8" sub recomendations

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Pauleo
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8" sub recomendations

Post by Pauleo »

I currently have 2-8" subs in my home made box. They are VERY old. I bought them in separate speaker boxes about 12 years ago. They are MTX Road Thunder II's. They were originally ported and had a tweeter on top of the box for each. About 2-3 years ago I purchased a Rockford Fosgate amp. I think it's only 200 watts or something. So now I have the whole thing together with an aftermarket head unit and I don't like it. Everything sounds good until I turn it up. Then those subs start to "fart" ...err... distort. Do you think it's cause the amp is too small or should I look into new subs?? Keep in mind that I don't want to shake the rearview mirror of the guy in front of me, but maybe shaking MINE wouldn't be so bad.

By the way, I have checked the gain on the amp and played with all the settings on the radio to no avail. Suggestions anyone???

(Also, the new box is not ported and I disgarded the tweeters.)
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Post by AZS10Crew »

If anything the amp might be too powerful for the subs. I was going to suggest turning down the gain and bass levels, but you seem to have tried that. Check the specs on your amp and speakers and make sure the amp isn't overpowering the subs.
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Post by Pauleo »

Thanks, Mark. I am fairly certain that the amp is just around 200 watts. The speakers, I have NO idea. I tried to look before I installed the subs in my box but I didn't see anything. I kinda thought it was the subs though. Everything sounds good at low volumes. It's when I start to crank it a bit that I have to turn the subs down. They distort well before the door speakers ever do! And that says a lot since I still am using the factory door speakers! I'll replace them someday. For now they'll do just fine.

So you think it's the subs? I hear about all these guys running 1000 watt amps and stuff. Mine's just a puny one. Could it really be over powering the subs?????

So, for a budget minded individual like myself, what subs would you recommend? Amperage, wattage, ohms???? Desperately need some help here.

Thanks!!!!!!!!
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Post by Pauleo »

:bump
Last edited by Pauleo on Mon May 09, 2005 7:46 pm, edited 1 time in total.
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Post by coreylubahn »

I have two Image Dynamics 8 inch subs and I have mixed feelings about them (though I think it's something with the box, or just the truck). It sounds great if you move your head towards the windshield some, but in normal driving position they only sound okay. I have a sealed box that is suposed to be the right dimensions but it might just be something with the phase of the soundwave and more importantly the wavelength. I think my normal driving position might be in exactly the wrong position in the wavelength were the sound is quietest at the frequencies that give you that big bass sound. As long as you buy a good sub (not the cheapest out there) that any company makes a good speaker, just watch the recommended wattages closely and try to get something that matches the amp you have. If you have an amp that puts out 200 watts RMS into one channel at 4 ohms and you want two speakers than you should try and find 8-ohm speakers and wire them in parallel (connect the positives together and the negatives together into the amp). When you connect speakers in parallel the load that the amp sees is "halfed" thus 2 8-ohm speakers will look like 1 4-ohm speaker to the amp. Then the power is split between the two, so your 200 watts would be split to 100W RMS to each speaker. Consequently you would really want to find an 8-ohm speaker with a 125-150RMS rating.

Also because of the small space behind our rear seats play close attention to the mounting depth of the subs you chose, the smaller the better in our trucks. Then it's all up to you or whoever builds the box to make sure that airspace requirements are met. From experience I would look for a sub that requires around .3 cubic inches per in a sealed box if you're going with two. My box goes about half way across the back of my truck and the seat no longer latches in the back position and my box is about .7 cubes.

Hopefully this gives you a good starting point. Personally I like anything made by JL, Polk, Image Dynamics, or Boston but there are many, many quality builders out there and these are the only ones that I have direct "sub" experience with.
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Post by AZS10Crew »

Sorry I didn't reply sooner...I can only check the board after work.

Anyway...I've got a pair of Rockford Fosgate 8" subs that are 400W peak in my truck now and they don;t distort much at all at higher volumes. They're powered by an 800W 2-channel amp (200W per channel RMS...which I'm assuming is close to what your amp is). I think I have these, but I'm not 100% sure. They're probably a discontinued model, but you might be able to find them somewhere.
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Post by Pauleo »

Thanks guys! I appreciate your help! As I said before, I don't know much about my subs other than the brand. I did a little research, however, and found that the latest vesions of my subs in the original enclosures that mine came in run around 100W RMS. So maybe that's it! My poor little subs can't handle the amp. That's why it distorts at mid volumes. I guess.

So if I go and INVEST (new word HJ taught me to descibe money put into my CC :wink: ) in some new subs, how should I be wiring them to my 2-channel amp? I mean, can I just run the subs parallel and still use both sides of the amp? Or do I need to just go ahead and commit 1-channel to 1-sub on each side? Does it really matter?

The reason I ask is because right now I have the subs running parallel and am only using 1-side of the amp.

But hey!!! :idea: Maybe that's the problem!!! If the subs are 4 ohms and I have them running parallel using only 1-channell of the amp, does that mean the amp is reading them as 2 ohms???? Ehhh. I don't understand this stuff!! :lol:
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Post by AZS10Crew »

I don't remember exactly how the wiring changes the impedence...I used to know but have drank since then. :mrgreen:

If you have a 2 channel amp, I'd run one sub off each channel. That depends on the amp's power though. If for example your amp is 200W RMS per channel (400W total) and 500W in mono configuration, then run it mono...but make sure your impedence levels are matched.

Crutchfield.com should have wiring diagrams for different sub configurations if you need help.
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Post by Pauleo »

OK. So I finally found my manual to my amp. It is just a Rockford Fosgate Punch 150S. Here are the specs:

4 Ohm load per channel: 37.5 Watts X 2
2 Ohm load per channel: 75 Watts X 2
4 Ohm load Bridged (Mono) 150 Watts per channel

I am running 2 subs off 1 channel. I am pretty sure my subs are only 100 Watts each. From what I understand, because I have the subs running parallel, that means that the amp is reading them as 2 Ohms each??? That means I am only getting 75 Watts from 1-channel and that's cut in half because the subs are run together??? That means I am only getting 37.5 Watts to each sub. Right??? Maybe that's why they distort. They don't have enough power at higher volumes. I don't know.

I would like to get new subs. But if I have to buy another, bigger, more powerful amp, maybe I'll just live with what I've got and invest the money in door speakers instead. What do you guys think?
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Post by AZS10Crew »

Your 2 Ohm mono power is probably going to be a little higher than 150W. When your impedence drops, your output usually increases (see your numbers of 4 Ohm load into 2 channels vs. 2 Ohm load). So that means you might be getting as much as 200W (maybe more) into both speakers at 2 Ohm. Also...those ratings from your manual are more than likely RMS numbers and not peak numbers (RF has a tendency to underrate their equipment) which means your peak output would be in the 300W (or higher) range at 4 Ohm mono...meaning around 150W+ per speaker when the volume gets turned up...which means your subs are overpowered.

In a nutshell...get new subs that are at least 200W peak. 8)
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Post by Pauleo »

Thanks!!!!!!!!!!! That's JUST what I wanted to hear! I didn't understand a WORD you just typed except for the "...get new subs..." part! I have been looking at the Sony X Plods. Do you have any knowledge of them?

(Also, I just figured out that my current subs are just paper. That doesn't sound too good right off the bat!)
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Post by AZS10Crew »

Well...pretty much all subs are paper...it's just whether it's resin reinforced paper or just cardboard style cones.

Sony X-Plod subs are pretty good I guess. To find out info, go to epinions.com There's usually good info on there as well as lowest internet prices.

I'd recommend a sub with 200W peak minimum...preferably one with 300W-400W peak. Just make sure the required sealed box volume and mouting depth fit with whatever box you're using.
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Post by teresav »

I have two 8" polks in one of those custom boxes built for crews (stuffed), run by a 240w max (mono) Kenwood amp. My rear view mirror shakes pretty good. They also make grills for the 8" polks....which I think you need with the seat pushed up against them. On sale at crutchfield right now. I'm extremely happy with them.
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Post by Pauleo »

OK. I'll have to check out epinions.com. Also, I was considering just going with one 10" sub instead. It's probably just as good as 2-8's, wouldn't you think? I guess I should quit whining on this board and just go buy some subs for cryin' out loud, but I wanna get the most "bang" for my buck so to speak! :wink:

Teresa, I have checked out crutchfield. Trouble is that I don't know what subs to buy. Mark's insight has been very helpful though. At least I know what Wattage sub I need. Maybe running one 10" sub with my amp bridged for mono is the way to go. (150 Watts per channel) That would bring up a new question!!!! What is bridging & how do I do it????

(You guys are gonna probably hate me after all this questions!!!!!! :roll: Sorry in advance. :oops: )
Last edited by Pauleo on Mon May 09, 2005 4:14 pm, edited 1 time in total.
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Post by coreylubahn »

Bridging means flipping a switch on the outside of the amp that basically connects the two internal power rails (channels) to make a single amplified channel...thus the term mono (or one). On most good amps bridging will produce a lot more power...and your amp is a good example. You have 37.5 watts into 2 channels at 4 ohms, or 75 watts total, but if you bridge (connect) the two channels you get 150 watts into 1 channel at 4 ohms...that's twice the power output.

As for impedance:

running in parallel: final resistance = (R1xR2xR3xR4...)/(R1+R2+R3+R4...)

running is series: final resistance = (R1+R2+R3+R4....)

You can do a lot of different things with subs depending on the impendance, the amp, the number of voice coils, etc. For instance my two 8-inchers are dual voice coil models (each voice coil is an 4-ohmer). So I run the coils of each sub in series thus making each sub look like a 8 ohm sub (4+4), but then I run the two subs in parallel making the whole thing look like a single 4 ohm speaker to the amp (8X8)/(8+8)=4. My amp was rated at 50X2 at 4 ohms or 250X1 at 4 ohms which means each sub gets 125 watts (and they are rated for 135 watts RMS...I don't pay attention to peak handling myself).

With your amp I would look for either 2 8-ohm single voice coil subs, or 2 4-ohm dual voice coil subs...and run them in parallel...either way your amp will see a single 4-ohm load. As for power rating, I would look for some subs with around a 100-125 watt RMS power rating...that should fit your amp nicely. Also make sure that when you wire everything up you are wiring to the terminals marked MONO on your amp and are flipping the switch (most amps have a switch anyway) to put the amp into MONO mode...you don't just wire them to one of the channels it should be like the positive left terminal and the negative right terminal or something like that to get MONO on the amp. Keep us posted and don't worry we're here to help (we all know how much help I've needed thus far...glad to give something back finally).
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Post by Pauleo »

Thanks for the input, Corey. I need all the help I can get! :lol:
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Post by AZS10Crew »

As far as total surface area, 2-8's is bigger than 1-10...and more surface area means more air moved which is basically what sound is (moving air). But power also has a lot to do with it. A single 6" sub that has a long cone travel and can handle tons of power can outperform a much larger speaker handling less power with shorter cone travel. It's all in how much air the sub can move. There's a powered sub box I've seen made by Sunfire that only has a 6.5" speaker (I think) in a 9"x9"x9" cube that weighs like 60lbs., has something like a 3" cone travel, puts out well over 1000W, and will outperform much lerger subs pretty easily. Of course it costs like $1000, but that's beside the point. :mrgreen:
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Post by Pauleo »

I sure am glad that I have found this board. Mark, I appreciate your help. I just wish that I would consult the board BEFORE I attempt something on my own. Like with my door speakers!!!! Anyway, that's all in another post. I better not get started on that here.

It sounds like I wanna go with the two eights. I guess that makes the most sense. Especially since I already have the box built for them.

Can't wait to get `em now!!!!
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Post by Pauleo »

BTW....

I bridged my amp and now my old 8's kinda sound a bit better! I don't know why but the do. They still distort at higher volumes so I am still going to get some new ones that can handle more Watts, but for now, I am almost satisfied. Besides, I just bought.... er.... invested in new door speakers so I'll have to wait a bit now for the new subs.

Mark & Corey, THANK YOU, THANK YOU, THANK YOU for all your insight!
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Post by AZS10Crew »

No problem...you can owe me one. :wink:
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Post by Walt »

I was fairly happy with my Kicker CompVR 8's for a while. Decent punch, and I was driving them with 90 watts each.
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Post by Pauleo »

Thanks for the input wamason. I still haven't decided on what subs to buy. I did see a pair of Sony X Plods on Ebay for like 70 bucks or something. I almost bought them but found nerf bars on there instead. Went that route so the subs are next in line.
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Post by adrenalnjunky »

I know it's too late to suggest this, but I'm going to do it anyway.

It has been my personal experience that a single 10" woofer can sound better than a pair of 8"s - although that is a generalization based on several things - enclosure design being a big one - but since most of you are building a simple 2nd or 3rd order sealed or vented style enclosure - spending $55 each for 8's versus a $110 10" - you can get a better quality 10, with better bass extension and power handling.

I know there's more surface area with a pair of 8's - but unless you're talking total SPL (which is pointless in either of the scenarios) - cone surface area is really a moot point.

Now some of the higher end 8's like a Kicker L7 solobaric, or anything that is designed for high power handling, is a different breed of animal as well.
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Post by Walt »

adrenalnjunky wrote:I know there's more surface area with a pair of 8's - but unless you're talking total SPL (which is pointless in either of the scenarios) - cone surface area is really a moot point.
I agree :D

Depending on the sub(s) you go with, mounting depth can be a deciding factor in your choice of size as well. 8's have always seemed to give me a bit more mid-bass, or atleast somewhere between bass and midbass, which I like. But when using a single 10, you can give the single woofer more air space.
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