Will a DSP fix my volume control? Volume too high at start & too low past halfway

[nkresho]

Will a DSP fix my volume control? Volume too high at start & too low past halfway

I installed a pair of amps a few months ago and still can't get my volume situation sorted out. It's working, just has bad granularity.

• 2016 S model (no fender audio)
• factory interior speakers
• factory head unit
• Using high (speaker level) inputs on both amps

4 channels of speaker level signal run from behind glovebox to trunk. This runs to the 4channel amp inputs. The front channel high-level input splits to the sub amp speaker-level input as well. On the output side of the 4 channel amp, another bundle of 4 channels runs back to the glovebox and then to the factory speakers.



4 gauge power to battery, distributed to 8 gauge to each amp

Alpine MRV-F300 (4 channels, 4x50RMS) to factory interior speakers
Alpine MRV-M500 (mono 500x1) to JL 10w3v2d4 (x1) in center of spare tire

The two issue I am having:

1. When I turn any audio source on, with the volume all the way down, I then turn it up one notch. That one notch is louder than it should be. There's no real quiet setting any more. It's like it comes on at volume 5, rather than volume 1. My wife is not happy with this function and regularly mentions it. It's noticeable.
   
2. When I turn the volume up, past 1/2 way, there's no audible increase in sound. It doesn't get louder, doesn't add more bass from the sub, no more distortion, no audible clipping, nothing... It just stays the same all the way to the 100% level.

volume seems to adjust appropriately from that one notch to about 1/2 way...

Gain control on both amps were set a number of ways to try to remedy this:

1. radio volume at about 80%, turn up gain until there's slight distortion of sound, then back down ~1/8th turn.
   
   Still no change at volume 1, still no audible increase past halfway
   
2. radio volume at 100%, turn up gain until there's slight distortion of sound, then back down 1/8th turn.
   
   Still no change at volume 1, still no audible increase past halfway
   
3. radio volume at one notch, leave gain all the way down.
   
   Still relatively loud at volume 1 on head unit. Pretty quiet to 1/2 way and to 100%

The 4 channel amp gains never make it past about 1/4 or 1/2. I can get distortion over these levels. The issue is that the distortion comes on at about 1/2 headunit volume just as it does at 100%.

So, I am thinking there's an issue with the factory eq curve. Protecting speakers or limiting distortion.

I'm plenty happy with the sub output. Bass is clean and appropriate to fullrange speakers. Still no real increase past halfway on the volume knob, but sounds in proper proportion to the rest of the system.

Here's what I think might be happening:

The factory system is sensing impedance (or something else?) at the amplifier's high level input circuit, and it's being confused, as it typically sees an actual speaker load. This could be affecting the low (level 1) volume as well as the past halfway volume.

Past halfway on the volume knob, the car is automatically limiting output to protect speakers. I'm not sure how this might be achieved. I'm equally unsure of how to bypass it.

I've read about mk6 or mk5 cars being able to VAGCOM out the factory EQ. I'm not seeing anything for our cars. This would be a great place to start, since it's free and I could do it easily.

If anyone is aware of any coding in VCDS, please share. I would love to try this first.

Here's a thread that gets somewhat close, but not exactly what I need. http://forums.ross-tech.com/showthr...-and-Fender-move-to-Dynaudio-Long-coding-help (first two posts)

Additionally, I've been reading up on the audiocontrol LC7i, JL audio FIX-86, and audison bit ten.

What do you all suspect I will see, with regards to problem 1 and problem 2, if I install one of these? They range from the $115 range (lc7i) to $340 (bit ten & JL).

Preemptive thanks

 

[Cruiser]

Is your sub amp input from four channel preout?

 

[nkresho]

My 4 channel amp doesn't have a preamp output.

I split the front L&R channels of radio output between the fronts (to the 4 channel amp) and the sub amp.

Incidentally, the sub has remote gain in the cubby under the steering wheel.

 

[nkresho]

Here's what i'm working with for amps:

I'm using both front and rear high-level inputs for the 4 channel. For the sub amp, I am using just channel 1 and 2 for inputs, same as 1&2 for the 4 channel amp.



4 channel amp has the high-pass filter enabled, crossed at about 80hz, f&r
Sub amp is fixed low-pass crossed and around 100hz, bass eq is at zero

 

[beardedGTI]

If I understand your post, you have the front speaker level running parallel to both inputs on both amps? What happens if you disconnect sub amp speaker level completely, make sure HU fade is centere, then re-adjust gain on speaker amp?

I don't have any experience/have never seen anyone parallel speaker level channels into amps before. Someone feel free to jump in and correct me, but I don't think you can connect amps that way. The speaker level inputs emulate a reactive load so the HU thinks it's plugged into a speaker like normal. So when you parallel them, you're effectively halving the impedance the HU sees which it probably really doesn't like, especially when you crank it. First step in troubleshooting though is to physically disconnect sub amp input and re-do set up procedure.

 

[Cruiser]

Correct, the impedance is now half of what the head unit was designed for.
Consider using a crossover such as Audicontrol 6XS or equivalent.
A DSP can do the same thing but more money and more features which is good if you want to spend time tuning

 

[beardedGTI]

My advice, if this was indeed the problem and you don't care about controlling volume fade from the HU, would be to simply run fronts to the 4 channel amp, and rears to the sub amp. My interpretation of alpine literature, the 4 channel amp will automatically sense and use only a 2 channel source if that's all that is available.

• Only left/right channel speaker level input is required. However, all speaker input leads (FL/FR/RL/RR) may be connected to prevent zero output when the head unit fader is adjusted.

If you do require the use of fade from the HU, then money will need to be spent on some fancy summing LoC's. But still, need to verify this is indeed the issue first.

 

[Cruiser]

Do the rears have full range? Most newer cars have a limited range going to rear speakers, no highs and no lows. If the system does not have a subwoofer from factory, then the front would have full range for sure. If the factory system has subwoofer, neither front nor rear have full range.
The best case for simplicity is an amp with preout,
But even then, my preference is not to run speaker level inputs. I rather would use a line out converter and use the rca inputs and the preout for sub amp

 

[beardedGTI]

That's a good question and something I don't know. I'd be kind of surprised if they were applying separate adjustments to the rear on the base stereo, but it's certainly possible. IIRC, they even went so far as to use the same exact drivers between the F/R on the golf. But if they are different signals, then prob best to use a lc7i to fix all of this. The fix-86 sounds a bit like overkill because I kind of doubt factory base stereo has time alignment that would need correcting.

 

[nkresho]

If I understand your post, you have the front speaker level running parallel to both inputs on both amps? What happens if you disconnect sub amp speaker level completely, make sure HU fade is centere, then re-adjust gain on speaker amp?

I don't have any experience/have never seen anyone parallel speaker level channels into amps before. Someone feel free to jump in and correct me, but I don't think you can connect amps that way. The speaker level inputs emulate a reactive load so the HU thinks it's plugged into a speaker like normal. So when you parallel them, you're effectively halving the impedance the HU sees which it probably really doesn't like, especially when you crank it. First step in troubleshooting though is to physically disconnect sub amp input and re-do set up procedure.

Yup. I actually just went to re-check, since it's been a while since I installed it all. I actually have the front and rear channels going to both amps. So each signal is split.

Makes sense.

Correct, the impedance is now half of what the head unit was designed for.
Consider using a crossover such as Audicontrol 6XS or equivalent.
A DSP can do the same thing but more money and more features which is good if you want to spend time tuning

I should have paid more attention to that. I just checked and one amp's inputs are higher than the 20ohm setting on my dmm. Going to have to crank it up higher and see if it's in the hundreds.

Do the rears have full range? Most newer cars have a limited range going to rear speakers, no highs and no lows. If the system does not have a subwoofer from factory, then the front would have full range for sure. If the factory system has subwoofer, neither front nor rear have full range.
The best case for simplicity is an amp with preout,
But even then, my preference is not to run speaker level inputs. I rather would use a line out converter and use the rca inputs and the preout for sub amp

It sounds like they have full range going to them. I set the gains separately from the fronts and didn't notice any difference in frequency response.

I think i'm going to try audiocontrol first. Ordering tonight.

Thanks everybody!!!

I'll report back soon.

 

[beardedGTI]

I should have paid more attention to that. I just checked and one amp's inputs are higher than the 20ohm setting on my dmm. Going to have to crank it up higher and see if it's in the hundreds.


It sounds like they have full range going to them. I set the gains separately from the fronts and didn't notice any difference in frequency response.

I think i'm going to try audiocontrol first. Ordering tonight.

Thanks everybody!!!

I'll report back soon.

It sounds like your trying to measure impedance on your amps input. You're unlikely able to do this with a dmm. Impedance is a little different than resistance and requires special equipment.

Before you spend any money on an audio control, why not simply disconnect the sub amp input to make sure this is indeed the problem. It doesn't cost anything and takes ~2 mins. Plus if you can verify rears have full range, I gave the solution above on how to fix without spending any money at all.

 

[hal]

He's not connecting two speakers in parallel to cause the headunit to see half the impedance. He's connecting two amps. Most people tap into the factory speakers to power a subwoofer amp anyway.

I would try to isolate the problem by connecting one speaker at a time.

But first, try a lower volume to set the amp gains and use a multi-meter to measure the voltage at each amp high-level input instead of listening to distortion. I think the factory head units clip way before 80%.

Alpine amps can usually deliver more than the advertised rating and you are using one capable of 50w rms to drive a 20w rms factory speaker. I'm not even sure how much better you expect the speakers to perform with an aftermarket amp.

 

[nkresho]

It sounds like your trying to measure impedance on your amps input. You're unlikely able to do this with a dmm. Impedance is a little different than resistance and requires special equipment.

Before you spend any money on an audio control, why not simply disconnect the sub amp input to make sure this is indeed the problem. It doesn't cost anything and takes ~2 mins. Plus if you can verify rears have full range, I gave the solution above on how to fix without spending any money at all.

Yup, was trying to measure the resistance of the speaker level inputs. I got a reading. 8.5 k ohms between positive and negative on each channel. From what i'm reading this is expected. In comparison to the factory speakers, this might be causing some of the issues. Especially since i'm effectively doubling this value with both amps connected.

Reviewing the literature, the lc7i gives 20k ohms of input resistance.

Literature for the alpine amps just says >10k ohms.

Rears are definitely full range. The tweeter and mid are audibly very similar to the front speakers. I isolated them when tuning the input gain controls and didn't hear a difference in output.

I did run without the sub connected for about a week, while I was working on my sub enclosure. I just unplugged the high-level input to the amp (signal-sensing turn-on). I didn't notice any difference in volume granularity at the time, but I wasn't looking for it.

I will give that a try again, and see if I can get full use of the volume control with just the one amp (4ch) connected.

And, not that I ever use it, but I do want to retain fade control.

He's not connecting two speakers in parallel to cause the headunit to see half the impedance. He's connecting two amps. Most people tap into the factory speakers to power a subwoofer amp anyway.

I would try to isolate the problem by connecting one speaker at a time.

But first, try a lower volume to set the amp gains and use a multi-meter to measure the voltage at each amp high-level input instead of listening to distortion. I think the factory head units clip way before 80%.

Alpine amps can usually deliver more than the advertised rating and you are using one capable of 50w rms to drive a 20w rms factory speaker. I'm not even sure how much better you expect the speakers to perform with an aftermarket amp.

What am I looking for voltage-wise when checking to set gain? I assume I'm measuring AC. Would I run a sine-wave through the head unit and see where voltage peaks? Never done it this way before (or heard of it).

Also, I am well aware of the effects of running 50w into 20w speakers. It sounds leaps and bounds better than stock, and I can listen to music on the highway with the windows down. Wattage does not damage speakers, distortion and over excursion do. My factory components are neither bottoming out or distorting at max volume. I'm happy with the output, just want to use my whole range of volume settings. For now, I have no use of the upper half.

 

[hal]

Sorry I'm a bit sleepy I meant measure the voltage out from the amp by setting the gain to output a voltage of 12.6V at each speaker when you set maximum headunit volume.

Disconnect the speakers and measure the voltage at the amp out and see how much you are getting as you gradually increase the volume. Your maximum shouldn't exceed 12.6v per channel.

I was thinking maybe the amp is what causes the loss of loudness post the 1/2 mark but then I can't say why both amps would do that.

Still, doesn't hurt to test each speaker separately first and re-set your gains properly before deciding to spend anything extra.

And never mind the head unit clipping point I mentioned. I would personally set it less than 80% but for you that will limit the dynamic range even more.

 

[nkresho]

Found an article describing the voltage measuring method of setting gain: http://knowledge.sonicelectronix.co...-amplifier-gains-using-a-digital-multi-meter/

This is the part I was not quite grasping:

Step 5: Now we must find the voltage that we need to set the gain to. Voltage = square root of watts x ohms. For example, a 500W RMS amplifier at 2 Ohms would configure like this: 500W RMS X 2 Ohms = 1000W. Now take the square root of 1000W and your voltage should be 31.62V if you’re running an amplifier with one gain control. Some amplifiers have 2 gain controls so treat it as two separate amplifiers. If the amplifier is 100W RMS by 4-channels for a total of 400 watts but has two gain controls, use the power output of ONE channel*and use that for your voltage calculations. (EX: Square Root of 100W RMS x 2 Ohms = Voltage for each gain control per channel.)

My 4 channel puts out 63 watts x4 @ 4 ohms (per birth cert). 63*4=252 Square root of 252=15.87v And I need to run a sine wave test tone of ~1000hz to see if I reach that voltage. I may just run a sweep and look for the peak.

Reading further on a few other forums, I need to do this test with a load on the amp (speaker and meter connected at the same time). I can check both ways.