|
Audio Asylum Thread Printer Get a view of an entire thread on one page |
For Sale Ads |
71.177.133.26
Hello guys,
I am running a somewhat 3-way speakers with Le' Cleach 350 horn, a bass reflex cabinet and a Fostex T90A(8 ohms)use as tweeter. The components are Altec 288C (24 ohms,115dB) for HF and Altec 416-8B (~99dB, 8 ohms)and the afformentioned T90A(104db). I attenuate the 288C about 15-16dB to match with the sensitivity of the bass driver using discrete components, the tweeter using an 8 ohm Lpad.
My question is between the 288C and the 416-8B drivers. Is there such a thing as a 24-ohm Lpad? Without resorting to active XO, what other "method" do you guys use to attenuate drivers with such a discrepancy in sensitivity between the two?
FWIW, I am running 1st order XO at about 900 Hz for the Altec 416, then about 15kHz from the 288C to the tweeter.
Thanks!
Abe
Follow Ups:
Works for me on many comps.
nt
It's at the bottom of the page.Just fill in your impedence and desired attenuation, it will tell you what resistor values to use.
The crossover design part is useful, too.
Edits: 02/28/12
Alpha Al,
I had been using that same calculator.
Abe
I used a 288C which read around 16 ohms and remember
talking with the guys at Great Plains Audio about this
anomaly. They said all, or almost all 288 read ~16ohms
rather than 24 ohms. They could make a 24 ohm one,
special, expensive. Treat your driver as a 16 ohm driver.
As I think you are saying that you are doing, set level
of the 288 with an L pad and then record the resistances
of each leg and calculate an attenuation--I monkey around
with an on-line calculator until the numbers fit. L pads
don't track well [or sound good] so after finding the
attenuation you've accomplished transfer that level to a
theoretical 16 ohm L pad and buy a couple Mills resistors.
--Carter
Thank you!
I will try your suggestion.
Abe
I have 1 288c 24 ohm looking to buy or trade for another 1 or 2.
Sorry Kloss! I only have a pair nowadays. Those I mentioned two posts up were from my friends.
regards,
Abe
I never knew Altec had a 24ohm diaphragm
Check the link..........
They definitely made 24 Ohm drivers. They were the early ones that said Altec Lansing Hollywood.
All that I have seen had the early red, white and blue decal.
Thanks for your input. My 288C's are all original, with Altec "24 ohm" sticker each on the cans. Their DCR readings are 17.7 and 17.4 ohms respectively. My friends, 5 of them, have the same type and theirs measure in the 17-18 ohms DCR as well. I do not know why these drivers can have 16 ohms Z rather than 24 ohms?
Thanks!
An 8 ohm altec will be 5 to 7 ohms and a 16 ohm will be around 12 ohms usually. One is nominal Ohms and the other is DCR.
I understand what you are saying. But my 288C's measures around 17 ohms DCR. Am I wrong in thinking that the impedance should be higher than 17 ohms (R+jL)?
Abe
The motional impedance will be much higher than the DCR, and depends on the horn you have loading it.
I really have a hard time believing that production tolerances could make such a huge difference. That would have to be very sloppy manufacturing, indeed! A 24 ohm DCR reading makes me think they are 32 ohm VC's. I am pretty sure Altec did make 32 ohm VC's for the 288.
Use an autoformer. I use these on my 288's and the work great!
http://www.ebay.com/itm/Autotransformer-fur-Hornspeaker-und-Altec-Crossover-/220957345672?pt=Lautsprecher_Selbstbau&hash=item3372158788
nt
The easy way to do it is to just use a 12Ω resistor in parallel with the driver, then use an 8Ω L-pad.Alternately, use a 48Ω resistor in parallel with the driver and then use a 16Ω L-pad. This allows the capacitor to be half the size for the same crossover point.
Edits: 02/27/12
djk,
Can I also use a T-pad where I use the source impedance (amp) as say 8 ohms then the load impedance as 16 ohms or 24 ohms and compute with 15dB attenuation?
Regards,
Abe
I wouldn't bother with a T-pad.
I would do the 16Ω L-pad, adjust it with test equipment, and then fine tune it by ear, then measure the resistances and replace with fixed resistors.
Calculators and test equipment get you close, your ear gets you the rest of the way.
I will do that.
regards,
Abe
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: