How to get started in designing OB speakers

acwd1950 · « **on:** 7 Jul 2008, 01:38 pm »

I am really interested in building a pair of OB speakers. But I have many questions and being very new to this design I came here to start with. After reading many topics on this website, I do believe they will get answered. So here it goes.
Question 1 How do you find the size of the baffle? Trial and error? or is there a magical figure?
Question 2 What driver parameters determine what driver would work in a OB?
Question 3 Is there a computer program to aid in designing OBs and where do I obtain it?
Question 4 Is a fullrange speaker better in a OB than a multi driver configuration?

As stated I am very new to this design. I have built, rebuilt, and refoamed speakers before so some of this isnt greek to me.
Thanks in advance.

Steve

MJK · « **Reply #1 on:** 7 Jul 2008, 03:55 pm »

Steve,

These are my thoughts on OB design. There are other methods but these have worked for me. I believe that this approach works well for both passive and active crossover options.

Question 1 How do you find the size of the baffle? Trial and error? or is there a magical figure?

I find the size and shape using computer modeling. But since this is such a quick and easy build, the cut and try method will also work if you don't mind using up some wood or cardboard.

Question 2 What driver parameters determine what driver would work in a OB?

I believe you need to think in terms of a two way design as a minimum. I like larger pro woofers with an fs of about 40 and a Qts of greater than 1.0. This will allow a floor standing OB design that is about 20" in width by 32 to 48 inches tall. If your Qts drops below 1.0, the bass will be rolled off. You will not get below 40 Hz with a flat reasonably sized OB without some EQ even if your driver has an fs of 30 Hz. To go lower passively requires an H or U frame dipole.

Question 3 Is there a computer program to aid in designing OBs and where do I obtain it?

I use my MathCad worksheets. I am not aware of any other software that includes all of the features that are in the worksheets.

Some people use the EDGE or XBaffle programs but they only give you part of the solution. As long as you recognize this and adjust the design to account for the missing elements these will probably work well.

Question 4 Is a fullrange speaker better in a OB than a multi driver configuration?

I believe that as long as the bass below 200 Hz is handled by a separate woofer that a full range driver or multiple drivers can work well. By crossing over in the 200 to 300 Hz range you can use the hump in the baffle response to your advantage. If you crossover higher then the SPL response will have a 3 to 4 dB hump in this frequency range .I personally like full range drivers crossed over to a driver like the Eminence Alpha 15A, that is my current recipe.

I am sure people can argue some of my basic comments, but that is what works and makes sense for me. You can't beat basic physics. There are two articles on OB design on my site and more on the way.

Hope that helps,

Martin

hum4god · « **Reply #2 on:** 7 Jul 2008, 06:08 pm »

here is some interesting read about the baffle buildng process that i found interesting:

http://www.hawthorneaudio.com/forums/viewtopic.php?f=2&t=1195

acwd1950 · « **Reply #3 on:** 10 Jul 2008, 01:58 am »

Ok heres a update on my first try on building OB speakers. I bought a cheap pair full range of six and half inch speakers. That was the biggest that I could find locally and if they didnt work out I could use them in a car. Anyways, mounted them on a piece of double wall piece of cardboard 19 1/2 by 44 inches, driver 32 inches off the floor and centered vertically. All I can say is WOW! For no more than they are they sound great. The detail is unbelievable. They do lack some on the upper end. The bass isnt too bad for a small driver but it does need some help and that will be the next project along with some better drivers and plywood baffles. I was very skeptical of this design but that has all changed. Thank you Mr King and hum4god for the information. Im sure I will have more questions later on.

Steve

DanH · « **Reply #4 on:** 10 Jul 2008, 07:32 am »

Read Martin J King's articles on the subject.

http://www.quarter-wave.com/OBs/OB_Theory.html

I built a pair of speakers based on his design and I really enjoy them.

http://www.quarter-wave.com/Gallery/Dan_OB_1.jpg

panomaniac · « **Reply #5 on:** 11 Jul 2008, 06:05 pm »

Quote from: DanH on 10 Jul 2008, 07:32 am

I built a pair of speakers based on his design and I really enjoy them.

Those look really nice, Dan. Don't know why , but they look like they came out of an old church. Cool!

bboru · « **Reply #6 on:** 10 Mar 2009, 07:55 pm »

Bit late in the day but the following link will take you to a dedicated page which has a lot of links using both vintage and modern speakers in ob designs. A very good site....see the lowest lines.

http://www.lampizator.eu/SPEAKERS/Loudspeakers.html

gainphile2 · « **Reply #7 on:** 12 Mar 2009, 10:55 pm »

Question 1 How do you find the size of the baffle? Trial and error? or is there a magical figure?

Baffle width should be less than 2 * driver dimension (midrange).

Question 2 What driver parameters determine what driver would work in a OB?

Tweeters: able to be crossed low around 1.5kHz (low Fs)
Midrange: nothing specific
Woofer: Some advocates high Qt, some other like SL likes Low Qt and then equalised

Question 3 Is there a computer program to aid in designing OBs and where do I obtain it?

The ABC dipole by MusicAndDesign (john K) is excellent. It actually guide you step by step from selecting drivers to building the baffle, measurement, and what to measure. At $15 it is really underpriced!
http://www.musicanddesign.com/A_B_C_Dipole.html

Question 4 Is a fullrange speaker better in a OB than a multi driver configuration?

Multi-driver and multi-amp is actually the path of least resistance.

Also, Linkwitzlab site is a goldmine to read.