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  #1  
Old August 10th, 2011, 1:05 PM
sisu1a sisu1a is offline
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Subwoofer Projects...

Hi All,

I'm still rocking TN1220's/Model 500 for my mains, and still loving them. I was exited to see talk of plans in 2010 to re-release this legendary sub since nothing beats it's space/bass ratio, but this doesn't seem to have happened yet (Pete?). I have an idea for Team Hsu in this regard, but that will be subject of it's own post...

Anyhow, I have been wanting to bring bass to my rear channels in my HT for some time now. The wallmount Magnepans (MG MC1's) I use for those channels sharply fall off <80Hz. I need discrete L/R subs back there since the speakers are close to the listening position and the x-overs need to be set so high to integrate with the Maggies.

I have a nice pair of 8" M&K drivers from an MX-70b that Fedex killed on it's way to me some years ago, that were begging to have something done with them. Solution to both problems: Make a pair of 2/3 scale TN's! The MX-70 was known for being more musical than punchy, and with their modest magnets baskets and surrounds, the construction of the drivers does seem more focused on voice quality/accuracy/efficiency than super high excursions or splitting SPL's, making them well suited for the task they've been chosen for.

I've taken careful measurements to get everything scaled correct although I'm using a 2" port (tuned ~30Hz...) since proper flares are not available at the odd size it mathematically comes out to. I'm gonna replicate the finish down to the black sock and 3 spiked feet, using top grade materials. I was wishing for another 250w Hsu plate amp to match the one I already have, but I opted for a Dayton APA150 (sexy little shoebox shaped stero/bride-mono A/B amp w/integrated volume & 18dB/octave defeatable x-over) to be used first by itself in stereo (50wpc@8ohm -meh) and later get anther to use them as monoblocks (150w@8ohm!). If anyone's interested I'll post some pics...

-Paul

ps. might be interested in a High End Cross Over unit for my mains if someone here has one lying around...

Last edited by sisu1a : August 11th, 2011 at 12:15 AM.
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Old August 14th, 2011, 11:02 AM
sisu1a sisu1a is offline
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UPDATE: Project moving along. Final design cabinet detail specifics locked down. Using the Sonotube program software, I calculated a 22" long 2"D port will tune the enclosures to 22Hz, and of course I'm using flares on both ends. Mocked up, they look really cool with the Maggies.

My APA150 showed up and well... so far it's a little disappointing as a sub amp in all honesty. I can live with a lack of punch (it's only 150w), but seems to lack definition a bit as well. I'm hoping a 'break in' run will improve it, but at this stage it is clearly not in the same league as the Hsu 250w amp I have. Pulling out my test CD and running sine sweeps only made me sadder. I had to fire up my TN1220's/Model500 and run a 5 minute 25Hz warble to rinse the disappointment out of my ears (and bones).

To the APA150's credit, it sounded excellent running my Ohm2XO's full range, it's just kinda weak sauce for a sub amp... BTW, I've hooked that 250w amp to several different subs, and every one of them sounded absolutely incredible; a testament to it's excellent design and construction. Much to my dismay however, my Hsu amp just developed that faint crackle-buzz that befalls so many older subwoofer amps NOOOOooooo!

I think my best solution would be the Hsu High End Crossover or next best the Outlaw ICBM, coupled to something like the Behringer A500 (cheap but very nice 2ch A/B, 230wpc@4ohm). Well, I've got a possible line on an ICBM so I've got my fingers crossed, but this project is getting expensive...

-Paul
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Old August 15th, 2011, 4:22 PM
Pete_Hsu Pete_Hsu is offline
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Thanks for the notes Paul, we are looking forward to seeing some pics of your project! So sorry that things stalled yet again on the reintroduction of the TN1220HO If you do have any suggestions or feedback, we'd love to hear it.

Sincerely,
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Old September 12th, 2011, 12:20 PM
sisu1a sisu1a is offline
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Overdue update... (long winded, sorry)

After a bit of a saga, I wound up getting an Outlaw ICBM-1, which I'm actually very impressed with, especially after learning I can stack the unused 12dB/octave high passes on unused channels (it has discrete high passes for 2 stereo pairs and 2 single channels!) together for 24dB, leaving me with the very desirable (some would say magic) 24dB/octave high pass, and I'm using the 'special slope' setting of 36dB for the low pass. For the time being, these are being powered by a spare Onkyo THX 100wpc HT receiver running the Maggies and these subs, which it is doing a surprisingly good job with but I digress...

This project took longer than expected for many reasons, but it gave me time to assess the parameters much better and modify my plan accordingly. I made a test rig setup right away after getting the ICBM, which let me play around with all the active parts while I was building the real cabs. My test cabs were made from the 17" long dropcut pieces from my 8.25" Quickcrete tubes that came in 48" lengths. I made some simple foamcore bottoms and used my 2" flared ports in them, at 4" long. The drivers, the foam bottoms, and the ports were all 'fastened' and sealed using Scotch35 electrical tape, and I threw in some scraps of poly-felt I had laying around for good measure. Needless to say, they were uhh, quite limited in what they were capable of doing if I pushed them, but still sounded better than expected and quite effectively demonstrated the importance of stereo sub capability when using high x-over points with nearfield speakers like I am with my Maggies, effectively turning my rear channels into bi-amped full-range speakers.

After playing with them for a short while, it was apparent something would need to be done about cabinet resonances, since a lot of sound was able to come through the rather thin walls of the tubes available to me now. Remembering reading about Ohm Acoustics using lead sheet to deaden the walls of their 'Sound Cylinder' line (I had 2 pairs of these at one point... awesome speakers BTW). After reading on the effectiveness of lead sheet for sound blocking, I couldn't resist. Get this: 1/16" thick sheet lead (4lb/sqft) is the acoustic equivalent of 6.5" of wood, or 2" of concrete!!! I found lead for about $1/pound at a local scrapyard, and bought a recycled piece that was 32x50", weighing in at 59lbs, which works out to about 5.3lbs/sqft. It was challenging to work with, without contaminating myself or my space, but I used lots of plastic sheeting, gloves, dedicated lead tools, and washed my hands about 1000x and threw a lot of things away as I went along.

CONSTRUCTION:
Recycle yard lead came all folded and bent so it was unrolled and pounded flat using a 2x4, then cut sized to tightly fit the inside as a butted-seam tube, leaving me enough for an overlap strip over the seam. I rolled it around the outside first, then worked in inside. The drivers are mounted on stacked MDF rings, with one inside the tube and one butted on the end, glued with cabosil-thickened aircraft epoxy. I mounted the driver rings first, then slid the lead tubes in, butting them against the rings. I used a 1oz bottle of penetrating superglue on each tube, letting it wick into the full joint, then fastened the overlap strip the same way. I spray glued poly felt over the lead once in place, for sound refraction as well as a barrier over the lead. The bottoms were next, which are also two layers of MDF, both of which mount inside the tube structure. The innermost disc butts against the lead, is potted in place with the same epoxy/cabosil mix, and has the speaker binding posts mounted to them. The bottommost layer screws onto that one, and is removable which allows me to play with port tuning if need be, and also allows me to change the sock since it will trap it. It also has the 3 spike feet on it and the flare of the port. I needed the speakers to be black before the sock goes on (so it doesn't show through the white underneath), so I spray glued black craft paper to the outside of the tubes, which also puts a protective layer over the last of the accessible lead contaminated areas.

I still need to get the pics off my phone, the my subs are mostly finished. I tried to capture most of the critical construction phases, but honestly wanting to take pics is what made this take so long since my space is too cluttered to easily get good shots. constructionwise, all that is left to do is to get the socks together and installed. I then need to take some shots of the full size TN's and the cute little Baby TN's together... SOON!

THE SOUND:
Just wow. I was very pleasantly surprised to hear how good the drivers really sound, once in proper cabinets. All that flab, distortion, and clipping went away and they now sound very tight and clean. I've been running the x-over at 100Hz, and getting very nice sound out of the deal. For the first time (for me anyhow), and quite unexpectedly, I am actually satisfied to listen to my rear channels as 2 channel stereo. This is also due to figuring out a little Maggie placement trick, which allowed me to significantly improve the dispersion of their soundfield as well, so I've been in audioblissland for a while now. Due to the extra clean and open nature of the Maggies soundstage, and the unstrained and seamless integration of the subs, sitting on my couch with the rears on now feels and sounds like what I can only describe as sitting inside a giant pair of headphones. When I run them as rears for HT, the additional immersion is just incredible.

With better amps, it will only get better. I have a Jolida SJ502 (60wpc tube amp) I'm going to use on the Maggies, and will be using a Carver M1.0t (200wpc magnetic field amp) for the subs. This project has really rekindled my interest in running my TN1220's in stereo as well, so I may be selling off my Model500 if I find a HSU High End Crossover or another ICBM, likely to then be powered by a Carver M1.5t (350wpc). I built these cabs to very high specs, to make them more future-proof. If I want to step up their performance another level, I can always just put in better drivers now that the cabs are done.

-Paul
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