825 Build Questions

[GM]

Ok, good to know, thanks!

Digital EQ can reshape the reflex BW, though if later OEM, GPA units sound as ‘muddy’ up high as the few I tinkered with way back when, then using XOs >500 Hz may prove very disappointing to some.

GM

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No fuss, it?s these types of scenarios that the most useful info sometimes surfaces.

Probably the most eye opening one for me was when I posted something about plywood 828 cabs based on my ~1975 knowledge and it tweaked enough folks that even lurkers challenged it.

Anyway, the upshot was that enough visible evidence was posted to show just how desperate Altec became later on to provide product. A7s made from a mix of cheap ply, MDF, particleboard [some cheaply covered with paper ?veneer?_ as seen from the inside], un-braced horn flares made from Masonite or similar that was obviously ?formed? in a series of bends on a metal forming brake plus other ?shortchanging? measures to use up as much scrap as practical.

Really sad and a pity those pics were lost unless someone made copies.

If you get a chance, audition TAD, GOTO, with the former maybe a ?tad? better and the latter at least a notch up from all but the earliest 515s and some say on a par with the best W.E., Klanghorn, RCA point source [cone mid] bass woofers.

GM

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The 411 is a great woofer...........

'Woofer' is right, I had a tough time listening to the Barcelonas at 500 Hz and forget the Santanas at 800 Hz. What a waste of beautiful cabinetry! Can't even imagine what they sound like XO'd up high in a small A7.

Made great 'subs' XO'd at 120 Hz in the partitioned A7-500s though.

GM

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As they get louder they get mushy which I attribute to all of the cabinet and horn ringing coupled with my concrete vault basement.

My question concerns crossover points. After much experimenting by ear, but no measurements, I have settled on about 2000 as a good crossover point. The driver plays flat up to 4K but above 2.5K I start hearing changes in the sound as I move from side to side and around the room. Clearly at this point the off axis response from the 15" falls off and becomes audible. What surprises me is that the driver can play up to 2K without hearing off axis issues. Is this a side effect of the short horn on the woofer? Is it better to use the higher crossover or a lower crossover?

Hmm, ?mushy? typically indicates an under-damped alignment down low, which isn?t uncommon with old VOTT cabs due to air leaks basically defeating much of its port tuning.

At 2 kHz, a 511 is just a wave-guide, so other than mouth reflections back to the throat causing peaks/dips in the response, there?s no ?ringing? going on.

The mid-bass horn begins ?pinching? the driver?s output above ~1695 Hz, so it seems reasonable that a ? octave above it would be obviously audible off axis.

Short answer: the small single driver VOTT mid-bass horn?s close enough ?ideal? horizontal blend to 511/811 through the XO BW = ~1200 Hz/800 Hz respectively based on Altec?s DI Vs Q measured plots and use some form of CD horn EQ to flatten it out to ?taste? [minimize horn ?honk?/mids ?grain?].

GM