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using car/home audio equipment as a part of your rig?

Discussion in 'Amps and Cabs [BG]' started by Casey C., Jul 9, 2002.


  1. geshel

    geshel Supporting Member

    Oct 2, 2001
    Seattle
    Thanks dude. (ego doubles yet again, wipes out small town) :D

    Funny because here in Seattle, nobody has heard of the place.

    It might not be so good much longer because the Board of Trustees has a hairbrained idea to eliminate the engineering majors (which are independently accredited) and go with a "one-size-fits-all" program with "concentrations". ACK! The faculty and alums screamed bloody murder about it and the plan is on hold right now but no promises were made. . .
     
  2. Hmmmm, just wanted to add my 2 cents, don't want anyone to get mad at me. I have my peavy combo within a metre of my computer, cos i run bass the the computer through it and i am yet to see any adverse effects on the computer. Thats just from my experience.

    Bassis.
     
  3. 1. In my spread sheet, the average EBP for subwoofers is 72 where less-than 50 specifies a sealed box and greater-than 100 EBP indicates a vented type. The median box size is 4.1 cubic feet, and the average box size is 7.6 cubic feet, for the subs I have in my spread sheet.

    2. I have 212 subwoofers cataloged. The average diameter is 12". They range in efficiency from 81.9 to 99.5 SPL. The average value is 90.1 SPL, and the median value is 89 SPL. Yes, this is not terribly efficient. Counterpoint, pull (1) driver from a typical 4x10 and measure how efficient it is *by itself*... comparing 1 driver to 4 drivers is an apples/oranges comparision. There is a significant mutual coupling advantage with 4 drivers. Compare 4 subs with 4 tens and things get a lot closer to parity.

    3. Absolutely. The voice coils on my subs will withstand 1,000 watts before they melt. The difference between a sub and conventional bass driver is the amount of *displacement* limitation that have at the bottom frequencies. Drivers with short Xmax values cannot accept anywhere close to their maximum melt-down power, because their cones will over excurse and destroy themselves. None of us play at 1 watt, so small signal measurements don't reflect the playing environment. At higher power, the small Xmax drivers cannot accept much power before they bottom out at low frequencies. This is why the tuning frequency is so critical.

    4. Absolutely. I run my subs as 8 ohm loads, rather than 2 ohms. This way I can run 4 of them instead of just one.

    5. The Cabin Effect is worth at least +20dB in the very lowest range. A sealed box rolls off at 12dB/octave, a known factor for all sealed boxes. The cabin gain is inversely proportional to the rolloff, hence an almost completely flat response to 20 Hz or below, inside the cabin. A vented box in the cabin is a booming disaster, because it has too much bottom.

    My four subs can be measured and compared to a 4x10 cabinet. This is a more accurate comparision because the number of drivers are the same. Using real world measurements, each of my 1x15 subs is worth an honest 89 SPL 1w/1m. A pair is worth 92 SPL, and two pair is 95 SPL. Hmmm.. my four 1x15 is exactly the same SPL as the Acme 4x10...

    At this juncture, we have four 15" drivers producing 95 SPL, and four 10" drivers in an Eden D410XLT producing a claimed 106 SPL *at an unknown frequency*. I did not response-plot the Eden box I tested, but can state with certainty it produces almost nothing at 30 Hz. And certainly not any 95 SPL 1w/1m... all it did was flap around. The D410XLT reaches maximum output around 81 Hz and falls off rapidly below that point.

    I can borrow the D410XLT from my daughter's bassist and do some response measurements when it stops raining.
     
  4. geshel

    geshel Supporting Member

    Oct 2, 2001
    Seattle
    After this thread I found this:

    http://manuals.harman.com/INF/CAR/Boxes and Parameters/KAPPA PERFECT 10-1 Enclosure Sheet.pdf

    Which I think is pretty enlightening on the subject. First, Infinity is a pretty well-respected company, and I think their Kappa Perfect subs have a pretty good rep. From what I see, they would make great car subs. But let's look at what's going on.

    First, Infinity rates the efficiency at "94 dB (in car at 40Hz)". Nice of them to provide a frequency, but the "in car" stuff is kinda lame. It's true that that's what matters, but it'd be nice to have a free-air / half-space number as that's something objective that can be compared to other speakers. The question is, in *what* car, in what box? The first half we don't know, but from looking at the charts we can see that the driver, in the bandpass box listed on the second page, hits about 94dB at 40Hz. The sealed box design only reaches 89dB at 40Hz, whereas the ported box hits about 99dB!

    These numbers are also at 2.83v, but since this is a 4-ohm driver that corresponds to about 2w.

    It's hard to tell for sure, but it looks like the "real" efficiency of the driver is about 85dB 1w/1m. A pretty big difference from the only number they make it easy to find, 94dB! If another manufacturer marketed an identical driver, and listed the "real" efficiency spec, nobody would buy it! Because the Infinity looks so much better.

    The "in-car" performance of the bandpass box is very nice, and if I put subs in my car I'd give these pretty serious consideration (love that 14mm Xmax!). But, it's really a shame that Infinity has to obfuscate things in their specs listing (as I'm sure they know what they're doing).

    This has just been one rather enlightening example. . .
     
  5. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Santa Ana, Calif.
    Former Technical Communications Developer, QSC Audio
    Just to make sure I wasn't hallucinating, I asked a couple fellow engineers if antistatic bags have any magnetic shielding properties. Everyone agreed that it would be a mighty feat if they ever did. ;)

    In order for such a bag to be a magnetic shield, it would have to have some amount of permeability. Just because a material has some usable conductivity, it doesn't mean it's permeable. Mu metal is permeable; so is steel, iron, and nickel. Copper and aluminum, for example, do not.

    Even the shield in a typical signal cable doesn't protect against magnetic fields, only electrical ones. In fact, an unbalanced signal cable has practically no protection against magnetically-induced noise. Balanced cable, OTOH, has two (sometimes four) signal conductors twisted together so that both the + and - conductors are as equally exposed to magnetic fields as possible. As long as the input and output the cable is connected to each have equal impedance to ground on both the + and - legs, the voltage induced will be the same on both legs--that is, it will be common mode--and will cancel out at the input.

    BTW, I can remember when RAM was magnetic; the computer I learned FORTRAN on in high school (1976–77) was an old NCR Century 50 that took up almost a whole room and had a whopping 32 KB of random-access magnetic core memory. The memory itself looked like a couple square inches of metallic fabric with thousands of tiny embedded beads. But magnetic RAM now is really antique.
     
  6. Way back when, I was an IBM field engineer and had the dubious honor of sewing a new magnetic core (donut) into the X/Y matrix of a failed core assembly. I got the assignment being the youngest and the best eyes (that has since changed).

    These were 32kb units that had their own built in heater to maintain them at 100 degrees, and required at least two guys to move one around. The larger 64kb units were on wheels, so one guy could push it around easy. I've moved a few of those at Bank of America, a long, long time ago.

    And replaced/aligned lots of heads in crashed disk drives, too. Other than being employed, I don't miss that stuff at all. I much prefer 120gb in a toss-out disk drive, and 512mb memory in a single stick. No heater required.

    :D

    For the record, I don't own a car with subwoofers, or one with even a tape player.
     

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