crossover question

[TimRawson]

So I built a min transmission line. Similar to pmc's smallest offering. Right now, great bass but need help on crossover. I am using a 8 ohm driver and a 6 ohm tweet (Seas). Insead on recreating l-pad manually, can I just add a 2 ohm resistor to make it 8 ohm impedence so I can use a stock L-pad(which are normally for 8 ohm drivers)?

Another quick question... if using a 3rd order and want to add another order at different frequency, where is element added, closet to driver? For instance, with 3rd order lowpass at 2K, have inductor, cap parallel, inductior. Can on just add inductor in series with woofer in which case it'd just add to latter inductance of the 3rd order filter?

[BobEllis]

You can add a resistor in series to make the L-pad "see" 8 ohms. Just keep in mind that if the tweeter XO was designed for a 6 ohm tweeter (as many are), you'll throw the response off and the 2 ohm resistor gives you around 2.5 dB of attenuation by itself.

You cannot just add another section to the XO - the sections interact. You won't get the corner behavior that you expect if you do that.

[TimRawson]

Another quick question... using a zobel on a pair of parallel woofers, does one calculate Re and Le? Is it 1/(1/R1 + 1/R2) and likewise for Le? Or being that they are same drivers, just 1/2 the values into the calculators?

Also, anything wrong with both a zobel and notch filter across a woofer? I've seen an example where the notch only had LC and not the R. Or can a sharp crossover like 4th order at 2kHz os so beat the cone breakup?

[Paul H]

Also, anything wrong with both a zobel and notch filter across a woofer? I've seen an example where the notch only had LC and not the R. Or can a sharp crossover like 4th order at 2kHz os so beat the cone breakup?

Nothing wrong with both, but they will interact to some extent.

What kind of driver is it?

Paul

[TimRawson]

Both these (only mentioned one) projects were to use leftover components and experiement with some enclosures (tline). So, made a small transmission line using dayton reference 6" and seas H1212 tweeters.

The other is to a pair of 5" dayton reference (rs150?) and dayton 1 1/8" silk dome to make a center channnel - somewhat temporary as I haven't completely settled on which speakers I'm going stick with in my family room. Currenlty using AE3's (rare), but miss them for 2 channel. Cold weather makes it hard to turn garage into workshop again, especially when it comes time to apply finish.

Many of the designs used the dayton ref tweeter. Want to stick with a tweeter I have. Also have some 27tdfc's. When warm weather returns (maybe earlier depending on itch), wish to build a speaker right.

Right now, too lazy and don't feel like investing more money to do it right by getting mic, mic preamp, wallin jig and speaker workshop. The tlines are only for experimentation and not critical listening. Would be cool if I could get them to sound right. But my space for crossover is limited and don't wish to use an external xover right now and again, trying to use up some components . For both, was hoping to get by with a 3rd order at 2000 hertz, add a zobel which appears critical with the big impedence rise in mid bass region and maybe light notch filter if needed.

[cjd]

Have you looked at my RS150/TDFC project? Might help some as a reference if you go that route, with the Silkie or TDFC.

[TimRawson]

Thanks... that is the ticket. For a center channel using leftover parts, 2 RS125's (5") and have both a pair of H1212's and TDFC's. Swapped the H1212's into the design since many seas tweets are similar and my mains (acoustic energy's) use similar looking tweeter that says made in norway, hmmm (except they are 8ohm though). What is the 0.05mH inductor on the high section for? Also, I use terminal strips rather than soldering everything and used mills resistors. Sound so so much better now... gives me encouragement to do more down the road.

Definitely need to get the appropriate gear (mic, mic pre and jigs) to do testing. Text book crossovers definitely a very steep uphill battle. Had tried the series xover route where one can supposedly tweak by ear, but gets too complex blending in other factors.

Now, to fix my mini t-line's (similar to PMC fb1) with RS150 (6") and use the TDFC's, or should I get another H1212? However, don't know what to modify on the lowpass section with only one woofer, diff impedence. One question that was never answered is when running 2 woofers (MTM etc), does the zobel change, double capacitance and 1/2 resistance?