculators I've found and tested are far of from the real deal and that makes me even more confused.
Click to expand...

This is a variant of the old "I don't understand what I am doing , but everything people are telling me is wrong" question....

What are the multiple formulas you have encountered? Have you considered that maybe they are all right?

Give an example of your inputs, outputs, and the Mfg recommended values. Have you considered that Mfg recommended values may differ from mfg to mfg for the same parameters?

Show us how you know the frequency calculators are incorrect.

Post your code (no I don't want it for myself) and I may be able to tell you where you messed up if I think it is time well spent.
 
#5
Ron E said:
This is a variant of the old "I don't understand what I am doing , but everything people are telling me is wrong" question....
Click to expand...

I'm not saying I know exactly to the detail what I am doing but I am no beginner either tough this is my first real project doing everything by myself from scratch. For me it is an interesting learning experience and by the end of the day i'll hopefully have my own snow-man built out of concrete...

Ron E said:
What are the multiple formulas you have encountered? Have you considered that maybe they are all right?
Click to expand...

Yes and that is why I made testbuilds, as stated I dont understand the mechanics in what makes one formula work and exactly how it works.


So the code:
Code: 
    class CalculateClosedSpeakervolume
    {
// vas = 1.45
// qts = 0.53
// qtc = 0.707
// fs = 84.8

// Returns 1.85 litres
        public double CalculateVb(double vas, double qts)
        {
            return vas / ((1d / (Math.Pow(qts, 2.0) * 2d)) - 1d);
        }
// Returns 1.86 litres
        public double CalculateVb(double vas, double qts, double qtc, double fs)
        {
            return vas / ((Math.Pow(qtc * fs / qts / fs, 2d)) - 1d);
        }
// Returns 0.81 litres
        public double CalculateVb(double vas, double qts, double qtc)
        {
            double qr = qtc / qts;
            double vr = Math.Pow(qr, 2.0);
            return vas / vr;
        }
// Returns 3.5 litres (this is for a vented box)
        public double Vented_CalculateVb(double vas, double qts)
        {
            return 15 * Math.Pow(qts, 2.87d) * vas;
        }
    }

Using the specs from the Dayton-driver I get the volumes in the comments, what raises my eyes are the difference between the calculations of the closed boxes (well obviously not the two first calculations) and how much more volume the vented box want. I also noted how much results differed from their recommended volumes. They recommend a vented box of 0,1ft3 (2.8 l) and a closed box of 0,03ft3 (0,85 liter) for me that is a big difference especially the vented box.
 
Last edited:
#7
Closed box simple calculations are:
Fc/Fs = Qtc/Qts = sqrt(Vas/Vb+1)

rearranging, you get Vb = Vas/((Qtc/Qts)^2-1)

The reason you get a different box volume is that PE uses a different Qts for their sealed boxes - usually around 0.8 instead of 0.707.

Typical simple vented box volume formulas are as found here:
Vented Boxes - DIY Loudspeaker Design

PE's suggested box volumes for vented boxes are never what I would choose. I have done a little investigation on it and it appears to be a way to sell more drivers by saying they go in small boxes...

In reality you can use whatever Vb and Fb you want, although some choices are better than others 😉
 
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