Dipole line-array idea

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#22
Actually all those B&G notch filters are centred at 5 kHz, width and depth beeing regulated by the resistances. The formula to use calculating notch frequency is: f = 5033/SQR(CxL) where C is measured in microfarad and L in millihenry.

/Erling
 
#26
I'm having an early summer holiday, so there's not going to happen much more until july the earliest.
Click to expand...

Hi StigErik

Any progress with this project? looking at the RD75 driver it seems that crossover and equalization network will not be as complex as your other project, which gives me a 'good feeling' and could allow for some analog filtering.

Erik
 
#27
Yes - my hope is to realize this speaker using a passive XO only, if possible. If not, then I'll add analog EQ. This will be an all-analog solution. 🙂

No progress yet - there's too many other things that needs to be done during the summer season here.
 
#29
And here's some progress! Build one speaker to check out the mechanical side of things. I was a bit concerned if the upper woofer could handle the weight of the other woofers, and if the rubber tarp straps could do it. Well, with double straps it looks good.

They are BIG! 🙂 More than 2 meter tall, 53 cm wide and 25 cm deep.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.
 
#32
They are up and running now! Have set a very very simple filter in my PC XO, adjusted by ear only. Will test it out with active filter first, and then build a passive filter later on.

No problem getting a good overall balance without any EQ apart from woofer dipole EQ. I can hear that the tweeter will need some EQ here and there, measurements will tell where and how much. No problem getting enough bass either, it works well far down into the 30 Hz range.

I think it should be possible to build a passive XO for this, and then add some bass boost with a simple active EQ before the power amp.

The woofers are connected four and four in parallell, and those two series are connected in series. Woofer impedance is approx 3 ohms, which is acceptable. Currently I'm using a 120W (into 4 ohms) amplifier, which is sufficient. 🙂
 
#33
I've measured things here now. Settled for XO at 200 Hz, as the big ribbon is flat to almost 100 Hz, and this without any baffle at all! There's a big broad peak at 5 kHz (as stated fom B&G, so no surprise), but otherwise response is very much like a pancake (flat...). The woofers are no surprise either.
 
#34
Have listened to them a bit now. Whow.... they really do sound great! I have a feeling that these are going to replace current dipoles I have!

One problem though -one of the ribbons is buzzing quite loud, starting at moderate levels. Its coming from a small area only, but very very annoying. I've sendt a mail to Parts Express (where I bought them) about this, maybe its possible to file a warranty claim or something? Only problem is that shipping them back to the US is gonna cost a fortune..... aaaargghhh :redhot:
 
#35
Looks very nice 🙂

Great to hear that they work with some filtering that can be easily accomplished in the analog domain. Furthermore, the utter simplicity in building makes it very attractive for me, as I have no quality tools for woodworking. Less appealing is the cost of the drivers, but maybe I can get away with a set of smaller B&G drivers and some WS25e woofers from Visaton (which are used in my current speakers)

Erik
 
#36
Very cool Stig!

How is the vertical dispersion on the B&G compared to your "old" hanging dipole with Mundorff tweeter?

Also: with such a low XO - could hanging 12" or 15" woofers be feasible (keeping uniform horisontal dispersion)? (e.g. 4 x AE Dipole15 per side?)
 
#37
The RD75 is a line-source down into a few hundred Hz, so the output looks like a plane wave. That means that the sound is the same in the entire area in front of the driver, from the floor and almost 2 meter above the floor. There is no loss of treble when I stand up from the listeing chair like with the Mundorf tweeter. Off-axis vertically (above 2 meters from the floor), there is almost no sound at all. It behaves very different from the point-source dipoles I have with the Mundorf.

I XO at 400 Hz now, the RD75 sounds better without being forced to play mid-bass. 400 Hz is possible with 12" woofers for sure, but its a bit on the edge for 15" I think.
 
#38
I've done a little measuring here. What was very obvious is that the line-source dipoles results in much more room feedback (reflections and "reverb"). From the ETC's I did in my room, the early reflections and the later decay was at least 10 dB louder than with my "old" dipoles. Surprisingly, the old dipoles was better off-axis as well, with less difference in frequency response between anechoic measurement and measurement including room reflections.

I also happened to voice the line-source a bit brigher than the "old" dipoles, that of course affected my subjective evaluation to begin with.

A few subjective opinions on the strengths of these versus the "old" dipoles:

The line-source dipoles:
Very smooth balance
Easy to listen to, little chance of listening fatigue, but a little "flat", not as involving maybe
Very big stereo image with lots of "air"

The "old" ones:
Dynamics are much better
Better "black background" in the stereo image
Better stereo image precision

That being said, the difference between the two is fairly small.
 
#40
Yes, I did try the H-frames with them as well, crossing over at 100 and 400 Hz. I feel that it might a good idea to cross over the ribbon even higher than 400 Hz, but I didnt try that. The thing is that the midrange dynamics is a bit "flat", good cone drivers should do it better I think.

The project will be on hold for a while now untill I get a fix for the buzzing ribbon. Hopefully B&G will accept a warranty claim.
 
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