I just recently got a 12" MTX 4000 sub... it is bridged to the rear channels of my MTX 6304 amp (giving it around 150 watts, underpowered... but whatever)
My 4 Polk side speakers are powered by the front left and right channels and I had a question...

at low frequencies, or when the gain/bass booster is pushed up all the way, the sub tends to 'boom' and gives out ****ty bass... at low volumes it sounds perfect...

Is it sounding this way just because the Sub is underpowered? or what steps should I take to solve this problem? It is wired correctly into a 'mono' configuration... so I am just confused...

its in a great box, and everything... so just give me some help!

 

You said it yourself...

 

Pretty much, plus bass boost and cranked gains make stuff sound like poo.

 

you can help a little by putting a little more polyfil in the box. It helps with those higher notes by softening them. If there is an adjustment for -/+ 12db at a certain freq. you should turn that down. If you use that to make the lower notes louder, it will also make the higher ones distort.

 

So the problem is more than likely I need a mono amp to power the sub so it is properly powered? That will more than likely fix the 'boomy/bloated' sound? I always thought that you can always 'underpower' a sub/speaker but you should never overpower it... I'm guessing this doesnt apply here because it is only getting 150 watts, but it still shouldn't be 'booming'... should it?

the sub hits all the notes fine... its just at the low frequencies it booms/bloats

but anyways...

does anyone have any suggestions on what type/wattage of amp I should use?

 

Well, wait. What is the RMS wattage of that sub. They are only like 200 arent they?

 

I don't believe simply "underpowering" a sub would make it sound like you describe. It seems more likely that you have your gain improperly adjusted, your crossover points wrong, bass boost wrong, or some combination of the three. These can cause VERY audible distortion. This word "underpowering" keeps popping up on these forums and I find it quite amusing. If you "underpower" any speaker, so to speak, to an enjoyable listening level WITHOUT clipping the signal to the speakers, that's a good thing. Any time you turn down your volume ****, you are "underpowering" your speakers. And the speakers like that. RMS ratings are merely CAPABILTIES, and are used as a warning for the user, so that he is aware of how far to go in setting up his system. It does not, and never has meant that the speaker in question HAS to be driven with that amount of power to be effective or perform properly. Especially if we are talking about going from 150 watts RMS to 200. That difference is laughable, in terms of being noticed audibly. In fact, if that amp is capable of 150 watts RMS and the sub can handle 200 watts RMS, then that's a pretty good set up. That is, IF everything is set up correctly AND the amp is not driven into clipping. However, if the user wants to treat a set up like this as if it's a 1000 watt RMS capable system, then you will get into issues like you describe. It is what it is, nothing more. It will not sound like some megawatt SPL set up.

 

I agree with 97f250. You have the gain and boost levels too high.

 

The gain adjustment is not a "booster", by the way. Or a volume ****. The voltage of the head unit's preamp outputs is what determines how you set the gain. You can't just arbitrarily turn the ****. If you have a multiple amp set up that will change how you set the gain to some degree. An example; if you have a head unit with 3 volt preouts(RCAs), which is pretty common, it will drive an amplifier to produce its rated power when the gain of the amp is set at 3 volts. The higher the output voltage on the HU, the less gain you need to use on the amp to drive it to its rated power, which is a good thing, within reason. If you have a HU with 5 volt outputs and your amp's gain only will adjust up to 3 volts maximum(pretty common), that is not a great match and the HU will drive the amp into clipping at a much lower volume setting on the HU, compared to the previous example. This can be a bad thing if abused. On the other hand, if you have a HU that has 1 volt preouts and your amp adjusts up to 3 volts, you will have to turn the gain "up", because of that lower voltage so that the amp can make its rated power with that HU. The tradeoff is a sacrifice of sound quality to some degree, compared to if the gain was turned down to 3 volts with a 3 volt HU. This is very often overlooked and/or disregarded as to importance, but it is very important to have a HU and amp/amps that are compatible in this way. Another example; let's say you had an Eclipse HU with 8 volt preouts, and a cheap amp with a gain maxing out at 2 volts. That HU would drive that amp into clipping at such a low volume that it would be unreasonable. This is another way that people ruin gear and maybe don't even know why.

 

all right... I think I got it now...

my gain on my sub is all the way up and the EQ is pretty low (help hit low notes)
(I shall fix this during my next drive)

the RMS on the sub is 200 with max power of 400...

I have a MTX Thunder 6304 amp... and is there anyway to change the Ohms on the amp? or does it automatically do that? cause it could be using 90 watts at 4Ohms or 165 at 2 Ohms... so yea... =-p

Power 12.5 VDC Input
2 Ohm Load 75 w x 4 Low Level
4 Ohm Load 37.5 w x 4 Input Select
Bridged 4 Ohm Load 150 w x 2 Crossover(s)

Power 14.4 VDC Hi / low @ 40Hz-200Hz -
2 Ohm Load 165 w x 4 Front/Rear Variable
4 Ohm Load 90 w x 4 RCA Output
Bridged 4 Ohm Load 325 w x 2 Full Range Only

Dimensions
(with ISO Feet)
Other Features
13.9" x 9.75" x 2.1" Thunder EQ
35.3cm x 24.8cm x 5.3cm

I have the rear speakers bridged so it looks like I am only getting anywhere from 82.5 watts to 40 watts! I may be reading it wrong or something... but does this help you guys understand it at all?

 

Theres your problem.

97f250 is right, your not going to notice a difference going from 150 to 200 watts (hence my 2nd post).

However, if your only sending like 150 watts to say a 500 watt driver, yes, you can come accross problems like that, again like 97f250 said. Unless its very super efficient.

I guess im not getting what your saying in the second part of your post

 

all ways over power subs, get bigger amp mono

 

I dont think so.
You dont need to send a speaker its rated power to get full output. Its not going to hurt anything underpowering a speaker either, unless you try to make up for it by cranking the gain and forcing the amp into clippin, and killing your speaker and maybe amp too. And if its VERY underpowered, like 100 watts to a 2000 watt speaker, it might sound a little shatty.

And what about the Infinity 1030 and 1230W;s, Rated at 300 wrms, and you sure the heck dont wanna go much over that, cause thats about its thermal and limits, much more and you can kiss it bye.
What about the 1000 watt RMS Pyle or Pyramid subs too? Id be impressed if they could take 400wrms.


Moral of my story-make sure your brain is in gear before you engage your mouth, or fingers.

 

Forget the 14.4 volt ratings. If you have a stock charging system in your vehicle, those are useless. I'm pretty sure that sub only was available in SVC 4 ohm, so if you have the 2 rear channels bridged, you are getting 150 watts RMS output to your sub. On the front 2 channels you are running 2 pair of speakers. If those are connected in parallel, the front channels are working into 2 ohms. So those speakers are splitting 75 watts per. The way the ohms "change" is by how speakers are configured when connected to the amp. An amp isn't a 2 ohm or 4 ohm amp. An amp is rated to be "safe" to use into a certain ohm set up based on the capabilities of the output devices, power supply, etc. These are a couple of reasons that seemingly "similar" amps can cost $75 at Wally World or $750 in a high end shop. It is true that "watts are watts" to some degree. But, if someone wants to listen to loud, clean, clear music over extended periods of time(and who doesn't?), then the equipment has to be up to the task, first of all, and adjusted properly, AND used properly. This example is where the average is separated from the above average. Over extended periods of high volume use a low end system will not be able to maintain an acceptable level of consistency. Most noticeably, you will begin to hear high frequency, ear piercing, almost painful distortion. This is instability in the equipment, caused by cheap components in the build process. Instability can be described as not being able to maintain consistency through all manners of use. Heat causes instability even in really good amplifiers, but in cheap ones, it's extreme. Heat buildup in the output devices of cheap amps does 2 things. It causes audible distortion and, at some point, failure of them, as well. That's why they're cheap and that is where higher end gear shines through.


A quick way to set the gains to where you are "in the ballpark". Turn all EQ settings on the head unit to zero or flat. Loudness too. Figure out what 85 to 90% of your head unit's total volume reading is. For example, if it goes up to 50, 42 to 45 is what we are shooting for. At that point most head units will begin to clip the signal it is sending to the amplifier. This is the highest volume you will want to use. Turn the gains down completely on the amp. Set the volume at 85%. Turn the gain up on the front speakers until you hear a little distortion, then back it off just a tad. Then do the same for your bridged sub channel. Keep in mind that when you equalize in bass and treble and loudness on the HU this causes it to clip at a lower volume. Much lower if you really crank things up. You cannot make any part of your system sound better or produce deeper bass or any such thing by equalizing on the HU. This is why there are dedicated EQs for that. This is not the ideal way to set the gains, but it is certainly better than what you had.

 

Ok... I did a lot of reading and studying up on my amp and sub... and I think I know my problem...

I think my sub/amp is set up for 4 Ohm at 37.5 watts per channel... meaning my sub (/w 200watt RMS) is only getting 75 watts total...

Would you guys know how I could change it so the subs are set up with 2 Ohm at 75 watts per channel? so I get 150watts instead of the 75 watts?

After reading reviews, specs, and other things, I am pretty sure this is why my sub sounds so under powered...

I'm going to keep looking around... but I'm still kind of new to this whole "subwoofer" thing so I may be missing something... if anyone could help me out with this... that would be great... thanks alot!

here is my equipment btw

MTX Thunder 6304 Amp
MTX 4000 12" Sub
4 Polk 60watt RMS door speakers

-=-=-=-=-=-=-=-=-=-
the Ohms on my sub are either 4Ohms or 8Ohms... and considering my amp would die if the sub was 8ohms... it is apparently a 4 ohm sub...

Ok... I think I answered my own question... you cant change the ohms on the speakers... and the amps just automatically adjust to the correct Ohm Level... so I would just need to buy a mono amp that has a 4Ohm lvl with at MOST 200 watts powering it... does this all sound right? just let me know if my head is in the right place