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Discussion Starter #1
Wanting to add a sub to my '98 Cavalier. I dont want to spend a lot of money or give up a lot of trunk space. Should I go with maybe a pair of 8" or a siglee 10" or 12" I am trying to save a much space as possible and would like to go with a single 5 channel amp. I was considering the Arc XXD5080 as it is a very small amp and provides enough power to run the 4 speakers, but only 200 watts at 4 ohms for the sub. Im starting to think this may not be realistic but was hoping to get some opinions on which way to go. I don't mind used equipment if it is in good shape, and I haven't decided to either go sealed or ported yet.
 

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How much power into 2 ohm loads? I assume around 300-400watt RMS? That's plenty. My Infinity Kappa 120.9w and (previously) RE SRX12D4 wired for 2 ohm both run nicely off 250watt RMS channel in a 1cu ft sealed Sonic Sub Box from sonicelectronix, after driver displacement, once they were fully broken-in (but I prefer Kappa). Another sub that could need even a little less power than these (according WinISD) is Image Dynamics IDQ12v3. I'd say, get one of these..
 

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Discussion Starter #3 (Edited)
This particular amp is not recommended for 2 ohm sub. Thats why I was thinking that my approach may be unrealistic, trying to run a sub on just 200 watts. I'd like to stay at 4ohms because everything i've read indicates that 4 ohm is better for sound quality. But I dont have any 2 ohm sub experience to compare that too. This is only my second system, first one is in my truck, a 12" running at 4 ohms, and it sounds great. Also I don't really want to set a budget other than to say how can I do it as cheaply as possible and still have it sound good. I'm not really looking to get loud.

Also, I haven't bought the amp yet, just the one I was considering. Currently have a 4 channel eD amp in there now.
 

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This particular amp is not recommended for 2 ohm sub. Thats why I was thinking that my approach may be unrealistic, trying to run a sub on just 200 watts. I'd like to stay at 4ohms because everything i've read indicates that 4 ohm is better for sound quality. But I dont have any 2 ohm sub experience to compare that too. This is only my second system, first one is in my truck, a 12" running at 4 ohms, and it sounds great. Also I don't really want to set a budget other than to say how can I do it as cheaply as possible and still have it sound good. I'm not really looking to get loud.

Also, I haven't bought the amp yet, just the one I was considering. Currently have a 4 channel eD amp in there now.
You can try Peerless XXLS12 or Dayton Reference HF 12 4ohm SVC subwoofers. Both are considered to have very good sound quality and they also tested well with specialized equipment for low distortions, etc. If you give them 200watts, they'll get louder than my Kappa on 350watts. The only downfall is that these drivers need relatively large sealed boxes. While one of XXLS vendors recommends to put it into a 1cu ft box, I'd prefer something like 1.4 or 1.5 cu ft. WinISD recommends something like 1.8cu ft for XXLS. (There are several versions of XXLS, I am talking about the one that's currently available from Parts-Express and other sources). Overall, I don't think there is a difference in SQ between 2ohm and 4ohm subs other things being equal, but if your amplifier is only 4 ohm stable, then use 4ohm sub I guess.
 

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Discussion Starter #5
a 1 cu ft box wouldnt be a problem if I built it to fit as close to the back of the back seat as possible. I'm curious though, why would you go to a bigger box then is recommended? What would be the advantage?
 

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a 1 cu ft box wouldnt be a problem if I built it to fit as close to the back of the back seat as possible. I'm curious though, why would you go to a bigger box then is recommended? What would be the advantage?

Based on a speakers T/S parameters there exists a "perfect" sealed box volume, in the sense of qtc=0.7, which according to my understanding gives the best compromise between transient response, low end extension, and power handling. If you reduce the box size, qtc goes up resulting in worse transient response and low end extension, and the subwoofer will handle more power at lower frequecies, resulting in better cone excursion control. The reverse happens if you use a box that's too big. This is somewhat of an arbitrary value, kind of like a rule of thumb. Some people say that qtc between 0.6 and 0.9 is just fine. Anyways, the vendors and manufacturers _always_ recommend 1cu ft box or smaller. Why? How many subwoofers would they sell if their recommendation was 2.5 cu ft sealed box? But anyways, to my untrained eyes, it seems like 1cu ft could work with XXLS, but it's not optimal for it. With a lot of subs, getting the sealed box a little off will not spoil the sound, though I personally would have tried a little bigger box in my car, maybe around 1.3-1.5cu ft, but certainly not 2cu ft because usually this results in very low power handling. This is probably not an issue with just 200watt RMS though.

If box size is a concern, you could try instead the 10 inch version of Dayton Reference HF. 1cu ft or smaller would be just about perfect for it. However, your amplifier would have to work a little harder since 10 inch sub has less cone area and needs more excursion to produce the same sound pressure.
 
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