So recently Mark@lowlife posted the use of high level inputs on higher end installs based on a great recommendation he received. I've always been under the assumption that low level (RCA) will yield better sound quality and use them whenever possible. BUT....this being a bike, not all car audio rules apply so I figure ---- hey why not, lets give it a try.

Using a Kenwood 998 Headunit, Fosgate T400X4AD Amp, PA style 6.5 in the fairing, Hertz HCX 165 in the lowers.

Setting the gains using the Fosgate input and output clip lights.

Input clip light with RCA - 35 out of 35/max volume (so no clipping input with RCA's)
Input clip light with HL - 30 volume (clipped at 30, this means I should not raise my volume higher than this).

Output clip light with RCA - 75% gain
Output clip light with HL - 40%

Started with PA style speakers in my fairing. Immediately I noticed it sounded "stronger" and a bit louder. I played a few hip hop songs and some slower RNB songs. I switched back and fowarth between RCA and HL and noticed RCA had better clarity to it --- it sounded "smoother", but the HL sounded a bit louder. I did this with about 5 different songs and each time came to the same conclusion: HL = Louder RCA = Sound quality. Ultimately decided the slight increase in volume wasn't enough for the loss in SQ. Left the PA speakers with RCA's.

Then moved to my lowers where I have HCX 165's. First listened to them with RCA's...they sound very warm in that location. Switched to HL's and bam...they were louder. I cranked the volume up and oddly enough they sounded better, the highs seemed louder and more pronounced. I thought maybe it was the song, still had something connected, perhaps a tweeter. Nope tried numerous ways and sure enough the HL won. Didn't think it was happening so I texted Gannicus some vids!! My guess is the PA style speakers are less forgiving and have a very high sensitivity. I've connected to "warm" sounding amps and the speakers just sounded muddy. The coaxials enjoy power more, my guess is when combine that with the lower amp gains the result was sounded better. I was very surprised. Now the catch here was then matching my gains so that all channels are maxed out around 30 to match the HL channel on the amp vs. 32-35 for the channel (and second amp) set for RCA's.

I'm not advocating one way or another because as you can see it sounded great for one speaker and crappy for another. Who knows how it will sound with a lesser quality head unit. What I will say is ---- Try it. If you're installing an amp and have some coaxial going in test both ways and report back and let us know how it sounded for you. I'm no engineer and can't break down the why's....but I liked the sound so much, I left the HCX channel connected via HL inputs.

My bike sounds better today than it did yesterday.

 

Good to hear. Since the weather took a turn for the worst around here and looks like it is here to stay I might have to pull the fairing and switch some wiring around.

 

Nice write up HAZE! I guess we live and learn something new everyday. I would have never believed it if I had not heard it with my own ears. I was getting bored and you just gave me something to do. Time to play

 

That's awesome feedback! Especially documenting the gain changes. The most interesting part is that SQ on coax vs PA were different!!
The way it was explained to me is that the bike noise doesn't cause an interference bc the noise floor is lesser than the signal. Anytime you can increase V from the HU, the amp doesn't have to work as hard to amplify allowing you to run gains lower...as Haze noted in his test. When you can run the gains lower it reduces the noise transmitted as a hiss or slight hum through the speaker. In turn that produces better SQ bc your clearing that noise from the audio. Which is one of the main reasons HU's like the Kenwood x998 are used by guys like Haze. 4v pre outs vs 2v on lesser HU.

Motorcycles don't have the same beefy charging system as a car. This is the main reason amps are so ineffient on them compared to cars. Look at the HD amps from JL. It's a D class amp with 4 x 150. I get more volume on the same speaker set up with a JL M400/4 than a JL MHD600/4. The bike just can't power the HD amp as well but it blows the M400/4 away on my boat that has 2 batteries. Yet both are D class amps. Since the bike lacks juice (even if the input at the amp reads 14.5 V it's not really consuming it) increasing the output from the HU by 1v should be a positive in getting the most from your system. So Haze may have gone from a 4v pre out to a 5v by running HL. This is why my normal start to building a system begins with the HU and amp. Running 2 small amps actually produces more power than one large amp most times bc the smaller ones are more efficient and only need to work a fraction of what the larger amp does to produce good power. Great post Haze with good documented stats from your testing. I NEVER would have predicted the effect on loud speakers would have differed from coax.

 

One thing I forgot to do, and I told myself to do it but forgot was to check the V from the high level inputs. I think from 75% gain to 40% gain it's going to be much higher than 5V. I think with the sensitivity from the PA speakers it was just too much juice. Perhaps if I had lowered the gains some I could get it to sound just as good....I was going strictly off the same gain clip light procedure I followed with RCA's.

 

I noticed a difference in sound, I have a stock HU, moto 6.2, hotunes tweeter bar, SS PN4.1000d, when I ran the pac audio loc, it kinda had a hollow sound, kinda airey, I thought it was me, reconnected the high level input,of course disconnected the loc,rca's,and it sounded more full,didnt say anything to my gf and she noticed it too, will see when I get to change out the HU ,but that will be a lil bit

 

I was going to ask you about that after reading your post. I would guess you did get higher than 5V, but was going on even a low end gain assumption. This could turn out to be a really good thread. I'm learning stuff already..

 

Haze - did you poke around with the X998 internal AMP OFF? you know it will improve SQ (over RCA of course).
Overall - very interesting findings (my engineering head is now wondering why; I got a "feeling" it has to do with dynamics... hard to explain what I mean)

 

Yeah with the internal amp off running RCA's there is better SQ...."in my garage". Never tested it on the road to see if there was a difference, but I liked the sound with the amp off that I never bothered with the HU speaker wire outputs until yesterday.

I'm telling you man, the speakers in my lowers sounded better.

 

AAWAV, are you wondering why the HL is producing better SQ and power from the HU? If you have an engineering back ground you might be able to make better sense of the effectiveness HL has on a bike vs. a car than me or others on here. Your input could be very valuable.

I think it's all relative to the charging system. A car runs off an alternator, where a bike runs off the battery. The stator on a bike keeps the battery charged while the bike pulls power from it. I understand this to be the limiting factor in powering additional equipment (such as amplifiers) that draws power from the bike. It explains the lack of efficiency of an amp on a bike vs. a car I feel.