focal tweeter tuning

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greenbroncoguy

Copper - Posts: 299

Joined: March 27, 2003

Location: Florida, United States

Posted: January 13, 2008 at 3:06 PM / IP Logged

I have heard many horror stories about the Focal TN-52 tweets sounding harsh or spitty up high, but after some reading on ECA.com, I have also learned that in the hands of the right tuner, they can sound great. I got mine fairly cheap, and they came bundled with a set of midbasses I wanted, so I think I will try and get as much out of them as possible before I trade them for something else.

Has anyone gotten good results from using these, and if so would you be willing to share some of your tuning knowledge?

Currently, I have them paired with DLS Iridium 6.3 midbass's, running active. While I know this is not ideal(IMO, the DLS midbass does not do too well playing up high - and it was not designed to), it is what I have until I can build A-pillar panels for my TG9's. I want to maximize the tweeters and keep them from sounding harsh, as the DLS are quite the opposite and are very natural sounding. I currently have the x-overs set at 50-2500hz @ 12db for mid bass, and 2500hz + @ 12db for tweeters.

Any takers?

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speakermakers

Copper - Posts: 231

Joined: January 02, 2003

Location: United States

Posted: January 13, 2008 at 7:23 PM / IP Logged

In my opinion you have one of the best tweeters ever engineered specifically for mainstream car audio. The trick to avoiding that harsh sound is to always be aware of comb filtering and take steps to avoid it. Comb filtering is when a change in the speakers phase occurs at a lower frequency that causes a ripple in the response. This ripple will repeat its self over and over again as frequency rises. In other words a simple alteration like poor equalization or reflective surfaces that effect 3khs can have horrendous effects at 10khz.

Here you can see the effects of comb filtering on what would otherwise be a flat smooth response. A shift in phase at 1khz causes problems throughout the pass band. This can be caused by tweeter location relative to the mid range, incorrect crossover frequency, incorrect equalization, and other things.

Incorrect crossover frequency selection is a common cause of comb filtering. Your tweeters have an Fs of 1955hz. The accepted rule of thumb is to always crossover tweeters at a minimum of twice the resonant frequency using a 12db crossover. This would be 3910hz in your case.

After you have established a good crossover point for your application, the next step is to equalize if you have the equipment. Always start by equalizing lower frequencies first and working your way up. This actually applies to all speakers of all types. If you randomly equalize you run the risk of inadvertently causing comb filtering. Then you will find your self trying to equalize a problem that you actually caused. Comb filtering can be masked by the way that an RTA displays its information. This is why many people don’t trust these machines. They don’t realize that they are equalizing improperly, and that the RTA lacks the resolution to display that. Like I said comb filtering can be avoided largely by taking steps to avoid it. The correct tool to use to view it in the event that you think it is the source of harsh sounding highs is an FFT analyzer.

All car audio systems suffer from this and most suffer a lot. I stress this because this is the absolute largest cause of bad sounding highs.

I hope this helps with your decisions.

greenbroncoguy

Copper - Posts: 299

Joined: March 27, 2003

Location: Florida, United States

Posted: January 13, 2008 at 8:26 PM / IP Logged

^^^ This is awsome info. It looks like this system will really be able to shine as a 3-way, and until I can get that in, I am going to have to compromise and settle for less. Without putting in a dedicated midrange or changing to a higher-playing midbass(or much lower playing tweet), I am not going to get the best FR...

Maybe I can try raising the tweeter's HP to 4khz w/ a 6db slope, and raising the midbass's LP to 2800hz w/ a 6db slope to see if that helps at all. I jsut don't want to raise the midbass's LP any more to avoid beaming - these DLS's already do not sound that great up high.

I just wanted to avoid using 6 & 18 db slopes b/c I thought I read something in my research that said using these slopes could cause weird phasing issues that would be difficult to work around. Is this true?

speakermakers

Copper - Posts: 231

Joined: January 02, 2003

Location: United States

Posted: January 13, 2008 at 10:26 PM / IP Logged

You’re on the right track. Making the most of what you have is what its all about. As far as the crossover slopes go I would not count on any specific slopes theoretical phase response. The information that you read is correct but applies to home audio applications. It of course is also valid in a car but in a car there are several other factors that will modify the phase response anyways. For instance the location and angle of your speakers. In a home audio application all of the drivers are typically mounted on a flat surface so phase characteristics are much more predictable. I could go on and on here but the skinny of the situation is always keep the theoretical phase information in mind (like using 12db slopes) but experiment and trust your ears, then make an educated decision. 12db crossover slopes will typically invert the phase of your tweeter but not the mid. So experiment with inverting the phase, and listening. Also in the event that you have equipment capable of time delay you can manually modify the phase of any speaker incrementally. You might seriously want to look into purchasing Auto sound 2000’s test discs part # CD-102 and CD-103. With these two disks you can definitively find the best phase, gain, time alignment settings.

What type of processor are you using for your crossovers?

greenbroncoguy

Copper - Posts: 299

Joined: March 27, 2003

Location: Florida, United States

Posted: January 14, 2008 at 9:09 AM / IP Logged

I am using the PPI DCX-730 - it has T/A, 1-4th order slopes, 3-way capable(6 seperate channels of processing), crossover selection anywhere from 20-20000hz, butterworth/LR filters(selectable) - basically anything I need to do as far as processing is concerned I can.

After I got off of work last night, I set my LP on the mids at 3khz, and the HP on the tweets at 4khz - I think I like that alot better. I also left the slopes at 12db for now. I think where most of my muddiness is coming from is my midbass's - I cut 1500hz/1000hz/750hz down about -5db and it sounds much better. I have not began EQ'ing the tweeters. I think I have my cart a little ahead of my horse here, as I need to get my mechanical phasing for all the drivers down first - I think that's where some issues lie as well.

Another question - If the slopes were to change the phase(say a 12db slope for a 180' phase shift(?) ), wouldn't just flipping the mechanical phase(+ & - wires) be different the taking the x-over away?

speakermakers

Copper - Posts: 231

Joined: January 02, 2003

Location: United States

Posted: January 14, 2008 at 10:38 AM / IP Logged

I am not sure that I understand the last part of your question, But yes. You must first make sure that electrical phase is correct, and yes inverting the phase at the tweeters terminals is the best way of compensating for a 12db hi pass with inverted phase characteristics. All processing should be done last.

greenbroncoguy

Copper - Posts: 299

Joined: March 27, 2003

Location: Florida, United States

Posted: January 14, 2008 at 12:04 PM / IP Logged

speakermakers wrote:

While your last response answered my question, I'll reitterate my comment. for clarity...

Doesn't introducing a 12db/ octave crossover into a drivers' signal path effectively create a 180 degree phase shift?

Also, wouldn't a 6db/octave slope cause a 90 degree shift - this is one that would make it difficult to tune around since reversing the mechanical phase(+ & -) would cause a 180 degree shift and not be able to compensate for the it - correct?

Now - isn't it true that flipping the + & - wires (electrical phase) is NOT the same as changing the acoustical phase( introducing a phase shift from a crossover slope)? In my last question I listed the terms mechanical phase and electrical phase - this was an error on my part. I should have used electrical and acoustical phase. My apologies...

speakermakers

Copper - Posts: 231

Joined: January 02, 2003

Location: United States

Posted: January 14, 2008 at 10:40 PM / IP Logged

Pat your self on the back. It is evident from your questions that you get all of this so much more than the typical enthusiast. It’s nice to see that once in a while. Theoretically a 6db crossover will have no phase shift. In the event that you want to account for phase shifts that are greater or less than 180 degrees then time alignment or physical relocation is your only practical option.

I have often wondered if crossover phase off sets the time alignment of that driver by one half cycle (in the case of a 12db), or if there is no time delay involved in a 12db crossover and re-inverting the phase simply sets things 100% rite. I honestly don’t know. I have also wondered, if the signal is delayed by the crossover (inverted with delay) wouldn’t the effects be frequency dependant and dependant on the type of filter (active or passive).

This last bit of pondering has led me to believe that there must not be a predictable amount of delay involved with any crossover design (but rather an instantaneous shift in phase with no delay). Active at least. If any one has information and references to the source of this information (not just opinions) I would be interested. Please post. Another thought That I have is that, I have read dozens of books on this topic and most of them written by ultra anal mathematicians and physicists. Never once have I come across any author describing the phase shift as an actual delay.

As I said before, even if you could calculate the exact effects of electronic phase you are still faced with the difficulties of overcoming acoustical phase shifts caused by speaker placement in the car environment. All of this knowledge plus time alignment capable processors is our saving grace!

greenbroncoguy

Copper - Posts: 299

Joined: March 27, 2003

Location: Florida, United States

Posted: January 15, 2008 at 12:21 PM / IP Logged

Well I have the ability to time align; is there a rule or formula I would use to see how much time alignment I would need (in addition to what I would use to account for path length differences) to account for the phase shift caused by the crossover? Also, what would I need to consider if I already had the electrical phase flipped on certian drivers, like my driver's side mid bass?

And thanks for the compliment - audio and electronics has always interested me ever since I was about 12-13, but ever since I've had a car I have not been able to get enough info or read enough about it :)

greenbroncoguy

Copper - Posts: 299

Joined: March 27, 2003

Location: Florida, United States

Posted: January 15, 2008 at 10:54 PM / IP Logged

Also, another question comes to mind: say you have a bandpass filter set on a driver. Each filter ( LP & HP) will have its own slope, so if they both had 12db/octave, would you combine them to view it as a 24db/octave slope, would they subtract from each other and have no phase shift whatsoever, or would they do something completely different?

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