Guy Landau Posted November 11, 2002 Share Posted November 11, 2002 Hi guys, All of the altec 511 talking had made me wanna experiment once again. I was thinking about replacing the k55v/k400 with Altec 311-90 horns which I currently have and I found Altec 290e drivers to go along with them. The real problem is that the k55v is 16ohm and the 290e is 4 ohm. I am using 1st order type A networks and would like to keep it that way.The problem is that I know nothing about designing crossovers (except copying them) The type A has 13mf cap for squaker and 2mf cap for the tweeter.Do you guys happen to know if I will need to change the capacitors value and by which ratio? Many thanks Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 11, 2002 Share Posted November 11, 2002 Guy, You can't figure what the sereis cap will be until you decide what autoformer tap you will be using. The impedance reflected back from the driver through the autoformer determines the value. The only other way is by adding a swamping resistor and keep the same cap. You will still need to know the final tap setting to figure the resistor value! Al K. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted November 12, 2002 Author Share Posted November 12, 2002 Many thanks,Al. Quote Link to comment Share on other sites More sharing options...
djk Posted November 12, 2002 Share Posted November 12, 2002 For the Altec 290E I recommend you put a 10 ohm resistor in series with the driver and then hook to tap #5 on the autoformer and increase the capacitor to 25µF. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted November 12, 2002 Author Share Posted November 12, 2002 Thanks djk, The 290E is rated as a 4 ohm driver and 106.5 db/spl @ 1w/meter when used with the 311-90. I guess that the sensitivity is nearly the same as the k55v/k400.Will it be better to leave the same tap (#4)? Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 12, 2002 Share Posted November 12, 2002 Guy, I disagree totally with DJK on this one. The resistor is a bad idea. He is butting heads with PWK here too. You might use the series R to get an idea of a level to start with but that will require instrments you probably don't have. Guessing at the tap setting to start off with and computing the swamping resistor with the idea if iterating to the targe makes far more sense! Al K. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 12, 2002 Share Posted November 12, 2002 Guy, I looked into the situation a bit more and a starting place might be to connect the 4 Ohm driver between taps 0 and 3. This is just a guess. That's a voltage ratio of 2:1. That means the driver will look like 2 squared or 4 times 4 ohms or 16 Ohms to the series cap that's driving it. The A network was designed for the K55 driver that is about 13 Ohms. When reflected back through the autoformer set at tap 4, it will look like 1.414 squared times 13 Ohms, or about 26 Ohms. This is what the 13 uF capacitor wants to see. Since the 16 Ohms is lower, you are going to have to change the 13 uF cap by the ratio of impedance change. So, 26 / 16 = 1.63. That means you need to change the 13 uFd to about 20 uFd (21 actually). This would be a lot easier if the impedance reflected back was greater than 26 Ohms, then you could swamp it and leave the 13 uFd cap alone. But, that's never how life seems to be! Try that and if the squawker level needs to be changed from taps 0 and 3 to something else, it's easy to figure the new cap value the same way. This is what I mean by iterating until you get the level you want. A series resistor or "L pad" to cut down the level divorces the driver's back EMF from the amp. That's what I believe causes resistor pads to suck the "life" out of the sound, as I have heard it described. The back EMF is actually stepped UP as it goes back through the autoformer! I think that is what PWK noted in the paper he wrote titled "The Trouble with Attenuators" years ago. Al K. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted November 13, 2002 Author Share Posted November 13, 2002 Thanks,Al. Well,I became a little confused here but I will give it a shot. I think that it is time to buy some literature about this topic. Quote Link to comment Share on other sites More sharing options...
djk Posted November 13, 2002 Share Posted November 13, 2002 An Altec 290E is 10dB down at 300hz and 7Khz, read the spec sheet. On second thought I an going to recommend putting a 14 ohm resistor in series with the driver, hooking it on tap #5 of the T2 autoformer, and drive the autoformer on tap #4 with a 32µF cap. The resistor attenuates the midrange and makes the driver flat from 400hz to 6.3Khz (-3dB points). The driver/resistor combo is now less sensitive that the woofer so we use the autoformer to match everything up. The 290E has very high voice coil inductance so a resistor in series cuts the mids more than it does the highs. The 311 horns have some good sized impedance peaks in the low end so a series resistor cuts the mids more than the low end. With a 14 ohm resistor the 290E measures ±1dB from 800hz to 5Khz. Of course I have 8 or 9 of these drivers laying around. And a calibrated mic. And an analyzer. And I used them. Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 13, 2002 Share Posted November 13, 2002 Guy, I still disagreed with djk here. I would call what he suggests a shortcut of sorts. I have done that sort of thing many times and it never seems work out well. Using the autoformer to step UP rather than down is valid, and PWK did that very thing in one of his patents, but to still use the resistor to cut it back down is still letting the back EMF go uncontrolled. Your objective is to improve performance over the stock K55 driver and horn combination. Cutting corners doesn't seem logical. The resistor WILL cause an audible degradation in sound quality and a calibrated mike, spectrum analyzer and all that other equipment won't hear it. Your ears will! You can try that rig if you like though. You won't damage anything doing so, but if that driver has as bad a set of specks as djk says, maybe it isn't much of an upgrade! If you do decide you want that combination, I think what you really need is an equalizer and a correct matching job between the network and the driver. That way you have the back EMF control and the ability to set the frequency response any way you like besides. Anything worth doing is worth doing right. Al K. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted November 13, 2002 Author Share Posted November 13, 2002 I happen to like the sound of the phenolic drivers and I guess that the Altec measures better than the k55v(correct me if I'm wrong) and all the other drivers don't go as low as the 290E so I guess that I have to use it or should I try just the 311-90 horn with an adapter and the k55v? Thanks Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 13, 2002 Share Posted November 13, 2002 Guy, I am a firm believer in trying one thing at a time. That's the only way to know for shore what change made what difference. If you can just screw the K55 on the other horn, do that first. You know the K55 will match the network, so you can then know what the horn alone sounds like. Fiddle with the driver and transformer / resistor choices later. Like I always say "one desaster at a time!" Al K. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted November 13, 2002 Author Share Posted November 13, 2002 I guess that I'll be starting with the horns but I'll have to order the adapters for the k55's first. Thanks Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 13, 2002 Share Posted November 13, 2002 Guy, Sounds good to me! Keep everybody posted on what you find. Al K. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted November 16, 2002 Author Share Posted November 16, 2002 Do you know how high can the k55v go? Thanks Quote Link to comment Share on other sites More sharing options...
Al Klappenberger Posted November 16, 2002 Share Posted November 16, 2002 Guy, The K55 (V or M) can be counted on to go up to 6000 Hz. NO HIGHER! Al K. Quote Link to comment Share on other sites More sharing options...
Guy Landau Posted November 17, 2002 Author Share Posted November 17, 2002 S*#t, I really wanted to try the JBL 2405 tweeters that I have and like very much. Thanks again,Al. Quote Link to comment Share on other sites More sharing options...
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