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Sound Quality in Car Audio

What is "sound quality"?

Measurement Mania

Not long ago, and presently in many circles, sound quality ("SQ") was said to be best represented by audio systems amplifying with the lowest Total Harmonic Distortion ("THD") measurement.

Overlapping the THD focus was realization and consideration of Transient Intermodulation Distortion ("TIM", AKA Slew-Induced Distortion "SID"), also a quantitative measurement said to better describe sound quality.

There are other measurements purporting to describe sound quality and maybe taken altogether the measurements give some ballpark sense of potential sound quality. But, "sound quality" in the human sense -- despite some authoritarian claims and challenges -- has so far eluded reduction to objective measurements and numbers.

Transistorized "Perfection"

Attainment of evermore absurdly "perfect" THD figures (0.001% THD, etc.) has most often been accomplished by means of solid-state/transistorized amplification for its usual real benefits of size, heat and cost reduction.

But The Emperor Has No Ears

In parallel with the increasingly measurement-oriented obsession (and claimed audible improvements) was growing awareness of decreasing 'sound quality' -- the better the numbers became, generally and often enough to persist, the worse 'the sound' became. Anecdotal evidence of this truth abounds, probably in every family. Look to practically any issue of "The Absolute Sound", "Stereophile" and similar publications.

Tubes Measure Worse But Sound Better

Meanwhile, tube amplifiers that boost audio power by means of electron valves have notoriously higher THD and TIM/SID measurements yet are often regarded as having better 'sound quality' compared to transistorized amplifiers. Debates of 'which sounds better, transistors or tubes?' have waged for decades in the popular press and throughout audiophile concerns.

Fundamentally Opposite Means of Amplification

There is enormous difference between transistors and tubes regarding their internal workings. From our Articles section:

Tubes use a charged electron plasma cloud in vacuum (see space charge), while transistors force audio signal current through something not unlike dirty sand --possibly why 'brittle, hard, sharp, gritty and scratchy' often describe "transistor sound" [April 2012, years after writing this we discovered Alexander Dumble, creator of what many musicians consider to be among the best-sounding guitar amplifiers ever made, concurs: "The difference comes down to this: The more fragile harmonics can survive in a vacuum tube, [versus how] they seem to be eliminated or squashed in a solid-state crystal lattice...electrons can survive [with greater fidelity] in a free-space vacuum where they have trouble in a crystal lattice."].

Difference in circuit complexity also bolsters Dumble's claim. Whereas rather linear tube circuits are usually simple, most transistor circuits require high negative feedback and more complexity. The All American Five was for decades a popular and common radio, requiring only five tubes in surprisingly simple circuitry. "Transistorization" happened for economy, not better sound -- in this case, cheaper was just cheaper. In terms of gracefulness, straightforward simplicity and perhaps ultimately sound quality, transistorized amplification seems to often fall short. See also How Does a Transistor Work.

Others have presented more esoteric conjectures: Listen from 3:15 into interview with Preston Nichols (Montauk / Philadelphia Experiment), regarding otherworldliness of electrons in a vacuum tube: 'In vacuum tubes... an electron is a particle and a wave, just like a photon is... electron in a vacuum becomes and operates as a wave... different set of properties for vacuum-conducted (wave) electron versus metal-conducted (particle) electrons... vacuum tubes hit the spiritual level... electrons are moving into another reality... electrons in a vacuum approach god / godliness.' -- "...Preston Nichols has developed a considerable reputation for his alleged involvement in time travel and secret government projects. However, it is not very well known at all that he was just as deeply involved in the music scene of the 1960's as rock 'n roll came to center stage in world pop culture." -- from Peter Moon's book "Music in Time".

Research, Understanding, Best of Several Worlds

On the other hand, leaps in design of transistorized amplification have been made by industry icons including Nelson Pass, Bob Pease, Bob Widlar, Walter G. Jung, and others. David Berning, one of the oldest and most respected audio designers, notably often combines tubes and transistors, excellently leveraging the benefits of each technology toward improving overall sound quality.

Digital Signal Processing ("DSP") introduces into audio equipment design the wonderful but complex mathematical manipulation of digitized signals. Izotope is well-known in pro-audio for its seemingly magical products. In mobile audio, "DSP processors" are used primarily to shape the equalization curve, apply steep crossover functions to split audio signals amongst the speakers best suited to handle the frequency ranges, and to apply various delays which aid psyco-acoustic perceptions of spatiality and enhance impact, coherence, clarity and "sound-stage". See below, however, for recent example of when digitalia goes too far.

Car Audio Sound Quality Round Table #1

"Panelists consisting of industry experts in home and mobile audio assembled in Scottsdale, AZ, on February 23, 2013, to discuss topics related to achieving sound quality in mobile audio, along with ways to grow the mobile audio industry."

Source: // whitledgedesigns

See also Earl Zausmer's BMW-540

"It sounds harsh and not pleasant." -- Verbatim email exchange on unpleasant-sounding 'all-digital' system and suggested fixes:

This regards digital-audio technology (D-AT) in general, we believe, not any particular manufacturer or equipment; rather, the audibly "harsh and not pleasant" plight of D-AT, it reasonably seems, would be manufacturer-agnostic. The digital quantization of innately (necessarily?) analog modes has esoteric roots (and debates) that span millenia, beyond "quantum mechanics" psyence and theoretical quantizability to Greek atomicity in lore. At what slices and dices fine enough, or in sufficient quantity, could parts indiscernibly reconstitute or even tolerably represent any whole? (ref Georges Seurat, divisionism / pointillism)

1. Initial email from an Audio Enthusiast in Amsterdam, early 2020

Hello, I have an audi Q5 with following audio equipment. It sounds harsh and not pleasant.

  • Audison Bit One.1 DSP
  • Audison Voce AV Quattro – 4x200W amplifier, two pieces
  • Hertz Mille ML 280 - 28mm Ndym tweeter,
  • Hertz Mille ML 700 - 70mm midrange
  • Hertz Mille ML 1600 - 165mm Ndym woofer

At home I have unico secondo tube amp + revel F206 speakers, sounds beautiful.

Now I’m looking for tube amp for in the car to replace audison amp. Also, I’m wondering whether replacing the amplifier in the car will improve sound, or do I need to replace the speakers also?

2. Initial response from Michael Milbert

I would start by using a tube amp as there is [arguably] a bigger difference between tube vs solid state than amongst speakers.

3. Audio Enthusiast:

Hi Michael, Thank you for your response. Is there anyway to test it with my current speakers (just replacing the amp)?

This is my current setup [image attached, see full-size diagram, upper-left]

4. Michael Milbert:

BaM-235ab and Liquid amps accept unbalanced audio signal on RCA connectors. Only 1.5Vpp is necessary to drive the amps to full power output (attenuators allow for much higher voltage levels). If your Audison Bit One can provide analog audio signal output, either BaM or Liquid should work directly in place of the Audison amps. If only a digital output is available from Audison Bit One, a DAC will be necessary between Audison Bit One and BaM or Liquid. From your diagram I presume your speakers use passive crossovers.

5. Audio Enthusiast:

The speakers use DSP crossovers inside the bit one, and a digital signal is fed from the bit one to the quattro. The DAC is inside the quattro amp. But the bit one does have 8 low level analog RCA outputs, see

So I would need to add some passive crossovers, which is not a problem.

6. Michael Milbert:

If you were to use a BaM-235ab, you might try feeding highs+mids (output mixed, as a stereo pair) from Bit One to L/R channels of BaM, then using passive crossovers between L/R tweeter and honker. This would let you keep much of your investment, but insert the BaM-235ab where it would make most sense, most audible impact.

7. Audio Enthusiast:

Today I removed the audison amps from my car, and just connected my home amplifier (unison secondo, which has two tubes), with three way crossovers directly to the speakers. It was hooked up as follows: pillars tweeters 4000+ Hz -3dB, dashboard mids 300Hz-4000) -3dB, front and rear doors lows (0-300Hz) 0dB. I simply used an extension cord to my home outlet for the 220V of the unison amp.

This sounded beautiful, and almost as good as in my house connected to my revel F206 speakers.

Unfortunately, this unico secondo home amplifier works only on 220V and not on 12V. However, it does mean that the audison amplifier was causing the bad (harsh, unmusical) sound, and not the speakers.

Regarding your suggestion of using the BaM-235ab for the high and mids (pillar and dashboard speakers, and the audison for the low (doors and trunk), is a possibility, but I'm quite hesitant to keep using that audison amp, knowing that it sounds bad. Do you have another suggestion?

Met vriendelijke groet, // Best regards,

8. Michael Milbert:

The BaM will certainly operate full-range and sound great. Because it has transformer-coupled output, like most tube amps, the lowest bass is probably not going to sound as taught and controlled as with transistorized amplification. If the unico tube sound is to your liking, the BaM is probably in that ballpark as it originally came from home audio: Tubey warm with airy soundstage and lifelike sparkle.

Glad you're hearing progress! Your finding echoes ours: The 'technical perfection' of digital is not necessarily pleasing to hear.

I would like to post our email exchange on, without your personal details, as it may help other people also suffering digitalia. Would this be okay with you?

9. Audio Enthusiast:

Sure you can post it. It was a huge revelation for me today. When I first received the Audi after the installer had put in the complete audison system (total cost $11k, 5 years ago), I was immediately disappointed. Then, I tuned the Bit One DSP with all possible settings and eventually found that the best of the worst was everything flat (timing and eq). But it was still awful. So today I removed the audison amps and dsp, and put the tube home amp (cable to the 220V socket of my home), plus two passive three way filters, and immediately bliss, on all songs and genres. And it's not like the audison stuff was cheap, on the contrary. Anybody interested in two reluctantly used Audison Quattro amps?

If I would use the bam for high and mid, what transistorized amp would you recommend for low (100-300 Hz) door speakers, if I add an active sub in the trunk also (40-100 Hz)?

10. Your turn, dear reader -- Anyone have a suggestion for a great-sounding transistorized amplifier? Please email us your experience and specific details and we will post here. An interested car audiophile in the Netherlands awaits.

Milbert Amplifiers, The Most Musical Amplifiers. Made in USA since 1986.
Milbert Amplifiers
The Most Musical Amplifiers
Made in USA since 1986

8051 Citation Drive #C
Gaithersburg, MD 20877 USA
phone 202-558-5502