We spend thousands of dollars on our audio systems just to end up guessing where our HU begins to distort. After all, assuming we are sending a clean signal to our amps is a rather risky way to go about things when setting up our systems.
Enter the SMD DD-1. For those who haven't heard of this yet... It is a distortion detector that was designed by D'Amore Engineering along with Steve Meade (the guy with the 30k watt Tahoe that everyone either loves or hates on YouTube)
Who he is, and what he does is beside the point, but the simple truth is that the DD-1 works. I run JL Audio in my car and finding out that the engineers at JL Audio got their hands on this tool, ran it through their tests against their O-scopes and gave it a thumbs up is rather reassuring.
It took me a few days to justify the purchase price of $160, but then I looked at it this way...
You buy a car for $25k and add a $2k Elite protection plan for peace of mind. This works the same way. You spent $2k on your system and this is merely a protection plan to ensure that you are not baking your equipment while enjoying it.
This is by no means a product endorsement, but I just had to give it props since I now know how far I can push my system and be sure that I am distortion free and my gains are set properly.
Those who are blessed with access to an O-Scope to set their gains will still only see clipping from the amp when tuning. The DD-1 actually shows distortion, which occurs before clipping. Bottom line is even if you aren't clipping, you may still be sending a distorted signal to your amp.
The point of this post is not necessarily to have everyone run out and buy one. In fact, I won't even tell you where you can get one unless someone asks, although you can easily find it online.
The real reason for this post is to possibly help out my fellow G35Driver community members by letting you all know where our Bose HU begins to distort.
Since I'm feeding my amp from the SUB OUT of the HU before the Bose amp, that is all I tested so far.
The results are as follows: With Bass, Treble, balance, and fader set to 0, the HU begins to distort when the volume indicator shows only 3 unhighlighted ticks. This means that the highest volume you should ever set your Bose HU to when tuning your setup is the second click of the volume **** (clockwise) while the volume indicator shows 4 unhighlighted ticks.
This is also the highest volume you should ever set your HU to when playing your system if you want to be absolutely sure you are sending a clean signal for amplification.
I can make a video of this and also test the full range outputs of the HU if there is enough interest. I mean, I've got to justify the money I spent on this thing somehow.
I sure hope this helps some people out. Enjoy, and happy bumping!

 

Doesn't the Bose equalize differently based on volume as they do with their other products? I would think this would skew any distortion test because the distortion is manufactured and intentional.

In any case, that is interesting stuff and thanks for sharing!

 

The Bose EQ appears to occur at the Bose amp, and since the signal is tapped before the Bose amp, it should not be affected by it. You are right though, Bose does quite a number on the output signal. But most every HU, be it Bose or not has a point of distortion. There are some aftermarket units that will produce a clean signal even at full tilt when playing a -0 dB signal. I really wish our HU did, but it doesn't appear to be the case. This is why it's important to note that our HU has a distortion point and not go above it to set up your system.

 

Isn't the level of the signal a huge variable in this test? Did you use a test cd? If it was the bass, what frequency was the test. I have some old cds that have a much lower playback volume than newer ones. Your ipod signal may have a different frequency response than the fm radio, ect. Bottom line, listen to your music. If it starts to sound muddy, you are losing the peaks and probly distorting. Oh, that fart noise coming from your subs, that is distortion, too.

 

For the sub amps, you use a 40 Hz tone recorded at -3dB for best quality, a -5dB tone for a compromise, and a -10dB tone if you are after the loudest system but with more risk of clipping. When your music is audibly distorting, you are way past the point of safety. And you don't even have to have the volume cranked to be distorting if the gain isn't properly set, or the head unit fails to output a clean signal when a certain DSP effect is activated that "appears" to improve imaging for example. So saying "just listen to the music" is like adding a supercharger to your engine and running 87 octane gas and listening for pinging before letting off of the throttle.
If you invested a good deal of money into your sound equipment and do plan to put it through its paces on occasion, wouldn't you rather have your equipment properly setup so your amp doesn't just die one day or you don't end up blowing your sub some time down the road? You'd be surprized how many people with rather expensive systems find blowing a sub or frying an amp to be a totally normal occurrence.
Anyway, you use a 1,000 Hz tone recorded at either -3dB or -5dB (again, depending on how conservative you wish to tune your system) to setup your mid and upper frequency amps. The head unit distortion point is found by using an unattenuated -0dB test tone.

 

The head unit only has 6 ticks? I thought it had more than that... I will have to check on my way home from work.

 

Yeah, I show about 12 ticks??? Maybe the nav and non-nav are different?

 

Sorry, I missed your posts somehow.
When you're in the tone control menu of the Bose HU, one click of the right **** is equal to one tick on the display and the tone controls can be adjusted from -5 to +5 with 0 being the center of the adjustment range (specified by a beep when you reach it).
When you're adjusting the volume, the Bose HU goes from 0 to 31 if you count the **** clicks. It takes two clicks of the volume **** to move up one tick on the screen. The maximum distortion free volume setting of the Bose HU is 24 out of 31 clicks of the volume ****. Hope this helps.