# Ocho's Revisited
**URL:** https://discourse.midwestaudio.club/t/ochos-revisited/774
**Category:** General
**Created:** [September 15, 2026, 9:02pm UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774 "2026-09-15T21:02:43Z")
**Posts on this page:** 14
**Page:** 1
### Author:  [@ScottS](https://discourse.midwestaudio.club/u/ScottS)
#### Post date: [September 15, 2026, 9:02pm UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/1 "2026-09-15T21:02:43Z")
Here is some background info…
One of the projects I had in the queue for a while was an 8" two way based on the SB Acoustics SB20PFC30-8 and a tweeter in the SEOS8 dome tweeter waveguide. Thanks to JR, I had some tweeters in house that look like reasonable candidates to try with the SEOS8 (the Seas 27TFFC). One weekend, a friend let me know about a pair of speakers at a thrift store and wondered if he should pick them up and how much to offer. I couldn’t resist so I said $20 and they took it. They were old Mitsubishi’s with vinyl wrapped particle board cabinets that were at least fairly thick and heavy. The model number is M-FS8.
This particular pair had some interesting customization.
Apparently these needed a midrange, 🤣 so the port was replaced with another driver. Pretty impressive, whoever did that must have redesigned the crossover.
Nope!
The bottom few inches is just a riser, so the overall box for modeling purposes is 32" x 10" x 12.5" out of 3/4" particle board for an overall internal volume of around 47 liters. This happens to be a favorable vented alignment for the SB’s.
Anyway, I wound up making a new baffle, rewrapping the sides, whipping up a quick crossover and bringing the “Ocho’s” to DIY Iowa 2025.
The quick crossover wasn’t perfect, but the speakers were at least entertaining (strong, dynamic bass and enough highs to generally balance that out). Consensus was that they would have made great dorm speakers “back in the day” which I agreed with. They were definitely not perfect. Below is the on-axis sim.
On axis treble is a little hot above 3 kHz and there are some phase alignment issues below that.
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### Author:  [@6thplanet](https://discourse.midwestaudio.club/u/6thplanet)
#### Post date: [September 15, 2026, 9:06pm UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/2 "2026-09-15T21:06:18Z")
Nice! Looks like some padding on that tweeter would smooth things out a bit. Definitely a good rocker set🤘🏼
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### Author:  [@ScottS](https://discourse.midwestaudio.club/u/ScottS)
#### Post date: [September 15, 2026, 11:32pm UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/3 "2026-09-15T23:32:04Z")
Post-show, I decided to finish up the measurement process and see what it would take to move more toward neutrality without losing the strengths that made the initial design fun.
I made some changes to both the woofer and tweeter circuit. The woofer low pass got a little higher in frequency and steeper. The tweeter circuit went from second to third order electrical, but also gained a resistor on the shunt leg. The result was to fill in some of the midrange to better align the woofer and tweeter levels across the crossover region. The changes resulted in the blue curve below vs. the previous gray curve.
Of course, on-axis isn’t the only thing that matters. One of the reasons to use a SEOS waveguide is to align off axis response between the woofer and tweeter, so let’s take a look at that. This plot is normalized with each curve at 10 degree increments from 0 to 180 degrees. The waveguide is doing a good job controlling the tweeter off axis response.
The CTA-2034 Analysis shows smooth predicted in-room response (orange curve) that aligns well with the -0.9 dB/octave slope I like to target. The red directivity curves (early reflections curve is darker red) are also smooth and well controlled.
Now, I still enjoy rocking out to these speakers, but now all of the midrange detail is also there and the highs are not fatiguing. I find myself listening to these quite a bit - even with some nice three-way floorstanders also available.
With Cinergy Audio still selling waveguides and the drivers still available, I will post the crossover design in case someone wants to try these.
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### Author:  [@Steve\_Lee](https://discourse.midwestaudio.club/u/Steve_Lee)
#### Post date: [September 16, 2026, 12:05am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/4 "2026-09-16T00:05:34Z")
Just a touch of PEQ on that design and, Voila! - Studio Monitor quality FR, Scott.
Awesome!
I have a suitable cabinet, those Seos WG’s and exact SB woofers here, just need the tweets and XO components to duplicate your design.
How wide are the baffles, Sir?
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### Author:  [@ScottS](https://discourse.midwestaudio.club/u/ScottS)
#### Post date: [September 16, 2026, 12:15am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/5 "2026-09-16T00:15:06Z")
Baffles are 10" wide.
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### Author:  [@Steve\_Lee](https://discourse.midwestaudio.club/u/Steve_Lee)
#### Post date: [September 16, 2026, 12:32am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/6 "2026-09-16T00:32:37Z")
Perfect, as my current 3way towers are the same width.
I I mis-spoke on the woofers - mine are the 4 Ohm version . . . They are a bit more sensitive than your 8 Ohm versions - probably need to 1/2? the value of L1 inductor but am lost on the the other 2 components you used to further shape the woofer’s response (C1 & C3).
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### Author:  [@Steve\_Lee](https://discourse.midwestaudio.club/u/Steve_Lee)
#### Post date: [September 16, 2026, 1:22am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/7 "2026-09-16T01:22:34Z")
My apologies for this ^ Scott, I forgot it was bad form to ask for XO mods to a published design.
The speakers look and measure great though!
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### Author:  [@ScottS](https://discourse.midwestaudio.club/u/ScottS)
#### Post date: [September 16, 2026, 1:49am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/8 "2026-09-16T01:49:38Z")
No worries. I think there are a few changes that would be needed to use the 4 Ohm woofer. Like you suggested, one would generally use half the inductance and double the capacitance for the larger cap. The small cap creates a tank filter working with the inductor. I think keeping that at the right frequency would require adjusting it in the same direction as the inductor. The real challenge is that the tweeter level also has to change to meet the woofer. If we are lucky, we just need to adjust padding resistors, but usually such exercises also require other component changes for best results.
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### Author:  [@Steve\_Lee](https://discourse.midwestaudio.club/u/Steve_Lee)
#### Post date: [September 16, 2026, 2:22am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/9 "2026-09-16T02:22:28Z")
Excellent!
The thing about developing passives is the wait time for parts and then ordering again/again to tweak.
- DSP avoids all of this . . .
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### Author:  [@Eggguy](https://discourse.midwestaudio.club/u/Eggguy)
#### Post date: [September 16, 2026, 11:59am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/10 "2026-09-16T11:59:59Z")
True. I have bought enough XO components to buy a very nice DSP. No regrets though.
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### Author:  [@KenRhodes](https://discourse.midwestaudio.club/u/KenRhodes)
#### Post date: [September 16, 2026, 1:10pm UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/11 "2026-09-16T13:10:40Z")
If you used the 4 ohm impedance plot and the 8 ohm frd you could probably get to 99% without taking any new measurements.
8ohm:
4ohm
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### Author:  [@Analogkid455](https://discourse.midwestaudio.club/u/Analogkid455)
#### Post date: [September 17, 2026, 4:51pm UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/12 "2026-09-17T16:51:23Z")
I like the small dip at 2500 hz. I hate that frequency! 😅 always seems to give me ear fatigue.
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### Author:  [@ScottS](https://discourse.midwestaudio.club/u/ScottS)
#### Post date: [September 21, 2026, 1:35am UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/13 "2026-09-21T01:35:53Z")
The dip wasn’t really intentional - just a consequence of the driver/cabinet. I will certainly agree that a dip there is far more pleasing than a peak.
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### Author:  [@Analogkid455](https://discourse.midwestaudio.club/u/Analogkid455)
#### Post date: [September 21, 2026, 10:17pm UTC](https://discourse.midwestaudio.club/t/ochos-revisited/774/14 "2026-09-21T22:17:08Z")
I figured it was unintentional but perfect spot for a dip!