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More tweaking 5/24/01 on my SunOnes
Graph 5 (1m): I did lower the lower woofer crossover point to around 215Hz. Since I was able to free up some capacitors, I adjusted the zobel on the upper woofer. Sounds okay, but a little thin on the bass, and still hear a bit of blare/glare on some tracks.
Graph 6 (1m): So with the adjust zobel on the upper woofer, I go back to the 350Hz crossover point for the lower woofer. A bit more bass on the low end returns, but still need more tweaking.
Crossover breakthrough 5/29/01 - Trust your ears.
I spent the last few days listening to various music sources to see if I could nail down the "something that wasn't right" when I was listening to the speakers. I finally decided to take some individual measurements of the woofers (in tandem) and the tweeter. I am using a dual-input terminal cup that allows me to just listen to either section if I remove the connection bars. So I made some cursory measurements of the woofers' crossover behavior on the frequency range over 2000Hz.
What I found out was shocking. I discovered that my upper woofer filter was not doing its job! Wherever it was crossing over, it was nowhere in the vicinity of even 8000Hz! Basically I had no woofer filtering and what I had been hearing as blare/glare was the upper woofer's cone breakup in the 3000-5000Hz range due it playing butt nekkid and fancy free!
Upon reviewing my calculations, I discovered I made a mistake in determining the impedance at the woofers' crossover point. I brain-farted and just used the zobel target impedance of 8 ohms when calculating for a 2nd order Butterworth. This is what threw off the filter component values I used for the upper woofer. I should have parallelled the upper woofer's zobelized impedance of 8 ohms with the lower woofer's non-zobelized impedance of 12 ohms for a nominal 4.8 ohms. Since I rearrange my components around, I fine-tune the capacitor value for the upper woofer's zobel with some of the freed up capacitors (this just means reducing the cap value from 24.4uF to 21.3uF which is closer to the calculated value).
I noticed that the tweeter filter needed some work as well (yet another brain-fart where I forgot to use the zobelized impedance when calculating the filter - instead of using 8 ohms, I used 6.5 ohms @2000Hz from the spec sheets from Morel's website). So I whipped up a different crossover network for both the tweeter and upper woofer, and see if I actually get some filtering action on both drivers.
5/30/01 - This is the start on the road to sonic recovery...
Graph 7 (3m): I decided to attack the XO design a little differently by plotting the response of the woofer (in tandem) and the tweeter, as well as the composite frequency response. This allows me to see what needs to be tweaked (because I know I didn't get it right on the first shot). As you can see, I now get the filtering I expect to get with the new upper woofer filter in place, its response is shelved down starting around 2000Hz, and the rest of the response is consistent with its frequency response above 2000Hz to 6500hz. Bear in mind the lower woofer is still contributing (albeit not as much as the upper woofer) to the over frequency response. Take note of the tweeter's response slope which starts too far past the desired XO point of 2000Hz, it appears to sloping off around 3200Hz. This gives me more food for thought.
Graph 7a (3m): Also, I've seen folks use graphs with the tweeters connected out of phase with the woofers to verify the phase coherency of the crossover point (you should see a big dip in the response around the crossover point). From this graph, you can see the dip around 2500-3000Hz is just past the target crossover point of 2000Hz. So this means more work on the tweeter filter.
I decide that the tweeter's zobelized impedance is too high in the pass band that I am concerned about. The nominal impedance of the Morel MDT30 is 8 ohms, but that's simply too high for the frequency range from 1500-20000Hz. I decide to junk the tweeter zobel from the tweeter filter, and rely on the natural impedance/frequency response curves of the tweeter for the crossover. Luckily for me, Phil Abbate was nice enough to measure my tweeter and midwoofer on my baffle, and produce the impedance/phase "zma" file, and the frequency response "frd" file for use for modelling in speaker software design packages. I looked at the "zma" file and looked for the value of the impedance in the 2000Hz range and above. I found that the impedance was around 7.2 ohms, and then it slopes down to around 6.5 ohms before rising upwards - the inductance of tweeters don't have as much of a detrimental effect that woofers do, so I decided to remove the zobel, and use 7.2 ohms for the impedance when calculating a new tweeter filter. Luckily for me, I had the right parts on hand to make this filter a reality for both speakers (I've been really lucky in this respect).
Graph 8 (3m): So with the new tweeter filter in place (ditching the zobel on the tweeter, and keeping it a simple 2nd order Butterworth with a 3.8dB l-pad), here is the frequency response: showing both the woofers, the tweeter, and the composite response. The tweeter filter is behaving as well as can be expected, the sloping is a bit harder due to the tweeter natural roll off at 2000hz. I thought about using a 1st order (12uF capacitor), but was more concerned with tweeter protection, so I went with the 2nd order BW filter. But this is okay because of the contribution from both woofers helps out in the crucial 2000Hz range. I leave the lower woofer crossover point around 350hz for now, and will evaluate it if I think the bass is too much.
Graph 8a (3m): Here's the tweeter connected out-of-phase graph, along with the in-phase response. As you can see, the dip is centered around 2000Hz now, so that's a good sign that the new revised crossover network is making a difference in the over speaker performance.
This part of the tweaking process is where the lightbulbs are going off in my head. Kind of a neat feeling. Now it's time for me to listen to more music CDs and see if there's anything that needs to be addressed in the crossover. Remember: Trust your ears.
PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
Graph 5 (1m): I did lower the lower woofer crossover point to around 215Hz. Since I was able to free up some capacitors, I adjusted the zobel on the upper woofer. Sounds okay, but a little thin on the bass, and still hear a bit of blare/glare on some tracks.
Graph 6 (1m): So with the adjust zobel on the upper woofer, I go back to the 350Hz crossover point for the lower woofer. A bit more bass on the low end returns, but still need more tweaking.
Crossover breakthrough 5/29/01 - Trust your ears.
I spent the last few days listening to various music sources to see if I could nail down the "something that wasn't right" when I was listening to the speakers. I finally decided to take some individual measurements of the woofers (in tandem) and the tweeter. I am using a dual-input terminal cup that allows me to just listen to either section if I remove the connection bars. So I made some cursory measurements of the woofers' crossover behavior on the frequency range over 2000Hz.
What I found out was shocking. I discovered that my upper woofer filter was not doing its job! Wherever it was crossing over, it was nowhere in the vicinity of even 8000Hz! Basically I had no woofer filtering and what I had been hearing as blare/glare was the upper woofer's cone breakup in the 3000-5000Hz range due it playing butt nekkid and fancy free!
Upon reviewing my calculations, I discovered I made a mistake in determining the impedance at the woofers' crossover point. I brain-farted and just used the zobel target impedance of 8 ohms when calculating for a 2nd order Butterworth. This is what threw off the filter component values I used for the upper woofer. I should have parallelled the upper woofer's zobelized impedance of 8 ohms with the lower woofer's non-zobelized impedance of 12 ohms for a nominal 4.8 ohms. Since I rearrange my components around, I fine-tune the capacitor value for the upper woofer's zobel with some of the freed up capacitors (this just means reducing the cap value from 24.4uF to 21.3uF which is closer to the calculated value).
I noticed that the tweeter filter needed some work as well (yet another brain-fart where I forgot to use the zobelized impedance when calculating the filter - instead of using 8 ohms, I used 6.5 ohms @2000Hz from the spec sheets from Morel's website). So I whipped up a different crossover network for both the tweeter and upper woofer, and see if I actually get some filtering action on both drivers.
5/30/01 - This is the start on the road to sonic recovery...
Graph 7 (3m): I decided to attack the XO design a little differently by plotting the response of the woofer (in tandem) and the tweeter, as well as the composite frequency response. This allows me to see what needs to be tweaked (because I know I didn't get it right on the first shot). As you can see, I now get the filtering I expect to get with the new upper woofer filter in place, its response is shelved down starting around 2000Hz, and the rest of the response is consistent with its frequency response above 2000Hz to 6500hz. Bear in mind the lower woofer is still contributing (albeit not as much as the upper woofer) to the over frequency response. Take note of the tweeter's response slope which starts too far past the desired XO point of 2000Hz, it appears to sloping off around 3200Hz. This gives me more food for thought.
Graph 7a (3m): Also, I've seen folks use graphs with the tweeters connected out of phase with the woofers to verify the phase coherency of the crossover point (you should see a big dip in the response around the crossover point). From this graph, you can see the dip around 2500-3000Hz is just past the target crossover point of 2000Hz. So this means more work on the tweeter filter.
I decide that the tweeter's zobelized impedance is too high in the pass band that I am concerned about. The nominal impedance of the Morel MDT30 is 8 ohms, but that's simply too high for the frequency range from 1500-20000Hz. I decide to junk the tweeter zobel from the tweeter filter, and rely on the natural impedance/frequency response curves of the tweeter for the crossover. Luckily for me, Phil Abbate was nice enough to measure my tweeter and midwoofer on my baffle, and produce the impedance/phase "zma" file, and the frequency response "frd" file for use for modelling in speaker software design packages. I looked at the "zma" file and looked for the value of the impedance in the 2000Hz range and above. I found that the impedance was around 7.2 ohms, and then it slopes down to around 6.5 ohms before rising upwards - the inductance of tweeters don't have as much of a detrimental effect that woofers do, so I decided to remove the zobel, and use 7.2 ohms for the impedance when calculating a new tweeter filter. Luckily for me, I had the right parts on hand to make this filter a reality for both speakers (I've been really lucky in this respect).
Graph 8 (3m): So with the new tweeter filter in place (ditching the zobel on the tweeter, and keeping it a simple 2nd order Butterworth with a 3.8dB l-pad), here is the frequency response: showing both the woofers, the tweeter, and the composite response. The tweeter filter is behaving as well as can be expected, the sloping is a bit harder due to the tweeter natural roll off at 2000hz. I thought about using a 1st order (12uF capacitor), but was more concerned with tweeter protection, so I went with the 2nd order BW filter. But this is okay because of the contribution from both woofers helps out in the crucial 2000Hz range. I leave the lower woofer crossover point around 350hz for now, and will evaluate it if I think the bass is too much.
Graph 8a (3m): Here's the tweeter connected out-of-phase graph, along with the in-phase response. As you can see, the dip is centered around 2000Hz now, so that's a good sign that the new revised crossover network is making a difference in the over speaker performance.
This part of the tweaking process is where the lightbulbs are going off in my head. Kind of a neat feeling. Now it's time for me to listen to more music CDs and see if there's anything that needs to be addressed in the crossover. Remember: Trust your ears.
PatCave; HT Pix;Gear;DIY Projects;DVDs; LDs
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