[djn]

Sorry for the ig-nance, but I am new to OB.  I am working on a project and the responce curve is fairly flat if I go with a 24" wide baffle board.  I first intended on using an 10" board with the EQ found in the EDGE program, but then I started thinking that if I could go with 24" in three peices (that is a front and two side) that add up to 24" it might still work.  Any thoughts?

[ebag4]

This has been my experience. 

While you can add wings or sides and still have OB, if you add sides they need to be more narrow the closer they are to the mid and tweets (or full range), deep sides located close to the mid/tweet/full driver kills much of the OB magic.  Temporary baffles and some experimentation with sides will flush this out rather quickly.

For OB bass it can make a lot of sense to use sides, going with "H" or "W" alignments work well too, just be carefull that the sides are not too deep or you can end up with resonance issues.

Best,
Ed

[mcgsxr]

The short answer is absolutely - an open backed box is still considered OB.

The advice above is excellent - and you need to be aware that the use of "wings" changes the polar response - as you add wings, you change from a figure 8 (equal on both sides of the baffle) to a cardiod.

Many will use wings on both sides of the baffle - ie an extension to the front and rear - it typically is easiest to explore with clamps, and then build to suit what you like at the end.

I continue to use wings on my main OB's, and will in the future too when I rebuild them - but, I will take care not to use wings with the wide band driver, just around the bass as noted in the previous post.

[Rudolf]

... but then I started thinking that if I could go with 24" in three peices (that is a front and two side) that add up to 24" it might still work.  Any thoughts?

In a way depth counts double compared to width. If you make the baffle 12" wide and add 6" deep wings that would be equivalent to 24" - by and large.
Keeping the wings no deeper than half the baffle width would be my advice to avoid cavity effects becoming troublesome.

I don't know if your project is for a wide range driver only or for two (or more) drivers. In the latter case you should indeed vary the depth of the wings according to the adjacent driver.

Rudolf

[djn]

Thanks All.  I am using 8(per side)  4" NSB (no stinking badges) Parts Express closeout drivers that have been sitting under my bed for 5 years.

In between the 8 drivers (4 on top and 4 under) there will be a 6"x6" JBL waveguide with the Selenium D210t compression driver.  The drivers naturally die off at 100hz and that is what I shot for in the EDGE program.  I have three subs that will take over from there.  From 1800hz on up it will go to the waveguide.

I really wanted to keep this narrow to begin with but don't want to loose the eff. by using the comp filter.


So, my next question is:  Can I just use one side?  So looking down at the speakers they will look like "L"s  ?

[mcgsxr]

Yes, you can use just one wing.

[D OB G]

I once (decades ago) made an "L" OB that worked really well.

There were 6 X 8" FR drivers.

Each leg of the L was about 1 meter high by about 700 or 800 mm.

3 drivers were placed in a vertical row on each leg, right next to the join.

Top and bottom on one side made a circuit with the middle driver on the other wing.
For the bass they were in parallel, giving nominally 2-3 ohms.
They were then in series with an air cored inductor, about 10 mH IIRC, 2 ohms, giving a more reasonable minimum impedance.

The mids were in series, with an L pad, to match the sensitivity of the woofers.

Below the baffle cut off, the woofers were counteracted by the low pass of the inductor.
Above the baffle cut off the woofers were low passed at the inductor 6 dB per octave slope.
Above the baffle cut-off, ther mids were essentially flat, and then rolled off below at high pass 6 dB per octave.

This gave an essentially flat response, first order crossover (truly a first order acoustic), with what must have been some ripple (didn't have test gear then).
(probably could have been improved with the "L" being slightly shorter on the mid side).

The design relied on the woofers and inductor interacting before the impedance rise that occurs with lowering frequency.
Howerever this still seemed to give something around 40-50 Hz (did reggae OK).

A long-winded attempt to describe what is essentially a pretty straight-forward design. 

David

[djn]

Thanks MC and D. I'll give it a try with the flat board first to see if I need the EQ.  If works out well with just the flat board, I will then cut it down the middle and fold the "wing" back.  I just talked to a friend last night and picked up two piano hinges 48" long so I can use those to adjust the angle of the wing.

Also, can someone check my work.  Here is a screen shot of the Edge program with "I think" the right data in the right place.  This is without the EQ circuit.  To me, the dip and bump at around 800 to 1000hz is only 2db so should not be an issue.  The wave guide will cross at 1600hz or so and I am concerned that the mids (as shown) die off to early.  My subs go up to 150hz and the shot shows it down 3db or so at 150hz.  Will that be an issue?  What do you think?

[SteveRB]

what are the benefits of an asymmetrical baffle -- the L-wing?

[djn]

For me, it is just a matter of space.  There is a very good chance that we will be moving for work and will most likely get an apt or condo for a couple years.  I didn't want that wide of a baffle and, if at all posible, I wanted to avoid the EQ circuit as it just adds more junk in the signal path.

I am using SS piano hinges to mount the wing so they will also be adjustable and fold up for transport.  I have been running very large tri amped horn systems for years but I should be able to adjust to this different sound (not better or worse, just differnt)

[SteveRB]

...to adjust to this different sound (not better or worse, just differnt)

i get the experimentation and size concerns. but, it's my understanding that the size of the baffle dictates the point at which front and rear frequencies cancel. Since the speaker output is basically horizontally symmetrical, the frequencies on the short side of the L-wing will still cancel fairly quickly.

It would be interesting to run a simulation with the same drives centred and with them off-set.

The L-wing might also help sound in an awkward room -- might also create a load of difficulties.

good luck / have fun.

[djn]

I did a sim on them in the EDGE program.  This is my first time futzing with OB and LAs, so it is all an experiment.

[Rudolf]

May be you would want to know the off-axis performance of your baffles. It will be quite different to both sides. My chart should be helpful:

[djn]

Thanks Rudolf, however, I am not sure how to use this.  I only sit in one listening position so I really never think about off axis responce.....unless I am missing something.

[Rudolf]

I only sit in one listening position so I really never think about off axis responce.... unless I am missing something.

It's possibly in anticipation of your next loudspeaker project. There is so much more to worry about than on-axis response only
This is just for starters:
http://www.harman.com/EN-US/OurCompany/Technologyleadership/Documents/Scientific%20Publications/13686.pdf