Good sub

[kipman725]

Well I got the subs and managed to get almost full t/s parameters. Using bassbox:

File: skytronic.bb6
-----------------------------------------
Driver Properties
Name: 902.163
Type: Standard one-way driver
Company: SKYTRONIC
Serial No: 902.163
No. of Drivers = 1
Fs = 33.5 Hz
Qms = 2.51
Vas = 66 liters
Cms = 0.404 mm/N
Mms = 56 g
Rms = 4.685 kg/s
Xmax = 6 mm
Xmech = 9 mm
P-Dia = 207.8 mm
Sd = 339 sq.cm
P-Vd = 0.203 liters
Qes = 0.67
Re = 7 ohms
Z = 8.4 ohms
BL = 11 Tm
Pe = 150 watts
Qts = 0.53
no = 0.358 %
1-W SPL = 87.5 dB
2.83-V SPL = 88.27 dB
-----------------------------------------
Box Properties
Name:
Type: Closed Box
Shape: Prism, square (optimum)
Vb = 52.83 liters
Qtc = 0.707
QL = 6.831
F3 = 49.77 Hz
Fill = none


not sure about the fill, having non apears to give me slightly more LF exstension. Maximum output is 110dB per sub @ 150W input. With two subs I think this means I get 116dB (6dB boost). However by using a linkwitz transform filter I will be cutting my power handling by upto 12dB in the 25 -50Hz range. I will use a very steep cuttoff filter (-24dB/octave) at 25Hz as they don't have any usefull power handeling. Seems pretty respectable for such low cost stuff.

[bjorno]

.. With two subs I think this means I get 116dB (6dB boost)..

Hi kipman,

In the mid bass at 80 Hz you'll get about 113 dB max. but not at 25 Hz. I vote for the use of 3 or 4 closed boxes. See picture 1(1)

b

1(1)

[kipman725]

Problem is the entire sound system has to fit in the car along with everything else for a year at uni so unless I build the stuff down in London I am very restricted for space. I already have two 0.89m x 0.3m x 0.3m open baffles to take. 93dB is quite low I could use a triode (or simlar solid state circuit) to soft clip any transiants that would cause damage to the sub?

[bjorno]

93dB is quite low I could use a triode (or simlar solid state circuit) to soft clip any transiants that would cause damage to the sub?

Hi kipman

I wouldn't worry.In my listening room things starts already to rattle around 90 dB SPL for frequency's below about 30 Hz.

Two of your sub drivers will produce above 102 dB at 42 Hz where the mid-bass octave ends and for listening music at this possible level is IMO loud enough.

I don't think you should include any transient protection for over excursion, its quite adequate if your sub amp is equipped with a 12 dB HP filter at about 20 Hz even if you are using a LT circuit too.

b

[kipman725]

well I now have one of the subs built in a 400x410x300mm box constructed out of MDF and even from a 30W amp and without equalisation, stuffing or even proper box seal this thing is monsterous. Will get it stuffed and sealed tonight and hopefully get some mesurments in.

[kipman725]

Freq response, done with crappy pc mic due to running over my test mic with my stupid weeley chair. F3 slightly lower than simulated, interesting cancelation at 350Hz not sure what thats about but outside of operating range so no big deal.

[kipman725]

2nd sub done. More than powerfull enough for my needs with two of them. Used old carpet glued to the insides as stuffing it seems to be quite good at attenuating >500Hz.

[GM]

Originally Posted by Moondog55

..........the advice given to me when I started was that OB speakers do not have much below 40Hz.

FYI, 30 Hz dipole woofer array: http://www.stereophile.com/floorloud...er/index5.html

GM