2xAutoTuba results from USAC / DB Drag Race

[Bill Fitzmaurice]

Yup. Infact shortly after, Gately started manufacturing and selling Nolte's "SnailShell" designs in clear plexiglass. They were deamed as being more efficient than a vented alignment. To me they just appear to resemble a Transmission Line:

Not transmission line, which is a quarter wave device, just like a horn. With a pipe length of about 32 inches it would have a resonance at about 115 Hz, at least an octave higher than it should be to be useful. It's a reflex box with an overly long duct. Very much a seat of the pants design.

[horst]

That's what I'm saying. I didn't have the heart to tell anyone there that I was consuming less than 50W. The judge knew because that's what I wrote down on the registration paperwork underneath "amplifier power".

I used the MCM 55-2421 per the plans, the boxes were built exactly as Bill prescribed.

just 28W?

next time really make a meal of it and hook it up to one of these amps
http://www.41hz.com/shop/item.asp?catid=14&itemid=39
a 25x50mm board producing 25W/channel
for extra oompf get the one with the bulk capacitor, still only 25x75mm big
hook it all up with some light duty bell wire to really rub in the salt

[AntonZ]

That's a nice idea, thanks. I've got a few of these small class D boards catching dust. Will check if any of them is happy with 12-14V. They are a lot easier to tuck away into some small cavity in the trunk than my current amp.

[bgavin]

The slanting internal panel in the above graphic is only that: a slanting panel inside a vented box with a long duct.

One of the nice things about that slanted panel is it is an excellent diffuser for high(er) frequencies.
It spreads them into a random bounce around the inside of the box, instead of straight back at the cone.
If the box is damped, they will be absorbed.

[CafSentryGnome]

so im guessing if i build 2 auto tubas my headlights wont dim anymore like they do with my 2x12''

[Radian]

*BINGO* -Stupid loud and no flickering lights. The amp in my Accord is installed in the trunk, and it's fed from a tap into power-antenna motor harness. That's a pair of 16ga wires that stretch the whole length of the car from the trunk to the body control module down by the clutch pedal.

Word of advice: Pack space becomes an issue with a pair of AT's. Don't stuff them in the trunk too tightly. They need "some" room to breathe. 2 AT's in the GF's Ion for the competition sounded ridiculously loud, however 2 AT's in my Accord, not so much. Their performance was not as anticipated even when powered directly from a battery and being fed the same voltage. The Ion has a fairly large trunk, allowing a few extra cubic feet around the cabs, whereas the Accord is very cramped with a pair shoe-horned in there. They take up the entire space of the trunk. One actually sounds better in that car, and that's fine by me. I still like to use the trunk. If you've got a minivan, full-size or SUV, you're golden, but if you've got a mid-size or compact and absolutely require maximum slam, I'd lean towards a single 18" wide HL-10c loaded cab to maximize the use of the space and allow the horn to work as intended.

Remember though...One 8" AT by itself will already rattle your nugget quite well.

[CafSentryGnome]

well my current box is (h)15x(d)20x(w)37 and there is a fair bit of room still in the there. so if there is a design that will fit in that spot i'll be very happy. with me over kill is the only option, you can always turn it down.

it seems ive been doing this all wrong now i'll have to do it the right way.

[paul_ulrix]

yes, one 8 inch already shakes seats and blurs the rear vision mirror, and everything that's loose on the car will ratlle.
My stock car speakers in the doors are distorting way before the autotuba is even breaking a sweat, i should probably upgrade + add another amp to get them on the same volume as the autotuba.

[Rickisan]

CafSentry Gnome said

my current box is (h)15x(d)20x(w)37 and there is a fair bit of room still in the there

14x15x32 is the "standard" AutoTuba dimensions. So you are good to go!

[CafSentryGnome]

i currently have 2x12'' Crossfire (BMF-1228) subs 375wrms 8ohm each powered by 2x380wrms @ 4ohm amp which im guessing is not putting out 380wrms on a 8ohm load. would a single mcm beat that in a 18'' wide auto tuba or will i need the HL-10c?

[John H]

Curious, what is the SPL rating on those 1228s ? I noticed they have no useful specs on their product page.

JH

[CafSentryGnome]

impedance 2 or 8 ohm
re 6.6
nominal power handling (RMS) 375w
max power handling 750w
dynamic power handling 1400w
voice coil 2.5'' 4 layer
magnet weight 85oz
frequency response 20-250hz
fs 26.8hz
qts 0.57
qms 11.49
qes 0.6
vas 2.1 ft / 59.3 lt
xmax 0.546'' / 14mm
84.6db 2.83v@1m

that helpful?
i think i have the old version of theses subs

[Clint Gale]

By my calculations those BMF-1228 should have a SPL of 110.5dB from 250w (125wx2).

An Autotuba with a HL10c should have a SPL of 113dB at 50w and 118dB at 150w.

I have a HL10c that i plan on building a 18" AT for. I have a Dodge Magnum so space is not a concern. I may reconsider the 18" wide version for a 16" depending on how the mockup fits.

[CafSentryGnome]

what would 2 MCMs do?
Edit: we already know what 2 will do, just dont know how it would go in a 18'' wide AT

Radian: what size were those ATs?

im guessing that making it wider increases the sensitivity in the lower frequency range?

what impedance does 2 MCMs have vs 1 HL-10c?

[Radian]

Radian: what size were those ATs?

14"x14"x32"

im guessing that making it wider increases the sensitivity in the lower frequency range?

Yep, just a touch, but over the entire response curve..you'd notice the difference if you A/B'd the standard and wide versions side by side at the same input level.

what impedance does 2 MCMs have vs 1 HL-10c?

When operating in the cab as designed, the MCM 8 and the HL-10C have the same impedence through the passband which is 8 ohms. I had my two boxes in parallel yielding 4 ohms.

Keep in mind, my results were actually not WOT for the two 8" AT's. Do to my gain structure (speaker level input from the head unit to the amp at around .9 volt without distortion, which is far from ideal) I wasn't able to achieve 14 volts at the outputs of the amp. Yes, you can go higher than 14 volts with the MCM 8, but that's my personal fudge factored power compression limit. HL-10C's are much brawnier than the 8's, but so are the price-tag's and weight.

The AT in either guise sounds just flat out better than a normal sub. They're completely honest to the music. You truly have to experience the copious, unfettered bass to fully appreciate what's up with this design. It's like being at a block party every time you sit in your vehicle. Sure, the other vehicles at the sound-off were crazy loud, but they sounded like $#!%. I'm in the Milwaukee area if you ever want a demo, and my GF's car is the one you see on YouTube if you're not near Wisconsin. Listen to the video with good heaphones and compare the sound coming from the AT to the actual Chris Cornell music videos to get an idea of the design's definition and sensitivity.