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Discussion Starter · #1 · (Edited)
Alright, I'm not upgrading the stereo in my SI right now, but I do want to do something in my pickup. Truck guys aren't quite as hardcore into audio equipment as import guys are, and my questions are not vehicle-specific anyway, so I'd value any input anybody has to offer.

I've got a 2003 F150 extended cab and will be building a box to fit under the 20% driver's side rear seat. I've been trying to decide between a JL 8W3, JL 10W1, and ID8 V.3. After doing some ready and talking to a few people, I'm sold on ID subs. I'm getting ready to order and ID8 v.3 d2 from woofersetc. I chose the 8" due to mounting depth limitations. The box will be approximately 13.5" in length, 12" deep, and 7.75" tall, and will be a down-firing enclosure. I will use 3/4" MDF for the sides and 1/2" MDF for the top and bottom to allow for maximum mounting depth. My first question is: how much room should I leave for woofer excursion? If I hold the mounting surface of the box 1" off the floor, I will end up with 5.75" mounting depth. How much room do I need to leave for this sub to prevent it from smacking my floor? If the mounting depth of the sub is 4.75", how much free space needs to be at the base of the magnet to allow the sub to function properly?

As far as an amp goes, does anybody know how much power an ID8 can actually handle? I posted up an amp a couple of posts down that I found that seems will work well, but I want to be sure. I could even wire the sub down to one ohm for max output.
 

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Go to a car show and you will see some installs in trucks that desotry the import scene!

I would steer clear of refurbs and Eclipse is like done making amps I believe but they have great stuff from what I have heard and I've heard great things about ID as well so you should have a great combo there.

The ID sub looks to be 250rms so you could run a single one @ 4ohms or perhaps 2 of the subs @ 2 ohms but personally I would want a little more than reccomended power, if you can find an amp that does say 600-700rms @ 2ohms then it would be perfect for the two subs.

Just make sure your box is built to specs and proper tuning as if you want the shot to chest feeling on say a double kick song you need a proper box and an amp with good dampening, thats how fast it responds to multiple singals of bass so it holds your subs and fire them again in rapid succession, well, so Im told, Hans will clear it all up if and when he sees this thread.
 

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Discussion Starter · #3 ·
Very true about the systems in pickups, this board just seems to have more traffic in the stereo section than some of the F150 forums. I put posts out on a couple F150 forums, and on the ID forum as well. You can never have too much information. I appreciate the comment about the damping factor. I will check into that. What is a good number for damping factor as a point of reference?
 

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For a sub amp Class D has become the norm and for speakers A/B reason being is class A/B are more geared towards SQ (so the SQ pepeople say, lol) for handing more dynamic music rangese and notes, where as D plays the boom boom and nothing else in my terms and what I use, lol.

Using class A/B amps to push subs for the most part is very innefficient as they generate a lot of wasted energy which turns into heat!

Great read:
Amplifier Classes

Short and sweet copy and pasta:

Class AB amplifiers are moderately efficient (depending on bias current) but notch distortion is eliminated by the idle (bias) current.

Class D amplifiers are very efficient but are generally used for non high fidelity or subwoofer applications.

class a/b vs class D - DIYMA.com

Some state that A/B sound better on there sub but for the most part eveyone gangs up on them the describe the "better" sound.

I use A/B for speaker and D for my subs and couldn't ask for more.

MB Quart has gone down hill from what I have read as they are owned by maxsonics who does Hifonics, Crunch...etc I would look at Eclipse still personally for what you have given so far.
 

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Discussion Starter · #6 ·
It seems the AB versus D war is like asking what is the best brand of exhaust. I've heard and understand the arguments for both sides. If I was running 12's, I'd definitely go with the class D for the efficient power to move those monsters. Given that I'm going with an 8 though, and am looking strictly for SQ, it seems reasonable to side with the AB side of the argument for my application. I've come to the conclusion that there are no absolutes in life in regards to most things, including this one. I hope to barely have the gain cracked open on this thing by running the D2 sub at 1ohm. I've of the opinion that this will allow the amp to run fairly cool and not put a huge draw on my charging system, while providing me with clean power. The Eclipse is still tempting though. I've ruled out several other really good looking amps, including Diamond, Kenwood, Phoenix Gold, RF, old school Kicker, and a couple of others due to their large footprint and my limited space/mounting options. An Alpine PDX or JL slash would be great, but I don't want to shell out for one of those. I strongly considered a PDX5, but my door speakers seem to do well enough from deck power for my purposes.
 

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First off, the woofer isn't going to excurse all that much. But that doesn't mean you should mount it an inch away from the floor of the truck. Sonically, you will be better off if you elevate the enclosure a little bit.

As for how much power the woofers can take, it depends on the application. For short bursts, you may be able to feed them close to 1000W RMS a piece. Obviously, you cannot play them at high volumes like that for any extended period of time. However, having a larger amplifier than necessary is never a bad thing. It will reduce distortion in the system, and the amp will not have to work as hard to control the speaker.

Amp wise, I wouldn't use either of those amps you were looking at... but of the 2, the Eclipse would be the better choice (pretty much anything is better than Kenwood).

Damping factor for any amplifier halves as you halve impedance, so for SQ, you will be much better off if you run the woofers at higher impedance (4 or 8 ohms). They won't get very loud this way, but the amp will have much more control over the speaker.

A/B vs. D.... there definitely is a difference. The class D stuff tends to sound robotic, and digital (because it is). However, they are more efficient, make more power for their size, and can handle lower impedance loads. The A/B stuff is more natural sounding, but is less efficient and they don't tend to offer A/B amps in large, powerful sizes. If you plan to run a pair of woofers, most A/B amps are 2 channel, allowing for stereo signal. This is very useful for an SQ application, where you can have one speaker recreating the material on the right channel, and the other the left. The only way to do this with a Class D woofer amp would be to use two of them, one on each channel.

If you are trying to get loud, class D is definitely the way to go. Wire the woofers down for a low impedance load (1 or 2 ohms, generally), and stick a class D amp on them in a big ported enclosure with a lot of port area. However, if you are going for SQ, wire them at a higher impedance (generally 4 or 8 ohms), and use a class A/B stereo amplifier, with one woofer on each channel, and place each woofer in its own dedicated moderate-to-large sized sealed enclosure.


Hans
 

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Discussion Starter · #8 ·
I just scored a deal on an amp. Boston Acoustics GT-40 for $43 shipped off the classifieds board. This one is capable of 3 channel operation. 55 watts RMS at 4ohms to my Polk 6x8's up front and 245 watts RMS to the sub at 2ohms. That should sound nice. If it doesn't, I'm not out much for trying.
 

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I forgot to answer your question about air space behind the magnet.

Sonically, having some space behind the magnet is a good thing, as deeper enclosures offer more space for the speaker's backwave to travel before contacting a solid object. Of course, sometimes, you gotta do what you gotta do to make things work in their given space. If you are porting the enclosure, the rule of thumb is to try to keep any part of the speaker at least the width of the port away from any enclosure walls, or the port opening. That would mean if you are using a 3" wide port, you would ideally want to keep at least 3" between any part of the speaker and an enclosure wall or the port opening... but again, sometimes you have to cheat a little.

Function wise, if the woofer has a vented pole piece (a hole coming out of the center of the magnet), then ideally you would want to leave enough space between the magnet and the back wall of the enclosure to allow for the hot air coming out of the pole vent to exit and disperse freely. In this case, you would want a space at least the width of the pole piece (at minimum) between the magnet and the back wall of the enclosure. If the pole piece isn't vented (or you are using it in a low-power application), you can physically get away with having very little space between the magnet and the back wall of the enclosure (1/2" or less, just enough space to keep the magnet from slapping the back wall of the enclosure when the front wall flexes). And yes, unless its built like an absolute tank, the front wall of the enclosure will flex a fair bit at high volumes.

But like I said, sonically, its generally better to make the enclosure as deep as possible for your application, without it becoming impractical. Obviously, physically functioning and sounding good are not the same thing.


Hans
 
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