mpeteritas

Anyone else have trouble getting a good flat sounding signal from the OEM preamp outs on a TSX? I have read previous posts saying that the OEM HU puts out a good flat low level signal.

I have a 2004 non-NAVI TSX. Are the preamp sections of the HU the same between NAVI and non-NAVI?

If I set Treble and Bass to 0, it sounds very treble and bass heavy through the preamp outs, and its tough to get it to sound flat with the Treble and Bass controls

Here's a summary of my current setup:
I have both sets of OEM preamp outs run to a rockford fosgates 400a4 amp in the trunk. Front speakers are disconnected until I get replacements because I couldn't handle listening to them any longer

I have replaced the 6x9s in the back with JL Audio VR series, which sound quite good, but I am not getting the flat sound I expected from reading people's posts on the OEM HU preamp outs... Maybe its the speakers, but I kind of doubt it. They sounded much flatter when I listened to them locally at a store. Any advice? Any detailed info on the signal from the preamp outs from a non-NAVI OEM HU?

-mark

bumpin

Mark,
I have had a similar experience with my 2004 TSX non-navi:

(1) using the stock HU and feeding the stock amplified signal that was going to the 6x9's into hi-level inputs in my sub amp, and driving 2 8's in a custom ported box, i noticed that around 45-55 Hz there was a large "peak", but the low bass extension was not very good.

(2) using the stock HU and feeding its PREAMP output to an outboard crossover and to the same sub amp and subs as in step (1), I noticed the 45-55 Hz "peak" did not exist anymore, and 35Hz and below was greatly exaggerated.

This leads me to believe that there is some signal processing going on in the stock HU, or stock amp (or both). My guess is the stock HU is boosting the low bass content to compensate for a shortcoming in the stock IC amp, and that "compensation" in the low bass is being noticed now that the stock amp has been taken out of the path.

Has anybody actually taken a frequency response measurement of the preamp outputs from the HU with the treble/bass set flat? It would help confirm these theories.

elduderino

Did either of you reach this conclusion with a real-time analyzer connected to the HU preamp output?

I am perfectly willing to beleive that there is processing in the stock amp (although a simple count of op amps on the signal processing board implies there ain't much).

I would also like to ask if anyone remembers the words that came after Punch on faeature lists? Like "Punch Equalization"? Rockford amps were internally EQ'd for years. Don't know if yours is...

But I have tested this HU with 20-20k pink noise, with an NT Instruments Acoustilyzer, and it was flat as a pancake at any volume. There was a noticable dip at 25K, which is to be expected with a lowpass filter inside all CD players.

So, yes, I have, and no, you're wrong : )

mpeteritas

Hi el dude,

My rockford amp is a power series and it does have a optional low end eq control. I have it disconnected, so it should be flat. I notice the same peaking on the high end as on the low end, for what its worth. Could be the amp, could be the speakers, but I think that's kind of unlikely. I got a flatter sound from my monsoon system in my last car VW Jetta (different speakers though).

This is good news, and really I hope I AM wrong. That would be excellent news, as far as I am concerned One question though... did you run this test on NAVI HU, non-NAVI HU or both. Please say both. I am worried they are different.

-mark

bumpin

Thanks for the info. I guess this box with 2 8's in it is a low bass beast, having supernatural powers from 20-35Hz . I don't have the bass EQ'd in any way. Maybe the way the box is loading in the trunk could be having an effect: the port from the box in the spare tire well is a few inches from the back of the car. According to WinISD, the tuning freq should be around 35Hz and with the enclosure volume of just under 2 cuft, the subs modeled a nice even response, not peaky. I haven't measured the actual tuning freq from the box inside the car, tho.

I'll take more low bass over one-note 50Hz bass anyway

elduderino

Rockford amps USED to have an EQ curve built into them - non-adjustable. Jim Fosgate actually had patented his listening EQ curve for in-car listening before Rockford bought Fosgate, and the original Punch amps used it. Don't know when they abandoned it, or if they did (it was a patent, and public companies like to use IP that they paid for and that sits on their balance sheet and looks like an asset: )

A search of the US Patent database only reflects Fosgate patents on surround sound, but this interview from a few years ago implies that the patent was granted and was simply not found by the search parameters I was using (I don't know the patent number!)

Jim Fosgate: I was an audiophile and I was playing around with Quadraphonic sound back in the '70s, and I had invented this equalizer circuit that became the foundation for the Fosgate Punch amplifier. I got a patent on the circuit and one thing led to another, and I just wondered what the car would sound like with equalization and more power. So I built one for my own personal use, and the thing totally blew me away, I just couldn't believe what it sounded like. We ended up putting the thing into production.

As far as non-nav HUs having different EQ curves than nav: No, I only tested nav, but that's silly.

The nav and non-nav speakers are identical, and the amps are identical - to assume that the OEM would try to make the non-nav sound "better" than the nav is not logical.

I would also question the source. I find XM Radio to sound heavy and EQd in the bass compared to the same song on the CD> I'd only use the CD for sonic eval - MP3s and sat radio are compressed and you don't control the algorithm that compressed them, so use good old Red Book CD-Audio for your reference.

mpeteritas

Very interesting... I think I need to try a different amp to see what it sounds like...

About content I have been testing with... I have only been testing from CDS mostly just rock stuff...CDS that I have been listening to on reference studio monitors and also my home system with a high end Yamaha amp, running paradigm reference studio/60s. So that's what I am comparing the sound to when I talk about a flat sound.

I may have to hook an analyzer up with some audio test disks to see what I get out. El dude, I am sure you are right about the Navi and non-Navi HUs being the same. I just haven't heard both of them to verify this.

-mark

mpeteritas

Hi Guys,

I did some analysis over the weekend. I captured the preamp output signal to PCM data at various volumes (10, 20, 40). I used a typical rock CD over a fixed 30 second clip to do the test. I evaluated the spectrum analysis over the entire clip. Overall the signal looked very close the original. I did notice a very small drop in the midrange, but I expected at least very minor differences. I want to redo the test using a test signal that would appear visually flat on a spectrum analysis.

El dude, what test signal should I use to make it appear visually flat? This way I can test several different volumes without trying to normalize the captured signal.

-mark

elduderino

I would use undifferentiated pink noise from 20-20k, both channels driven.

You can get test CDs at Autosound2000.com or on the IASCA test CD. I'm sure there are files you can download with this signal on a .wav file... or I bet you could use this:

http://www.nt-instruments.com/X0-ASP...X1-default.htm

C The "S"

Sorry if someone else mentioned this ( I skimmed the other posts). But you may want to look into the JL Audio Clean Sweep. This should help you out with your problems.

elduderino

Ahem (BULLSHIT) Ahem.

C, there are a lot of posts on this. I suspect you don't understand what's happening in the car, and the CS is just not anything that an Acura owner needs.

C The "S"

Not really sure what you're calling BS on. Are you saying the Cleansweep doesn't work?

elduderino

I'm saying that you are recommending a $400 product with speaker-level and balanced-line inputs and an EQ in it in order to interface with a single-ended preamp output with flat frequency response.

I'm not calling BS on JL... I suspect the Clean Sweep works in some applications - but I am calling it on anybody's recommendation to spend $400 on a problem that doesn't exist.

It can take balanced outputs. TSX's don't have them.

It can take speaker outputs if that's all your deck has. TSX's don't have them either.

And the output of a TSX HU has no equalization.

So why would you tell someone to spend $400?

(Note: That "bullshit" should probably have been a couple of sizes smaller... it's hard to tell what size it will end up with the forum format SW... but I still think it's the right word. The Clean Sweep has been brought up many, many times in this forum.)

C The "S"

Well now that I've read through the whole post, first I didn't realize that the TSX had preamp outputs and second I did not know that the TSX has a flat response, where as most factory systems do not have a flat response.

elduderino

I politely and respectfully suggest that you don't KNOW that to be true... someone told you that. But you don't know that out of your own experience, do you?

C The "S"

What part are you saying that I don't know out off experience?

C The "S"

elduderino:
It almost seems as though you're all knowing in this section, didn't mean to step on anyones toes. I'll just keep my mouth shut now. I shouldn't have jumped into the thread, my apologies sir. I'll let you run the show over here. No more posts for me in the audio section.

elduderino

My o.o2 is post all you want, but read before you post. There's a lot of info already in here, and you seem to have started lecturing before reading, especially on this preamp topic, which is one that I've been posting about for a long, long time, and have a great deal of attachment to.

The Clean Sweep has been discussed a lot, and I believe the marketing from JL about "most cars having EQ" is untrue, because most cars the OEM won't pay for EQ circuitry. I've heard a lot of people repeating this statement, but I haven't come across anyone yet who's RTA'd the preamp out of very many cars - which is of course how you'd check that. So I asked how you knew that.

C The "S"

I was never lecturing anyone, just making a suggestion. I did also preface my suggestion by saying that I skimmed the thread. Let me rephrase my statement about OEM built in equalization. You're probably right about many low priced vehicles, but on many of the high end cars who are using systems by Bose, H/K, Nak, Mark Lev I believe they have some equalization built into them. I have not RTAed all the cars out in the world, I'm sorry that I made such a blanket statement I should have been more specific your highness.

elduderino

Two things:

1) I agree taht many expensive cars have eq.

2) At least you're being adult about being called on your "type first, read later" apprach.

elduderino

I had an edit for this and the phone rang.

If I totally ignore every post I have ever made here, it's true that there are many, many knowledgable posters about car audio on this forum. Forget me - to ignore what they've said before and post answers without reading anyone else's comments smacks to me of a lack of humility.

That's it. Smart ass comments aside.

mpeteritas

see thread for my final analysis:

https://acurazine.com/forums/audio-video-electronics-navigation-22/testing-how-flat-tsx-head-units-preamp-outs-314155/

-mark