Nismo audio upgrade- critique my planned setup

2fast4thelaw

You doubt becasue you and 95% of enthusiasts out there dont understand how crossovers really work. They do much more than filter frequencies. You can alter the phase and shift the time alignments on the drivers to compensate for tweeter location and for the material it reflects off of like glass vs plastic, leather, or even carpet. Crossover design is a science that is used in DIY world of car and home audio. Some people think its a bandaid solution and it is if you use inferior quality speakers ie "BOSE" but it does work!

I have been doing DIY for 15 years and I have developed my own custom software for crossover and enclosure design. If anyone is interested in it I might even share it.

__________________
To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be.

speedfreak28

Im curious how your changing the phase in your passive crossovers. The phase you can control through the crossover is electrical by utilizing different crossover slopes. You said you were using the focal passives so Im lost there.
Also phase as you refer to it being affected by the vehicles acoustics is not controlled through the crossover but rather through the install, aiming, and level matching primarily. Im also curious how you're utilizing time alignment with a passive network. You would only be able to adjust the stage left and right. Time and Frequency of a driver are two different functions, correct me if Im wrong. Also if you are using a passive filter time alignment wont help with height of your tweeter and the only way you can change phase without moving the tweet is to adjust the slope, affecting the electrical phase.

Again please dont take my comments the wrong way. I hope Im not out of my league because I'd like to think we can have an intelligent discussion. Id be curious about the program you made for crossover design. It could be a nice tool to add to my collection.

2fast4thelaw

I apologize if I came off a bit negative, anyway this forum is about sharing information and this is a bit lengthy so here goes.

The problem with stock passives is they are designed primarily for having the mid and tweet close to each other and on the same baffle or panel. This largely why they get a bad rap especially if you are forced to put components in unconventioal places. Basically a car is an unconventional envornment for audio. In order to resolve these problems we have to re-design our passive crossover network and taylor it for our envoirnment.

Phase and crossover slope are 2 separate entities and in this case slope remains unchanged.

Now adjusting the phase is a whole other science. Car speakers are optimized to perform well off-axis (speakers that play indirectly) vs home speakers that are optimized for on-axis (pointing directly at you). No matter how good off-axis speakers are, they will still sound better on-axis.

What I try to do is put the tweeter on axis by adjusting the phase anywhere between 90 and 270 degrees. In doing so this will change the time alignment between the mid woofer and the tweeter. You can calculate your resistor values that you will need to correct the change in time alignment. Let’s say you have a lot of carpet in your car, then you want your time alignment to be quite advanced because of the non-reflective materials in the car. If you are reflecting off of glass then you need to go the other direction because of the reflective material.

Applying this to the Z:

I chose to use the stock location for my mid’s and tweets. What I did was roll my tweets 270 degrees off-axis by changing the values in the resistors on the passive crossover. (I will explain why I did this later) Since they are reflecting off of glass I used the lower settings on the crossover volume to cut a little output from them to compensate for the db gain from the reflection from the windshield.

In the Z, the distance between the tweets and mid’s are about 18 inches but again the fact that they reflect from the windshield made the phase invert. I not only had to flip the phase 180 degrees to put them back into phase, but I added an additional 90 degrees to make the illusion that they were in front of my face. This was a total of 270 degrees of phase adjustment.
In order to get my values I had to reverse engineer the Focal passive crossovers.

These crossovers are 3rd order Butterworth 18/db octave crossovers so they were not that complicated. I just punched in the component values in my software and then my software program spits back the values after I have it calculate the phase I want.

I just had to order some 1% tolerance resistors and capacitors of equal quality and replaced the components.

This still changed some behavior of the tweeter and mid woofer relationship but remember I have a 13 band parametric eq which fixed this problem and I was able to blend them perfectly, at least to my ears.

My imaging is dead on and dramatically better than it was just rolling with the stock passives.

__________________
To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be.

speedfreak28

The problem with using the 13 band EQ through a passive filter ( Im assuming an eqx or something similar is that you are not adjusting the characteristics of the individual speaker but the whole passive network. this makes it really difficult to accurately tame peaks in an individual speaker because you will change the characteristics of the other as well. Heck, phase can change with frequency as it comes off a speaker. Also what may sound flat to you and imaged dead on may not be the same on an RTA. Realistically unless its a competition vehicle whatever sounds good to you should be your ultimate goal. SQ is subjective, measured SQ is not

2fast4thelaw

I had to heavily paraphrase to keep it from being a book but I will touch on your notes.

What i first was trying to say is I did not change the slope of the crossovers. Also Phase and slope only directly affect each other in simple passive crossovers without phase compensation. Any decent passive crossover will have phase compensation. In my Focal crossovers they compensated for that shift so I had to alter them.

Also since I have my own software I calculate time alignment by distance between tweeter and mid woofer becasue its a more stable constant since once the drivers are installed they will never move.

A Zobel network is already designed into the Focal passive crossovers because the Focal tweeters are actually 8 ohm and the woofer is 4 ohm. I altered the values in an attempt to undue the phase compensation that was designed into the crossover which put me exactly where I wanted to be at 270 degrees off-axis.

I left the mid woofers as they were (off-axis) as I only needed to alter the tweeters in my installation. I did this to keep it less complicated becasue I knew I could use my eq to blend them.

I wasnt using the EQX to tame individual speakers but to tame the peaks at each octave. I also first tune the system by my ear as what sounds best to me. I then record my settings as my reference point. If and when I have my car RTA'd for competition I can record those settings as a competition reference point so I can go back in forth. Perfectly flat is not always ideal for all music for everyday listening at least for my tastes.

Remember, there are a hundred ways to skin a cat. What I did made a big improvement and greatly enhanced my imaging and overal tonality of the system. If I could have in hindsight I would have used the 3-way Focal poly kev set and had even more improvement. I wanted to keep the stock appearence and that would have been nearly impossible.

__________________
To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be.

speedfreak28

LOL funny you use the metaphor theres more than one way to skin a cat, It was exactly my thought when typing my last response. It just seems that you're taking the longest way to achieve the results, I was under the impression you had the car RTA'd. You can calculate all you want but without figuring out the vehicles internal volume and resonant frequency the crossover design was just a guess. This is why I prefer an electronic crossover. Essentially all the componets you changed in the crossover usinga program are a guess without measuring in car with an RTA. You cant figure out the phase diffence form the reflective materials without one.
Id scrap the passives all together and maybe use a DQX for all your tuning. There are som any in car variables that effect overall phase and stage height that in a competition SQ vehicle you have to be able to make small adjustments. In my truck I had been running a Clarion DRZ9255 and a DQX to take care of those issues. Now for a non competition vehicle, the passives will do the job just fine.
I would be interested in hte program you use Ive used a few different programs but theres always more to learn which was the original point I was trying to make to you...

2fast4thelaw

My methodologies may not be very efficient and you are correct, I have no way of calculating the inside of the car or measuring the refraction of sound from different materials. Much of what I have done is an educated guess and I am no where near exact but I am in the ball park.

The reason I chose to retain and modify passives is becasue I have years of experience playing with them and I enjoy doing it. Most of my experience comes from home audio which follows the same basic designs, but car audio enviornment throws a twist which makes it a challenge I couldnt resist.

As far as software is concered, I didnt like anything I found so I wrote my own software and over the years built upon it. I would be more than happy to share it with you but its not compiled and I dont have a compiler so I can't package it into a neat little installation file.

I have some really old programs that are more basic that were done in excel that are usefull. The crossover calc is only 1st and 2nd order crossovers and its basic but its usefull for building custom passives.

__________________
To the optimist, the glass is half full. To the pessimist, the glass is half empty. To the engineer, the glass is twice as big as it needs to be.