[SteveRB]

Hello,

I've been following this page for some time now. I have just finished my first open baffle project. It is the MJK design with one modification: i substituted the Fostex FE108E.

[SteveRB]

I'm very pleased with the results already. the set-up is just for testing -- seeing as how this is my first OB project. I have a few questions regarding tweaking the design that i hope some people here may be able to help with...


1. what is the relationship between the baffle area and bass response (ie, generaly accepted theory)?


2. could changing the shape of the baffle from rectangular to something more rounded or wider at bottom contour the frequency response?


3. The Fostex driver is a little loud compared to the Emenance. Are there solutions for reducing the output of the full range driver?


Any help out there would be much appreciated. I've got a good (visual) design background; so, once i settle on a sound i plan on going to town with the way they look.

[smbrown]

In adjusting levels a simple L-pad on the Fostex might be the most effective. Once you've got it dialed in you can replace it with fixed R's of appropriate value.

[Rudolf]

1. what is the relationship between the baffle area and bass response (ie, generaly accepted theory)?

http://www.musicanddesign.com/Equivalent_Baffles.html

2. could changing the shape of the baffle from rectangular to something more rounded or wider at bottom contour the frequency response?

Wider at bottom will enforce the low frequency response if the bass driver is near the bottom too.
EDGE can help you to estimate the results of different baffle shapes.

[Anglo]

...just one thing.

You do want to advance these puppies from the wall.  To me, they are way too close from an unabsorbed wall.  Major cancellation going on.

Nice project!

[SteveRB]

Anglo,   Thanks. i've been playing with placement last night. they are about 12" further out from the wall and further apart from each other. Do you have any simple suggestions for wall treatments behind the speakers?

Rudolf,  This is exactly the type of info i was looking for... i appreciate the link. I will be able to go through the info in detail this weekend. As for the Edge -- i hope it                 works on my Mac

I've also got a PM regarding inserting a resistor 0.5 - 2.0 on the fostex. I'll be working that out this weekend too.  I will also be following up on the MJK article regarding U-frames. Maybe i can get the bass extension to 30...

[Anglo]

Hi

If you can't get them further away from that wall than some absorption is a must IMO.  A sheet of Owens Corning 703 flips the trick, but IMO it does `muffle`up the mid range that is oh so beautifully open in an open baffle.  You do however get a little more harmonics in the lower mid section as you will notice when approaching it closer to the wall.  The problem though is cancellation.

Anyways, enjoy the world of OB!

[scorpion]

astronout_glen

Please let us know when you have experimented with the MJK U-baffles !
Otherwise your baffle should be quite OK for the rest.

/Erling

[SteveRB]

Of course i'll post my progress. My Dad is in town this week for a last minute business trip. so my ability to play around with the speakers will be limited.

[SteveRB]

I have done a little adjusting to the construction of my new MJK OB. After reading his paper on U and H frames i have decided to add a simple U on the back. I can say the adjustment focuses the sound and brings an amount of rumble to the room that was not present before. I will still be adding a resistor to the fostex; however, i am very happy with the level of bass.

The U is 7.5" deep and maintains an area of 18"x18" surrounding the driver.

I do not have the capabilities to measure the response of the speakers. By my ears and in my room they sound pretty good.

I will add a quick set of drawings for this crowd to comment. Please let me know your thoughts. I appreciate the experience and education of the users in this circle.

[iON]

Hi Steven! As an dipole devotee it's always nice to see other people discovering the wonderful world of OB.

Regarding the wall behind the speaker I think that it can be beneficial to put an diffuser there. With som artistic touch it can even look good!

Keep up the good work!

[scorpion]

Nice drawings, Steven !

And your experience is in line with MJK's predictions.

Perhaps we should give the reference to the new MJK article which compares passive flat baffle, U-baffle and H-baffle performance with som really interesting results: http://www.quarter-wave.com/OBs/OB_Theory.html . The U- and H-baffles are kept short and small to prevent resonances.

Basically you will with Eminence Alpha 15 gain low frequency and flat bass response but loose efficiency with the kind of short U-baffle you have
extended the baffle with. In the low end you will have a response almost ruler flat down to 30 Hz and the overall loss will be 4-5 dB compared to the flat baffle.
For a balanced output you certainly will have to take down the Fostex.

/Erling

[DanH]

I finished my M J King open baffle speakers this past weekend. I am getting plenty of bass in my setup. I did add wings to the design but my main concern was looks. I did not think my wife would go for a speaker with the guts hanging out in full view in the living room. Everything I have tried on them sounds good except female voices. They sound kind of peaky and irritating so far. I am thinking this may be a break in issue with the fe103e. I did some research and it seems some people have used notch filters on the fe103 centered around 7k. Has anyone else had this issue with the fe103?