19 replies to this topic

[scraverX]

So, I got the opportunity to listen through the Judging material for this year at the ACT Test and tune.

One thing I discovered is I had a phase issue - this I'm working on figuring out already as I understand the principle and how to solve it.

The next thing I'll need to look into is some Frequency Steering that also exhibited it self quite openly during the listen through.
Now I know what this "sounds like" but could someone possibly give me a little more of the technical side and perhaps explain in simpler terms how I might go about fixing it?

Thanks in advance.

[Dan_Vx]

http://www.mobileele...uency-steering/

[scraverX]

Yep, should have searched Thanks for that, gave my memory a kick which is what it needed. Seems like I'll need to play more with level adjustments and maybe tweak my eq settings.

[Dan_Vx]

Good read I had NFI what it was.

[scraverX]

As I said in my first post, I sure as heck know what it sounds like.

[muzzy66]

From my experience the biggest culprits for frequency steering are uneven frequency response and imperfect timing between drivers.

When one driver is louder then another (say tweeter louder then the mid) the image tends to shift towards the tweeter. It's not only entire driver levels that can cause this - having a significant peak in your frequency response can also cause it. For example, if you have a 6dB peak at 6khz it could cause the image to shift towards the tweeter when that 6khz frequencies are played on the source. Finally, it can also be caused by different FR on different sides of the car - the perfect example of this is the typicall 2-way car audio setup with midbass off axis in the doors. The driver midbass is typically about 60 deg off axis, while the passenger midbass is typically about 30 deg off axis - due to the variation in offaxis response at different angles, you will get more upper midrange information (1.6khz - 3khz) from the passenger side then from the driver side, and hence it will cause the image to 'shift' towards the passenger side of the car when sound within that frequency range is played back.

Timing is another thing that can cause frequency steering at times. If the mid is much closer then the tweeter, the midrange frequencies will reach your ear before the highs do - this can allow your ears to distinguish these as two different signals, and it can potentially cause frequency steering effects as above. I do find it's usually a FR thing though.

To treat this my solution has been to ensure that the install is as symmetrical as possible, and that your system is tuned to give as flat a FR as possible with minimal gaps and peaks. This sometimes requres playing around with crossover settings and (if it comes to it) EQ. It's quite possible that distortion issues can also contribute to this.

[BMWTurbo]

For a single seat.

A fairly accessible way to counteract this is to get a set of 1/3rd octave tones and play each one adjusting left and right eq level in order to 'move' the centre image to the same location in the dash for each band as best you can.

In order to not change the overal level of the band you are adjusting, make sure you +1 ones side and -1 the other so they roughly equal out.

This will work well for the higher bands >1.5k/2k, but you'll probably find L/R T/A much more usefull for the lower freq bands <1.5k/2k though you will need to level match also.

[syd-monster]

Rich, since I had a chance to judge/listen to your car on the w/end I want to help you tune it.

Can you tell me more about its install. (treat me like as if I've never seen i before, like I don't know anything about it).

1. What components makes up the front stage? (is type and size, no need to mention brand)
2. Where are they installed?
3. Is it a passive or active set up?
4. What tuning capabilities/equipment do you have?
5. In a nutshell, do you have & what is your basic tune? (ie a tune you always come back to if you experimenting went wrong/or too far)
6. What frequency do your subs x-over at and slope
7. What is the basic sub set up (ie x2 12's sealed)?

I think we can get something more positive for the next round, since you have to do it and I will only ever judge it from a judges POV and the MEASQ rules, we may need to consider two tuning settings.

[scraverX]

1) Front stage consists of:
6.5" reinforced (Kevlar/FG) polly cone mid-woofer
~1" polymer treated Silk dome Tweeter

2) Locations:
Mid-woofer is located low and forward in the door behind factory trim - door trim/grill is actually curved slightly (not sure if this would make a difference) but one might assume the speakers are angled slightly forward just looking at the door trim
Tweeter is mounted in the factory Sail position - the shape of which would have them angled slightly on axis with the opposite seat (there's also likely an early reflection off the side glass)

3) Setup is Passive Bi-amped - I'm unsure of the frequency and slope on the crossovers

4) Tuning capabilities/equipment:
I have an Audison bitOne (and dedicated laptop).
In a nutshell I would say I can set almost anything for either individual speakers or pairs of speakers. (can give WAY more detail)

5) Basic tune was set by FHRX. It stages quite solidly in front of the drivers seat. I revert to a modified version of this tune with my own TA settings. Sometimes it seems to stage near centre dash, other times in front of the drivers seat (this is where I'm convinced my ears are tricking me but I could be wrong) - the one thing I retain is the EQ settings which I think is what gives me my good linearity.

6) Subs are crossed at 70Hz, 24db slope

7) Basic sub setup is 2x 10's Sealed, single chamber enclosure - I'm unsure as to the volume - enclosure is located in the left corner/side of the boot.

Edited by scraverX, 07 February 2012 - 05:26 PM.

[syd-monster]

hmm, ok. You have Bit1 but still using passive x-over?
Would you be willing to wire 100% active provided you have the amplification?

[scraverX]

Not only do I have the amplification - currently 2 amp channels feed each x-over (one for tweet, one for mid-woofer) but with the x-overs being in the boot I already have the wiring running from boot to each door so it should be a simple matter of disconnecting and re-connecting.

[syd-monster]

OK great!!! Hopefully you may humor me and we can get somewhere with this . For the below you will need to be confident in tuning with the Bit-One and some basic wiring skills...

1. First thing, please write down every current setting & wiring set up you have now as is. Makes full notes, because shold "something*" happen, its best you have a reference to turn to wire & tune everything again. Just in case, you always need something to go back (a base/reference) and also make a note of the drivers seat position if you have one for competition. Many competitors have it right back and on a slight lean, make note of that too, seat position makes a big difference. I also wan't you to write down the temperarture inside and outside the car... if you can do this in a place under shadow that you can return to time & time again that is reasonably repetable.

2. Wire your system 100% active. That is by pass the PPi crossovers all together (leave it in there for looks if you like). Essntially each front stage speaker will have its own channel on your amp powering it. EG; channel 1 connected to Left Hand Side tweeter, channel 2 RHS Tweeter, channel 3 LHS Mid, channel 4 RHS Mid. Also make sure phase (that is all the positives and negatives) are 100% right to each speaker. This is critical. Sorry if this sound patronising, but I need to cover all possible avenues.

3. Likewise on the RCA output of the Bit-One, one RCA should be going to each channel input. So from the Bit one you should have 5 RCA's, 1 to 4 are for each individual channel input to the amp and correspond with the correct speaker. 5th RCA is for sub.

4. Make sure all Amp x/over, boost, EQ settings on the amp are set to 0 or off. That is other than gain, we don't want the amp to have any signal processing. Let the amp, amplify, you have a Bit-One that can do the processing. I would also wind all gains to minimal and equal, as we will set those a little latter. However, generally speaking, the less gain wound on an amp, the lower the noise floor. From memory your's is pretty low as it is, but best you check it anyway.

5. Make sure ALL outputs from the 7200MkII have nill processing, boost, xover, etc, not sure how its wired, but try to have the RCA outputs playing full range, what ever is feeding the Bit-One, make sure they get every bit of music to it.

**Because you have so much processing potential in your car I need to start a-fresh, that is what ever settings you have on the 7200MkII, on the Bit-One, on the amp, on the passive-Xovers, we need to establish a level were we minimise what is influencing the signal and just let the Bit-One handle it all. This will help minimise phase, timing issues and any other unknowns.


5. Once you have it all as above and are comfortable with what you got, park the car in that same place you did for 1. and also see if you can somehow be at similar temp range. That is you don't want to be in blistering heat one tuning session and then in caberra-cold the next tuning session. Get some masking tape and place a dot or strip in the centre of your windscreen, that is measure it across with a tapemeasure and put a strip of tape down the middle, this is to give you a visiual reference as to where centre is.

6. Lets begin, plug in computer to Bit-One and start the tuning process, you can even start from scratch and run the set up disc, infact I think the Bit-One makes you do that anyway?? (can't remember). Remebering to select the style of install you have, that is pair of tweets and mids at front and sub out back. Make sure everything is set to flat, no EQ as yet, no TA etc.

7. I want you to concentrate on running JUST the front stage by itself and in particular the mid, this will be our key tuning speakers. Using the Bit-One mute the subs & tweeters. Set a basic cross over for the mids so they play from 70 to 80Hz (24dB slope) and up. Basically the mids, will play just about all the music from midbass and up to roll off.

8. Play a reference disc, a track with a solid centre image, one you know well, probably a speaking voice eg the speaking tracks on UDD or Alpine First encounter (learn it on a HiFi stereo first if you have to). Bring volume to a comfortable level, hopefully judging volume. With your seat in comp position (as per 1). Make a note of where they are speaking from, where is that centre image. It's likely & infact you should hear it off to the right and a little low, don't worry about height right now just concentrate on left to right. You will probably want to select "repeat track" on the 7200Mkll now.

9. With the voice still playing, (With no EQ or TA), try fliking between the phase on the BitOne on the "invert phase" selector on the screen. Try with the right first, listen, make note. The return to normal and try the same with the left & make note. You should have heard a movement of the centre image (better or worse). Choose the one that puts the image closes to middle. It may be that the best or closest was both in normal phase, infact I dare say it will be. If not what ever brought that voice as close to centre as possible, leave it there, choose to have it so its just closer to the right (drivers side) than the left side of the stage if the changes are either side of centre.

10. Next, on the TA side of things, begin to delay the RHS mids 0.01ms at a time. Listen each time what it does to the voice, each time time you add delay. See if you can get it to move right across the dash, deliberately going past centre. The bring it back to centre. I think you will find you will only need very little delay one the RHS mid to centre it (dont worry about height). Write down all these settings. You should have a voice playing in the centre in line with the line you marked on the screen.

11. Now mute the mids and un-mute the tweeters. Set a basic x-over point of Hi-Pass about 2Khz/24dB for the tweeters and repeat step 9. Again i think they will probably all stay in phase. Don't have them up too loud, 2Khz on the tweets (most tweets) is quite low.

12. Reduce the gain/amplitude level on the RHS tweeter by about 2 clicks or 2dB. I can't remeber how this is done on the BitOne. This is where a tweeter has both types of frequency steer, in both time & amplitude. Test between 1, 2 or 3dB and see what centres the voice best, if the steps move it too much or too ambigous, choose to have it so its just closer to the right than the left side of the stage, if changes are either side of centre. Then in the TA delay again by small steps, listening one at a time to what puts that voice in the centre. Again I think you will find only a small amount of delay is needed. Get is as close to centre as possible and make a note.

13. Next unmute the mids and set a low pas crossover point on the mid of about 2.2Khz, and bring the tweeters up to 2.5Khz something like this (all at 24dB slopes). Having all 4 speakers playing, play/test/try with the intereaction point between the 4 speakers, go higher and higher, but don't play that tweeter much less than 2.2Khz, I dare say It can't handle it. Keep testing and listening to different points, you may even want to overlap the frequency, that is have the tweeter play down to 2.5Khz and the mid up to 3Khz... see what sounds best to you. I dare sugges that you will find it best with the mid playing to 2.2Khz or close to and the tweeter playing from 2.5Khz and up. This should also lift your sound stage but also different Xover points will have different centre images, again choose the one that sounds best or most centered.

14. Mute and unmute each pair of speakers one will sound more centered that the other, adjust as needed. That is if the mids are a little too much to the right, then add some minimal delay. Vice versa do the same for the tweeter. Flick between each pair and then all 4 on etc and adjust as needed.

15. Have a break! , write down it all, save it. etc. Get a cold one... a cigy what ever... chill as you don't want getting fatigued or bored of the same repetive voice.

16. Now its time to bring in the subs, level and phase will be important here, playing a full musical track you know well. Set the gain (that knob on your dash perhaps) up/down so leanrity remains as always. Test inverting the phase and back again. Also try different xover points, 60, 70, 80 etc. see what sounds, best. Use a track you know well for this. If the sub is dragging your sound stage back, the try a lower x-over point. Or delay ALL 4 speakers of the front stage in equal amounts, ontop of what delay they already have, to bring the sub forward (only if necessary, you may be happy with where it is already). That is if both the right tweet and mid have 0.09ms delay, then that should be a constant. So if you want 1ms of delay, then left mid and tweet will have 1ms each but the righ will have 1.09ms each. This keeps the righ/left/centre image in perspective, but your trying to match up the front stage to the subs. Again try in/out phase on the sub again, test, make a note and save settings.

17. Hopefully you should have a solid centre image now. Save settings and listen to your fav tracks, go for a drive etc. enjoy it now, make notes if you spot something odd. etc.

18. EQ to your liking, personally I run no EQ at all.

19. Go back and repeat the above but save a different setting (I remember you can save different settings on the BitOne), but do one in direct sunlight as the different temp will have an effect on the sound... do the same perhaps in a very cold spot, with the A/C, so you can have 3 different settings saved. This will help you at comps as Canberra has such weather extremes that you may need use the different settings.

see how all that goes, hope that helps... let me know & if not you can always go back to what you had in step 1. Its not like the car sounds bad, its just that your so close... Again change no equipment, what you have i great. just needs the fine tuning. The only thing I may sugest is perhaps that you may need to consider install later on if you don't end up happy with the above.

[scraverX]

Got it, now I need to find somewhere I can work that's out of any potential weather.

[Spink!]

Underground car park!

[iluvmusik]

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Edited by iluvmusik, 12 February 2012 - 08:21 PM.