Need help with setting car crossovers and EQ (Helix DSP)

[davmol]

Edit: recently changed the title to make a bit clearer.

Bit of a lengthy one, but figured best to give all the info upfront and (hopefully) avoid too much confusion and assumptions.

I'm upgrading my car stereo and have some initial measurements. I have limited experience with REW and PEQ but not much beyond basic SPL measurements and automated processes, such as with WiiM room correction on my hifi. I did try the Helix "TunetoTarget" Beta function but it just seemed to cut all the bass from the system, so I'm probably doing something wrong with there with gains etc, hence now I've just captured the measurements in REW and now coming here for some advice. I'm mainly struggling with what to do next to achieve the best results with what I have, and hoping to better understand what is fixable with EQ, and what might need adjustments to speaker positions, or replacement drivers if really necessary.

Preference wise, I'm not a bass head, mostly listen to rock, blues, some pop, and favour clarity and balance over heavy bass lines. Generally with EQ on headphones I favour a harman curve and I have generated a house curve with a small dip at about 4k because I find that particular frequency unpleasant at higher volumes. Finally, I'm in my late 40s and these days would struggle to hear anything much beyond 13k in a blind test, so regardless of any tweeter's ability to generate "air" and "sparkle", I'm not likely to hear any of it!

Car: 2012 Audi B8 (facelift) S4 Avant - UK RHD - 10 speaker Audi Sound System (non-B&O). I'm happy to do some modifying, like small dash mount tweeters, but no custom fibreglass pods etc, as I want to keep the car relatively stock looking.

• Amplifiers (inputs are high level after the stock audi amp):
  • Helix 206DSP (6 channel amp with 8 channel DSP - extra 2 DSP outputs are line level into the 204DIRECT)
  • Helix 204DIRECT (used for front and rear subs)
• Speakers (these are all installed already):
  • Front:
    • Doors (low down) - 6.5" woofers - Focal Access 165
    • Dash L/R (firing up into windscreen) - 3" full-range - Faitalpro 3FE22
    • Dash Centre(firing up into windscreen) - stock Audi 2.5"-ish soft dome by the looks of it.
      • I have tried a Dayton RS75 in the centre as it is relatively cheap and popular in the audi B8s, but I'm not sure after measuring it, will show further down.
    • Sub (under front passenger seat) - ESX Quantum Q168P, passive sub
  • Rear:
    • Doors (low down) - ignore for now - Focal Auditor RCX-165 6.5" coaxial (never have rear passengers, likely will remain on stock amp and used as low volume rear fill)
    • Sub (upgraded driver in the factory location, which is under floor / spare wheel) - Kicker 6.75" 48CWRT672 (just the driver upgraded)

Steps taken so far:

• Set input gains on the 204 and 206 using the Helix track played direct on the head unit, at volume 22 or 34 (after 22, there will be audible distortion from stock unit).
• Using Focusrite Solo and line output from the 206, I have run AISA using the Helix DSP PC-Tool and fixed / flatted all the input signals.
• Set crossovers as 24db L-R at lowest / highest safe values so I could capture raw output.
• Run the automated time alignment using the Helix PC-Tool, using fixed mic at drivers seat headrest / ear position.
• Captured moving average measurements from drivers seat (right side remember..) for each driver independently.
  • Calibrated Emotiva EM-01 USB calibrated measurement mic and file was used for this process - 100 averages taken between left and right ears.

Below are the raw outputs (1/12 smoothing) from each driver at moderate volume (11 of 34), along with the noise floor and my preferred target curve in white.
Subs in yellow/orange, woofers are blues, "full range" tweeters are greens and red is the centre speaker.

Just for info, here is the Dayton RS75 which I dropped into the centre to try out, which which is much lower sensitivity than the other speakers anyway, but I wondered why the huge dip vs the Audi stock speaker? Is that just reflection and possibly making a bracket to tilt it a little more forward might flatten it out a bit?

The doors look particularly problematic to EQ - the Focal woofers were installed 5 years ago as part of a passive crossover component set, so they are meant to cover up to 4k but I guess those huge dips around 200 and 500 might mean I should maybe cross them very low (at maybe 400hz?), and let the dash drivers take on the rest?

Left side, including centre and left tweeter for reference:

Right side:

It definitely seems a bit trickier than following the general online advice of "set it all to 24db Linkwitz-Riley and just run auto EQ"

 

[Mark185]

The dips at 200 and 500 Hz are very likely nulls due cabin resonance modes. For example wavelength of sound at 500 Hz is ~ 0.68 meters or 2.25 feet. That probably is close to the distance between door panel and center console. You can't EQ a null like that so yes, if you can crossover to a dash or A pillar mounted driver at ~200-300 Hz, you should get a better result.

 

[superJohn]

To start with, I’d apply these settings for myself:
Mid-bass drivers: 80 Hz to 600 Hz.
Mid-tweeters: from 600 Hz upwards.
Use 4th-order Linkwitz-Riley crossovers for all channels.
Subwoofer: up to 63 Hz, using a 2nd or 4th-order Linkwitz crossover.
Apply a time delay of 1.3 milliseconds to the right mid-tweeter, and 1 millisecond to the right mid-bass driver.
Disable the center channel.
Also, disable the "Virtual Machine" feature in Helix.
If you plan to use rear speakers, apply a time delay of 7 ms to the right rear and 6 ms to the left rear.
You can fine-tune these delays by ear later to ensure the rear speakers don't pull the soundstage toward themselves.
It’s about a half-hour job.
It takes longer if you do measurements, though.
Use the equalizer to cut down any frequency peaks; leave the dips alone until you understand their underlying cause. Or better yet—just don't touch them at all.

 

[superJohn]

To avoid ruining your eyesight on graphics like these, set the anti-aliasing to 1/6—or even 1/3.
At least then something will be distinguishable)

 

[davmol]

So I've been working on this for a while and come across some bits on various forums and youtube channel. The car (Audi S4-B8 model) has settings coded into the car which alter the profile. I used VCDS to change the sound profile setting to "External Amplifier" and this then produced a ruler flat (input) response on all channels from 100hz to 20khz, so I no longer need to EQ each input channel. However, I noticed that the volume control has a dynamic bass control with bass increasing at lower volumes, which is why the bass response was huge in my REW charts above.

Here is a chart of the bass response at volume 5 (red line off the charts) going up by 5 volume steps at a time to the max of 34. Typically level 10 (blue) is about as quiet as I would listen. Level 15 (green) is normal, 20 (yellow) is loud and 25 (pink) is the absolute max I could ever tolerate (input gains set at volume level 26). The dark red at the bottom was the input EQ correction I applied at the max gain volume of 26, and there is only minimal bass response change from then up to 34 at that point:

Problem now comes on what to do in respect of output measurement and EQ. I could stick some earplugs in anddo some pink noise recordings at volume 26 (where the input level clips are set), but would it be better to instead flatten the bass response using the input EQ at volume 15 (typical listening level) and do my output EQ at that level?

 

[Mark185]

I would use the DSP to create 3-4 different tunes for different volume levels and then switch between the presets as appropriate. You will need a Helix Conductor to have remote control but that is the best way to deal with the variable bass boost from OEM stereo. Issues like this are why I replaced my factory head unit in my BMW E39 with an android touch screen head unit and ran optical cable from that to my Helix DSP. I get that you want to keep something as rare as an S4 looking stock.

Another way to approach this which is simpler is to just set the volume on the OEM head unit to a level with minimum bass boost and don't touch it. Then use a Helix Conductor to control volume.

 

[davmol]

Thought I'd give a bit of an update, now that everything is sounding great. One of the subs needed polarity reversing which filled a bit of a hole around 70-90hz, and figured out the problem with the automatic EQ feature Tune-to-Target (TTT), where the bass kept disappearing. I realised that the RTA simply wasn't picking up much below 50hz so when I was telling TTT to tune from 40 to 18000, the bass level was set 100db down (or thereabouts), hence having no output from subs at all after EQ was run. When I set it from 55hz (to be safe) to 18000, then everything worked perfectly, and the sub starts naturally rolling off below that anyway, so not much to fix. Not sure why it wasn't recording below about 50hz, because REW with the same mic did show everything down to 20hz (rolling off steeply from about 40). TTT is a beta feature, so possibly just a bug and maybe it'll get fixed at some point, but just mentioning it here if anyone else is having similar issues with "missing bass" after running the auto EQ.

In terms of output, I bypassed the cheap and nasty android-auto box's no-name DAC by using a Bluetooth LDAC to optical converter, going directly into the helix optical input. So when I'm running android auto, I send audio through the helix (had to use the AAWireless Two+ dongle to allow that option to split out the audio), and then when using car radio or anything else, it just uses the car system, where I just flattened the input signal at my normal radio listening volume (using helix AISA) before running TTT to chosen house curve.

Finally, as recommended, I purchased the Helix Conductor Pro, to be able to control just the optical input volume, although I really like the additional tone controls and preset selection that it offers. Here it is fitted in what I felt was the most aesthetically pleasing location - before:

After:

Thanks for the advice, and here are some links for any others playing around with factory Audi B8 variants / MMI 3G.

VCDS cable and software that I used to set the factory radio sound profile to "external amplifier", which removes the factory DSP from each channel (but not the dynamic bass as per previous post).

Bluetooth LDAC to Optical Converter that I used to plug into the Helix 206DSP optical input. Very basic, but rock solid connection and everything sounds good, and it's very cheap!

AAWireless Two+ Dongle which is an android auto / carplay wired-to-wireless converter. I believe carplay allows users to select an audio output, so this really wouldn't be needed, but Android-Auto does not allow audio to be split out, with everything going via wifi. This dongle is a godsend, because it has a setting in its app developer options to redirect the android auto nav and media streams to an external Bluetooth source.

Fyi, if you don't already have a carplay/ android auto box for your Audi B8 variant, then also worth taking a look at the new mr12volt offering, which directly integrates with the car's MOST optical ring, meaning audio is processed via the car's dac and no need for separate optical converter and separate volume control. The factory Audi Sound System's DAC does sound very good to my ears, based on me listening to tracks via the inbuilt hard disk, bit you will still have to manage the bass control from the factory head unit.