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Multi-Way Conventional loudspeakers with crossovers

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Old 30th April 2017, 08:11 PM   #1
zcables is offline zcables  United States
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Default Waveguide Transmission Line Monitors

I recently picked up this pair of large stand mount home brewed speakers using Vifa XT25TG30-04 and Dayton RS180-8; thanks pjblakey!. The waveguides are turned from cherry wood and profile is taken from Zaph Audio website. The enclosures are transmission line and scaled similarly to PMC twenty series. They were designed and tested using MiniDSP, but my goal is to finish the speakers and build a passive crossover that makes these sing.

With an initial guess based on the previous electronic crossover, I started with a 2nd order 2-way crossover, the speakers had an impressive start. To no surprise, the bass has great depth and extension for a monitor (bookshelf) speaker for the size due to the TL design, and they will not require a subwoofer for music on first impressions. I have some phase issues to deal with on the tweeter, but as of right now, these would already be good off the shelf speakers without further tweaks. The sound stage is great and the body and sense of space of the music reproduction is just as good.

My next step is to adjust the crossover point up a little from 1800hz, drop the output of the tweeter a little, and see if the frequency response would benefit from a notch filter or two after that.

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Old 30th April 2017, 08:21 PM   #2
Face is offline Face  United States
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You may only need a 1st order electric plus lpad for the HF circuit. Possibly a notch as well. Textbook filters will not work well with a waveguide.

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Old 30th April 2017, 08:56 PM   #3
zcables is offline zcables  United States
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Only 1st order crossover between the woofer and the tweeter, plus tweeter attention and a possible notch? I ready Zaph's write-up of the TMM Waveguide and that's what he used, but it was also a different tweeter and I know that often tweeters can fry with anything less than -12dB.
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Old 1st May 2017, 02:20 AM   #4
seanny is offline seanny  United States
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A tweeter in a waveguide give you some cushion in the lower frequency range.
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Old 3rd May 2017, 10:12 PM   #5
zcables is offline zcables  United States
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Based on the manufacturer graphs on the woofer, it appears that the frequency response start to waver from 1.5kHz - 2.5kHz, but then really drops off after 3kHz. So possibly a 2kHz 6dB crossover would be an appropriate match for rolling off the top end of the woofer until it gets real ugly at 4kHz, and still be a high enough point with the tweeter waveguide mounted? Due to the nominal 4ohm tweeter and 8ohm woofer, tonight I'm going to try a 20uF cap on the woofer and a .6mH coil on the woofer and see where it gets me. I'm also going to try a 16uF cap and .5mH inductor for what should be a 2.5kHz which should be beneficial to the tweeter, but may be detrimental to the response of the woofer.

I'm also going to try a 6dB L-pad on the tweeter as a start.
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Old 6th May 2017, 07:02 AM   #6
zcables is offline zcables  United States
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Testing
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Old 6th May 2017, 01:05 PM   #7
Face is offline Face  United States
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Measurements?

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Old 7th May 2017, 12:49 AM   #8
zcables is offline zcables  United States
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Coming.

For the sake of testing, I know putting two inductors in series creates a total inductance of their added values. Can this reasonably be done in crossover testing without negative effects? Maybe addition of the coils resistances? i.e. I'd rather add a 0.1mh to a 0.5mH for testing than purchase a 0.6mH coil for a possibly unsuccessful test.
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Old 7th May 2017, 01:08 AM   #9
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You'll be fine.

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Old 14th May 2017, 12:31 AM   #10
zcables is offline zcables  United States
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2kHz crossover point sound more natural to my ear than 2.5kHz, but does have some piercing HF energy that probably needs to be tamed. Next will be measuring the frequency response and tweaking.
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