Audio gurus help me out!

[02_Legacy]

I keep blowing subs and I don't know why!?!?
So here is the equipment
Rockford Fosgate R750-1D amp, its specs are 750 RMS x 1 at 1 ohm.
My first two subs were both Pioneer TS-W2502D2's. This is a 10" 2 ohm DVC sub rated at 800 RMS. The sub was installed in a sealed box that I made from 5/8 mdf, it was the proper capacity for the sub and was glued and stapled, it had no leaks (well one really small one where the wires ran through). The first sub something happened internally, i'm not sure what but when it blew the cone assembly became very stiff, you could not move it. The second subwoofer I was more careful with but eventually the cone separated from the surround leaving a hole about 1 to 2 inches long.
The third subwoofer (which I just installed 3 days ago) is a Alpine type R SWR-10D2 also a 10" 2 ohm DVC woofer rated at 1000 RMS, same box and on my way home today it stopped working. This time the cone is easly moved, I think the cone may have separated from the voice coil.
A little more info, I leave the gain right in the middle, and out of a possible 35 I never turn my head unit over 25 so i should not have a ton of distortion, I do not notice any and I do not have the equipment to test for distortion. I listing to a lot of dubstep and some hip-hop/rap so my subwoofer gets used a lot but am I wrong in thinking it should be able to last at least 3-4 bass heavy songs in a row? As a matter of fact now that I think about it I pounded on that sub for 30 min stright last night, however the sub blew the first song on my way home from work toningt
So am I just the unluckiest person when it comes to subwoofers or am i missing something? Help me out!

[chuckthefuk]

More info please..

How are these connected? Parallel / Series? How are the DVC's wired up? How are they wired to the amp?

Please post pics of your amp settings (dials) / wiring

[RandyMarsh303]

Like chuck said we need more info on the way you have it wired. I can almost be certain that part of your problem is that rockford amp. That stuff is garbage half the time IMHO its dual product with a differant name.

Also it does not make sense to me that you have a 1 ohm amp and 2ohm sub. They should be matched. Maybe I'm wrong here but read up on ohms law, there is a good tutorial on jl audio. Website.

What it sounds like to me is you need a better setup. If you listen to dubstep you are very used to a ton of bass and those subs you listed may not provide what you think they should. I went through four jl w0 before I realized I just needed a better sub. I have two jl w6 12s with a jbl amp and it POUNDS ALL DAY LONG. Now I wish I had an alpine pdx or a jl 1000/1 amp but the jbl does the job. If you like alpine I would check out the type x . It's about 250 online and will give you some serious bass.

Sorry for any mispelling this is from my phone

[02_Legacy]

Well my mom has the camera right now so I can't get you pics but I can tell you these things.
The subs are wired in parallel, I have 4 wires coming off the sub, 2 positive and 2 negative and they meet at the amp and are connected together at the amp output. (@RandyMarsh303 this is why I have a 2ohm sub and a 1 ohm amp. The subs have two 2ohm voice coils, when they are wired parallel they result in 1ohm, basic ohms law :smt002 )
The ultrasonic filter is set at 20hz and the low pass filter is set at 85hz. The gain and punch EQ knobs are both slightly above the center. The box volume is .66 cu ft.
And what I don't get is that the alpine sub went within 3 days of me installing it even though I am under driving it by 250 watts...

I am going to go to a local place that deals with car audio on Friday and see what they have to say, hopefully I can get this figured out because I am not putting another sub in until I know that I am not going to blow it.

[Crowboy]

If it would help, I can probably get some images to also explain the following, but we'll try with words because they're handy.

First, the quickest way to blow any speaker is to run it with too small of an amp. I have blown a woofer rated at 100W RMS with a 5 watt amplifier. (Granted, I was trying to blow it...) The problem is with the shape and energy of the waveform and the way it moves (or attempts to move) the mass of the speaker cone and voice coil. Picture a pure sine wave, we'll pretend it's at 80Hz. It's all round, no sharp corners to the waveform at all. We're using the amplifier to generate the powerful electrical signal to move the speaker cone to exactly match the waveform. Because of the nature of a sine wave, even the acceleration and deceleration of the cone is smooth (differential calculus: derivative of position is velocity, derivative of velocity is acceleration, derivative of a sine is a cosine...)

Now imagine you have an underpowered amplifier that reaches the limit of power it can put out. Imagine that nice smooth sine wave with the top and bottom cut off. Now you are asking the cone to make abrupt stops and starts to try and match the waveform. The target velocities and accelerations go through the roof. Current and heat build up quickly in the voice coil windings either melting the glue that holds the winding causing the coil to seize (as the first Pioneer), over accelerating the cone causing the surround to tear (the second Pioneer) or melting the coil wire itself causing an open circuit (the Alpine)

Dubstep has extremely challenging waveforms since they are created electronically. The low frequencies tend to have harmonics which can combine with the root frequencies to make waveforms with sharp corners similar to our imaginary "clipped" waveform.

As far as longevity and how long subs can produce near-impossible waveforms: back in the 90's I saw personally a 1500 watt 18" electrovoice sub blown with a 500 watt amp with a single bass note from a keyboard. Electronic sounds don't have to follow the laws of physics, until we try to let them out in the air.

Anyway, given the same Ohm's Law as well as Joule's Law, we get P=I^2*R so for a 1 ohm load, the Rockford amp is putting out 27 amps RMS or about 14 amps per voice coil. Through a coil wire the thickness of a mechanical pencil lead. This only works when that energy is dissipated as mechanical movement of the cone. As soon as we start asking the cone to move in ways the laws of physics won't let it (abrupt stops and starts) that energy has to go somewhere and it comes out as heat in the voice coil.

So, the solution is actually a bigger amp. For the Pioneer subs you mentioned, you should run an amp that can provide 1600 watts RMS at 1 ohm with less than 5% total harmonic distortion (THD). This large of an amp will get spendy quickly, so the cheaper route (and I'll probably annoy some with this) would be to pick up another R750-1D and run one amp per voice coil. That would give you 500 watts RMS at 2 ohms per coil for a total of 1000 watts into a nominal 800 watt sub.

And, turn off the 18dB boost at 45Hz "Punch EQ". That could be part of what is causing the clipping and blowing speakers. If you want a guarantee that you won't blow any more subs, the only way to do that is to unplug them. Even a well matched system will blow up if you turn it up too far.

Full disclosure: I helped Rockford Fosgate out in the late 90's just after they had purchased Hafler and were attempting to go after the nearfield studio monitor market e.g. Genelec, Thiel, Yamaha, B&W. Never really liked their car audio stuff, but much of the Hafler stuff was excellent. Then I went to engineer microphones, record needles, and electronics for Shure for 8 years.

Zack

[02_Legacy]

cool thanks for taking the time to write all of that. I understand what you are saying. Tomorrow I will be going to that local audio place to see what they say, if nothing else I am hoping they will be able to test my setup for distortion. The next step is upgrading my 10 to a 12 or 15. Truth is I am trying to get the same volume out of this 1 10" that I was trying to get out of my previous setup of 2 12's running 120 RMS.

Maybe you can tell me this: What is the difference between a 100RMS sub and a 1000 RMS sub?

[Crowboy]

There are a bunch of little differences between any given 100 watt sub and a 1000 watt sub, kinda like the differences between a 100 WHP car and a 1000WHP car. The changes make the speaker (or car) capable of dealing with increased power.

In high power handling subs, the chassis will be sturdier, total excursion of the cone is usually greater, cone suspension is burlier, the magnet is larger. As far as blowing speakers, the weak link seems to be coil design, so the coil wire in high power subs is usually heavier gauge which can hurt sensitivity (the ability of the sub to accurately reproduce quiet sounds) and more thought is put into how to cool the coil when the sub is in use.

Ultimately, you are trying to do a certain amount of work (force x distance) with the speaker cones. Force applied is a function of cone area, so to replace a large amount of cone area (2 12" cones) with a smaller cone (1 10" cone) you'll need a 10" with more excursion to do the same amount of work. It can be harder to reproduce extreme low frequencies with smaller cones as well. If you want the deep drop bass, you want at least a 12", 2 would be ideal. Even a pair of parallel 10" will be better than a single one. A 15" can be hard to fit in to our cars, but if you can do it, that will be best for extreme low end.

Zack

[02_Legacy]

Thanks for the reply, I went to the local audio place and they told me pretty much the same thing you said in your first post and he to recommended that I get another amp and put one on each voice coil. In addition to what you said some things he added were the fact that I am using an Ipod which he says have are horrible for producing sound that is already distorted, so my headunit may be getting distorted imput before it even amplifies it, and the fact that the amp is ran at 1 ohm. He says that he doesn't care if the producer of the amp says it is 1 ohm stable no amp should ever be ran at 1 ohm. Also he strongly suggested a ported box saying that it will create more volume to the point that I may be able to turn down the amp, get the same volume, and have less distortion.
So for now I am turning all this in my head thinking about my next move, weather to try with another larger sub with this amp, see if I can get my alpine replaced and think about another amp, or start over from scratch. In the mean time I am going to look into how to properly build a ported box.

[Crowboy]

The way iPods or specifically, compressed audio files, deal with the waveform usually gives pretty accurate reproduction of low frequency material. The problem comes in with gain matching. If you are running your ipod into the head unit through the 3.5mm jack it is possible that the amplifier in the iPod overdrives the input stage of the head. Solution: turn down the iPod, turn up the head unit. If you are using the multi-pin connector (if the head unit also charges the ipod) then the iPod's headphone amplifier is bypassed (volume on the iPod doesn't work anyway) and things usually work out well.

For speaker impedance, I personally don't like to run any lower than 4 ohms mainly because the resistance of the speaker wire becomes significant and changes the sound. If you have a 1 ohm amp and 0.1 ohm resistance in your speaker wire, the wire represents 10% of the total impedance. It's hard to find a multimeter that reads resistance to greater precision than 0.1 ohm so you really don't even know how much resistance the wire could be contributing. Running 4 ohms drops that same 0.1 ohm wire to 2.5%, a lot less significant. You can look online to find resistances per foot for various gauges of copper, aim for a wire resistance of less than 1% of the total impedance.

Ported boxes will give more kick and a properly designed one will give a fairly smooth frequency response to the designed low frequency (a function of box volume, port length, and area) then drop off sharply. A poorly designed box or one that is not well matched to the driver will usually result in a peak a bit higher in frequency than the low cutoff point. It will kick at that frequency and sound pretty good, but a song with multiple bass notes will have some notes reproduced louder than others. A well designed sealed enclosure on the other hand will have a very smooth response but will taper off gradually towards the low end. Without a very large driver, the sealed enclosure probably won't give you the super deep bass, but will be very smooth for music that has more than the single "boom car" bass note. Not all speakers are designed for ported enclosures, if you go that route make sure you pick subs that are rated for a ported enclosure.

Good luck!

Zack

[tpatten]

I also notice that you mentioned your amp is 1 ohm and you have to remember that the lower the ohm load, the lower the quality which has been known to blow subs.

[02_Legacy]

I also notice that you mentioned your amp is 1 ohm and you have to remember that the lower the ohm load, the lower the quality which has been known to blow subs.

First off, welcome to the forums!
I have decided to keep the amp and just recently I bought two pioneer woofers that are 4 ohm SVC so I will be running the amp at 2 ohms instead. I also found out that I was getting alot of distortion from the bass boost on the headunit. As a matter of fact if I turn off the bass boost on the head unit, I can turn up the gain and get the same volume but a much crisper sound. I will hopefully be hooking up to an o-scope in the near future to verify my suspicions.

[ScaryFatKidGT]

I also notice that you mentioned your amp is 1 ohm and you have to remember that the lower the ohm load, the lower the quality which has been known to blow subs.

First off, welcome to the forums!
I have decided to keep the amp and just recently I bought two pioneer woofers that are 4 ohm SVC so I will be running the amp at 2 ohms instead. I also found out that I was getting alot of distortion from the bass boost on the headunit. As a matter of fact if I turn off the bass boost on the head unit, I can turn up the gain and get the same volume but a much crisper sound. I will hopefully be hooking up to an o-scope in the near future to verify my suspicions.

Wow the new Type-R's have double the RMS watts of the old.

I have 2 13.5" JL W3v3's powered by a Alpine MRP-M1000 and the are so freaking loud haha, I wouldn't go with the same amp but that isn't really an issue sense the MRX-M1000 is there new one, idk how it works but hopefully better than the MRP.

I think you should quit messin around and get 2 12" Type-R's or something similar if you want it that loud.