A little help on a crossover point

[Mazeroth]

Now that I'm up and running with SoundEasy I want to tackle my first passive speaker project, which will be a thin floorstanding MTM for my brother. I have 4 RS125s sitting here along with a couple of the Vifa XT25SC50-04 neo ring radiator tweeters so I am thinking of doing an MTM with them spaced very closely (almost touching) with the tweeter to their side. Looking at Zaph's distortion measurements these guys can get rough under 2khz but wanting to make sure I took my own distortion measurements which came out just a tad better than his. Right now I'm thinking of crossing them over LR-4 around 2.5khz but if you think I should go higher or could take them a little lower please let me know. I'll probably build them ported since they'll only need a little over 0.3 ft3 so if he wants to add a sub later on he can stuff the port and have an F6 right at 80hz, making it not too hard to cross to the sub.

Here are the distortion plots I took. They are labeled from 90 dB @ 1 meter up to 100 dB @ 1 meter. He does like to listen to loud rock once in a while so we may need to take that into consideration with the crossover point and the strain on the tweeter.

Thanks!

90 dB @ 1 meter


95 dB @ 1 meter


100 dB @ 1 meter

[Dennis H]

Run, some distortion plots on the RS125s and it should help you pick a point. Too low the tweeter distorts. Too high the woofers distort.

[fjhuerta]

I believe you'll be limited by the woofer's upper range frequency response. I don't think you can take it any higher than 2.4 KHz LR4!

[Mazeroth]

I was going to take the measurements of my RS125s tonight or tomorrow to paint a clearer picture but wanted to see what you all thought about how well this tweeter would perform and where you felt it would cross best. Let's just assume the woofer is -80 dB from 20 - 20 khz. and isn't an issue :B

When you look at distortion profiles what are you looking for in terms of a suitable crossover point? Do you try to keep certain harmonics below a level, say, always below 1.0% or maybe 0.5% ? Also, how far up or below the response do you check for the given slope you're using? Say, for instance, you're going to use a 24 dB/octave slope on a tweeter. If you choose a 2 khz. crossover point that response will be 6 dB down at that point, -18 dB at 1.5 khz. and -30 dB at 1 khz. However, with a 12 dB/octave slope it won't be nearly as attenuated. How do you apply the slope into the equation of where to crossover, or is it more or less just knowing from experience? I'm probably looking to far into this.

Thanks.