mono amp powering stereo speakers

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g.fewkes

Member - Posts: 6

Joined: February 02, 2009

Location: Washington, United States

Posted: February 03, 2009 at 10:42 PM / IP Logged

hey all

i have 2 rockford fosgate 5 1/4 speakers currently being powered by my head unit (Pioneer Premier DEH-P7800MP). the head unit provides 50 watts peak, around 20-25 watts RMS. The speakers handle 60 watts RMS.

They distort like crazy when i get into the higher volumes simply because i do not have an adequate amount of power to the speakers, which could eventually cause them to blow from under powering.

i have a spare JBL Touring 301.1 mono sub amp used with my previous system, i have since made a huge upgrade :), that i was considering using to power my rockfords.

I know that it can be done, i am just curious on what kind of sound i will get, and if the signal to noise ratio will make a big impact. the amp has 2 speaker inputs(2 positive terminals and 2 negative) but it still projects a mono signal. i know i wont have the stereo effect but i was hoping it will do for now until i complete my current system i am working on.

current set-up:

Previously mentioned head unit

2 rockford fosgate 5 1/4s(60 watts RMS)

2 Kicker L7 10s in ported box(BC Car Audio, Bremerton, Wa)

ZX1500.1 Amplifier

4 AWG welding wire (Not solid core) super-flex

Working on purchasing 2 SETS(4 speakers total) of Kicker RS65.2(6.5" components 100 watts RMS each speaker)

+++gabe+++

haemphyst

Platinum - Posts: 5,054

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Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: February 04, 2009 at 12:03 AM / IP Logged

1: You CANNOT blow speakers with too little power, (try us all on this one... we dare ya!) it is a physical impossibility.

2: If there is a non-defeatable low pass filter, you can't use it like that, unless you want "subs" in the doors.

3: If there ISN'T a filter, or it a defeatable filter, sure, you can do it. It'll sound like crap, but you can do it.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

i am an idiot

Platinum - Posts: 13,673

This member consistently provides reliable information

Joined: September 21, 2006

Location: Louisiana, United States

Posted: February 04, 2009 at 5:38 AM / IP Logged

Stereo means 2 separate channels of information. Ever seen a 3D movie, well a stereo system does the same thing audibly that the 3D movie does visually. Stero separation is an important part of a system. You will lose that if you install a mono amplifier on your upper frequency speakers.

http://www.cdtaudio.com/pdf/stereo_%20sep.pdf

g.fewkes

Member - Posts: 6

Joined: February 02, 2009

Location: Washington, United States

Posted: February 04, 2009 at 1:43 PM / IP Logged

haemphyst wrote:

1: You CANNOT blow speakers with too little power, (try us all on this one... we dare ya!) it is a physical impossibility.

2: If there is a non-defeatable low pass filter, you can't use it like that, unless you want "subs" in the doors.

3: If there ISN'T a filter, or it a defeatable filter, sure, you can do it. It'll sound like crap, but you can do it.

Underpowering a speaker will infact blow it. sending a distorted signal to the voice coil will cause it to blow. i have talked to Bob Craft owner of BC Car Aduio, he has had 10 Kicker CVR returned this last year due to underpowering. He has been in the business for 30+ years

after posting i looked at the JBL amp and noticed that there is no switch between hi-pass and lo-pass filtering. problem solved, need a 2-channel

+++gabe+++

g.fewkes

Member - Posts: 6

Joined: February 02, 2009

Location: Washington, United States

Posted: February 04, 2009 at 1:46 PM / IP Logged

i am an idiot wrote:

http://www.cdtaudio.com/pdf/stereo_%20sep.pdf

i realize that, i just hate the fact that i cant rock out to anything without a distorted output. i dont have the money for a 2 channel currently and have access to a mono. all i wanted to achieve was greater volume with less distortion.

thanks for the reply

+++gabe+++

g.fewkes

Member - Posts: 6

Joined: February 02, 2009

Location: Washington, United States

Posted: February 04, 2009 at 1:52 PM / IP Logged

g.fewkes wrote:

haemphyst wrote:

1: You CANNOT blow speakers with too little power, (try us all on this one... we dare ya!) it is a physical impossibility.

2: If there is a non-defeatable low pass filter, you can't use it like that, unless you want "subs" in the doors.

3: If there ISN'T a filter, or it a defeatable filter, sure, you can do it. It'll sound like crap, but you can do it.

after posting i looked at the JBL amp and noticed that there is no switch between hi-pass and lo-pass filtering. problem solved, need a 2-channel

here's more of an explanation

"Underpowering a speaker is likely to damage the voice coil due to the excess heat created by distortion. This distortion, called clipping, is created when the amp is not able to supply the power demand when the volume is turned up. If you turn the volume up very high without the power to back it up, you'll end up clipping the signal coming out of the amp. The speaker will try to reproduce this clipped signal, and if played under these circumstances for any length of time, the speaker will not last very long."

-http://www.rhythmism.com/forum/archive/index.php/t-11306.html

+++gabe+++

j.reed

Copper - Posts: 716

Joined: January 05, 2009

Location: Arkansas, United States

Posted: February 04, 2009 at 3:28 PM / IP Logged

g.fewkes wrote:

haemphyst wrote:

1: You CANNOT blow speakers with too little power, (try us all on this one... we dare ya!) it is a physical impossibility.

2: If there is a non-defeatable low pass filter, you can't use it like that, unless you want "subs" in the doors.

3: If there ISN'T a filter, or it a defeatable filter, sure, you can do it. It'll sound like crap, but you can do it.

after posting i looked at the JBL amp and noticed that there is no switch between hi-pass and lo-pass filtering. problem solved, need a 2-channel

here's more of an explanation

-http://www.rhythmism.com/forum/archive/index.php/t-11306.html

Bob Craft from what ever shop has had 10 speakers sent back from underpower?! No from clipping. The reason for this is because the dumba** that owned the amp or installed it decided to crank up the gain as a volume knob. With correct amplifier install/gain settings you are not going to blow a sub, As for this underpower myth. The clipping almost always sends direct DC current to the sub. Therefor the sub is being overpowered from DC current. which is creating the exesisive heat. Not the fact that the sub is receiving less than it rated power. Why is this problem more comin in smaller amps being used? because when we over power you can hear sub bottom out telling you to turn it down. With a smaller amp and a noob installer or someone gaining it up. They think it is a volume knob because it not enough to bottom the sub out. Anyone that thinks a sub will blow from just being less power put on it than its max has to be a complete moron. The problem you are describing is from clipping. Not from under powering. 2 very different things.

https://www.the12volt.com/installbay/forum_posts.asp~TID~74226~PN~1 check this tread out it will open your eyes. The sub has to be over powered in one shape or form for it to blow.

mono amp powering stereo speakers -- posted image.

haemphyst

Platinum - Posts: 5,054

Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: February 04, 2009 at 5:03 PM / IP Logged

1: DC, in and of itself cannot blow a speaker, either. Read on.

2: Whether they are returned or not, and whether he has been in business for a hundred years, you CANNOT BLOW A SPEAKER FROM UNDERPOWERING OR DISTORTION.

Here is what happens: When an amplifier clips, the average output power increases from it's RMS power to it's maximum power. The harder you clip it, the higher the average power. If you have a woofer rated 500 watts connected to an amplifer rated only 200 watts, that speaker will not, and cannot EVER blow. The amplifer cannot ever make more than twice it's RMS rated power, or 400 watts. Even at 100% distortion, you CANNOT blow a speaker, end of story.

RMS = peak * .707 The inverse of .707 is 1.414. If you have 1.414 times the voltage across a given load, you will push 1.414 times the current. 1.414 times 1.414 equals 2. At 100% clipping, the amplifier is pushing 1.414 times the RMS voltage, making double the RMS rating. i.e. a 200 watt amp will make 400 watts.

Now, if you have an amp rated at 300 watts on that same 500 watt speaker, and you are driving the amp hard enough, it is very possible that you can force the amplifier to produce over the safe 500 watts, because that 300 watt amplifier CAN produce over 500 watts if driven hard enough, and therefore blow a 500 watt woofer. THERE is your underpowering myth. Bob Craft needs to get a little education in power, and that's the end of that argument.

(Like I said... try us.)

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

j.reed

Copper - Posts: 716

Joined: January 05, 2009

Location: Arkansas, United States

Posted: February 04, 2009 at 7:19 PM / IP Logged

haemphyst wrote:

1: DC, in and of itself cannot blow a speaker, either. Read on.

I have heard from an engineer that if clipped the toriod of the PCU of the amp can send almost direct DC current directly to the sub. Is this not true? And if it is true is the DC current not enough to get the coils hot enough to go to failure? I would think it is. This would meen the sub would still be overpowered by the DC current. Am i missing something?

haemphyst

Platinum - Posts: 5,054

Joined: January 19, 2003

Location: Michigan, Bouvet Island

Posted: February 04, 2009 at 8:37 PM / IP Logged

1: I would be willing to bet that this is not what he said, perhaps you simply misunderstood. Any "engineer" will know that no transformer can pass DC. (Pulsed DC is NOT DC.) In a heavily clipped situation, the output rails of the amplifier are directly connected to the speaker, as though the output devices were not even present, but this is not the toroid passing DC. The power supply is still doing EXACTLY as it is designed to do, the failure is in the output devices being told to "turn on" to a point beyond what the power supply rails can supply.

2: Even if a transformer COULD pass DC, (in a WORST case scenario, i.e. a shorted transformer) the input side would only have 12 to 14 volts available to pass. 14V across 4 ohms is only 51.84 watts peak, ever. Even across a single one ohm voice coil, 14V can never achieve anything higher than 207.36 watts. In neither of those cases would there ever be enough power to blow a respectable woofer.

3: The toroid in an amplifier is already driven in a "clipped" mode. The input side in only driven by 12V square waves. The AMPLITUDE of the waves are ALWAYS the same - battery voltage, minus device drop; to get more power out of the supply, the duty cycle is changed, meaning the "time on" vs. the "time off" changes.

It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

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