3-way crossovers for Altecs

[joebelly]

Thanks Everybody!

I appreciate all the advice. I think I will start small by just readjusting to the Altecs, to the dampening, and then probably try some JBL 2405 like ngccglp. My question is where do you find some 2405's? I took a quick scan on Google for a set and did not come up with any thing. Are these rare? Does any body have any for sale or could point me in the right direction?

Joe

[LICORNE]

Try this.

http://www.jblpro.com/pages/componen...drvs.htm#2405H

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[Tom Brennan]

Joe---You can EQ the compression driver for better highs, the Hiraga circuit is such an EQ built into a passive crossover for the A5.

Or use an outboard equalizer.

JBL tweeters are common on Ebay and at Jammin Jersey, an outfit that sells used drivers and such at www.jamminjersey.com

[endeeinn]

I too when the route of 2405 slots but could never get things quite right, then I tried the Altec compensation/horn equalization curcuit and sold the slots. You can find the circuit here on the board just search for 'compensation' or "equalizer" Just a few resistors and caps and you'll be hearing the highs as they should sound.

[speakerdave]

At The Mastering Lab, when their midrange was an Altec 511E with 288-16G they used the EV T350 on top, based on what I've gleened from the web. They used this setup for their big monitors well into the '90's and may still be using it for all I know, although they have a new lab where they've installed smaller speakers for surround mastering. You will probably need to make your own crossover, as they did, no matter what tweeter you use. I don't think their circuit for that application has ever been published.

David

[ngccglp]

Hi,

Following the discussion here, I made the RC circuit with R8 and C2.2 uF for my 288-16G. Guess what? It works!! The mid is much tone down and I can hear a lot more bass.

May I know the relationship of the R and C to the mid freq? i.e. If I increase the value of C will the mid increase or decrease? Also what is the effect of varying the R?

Thanks.

[sguttag]

I just checked with my tech sheet (back in the office) and I was correct...the JBL 2405 is with the older JBL convention (opposite of most other drivers, including Altec). + voltage on Black creates a forward motion of the diaphram.

Steve

[GM]

Originally posted by ngccglp:
Hi,

Following the discussion here, I made the RC circuit with R8 and C2.2 uF for my 288-16G. Guess what? It works!! The mid is much tone down and I can hear a lot more bass.

May I know the relationship of the R and C to the mid freq? i.e. If I increase the value of C will the mid increase or decrease? Also what is the effect of varying the R?

Thanks.

<font size="2" face="Verdana, Helvetica, sans-serif">Greets!

The resistor acts as a voltage divider, lowering the horn's mass corner (shelves it) and the capacitor acts as a bypass cap to tonally 'lift up' the shelved highs. For a small format driver though, the cap needs to be much smaller, between 0.1 - 1.0 uF depending on the app. WRT the resistor value, a compression loaded horn wants to 'feel' a matching impedance, so normally a 16 ohm driver will require 12.5 -16 ohms depending on what sounds best. I used a cheap RadioShack 25 ohm pot to find what worked best, measured it, then assembled a fixed resistor to replace it.

For most folks, this yields an adequate amount of highs, though it's only over a fairly narrow 'sweet spot' due to horn beaming. For a wider one and/or more HF extension I recommend the Fostex FT96H or T90A depending on how much efficiency is required.

GM

[joebelly]

ngccglp,

I will probably get some 2405's more sooner than later. They are easier to find than I thought. If I understand your mod correctly, you ran lines paralell with the horns, tapping into their lugs, and connected a capacitor on the positive line only. The positive line w/cap from the horn then goes to the black lug of the 2405. The other wire from the horn goes to the red lug of the 2405. I see the values you recommend, but what type? I assume voltage and current are so low that it is not an issue.

I have to say that I got a lot more responses than I thought I would get. I also like the side discussions that occur. I have owned and sold a lot of equipment in the past. My student loans payments years out still prove it. (Hint: Do not use student loans for stereo stuff like I did. It is meant for beer, I mean rent and books.) Any way, in the future I hope I can contribute in some way to this forum.

Joe

[ngccglp]

Hi GM,

You are right about the compression driver wanting to feel a matching impedance load. I was experimenting with the 30904 circuit for my 288-16G, doubling the resistors and halving the cap value. At first I only had a 10 ohm resistor at hand to use for the shunt. Later I connected a 2.2 ohm resistor to make the shunt 12.2 ohm. The sound of the 288 changed, much more transparent and airy, good extension in the highs too.

Anybody had similar experience? Is there an optimal value for the 288-16Gs?

Thanks.