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Discussion Starter · #1 ·
I have a 2015 JKU 130 HU (no alpine amp). I’ve upgraded the speakers with the 77kick10’s and 77kick25s. I added my own amp and I’m using a passive PAC LOC (transformer isolation). I polyfilled the speaker boxes and added deadener to the insides of the speaker boxes.

Some questions for you audiophiles:

1) Even in stock form, I heard some light hissing through the speakers at low volumes on FM, Sat and through the Ipod input. The hissing almost sounds like a phaser effect from an electric guitar. The hissing is amplified with my amp. I even hear this when changing Sat stations. Perhaps most people wouldn’t notice this, but it bugs me. Is this just the way the Jeep HU’s are?

2) I have a spectrum analyzer and a sweep audio source so I can look at the entire frequency response or focus on certain ranges of my system. Down low, the 77kick25s are flat to about 100 Hz then at about 80ish Hz they drop off by about 6dB. There is also are resonance at about 45ish Hz. The resonance causes some distortion with the thumps. The 25’s are a little loud from a balance standpoint with the 10’s because of their location up front, and I’d like to attenuate them some and get rid of the low frequency distortion. The 25’s handle a little less power than the 10’s too, and since they are driven in parallel, the 25’s become limiting. For the 25’s, I’m torn between using a simple LPAD to drop the output some or using a bass blocker with a 400uF capacitor (~100Hz). I have both resistors and bass blockers on order. Both will help with the 45ish Hz resonance/distortion. What do you recommend?

3) I read a few times here that the factory HU reduces the bass at high volume levels. Is this really true? If so, how does the upgraded factory audio system handle the varying levels of bass at different volume levels since the HU feeds the inputs for the factor amp?

4) Are the signals sent to the fronts and rears the same from the factory HU? I’m not worried about volume, but from a frequency perspective?

5) Do the Raxiom HUs have better audio characteristics than the factor HUs?
 

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1) Even in stock form, I heard some light hissing through the speakers at low volumes on FM, Sat and through the Ipod input. The hissing almost sounds like a phaser effect from an electric guitar. The hissing is amplified with my amp. I even hear this when changing Sat stations. Perhaps most people wouldn’t notice this, but it bugs me. Is this just the way the Jeep HU’s are?
I never noticed a hissing issue when I had the 130. You can disconnect the RCA's from the Amp to see if the hiss is coming from the Amp or not. If the hiss goes away then the hiss is in the signal from the HU. If it does not, then the amp itself is introducing the hiss.

2) I have a spectrum analyzer and a sweep audio source so I can look at the entire frequency response or focus on certain ranges of my system. Down low, the 77kick25s are flat to about 100 Hz then at about 80ish Hz they drop off by about 6dB. There is also are resonance at about 45ish Hz. The resonance causes some distortion with the thumps. The 25’s are a little loud from a balance standpoint with the 10’s because of their location up front, and I’d like to attenuate them some and get rid of the low frequency distortion. The 25’s handle a little less power than the 10’s too, and since they are driven in parallel, the 25’s become limiting. For the 25’s, I’m torn between using a simple LPAD to drop the output some or using a bass blocker with a 400uF capacitor (~100Hz). I have both resistors and bass blockers on order. Both will help with the 45ish Hz resonance/distortion. What do you recommend?
This is one reason I don't like the idea of replacing the factory component system with multiple coaxials per channel. You now have multiple speakers on each channel capable of covering ~200hz and up while only one of them is useful below that. The result will be a very lean sound. There is no doubt the 3.5" drivers need a bass blocker; 100uF will be a 400hz 1st order HP filter. And yes, an L-Pad can be added to the 3.5s to attenuate their output. I highly suggest a traditional component setup OR go with a 3.5" coax (or fullrange) in the upper dash and a mid-bass in the lower dash (a 3-way system if you will). Regardless, you shouldn't have multiple drivers on the same channel covering the same frequency range. You could also try disconnecting the tweeter on the 6.5 coaxs...the ones in the 3.5s are more than enough.

3) I read a few times here that the factory HU reduces the bass at high volume levels. Is this really true? If so, how does the upgraded factory audio system handle the varying levels of bass at different volume levels since the HU feeds the inputs for the factor amp?
My RTA analysis of the system showed the bass start to get reduced around 22-33 on the 130. Of course this might not be a reduction from a flat signal, but could actually be a reduction of a loudness feature (one that boosts bass/treble at lower volumes). I did notice that there is very little output below 50hz regardless of the volume. This was evident when I switched to an aftermarket HU and suddenly there was actual lower bass without any change to the amp/speakers I was already using with the stock HU. The Alpine upgraded system does some signal processing either via the CANBUS or the amp. This is why it's able to have different profiles for top on vs top off. It's also why you lose fade with the Alpine system unless you go with the iDatalink Maestro harness which communicates with the CANBUS.

4) Are the signals sent to the fronts and rears the same from the factory HU? I’m not worried about volume, but from a frequency perspective?
As far as I could tell, they were the same.

5) Do the Raxiom HUs have better audio characteristics than the factor HUs?
No clue, but if you care about SQ, then I wouldn't get any aftermarket HU that doesn't have both time alignment and a much better EQ (either 13 band fixed or a 9 band parametric).
 

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Discussion Starter · #3 ·
webwarmiller,

Thanks for the info!

"I never noticed a hissing issue when I had the 130. You can disconnect the RCA's from the Amp to see if the hiss is coming from the Amp or not. If the hiss goes away then the hiss is in the signal from the HU. If it does not, then the amp itself is introducing the hiss."

It sounds like a swishing sound. It's not real loud and any normal music volume buries the noise. I disconnected my RCAs from the PAC to the amp and the sound went away. I disconnected the input to the PAC (with the amp-PAC RCAs still connected) and the sound also went away (I wanted to see if the PAC was picking up noise). I really think its coming from the head unit. Almost if the the HF circuitry is being aliased down into the audible range.


Could you please expand on this a little more:

"I highly suggest a traditional component setup OR go with a 3.5" coax (or fullrange) in the upper dash and a mid-bass in the lower dash (a 3-way system if you will). Regardless, you shouldn't have multiple drivers on the same channel covering the same frequency range."

The bass blockers I have on order are a high pass for ~100 Hz and above. You mentioned a 100uF for ~400 HPF. Do you think the 400 Hz HPF would be better?


"My RTA analysis of the system showed the bass start to get reduced around 22-33 on the 130. Of course this might not be a reduction from a flat signal, but could actually be a reduction of a loudness feature (one that boosts bass/treble at lower volumes)."

I noticed this too. It seems like a loudness feature. At low volumes my bass seems to be boosted.


I did notice that there is very little output below 50hz regardless of the volume."

I noticed a sharp cut off below 50 Hz. I'm boosting the 40Hz range and it helps bring that back, but still not there.

What head unit do you have, if you don't mind me asking?
 

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webwarmiller,
I disconnected my RCAs from the PAC to the amp and the sound went away. I disconnected the input to the PAC (with the amp-PAC RCAs still connected) and the sound also went away (I wanted to see if the PAC was picking up noise). I really think its coming from the head unit. Almost if the the HF circuitry is being aliased down into the audible range.
Are there any changes to the sound if the engine is running or not? Does it change pitch in relation to the engine RPM?

Could you please expand on this a little more:
"I highly suggest a traditional component setup OR go with a 3.5" coax (or fullrange) in the upper dash and a mid-bass in the lower dash (a 3-way system if you will). Regardless, you shouldn't have multiple drivers on the same channel covering the same frequency range."
Think of it in terms of a home 2-way speaker that has a woofer and a tweeter. If you were to upgrade, would you replace that single speaker with two separate speakers, each with its own woofer and tweeter? Of course you wouldn't. You would replace it with a single 2-way speaker (woofer/tweeter) or perhaps a 3-way speaker (woofer/mid/tweeter). Why people are replacing the stock component system with multiple coaxials baffles me.

The bass blockers I have on order are a high pass for ~100 Hz and above. You mentioned a 100uF for ~400 HPF. Do you think the 400 Hz HPF would be better?
A typical 3.5" speaker only has a usable range down to about 150hz or so and even that is pushing it. A 100hz bass blocker does not BLOCK all frequencies below 100hz; it's simply the -6dB point of the 1st order HP filter. You'll be 12dB down at 50hz, 18dB down at 25hz, etc. That's simply not a high enough crossover point and/or a steep enough slope (6dB/octave) to allow a 3.5" driver to play very loudly before reaching its mechanical limit. A 400hz 1st order filter means you'll be 18db down at 100hz and 24dB down at 50hz which is quite a good deal more protection for the driver. This will allow the driver to play a good bit louder before breaking up.

What head unit do you have, if you don't mind me asking?
Alpine CDE-W265BT. I'm not a touchscreen fan and it's the only current non-touchscreen double din unit on the market that gives me time alignment and an advanced EQ (9-band parametric).
 

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Discussion Starter · #5 ·
webwarmiller,

Thanks for the advice and insight.

"Are there any changes to the sound if the engine is running or not? Does it change pitch in relation to the engine RPM?"

This is with the engine off. I can hear it with the engine running too. No change in noise with engine RPM that I can tell.


"Think of it in terms of a home 2-way speaker that has a woofer and a tweeter. If you were to upgrade, would you replace that single speaker with two separate speakers, each with its own woofer and tweeter? Of course you wouldn't. You would replace it with a single 2-way speaker (woofer/tweeter) or perhaps a 3-way speaker (woofer/mid/tweeter)."

I see your point - thanks


"A typical 3.5" speaker only has a usable range down to about 150hz or so and even that is pushing it. A 100hz bass blocker does not BLOCK all frequencies below 100hz; it's simply the -6dB point of the 1st order HP filter. You'll be 12dB down at 50hz, 18dB down at 25hz, etc. That's simply not a high enough crossover point and/or a steep enough slope (6dB/octave) to allow a 3.5" driver to play very loudly before reaching its mechanical limit. A 400hz 1st order filter means you'll be 18db down at 100hz and 24dB down at 50hz which is quite a good deal more protection for the driver. This will allow the driver to play a good bit louder before breaking up."

When I put my microphone near the 3.5", I see a flat response to 100Hz then is starts to drop as I go lower. Now I'm re-thinking my original cutoff frequency. I have to think about imagining too. It might be a trial an error thing testing different capacitors.


"Alpine CDE-W265BT. I'm not a touchscreen fan and it's the only current non-touchscreen double din unit on the market that gives me time alignment and an advanced EQ (9-band parametric)."

The high number of equalizer bands and being able to time shift seem pretty attractive. I have to look into this further.
 

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The hissing is most likely being picked up by the RCAs from your POWER cable on the amp. Move them to the opposite side of the vehicle and/or buy very high quality insulated wire.
 

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Definitely possible, but ....

I'll also add that when I added an amp and AudioControl DQDX to my RHR730N head unit, I encountered some hiss/noise that I don't think was caused by the power cable.

I believe the factory head unit really does just introduce a bit of noise, but it's pretty well masked in the factory OEM setup because the power amp isn't really amplifying the original signal enough to matter. (If you play music tracks saved to the internal hard drive of the 730N and skip forward/back between them, you can often hear a little bit of digital "static" that sounds like RF noise from the hard drive loading data.)

I wound up turning down the input gain on the AudioControl to nearly the minimum and turning up the output gain from it to keep the hiss at levels no greater than the OEM system had. But when I "optimized" the levels like the AudioControl instructions recommend to get the highest signal level possible without distortion -- it was pretty bad.


The hissing is most likely being picked up by the RCAs from your POWER cable on the amp. Move them to the opposite side of the vehicle and/or buy very high quality insulated wire.
 

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I replaces everything in my 2013 and I noticed hissing also. Clarion NX604, Alpine PDX5, Polk coaxial up front and component in the bar.

I turned the gain in the amp down and it lowered the hissing immensely. Because the some head units output 4v you dont always need the gain above 50%. Also set the crossover to the lowest setting.
 

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Discussion Starter · #9 ·
The hissing is most likely being picked up by the RCAs from your POWER cable on the amp. Move them to the opposite side of the vehicle and/or buy very high quality insulated wire.
I can't say yes or no. My amp is under the passenger seat. My power wires run under the door sill and into the engine compartment. My RCAs are run along the center console. I'm using shielded coax RCAs vs twisted pairs.
 

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Discussion Starter · #10 ·
I'll also add that when I added an amp and AudioControl DQDX to my RHR730N head unit, I encountered some hiss/noise that I don't think was caused by the power cable.

I believe the factory head unit really does just introduce a bit of noise, but it's pretty well masked in the factory OEM setup because the power amp isn't really amplifying the original signal enough to matter. (If you play music tracks saved to the internal hard drive of the 730N and skip forward/back between them, you can often hear a little bit of digital "static" that sounds like RF noise from the hard drive loading data.)

I wound up turning down the input gain on the AudioControl to nearly the minimum and turning up the output gain from it to keep the hiss at levels no greater than the OEM system had. But when I "optimized" the levels like the AudioControl instructions recommend to get the highest signal level possible without distortion -- it was pretty bad.
This is similar to the hiss or swish I hear when changing Sat channels or song on a USB.
 

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This is with the engine off. I can hear it with the engine running too. No change in noise with engine RPM that I can tell.
Not a ground loop issue then. Most likely just a slightly dirty signal from the HU.

When I put my microphone near the 3.5", I see a flat response to 100Hz then is starts to drop as I go lower. Now I'm re-thinking my original cutoff frequency. I have to think about imagining too. It might be a trial an error thing testing different capacitors.
Simply being capable of playing down to 100hz and being able to play that low at the max volume you will listen to the system are two completely different things. Since they are free-air in the upper dash there is zero cone control that an enclosure would provide.

The high number of equalizer bands and being able to time shift seem pretty attractive. I have to look into this further.
I would say they are paramount in trying to achieve better than just OK sound quality. Let me put it this way. I would rather have a $100 speaker budget along with time alignment and a full featured EQ than a $1,000 speaker budget without time alignment and a full featured EQ. Even the most expensive speakers in the world will have frequency abnormalities within a vehicle's interior. Time alignment is the difference btw the driver's side upper dash speaker being overly dominate and hearing a singer's voice appear to come from over the center of the dash.
 

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Discussion Starter · #12 ·
I replaces everything in my 2013 and I noticed hissing also. Clarion NX604, Alpine PDX5, Polk coaxial up front and component in the bar.

I turned the gain in the amp down and it lowered the hissing immensely. Because the some head units output 4v you dont always need the gain above 50%. Also set the crossover to the lowest setting.
Interesting, this almost sounds like you had noise entering your amp. However, I can try this by increasing the gain on my PAC LOC and turning my amp gain down to see if this helps.
 

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Discussion Starter · #13 ·
Not a ground loop issue then.
Simply being capable of playing down to 100hz and being able to play that low at the max volume you will listen to the system are two completely different things. Since they are free-air in the upper dash there is zero cone control that an enclosure would provide.
I was actually thinking about sealing the opening for these. I was hoping this would help dampen the resonance at 45ish Hz.

I might try an experiment. Since the 6.5s point at your knees and the 3.5s point up, I might sweep a tone and see where the 3.5" are dominating and make a crossover for around that frequency.
 

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I would get a high quality twisted pair of rcas. What brand are you using right now? Don't bother with a noise reducer they have never worked for me.
 
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