Splitting crossover

[Kineticmac]

Hey guys,


First of all I want to thank everyone for all the effort put into this forum. Everytime I google anything about audio I end up here. Audio is way more complex than i first thought possible.Also too many opinions which makes it hard for a novice to make choices.
I'm still learning so please bare with me.
I want to build a budget 5.2 surround system,doubling as a stereo system,using a Denon AVR-X4500H:
DENON US
I plan on build the left and right front speakers using Joe D'Appolito's Thor Design
http://www.seas.no/images/stories/diykits/thor/audioXpress_Thor_Review.pdf
The center speaker will be a modified version of this (same volume and line lenght).
As the surround speakers need to be as small as possible(wife factor), i was thinking of using 2 full range fostex drivers in a closed enclosure:
https://www.fostexinternational.com/docs/speaker_components/pdf/fe108ez.pdf
The 2 Dayton DCS305-4 subwoofers will be mono, power by a hypex plate amp FusionAMp FA501 also a transmission line:
https://www.hypex.nl/documenten/download/1711
Crossover for the Thors
http://www.seas.no/images/stories/diykits/pdfdataheet/filter_thor_odin.pdf
The reciever is too weak for the front 3 speakers so i was thinking of bi-amping since bridging seems impossible. The crossover for the thors is designed for 2 woofers in parallel. I only have a very basic understanding in electronics.
Here are my questions:


1. Am i correct in assuming that in order to seperate the woofers that you need to build 2 crossovers with L1 half the inductance and half the wire size and also double the resistance R1? What are the right values?
2. The schematic does not mention the dissipation power of the resistors. Which ones should i choose?
3. Is the Fostex FE108EZ the right choice for the closed surrounds? (Qts a bit low) Should i use other ones?
4. The rms power of the fostex driver is much lower then the reciever power output. Do i need put put something in between so that they don't blow up when somebody sets the amp too high? If so what?


Any advice is of course welcome.

 

[indianajo]

I want to build a budget 5.2 surround system,doubling as a stereo system,using a Denon AVR-X4500H:
DENON US
I plan on build the left and right front speakers using Joe D'Appolito's Thor Design
http://www.seas.no/images/stories/diykits/thor/audioXpress_Thor_Review.pdf
The center speaker will be a modified version of this (same volume and line lenght).
As the surround speakers need to be as small as possible(wife factor), i was thinking of using 2 full range fostex drivers in a closed enclosure:
https://www.fostexinternational.com/docs/speaker_components/pdf/fe108ez.pdf
The 2 Dayton DCS305-4 subwoofers will be mono, power by a hypex plate amp FusionAMp FA501 also a transmission line:
https://www.hypex.nl/documenten/download/1711
Crossover for the Thors
http://www.seas.no/images/stories/diykits/pdfdataheet/filter_thor_odin.pdf
The reciever is too weak for the front 3 speakers so i was thinking of bi-amping since bridging seems impossible. The crossover for the thors is designed for 2 woofers in parallel. I only have a very basic understanding in electronics.
Here are my questions:


1. Am i correct in assuming that in order to seperate the woofers that you need to build 2 crossovers with L1 half the inductance and half the wire size and also double the resistance R1? What are the right values?

4. The rms power of the fostex driver is much lower then the reciever power output. Do i need put put something in between so that they don't blow up when somebody sets the amp too high? If so what?

Sub woofers don't need separation. The stereo image on LP's does not separate the bass much between left & right. The wavelength of 60 hz lower is bigger than your room, usually, so reflections etc mess up the location of the bass as much as the program source. If you parallel wire your sub woofers you've halved the impedance, so make sure the amp channel is capable of that. Really one subwoofer should be adequate IMHO.
Bands put a limiter between the mixer board and the amp driving sensitive speakers to avoid blowing a speaker up. Since you're using a receiver, the program source (FM radio) and amp have no separation to insert the limiter.
I suggest you could clamp your low wattage speaker with a parallel NTC high power resistor, say 4 ohms cold 1 ohm hot, series a 2 ohm high wattage resistor. (bigger wattage than the receiver channel will put out.) The NTCR will heat up and suck the power away from the driver. A better solution would be to buy a higher power driver. Another better solution is use the receiver as the line level source only, and use a separate amp to power the low wattage driver, one that won't blow it up. An amp with lower power rails, say 24 v or 18v single or +-12 to +-9 v. A chip amp.
That thor plan is for a 400 W capable speaker, so in the crossover you had better use 200W + capable resistors, unless you calculate the actual current as lower. I'm not going to calculate it. P=(I^2)* R. Thrashing through a network to calculate the currents is a hour or more process by hand, but there should be a computer program out there that does that these days. Spice of course. Spice runs on computers much more up to date than mine, and I am not into the constant updating required by windows & apple.
I don't build speakers so I'll leave the rest up to someone else. Best of luck in your endeavor.

 

[Kineticmac]

Sub woofers don't need separation. The stereo image on LP's does not separate the bass much between left & right. The wavelength of 60 hz lower is bigger than your room, usually, so reflections etc mess up the location of the bass as much as the program source. If you parallel wire your sub woofers you've halved the impedance, so make sure the amp channel is capable of that. Really one subwoofer should be adequate IMHO.
Bands put a limiter between the mixer board and the amp driving sensitive speakers to avoid blowing a speaker up. Since you're using a receiver, the program source (FM radio) and amp have no separation to insert the limiter.
I suggest you could clamp your low wattage speaker with a parallel NTC high power resistor, say 4 ohms cold 1 ohm hot, series a 2 ohm high wattage resistor. (bigger wattage than the receiver channel will put out.) The NTCR will heat up and suck the power away from the driver. A better solution would be to buy a higher power driver. Another better solution is use the receiver as the line level source only, and use a separate amp to power the low wattage driver, one that won't blow it up. An amp with lower power rails, say 24 v or 18v single or +-12 to +-9 v. A chip amp.
That thor plan is for a 400 W capable speaker, so in the crossover you had better use 200W + capable resistors, unless you calculate the actual current as lower. I'm not going to calculate it. P=(I^2)* R. Thrashing through a network to calculate the currents is a hour or more process by hand, but there should be a computer program out there that does that these days. Spice of course. Spice runs on computers much more up to date than mine, and I am not into the constant updating required by windows & apple.
I don't build speakers so I'll leave the rest up to someone else. Best of luck in your endeavor.

Hey Indianajo. Thanks for the reply but I think you misunderstood. The reason i want to split the woofers (not subwoofers) in the front speakers, is that the AVR reciever does not have enough output power to adequately drive the woofers. It's only around 100W all channels driven while the speakers are 2x100W each.
To solve this problem I tought of using 2 channels for each woofer(bi-amp).

So the speakers change from 200W 4ohm to 2x100W 8ohm.
That's why the low pass filter and probably the RLC filter needs to change but I'm not sure how.

I hope this explains it better.


Your probably right about the Fostex full range driver. I wanted to keep the speakers as small as possible but I guess going slightly bigger saves me a lot of hassle. The bigger one is 80W which should be ok i think.

 

[indianajo]

If your front channel crossover point is 800 hz or above, you can buy a prebuilt crossover from parts-express.com. One each for left and right front. You buy those by specing crossover point, speaker impedance, wattage max.
Then hook the high output up to your high drivers, hook the low output up to an L-pad. That is a resistor divider, to drop the low side from 30? v max of the receiver, to 1.6 v max of the input to an amplifier. Like have a 1800 ohm resistor series a 100 ohm resistor, crossover output top of 1800 to bottom of 100, input of woofer amp top of 100 ohm to bottom of 100 ohm. Pick resistor range depending on wattage of receiver channel W/Z(speaker impedance wattage is rated at)=V^2.
Then hook that 1.6 v signal to the input of an amplifier you driver the woofer with. That is for 54 hz to 800? (or 2000?) hz.
Again, in a room of a house the subwoofer can be single. 5 channel movies (dvd) have an earthquake on the left side back, and in a 120' wide x 200' deep movie theater that sounds comes from the left rear. But in a home the low freq sound might come from anywhere due to the folding of the waveform and reflections from the walls.