[jcg0322]

I am repacing the xover network on a set of 1974 vintage Jensen 3-way speakers. It has a simple 1st order network and I intend to keep it that way. The speakers are a 15" woofer, 2 4" midrange and a dome tweeter. The problem is a low pass filter inductor which is used by the woofer. I cannot identify the original value as it has no markinigs. I measured it with an LRC meter at .56mH so this component is obviously way out of tolerance. I would appreciate to hear input from the speaker experts in this forum to suggest a typical frequency for a 15" speaker; a ballpark figure for a starting point. I need to calculate a value for the purchase of a new inductor.
Thank you for the help.
Jack

[Æ]

Inductors won't change value regardless of how old they are unless they were abused considerably. You have a pair of loudspeakers? Well then measure both inductors out of circuit. Tell us if they are both .56mH. Typically the low pass frequency for a woofer would be at the same frequency as the high pass, or the starting band pass frequency of the midrange.

The beaming (ka) of a 15" woofer is going to kick in somewhere around 650-700Hz. Usually you wouldn't crossover a woofer much higher than where it begins to beam, however in your case the lower frequency limit of your midranges would be the determining factor.

[Æ]

See attached nomograph, courtesy of David Weems.

[face]

Cool chart, but I wish it was that simple Alan. 

[Æ]

Cool chart, but I wish it was that simple.

It was for Jensen!

So, do you think he has the time, tools and where with all to generate .frd and .zma files and plug them into PCD?

KISS, Keep It Simple . . . But please feel free to talk him through the purchase and use of a woofer tester, soundcard, microphone, software, etc, etc. Or he can just ship the loudspeakers to you. For a nominal fee you can take care of it for him.

[face]

I have no trouble spending other people's money.   

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-790

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=390-804&FTR=woofer%20tester

http://audio.claub.net/software/jbabgy/PCD.html

At least the software is free. 

Hope all is well Alan.

[Æ]

I have no trouble spending other people's money.

He only wants to replicate the original, a first order network, circa 1974. I could drum up something quite usable in no time (maybe two hours). Hey, it worked for David Weems!

[jcg0322]

Alan,
What you have stated makes perfect sense. It is nice to talk to someone with intelligence and experience. I will take apart the other speaker box tomorrow and measure the inductance of that coil.
But it is already making sense because the midrange capacitor (8uF) has a cut-off frequency of 2400Hz. The bass filter coil with an inductance of .56mH has a cutoff frequency of about 2300Hz. Very close. Just as you said.
Thanks Alan.........

[Æ]

Alan,
What you have stated makes perfect sense. It is nice to talk to someone with intelligence and experience. I will take apart the other speaker box tomorrow and measure the inductance of that coil.
But it is already making sense because the midrange capacitor (8uF) has a cut-off frequency of 2400Hz. The bass filter coil with an inductance of .56mH has a cutoff frequency of about 2300Hz. Very close. Just as you said.
Thanks Alan.........

All the answers you received were intelligent ones, regardless of who replied.

To me, 2300-2400Hz isn't midrange, it's treble! I generally think of midrange as being below 2000Hz.
Categorizing it: 16Hz-160Hz is bass, 160Hz-1600Hz is the midrange, and 1600Hz-16,000Hz is the treble, sort of. . .

You're welcome.

[neobop]

Jack,
Why don't you use the old coils?

[jcg0322]

AE,
The other coil measured .55mH so these inductors are probably good. I just don't agree with Jensens' choice of values. I don't think the cut-off frequency should be 2.3kHz for the bass. Maybe a 3.2mH coil would be better, putting the fco at around 400Hz. I will look at the links you posted.
Thanks.

[face]

How do you know that is the cut off frequency, from a chart?

[jcg0322]

face,
I didn't use a chart. I used the equation for cut-off frequency.
Why are people so mean in this forum?
That's it I'm gone.........goodbye.........adios..... ...no thanks

[srb]

Why are people so mean in this forum?
That's it I'm gone.........goodbye.........adios..... ...no thanks

?
 
I looked in the IGW to see if there were some posts removed from this topic that I missed, but there were none.  Must be some underlying subtext that I'm just not seeing.
 
Steve

[Æ]

?
 
I looked in the IGW to see if there were some posts removed from this topic that I missed, but there were none.  Must be some underlying subtext that I'm just not seeing.
 
Steve

It's the internet. . . people will get offended over perceived wrongs, upset over the least little thing.

[Æ]

AE,
The other coil measured .55mH so these inductors are probably good. I just don't agree with Jensens' choice of values. I don't think the cut-off frequency should be 2.3kHz for the bass. Maybe a 3.2mH coil would be better, putting the fco at around 400Hz. I will look at the links you posted.
Thanks.

Well anyway, if you care to hang around just a bit more, I have some ideas on how you could revamp the entire crossover, while still keeping it first order.

[Letitroll98]

Nope, I didn't delete anything.  Unless a higher authority stepped in and removed something that was posted, I can't see what the affront was.