9-driver SLAs L/C/R and TT/THT Home theatre odyssey

[maxmercy]

First impressions first, measurements to follow later.

I've had the Table Tuba for a year, and it was a great match for my old LCR system (Cambridge Soundworks New Ensemble mains, Center Channel Plus, and The Surround 5.1 speakers). The first impetus to build a BFM design came from my old 12" sealed sub's plate amp going south after 7 good years of service.... The old system was good for watching movies at around 20 to 25dB below reference...

So I built the TT exactly to spec, and outfitted it with an Oaudio 300W BASH amplifier. Wow. Much more low end than the old 12" could manage, without even heating up the amp...but as I was doing more reading, and more measuring, I found out that the TT (like all designs) had limitations. The main limitation being my room. I had peaks and valleys all over the place, peaks and valleys that simply would not show up when I tested the TT outside. So I built bass traps and purchased a BFD and used Room EQ Wizard Freeware to tame the frequency response...now I could watch movies at 20dB below reference with clean response to 25Hz and I had a better idea what the sound mixers heard when they mixed the films...but the frequency response was only perfect at one seat. Everyone else got a compromise, so I averaged out the 3 main listening positions, and corrected for the faults they shared to get a better experience for all watching...but I kept the settings for the single seat in another preset for when I would watch alone...

But curiosity seldom remains idle...so I decided to find out what listening at 15 or 10dB below reference was like...and I began to probe the depths of the Table Tuba.

[maxmercy]

I found out that at higher volumes, the Table Tuba begins to complain. At first I thought it was a bad driver, but then the forum discovered that the MCM 8" woofer has 8mm of Xmax, not the 16mm once believed...

I then decided that I needed to high-pass the TT in order to get non-distorted, clean output at higher volumes. So I bought a Harrison Labs HP-SUB unit. Do not waste your money on this. It states that it is a 12db/octave high-pass, but it is only a 6db/octave unit, after measuring myself. I sent the graphs to Harrison Labs, and they ignored me. Lesson Learned. I also learned that the HP-SUB unit introduces plenty of distortion into the signal chain. Clean output at 20Hz was higher in volume with the HP-SUB disconnected than when it was in-line. That was the final decision-maker for me. It resides in a junk drawer now.

So, I used my BFD to high-pass the TT, and got great results when I used a steep 'High-Pass' at 25Hz (basically response would fall off a cliff at 25Hz with a 20Hz -48dB narrow filter). Now I could enjoy movies at 15dB below reference (with a 3dB boost in the low end), all the way down to 25Hz, except for a few exceptions...

Things like the THX Cavalcade trailer, some scenes in Episode II of Star Wars, and especially scenes in the Incredible Hulk just would still make the TT complain a little. So I increased the high-pass equalization to 30Hz by decreasing the Q of the filter, and I got -15.0dB nirvana. Great sound, better impact, but now when I pushed to -12.0 dB, I got distortion from my main and center channels....they just sounded 'strained'....

[maxmercy]

So the plan was set...I wanted 10dB below reference listening as low as I could go. The TT would really only allow this to around 30Hz (clean output), with the steepest of High-passes keeping it in line. The mains began to complain at -12.0dB.

Basically, I was getting great sound at 12dB below reference, about as well as average movie houses can give it...but of course, I wanted more...extension.

So I decided on SLAs for L/C/R, as I could not mount TLAHs due to bass traps in corners...and I kinda wanted the tall, sleek look. My receiver was not rated for anything less than an 8 ohm load, so I decided to make mine 9 woofer, 18 tweeter SLAs. Also, a THT was in order to get that last octave. The driver the THT was designed around (no longer available) had 16mm of Xmax. The now recommended driver for the THT has 8mm of Xmax. The driver I chose has 14mm, to get that last extra bit of output below horn loading. I also chose it due to the rave reviews it gets as far as it's low distortion capability, and the fact that Bill had OK'ed it in the past...

Construction for the SLAs was a bit tedious, using a Jasper jig to cut 27 holes for the woofers and 54 recesses for the tweeters was NO FUN. After that, it was a breeze. My center SLA had refigured angles between baffles (8 degrees between each) for an integration distance that nearly matched that of the original SLA in the plans...

I finished the SLAs in red Mahogany stain and clear, polished lacquer over the Baltic Birch...and made stands to match. Then I started on the behemoth, the THT.

[maxmercy]

After building a TT, the THT came together much more quickly than I expected. After giving the PL 24 hours to cure, I fired it up in the center of the living room. It was as if I was listening to the difference between my old sub and the TT...

The THT is amazing. I remember playing track after track, scene after scene, and realizing that there was plenty of content below 30Hz to be heard (and especially felt) at 12dB below reference... The amount of output was astonishing. The TT could only give me low 80s dB wise at 20Hz before audible distortion crept in, with wall loading. I simply could not find an upper limit at 20Hz for the THT, even as I was approaching 110dB, without wall loading... I decided to stop and get to finishing the THT...I used the same stain and lacquer finish as I did on the other speakers. It took an entire gallon of lacquer to coat this thing. The measurements may not tell you this is a much bigger sub than the TT, but make no mistake, the THT is a MONSTER. It will dominate a small room, unless stood up (I couldn't, as the driver I chose has more than 5% sag).

So now, it is all set up. I have a new reeiver to handle the equalization the BFD used to, a Denon with MultEQ XT on board. Great news is that is also equalizes the SLAs for me as well, and my surrounds. MultEQ XT's greatest flaw is a low-end boost it gives incidentally when doing a level adjustment so that when switching between MultEQ on and off, the volume will sound the same. This 9dB effective low end boost overpowered my Oaudio's HP filter (I got the 500W Oaudio amp for the THT). The Oaudio amp has an adjustable subsonic filter/boost, and when set to 25Hz, the MultEQ XT boosting problems went away, but I also lost precious clean dBs in the 15-20Hz range...I needed a better solution...

[maxmercy]

So I purchased a Reckhorn B-1, and used it's subsonic filter (claimed to be 24db/octave, I measured it at around a 12db/octave slope, strangely enough).

Anyway, the Reckhorn does not introduce any distortion I could measure, and it does it's job perfectly. With my Oaudio amp's subsonic set at 16Hz, and the Reckhorn set around 12-14Hz, I get INCREDIBLE low end, at 10dB below reference. Flat to 16Hz, useful output (can be felt) to 12Hz. Nothing audible or tactile (unless your head is in the horn mouth) below 11Hz.

Note, this is with a 3dB boost in the low frequencies. My receiver has an active EQ function (Audyssey Dynamic EQ) that compensates for the ear's decreased ability to hear the lowest and highest frequencies as the volume is lowered, and applies EQ to compensate, so the same impact and clarity can be heard below reference level...kind of an advanced 'loudness' control. It also boosts the levels of the surrounds so that all the sound does not collapse to the front at lower volumes. Many mixing engineers were brought in to set up the parameters of the Dynamic EQ system, and I really like it.

So, overall, what does it sound like? Real. Like you are in a top-notch cinema, only half as loud, and with greater extension than is available in any THX or IMAX cinema. The only limiting factor is how much your ears are willing to take (seriously, I usually watch now at -15.0 or -20.0dB, and show off the system at -10.0, unless I want to get rocked). Watching more than 1 movie in a row at -10.0dB will leave your ears ringing....Reference levels are simply too damned loud for me, and I am a former Marine...I can't imagine Hollywood mixers having too many hair cells left in their cochleas....

The SLAs work beautifully all the way to -10.0dB, no shortcomings. Audyssey high-passes them at 120 or 150Hz, depending on where Audyssey decides where their -3.0dB point is (it does this for each speaker, and sets the proper delays, as the sub is effectively 25 feet away from the listening position compared to the mains, around 11-12 feet away), and sets up the crossover accordingly.

As time goes on, I'll probe the limits of each speaker (vertical SLA, Horizontal SLA, THT, TT) in graphical form with THD graphs to show what they perform like on paper....I'll also post up some more pics...

JSS

[djohnson573]

Great write up! I really enjoyed reading this and have learned a lot from you regarding home theater. Thank you for taking the time to post this.

[Scott Brochu]

WOW!
You did your homework and then some. Very good reads, thank you for posting.
Whatcha building next

[Turntablist]

Great reading!

I'm quite impressed with your endurance!

Congratulations to a perfect hometheatersystem!

[maxmercy]

Gonna try my hand at some surrounds, actually. But first, I need to finish 2 surfboards before winter so I'll have something to ride this fall/winter season on the coast...

As far as perfect, it's as close as I can get with only one sub...the only way to get even low freq response across a seating area in a small room is to have multiple subs cancelling room modes out. Otherwise, you can equalize perfectly for ONE position. With 2 subs, you can have one row of good listening. 4 subs can give you multiple rows. There are no advantages to more than four. BTW - this is for a rectangular room. The science makes perfect sense, but in a home with hallways and kitchens and flimsy doors to contend with, I don't think the results will be as good as theory predicts, but I think it will be an improvement....Maybe someday, I'll build the ultimate HT. For right now, this is it. I cannot complain at all. For less money than a really good manufactured subwoofer costs, I outfitted an entire home theater, TV and all.

I thank Bill for cranking out such great designs for us to enjoy, and the forum for such great info, especially the Educational Links that Sydney so diligently keeps up with, and the help everyone gives. Without these designs and forum, I'm sure I would be still wondering what a clean 20Hz sounds like at 105dB....

JSS

[myn]

Great write up. I really enjoyed reading your build thread. Ultimately your info convinced me to choose the Tuba HT over the Table Tuba. Thanks for all of your help and tips

[maxmercy]

OK, here are graphs as promised. These are the caveats, though. This is at one listening spot. My receiver setup measured in 8 separate positions, and using fuzzy logic, it decides which problems to correct so that all seats get as good an experience as possible. The room was not set up the way it usually is for movie watching (furniture in different places, the center channel shows the most change, as there is usually a couch between where I measurerd and the speaker), so it may affect the graphs. If I were to do a re-setup with all my measurement positions on the center seat, I'd get an almost perfectly flat graph (I've tried it)....but re-setup takes almost an hour, and I was pressed for time to generate these...The equalized graphs show what Audyssey does to the response, as well as the bass boost it adds at lower volumes, depending on the strength of the signal (less boost for stronger signals). The signal sent to the AVR was at -10.0dBFS, and my volume control was at 10.0dB below reference. All graphs have 1/3 octave smoothing, and only go to around 3kHz, as my mic has a huge response spike at 5kHz and is very inaccurate above 5kHz.

Left SLA (light green with Audyssey eq)
http://picasaweb.google.com/lh/photo/Mp ... directlink
Right SLA (purple with eq)
http://picasaweb.google.com/lh/photo/wd ... directlink
Center SLA (blue with eq)
http://picasaweb.google.com/lh/photo/1t ... directlink

[maxmercy]

Both L&R together (light green with eq):
http://picasaweb.google.com/lh/photo/X- ... directlink
All three without eq:
http://picasaweb.google.com/lh/photo/Bi ... directlink
All three with eq:
http://picasaweb.google.com/lh/photo/kx ... directlink

Subwoofer (dark green with eq)
http://picasaweb.google.com/lh/photo/rQ ... directlink

Sub + mains (purple with eq):
http://picasaweb.google.com/lh/photo/S7 ... directlink

JSS

[myn]

Excellent . Thanks for posting the graphs.

Regarding the 45hz dip with the THT. Do you think thats the room or the sub?

[maxmercy]

The room. Move over to the right two feet, and that dip becomes a boost...

JSS

[maxmercy]

Well, I finally have the numbers of TT vs THT in the depths...

Hz TT THT
12.5 70dB 13% 88dB 5%
15 72dB 11% 94dB 5%
17.5 72dB 11% 105dB 5%
20 82.5dB 5% 110dB <2%
22.5 96dB 5% 110dB <2%
25 99dB 5% 110dB <2%
27.5 105dB 5% 110dB <2%
30 106dB 5% 110dB <2%

All measurements done at centered listening position. From 30Hz on up it's more of a wash betweeen the two, but the THT just spanks the TT in the 15-30Hz octave, and does so while relatively 'coasting' along.

So if you are deliberating between a TT or a THT, it all depends on how much you want that last octave...

JSS