single 12" sealed side channel

January 2021,

While tinkering of the next house I'll be buying soon. I realized that Dr. Floyd Tool in his book was wrong in describing 5.1 to be superior to 2.0 stereo reproduction (or 2.1 if you add dedicated subwoofers)

After lots of experimentation in my Montreal apartment with 2.0, 4.0, 5.1, 6.1 and 7.1. I vastly preferred 7.1 over 5.1 given few twist were done over the regular 7.1 configuration.

The recommended placement of Dolby 7.1 isn't followed, I seriously dislike the feeling of the side surround speaker to be at 90degree from the listening position. No tuning can make me like it, I always dislike the resulting sonics.

Though my setup fit somehow into ITU 7.1 placement. I prefer referring to it as hybrid Sony SDDS and ITU inspired configuration and must confess that I adjust the gain for the side channel at about 3.5dB lower than the mains.

ITU 7.1

As you can see, ITU is very vague in the recommended placements it provide, observe that the rears and side channels, as long as they are in the grey zone it is considered good. Well their placement do matter a lot I discovered.

Since I'm using the center channel as a 3rd mono woofer for my L+R channel, meaning the center does play only from 55hz to 78hz... Not exactly as planned but that what worked out to be the best compromise in my room. I also had to reduce the spacing between my L+R channel.

My L+R are at 25 degrees and my sides are a 50 degrees, lastly, my rears are 110 degrees.

I liked 30 degree better when the center channel was used but without the center being active, I use 25 degrees, it seems to be the best option.

That means that my 5.1 horn system waiting to be installed in my yet to be bought house, has to grow yet again, to meet the 7.1 requirement!

I have to plan on building a pair of side channels. Since they are significantly less taxed than the rears. Yes, the quantity of information being reproduced and the average outputs level of the side channel is the lowest of them all. No need for a 4x 15" bass bin here. I'm so happy as I didn't wanted to build another pair of 450 pounds monster bass bin again.

I've decided to do away with only 2 ways. It may grow to 3 ways later but 2 ways is the plan for now. I've bought a pair of JMLC horn with a cut-off frequency of 1.2khz and a pair of FaitalPro HF108. This combo should be solid down to 1.6Khz. I may even try a bit lower cut-off, maybe I shall have bought a bigger horn or a 1Khz tractrix, I don't know.

Finding a suitable 15" that can play from ~50hz up to 1.6Khz is not exactly feasible so I've decided to buy a 12" mid-bass driver instead. The Precision device PD12SB30 were on sale at www.Solen.ca and I pulled the trigger. I already had a pair of Precision device for my rear channel so the sonic match should work.
The PD12SB30 is the same as the newer PD123C10 with a slightly different T-yoke backplate, both datasheet show the exact same data and graph... Way to go Precision Device, use a new name for a driver and call it a new driver. LOL.

the free air impedance sweep show a resonance at 314hz, both driver have it. It wasn't shown on the datasheet but mfg. always hide flaws in their graphs. The 1K5Hz resonance are also a tad troublesome as it will fall within my intended crossover point but I'll find out more once I measure them in a proper box with EQ applied.

I'm very happy to see that the Fs is within specs at 47.7Hz. This is a new driver, with burn-in and suspension softening, the Fs should fall down to 46 or 45Hz. 3%-5% change is quite realistic for such driver.

I think that a 40liters sealed enclosure will work great.
T&S parameters suggest a sealed box of 40liters will have a -3dB at 110Hz but once I add some equalization, reaching ~55hertz won't be an issue.

Update March 2022.

I finally built a pair of sealed box for the 12''

I'm sorry, I totally forgot to take picture along the way but I followed my usual strategy of:

-generous internal volume for a low resulting system Qtc

-significant internal bracing

-double thickness 5/8'' all around (my local hardware store was temporary out of 3/4'' sheet of plywood so I went with 5/8'' thickness)

Initial test setup:

-Selenium HL14-50N horn

-Radian 760NEO

-This combo is good from about 800 Hz-8 kHz (the Radian 760NEO isn't extremely good above 10kHz)

-PD12SB30 in a sealed cabinet (internal volume of approx 55 liters)

-good 55 Hz to 600 Hz but somehow ragged above that

-The 12SB30 has a strong peak at around 780Hz, this was unexpected from the datasheet and I had to somehow fix this.

Note, I've reinforced the bottom of my broadband diffuser to support the weight of the 12'' cabinet. I've even added 2 caster wheels.

New generic horn bought off Ebay:

The Selenium HL14-50N horn is so tiny in comparaison. The Ebay horn is 18'' wide and doesn't incorporate a diffraction slot.

With the bigger horn, the Radian 760NEO can now confortably play from 600 Hz-8 kHz (low end being limited by the 760NEO as the horn support frequency down to about 500 Hz)

-PD12SB30 in a sealed cabinet can now be crossed lower and I can get rid of the strong 780Hz mode of the woofer.

Test setup #2.

-Radian 760NEO (600 Hz - 20 kHz)

-PD12SB30 (55 Hz - 600 Hz)

I had to hide the 2 dedicated amplifiers behind the horn, I may change that later and maybe build a small shelf or something.

Further change:

I plan on adding a high frequency driver above the 760NEO as it kinda of struggle above 8 kHz (need a lot of DSP and resulting rise in distortion product isn't optimal.

I have a pair of B&C DE35 laying around, collecting dust, that I will use for initial testing.

The DE35 would be decent from around 9 kHz and up. I just need to build yet another pair of small monoblock amplifier. I already have like 22 of them playing in the system. Why not go to 24 small monoblocks... hein, why not?