Help me balance SQ and SPL and weight for my sub - diyAudio
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Old 23rd February 2007, 05:09 PM   #1
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Default Help me balance SQ and SPL and weight for my sub

Ahh I havent been here in a while but I've got an itch to build a higher quality car subwoofer. I figure I'll put this in here rather then the car forum since more DIY enthusiasts frequent here.

Last night I tuned my car with my Velodyne SMS-1's analyzer (that I usually use in my home system). Put a display monitor on my hood and analyzed away. I adjusted the phase and EQ settings on my AudioControl crossover to optimize the sound.

I currently use a commercially made 15" car sub (of decent quality but its stamped steel) in a 1.75 cubic foot sealed sonotube in the back of my car. As expected there is the typical car audio bump from 35-65 Hz. After the phase correction and EQing it sounds pretty good, however it only plays to about 33 Hz before it rolls off. i pushed the 25 Hz EQ a bit to get a little more extension but still its dissapointing. In a car it should be easy to get to 15 Hz.

Sooooo.... I'm looking for some suggestions:
I require:
-High quality sound AND ability to get somewhat loud
-Ability to play flat to 20 Hz in a sealed enclosure in a car with minimal EQ "push"
-12" or 15" (or in between) preferably 15"
-4 ohm, single or dual 4 ohm voice coil (no 8 ohm SVC's)
-high power handling
-Light weight
-Passive radiator or sealed chamber (no bandpass or ported)
- not to be ridiculously expensive
-work in a 1.5-2.5 cubic foot enclosure


I looked at Parts Express they have some Dayton drivers that look appealing, though the beefier ones are too heavy.


Madisound recommended the following drivers to me:
1) 15" Aura Sound.
Its too expensive and way too heavy so its out.
http://www.madisound.com/cgi-bin/ind...56.6182&pid=98

2) Peerless XXLS 12" with 12" Passive radiator
http://www.madisound.com/cgi-bin/ind....6182&pid=1790

3) Scan Speak 10"
http://www.madisound.com/cgi-bin/ind....6182&pid=2012
http://www.madisound.com/pdf/scanspeak/26w_4867t00e.pdf

High quality indeed, but from the specs and power handling it isn't gonna get too loud.

I know this is a difficult preposition but right now I'm liking the Peerless 12 + passive combination right now. I'm all ears!

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Old 23rd February 2007, 06:11 PM   #2
owdi is offline owdi  United States
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1.5 cu ft. is really small for a 15" sub. If you want response down to 15hz you will need to build a low Q sealed sub. Something less than .65 should be good.

For car audio I like to use two drivers, pointed away from each other. This will greatly reduce mechanical vibration without requiring a very heavy enclosure. Since you have only 1.5 - 2.5 cu. ft. to work with, you would have to use two 10" drivers. Anything bigger will not give you the low Q you need.

It sounds like your budget is around $300. How about a pair of Peerless 10" XLS drivers in 2 cu ft?

Dan
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Old 23rd February 2007, 07:31 PM   #3
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Thanks for that reply. This is pointing me in the right direction. I looked at the Peerless driver, looks pretty good.

I remeasured my enclosure, it is actually 2.2 cubic foot. I'm starting to like the 2 10" idea. I'm going to crunch some numbers, I'm also considering 2 of the previous-mentioned Scan-Speak woofers.
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Old 23rd February 2007, 08:28 PM   #4
beerman is offline beerman  United States
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Don't forget about cabin gain.

Design a sealed enclosure's F3 to fall within the cabin gain range and you're set. That's not difficult with most 15s.

WinISD's forum has a thread detailing to model it with the Linkwitz transform function in the WinISD Pro software (free alpha release download), though a few graphs are null and void.
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Old 23rd February 2007, 08:39 PM   #5
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Right, this is going into the back of a C5 Corvette coupe. I have the luxury that the woofer is actually in the same airspace as me (rather then in a trunk, for example). I'm not sure what the cabin gain is. The car is relatively sensitive to weight in the rear, so I'm trying to keep it as light as possible.

I use BassBox Pro and it does have transform function modeling, however like any software generated "theoretical calculations" it isn't always accurate. I calculated solid performance to 17 Hz with my current setup, but its obviously way off the mark It also does not do passive radiators.

I may order the Peerless 12" with Passive Radiator. I've never played with a passive setup before and think it will be a sweet sounding rig without too much work.
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Old 24th February 2007, 08:32 PM   #6
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Well I may have figured out why my current sub wasn't playing that low. The AudioControl 24XS crossover I'm using for bass/midbass has a preprogrammed 33 Hz, 18 db/oct high pass filter. WAY too high. Couple that with 15 Hz high pass on the Audiocontrol DQX low pass on the EQ unit and thats a major slope. I'm going to change the resistor values and hopefully reprogram it to 15 Hz and I'll report back. I'm having a hard time finding 360K-480K ohm resistors though
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Old 25th February 2007, 01:39 AM   #7
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YUP! That's what it was. Turns out the local Radio Shack had 470K ohm resistors. Though they were 1/2 watt and 5% carbon. They will do for now. They were physically a bit large to fit in the slots so I had to pursuade them to go in. After I put them in the subwoofer definately plays lower, both to ear and to RTA. Woo hoo!

I will now order 1/4 watt metal film 1% resistors.
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