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Discussion Starter · #1 ·
Been doing quite a bit of research on the factory amplifier. I feel I have determined the cause of the right front door being weak. By design the Infinity amplifier sends different frequencies and different levels to each of the six speakers. For example look at this comparison of the left and right front door speakers (Note: the scale is different on these two images each horiontal line represents one volt):

I don't know all of the technical details why this is done. I imagine by altering the sound they are able to create a more pleasing audio experience. But it seems that most of us that no longer have factory speakers don't agree.

If you look at the schematic (http://www.3si.org/forum/attachment...-amplifier-schematic-1-3-3s-infiity-amp-7.pdf) you will see that resistor R166 is missing from the left channel (top center of page). R266 is the complementary resistor for the right channel and is not missing. The combination of R265 and R266 create a voltage divider for the right channel. This is the primary reason why the right channel is "weaker". Removing R266 will increase the right channel output significantly. For those of you who know a little about electronics, you will notice that R165 and R265 are significantly different in value. This seems like it would cause a significant difference in output. But since the current requirements of the pre-amp are so low the difference is negligible. Here is a comparison of the right front speaker with and without R266 (Note: the scale is different on these two images each horiontal line represents one volt):


I have also experimented modifying the filtering in the amplifier to get a more flat frequency response from the amp. So far I am very pleased with the results. My Kappas have come to life! I will post on this seperately after some more testing.

For more detail check out:
http://www.3si.org/forum/f6/infinity-amplifier-frequency-response-data-435072/#post5043592
http://www.3si.org/forum/f6/infinity-amplifier-schematic-1-3-a-434334/#post5033719
 

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Hmmm I wonder if this is why both my RT/TTs with infinity stereos sound horrible when compared to my ES without infinity. All 3 cars have aftermarket head units.
 

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Discussion Starter · #3 ·
Hmmm I wonder if this is why both my RT/TTs with infinity stereos sound horrible when compared to my ES without infinity. All 3 cars have aftermarket head units.
Output is half the story. The frequency range sent to the doors is also very restricted. It looks to me like they wanted to have all the highs going to the dash speakers (see the other posts referenced). Now combine this with an aftermarket HU and aftermarket speakers with crossovers (also limiting frequencies) and you've really compromised the system.

I'm also wondering if the way they are doing the frequency limiting in the amp is adding additional noise and distortion to the signal.

More to follow..... ;)
 

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Just a rant:
I think it’s a no brainer to say the factory infinity speakers are more efficient down low too. Then again speakers don’t have flat response curves and maybe (hopefully) the amp compensated for this. So what sounds good for oem infinity budget speakers may not for their better let alone their best. Like they give two shits. So put a set of real speakers with a true flat response in there. (I don’t know if infinity even makes any) Does the modeling work in reverse? Say from factual data that includes actual reproduced speaker db’s from supplied frequencies? Then there is the premature 1/2 to 2/3 volume distortion. It’s just too many nails in the coffin. The newer Mitsu amps are better. Better than just an aftermarket radio (except for the 31w Panasonics they made).

Bottom line you can fine tune this pos all you want and it’s still junk.
 

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Discussion Starter · #5 ·
Just a rant:
I think it’s a no brainer to say the factory infinity speakers are more efficient down low too. Then again speakers don’t have flat response curves and maybe (hopefully) the amp compensated for this. So what sounds good for oem infinity budget speakers may not for their better let alone their best. Like they give two shits. So put a set of real speakers with a true flat response in there. (I don’t know if infinity even makes any) Does the modeling work in reverse? Say from factual data that includes actual reproduced speaker db’s from supplied frequencies? Then there is the premature 1/2 to 2/3 volume distortion. It’s just too many nails in the coffin. The newer Mitsu amps are better. Better than just an aftermarket radio (except for the 31w Panasonics they made).

Bottom line you can fine tune this pos all you want and it’s still junk.
You could model it in reverse to a point. You would be limited to the existing circuits and just changing the passive component values of the filters. My personal belief based on modeling the circuits and listening to the modifications I have made so far is that we should use the EQ for that function.

Unmodified with aftermarket speakers it could easily be deemed junk. My factory speakers were never good so I don't know how it sounded stock. What I can tell you is most people who have listened to my modified unit think it sounds very good (and very loud). Here is a comparison of the right front channel before and after modification (Note: The vertical scale is different! Each horizontal line is one volt). I want to run this a while before making any posts on it. Extended use could cause excessive heat or other problems.
 

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You could model it in reverse to a point. You would be limited to the existing circuits and just changing the passive component values of the filters. My personal belief based on modeling the circuits and listening to the modifications I have made so far is that we should use the EQ for that function.

Unmodified with aftermarket speakers it could easily be deemed junk. My factory speakers were never good so I don't know how it sounded stock. What I can tell you is most people who have listened to my modified unit think it sounds very good (and very loud). Here is a comparison of the right front channel before and after modification (Note: The vertical scale is different! Each horizontal line is one volt). I want to run this a while before making any posts on it. Extended use could cause excessive heat or other problems.
If thats the actual (lower) plot thats good. It's flat. The speakers and their crossover take care of the rest and the EQ would fine tune it. But if you listen you will see using the EQ can add distortion. In my instance I believe I had to adjust the 200w door speaker ch's not to pass lower than 40-60hz. It was 2 years ago I forgot the actual freq.

You've got to agree without that mod the 3k amp is junk. I agree the factory stuff can be loud, remember I've tested it in db's, and I had to use ear plugs. :) The 315w montero system really drew a crowd too.
 

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Discussion Starter · #7 ·
In my instance I believe I had to adjust the 200w door speaker ch's not to pass lower than 40-60hz.
I'm still making use of the high pass filter so it is reducing the output (reducing not blocking) at lower frequencies. The cut off frequency of the filter is 40 Hz. You can see the lower output on the graphs.

Based on my research, this means at 40Hz the output is reduced by 3db. At 20Hz (one octave lower) the output is reduced by 12db. Since a decibel is a measure of power, the relationship to voltage is not linear. I don't really understand this very well.......

In terms of peak voltage: Simulations show the output at 40Hz is 50% the output at higher frequencies. The output at 20hz is 15% of the output at higher frequencies.

Still liking the sound of my modifications very well. :p
 

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I'm still making use of the high pass filter so it is reducing the output (reducing not blocking) at lower frequencies. The cut off frequency of the filter is 40 Hz. You can see the lower output on the graphs.

Based on my research, this means at 40Hz the output is reduced by 3db. At 20Hz (one octave lower) the output is reduced by 12db. Since a decibel is a measure of power, the relationship to voltage is not linear. I don't really understand this very well.......

In terms of peak voltage: Simulations show the output at 40Hz is 50% the output at higher frequencies. The output at 20hz is 15% of the output at higher frequencies.

Still liking the sound of my modifications very well. :p
The door 6.5" speakers won't reproduce 40hz at the same db level they will 150hz either. Thats for the sub. Whats worse about the decible output is doubling the power will give you about a 3 dB gain
Accuton C173N-T6-90, 6.5" speaker spec sheet
 

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Skeptic
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Interesting analysis. Is all equalization taking place in the amp, or would the stock speakers sound different if driven by the stock amp fed by an aftermarket HU?
 

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The headunits will basically sound the same either way thru the amp.

I know you're worried about the system sounding the same. But it's all a combination of the right components. Been there done that times about 20. It was part of a fun father son project back then. My son who was an ee student at the time got his ass kicked on every system he tried until he did the Diamante amp installation in a 97. (it was my amp) I still can hear him blowing speakers in the yard on one system. LOL He had this new $250 alpine radio that sounded like shit. So I put a Mitsu harness on a Pioneer FH-P700. It taught him a few good lessons. Between us there was 10 plus cars put back on the road, they all needed sound system help. I made over 25 Digital climate control kits back then so you would not believe the parts cars we ran across to get the other cars back to great condition. Heck I'm using a Spider convertable switch in the Stealth. There was a wide variety of systems in those cars too. BUT Most of the cars fixed and sold were stock infinity systems either converted, repaired, or retrofitted.

Right now I've moved on and have only front components and a 10' sub. Now there's over 200w a channel up front so other than having an 06 infinity double din radio....it’s no comparison to stock…….. but the 315 watt mitsu system in the 99 with Diamond comps, stock rears, and a Nissan sub still has my respect.
 

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Thanks. That explains why the nice aftermarket 6x9 speakers I tried sounded worse (I reverted to stock - discussion). So while the HU can be changed independently, the speakers and amplifier must be changed together. Is this common knowledge among folks incrementally upgrading their systems? Does the 315W amp not exhibit such equalization? That might help explain your findings.
 

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I got lost after the first post. Just tell me what to buy and where to put it. :p
 

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Thanks. That explains why the nice aftermarket 6x9 speakers I tried sounded worse (I reverted to stock - discussion). So while the HU can be changed independently, the speakers and amplifier must be changed together. Is this common knowledge among folks incrementally upgrading their systems? Does the 315W amp not exhibit such equalization? That might help explain your findings.
Must have taken a few minutes to find those posts. :)

I think it's underdriven speaker syndrome. It's the wrong speaker for the amps capabilities. I loved the Diamond 661 and 361 components for the fronts. There's a link in the sig for an install. For the rears I like stock coaxials best. I did find some 6x9 quality branded speakers in our restoration projects but they didn't have the umph the stock rears did. Anyway my current 7" D971's in the doors really suprised me. The doors are deadened and there's a back wave pad in back of the door speaker. The rears are not in use.

I hate to say this but there's probably some decent low end coaxial pioneers out there that would fit the bill. The bill being a speaker that has better bass characteristics at a low power level.
 

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My right front (dash) speaker is blown, so I just bought this package for a good price. If anyone needs something, let me know...



 

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You should be ok with the dash and door speakers. The rears are hard to tell if they're the coaxial version or the version where they just added a center cone.

The radio will not have steering wheel controls. It's plug and play minus the steering wheel controls and changer. Not sure if the amp has the channel issue?? But it is plug and play so you can test it.

The radio also only will work with a 10 disc changer, and they aren't reliable. But pioneer ip buss changers can be used with an adaptor. The adaptor also has rca inputs. I've posted on all of this changer info.
 

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Was looking for pics for another post and found the instructions for an adaptor.

You can play the drums on those changers :)
 

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Thanks. The parts are:

- Infinity head unit (MR225577)
- Infinity amp (MR158402)
- 2 Infinity dash speakers (MR751693)
- 2 Infinity door speakers (MB954761)
- 2 Infinity rear speakers (MB954762)

I will probably just keep the one tweeter I need and sell the rest, so if anyone sees anything they need, please let me know!
 
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