Questions about the weakness of my sub. - diyAudio
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Old 14th July 2004, 12:22 AM   #1
S.C is offline S.C  United States
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Join Date: Jun 2003
Location: Milpitas
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Default Questions about the weakness of my sub.

Somebody had already known that I built a sonotube sub for my car, but I have problems after a month of tuning.

This sub is running pretty good with my Blaupunkt PA2150, a 180W 2channels/ 400W bridged amp, in my 96 Honda Civic coupe.
However, I started to notice the sub was like cliping ( or maybe it isn't) as soon as I opened up the trunk lip. Is it really cliping?

This is my first setting:
HU: High pass 170Hz cut off, Low Pass thou
sub amp: Low Pass 250Hz cut, the maximum of the low pass (from 50-250Hz)
It sounded really good although some bass might sound muddy, the high pass 170Hz made the front speakers sound good, and the sub could really intergate into my car without noticing it. I can notice the quality of bass from the sub is way better than my 6 speakers woofer units. Eventhough it sound good in the car, I notice some weird sound when I listern to the sub from the opened trunk.

This is my 2nd setting:
HU: HP 100Hz, LP thou
Amp: LP 100Hz
After playing around with the setting of LP in the amp, I came up a solution that the weird sound will be elimate when I set the LP to 120 or lower. However my sub FR rating is 40Hz-500Hz, how come it sound weird after 120Hz, and it sound prefectly fine with 120 to lower with whatever setting of the V into the amp.

Ok, finally I came up these possibility:
1. the sub is in isobaric system so it can't handle higher than 120Hz. This is a guess only.
2. My sub enclouse is too small that affect the FR, and I think this is the most possible.
3. My sub amp have problem which is already underpower, but I don't see this to be a problem that the 120Hz to lower won't souind weird or clip in the lowest to the highest setting of the V in on the amp

These is the spec of the Sub, amp and hu. I have a sonotube sealed sub in a little bit small than 1.25ft/cu enclouse.
Subwoofer driver: JBL LC-S1200W
Recommended Amplifier Power Range: 12-200W
Sensitivity: 91dB
Frequency Response: 40HzV500Hz
Mounting Depth: 5" (127mm)
Cut-out Diameter: 10-3/4" (273mm)
Thiele and Small Parameters
Nominal Impedance: 4 Ohms
Revc: 3.45 Ohms
Fs: 27.4Hz
Vas: 124 Liters
Qms: 3.18
Qes: 0.37
Qts: 0.33
Mms: 109.2g
Levc: 2.2mH
Sealed-Enclosure Specifications
Enclosure Volume 1.25 cu. ft. (35.88 Liters)

HU: Kenwood KDC-MPV5205 MP3/CD reciever:
- Preout Level/load (During Disc Play):
2000 mV /10 kOhm
- Preout impedance:
< 600 Ohm

Amp: Blaupunkt PA2150 Class T Amplifier
"Birth Certificate"
1.RMS output power : bridged (4Ohm) @ 1.0% THD
= Min power in any channel 480 Wrms.
2.RMS output power : non-bridged (2Ohm) @ 1.0% THD
= Min power in any channel 180 Wrms.
3.@ Rated power, bridged mode - 51 Amps
4.@ Rated power, non-bridged mode - 32 Amps
5.@ 33% rated power, non-bridged mode - 11 Amps
6.@ 10% rated power, non-bridged mode - 5 Amps
7.@ idle - 1.5 Amps
8.@ Rated power, non-bridged
A weighted
Average Value for all channels >100db
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Old 15th July 2004, 12:10 PM   #2
tuneman is offline tuneman  Australia
diyAudio Member
Join Date: Feb 2004
Location: pitts of hell!!
first off subs don't clip, amps do!
are yours gains setup right? mabe your driving it to hard!

the second crossover settings are my choice! 100hz low pass and 100hz high pass,
170 is a bit high for your fronts and 250 is way to high for your subs, you will be getting some serious midbass coming through and just sounds bad as well as pulling your soundstage backwards.

a general setup for crossover points would be-
front speakers- play from somewhere around 80 to 100 hz and up
sub- plays from say 80 to 100hz and down
your isobaric setup is fine, remembering that they are by nature quite inefficiant, and you have no need to play any higher than 120hz!
for a 10" its not a bad sise but could be bigger to make up for its inefficiency in a isobaric setup, dont expect that much low freq from it setup that way.

when you open the boot you lose power handling due to pressure loss! due to the loading effect of having it in a boot, its quite a common problem but nothing to worry about seeing as its normally closed
my best assumption is you need to go over it and set your gains properly, buy the sound of it you have been using them like a volume control! not good
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Old 26th September 2008, 01:35 AM   #3
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Join Date: Sep 2008
I'm with Tuneman check your device settings on the amplifier. As for "clipping" or distortion when the trunk is open... 1st check the phase/polarity of your woofer, then check your box volume. If your enclosure is tuned correctly it should sound the same no matter what, trunk open/closed, doors/windows open/closed
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Old 26th September 2008, 02:26 AM   #4
jol50 is offline jol50  United States
diyAudio Member
Join Date: Nov 2007
Isobaric, you mean you have two subs in the tube?

I never run a sub over say 70Hz at most. If you don't have midbass then you need to work that out with your mids. A trunk (boot) will act like a weak LP and lower it more than what the crossover is set, but not that much I think 100 is too high. You could try to stuff the box to smooth it out, but if that is one driver in there sealed it will be tight. I always go larger than minimum recommended, manufacturers love to list too small a box. Unless you like the SPL type sound, I don't like 50Hz only I want 30 at the least. Running that kind of power I would have tried a larger ported tube, but that's up to you and maybe you can't have larger in space you have.

Car should sound reasonably good without the sub, if not then deaden your doors/etc and try to get more midbass. Turn the bass up on the HU and lower your sub gain and stuff like that. Also try moving it around in trunk. Nearly any sub will sound strange crossed at over 100+ IMO, but I do have a P5 explode 12 I test with that works ok full range. I'm guessing it has a lot of inductance, maybe the cone is heavy. Most subs blast at 100hz this one peaks at 50-70 in a recommended 1.2cf sealed I think it is, and is stuffed because I could not get it to sound right in a car.

If you really want to run it higher than 100hz, then you need a parametric or low tuned enclosure to smooth it out in my experience. Sometimes you can get it to work with an adjustable slope or dual LP crossovers, you need to cut the above 80Hz down so it fills in and you really don't hear it from the sub. Has to be adjusted to the car/sub setup. Used to do this a lot with IB subs to pump up midbass without you thinking the subs were doing it. If not right the sub will localize itself.
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