[10Y]

I have read the whole thread with great interest.
Knowing nothing of the drivers, but something about ob.
In my experience the woofer helper is near impossible to get right just as much as a tweeter is.

The greatest all round ob I have heard is using single driver in Briggs formula as per JE labs.
I prefer the seamless portrayal in the key areas of human hearing, to a system sloth extension beyond the critical key tonal frequencies, which always destroys the tonal perfection.

Most  are implemented to satisfy the critics who want to measure 20 hz to 20 khz

Better to build speakers for tone in the midrange and allow the extremes to roll off.the seamless integration is worth far more than the laboratory perfection.unless you are a robot.

[panomaniac]

Your experience is limited, then. 

[Tyson]

As a counter opinion - single driver speakers have never sounded good to me, whether OB or not.  I think it's phase, time, and the physical off set of the drivers (particularly the mids/highs), that bother the single driver fans.  IMO a lot of that can be avoided with good design and good driver choices.  For example, I run a pair of coax drivers, with the mids running 80hz to 2000hz.  The physical co-location of the drivers helps enormously with the overall coherency of the sound. 

Another valid approach would be to use a very wideband midrange like a tall ribbon, which can run from 200 or 300hz up to 5khz or so.  Then the physical off-set of the tweeter doesn't matter very much. 

The worst option is to combine physically separate mids and tweeters, and also choose a crossover point between 1 and 3khz, that's very audible (to me at least), and I think it's this particular combo that the single driver fans find odious as well.  But, just because "most" speakers use this combo doesn't mean that they all have to.

[panomaniac]

Yes indeed.  I feel that single drivers have a lot going for them, but ultimately leave me unsatisfied.  I've owned a few.
Getting drivers to blend well is difficult, but not impossible, it does take skill and practice.

To me, saying something like "In my experience the woofer helper is near impossible to get right just as much as a tweeter is" would be akin to going on a piano forum and saying "Don't bother playing any Liszt Transcendental Études, I've tried them and they never sound good." "Stick to fur Elise instead."  OK, a valid view of your experience and skill level, but not everyone's.

If you get my meaning.   

[Rudolf]

"Don't bother playing any Liszt Transcendental Études, I've tried them and they never sound good." "Stick to fur Elise instead."  OK, a valid view of your experience and skill level, but not everyone's.

Very nice example indeed.
With every next step in experience I take, I'm more inclined to say "I haven't managed yet ..." instead of "... it can't be done".

[JBspeakerman]

Yes, it is possible.  IMHO, seamless sub woofer integration is relatively easy with the large Altec duplexes because the 15" bass section has a lot of displacement, low FS and high enough Q once you include crossover RG.  I am assuming either a passive or active sub woofer low pass and passive low and high pass on the duplex.

BTW, in an OB situation it is more appropriate to think of the duplex woofer section as a mid woofer/mid range.

When operating on the narrowest practical baffle, (approximately 17") any of the 604 or 605 mid woofers will play more or less flat down to 100 -150 Hz depending on actual Q.    With a 18" -20" baffle width and shallow 3-4" rear wings you are more or less flat into the mid - upper 80's. 

What this does for you is allow you more flexibility at shaping the sub woofer and mid woofer responses, which leads to better, seamless integration.  The big 15" mid woofer really helps you with its better than 5 MM peak X-max and 130 Sq. In. surface area.  There is enough there to play well over 100 db down below 80 Hz with out coming close to X-max in an OB application.

With my 2008 LSAF demo OB I used a standard 100 watt plate amp driving an Eminence 18" PA woofer.  The 18" was mounted on a 20" wide baffle with 12" effective depth rear wings.  This configuration yields an F= of about 80 Hz with the baffle face about 40" from the rear wall.  BTW, this woofer has a VERY low Q of .22 and Xmax of 6 mm.

By using the plate amps existing 2nd order set somewhere in the mid 30's and by adding a large inductor to realize a 3rd order roll off it now is simple to match with the Altec mid woofers OB created 1st order roll off.  With the 18 sub and the Altec 15 having very similar acoustic centers it all falls into place.  You can NOT tell where one or the other woofer starts or leaves off.

You can read more about the sonic results and impressions as well as the look of this set up here:

http://www.dagogo.com/View-Article.asp?hArticle=534

and here:

http://positive-feedback.com/Issue37/lonestar_08.htm

and here:

http://audioroundtable.com/General/messages/5103.html

As best we could measure, the in room response -3 was in the upper twenties and we never exceeded 40 watts on the plate amp.  1-4 wats or so with the ASL integrated was typical.  This system is capable of 110 db and more without strain.  Late night LSAF visitors will happily attest to this.