[Michael V]

Here are some unabashedly ugly test baffles, using vintage Altec drivers.  The midbass is a 414Z, which is running fullrange (apparently up to 4khz or so).  From someone's measured specs they have a low Qts (<.3), yet in this baffle and room they extend to 80-90hz before dropping off precipitously. 

The bent horn is a 32A, which is an old Western Electric design that Altec produced for one of the VOTT units (A8?).  It loads an Altec 808 compression driver, whose crossover freq. I am playing with presently.  What I'm exploring in this baffle is how to get the benefits of OB in the mids and below, which I really really like, while retaining greater image focus and horn-like dynamics.  Seems like a natural fit.

One question for the experts - any issue with the two drivers' magnets being so close?  There's about 2" in between, and no discernible noise.







Sorry for the poor image quality.

Regards,
Michael V

[X5nut44]

Hello Michael,

If you ever decides to sell the Altec Horn and woofer let me know.

[Michael V]

Here's the result of that experiment:





I would have posted an update but feared an OB backlash!

The 414 works surprisingly well on open baffle, but in a 3.2cf box I find it just barely gives me enough LF extension without any bass augmentation.  Mid-50's bass extension is not great, but the speed and articulation are the best I've heard.

Plus, with 100db sensitivity I drive them with my new 46 SET amp.  Its power output is a whopping 1200 milliwatts.

Cheers

Michael


PS I do have a pair of Altec 32 horns left over, please contact me privately if interested.

[JoshK]

I'm curious if you have ever verified the 100db/w sensitivity?  I've always doubted it.  It very could be true, but I thought Altec quoted at 4ft for one.  That shouldn't make a huge difference, but it isn't the standard.  Anyway, just curious.

[mcgsxr]

Always good to find the optimal (subjective often) enclosure for your drivers.

Glad you tried OB anyway!

Hey, I own a couple of sets of non OB speakers too - shhhhhh.   But, the main system for me remains OB.

[Michael V]

I'm curious if you have ever verified the 100db/w sensitivity?  I've always doubted it.  It very could be true, but I thought Altec quoted at 4ft for one.  That shouldn't make a huge difference, but it isn't the standard.  Anyway, just curious.

Not scientifically, but they're right around there.  I have to pad down my 802-8G's about 12db to match.  Altec rated the 414's at 99db @ 4ft, so at 1M they're actually a bit more sensitive.

I've built a few other OBs, and they do some things very, very well.  I've never been satisifed biamping in the longterm, and definitely prefer low-powered tube amps.

[xecluded]

Plus, with 100db sensitivity I drive them with my new 46 SET amp.  Its power output is a whopping 1200 milliwatts.

How do you like the sound of the 46 VS 45 tubes in your SET amp.

[Michael V]

The 45 has a different pinout, so I haven't tried them in this amplifier.  If I had to hazard a guess, I'd say the 46s sound more luscious and full-bodied.  45s are excellent too - just a different flavor (a bit on the cool/lean side IMO).

[xecluded]

Great.  I will have to order the adapter and try the 46 on my amp.  Thanks.

[Plink]

Nice cabinets, Michael.  I didn't think this experiment was going to work out with a desired open baffle.

One can listen to Altec horns in the nearfield and it works nicely in my experience (4 feet or so).

I switch in a 46 amp with my Model 19s and while the sound is fantastic, I do notice the distortion if I turn it up too loud.  When I want to turn it up, the 300B goes back in. 

I quite easily prefer the 46 tube over the 45.  Although, I haven't tried any exotic 45s.

[Michael V]

That actually surprises me.. I've used the little 46 amp on various speakers, including Spendor SP100s which are something like 92db.  Listening at moderate levels in a medium sized room, we didn't hear any noticeable distortion.  Past a certain point on the volume control, the bass levels off.  Of course that's a kind of distortion but probably not the kind you're hearing.

What topology is your amp?  With such a wimpy output tube, you just can't afford to lose anything in the driver stage.

[Plink]

If you can re-read my comment, I said "if I turn it up too loud".  Perhaps I should explain.  When I say turn it up too loud, I'm talking really loud for rock (something I couldn't listen to for more than a song) or if standing much further away than nearfield.  My 300B clearly can go further here. 

Incidentally, I just listened last night to the 46 with a shaded dog mono and a level plenty loud enough and sound was incredibly dynamic and smooth.  Startling dynamics, actually.

The amp is basically the Bugle circuit...5751 or 6072 SRPP input/driver going to the 46.  The 46 is not run as hard as the 45 (consistent with tube manual operating points) and I'm getting no more than 1.25 watts (a switch on the amp toggles between operating points for 45 and 46).  I cannot really tell a difference between 46 and 45 other than I like my 46s better. 

Technically speaking and I'm sure you know this since you build things, if I go above 100db on my speakers, the tube will distort.  I do think some people have a hard time noticing such distortion because tube amps clip gracefully (not saying you do).  When I bought my Model 19s, I asked people what SET was compatible.  Some said nothing lower in output than 300B and others said 45 would work easily.  ???

[bellicon]

Here's the result of that experiment:





I would have posted an update but feared an OB backlash!

The 414 works surprisingly well on open baffle, but in a 3.2cf box I find it just barely gives me enough LF extension without any bass augmentation.  Mid-50's bass extension is not great, but the speed and articulation are the best I've heard.

Plus, with 100db sensitivity I drive them with my new 46 SET amp.  Its power output is a whopping 1200 milliwatts.

Cheers

Michael

Hi Michael, I’m a newbie to DIY speaker design. However, I do have a pair of GPA Altec 416 midwoofers in sealed boxes. http://www.greatplainsaudio.com/downloads/414-8B%20Spec%20Sheet.pdf The 3 cu ft boxes cut their low end off below 70Hz. The low diffraction boxes (with rounded prefab corners from http://www.tapeease.com/ ) were designed by fellow diyaudio.com member Gary Dahl, who uses them below his Azurahorn/Radian combo. Gary uses the Altecs from 70Hz up to 700Hz. Indeed, he chose the 416s for his midbass drivers because of their frequently acclaimed tonality- almost certainly due to its Alnico magnet and the low distortion from its underhung voice coil. http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-781.html and http://www.enjoythemusic.com/magazine/equipment/1009/lowther_high_efficiency.htm
Gary uses AE 15” subs with passive radiators. 

Thus, because I want to use OBs in a small room-where the left OB would produce little, if any, LF response being too close to the sidewalls and only 3 ft of open space behind it-I thought of setting a midrange OB (and maybe a ribbon tweeter as well to the side or above it) atop each Altec box. Sealed speakers are more forgiving of less than ideal room placement and the Altecs, handling 700Hz to 70Hz, would thus take  boundary problems away from the OBs above it.
 
I would be using one of my Rythmik 12" sealed servo subs between the Altec 416s.

What midrange driver would you most recommend for this app?

The Altec 414 that you tested in an OB? http://www.greatplainsaudio.com/downloads/414-8B%20Spec%20Sheet.pdf  However, its 96db to the Altec 416’s 98db.

Maybe one of the Alnico or other drivers from Supravox? http://www.supravox.fr/anglais/les_hp.htm

Or either the Eminence Definimax 12" http://www.eminence.com/pdf/Definimax_4012HO.pdf 

or the Beta 12 LTA? http://www.eminence.com/pdf/Beta_12LTA.pdf

They are 96.2 and 97.7db, respectively. The latter seems especially popular among OB builders, plus being a perfect sensitivity match for the Altec 416.

Which might be the ideal midrange for my situation?

Tweeter selection obviously will be the tough choice, given the sensitivities of the drivers to be used below it. Though $$$$, it looks like the only game in town is the RAAL Lazy ribbon.
https://www.madisoundspeakerstore.com/ribbon-tweeters/raal-lazy-ribbon-9-ribbon-tweeter/ 
Excellent dispersion and > 100db.

Do you think this hybrid OB idea will sound good?

Will it do so without active crossovers?

Please advise on drivers.

Thank you. 

[roscoe65]

Here's the result of that experiment:





I would have posted an update but feared an OB backlash!

The 414 works surprisingly well on open baffle, but in a 3.2cf box I find it just barely gives me enough LF extension without any bass augmentation.  Mid-50's bass extension is not great, but the speed and articulation are the best I've heard.

Plus, with 100db sensitivity I drive them with my new 46 SET amp.  Its power output is a whopping 1200 milliwatts.

Cheers

Michael


PS I do have a pair of Altec 32 horns left over, please contact me privately if interested.

Michael,

Sorry to revive an old topic, but you have given me some inspiration.

I have a set four 414A's, a pair of 802D's, and a pair of 32A's.  My original intent was to sell off a pair of 414's and make a two-way using a 614 sized cabinet.  However, your experiment with OB along with an Altec 9844 thread on Audiokarma gave me an idea.  The end result of that thread was running the speakers as a 2.5 way provided the best result.  The compression driver was crossed over to a single 414A, and the second 414A was brought in at about 200hz using a 20mH inductor.

This approach offers the simplicity of a simple two-way crossover, with the second 12" driver coming in as a bass adder.