Also, How critical are the resitor values given that the tolerances of most power resistors are 5-10%? The reason why I ask is in my search for parts sometimes I cannot find an exact value, (15ohm instead of 16, 27ohm instead of 25, ) and I'm wondering if I vary this slightly if it will be audible. (especially on the tweeter)

Would you recommend that I not vary from a round port? I tend to favor how a rectangular port can sometimes be less prone to noise. Can I do a rectangular port as long as the total port area remains the same?

Thanks for your patience- I bet you just love it when guys ask questions about changing your (proven) design....

Eat Mo' Hot Sauce...
crazychile

36 watts will be fine for most designs. Actually, around ten watts would probably be enough for what most people are using. I believe Wayne recommends his resistor values assuming you intend on running a great deal of power through your speakers, like 300-400 watts. If you are running yours with around 100 watts - which is plenty - you only need perhaps 20 watt resistors in your CD crossover.

The impedance compensation is a little different. You should try to keep the wattage value as high as you can, but this isn't as much of a problem. You can use the dummy load resistors from PE which are 100 watts or even 200 watts in 4 ohm or 8 ohm models.

As far as resistor tolerances go, I personally think within 10% of the intended value is acceptable and not noticable, although some people might disagree. I aim for the closest possible numbers, but I won't lose any sleep using a 9 ohm resistor when it should be 10 ohm, or whatever. 15 instead of 16 and 25 instead of 27 is a very acceptable tolerance, no worries.

As for square ports, they will work just as well as round. In fact, some others have used square ports on four pi's, and Wayne's PiAlign gives you the choice of square or round ports. I think he just doesn't do it because it's not worth the trouble when you can easily use a prefab'd round port.

Hope I covered everything.

Adam

Eat Mo'Hot Sauce,
crazychile

Let's talk power distribution in music... I am a musician. I can tell you of a band I played in, and we were pretty well balanced for power. This was a 5 pc 50's/60's rock and roll band. The synthesizer and guitar each had little Peavey 40W RMS amps with a single 12" spkr. The drummer had NO amping. The PA, with all voices and my sax, was 240 watts, but just barely cranked, about 2 on the 0-10 of the knob.
The bass player had a 300 watt amp, and was fairly well in balance with the band.

In real music, as opposed to sinewaves, about 90% of the power is in the bass frequencies under about 300 hz. On top of that, the peaks are many times more than the average level.

OK, so you are reproducing that music with a 100 watt amp. The amp is just on the verge of clipping, or occasionally does clip slightly at its full 100 watts output. The AVERAGE music power coming out is only about 10-15 watts. And of that, most of that is going into the bass frequencies.

So, your tweeter and resistors there are only absorbing a few watts. Just don't do anything stupid like jerking leads out of sockets while cranking on the amp. THAT pop will blow a tweeter in a milisecond. Also, when you drive the amp into distortion, all that energy in the corners of that squarewave being generated is high level, high frequency stuff. And that goes straight to the tweeter and zaps it. That is why you easily can blow a tweeter with too small an amp.

Let's talk power now... if you want to sound twice as loud, well, though 3 db increase is a doubling of power, it is barely noticable. To most people, if you want to sound twice as loud, you need to increase around 10 db, which is a 10x increase in power requirement. So, if your 50 Watt RMS amp is not cutting it, forget that 100 or 200 watt amp you have your eye on... better go for 500 watts if you really want to hear a difference.

Now, you are running some 100 db/wt/mt very high efficiency Pi Spkrs. In your living room. Well, you will be feeling real pain before you burn out 10 watt resistors.

You get into a large hall, say, a civic auditorium, well, you need MORE POWER, but for home use, you are OK, guy.

It's called a subsonic filter (as I'm sure you know), but I certainly would not do this with passive components. You'd need something like a 50 mh inductor just to do a passive 1st order high pass at 25 Hz. That *will* degrade sound big time.

Every component in the signal path degrades the quality. Subsonic filters should be done activally only.

I included a chart of power input vs frequency in typical musical material.

While a subsonic filter will help on ported boxes, in the region where the woofer is unloaded, and bounces around, but will also prevent you from wasting a lot of amp power with a sealed box, too.

I am not sure I really understand what your chart is supposed to represent.

Like 50% of the energy is located below 315 Hz, roughly 75% of it below 1.25 kHz (and thus 25% above), etc. etc...

Adam