12" sub and 300W amp....yay or nay?

I've been reading a lot on box design. The sub came with instructions for boxes. I think I'm going to build a vented enclosure. For that, it states that the box volume must be 2.00ft^3, including driver and tube displacement, the tube has to be 4" diameter and 12.26" long. These are the instructions from Infinity for that enclosure. Is there anything else I would need to know aside from actually making the box to those specifications?

Thanks,
Trav

12" sub and 300W amp....yay or nay?

For Xmas, I got an Infinity Reference 12" sub. It's rated 1230W MAX and 300W RMS. The amp I intend to drive it with will be a Jensen 2-ch. amp. It is 300W MAX and 200W RMS when bridged @ 4 ohms (which is what the setup will be since the sub is 4 ohm rated).

Will the amp be alright for the application, you guys think?

Also going to build my own box. Would you guys recommend sealed, vented or bandpass?

Late,
Trav

The amp will work with that sub. Ideally though, you want to match up the RMS rating of the amp to that of the sub or go a little over as it's preferable to slightly over power the sub than underpower it.

The box type depends on what you want from the sub, how much space you have to work with and (most importantly) your skill level in carpentry. A sealed box will produce tighter, punchier bass (SQ) than the restan in general and with a small volume where a bandpass box will give you "boomier", frequency specific bass (SPL) from a larger box. The ported boxes fall somewhere in the middle and, when designed right, can yield good SQ/SPL from a mid-sized box.

I would recommend using WinISD to help design your box and read some books on it too. The more you know about boxes now, the better your first box will be.

Alright - I downloaded a couple of sub box design programs. I put in the information (Vas, Qts, Xmax, Fs) and two of them say that for a ported enclosure (which is what I've chosen), the volume should be 4 cu. ft. However, the instructions from Infinity say 2.0 cu. ft. (including speaker and port displacement). Which should I go with??

Yall think I should go with a rectangular or a wedge shaped box??

Trav

Alright - I downloaded a couple of sub box design programs. I put in the information (Vas, Qts, Xmax, Fs) and two of them say that for a ported enclosure (which is what I've chosen), the volume should be 4 cu. ft. However, the instructions from Infinity say 2.0 cu. ft. (including speaker and port displacement). Which should I go with??

Yall think I should go with a rectangular or a wedge shaped box??

Trav

The volumes that the programs give you, as well as those from the manufacturer, are "suggestions". Knowing this I would stick with volumes close to that of the manufacturer's suggested volume. They designed the speaker so they know how to make it sound best.

The box shape depends on where you'll be putting it. Right now I've got a small rectangular box but will be making a wedge to fit into my trunk better.

Also on the topic of shapes, some people feel that a wedge is better as it eliminates interference of sound waves since the walls are not parallel. Of course there are people that don't share this opinion.

Yeah - I've decided to go with a wedge shape also. It'll be 16" high, 20" wide, 20" bottom depth and 9" top depth.

I'm using PVC pipe for the port. It'll be 4" diameter and 12.25" long. Any ideas on how to secure the pipe to the box surface, other than being meticulous with cutting the hole and gluing it in?

Thanks,
Trav

if you're concerned about the clearence of the port you can always bend it. Cut it a little short and get an elbow to connect and redirect the port. This way the end is away from any walls and you've got the required length.

Aight - I started building the above box and scraped it b/c the port ended up way to close to the back of the box. So, then, I got the idea to steal from someone a little smarter - Q-Logic. Crutchfield recommends a 1.75 cu. ft ported box made by Q-Logic. Sooooo...it's now:
width: 16-3/4"
height: 16"
bottom depth: 18"
top depth: 13-3/4"

I used PCV pipe for the port and mounted it on the top. The opening inside the box is a little close to the bottom - like 3.5" and the port diameter is 4". I'd have liked for it to be a better clearance, but whatever....if it doesn't work okay, I can always build another.

All I have left is cutting the mount hole for the speaker and securing the front panel and I'll be done.

Late,
Trav

I thought I replied to this thread earlier but it didn't go through.

Do not purchase the Jensen amplifier. They are vastly over-rated in their power output and have extremely poor power supply filtering capacitors. This leads to a product which just doesn't hit hard enough. You're going all out on your sub and you're wasting it by going with a Jensen amp.

I opened one of their amps up too. The chassis is all big, but the actual amp board measures only 4x4" ! It didn't even use true Mosfet transistors on the output stage, it used a 25 watt RMS IC which was in a bridged configuration. This is the same IC found in any of today's decent head units, i.e. Pioneer and Kenwood.

Would you want to drive a nice sub with your head unit's rear speaker terminals? I sure as hell wouldn't.

I'm not saying you have to go all out either. Here's some suggestions:


This is a 300 watt into 4 ohms bridged Fosgate amp for $119. Fosgates are always under-rated. My 150 watt 1 channel Fosgate sub amp came with a birth certificate for 218 watts RMS!

http://cgi.ebay.com/ws/eBayISAPI.dl...5740156682&rd=1

This one is buy it now for that price and they have 5 available for the next 6 days.

It would be a perfect match for your sub.

Better yet, I would get this one from Kenwood:

http://cgi.ebay.com/ws/eBayISAPI.dl...5740485139&rd=1

This unit puts out 460 watts RMS bridged into 4 ohms. You can back off on the gains on it and it will also be a perfect match for your sub, especially since its 800 watt peak power will be a good match with your sub. I just finished installing a similar Kenwood setup for a friend a few weeks ago. The SPL is so strong that we will be entering into competition for the lowest speaker volume class. 2 others have asked me to duplicate the setup for them as well.

Even though the Kenwood is factory refurbed with a 30 day warranty, its only $70 buy it now! That's the best deal for your sub, considering all factors.

Actually, it's not an issue of which amp to buy b/c I already own it. I have a Jensen 400W 4-ch. amp running the front and rear speakers. The 300W Jensen I am now using was one I already had. I've already set the system up and it is working fine. The ONLY probem I've had is overheating. The amp shut itself off b/c it got too hot, but this was only because I didn't have it tuned properly. With the aid of an oscilloscope, it's running great now. There's no doubt that a more high powered amplifier would make my sub sound a lot better, but the one I have will suffice for now.

The reason I chose Jensen: it is one of VERY few amps that had ALL the features I was looking for including:

Adjustable HPF/LPF 40-400hz on all channels
Affordable
preamp input and output for multiple amp installations.

The adjustable HP/LP filters are a big plus in my world. I don't want to be limited to 80hz for either LP or HP filter b/c perhaps 80hz is too much bass, or not enough for the particular speaker. It eliminates the need for external crossovers and ultimately saves speaker lives.

A new amp, likely one that you're suggesting, will be in the near future. However, for now - the one I have will do okay.

Trav

Well since you already own it and your happy, then that's what's important. I'm using Jensen subs because they came in a nice quad port bandpass dual 10" package for a decent price with employee discount. SPL is good with them for the money, but sound quality is definately an issue compared to the Fosgate and Kenwood systems I engineered for my friends who had hundreds of dollars to lay down.

I'm sure you plan on upgrading eventually. It will be a night and day difference when you do too! Enjoy the system...