amp cutting out

mocpac · Post by **mocpac** » Sat Jan 14, 2006 12:42 am

put it at 4ohm and check the specks of the amps. Also what tipe of subs are conected?

daewoomofo · Post by **daewoomofo** » Sat Jan 14, 2006 1:14 am

2 mtx thunder 5500 12's in a ported box

jorge · Post by **jorge** » Sat Jan 14, 2006 1:47 am

Thats sound a low ohm. Put them at 4ohm and check...

TheGreatAndPowerfulOz · Sat Jan 14, 2006 1:50 am

Are the subs dual coil?

If eac sub has 2 coils, and each coil is 4 ohms, then one possibility is you are running the amp at 1 ohm, which will make it turn off just like you describe.

If eac sub has only one 4 ohm coil, then the amp may not like running at 2 ohms.

As suggested above, if the sub is indeed a single coil 4 ohm speaker, try one sub at 4 ohms and see if the amp continues to turn off.

Cliff

daewoomofo · Post by **daewoomofo** » Sat Jan 14, 2006 2:16 am

yeha they only have one 4ohm v/c each ill try running at 4 ohms, thing that sux is it wont be as loud

delphis · Post by **delphis** » Sat Jan 14, 2006 2:26 am

daewoomofo wrote:yeha they only have one 4ohm v/c each ill try running at 4 ohms, thing that sux is it wont be as loud

well that isn't necessarily true because the maximum dB output you can receive from doubling the wattage is no more than 3 dB.

daewoomofo · Post by **daewoomofo** » Sat Jan 14, 2006 2:39 am

3 db = twice as loud

delphis · Post by **delphis** » Sat Jan 14, 2006 7:24 am

actually the human ear can barely even detect the difference in 3db of volume unless of course there was an A B comparrson but even then most well trained ears would have a hard time with it.

Post by **PrecisionBoost** » Sat Jan 14, 2006 6:31 pm

Who designed your ported sub box?

What most people don't understand is that the speaker impedance ( 4 ohms ) changes with frequency.

Impedance represents the inductive load on the amplifier.... so it's the most important factor in determining power handling capabilities.

This might be confusing.... but your sub box also affects the subwoofer impedance.

So...... if your sub box is designed incorrectly it's possible that your amp is seeing an impedance well below 2 ohms (possibly a half ohm or less) during certain frequencies.

Your amp will only take this so long.... eventually it will lead to overheating and thermal shutdown.

Subwoofer/box dynamics are very complex.... unless you have a math/physics/electronics background it would be very hard for me to make you understand how the impedance changes.

Another possibility is that your amplifier is damaged.... a bad thermal sensor would kick of the amp just like your talking about.

Post by **PrecisionBoost** » Sat Jan 14, 2006 6:39 pm

delphis wrote:actually the human ear can barely even detect the difference in 3db of volume unless of course there was an A B comparrson but even then most well trained ears would have a hard time with it.

That is not 100% entirely true...... yes.... your statement is generally correct.... but it depends on the frequency.

Here is a nice description.... http://en.wikipedia.org/wiki/Decibel

daewoomofo · Post by **daewoomofo** » Sat Jan 14, 2006 6:43 pm

car tunes designed my box. its in the range of mtx's ported box recomended size.

delphis · Post by **delphis** » Sat Jan 14, 2006 6:55 pm

Erfinder@PrecisionBoost wrote:
delphis wrote:actually the human ear can barely even detect the difference in 3db of volume unless of course there was an A B comparrson but even then most well trained ears would have a hard time with it.
That is not 100% entirely true...... yes.... your statement is generally correct.... but it depends on the frequency.

Here is a nice description.... http://en.wikipedia.org/wiki/Decibel

ya I know, but everyone thinks that doubling the power of an amp will drastically increase the volume output. I went to audio engineering school and understand most of the in depth concepts of amplifiers and output volumes.

Post by **PrecisionBoost** » Sat Jan 14, 2006 6:57 pm

Here is the info I'm getting from you..........
rockford 700s (2 ch) the 700 is cutting out
im running the amp in 2 ohms (2 4 ohm subs)
2 mtx thunder 5500 12's in a ported box

Ok... perhaps I'm confused.... so are your saying that your running both subs in parallel ( both positives together... both negatives together ) and you've attached them to the "bridged" single channel output of the amplifier??

When you bridge the amp....you decrease it's impedance handling capacity by a factor of 2

So... if it's says it's 2 ohm stable you can only run 4 ohms in a bridged mode

Your amp must say that it's 1 ohm stable to run two 4 ohm subwoofers off the bridged outputs.

Well..... I just spent 10 minutes looking around a few forums about the 700S...... and I have bad news for you

The amp is only capable of supporting a 4 ohm load in the bridged mode...... and it's only 2ohm stable in non-bridged mode

So.... your screwed... you will have to run them in a non-bridged mode.... one speaker on one channel.

Your only other choice it to add two more speakers, get dual voice coil subs or 8 ohm Subs.

You could put two speaker in series....

so (+) amp output to (+) of speaker 1.... then attache (-) of speaker 1 to (+) of speaker 2 and finally the (-) of speaker 2 to the (-) output of the amp

you would wire speaker 3 and speaker 4 the same way

So... speaker 1 + 2 = 8 ohms and speaker 3+4 = 8 ohms

Then you run them in parallel (+) speaker 1 and (+) speaker 3 attached together to amplifier (+) bridged output terminal and (-) speaker 2 and (-) speaker 3 attached together to amplifier (-) bridged output terminal

So two 8ohm sets in parallel gives you your 4 ohm load.

With the dual voice coil subs...you wire them for 8 ohms impedance and run the two in parallel off the bridged channel to get a 4 ohm bridged load

With the 8ohm single voice coil subs you wire in parallel like the DVC subs.

Sorry to break the bad news to you..... buy your amp sucks ass.... Rockford is a decent name.... but it's overpriced for what you get.

daewoomofo · Post by **daewoomofo** » Sat Jan 14, 2006 7:05 pm

thanks for the info. i only apid 190 (shipped) for the amp on ebay. it retails for like 400 from what ive heard. ill look into getting some different subs. thanks to all who offerd me some help and info!

Post by **PrecisionBoost** » Sat Jan 14, 2006 7:11 pm

delphis wrote:ya I know, but everyone thinks that doubling the power of an amp will drastically increase the volume output. I went to audio engineering school and understand most of the in depth concepts of amplifiers and output volumes.

Cool.... I've never met an audio engineer.... I don't think we even have that up here in Canada... I think the mechanical engineers do most of the acoustical design in industry.

I was in Petroleum engineering and then electronics engineering technology....so I have a pretty good math/physics/electronics background.

I don't want to get too off topic.... I've allways said "more speakers..... not more power"

I have eight JLAudio 8W1 8" subs and two Alpine 6081 8" subs

Most people don't realize that four 8" subs have more surface area than a single 15" sub.... therefore you can achieve amazing bass out of eight 8" subs.

A 15" sub has 177 square inches of surface area and each 8" sub has 50 sq inches of surface area so four 8" subs will have more bass than a single 15"

The 8" subs are more controlled and produce better bass notes in my opinion.... the cone surface is typically stiffer and therefore less distortion.

I'm sure there are people that will argue that point...... but think about it.... how many high end home speaker systems have more than an 8" subwoofer???? If 15" subs were any good.... they would be in heavy use in the high end homeaudio stuff