-
charles--------i have found that the midrange output of the larger drivers is usually far in excess of what they need to be to sound well balanced with most LF woofers even if you are using the 515--------remember that in most large format driver applications there was more than one woofer to each HF driver--------in one of my systems (515 in 828 with 288 on 311) i have a similar network and i use it with the 4dB (if i remember correctly) attenuation setting--------on another note------i cannot remember if the the 800G has inductive compensation (zobel) for the LF woofer or not but if it is one of the ones that doesn't you will invoke a giant improvement in overall midrange quality if you add it-----i know for sure the N-500C doesn't have it-------for all the quality engineering and design efforts that went into the altec drivers the crossovers left a lot to be desired-------it is amazing how primitive their design really was------they were almost textbook circuits with little or no use of compensation networks for either the LF or HF drivers-------perhaps it was a shortcoming of designing only a few "fit all" devices to fit all the possible horn woofer combinations........RC
-
In my experience the 1" drivers actually have better
LF response (the 288s naturally roll off at 500 hz).
This is only of value if you are experimenting with
lower crossover frequencies.
-
I wonder which 288 you are speaking of. The later versions, 288G-L have better LF then the C mdoles. In my experience, it depends on the horn. On something like a MR42 or 203, they hold up quite well to under 400Hz, however at extremely reduced power levels. Remember the principal of constant velocity applies here and the more you excert the diaphragm the less overall power it will handle at lower frequencies. Jim
-
Hi Jim
Yes, I was refering to the early wrinkle-paint 288C.
But I don't think I got much better response off a
later 288G (on a large horn , sweep freq test down
to 200 hz). This kind of turned me off 288s. Of
course this has no revelance to 99% of users who
will crossover at 500hz or higher. Drivers that I
found to have good sub-500hz performance were : 802
(especially with custom large absorptive rear cavity - which lowers resonance also)
(what a great driver the 802 is!). Other good
performers were the Western Electric 594 (LF
performance limited only by horn) and the JBL 2440
wasn't bad either. I haven't tested a TAD , nor
would I want to as there are so many fine U.S.
products . After all, America invented the compression driver.
-
I beleive the 288 driver you used as a reference, gray crinkle paint, is the 288B. The 288B has a loading cap and a magnetic shorting ring directly under the voice coil that prevents the diaphragm from venting into the pot casting. When you combine this with the limited back area under the loading cap, yes the LF performance would be limited. The later 288s have an expanded area behind the diaphragm and the pot casting under the diaphragm to breath into. Their diaphragmatic resonance is far lower and their LF performance is dictated by the horn. However as I said in the previous reply they will handle very few watts at these lower crossovers. An example of this would be the WE 555. It was commonly used on the large snail-shell type theatre horns down to 54Hz. At the lower frequencies it's power handling was expressed in milliwatts. However the same driver on a WE straight axis trumpet was probably about 20 watts. Th WE 594, according to the old ERPI/Altec guys, was quite fragile and broke easily. be careful, I have no idea where you can get a replacement diaphragm. From my experience with 288s VS 802s, the 288s win hands down. They have an ease of reproduction not found in almost any other driver, they also have an HF extension not found in any of the larger diaphragm drivers like the JBL 2440. You have a set of precious antiques. For others my opinion is if you want to go to 300Hz, I would reccommend a 290 driver with tweeter. Jim
