Altec 616-8a crossover ideas

**Elitopus1** · July 27th, 2016, 08:59 PM

Yeah it was UPS. It wasn't entirely their fault though. If the woofers had been individually boxed this probably would not have happened. The seller followed all the basic insurance requirements of 2" of padding etc, but he obviously was not familiar with shipping woofers.

I asked about the packing before buying. He said they were well packed with foam board. He sounded knowledgable.... You know the rest of the story. He must have had some help with the packing. He at least bolted them together.

I have been talking with a friend who repairs speakers. I might send one to him and see if he can carefully unglue the surround and spider, then maybe fix the magnet.

**Phil-G** · July 27th, 2016, 09:51 PM

i figured. seems every time I get a delivery from them. it looks like they rolled them down several flights of stairs.

**Elitopus1** · July 27th, 2016, 11:13 PM

Yeah I use Fedex for shipping big/heavy stuff and Usps for shipping small things. Ups is usually quite a bit more money.

**Elitopus1** · August 16th, 2016, 01:10 PM

I heard back from Gordon W yesterday. He has my woofers up in Georgia. He said he managed to unglue the surrounds and reshim the voice coils. No more rubbing! Now as long as they can survive the short trip home I can put them in the 612c clone cabs I have been working on.

I am thinking since the magnets were not shifted that the woofers were not tested very well before I bought them. When I tested them with music I could hear the rubbing, but not nearly as bad as when I ran a sweep. It was very obvious then. I guess thats the risk of buying audio gear from a non audio person.

This is the 3rd speaker project that Gordon has worked on for me. He is a really nice and talented guy. I'm very happy that I could keep the speakers mostly original.

I'll post up some pics once I get them back and mounted. I am still trying to figure out what to use for xovers. I guess I'll start with the originals or biamp until I get something else going.

I also have to figure out how to fit all these speakers in my listening space. I have the A7 system, the 817 system, the 612c clones, and also some 620 cabs in storage that I want to put 604G's in. I might have to get rid of something! I have been telling the wife that we need a house with a big detached garage. So far no luck

**Elitopus1** · September 4th, 2016, 08:33 PM

My woofers arrived back from Georgia. I mounted them in my 612 clones cabs. The cabs still need to be sanded, painted, and finished but I just couldn't wait.

They sound OK with the stock crossovers. I am assuming the caps are out of spec on those. Also I have heard that the stock crossover actually starts to roll the HF off after about 12khz.

Anyways I plan to try biamping to see how they sound. I want to play around with crossover points and see when the woofers start to roll off. I want to run a 1200hz crossover but that might be too high for the JBL style woofer.

I need some extra room for these. Hey maybe I can hang them from the ceiling?

**Elitopus1** · September 11th, 2016, 08:58 PM

I have listened to the woofers as is for a little bit and now I want to rebuild the xovers. They have

2x 14uf caps
1x 18uf cap
2x 1.8mh coil
2x resisters 8 ohm

They are 1khz per the literature. According to my xover calculator a 2nd order butterworth xover has a 14uf cap and 1.8mh coil per driver. I am thinking about rebuilding these as that.

The xovers do not have a HF level control. The HF seems rolled off on these. Could that be what the resisters and other cap are doing?

**Elitopus1** · September 14th, 2016, 11:26 AM

A couple of pics of the drivers in finally finished 612c clone cabs

**bowtie427ss** · September 14th, 2016, 01:52 PM

According to my xover calculator a 2nd order butterworth xover has a 14uf cap and 1.8mh coil per driver. I am thinking about rebuilding these as that.

You MUST know the actual impedance of the drivers at the XO frequency to calculate with any degree of accuracy.

Using the driver's spec'd nominal impedance to calculate and design a network isn't going to get you far enough into the ballpark to see the game.

Fundamentally, calc'd 8 ohms HF and 8 ohms LF yes, both C1 and C2 in a butterworth slope would be 14.06mfd and L1 and L2 would both be 1.8mH. That ain't NEVER gonna happen in the real world.

Now, let's plug in some real world numbers.

This is entirely for the sake of example let's say your woofer actually measures 6.9 ohms @ 1khz, and the compression driver measures 11.7ohms @ 1khz. Now, look at what this does to the component values for a 2nd order butterworth slope. C1 9.62uf, C2 16.3uf, L1 2.63mH, and L2 1.55mH.

If you want to calculate correctly, you MUST use the actual driver impedance @ XO frequency.

**Elitopus1** · September 14th, 2016, 03:30 PM

Originally Posted by bowtie427ss

You MUST know the actual impedance of the drivers at the XO frequency to calculate with any degree of accuracy.

Using the driver's spec'd nominal impedance to calculate and design a network isn't going to get you far enough into the ballpark to see the game.

Fundamentally, calc'd 8 ohms HF and 8 ohms LF yes, both C1 and C2 in a butterworth slope would be 14.06mfd and L1 and L2 would both be 1.8mH. That ain't NEVER gonna happen in the real world.

Now, let's plug in some real world numbers.

This is entirely for the sake of example let's say your woofer actually measures 6.9 ohms @ 1khz, and the compression driver measures 11.7ohms @ 1khz. Now, look at what this does to the component values for a 2nd order butterworth slope. C1 9.62uf, C2 16.3uf, L1 2.63mH, and L2 1.55mH.

If you want to calculate correctly, you MUST use the actual driver impedance @ XO frequency.

I'm trying to figure out if I want to redesign the stock crossovers. I'm pretty sure the two resisters are in there for evening out the horn level. I don't know what the 18uf cap is for. The two 14uf caps and two 1.8mh (I tested them and they are 1.8mh) inductors would equal out to a 1khz crossover for 8 ohm drivers. What it does with the actual impedance of the drivers I don't know. It either raises or lowers the crossover point from the 1khz that the literature lists.

Also these are 8 ohm LF and 8 ohm HF from the factory. I have thought about buying 16 ohm phragms for the horn. If I am redesigning the xover I would be better off with the 16 ohm horn if I want to run without a pot of L pad.

I have the terminals setup on the cabs so I can use an external crossover until I decide what to go with.

**bowtie427ss** · September 14th, 2016, 07:55 PM

OK, here's where i think you are missing the picture.

When calculating/designing crossovers, ONLY the impedance at XO is really relevant.

Because impedance curves aren't readily available for your 616's, i chose a woofer everybody will be familiar with, the 416-8B.

I don't think that anybody will argue that the 416-8B is what we call an "8 ohm woofer". But, one must understand that just because a woofer is rated nominally at 8 ohms, doesn't mean it will be 8 ohms at any given frequency. In fact, i can guarantee you that at almost ANY frequency the actual measured impedance will be ANYTHING BUT 8 ohms.

Below is a graphic representation of the impedance curve of the 416-8B woofer. The graph shows the impedance to be in the neighborhood of 16 ohms at 1000hz(1khz). Using crossover components calculated at 8 ohms would result in a crossover point far different than the desired 1000hz. The 616 LF will have a similar impedance curve that shows a sharp peak at cone resonance, from their as the frequency increases the impedance will drop, usually reaching a minimum somewhere in the 5 to 6 ohm region, and then will usually steadily rise with frequency from there.