Open baffle Woofer Characteristics

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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.
 
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.
 
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.
 
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. :)
 
All i wear is white socks.

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
 
What i have found out Bricilo is even with a ruler flat response the room can affect the FR curve.Not only the room but positioning of the speakers as well as many factors.
On the Hf tuning i have found that i usually dampen the trebel when i encounter "hard " rooms, ie. no carpets very little soft furnature ect ect.The opposite is applied when there is a "soft" room.
LF resonse is usually dependant on room size and dimensions.There i just do the best that i can.
Most ppl are NOT audio types and there is a limit on what i suggest as far as room treatment.
In my experience most ppl out there have never heard a higher end sound system (what ever definition higher end means) so when they do hear one they either go one of two ways.Either they fall in love with it or hate it.I actually had one younger person claim he didnt like it because he could hear the words and actually wanted the bass and trebel to drown out the mids.
ron
 
To All; my apologies for "posting and running" but some of my grandchildren needed babysitting and I am the first call on the list.

I have no experience with active EQ, but understand the risk of overdriving a unit. My reason for using an OB configuration is that I have a small room yet would like the accuracy of a 12" woofer without the accompanying 100db plus wack, so baffle step is not much of an issue, it is accuracy that I am seeking.

I have found a new 12" driver from Eminence's Deltalite series wich looks promising, the 2512. It has a .4 QTS, efficiency in the 90+ range and looks like it would move a substantial amount of air, (Vd=154cc). X-max is small but the Neo-d magnet is not large and I would be driving it with a triode rigged dynaclone that only delivers about 8 Watts.

Will continue the process and let you know the outcome.
Thanks again for the info.
 
Have you checked out the linkwitz site????

www.linkwitzlab.com

He goes over in great detail what parameters are important for open baffle woofers. There are also a few excel spreadsheets so that you can calculate max spl vs freq. and such.

For that matter I am currently running to peerless 831727 10" drivers in an upright H baffle. I think if i remember correctly I should be able to get to 35-40hz at 106db output before I rolloff toward the low end. Some point soon I should get some pictures posted of what I got.

best of luck
-dave
 
Peter,

Are you using a tweeter (or tweeter line) to help the Tang Band W3-871S drivers in the treble area? My experience with my Needles array (16 W3-871S drivers and a Aurum Cantus G3 ribbon per side) is that the comb line gremlins will start to bite you above 3000-4000 KHz. A crossover is necessary if you expect high quality results.

You might want to read what Linkwitz has to say about driver diameter for use in dipole speakers. He uses 8 inch Seas Excel drivers in his Orion design.

Jim
An externally hosted image should be here but it was not working when we last tested it.
Near Field Line Array White Paper
 
Jim; Thanks so much for your comments. I had not planned on using a tweeter with the 871's. My initial thoughts were for 8 units per side, 4 in boxes and 4 OB, and had not considered the comb effect. I am now coping and will read your white paper as well as examine Linkwitz' comments on the size of OB drivers.

The arrays that you have created are quite beautiful, what drivers are you using in the larger units?

Pete
 
Peter,

The larger array in that photo is the Linus 2 which uses 10 Vifa TC14 drivers and 8 Silver Flute YAG20-1 (same as Parts Express Pt2) planar tweeters per side. The Linus 2 is available in a kit from:

www.selahaudio.com

The Needles design with the TB 871's and A-R G3 is available as a kit from:

www.creativesound.com

You really, really need to use a tweeter or a tweeter line to realize optimum performance as you will have comb lining and loss of sensitivity if you run a line of the TB W3-871S beyond 3000-4000 Hz as I said before.

Jim
 
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