L-200 woofer changes

[Earl K]

I think the first thing I'll do is try a buncha different LE85s to get a statistical "feel" for whether the 1350 Hz peak is coming from the filter or the driver/horn/lens. I'm reluctant to start tweaking the crossover circuit until I establish it as the source. I've made plenty of crossovers that work beautifully on just one driver here.

- That's a wise approach. This forum is lucky to have someone such as you ( with enough LE85s ) and the test gear ( and the willingness to use it ) to get to the bottom of this question.

Also want to take a more detailed look at whether cascading the UHF on the MF yanks the main MF highpass around any. First look said not, but I'm not 100% confident of that.

- It's worth the look. The cascade approach / should offer more overall impedance isolation / than the "traditional" topography . I'd suggest running WT2 impedance studies, for both wiring scenarios.

In the course, I'll try your mod and show what happens. It's clear I can't put this away just yet....

- Well, LCRs do eat up resources / its better to know if they are truly needed .
- OTOH, NP electrolytics bypassed with 1 uF polyfilm caps are a cheap enough alternative . Coils can be "right-sized" towards the correct impedance /further driving down their cost ( ie 22 gauge wire types or smaller ). I'm not sure if you remember / but Giskard showed ( in a nice graphical comparison ) that there's no effective difference ( in the notch ) at how one arrives at the correct total value for "R" ( in the LCR ) .

[toddalin]

Also want to take a more detailed look at whether cascading the UHF on the MF yanks the main MF highpass around any. First look said not, but I'm not 100% confident of that.

In the course, I'll try your mod and show what happens. It's clear I can't put this away just yet....

When I tried the three wiring schemes (i.e., cascaded after L-pad, cascaded before L-pad, and non-cascaded, I found some minor variation in drive levels and crossover freqs for the mids and highs. If I remember correctly, the variation was less than 20 Hz.

Readings were obtained driving the crossover with a function generator and a/c voltage readings obtained with a digital multi-meter.

[Zilch]

Thanks, Todd. I confirm your findings:

First study: Does cascade versus direct drive yank the slopes or crossover points around?

Nope (top).

Not at UHF XO, either (middle).

There are some minor variations in the bandpass area, tho (bottom).

I'm back on L200 with behavior similar to previously. Outta phase summing (subtraction, actually,) is shown in black.

Dip in measured 2235H response slips the XO frequency down to 754 Hz. Some of that may be room stuff. I can't get decent windowed quasi-anechoic MLS in the 700 - 800 Hz range....

[Zilch]

Second study: The 1350 Hz peak.

Four LE85s with the same horn and lens.

Orange is the red one on a different HL91, same vintage.

There's a peak at 2 kHz, too. Which is bigger is driver dependent.

I'm callin' it "Ripple."

Compare to the original measurement here:

http://audioheritage.org/vbulletin/s...6&postcount=36

A broad, shallow notch from 4 - 8 kHz would tame any perceived over-brightness.

I don't hear any.

Ship it?

[I'm building up a pair of DMTP XOs. We'll see more over there when they're done.... ]

[Earl K]

Zilch ;

re; post #48,

- It's all very interesting . Nice work !

- It still appears to me that the lowpass section of this network needs work . - IMO, the effective F3 needs to go upwards ..
- Moving the lowpasses F3 upwards, will worsen the "bump" that exists in the 2235H stopband ( down around 950 hz ). This should make worse the existing ripple of the composite response in the 1K area. One solution would be a series LCR ( as a conjugate ) set to 950 hz and inserted between the existing passives ( in the lowpass ) and the woofer . This is a tricky area to work in since it's so close to F3 .

re; post #49,

- The ripples ?
- I see spots for 4 Series LCRs within that horn circuit ( at the present magnification ) .
- What does a lower-rez shot look like, such as one from your Behringer ?
- Sometimes it pays to squint ones' eyes ( to figure out if this stuff is worth going after ) .

Ship it?

- Sure, ( if you stop showing us these high-rez shots of all the "hills & dales" )

[Zilch]

- What does a lower-rez shot look like?

Squint away....

[Zilch]

mbottz: I think we're done, Mike.

Build ON!

L3 is 18 Ga, PE #255-216

L4 is 20 Ga, PE #255-024 unwound to 0.16 mH

I'm running with UHF connected before the MF L-Pad right now.

PM me if you have any questions.

Thanks again to Johnaec for loaning me the 2405Hs....

[mbottz]

mbottz: I think we're done, Mike.

Build ON!

L3 is 18 Ga, PE #255-216

L4 is 20 Ga, PE #255-024 unwound to 0.16 mH

I'm running with UHF connected before the MF L-Pad right now.

PM me if you have any questions.

Thanks again to Johnaec for loaning me the 2405Hs....

Thanks for all of your help on this Zilch. Let me see if I have the recipe right. Attached is the schematic to build with the modifications for L3 and L4 as posted above. This will work well with my 2225H's, LE85's, L91horns, and an added 077 tweeter. Am I understanding you correctly?

Thanks

MB

[Zilch]

Nope, this be the one: