A newbe question about woof/tweet impedance in a cab.

[nh36000]

All;

First, I use a pair of Realistic Nova-15s as recording monitors. The foam around the cones disappeared after 30 years or, so, and I replaced them with Goldwood 8s. Parts Express touts them as full range speakers and I've put 15 Hz., from an SG, through them and they reproduced that well. These Woofs get down there. Now more.

I have a pair of 8 Ohm, 2 way X-overs to put in. I noticed, though, that the Woof impedance is 8 Ohms and the Tweet impedance is 6 Ohms with a 4.7 Ohm, 50 v. cap., wired in, in series with it. I'm guessing it's a high pass filter. I'll have to say, though, they sound a bit sharp compared too the 'BIG' ones I listen to otherwise.

I've crunched numbers to figure out resistance needed to drop voltage and found Watts needed to keep resistors from getting hot. I know how to do that.

So, would I be able to series wire in, a 2 Ohm resistor at 125 Watts, if the speakers are originally rated at 65 Watts? The 8" speakers can handle more than 65 Watts, though. I'm concerned about the health of the tweets.

Any help, please. How do I put the 8 Ohm X-over in with a 8 and a 6 ohm pair of speakers? Impedance's don't match.

Lu.

 

[onplane]

I have a pair of 8 Ohm, 2 way X-overs to put in. I noticed, though, that the Woof impedance is 8 Ohms and the Tweet impedance is 6 Ohms with a 4.7 Ohm, 50 v. cap., wired in, in series with it. I'm guessing it's a high pass filter. I'll have to say, though, they sound a bit sharp compared too the 'BIG' ones I listen to otherwise.

I've crunched numbers to figure out resistance needed to drop voltage and found Watts needed to keep resistors from getting hot. I know how to do that.

So, would I be able to series wire in, a 2 Ohm resistor at 125 Watts, if the speakers are originally rated at 65 Watts? The 8" speakers can handle more than 65 Watts, though. I'm concerned about the health of the tweets.

Any help, please. How do I put the 8 Ohm X-over in with a 8 and a 6 ohm pair of speakers? Impedance's don't match.

Lu.

Your Nova 15's are nominal 8 ohm speakers. Thus the 8 ohm woofer you bought should work with the xovers in the Novas. You rarely ever put a resistor in series with a woofer. This causes all kinds of sonic problems.

Now, whether the balance between tweeter and your new woofer is correct is another matter entirely. That is more a function of the woofer's sensitivity. If the woofer is more sensitive (woofer dominates and over powers the tweeter), what you would do is REDUCE the value of that 4.7 ohm resistor in series with the tweeter.

If the woofer is less sensitive (tweeter dominates and is over bright), you would increase the resistance of that 4.7 ohms OR add an additional series resistor.

Hope this helps...
Regards,
Jerry

 

[nh36000]

onplane;

If it matters, the 4.7 Ohms isn't about a resistor, it's a capacitor. So, if the highs are a little strong, should I forget the 2-way X-over and put a bigger cap in to squelch the highs a bit?

Lu.

 

[swechsler]

Changing the capacitor value will change the crossover frequency, not reduce the total output. Putting a resistor in series with the tweeter will likewise change the crossover frequency. If you want to reduce the output level of the tweeter, put the resistor between the input terminals on the speaker cabinet and the cap, not between the cap and the tweeter.

 

[mhardy6647]

... or use an L-pad (variable or fixed), ideally at the nominal impedance of the tweeter.
This would be easier to achieve with a fixed L-pad
Here's a handy calculator.

http://www.sengpielaudio.com/calculator-Lpad.htm

 

[nh36000]

Gents;

swechsler, thank you for information there. Some characteristics I didn't know. And mhardy, 'ahh, some numbers'. I like that.

Here is what I did this evening.

I wired up both speakers with the X-overs. One, using the cap in series in the tweeter circuit and the other without. The one using the cap is boomy, lots of low end and the other is tinny. I would be happy with something in between.

Calculations require a target dB drop. I have no way to meter the frequency response of a speakers output. I could only guess at that.

I'll get back to this tomorrow. I have some ideas on how I might gauge something like this.

Lu.

 

[borus]

Do you mean to say you ran the tweeter with out any cap? and the system sounded tinny? or did just the tweeter sounded tiny?
you should never run a tweeter without a cap to protect it. You must know this. Can you post a pic of what you have?

 

[musichal]

There is no way you were hearing 15hz from that speaker - harmonics, overtones, whatever, not the fundamental.

 

[nh36000]

musical;

It was a while ago that I put low frequencies through my speakers. Maybe I was remembering the sound through the big speakers.

You may be right, I'll look up the specs on those again. I have a pair of 3-ways here and the Goldwoods reproduce a lower frequency than those 3-ways do. Just saying!

borus;

I hope I didn't damage anything running the speaker without a cap in the tweeter circuit. It was late last night and I listened to them for a minute, just to compare.

The whole speaker sounded tinny, lots of high end.

The X-overs are Dayton Audio X02W-2K. Cross over at 2K and are 2-ways. You can find photos at Parts Express.

The one with the cap wired in has the cap between the + terminal of the X-over's tweeter output and the + terminal on the tweeter, in series. Woof and tweet are grounded at the input terminal at the back of the speaker.

I'll get in there and hook up the cap in the other speaker.

Lu.