[nodiak]

http://www.troelsgravesen.dk/OBS.htm

A nice simple study of a midwoofer on various OB panels. Just sharing it as I found it to be a good ob 101 example of what can be going on in a given situation, it's been on ob threads before. It was innitially meaningful to me in the approach of 3 way systems with ob midrange, as well as using widerange drivers in ob on bass boxes of any type (sealed, vented, tl, ob.).

For a first project it may be helpful/interesting to those that want a more shoot from the hip approach, and don't have the time/equipment to get more involved right away. Sometimes a more raw approach is enough to satisfy the itch, and maybe there just isn't time for anything else. Good to see these comparisons, state of the art or not.

Even more interesting is the link to a review of the 1956 Wharfdale dipole on the bottom of the page. You really gotta check that out...great to hear thoughts in 1956 about how it was a retrograde step to a 20 year old design...Also good to read the understanding of the principles then.

Don





 

[Bob in St. Louis]

Interesting, thanks Don.

"WHAT WAS OLD, IS NEW AGAIN"

Bob

[JohninCR]

It's a real shame because good work went into that study by
someone who knew what they were doing.  All of the comparisons
are invalid because the measurements were taken in the nearfield
at a half a meter.  While I understand that nearfield is necessary to
take the room out of the equation, it also greatly discounts the
effect of the rear wave along with how it acts with changes in baffle
size and shape.  Unfortunately it makes us unable to draw any
conclusions from the data.

Once I learn how to do proper measurements efficiently, I plan to
do something similar but measure from a typical listening distance. 
Yes the room will come into play, but with speaker position and the
room as constants, I believe we'll be able to derive some useful data.
Also, I want to include comparisons that put my viewpoints about
folded baffles, edge diffraction, etc "under the microscope".

[D OB G]

Hi JohninCR,

From my experience, it is essential to perform measurements from the listening position.

I use an "Imp" by Liberty Instruments, and it reveals that minor rotations of a flat baffle affect the frequency response, both in cut off freq and in smoothness of response.

I now make my bass baffle adjustable around a vertical line compared to my FR, mid-range, baffle, and optimise the reponse for each.

Typically they both need to be at 90 degrees to the line to the speaker, but as you say, room effects mean that the bass baffle may need some subtle tuning. 

David