This design is an easy place to start, so yes, you can use two eights per speaker. Don't skimp on baffle size, you can't get quite as deep bass as the lower fs & larger area drivers, but you'll be close with 80% of the cone area and a slightly higher Q.
You would need a different filter on the bass, start with a zobel to give the 10mH a chance, you may still need a notch for the twin peaks between 2&3k.
The Tc9 is worth getting for ease of use, the ps95 is good, but a different beast than the Tc9, if you use it start with a clean sheet, John's filter is well tuned, and only needs level adjustments for most builds and rooms.
You would need a different filter on the bass, start with a zobel to give the 10mH a chance, you may still need a notch for the twin peaks between 2&3k.
The Tc9 is worth getting for ease of use, the ps95 is good, but a different beast than the Tc9, if you use it start with a clean sheet, John's filter is well tuned, and only needs level adjustments for most builds and rooms.
Ok, I can start with an Lpad to get the right attenuation for my room. So what do you mean with changing the resistor to tilt the Vifa? What does the shelf filter add?
The coreect level for my room will be a great to start with and perhaps the only thing to fix...
The shelf filter actually takes away.
The Vifa has a rising response that needs to be flattened. If you have a look at the crossover here:https://www.diyaudio.com/community/threads/fast-fun-inexpensive-ob-project.110583/post-6507952
You will see a cap a coil and a resistor in series with the Vifa. The coil flattens the rising response of the Vifa. The resistor R2 that is in parallel with the coil sets how much the response if flattened. Higher values of the resistance push down the top end more. Lower values allow more rise. You can adjust the tonality of the Vifa simply using R2. Lower value of R2=brighter, Higher value of R2=duller.
Excellent answer, thankyou. I cannot say that the Vifa needs adjustment in its flattening right now, so I will begin to adjust the level of them. Just ordered two L-pads 😊...The shelf filter actually takes away.
https://www.diyaudio.com/community/threads/fast-fun-inexpensive-ob-project.110583/post-6507952
You will see a cap a coil and a resistor in series with the Vifa. The coil flattens the rising response of the Vifa. The resistor R2 that is in parallel with the coil sets how much the response if flattened. Higher values of the resistance push down the top end more. Lower values allow more rise. You can adjust the tonality of the Vifa simply using R2. Lower value of R2=brighter, Higher value of R2=duller.
Did some listening today and it is amazing how much a change of position make for the base. I will get a class D amp for more power, they do need more of that.
Half the impedance means half the inductance. Sounds great, doesn't it - BUT the currents are twice as big, so you still need the same core size - and half the turns of twice the cross-sectional area for the winding!
A zobel is a filter on impedance. By flattening the impedance it allows the simple low-pass to operate in a more consistent fashion,
so that does not become useless at higher frequencies.
A simple filter with a zobel has less phase shift than a higher order filter, although ironically it has one more component.
You can play with the response a little by strengthening or weakening the resistor.
so that does not become useless at higher frequencies.
A simple filter with a zobel has less phase shift than a higher order filter, although ironically it has one more component.
You can play with the response a little by strengthening or weakening the resistor.
Yes a Zobel circuit will help flatten the woofer impedance curve, making the crossover more like it would be with a simple resistor.
Below is a chart of what the electrical response of the 20mH coil would be with the GRS-15". This called the filter factor. Notice that with the Zobel* (red) the curve is an almost perfect 1st order low pass falling 6dB per octave. Without the Zobel (blue), the filter flattens out above 1kHz making a shelf. The shelf is at -25dB, that's the most attenuation you'll get. You can try the Zobel to hear if you like it or not. It will effect the top end of the woofer response.
*Zobel of 10uF+10R
Below is a chart of what the electrical response of the 20mH coil would be with the GRS-15". This called the filter factor. Notice that with the Zobel* (red) the curve is an almost perfect 1st order low pass falling 6dB per octave. Without the Zobel (blue), the filter flattens out above 1kHz making a shelf. The shelf is at -25dB, that's the most attenuation you'll get. You can try the Zobel to hear if you like it or not. It will effect the top end of the woofer response.
*Zobel of 10uF+10R
Well on paper two woofers in parallel means 4 ohms, so you would use 10mH. However...... When I did two 15" in parallel I still needed at least 15-18mH. No free lunch. It's just the way the baffle size and woofers worked out. Having never run 2x8" I'd only be guessing at the inductor value needed. I would not go smaller than 12mH, for sure.
Don't worry too much about the Zobel. At such a low crossover point, it isn't as critical as it is with a higher crossover point, I'll see if I can figure out an approximate set of values for two woofers in parallel.
Don't worry too much about the Zobel. At such a low crossover point, it isn't as critical as it is with a higher crossover point, I'll see if I can figure out an approximate set of values for two woofers in parallel.
https://www.parts-express.com/Jantzen-5241-15mH-15-AWG-P-Core-Inductor-255-128
I was thinking of ordering this, even though it has gone up $7 since I last looked at it this morning.
Would this be a good place to start, Pano?
I was thinking of ordering this, even though it has gone up $7 since I last looked at it this morning.
Would this be a good place to start, Pano?
Ouch! Yes that would work, I've used those but at a smaller value.
You can also use the inductor out of the Dayton 100Hz low pass.
https://www.parts-express.com/100-Hz-Low-Pass-8-Ohm-Crossover-266-446
It should be 18mH. And you can always unwind it if you need to hit a smaller inductance.
You can also use the inductor out of the Dayton 100Hz low pass.
https://www.parts-express.com/100-Hz-Low-Pass-8-Ohm-Crossover-266-446
It should be 18mH. And you can always unwind it if you need to hit a smaller inductance.
A note on crossovers.
The big 20mH inductor in series with the woofer forms a 1st order low pass at about 60Hz. If you can't get the inductors, you can try an active low pass on the woofer. Start with 60Hz low pass, first order - and that will get you close. The inductor has a DC resistance of about 0.6 ohms, so you might try two 1.2 ohm resistors in parallel connected between the amp and the woofer. Use 10 watt or better. This series resistance changes the Q of the woofer, slightly bumping up the bottom end. That will bring the active closer to the sound of the passive crossover. It's cheap and easy to try.
The big fat inductor also changes the way that the woofer and amplifier interact, which you will not get with an active crossover. Part of what makes the Manzanita work is that big iron core inductor. But if you can't get one, or just want to try active, then the info above should help.
The big 20mH inductor in series with the woofer forms a 1st order low pass at about 60Hz. If you can't get the inductors, you can try an active low pass on the woofer. Start with 60Hz low pass, first order - and that will get you close. The inductor has a DC resistance of about 0.6 ohms, so you might try two 1.2 ohm resistors in parallel connected between the amp and the woofer. Use 10 watt or better. This series resistance changes the Q of the woofer, slightly bumping up the bottom end. That will bring the active closer to the sound of the passive crossover. It's cheap and easy to try.
The big fat inductor also changes the way that the woofer and amplifier interact, which you will not get with an active crossover. Part of what makes the Manzanita work is that big iron core inductor. But if you can't get one, or just want to try active, then the info above should help.