This is primarily what dual driver adapters are for.Originally Posted by Panomaniac
GM
Loud is Beautiful if it's Clean! As always though, the usual disclaimers apply to this post's contents.
Hi Mike, From research I did the only Altec driver of the large format capable of going that low is the 288C maybe something to keep in mind when using the 803's I'll try and find that info for you.
HMM..curious where that's from.
All of the big Altecs should go to 300 at realistic living room levels.
Especially the 290.
They won't handle full rated power at 300.
But lots of 290's were run in public address with only capacitors to protect them.
Your neighbors called. They like your music.
Hi Panomaniac,
This is really a great detailed kind of a thing from your side....and many many thanks for this. I was really wanting to see something like this as I am in the process of hand building a pair of A7s for myself. Pls keep it up.
Pls correct me if I am wrong.
I think iron-core inductors are like that. Unless a sizable amount of current passes thru them, they will be less than the prescribed value. They are not linear in the graph. But for the VOTs it was not a setback as they were meant to pump away at very high & constant volumes. Also the reduced resistance of the iron-core inductors were an added bonus.
Another interesting point to note here is that, in a standard 12db crossover, if the value of the inductor is a little reduced (as is the case here) while the capacitance value is alright, it will infact put a slight bulbous rise (IIRC...nearly 2 db), at around the crossover point. Which is probabely why the A7 sounds much better at high levels compared to lower ones. Also as they are very efficient units, the mismatch becomes much more apparent.
For home use, IMHO one should either go for air-cored inductors or active X-overs.
Thanks again for the great thread.
Hey guys, thanks for the kind words and good ideas.
I did a little work and measuring and found that the 291/803 will actually play flat down to ~250Hz. Roll off under 250 is 6th order Butterworth. I.E., it drops like a stone. To get this, the midrange has to be pulled down about 7dB. That flattens it out.
Trouble is, phase has gone wacky at that point, so good luck matching phase at the crossover point. Distortion is higher at the bottom of the range, too. So minimum 400Hz, or 500Hz to be safe. Would be interesting to see if the "Giant Voice" drivers could do a better job down low.
So happy Thanksgiving. See you soon!
Hi OG, I was looking for that,can't find now. That is a good question.I think it was one of those sheets from Altec on their 803 Multicellur horns where they say recommended drivers. 288C,290,etc.... Mike if you have a spare 288 maybe you can try it to see if it helps. Regards ~ JOHN
I can see where that is confusing.Hi OG, I was looking for that,can't find now
Altec likely just recommended the driver that was current at the time of the sheet. Why recommend old drivers if you are in the business of selling new ones? And of course you can't recommend 288D's if they don't exist yet.
Your neighbors called. They like your music.
Well the 288 and 291 (I think) were spec'd for 500Hz. I thought that might just be because of being spec'd on a 500Hz horn. But even on the 300 horn they drop like a stone under 250Hz, so crossing them an octave above that is a good idea. Keeps it out of distortion, phase problems, excursion, etc.
I may try to get them down to about 425 acoustic, but if they don't sound good down there, no point in it. Will be interesting to find the sweet spot.
But that is the fun part isn't getting to play with all the different horns,drivers,etc..let me pose this question which driver did Altec recommend for the 803 multicell all of their large format drivers are 500 hz the 803 is 300 hz horn so they have no driver that goes to 300 hz does that make sense
A good question! The 290 driver, AKA "Giant Voice" seems to be what was meant for the 300Hz horns. I'm sure someone here can verify. They can play low and had a phenolic diaphragm. Could handle a lot of power.
Almost bought a pair, but I'm sure the 288 is much better for my app.
The 300 Hz horns were originally for voice paging.
And Altec did recommend a 300 Hz driver.
This sheet states the 288 to handle 10 watts from 300 hz up. Just a little hard to read.
http://www.lansingheritage.org/image...1947/page3.jpg
The field coil 287 was rated to 300, and the permanent mag 387 also, at 20 watt "peaks" when less than 12 dB/octave, ie just a protection capacitor...
http://www.lansingheritage.org/image...943/page07.jpg
I suspect somebody had an attack of honesty and changed the 20 watt "peaks" to 10 watts for the 288 spec.
Of course at 98 db from 1/10 watt, you don't get a lot of volume at full power, but note the dual driver adapters as GM mentioned...and things weren't as loud in those days.
As the need for volume went up so did the need for power handling, therefore the 290. But the Aluminum frams were used regularly from 300 for voice paging early on.
Your neighbors called. They like your music.
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