Open baffle Woofer Characteristics

[Peter Menting]

Am building a line array using TB871's down to 200 Hz but would like to use an open baffle for the low end. My question is this; what characteristics should I look for in a woofer to use in an open baffle application? Your comments would be appreciated.
Pete

[ronc]

High Qts, .7 or greater, i have found larger drivers to work better than smaller on OB apps.
ron

[RHosch]

High Qts isn't necessary if you use active equalization. Due to the dipole rolloff, you should be looking for raw displacement for sure... the more the better. Also, since the backside is exposed, you want a clean and fairly open basket and vent geometry to prevent audible chuffing from the rear.

[ronc]

Never use EQ unless its totally necessary.I would perfer to do it mechanically.
ron

[RHosch]

A speaker is an electro-mechanical device. As such, why is electronic equalization any different than mechanical equalization? Both should have the same resultant amplitude and phase properties, but the electronic route gives you much greater flexibility and control.

[Nappylady]

Electronic also pushes the heat boundary of the voice coil faster than mechanical EQ.

There is a limit to what you can do with mechanical EQ though.

The simplest method to EQ a dipole speaker is to get one with a specific Fs and high Qts, and make the baffle such that the dipole rolloff happens the right distance away from Fs that it's maximally flat--I believe Mr. Linkwitz refers to this as a "crude EQ".

Active EQ is more expensive, introduces another set of opamps into the signal chain, more noise, more power supplies, cables, distractions... and it's orders of magnitude more flexible. No matter what, response about an octave below Fs is about the best you can do.

[ronc]

IMHO the less in the signal path the better.
ron

[RHosch]

And I can certainly respect that opinion. I think this is similar to the 1st order vs. higher order crossover question. There are tradeoffs to be made each way. All other things being equal, I'd love a single full bandwidth driver with no crossover and perfect characteristics for a dipole application. But... all other things aren't equal.

It's a choice that has to be made. IMHO, the signal has been through countless op-amps, discrete components, questionable potentiometers, and who knows how many A/D-D/A stages (the latter two items occuring mostly in the recording studio), so a few more op-amps isn't going to kill any magic. Not to mention that when drivers are spewing out distortions in the few percent range at best (much worse most often), I can live with a few hundredths of a percent of electronic noise introduced.

But you're absolutely right... if I could avoid it, I probably would. The loss of flexibility isn't worth it for me, but it certainly might be for you and many others. I guess that's why there are as many variations of speaker designs as there are colors of socks.

[ronc]

Hay i am a hillbilly texan.
Currently all i build is single driver horns ,fostex Fe-103e and the Fe-166e, but i am getting in some Fe-168 sigmas for a test run to see what kind of app i can go with.
Amps are Gainclones LM3875T in the inverted confg.with a pre based on the TDA1254a chip.Yea everyone is gonna say that its more in the signal path and has EQ (kinda ,sorta) but as i build these for re-sale i have found out that all rooms are not created equal.When i install this combo , amp/horn, i run my signal generator into the amp with the horns placed in the desired position and tune the LF & HF to the room conditions.As the pots are internal and not accessable to the buyer(or at least i tell them not to dink with the controls) i can get a fairly flat response.
I really like OBs but have found the response from rear loaded front firing horns(especially with single drivers) to be better.
ron

[ronc]

Pre is based o the TDA1524a chip,geee guess i should preview before posting.
ron