Coaxial 3-way passive floorstander - Seas H1333 and Dayton RS225S

[alexclaber]

The cost and complexity of my previous H1333 plus Linkwitz Transform XLS10 concept has got a bit overwhelming so I'm looking at a passive alternative with similar characteristics.

How viable does it sound to have a 7" coax crossing over passively with a 2nd order electrical filter to an 8" woofer at 200Hz? With the woofer in 40 litres tuned to 30Hz, F3 is 35Hz and it can handle full power from my 50W/ch amp without exceeding Xmax.

The passive low pass on the woofer looks easy to achieve but the impedance peak of the coax looks like it will need an LCR to get correct filter response.

This looks like it will achieve good coherence (important due to relatively close listening positioning), low distortion (due to minimal excursion from the coax) and strong clean bass output (high Xmax and low F3) but I'm sure there must be something I've overlooked!

Alex

[sreten]

Hi,

For those two drivers most of the baffle step would need to be
built into the H1333 to work well, its an unusual choice for a
3-way, one could argue a 2.5 way would be more effective.

By overdamping the H1333 one can ensure the other driver
does more of the bass work and this would have a slightly
underdamped alignment so they add to what you want.

/sreten.

[alexclaber]

I'm intending to place these relatively near the back wall so will have very little baffle step correction if any. The reason for the 3-way design is to minimise excursion on the coax and thus reduce the effects caused by a moving waveguide on the tweeter, with the other benefit being lower distortion in the mids due to lower excursion.

Alex

[Mark Seaton]

Hi Alex,

A coax in a 3 way configuration works quite well.

The tricky part is implementing a passive crossover, particularly one which allows a low crossover frequency. While the production version of my Catalyst uses a much higher power coaxial, this prototype/beta unit worked very well within its limits (limited by the tweeter), and sounded quite good IMO.

The crossover design is a major factor, and while I went fully 3 way active in the final version, the one depicted uses a passive XO on the coax with and active crossover handling the bass to coax transition. Ideally you want to keep the crossover in the 150-300Hz range to minimize off axis variations. With physically smaller drivers you will have less issue with a crossover near the upper limit, as spacing can be tighter.

I also helped with the JTR pro speakers which use an 8" and 12" coax mated to pairs of same size woofers in vented boxes.

Again, the passive crossover below 300Hz can be tricky, and MUST be modeled with real impedance curves, and do keep and eye on the impedance minimums.



Best of luck with the project.

[alexclaber]

Originally posted by Mark Seaton
Again, the passive crossover below 300Hz can be tricky, and MUST be modeled with real impedance curves, and do keep and eye on the impedance minimums.

Is that with measured impedance curves or will simulated magnitude/phase curves from WinISD or similar be sufficient?

Alex

[sreten]

Hi, See Zaphs blog for some H1333 measurements, /sreten.

[alexclaber]

Originally posted by sreten
Hi, See Zaphs blog for some H1333 measurements, /sreten.

Thanks, very interesting! Look forward to his analysis of the results.

Alex

[alexclaber]

For the passive crossover @ 200Hz, should I be using an LCR on the woofer's impedance peak above the tuning frequency, another on the midrange's impedance peak, and then Zobels on both, and leaving the woofer's lower impedance peak uncorrected?

Alex

[alexclaber]

Just worked out the numbers using WinISD Pro for impedance plots and Elliott's info on passive crossover design. Zobels and LCRs as suggested in my previous post. Then putting those numbers into the Passive Crossover Designer spreadsheet generates a plot for the low/mid area that is flat within +/- 0.75dB.

Alex

[alexclaber]

Looking at the few crossover designs for the H1333 I'm thinking they're all unusable because I'll be using a larger baffle and close to wall positioning will little or no baffle step, and it looks like the BSC is totally integrated into these crossovers, including tweeter padding etc.

Confusingly the SEAS Loki crossover appears to be a 2nd order woofer with a 3rd order tweeter (with an additional paralled cap/resistor in series before the crossover presumably to add treble), which leaves me puzzled about the phase at the crossover point.

Is there anything notable I should consider in designed a crossover for a coax design?

Alex