My RS180 MTM Design

[fdieck]

Don- I don't know that an LC is simpler/better than another LC. Both series and parallel are notch filters.
Later,
Wolf

I agree ..... you don't know.

[fdieck]

I got distracted and didn't finish.... sorry. The two different approaches do present different input impedances to an amplifier at high frequencies and could in some cases affect amplifier stability with the case where the notch filter with two capacitors in series appear between the input and ground connections of the speaker.

[fdieck]

http://www.eetimes.com/document.asp?doc_id=1274906

[Wolf]

I got distracted and didn't finish.... sorry. The two different approaches do present different input impedances to an amplifier at high frequencies and could in some cases affect amplifier stability with the case where the notch filter with two capacitors in series appear between the input and ground connections of the speaker.

I know that a tank provides amp instability in some cases by providing an ultrasonic short without a resistor tagged along. BUT- that is not what I was getting at, Fred. I was meaning that Jeff's circuit is a notch filter, just like what 'Everyone else used a notch filter' is a still notch filter. I know they work differently, and some work better for certain applications, but that wasn't my point.

Later,
Wolf

[Jeff B.]

As a general rule of thumb, the series notch is usually better when dealing with out of band issues and the parallel notch is better for in-band issues. If you look at designs by other experienced designers like Bamberg, Kreskovsky, Murphy, etc. you will see that they tend to follow this convention also.

[Jeff B.]

I know that a tank provides amp instability in some cases by providing an ultrasonic short without a resistor tagged along. BUT- that is not what I was getting at, Fred. I was meaning that Jeff's circuit is a notch filter, just like what 'Everyone else used a notch filter' is a still notch filter. I know they work differently, and some work better for certain applications, but that wasn't my point.

Later,
Wolf

It all depends on how the components are laid out. My circuit does not do that because the series inductor controls the high frequency input impedance.

[fdieck]

It all depends on how the components are laid out. My circuit does not do that because the series inductor controls the high frequency input impedance.

We are referring to the parallel notch with a small cap across a large baffle step inductor that appears in series with the cap to ground on many second order woofer low pass filters. It makes me a bit wary when this cap becomes close to value of the cap used in series with a 5 to 10 resistor used for a zobel network on the output of typical power amps.

[Jeff B.]

We are referring to the parallel notch with a small cap across a large baffle step inductor that appears in series with the cap to ground on many second order woofer low pass filters. It makes me a bit wary when this cap becomes close to value of the cap used in series with a 5 to 10 resistor used for a zobel network on the output of typical power amps.

Yes, I agree with you on this layout......

[Wolf]

Agreed on all counts, fellas.
Wolf

[AlexRivera]

Hi All,

I got my hands in a pair of R28AS-4 so I'll try to implement the original design in a Trans Laminate cabinet, what would you recommend as far as crossover components go?

I'm not asking about $150 dollars Caps but more about what's the recommended quality to get the closest to the original design?

I wish I was experienced enough to be able to tell from the picture what components Mr. Bagby used .



Thanks,
Alex

[Wolf]

Panasonic mylar caps, Jantzen air-cores, and an NPE cap. I think that is the tweeter xover only.

Later,
Wolf

[AlexRivera]

Panasonic mylar caps, Jantzen air-cores, and an NPE cap. I think that is the tweeter xover only.
Later,
Wolf

Thanks Wolf!

Looks like those don't exist in anything bigger than 10uF, at least I haven't been able to find them, that's why it looks like he may have used 2 X 10uF in parallel to fit the 20uF needed in the woofer.

I'm not sure what he meant when he said that Poly Caps can be "Pretty Salty" for the 50uF on the tweeter but I guess that's bad? That's why is safer to stick to the NPE right?

Best,
Alex

[bullittstang]

"pretty salty" means expensive. A 50uF in a poly might be $15, where a NPE would be $1.10. Any decent poly for everything but the 50uF in teh woofer circuit (there use a NPE) and you will be fine. I typically use Dayton poly caps, or Audyn.

[AlexRivera]

"pretty salty" means expensive. A 50uF in a poly might be $15, where a NPE would be $1.10. Any decent poly for everything but the 50uF in teh woofer circuit (there use a NPE) and you will be fine. I typically use Dayton poly caps, or Audyn.

Hahahah, struggling with slang here, OK, I got it now.

Thanks Paul!

[Jeff B.]

Hi All,

I got my hands in a pair of R28AS-4 so I'll try to implement the original design in a Trans Laminate cabinet, what would you recommend as far as crossover components go?

I'm not asking about $150 dollars Caps but more about what's the recommended quality to get the closest to the original design?

I wish I was experienced enough to be able to tell from the picture what components Mr. Bagby used .

[ATTACH=CONFIG]n1337026[/ATTACH]

Thanks,
Alex

That picture shows the passive filtering for the amplified version of the speaker. That's not the crossover for the passive version of the speaker.