My Hi-VI B3S Bipole Center Channel Project

[owdi]

First, thanks to diyaudio.com and zaphaudio.com for the resources I needed to get this project off the ground.

I've been looking for an inexpensive project to cut my teeth on, and after reading the comparison of 10 wide range drivers at Zaph Audio I decided to try a center channel using the Hi-Vi B3S. My goals are:

- Entire speaker costs no more than $50
- 8 ohm amplifier friendly
- cover 150hz - 18khz +-3db
- 85db w/ 105db peaks at listening position 8 ft. from TV

To avoid using a baffle step compensation circuit I decided to use two drivers. The BSC would have pushed efficiency far too low, and the price of an additional B3S was well within budget.

I decided to arrange them in a bipole configuration rather than both drivers facing forward for two reasons. First, since the primary purpose of a center channel is to recreate the human voice, a single speaker seems like the best solution. Second, the bipole configuration should minimize enclosure vibration.

The front driver will have a notch filter centered at 8khz to flatten a nasty peak, caused by the metal cone of the B3S ringing. The back driver will have a some kind of a low pass filter, probably a simple first order. I will use a resistor to pad down the back speaker in case there is a midbass bump.

Parts list:
2x HiVi B3S ($19.14)
1x 0.8 mH air core inductor ($2.75)
1x 0.1 mH air core inductor ($1.58)
1x 4.3 uF capacitor ($1.86)
1x 8.0 ohm 20 watt resistor ($0.69)
1x 30 ohm 10 watt resistor ($1.25) *non-inductive
1x fancy binding posts ($6.88)

I priced everything out at both partsexpress and madisound, they were very close to each other. I chose partsexpress because they could give me a shipping quote without any hassle. Total price was about $45. You can bring that down below $40 by using standard binding posts instead of fancy ones.

Now to the testing....

(note to self, add pictures)

Dan

[owdi]

The speakers have been waiting patiently for two weeks now while I found the time to figure out how to use Speaker Workshop. My first impedence measurements don't look great, but they are good enough to see that I need to break them in before taking further measurements.



The manufacturer quoted fs is 80hz... mine are nearly half an octave above that!

I will save you the horror of my impedence jig :-), I built it by hacking up an old set of headphones and $5 in ratshack parts.

I'm breaking the speakers in by repeatedly playing a 10 second 80-120hz sweep, with left and right channels out of phase. I can't hear the bass, but I can sure hear the harmonic distortion. I'll do this for about two days, after which I hope fs is below 100hz.

Dan

[edjosh23]

I built some bipole B3S's for my girlfriend. They were originally monopole, but were too ineffecient for her amp, which was actually made for 4ohm speakers. I went back added another woofer on the back, although the box may be a little small, the sound is fuller than ever and is much better.

Good Luck,

Josh

[owdi]

edjosh23 - did you take any measurements? Did you use a filter?

After one day of break-in, the fs of both speakers dropped by 5hz. The enclosure is cut, and half glued together. I rounded the back of the speaker cutout to promote airflow, but the fit is so tight I need to cut more.

Some progress pics..







Dan

[westend]

The B3s's are a nice looking speaker, too. Good luck with the build. I was looking at these, also.

[pasomark]

Hey looks like it's becoming a great looking project. I'm building Krutke's sealed speaker right now. If it goes (sounds) good then might do a center channel as well with the HiVis. Let us know how it sounds to you, room size, preferred listening volume...
Just a basic question: how are you connecting the male connects of the speaker--are you using female connects or just soldering?
Thanks for your expertise
Mark

[owdi]

Originally posted by pasomark
Hey looks like it's becoming a great looking project. I'm building Krutke's sealed speaker right now. If it goes (sounds) good then might do a center channel as well with the HiVis. Let us know how it sounds to you, room size, preferred listening volume...
Just a basic question: how are you connecting the male connects of the speaker--are you using female connects or just soldering?
Thanks for your expertise
Mark

Running full range, near field, and open baffle, they were great with simple music. To my ears, acoustic guitar and the human voice sounded outstanding. Once the music became more complicated they started sounding muddy.

... more later.. just completed first acoustic measurements and they came out horrible... I need a better mic and sound card

Dan

[owdi]

After watching a few movies using this center I've decided to scratch this project. While clarity is great, this driver just doesn't have the output for HT use.

The new plan is use these drivers to build a pair of multimedia speakers for work, where high output and bass are not a priority. I've already purchased the parts for another notch filter and BSC circuit, now I just need to duplicate this enclosure find an amplifier.

Dan

[pasomark]

Owdi--do you think the HiVi have sufficient output for surround back speakers in a HT set up? Just asking b/c its been suggested 5 of these speakers would make a decent HT setup but you clearly aren't impressed with the output ...at least for the center (and then assuming the front) speaker.
Also, what size connection do you use on the speaker wire to the HiVi?
Mark

[owdi]

Originally posted by pasomark
Owdi--do you think the HiVi have sufficient output for surround back speakers in a HT set up? Just asking b/c its been suggested 5 of these speakers would make a decent HT setup but you clearly aren't impressed with the output ...at least for the center (and then assuming the front) speaker.
Also, what size connection do you use on the speaker wire to the HiVi?
Mark

I agree that 5 of these could make a decent HT setup, so long as you're not looking for high output.

My speaker wire was thin, 5 feet of 24 awg to each speaker, and the speakers were wired in series w/ no filter. My amplifier is capable of 50wrms at 16ohms, so lack of power wasn't the problem.

I have to admit that my decision to stop this project was influenced by wanting to try these as multimedia speakers. My computer speakers here at work are junk.

Dan