N 500 C

[Stovebolt6]

Hi all,

I am putting together a pair of cabinets using 511b/909a 16ohm and 515e 16ohm for home use. Are the the N-500-C crossovers the right choice? Is the attenuation done with an autoformer? Are they worth $300? If they are what makes them so good? If not, is there another Altec crossover that would be a better choice?

Thanks for the help!!

Dan

[Roland N R]

Active XO is better...check Marchand Kits. 515E is not best for horn enclosures, does better in ported enclosures.

[Stovebolt6]

Its going in a ported enclosure and will be part of a HT system. The HT is an integrated amp so i need a passive crossover. Just wondering if the N-500-C is the right choice as far as passives go?

[Stovebolt6]

Don't know if this is the right way to do this, but I just changed my avitar to show the cabinet in progress. It will be tuned to 40hz.

Now I just need to finish the Cabinet and get the right crossover!

Dan

[GM]

>515E is not best for horn enclosures, does better in ported enclosures.
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You're kidding, right?
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>Are the the N-500-C crossovers the right choice?
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Well, it's a 500Hz 2nd order textbook XO for 16ohm drivers if that's what you mean.
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>Is the attenuation done with an autoformer?
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IIRC.
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>Are they worth $300?
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Only if someone is willing to pay it.
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> If they are what makes them so good? If not, is there another Altec crossover that would be a better choice?
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They have decent components. None I'm aware of. I wouldn't pay it, but if you're not willing to do a bit of experimenting with XO design then I don't guess you have much choice.

Cool cabs BTW.

GM

[Stovebolt6]

Jeff,

Thanks for the help and kind words! The spacing in the vertical plane will be 11.25in. Will this offset make a huge difference at a listening distance of 13ft? I never considered time alignment!

I have the cut sheets for the 909-16a. The freq response spec for the driver is 500hz to 20khz. There is a graph showing the frequncy response plot on a 511b. I may be reading the graphs wrong but it looks to me like the SPL at 500hz on the 511b is 83dB, at 1khz 82dB, at 5khz 80dB, and at 10khz 80dB. Do I have the right specs?

I'm not afraid of building my own crossovers. I was thinking of buiding a standard 2nd order Butterworth with 3-4 dB of attenuation. Is the N500C a second order device? It seems like the CALSOD sofware is something you have to purchase. Is there a freeware program or shareware program that you could recommend that would be suitable for modeling the crossovers?

Thanks for putting up with all the newbie questions and once again, thanks for the help!

Dan

[jmarkwart]

Dan,
I don't believe an N-500C is the right choice in your application for two reasons. First, 500Hz is not an optimum point, as the 909-16A/511B combo's SPL magnitude rolls off rapidly below 1KHz. (See the old Altec tear sheets for the 909 sries) Second, your cabinet (nice work BTW!) does not align the driver voice coils in the same vertical plane, and therefore requires the crossover selected to compensate for the phase shift bewteen drivers at the chosen crossover point. I'm not sure if Altec ever built a crossover that suited your drivers and their spacing, but they may have! What will the horizontal spacing be between the two driver's voice coil centers when they are mounted in the cabinet? To be thorough and accurate you probably need to model the driver's Z and SPL responses with a software package like CALSOD, and then experiment with various crossover configurations until you get an acceptable combined driver/filter response. Then build it.
Good luck,
Jeff

[jmarkwart]

Dan,

>The spacing in the vertical plane will be 11.25in. Will this offset make a huge difference at a listening distance of 13ft?

To quote Alex Badmaieff from Altec's Loudspeaker Enclosures, Their Design and Use, "It is essential to maintain proper phase relationship between the low and high frequency units at the region of crossover. At crossover, they radiate with equal intensity, and if their phase is not correctly controlled, their outputs may cancel or combine in an unfavorable manner." I couldn't have said it better. At a crossover point of 500Hz with 11.25in of horizontal spacing, the phase shift between your drivers is 150 degrees; at 800Hz it would be 239 degrees. If you don't consider this in your crossover selection you could wind up with a system SPL magnitude deviation of 5-10dB or more at crossover. I think you could hear a 10dB dip in the midrange at 13ft! Remember, it's not initial arrival times I'm talking about here, it's system SPL magnitude at crossover. There is an excellent discussion of crossover phase considerations in Speakerbuilder issues 1 and 2 of 1995 that puts this in perspective.

>I have the cut sheets for the 909-16a

You have the right spec but I think you're looking at the impedance plot and reading the SPL scale on the left hand vertical scale. The impedance magnitude is read off the right hand vertical scale. SPL magnitude (what you hear) is the upper plot, and its magnitude is read off the left hand vertical scale. See what I mean about output at 500Hz?

>I'm thinking of building a standard second order Butterworth with 3-4 dB of attenuation.

A symmetrical Buttewrworth is not a bad choice where you have from 0 to 70 degrees of phase shift and use a reverse polarity (acoustic) connection with one driver, or 80 to 180 degrees of phase shift and utilize the in-phase connection. These will produce either a 2-3dB hump (reverse connection) at crossover, or a null, when reversed. Above 180 degrees the error grows.

>Is the 500C a second order device?

The N-500C is a parallel, symmetrical, Butterworth second order (L= 5.4mH, C=18.9uF) filter with an input impedance of 12 ohms, according to my schematic. I believe it was connected to its loads via matching transformers. If you attached your 16 ohm loads directly to it you would have a significant dip in SPL near the crossover, no matter which polarity you connected with, due to the rolloff of the 909/511 combo.

>It seems like CALSOD software is something you have to purchase

I don't know of any freeware or shareware that will do what CALSOD will. I looked and finally bought CALSOD to model my 604Bs for a recent crossover upgrade I just completed. I've used IMP and PRAXIS in the past for direct measurements, but CALSOD did exactly what I needed to design a crossover at a reasonable cost.

Jeff

[Stovebolt6]

Jeff,

Where is the best place to get CALSOD? Will the less expensive version do what I need it to do, or do I need to get the $300 pro version? Should I be measuring from the voice coils to the front of the motor board, or from the surface of the cone or diaphram? Does CALSOD have a driver list to pick from or will I need more test equipment to measure parameters?

Once again, Thanks in advance for any help!

Dan

[David Deratany]

Reading the foregoing, I get the impression that the amount of lf time delay depends on the particular crossover frequency. Is this correct? How would I go about making the calculation for 416 and 511/902 crossed over at 1200 hz? Is there a program available on the net I can use for this? Or do I just need to align the mounting surfaces of the drivers and reverse the phase as mentioned in the Altec tech paper?