It's the MS xo design, didn't change anything on this end.
It's a nice speaker, either my ears are getting accustom to them, or the large cap and tweeter are just breaking in.
Post 104 (& back) http://www.diyaudio.com/forums/multi-way/227018-canned-crossover-design-what-next-11.html
It's a nice speaker, either my ears are getting accustom to them, or the large cap and tweeter are just breaking in.
Post 104 (& back) http://www.diyaudio.com/forums/multi-way/227018-canned-crossover-design-what-next-11.html
It's not for the inductance at all. It's to minimize resistance ripple. The 33 ohm resistor will minimize the amount of impedance swing around resonance, and affect not much anywhere else in the impedance. 33 ohms is also going to attenuate less than a decibel when placed across a tweeter. This is an effective tool without using a full notch, and getting positive results. A 5W 33 ohm resistor costs 39c, and at that resistance value, a 5W will be enough.
It also allows a wider 'easy range' than without it present. What's the downside, honestly? I don't see one.
If you measure FR with a 100uF cap on it, you'll protect the tweeter. Measure this with and without the resistor....You'll hear it too.
Later,
Wolf
My sample of an XT25
Fs 524 Hz. Zmaz 16.6 Ohms, Re 3.3 Ohms,Qts .576, Z @ 2K, 3.7 Ohms.
With a 50 Ohm in parallel
Zmax 10 Ohms, Re 2.8, Qts .566. Z @ 2K.... 3 Ohms.
Just don't see an advantage unless you are trying to use it way too low to start with, and it is a band-aid for a poor choice. Anything less than 2.5 second order I would not do due to the energy decay issues it has down low. First order I would not do below 3K. That's 2 and a half octaves so you should be fine. This just seems like a fix to a problem that should be avoided in the first place. If the crossover is picked more appropriately, you don't need the $2 resistor in the first place. I have to build a full system to see if what you say about "it sounds better" I can hear. That is the bottom line. I don't have any mid-woofer handy that I could use anywhere near 2K first order.
Fs 524 Hz. Zmaz 16.6 Ohms, Re 3.3 Ohms,Qts .576, Z @ 2K, 3.7 Ohms.
With a 50 Ohm in parallel
Zmax 10 Ohms, Re 2.8, Qts .566. Z @ 2K.... 3 Ohms.
Just don't see an advantage unless you are trying to use it way too low to start with, and it is a band-aid for a poor choice. Anything less than 2.5 second order I would not do due to the energy decay issues it has down low. First order I would not do below 3K. That's 2 and a half octaves so you should be fine. This just seems like a fix to a problem that should be avoided in the first place. If the crossover is picked more appropriately, you don't need the $2 resistor in the first place. I have to build a full system to see if what you say about "it sounds better" I can hear. That is the bottom line. I don't have any mid-woofer handy that I could use anywhere near 2K first order.
I know this thread is about first-order series, but the direction has strayed here. My usage of the XT25SC50 was with a second order series electrical circuit at 2.66kHz, creating a BW3 acoustic rolloff, required the resistor to sound right. The TG30's I had have Zmax of about 25 ohms, and that is substantial in terms of response. The SC50 showed more like the 16 you showed. The 50 ohm resistor is not low enough in value to work well. It needs to be in the neighborhood of 25-35 ohms, depending on any level of cut you also want. Go too much below that, you get impedance issues. Go too much over that, the results are minimal.
The reason damping the Fs works here, is that the peak is fairly broad, and will increase modulation of the radiator the closer it gets to Fs. This is simple to understand as Fs is the point at which the diaphragm moves the easiest with very low input level. If you damp the 'rise' with decreasing freq towards Fs, the HD will go down.
I agree that 3kHz first order is a better solution, but 12dB even there is more likely. 3.5kHz first order would be my starting point.
However, the way I used it- it was night and day with/without. It's not some cheap trick, but something that actually does work. I really like the XT tweeters, regardless of HD signature in the topend. I guess you don't have to take my word for it, and are entitled to your opinion, but using the active rolloff in the measurements will not reveal any differences done as you have stated.
Later,
Wolf
The reason damping the Fs works here, is that the peak is fairly broad, and will increase modulation of the radiator the closer it gets to Fs. This is simple to understand as Fs is the point at which the diaphragm moves the easiest with very low input level. If you damp the 'rise' with decreasing freq towards Fs, the HD will go down.
I agree that 3kHz first order is a better solution, but 12dB even there is more likely. 3.5kHz first order would be my starting point.
However, the way I used it- it was night and day with/without. It's not some cheap trick, but something that actually does work. I really like the XT tweeters, regardless of HD signature in the topend. I guess you don't have to take my word for it, and are entitled to your opinion, but using the active rolloff in the measurements will not reveal any differences done as you have stated.
Later,
Wolf
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I don't think anyone who has given some thought to the Fs resonance with the excellent non-ferrofluid Vifa XT25 tweeters doubts what you say wolf_teeth. That 500-600Hz energy is best dissipated before it causes large non-linear excursion with low order filters. The 3 ohm resistance is too low too, and needs a series resistor around 4 ohms. Troels Gravesen ALWAYS adds one. 
I really don't warm to series filters, just because they don't have the flexibility of parallel designs. But here's a design using the smooth Vifa polycone P13WH and a 93dB 6 ohm DC standard ferrofluid tweeter:
Surround Vifa Baby - Polissage [REAL] - Enceintes - DIY: Amplis et Enceintes - FORUM Allinbox
How's your French?
Quite Acoustic Reality. I can see a case for a Zobel of 1uF and 7.5R there to fix that rising Frequency response. I take it you understand that the 0.1mH tweeter air coil must be as good as you can possibly get. Low DC resistance to avoid low frequencies breaking through.
I really don't warm to series filters, just because they don't have the flexibility of parallel designs. But here's a design using the smooth Vifa polycone P13WH and a 93dB 6 ohm DC standard ferrofluid tweeter:
An externally hosted image should be here but it was not working when we last tested it.
Surround Vifa Baby - Polissage [REAL] - Enceintes - DIY: Amplis et Enceintes - FORUM Allinbox
How's your French?
Quite Acoustic Reality. I can see a case for a Zobel of 1uF and 7.5R there to fix that rising Frequency response. I take it you understand that the 0.1mH tweeter air coil must be as good as you can possibly get. Low DC resistance to avoid low frequencies breaking through.
An externally hosted image should be here but it was not working when we last tested it.
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My thought on the tweeter resonance is to stay away from it instead of patching a poor choice.
Back to serial crossovers. I agree with Steve in that they are a bit less flexible as the effect on the transfer function is not as predictable due to the driver reactive portions effecting the OTHER driver more. This can of course be worked out. Model it in Spice and see what you get. Not quite as simple as one assumes.
Now, how to add BSC and any filters needed to make the drivers behave, like a notch for the woofer breakup as that first order crossover is going to push it way higher than one may want. Parallel filters only? A series would effect the other driver as well would it not.
Back to serial crossovers. I agree with Steve in that they are a bit less flexible as the effect on the transfer function is not as predictable due to the driver reactive portions effecting the OTHER driver more. This can of course be worked out. Model it in Spice and see what you get. Not quite as simple as one assumes.
Now, how to add BSC and any filters needed to make the drivers behave, like a notch for the woofer breakup as that first order crossover is going to push it way higher than one may want. Parallel filters only? A series would effect the other driver as well would it not.
That site is long gone.
Series 1st order xos are done most successfully if high quality, well behaved drivers are used.
SXO Comments
I know this thread is old, but I thought maybe I'd blow the dust off it for a few comments. Series cross-overs! In the published schematic, the 3.3 ohm resistor that you are using as a padder (voltage divider) for the tweeter has multiple duties and affects. Beside attenuating the tweeter, it also provides a minimum impedance for the left-hand LR circuit at resonance, otherwise it would get dangerously low. Additionally, it lower the Q of the filter and broadens the bandwidth over which the woofer will operate.
The other resistor in the Zobel position for the woofer will have similar affects. Series cross-overs are very complex and every component has a major role, but also multiple minor side-effects. I wish I had a better handle on them, and I used to teach advanced electronics. Regards.
I'm sorry, but this is wrong. As long as there is a component in series to create the voltage divider, and not necessarily a resistor, the shunt resistor will attenuate the tweeter.
In the network of a SXO, this is an example of one:
In this example, the 3.3 ohm is the series L-pad, and the 30 ohm damps the Fs mainly for a flatter tweeter-system impedance. Yes- this is a second-order electrical xover, BW3 acoustic.
Later,
Wolf
I know this thread is old, but I thought maybe I'd blow the dust off it for a few comments. Series cross-overs! In the published schematic, the 3.3 ohm resistor that you are using as a padder (voltage divider) for the tweeter has multiple duties and affects. Beside attenuating the tweeter, it also provides a minimum impedance for the left-hand LR circuit at resonance, otherwise it would get dangerously low. Additionally, it lower the Q of the filter and broadens the bandwidth over which the woofer will operate.
The other resistor in the Zobel position for the woofer will have similar affects. Series cross-overs are very complex and every component has a major role, but also multiple minor side-effects. I wish I had a better handle on them, and I used to teach advanced electronics. Regards.
I don't find them extremely difficult, and just another way of doing things.
In the quasi-12dB or 0.5 Zeta SXO, you get half impedance at resonance of the 2 components in the main leg, and a 12dB slope with 2 parts. There is no resistor in that 3.3 spot for that type. True- the 3.3 is a load stabilizer and a friend to the amplifier.
Later,
Wolf
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