can anyone tell me if it is possible to disable the the auto bass attenuation feature on the stock HU? maby some may not have noticed but like most stock head units the bass will get softer the more you turn up the volume. I think this is to prevent the crappy speakers from distorting.is there anyway to stop it from doing that?

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formerly 98 prelude type SH

Currently 2001 Acura 3.2 TL With Navigation Black/Ebony

 

i have noticed that prelude

i always assumed that since the mids were getting louder, it drownded out the sub, and just gave the impression that the sub wouldnt hit harder. when i have the volume all the way to the max, i adjust the bass control, and it seems like the sub doesnt adjust much at all. im not sure

 

I found this information and i copied it here maby someone can make some sense of it.
What Is The Frequency Response Of The OEM System?

[AW] Acura-Bose head unit Frequency Response

I made some measurements that may be of interest to anyone making after-market audio enhancements to his NSX. In summary, the head unit supplied with the NSX provides what is commonly known as "loudness compensation." This is a bass boost that gets progressively stronger as the volume is turned *down*.

In home audio the conventional "reason" (excuse?) for this is compensation for the Fletcher-Munson curve, which is a measurement of human hearing sensitivity that shows sensitivity to bass falling off as volume decreases. This "feature" is defeatable on any reasonably high-quality home audio unit.

In an automobile there may be an additional motive, namely that the spectrum of background (mostly road) noise in the car is dominated by low frequency energy. Thus, if the stereo volume is comparable to or slightly above the background noise you may need bass boost to provide subjectively flat response in the presence of large amounts of low-frequency noise. On the other hand, when the volume is *way* up, such that the signal to background-noise ratio becomes significant, the designers may have felt the bass boost was not needed. Or they simply observed that the power-amp/speaker system wouldn't be able to provide it without distortion. Who knows?

Disregarding for the moment whether or not this compensation is a good thing, here is the frequency response of the CD-player/head unit output (i.e. before the power amps, which may contain equalization of their own). Measurements are dBV (i.e. decibels re 1 VAC). All measurements taken using Denon Audio Technical CD, 38C39-7147, and a Ballantine VTVM known to be flat over the audio frequency range, and monitored on an oscilloscope.

The column headings are the volume control position as "o'clock" i.e. 9:00 means the white tick mark is straight to the left, and 12:00 means it's straight up.


Hz 9:00 10:30 12:00 1:30
40 -21.5 -12 -7 +1
100 -19.5 -20 -12 0
315 -34 -25 -13 0
1001 -35 -26 -13 0
3149 -35.5 -26.2 -13 0
6301 -35.5 -26.5 -13 0
9999 -35.5 -26.5 -13 0
15999 -35.5 -26.5 -13 0
17999 -35.5 -26.5 -13 0
19999 -35.5 -26.5 -13 0

Boost@40Hz: 14 14.5 6 1

So, what we have here is a head unit that adds substantial but variable bass boost until you get the volume *really* cranked up. The frequency of peak compensation appears to have a period of about 35 mS, i.e. ~30 Hz. (I have no easy way to measure that with a frequency counter).

A prize to the first person who tells me how to disable this loudness compensation inside the head unit. This is not a quiz; I don't know the answer, but I wish I did.

The first idea that springs to my mind is assume that the volume control has a "third" (and/or fourth) variable resistance that controls the "loudness compensation", find it, and substitute an appropriate fixed resistance, i.e. that which corresponds to a "high volume" setting. For this we need to disassemble the head unit, which I have done partially in the past. But not yet to the point where I exposed the volume control potentiometer terminals. Hmmmm.

[TM] Short of actually disabling this loudness compensation "feature," you can install aftermarket speakers, amp and crossover with level. Set crossover level for low input sensitivity. This causes you to turn the volume control to a higher level (eg 12-1 o'clock) where there is less loudness compensation.


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formerly 98 prelude type SH

Currently 2001 Acura 3.2 TL With Navigation Black/Ebony

 

VERY interesting info, preludeshfan!

Here's my take on this.... :

Loudness compensation *IS* a good thing. As your copied text says, the human ear is less sensitive to low AND high frequencies at low volumes. A loudness comp circuit will boost these bands so that the sound appears 'fuller and richer' at low volumes.

As I recall, most HOME audio systems' loudness contour circuits are FIXED in boost; they apply the same +12db (or whatever) boost at 100 Hz and 10Khz REGARDLESS of volume level. You are describing a circuit that TAKES INTO ACCOUNT the volume level automatically; that is, at higher volumes, the boost is attenuated.

I say that is a GOOD THING.. I agree that like on most aftermarker HUs (and most home receivers, too) the circuit should have an ON/OFF switch, so you can switch the circuit in and out at will...

Note also that really high-end home equipment has NO TONE CONTROLS or loudness comp circuitry at all; the thinking being that real audiophiles would not want the electronis modiying or shaping the input circuit at all.

TL Daddy brought up a real interesting point... there is a unit attached to the stock HU... maybe this houses the loudness comp circuit you desribe.. or IS THERE OTHER EQ CIRCUITRY BUILT IN???

Before putting $$$ into modifying my stock system, I'd sure like to know if I can feed an un-eq'd signal straight to an aftermarket amp/line converter!!!