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#### David970

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Hi.
First of all, I would like to introduce myself, because I am new to this forum. I hope that I will be seen here more often
I have a few questions in regards to an appropriate tuning of a car amplifier, which I am happy to be the owner of since yesterday, after my entry level active sub.
Unfortunately, I do not have access to any high end tuning gear, but I have a DMM which apparently does its job.
I know already that the formula is V=sqrt(P x R). And this is where my confusion begins. Below is my current setup:
Subwoofer: 1200W peak (350W RMS), 4 ohms.
Amplifier: 500W peak (65W x2 @ 4 ohms, 85W x2 @ 2 ohms).
I have decided to bridge a subwoofer, since all the speakers are wired directly to the stereo (has 4x55W). Now, I have heard that bridging a subwoofer causes its resistance to drop in half. Is this true? And does that mean that I have to input 2 ohms into a formula? I would be very grateful if anybody could work out the voltage for me, or at least suggest my power and resistance values. Thank you in advance.

#### gijoe

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I think you’re confused by some terminology. You don’t bridge speakers, you bridge amps. Is your sub a single, or dual voice coil? If single, than 4 ohms is what you get. Of dual, you can wire the coils in series to 8 ohms, or parallel to 2 ohms.
Regarding the amp, is it a 2 channel amp? Do you know it’s bridged specs? Bridging is when you tie two separate amplifier channels together, many amps won’t handle a bridged load below 4 ohms.

#### David970

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i’m sorry. I should’ve mentioned i am a newbie. Learning slowly though haha.
It is a 2-channel amp. It has a BTL (bridge-tied load) markings on positive and negative terminals of each channel. I read online specs too just to be sure. Also, the sub doesn’t have dual voice coil if that helps.

#### miniSQ

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What amp and what sub? I can assume here, but knowing the model numbers would help to confirm. I will assume the amp is 4 ohm stable when bridged and not 2 ohm, so i need to confirm that.

In this case assuming the sub and amp are compatable, i would suggest setting the gain with your ears and not with a dmm to start. Just set all your bass settings to flat and turn off any bass boost, and turn the gain fully counter clockwise. Put in some music with strong bass notes and turn the rest of the system up to about as loud as you would ever listen to it. Then while its playing, turn the gain up until you start to hear it distort, or a clipping light comes on and then back it down a bit. Thats all there is too it.

#### David970

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What amp and what sub? I can assume here, but knowing the model numbers would help to confirm. I will assume the amp is 4 ohm stable when bridged and not 2 ohm, so i need to confirm that.

In this case assuming the sub and amp are compatable, i would suggest setting the gain with your ears and not with a dmm to start. Just set all your bass settings to flat and turn off any bass boost, and turn the gain fully counter clockwise. Put in some music with strong bass notes and turn the rest of the system up to about as loud as you would ever listen to it. Then while its playing, turn the gain up until you start to hear it distort, or a clipping light comes on and then back it down a bit. Thats all there is too it.
Sobwoofer: Sony XS-L122P5
Amplifier: Sony XM-N502
I tried to set gain by ear with a 50Hz test tone, and couldn’t really detect clipping. Same thing with my active sub, so clearly my ears aren’t sensitive to this. Also, I wish there was a clipping light on the amp. Would make my life so much easier.

#### miniSQ

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So it looks like the amp and sub are compatible. So try it the way i suggested using music. You are only going to get about 100 watts from that amp and with music it should be relatively easy to tell when it starts to break up.

#### David970

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So it looks like the amp and sub are compatible. So try it the way i suggested using music. You are only going to get about 100 watts from that amp and with music it should be relatively easy to tell when it starts to break up.
I tried already like I said before. I just get a gradual bass increase, but can’t really tell when it starts to break up myself. I only went about 3/4 of a knob though, but I am afraid of going any further. I will try again tomorrow.

#### miniSQ

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I tried already like I said before. I just get a gradual bass increase, but can’t really tell when it starts to break up myself. I only went about 3/4 of a knob though, but I am afraid of going any further. I will try again tomorrow.
I thought you said you did it with a 50hz tone. I suggested doing with music.

#### miniSQ

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But if you do want to use test tones here is a nice tutorial.

#### Destarah

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great replies here but I thought it might be helpful to directly answer the original question regarding voltage.
Some tech spec background (from Sony website)
XM-N502 rated for 85x2 @ 2 ohm ... bridged rating of 500x1 @ 4 ohm is useless marketing drivel "max" power, in theory this amp should do about 170x1 @ 4 ohm (sum of 2-channel 2 ohm rating).

170W @ 4ohm would be 26.8V ...

Procedure - disconnect the sub wiring from the amp, set all EQ functions to flat on the head unit, lower the gain on the amp to minimum, select A/C voltage on the DMM, connect the DMM to the amp, play the 50Hz test tone, turn up the head unit to about 75% volume, slowly increase the gain on the amp until the DMM reads no more than 26.8V

Hope that helps

#### miniSQ

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great replies here but I thought it might be helpful to directly answer the original question regarding voltage.
Some tech spec background (from Sony website)
XM-N502 rated for 85x2 @ 2 ohm ... bridged rating of 500x1 @ 4 ohm is useless marketing drivel "max" power, in theory this amp should do about 170x1 @ 4 ohm (sum of 2-channel 2 ohm rating).

170W @ 4ohm would be 26.8V ...

Procedure - disconnect the sub wiring from the amp, set all EQ functions to flat on the head unit, lower the gain on the amp to minimum, select A/C voltage on the DMM, connect the DMM to the amp, play the 50Hz test tone, turn up the head unit to about 75% volume, slowly increase the gain on the amp until the DMM reads no more than 26.8V

Hope that helps
Do you really think that Sony amp will play out to 170 watts clean? That is why I suggested tuning it by ear if possible.

Sent from my SM-G965U using Tapatalk

#### Holmz

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great replies here but I thought it might be helpful to directly answer the original question regarding voltage.
Some tech spec background (from Sony website)
XM-N502 rated for 85x2 @ 2 ohm ... bridged rating of 500x1 @ 4 ohm is useless marketing drivel "max" power, in theory this amp should do about 170x1 @ 4 ohm (sum of 2-channel 2 ohm rating).

170W @ 4ohm would be 26.8V ...

Procedure - disconnect the sub wiring from the amp, set all EQ functions to flat on the head unit, lower the gain on the amp to minimum, select A/C voltage on the DMM, connect the DMM to the amp, play the 50Hz test tone, turn up the head unit to about 75% volume, slowly increase the gain on the amp until the DMM reads no more than 26.8V

Hope that helps
That is great.
If the tones are full scale, one could also do it at 100% instead of 3/4.
Which would be totally clip free, but likely would be too low with some music.

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#### Destarah

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@ Holmz - the problem with 100% is that typically the head unit will be clipping the output signal, 75% is a safe bet for a clean output from the head unit.

#### David970

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great replies here but I thought it might be helpful to directly answer the original question regarding voltage.
Some tech spec background (from Sony website)
XM-N502 rated for 85x2 @ 2 ohm ... bridged rating of 500x1 @ 4 ohm is useless marketing drivel "max" power, in theory this amp should do about 170x1 @ 4 ohm (sum of 2-channel 2 ohm rating).

170W @ 4ohm would be 26.8V ...

Procedure - disconnect the sub wiring from the amp, set all EQ functions to flat on the head unit, lower the gain on the amp to minimum, select A/C voltage on the DMM, connect the DMM to the amp, play the 50Hz test tone, turn up the head unit to about 75% volume, slowly increase the gain on the amp until the DMM reads no more than 26.8V

Hope that helps
That’s exactly what I wanted. Thank you ever so much ! I am going to do this once I get to my car.
Also, in regards to my stereo functions; can these be tweaked once the subwoofer is tuned at 26.8V? Just considering crossover (80Hz LPF on the sub with 80Hz HPF on the head unit perhaps? Just to separate the low frequencies between the sub and speakers) Thank you once again.

#### Destarah

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yes, especially if you are using a 50Hz test tone to set the level on the amp. In that case as long as you haven't done something nuts like set a highpass filter on the sub channel all the crossover settings and such can be dealt with afterwards.
Fair warning, you may also end up turn the sub down if you find the front end cannot keep up, don't hesitate to do that ... balanced sound better (to me and most other people)

#### minbari

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@ Holmz - the problem with 100% is that typically the head unit will be clipping the output signal, 75% is a safe bet for a clean output from the head unit.
that is his point. if you set it at 100%, when you listen to it at 75%, there is no way you would be pushing the system to 100% you would be sacrificing some potential power though.

as for the OP, please dont set it with a DMM. biggest waste of time in audio. do it by ear.

miniSQ

#### Destarah

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not sure I understand the 100% argument. Setting the amp gains using a signal that is being clipped seems like a bad idea. Consider the following hypothetical ... the head unit starts clipping it's output at 85% volume, you set the gains on the amp with the head unit at 100%, now any time you turn the head unit up past 85% you will be amplifying a clipped signal.
Maybe I am looking at it the wrong way, but it sure seems like a better idea to not set the system up while pushing the head unit all the way to max output.

Also not sure why you think setting with DMM is a waste of time ... perhaps you could explain.

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