# How do you do the math for a open baffle speaker?

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#### Jeffrey 01

Happy holidays everyone. I'm almost done with my little ported A.N. super 3s speakers. Update the boxes have to be redone because I used the wrong saw blade on my wood). Ugh what a pain now back to square 1). So now I'm looking at building a near field desktop open baffle speaker. I didn't see any programs to use for the front baffle formula? I thought I read somewhere that a higher qts is better for a open baffle speaker? So I do have a few programs that do my boxes and crossovers and I do measure all my drivers before I even start on my builds. So is there a book or something that will tell me how tall and wide my front baffle needs to be for my driver's? So they don't sound to thin or to bloated? I hope I posted this in the right forum? Cheers Jeff

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#### Galu

I thought I read somewhere that a higher qts is better for a open baffle speaker?
Hi Jeff!

Do you intend to use electronic bass equalisation?

An open baffle speaker using a passive crossover should have a high Qts (I've seen > 0.77 quoted, 1.0 being the target). A low fs is not required as there is no box to raise the cone resonance frequency.

A small circular baffle of diameter 0.57m would have a cut-off frequency of 200Hz.

A rectangular baffle will stagger the half-wavelength cancellation by introducing three dimensions - corner to corner, height and width - and, as a result of the different dimensions, complete cancellation will not occur until a much lower frequency.

A height of 0.57 m would be a good start for experimentation purposes and remember that, when placed on a desktop and near a side wall, extra bass gain is provided.

#### Galu

You just beat me to posting that SJ!

Scroll down to B - Open-baffle loudspeakers

#### perceval

If your desk placed near a wall, OB might not be perfect.

They need space to breathe and near wall reflections are frequency killers.

#### Galu

You asked for the math, Jeff.

Bass cancellation occurs when the distance from the front of the driver to the rear of the driver is one wavelength. In that case, the baffle radius would be half a wavelength.

Using the wave equation f = v/λ we can calculate the roll-off frequency for any baffle radius. Since λ = 2r we get the final equation f = v/2r.

e.g. For a baffle of radius 1.0m and taking the velocity of sound as 340m/s we get a roll-off frequency of 340/2.0 = 170Hz.

However, the roll-off is very gentle and the bass will only be 6dB down at 85Hz.

Of course, we would avoid the use of a circular baffle to gain extra bass extension and mounting the driver off-centre helps smooth the response.

At the end of the day it is experimentation and not maths that will win the day!

1 user

#### hitsware

for Fc ~ Fs ( important with O.B. since gain below Fc is wasted movement )

Fc = 360 / ( B.W. * Qts )

#### Galu

Fc = 360 / ( B.W. * Qts )
Thanks hitsware!

I'd be interested to see the derivation of this equation - any reference source I could go to?

I presume B.W. means baffle width?

#### Jeffrey 01

Wow my friends. Thanks for the repys. Sorry for a late reply? I got a new phone and when I get a e mail it no longer lets me know? Yes I asked for the math lol. I will write the formulas down and start working on my speakers. Thanks for info about the speakers being to close to the walls on my desk top. Also I agree that the best experience in life is trial and error. Learning what sounds good or not to you. Funny I was friends with a sales guy at a local HiFi shop. He told me a few things. First off he said there is nothing like going to a live concert. He said your ears are the best speakers you have. He also told me it's all hype with speakers and drivers and wires. He had Lowther pm6's in the headlen horn. Never heard them just saw pictures. Last but not least. Before he retired he brought them into the HiFi shop where he worked to see what people thought? So (now a long gone company ) and from California called Moth Audio and their full range speakers. Sorry if I got side tracked but without being friends with him I would have never gotten into building my own speakers and diy. Well again happy holidays and I will start working on the O.B. project. God's blessings. Jeff

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#### Jeffrey 01

Thanks again my friends. You have all been very helpful to me. I will look into this later this weekend after Christmas and working. Thanks again. Jeff

#### woody

Here is a program Martin King talks highly and may have used it in designing his open baffles. By the way Martin King's articles answer a lot of questions and his designs are highly regarded, cheap and easy to build.

Tolvan Data

#### Jeffrey 01

Here is a program Martin King talks highly and may have used it in designing his open baffles. By the way Martin King's articles answer a lot of questions and his designs are highly regarded, cheap and easy to build.

Tolvan Data

Thank you for the link Woody. I just found this website a week ago. Thanks for the link and the info. Cheers. Jeff

#### Jeffrey 01

Hi Jeff!

Do you intend to use electronic bass equalisation?

An open baffle speaker using a passive crossover should have a high Qts (I've seen > 0.77 quoted, 1.0 being the target). A low fs is not required as there is no box to raise the cone resonance frequency.

A small circular baffle of diameter 0.57m would have a cut-off frequency of 200Hz.

A rectangular baffle will stagger the half-wavelength cancellation by introducing three dimensions - corner to corner, height and width - and, as a result of the different dimensions, complete cancellation will not occur until a much lower frequency.

A height of 0.57 m would be a good start for experimentation purposes and remember that, when placed on a desktop and near a side wall, extra bass gain is provided.

Sorry for the late reply. I am using no active filter due to me just playing back round music and it is going to be a casual speaker not a sit down and listen to them for hours. I do plan on making a Open Baffle tower later this year but, I need to finish my A.N. project and then start on my Little Desk top open baffle project. Then I will start looking into this deeper and what I need to get for the right sound. By the way I really Enjoyed the Hawthorne open baffles years back at the Audio Karma hifi show. I think they were all passive crossovers if I can recall it right. Cheers Jeff

#### Galu

Thanks Jeff!

I hope you will report back on your findings when you eventually find the time to start on your desktop open baffle project.

I hope the information supplied gives you wings - possibly side wings to both support the baffle and extend its width!

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• OB with wings.jpg
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#### Jeffrey 01

Thanks Jeff!

I hope you will report back on your findings when you eventually find the time to start on your desktop open baffle project.

I hope the information supplied gives you wings - possibly side wings to both support the baffle and extend its width!

Thanks Galu for the picture I really like it. Looks like you have done your own open baffle build. . I will keep you in the loop. It might be a little while I am thinking of around the First of March I will start really getting into the build. I need to read up some more and work on a few other things before I start this project. Also your welcome to p.m. me if you need to. Happy blessed new year. Cheers. Jeff

#### Jeffrey 01

Happy New year everyone. So here's the up date. I bought Dayton audios 3 1/2 full range drivers and will be working on my first Open Baffle speakers as soon as my other project is done. Cheer's Jeff

#### Galu

Happy speaker building in 2020 Jeff!

Out of interest, which Dayton Audio 3-1/2" version did you buy?

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