The 4,5 ohms resistor sets the volume of the Vifa FR, it works as an attenuator. The 8 ohms together with the 2 mH inductor adjusts the top end, the 8 ohm adjusts the volume of the upper frequencies. Depending on your taste, room, music, speaker placement, blood pressure etc. you can tweak the two resistors in order to get a more refined sound. But you should start with the given values. Have fun!
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Active filtering has been mentioned several times in the thread. Here is a recent post.
https://www.diyaudio.com/community/threads/fast-fun-inexpensive-ob-project.110583/post-7033913
https://www.diyaudio.com/community/threads/fast-fun-inexpensive-ob-project.110583/post-7033913
Hi,
as I wrote somewhere I'm working on my own OB construction, going the hard but educative way, a thread will follow soon.
Why I'm writing here is the xo. I ended up crossing the woofer at about 100 Hz, above there is an FR, crossed much higher, and it sounds better and better. But - it shouldn't work, just like the Manzie shouldn't work. Woofer crossed at about 100 Hz, but the little Vifa can't possibly go down that far, and is crossed far above with 6 uF. So it shouldn't work, but it does. There should be a huge gap/trough between 100 Hz and 3-4 kHz. But there isn't. Is there an explanation?
Many thanks in advance!
as I wrote somewhere I'm working on my own OB construction, going the hard but educative way, a thread will follow soon.
Why I'm writing here is the xo. I ended up crossing the woofer at about 100 Hz, above there is an FR, crossed much higher, and it sounds better and better. But - it shouldn't work, just like the Manzie shouldn't work. Woofer crossed at about 100 Hz, but the little Vifa can't possibly go down that far, and is crossed far above with 6 uF. So it shouldn't work, but it does. There should be a huge gap/trough between 100 Hz and 3-4 kHz. But there isn't. Is there an explanation?
Many thanks in advance!
I am afraid you are confusing filter placement with crossover point.
The crossover point is where two drivers are contributing equally to the sound level.
Lacking resonant peak filters and zobels, gentle filters rarely provide crossover points close to their theoretical -3 or -6db points.
The crossover point is where two drivers are contributing equally to the sound level.
Lacking resonant peak filters and zobels, gentle filters rarely provide crossover points close to their theoretical -3 or -6db points.
Yes, I know both 
Maybe I was unclear.
The Manzie has a first order low pass filter for the woofer, with an 18 (or 20) mH inductor, which means the filter is set at about 70 Hz, so we get -6dB at about 140 Hz (please correct me if I´m wrong).
For the FR there is a first order high pass filter with 6 µF, which means it is set at about 3,4 kHz, we get -6 dB at about 1,7 kHz (again, please correct me ).
But what happens between 140 Hz and 1,7 kHz? The two drivers meet at about 200 Hz, this is about -8 dB, and there is a trough, in the simulation it would look like on the picture below (I hope I have the right frd-files for the Peerles woofer and the TC9). That´s what I don´t check
Or is it just the electrical crossing, and is the acoustical a different thing?
Or am I completely wrong?
Thanks for any explanation in advance.
Maybe I was unclear.The Manzie has a first order low pass filter for the woofer, with an 18 (or 20) mH inductor, which means the filter is set at about 70 Hz, so we get -6dB at about 140 Hz (please correct me if I´m wrong).
For the FR there is a first order high pass filter with 6 µF, which means it is set at about 3,4 kHz, we get -6 dB at about 1,7 kHz (again, please correct me
).But what happens between 140 Hz and 1,7 kHz? The two drivers meet at about 200 Hz, this is about -8 dB, and there is a trough, in the simulation it would look like on the picture below (I hope I have the right frd-files for the Peerles woofer and the TC9). That´s what I don´t check
Or is it just the electrical crossing, and is the acoustical a different thing?
Or am I completely wrong?
Thanks for any explanation in advance.
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I found it
Well, it's a combination of electrical and acoustical crossing, so the real crossing point of the woofer is at 750 Hz, despite of the 20 mH, I never would have thought. The baffle and the xo together gives a 2nd oder, that's why the FR is connected with reversed polarity. Everything is slowly starting to make sense
Well, it's a combination of electrical and acoustical crossing, so the real crossing point of the woofer is at 750 Hz, despite of the 20 mH, I never would have thought. The baffle and the xo together gives a 2nd oder, that's why the FR is connected with reversed polarity. Everything is slowly starting to make sense
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In this post there is an explanation of how the crossover works:
https://www.diyaudio.com/community/threads/fast-fun-inexpensive-ob-project.110583/post-4573958
Although no spelled out in detail it does mention how the very low electrical crossover point helps to flatten the woofer response. Remember, this woofer is not in a box, nor is it on an infinite baffle. The bass frequencies wrapping around the baffle to the back side cancel out each other. Therefore the woofer has much more top end than it should (less bass). The very low 1st order crossover flattens the woofer response putting its acoustic roll off around 700 Hz.
I’ll try to post some graphs to show this.
https://www.diyaudio.com/community/threads/fast-fun-inexpensive-ob-project.110583/post-4573958
Although no spelled out in detail it does mention how the very low electrical crossover point helps to flatten the woofer response. Remember, this woofer is not in a box, nor is it on an infinite baffle. The bass frequencies wrapping around the baffle to the back side cancel out each other. Therefore the woofer has much more top end than it should (less bass). The very low 1st order crossover flattens the woofer response putting its acoustic roll off around 700 Hz.
I’ll try to post some graphs to show this.
This is just a simulation, NOT measured, but it does illustrate well what happens with the response of a 12 peerless on the Manzanita baffle. It shows what happens when you put a large inductor in series with the woofer. Blue is no inductor, Red with the inductor. With no filter or EQ, we see the rising response of the woofer that is caused by the OB bass losses. Pop a big fat inductor on it, and the response flattens.
Seen here (a little bit) is the baffle peak that when flattened, makes a top end roll-off of the woofer. This sim does not show the natural roll-off of the woofer the top end which will make the roll-off even steeper.
That's the basic John Busch OB trick. You know, like the click bait ads "Use this one weird trick to fix your OB!"
It works great, but you lose a lot of woofer sensitivity. Often 10 dB. But that's what you have to do to get a proper tonal balance. Too many OB builders don't understand this, or don't want to trade away the sensitivity and so end up with a poor tonal balance, not enough bass. If you want OB bass, you need either a huge baffle, or you trade away sensitivity. That's the physics of the Open Baffle.
It took me a long to to understand what John was doing, because I was so used to normal boxed woofer crossovers that work just on the top end of the woofer response. This crossover is both EQ and crossover rolled into one. I hope that is clear from the graph above.
Seen here (a little bit) is the baffle peak that when flattened, makes a top end roll-off of the woofer. This sim does not show the natural roll-off of the woofer the top end which will make the roll-off even steeper.
That's the basic John Busch OB trick. You know, like the click bait ads "Use this one weird trick to fix your OB!"
It works great, but you lose a lot of woofer sensitivity. Often 10 dB. But that's what you have to do to get a proper tonal balance. Too many OB builders don't understand this, or don't want to trade away the sensitivity and so end up with a poor tonal balance, not enough bass. If you want OB bass, you need either a huge baffle, or you trade away sensitivity. That's the physics of the Open Baffle.
It took me a long to to understand what John was doing, because I was so used to normal boxed woofer crossovers that work just on the top end of the woofer response. This crossover is both EQ and crossover rolled into one. I hope that is clear from the graph above.
Hi,
Has anybody built this type of Manzantia with front wings, which I guess would make of it an H design. See pictures in post #3170. How does it perform compared with the basic version?
D
I've not built or heard this version of the Manzi. But some things come to mind.
The wings likely are to increase the efficiency of the woofer. That makes the speaker easier to drive and perhaps cuts down on crossover parts. John was always trying to design stuff that sounded great and was cheap to build.
Pano mentioned the sides being uneven to reduce cavity resonances. John used a similar approach on the Widowmaker III (below) although I'm guessing a big part of the wings was to keep the size of the front baffle less wide. He had a tough time selling his speakers as they tended to be pretty large and wide. Sounded great, thought. So on the Manzi it was likely a similar attempt to keep the baffle smaller while keeping the bass intact.
All guesses. It'd be interesting to hear this design compared to the Ultras as they use the same parts.
Maybe Pano has some insight.
The wings likely are to increase the efficiency of the woofer. That makes the speaker easier to drive and perhaps cuts down on crossover parts. John was always trying to design stuff that sounded great and was cheap to build.
Pano mentioned the sides being uneven to reduce cavity resonances. John used a similar approach on the Widowmaker III (below) although I'm guessing a big part of the wings was to keep the size of the front baffle less wide. He had a tough time selling his speakers as they tended to be pretty large and wide. Sounded great, thought. So on the Manzi it was likely a similar attempt to keep the baffle smaller while keeping the bass intact.
All guesses. It'd be interesting to hear this design compared to the Ultras as they use the same parts.
Maybe Pano has some insight.
Attachments
I finished adding the woofer trap to the Ultras. At first, it was a minor difference. I would change the balance from L to R as I listened to tracks. After an hour or two of listening, I am glad I upgraded. I think Pano put it best - there was a bite to the woofer midrange, an edge to it that is tamed using the trap.
Overall, the sound is much more natural and flattens, what seemed to me, a certain midrange frequency peak.
Overall, the sound is much more natural and flattens, what seemed to me, a certain midrange frequency peak.
