Slanting open baffles for Full rangers...

Hi everyone,

I was just studying some open baffle design. And I came across this one for Visaton..

NoBox BB

I realised after looking at the plans in detail, the box is slanting, which also implies the drivers are slanting. I was wondering what benefit would that have.

Then a few thoughts came to mine. I rmemebered that one time as I was trying my full range cast frame Audio Nirvana 15, it sounded nicer when it was a bit slanted (still sitting on a chair without a box/baffle). It sounded smoother and less shouty. A point to note, the speakers are not broken in yet.

I was thinking of two possibilities why it is that way.

1) Being slightly slanted, you would be listening to the off center frequency response which would mean a bit of beaming at the upper frequency and hence a lower response on the highs. this sort of serve as a baffle step filter in some way and reducing the highs... I suppose that is why it sounds less shouty. Looking at the B-200 datasheet, it can be seen that at about 10-20 degrees, it is a 5dB cut, which would be just nice if you were trying to implement a baffle step filter...

http://www.visaton.com/en/chassis_zubehoer/breitband/b200_6.html


2) If the speakers are slightly slanted, the response when you are directly in front of the speakers are actually the ones for 5 degree off axis. When you are standing in front in between the two speakers, the off axis response is probably around 30 degrees. The difference in frequency response between 5 degrees and 30 degrees is less and hence causes less variation to the frequency response and creates a more even frequency response when one is moving around the room.

Or it could be just purely for aesthetic purpose...

Anyway, would love to hear your thoughts about this...

Oon
 
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It is not about listening off axis, but precisely on axis. Driver height of the B200 above floor is 80 cm. Younger people in Germany (or Western Europa) tend to have their ears at about 1 m height when seated. So Visaton had to tilt the driver to make people listen on-axis.

If you look at these measurements of the B200, you find the 15° curve not worse than 0°. But 30° has really lost many high frequencies above 5 kHz:

http://hifi-selbstbau.de/images/stories/chassis/visaton_b200/B200_1A_SPL.png

If you keep in mind, that many people in this country have their ears at 1,6 - 1,7 m when standing, you need to slant the baffle to allow for good listening in that position too.
 
Hi Rudolf,

Agreed on that part on aligning it on axis when the person is standing but when the person is sitting, At ear height of 1m. He would still be listening off axis but maybe not so much.... unless of course he is only a metre away or something like that. But I could agree that putting it at a slant means the person is always within +/- 15 degrees of the axis whether he is standing or sitting and thereby creating a more stable listening environment and improving the sweet spot.

However looking at the freq response graph. I would think that listening at a bit under 30 degrees or so of axis will give the flatest freq response. Which is what the person will hear when he is sitting in the center a few metres away... so in this case and I suppose in many other 8 inch drivers baffle step compensation is actually not necessary due to natural off axis roll off?

Oon
 
Hi Rudolf,

After some further thoughts on this. I think you are right. It will be exactly on axis at about 2 to 3 metres away in front of the speaker. There seems to be a baffle compensation filter built into the crossover, hence no real need to listen to the speaker off axis to get a flat freq response.

On a more generic note if one were to listen to the speakers off axis, for example the speakers facing directly forward would it be necessary to incorporate a baffle step filter at all since the center position is actually off axis.

Oon
 
There seems to be a baffle compensation filter built into the crossover, hence no real need to listen to the speaker off axis to get a flat freq response.
Hi Oon,
that's not a baffle compensation, but compensating the step in the driver response. You can see the different influences of baffle and crossover in a Boxsim simulation:

NoBox BB chassis.gif

On a more generic note if one were to listen to the speakers off axis, for example the speakers facing directly forward would it be necessary to incorporate a baffle step filter at all since the center position is actually off axis.
If you look at the NoBox' on-axis response on the Visaton website, it is gently rising from 300 Hz up. But the NoBox must be toed-in to give a (somewhat) linear response at the listening position in a standard stereo triangle.

Personally I would never use the B200 in a dipole application.

Rudolf
 
Hi Rudolf,

Thanks for your response. Since we are at this topic, might ask for your opinion for this speaker build.

http://www.diyaudio.com/forums/full-range/230931-15-audio-nirvana-open-baffle-request-proposal.html

My objective would be to build a audio nirvana 15 inch. It will be suplemented by a ribbon tweeter at the top and a 15" woofer at the bottom.

The baffle is a U frame with slanting sides, very similar to NoBox. It will be a bit taller at about 5 feet. The audio nirvana 15" is located at ear level. I am thinking of tilting speaker to reduce the rising frequency response, so I don't have to install a filter to compensate for it. The idea is the frequency response should be as even as possibe on axis and off axis. The audio nirvana 15" is only for mid to higher mid only, the really high end (probably 10kHz) onwards will be from the ribbon tweeter.

The woofer below will be biamped.

Would like to hear your opinions and advice on this build...:D

Oon
 
Sorry Oon,

I can't help you much with this project. I once looked into an AN OB project with a smaller driver:
Where next on my Open Baffle adventure, Advice please.

Somewhere on the way Danny Ritchie joined the discussion and I left the field, since Danny obviously has a lot of first hand experience with those drivers.
I haven't seen measurements of the AN 15, but some of the AN 10:

Audio Nirvana AN10 Super

That driver has the same problems as the B200 and I don't see an OB application for that driver (or its bigger brother) really productive.

Rudolf
 
With both drivers you can't achieve a good balance between on-axis response and power response IMHO. If you EQ the B200 for 30°, you will have a nice power response, but far to much at 0-15°. If you EQ for 0-15°, the off-axis response will be dull.
The AN doesn't even give you the chance to EQ for a defined axis because everything off-axis is a lobing chaos.

The sharp step from 600-2 kHz can't be EQed fully with a passive crossover. There will always be a certain "presence" with those drivers, which makes them attractive at first listening, but can lead to listening fatigue when recordings are already "present" by themselves.

I would try to get the best balance at the listening position by toe-in of the baffles, not by EQ. Slanting the baffles will help too.

Rudolf
 
Phase plugs strongly effect this behaviour of the stock B200.

VISATON 10.05.2006, 10:00
Natürlich haben wir beim B 200 auch mal ein Phaseplug ausprobiert. Es gab keine Verbesserung, weil die Dustcap als abstrahlende Kalotte wirkt. Ich habe sogar schon mal die Seidenkalotte eines Hochtöners auf die Schwingspule geklebt. Besser war das auch nicht.
My translation of this original comment from the designer of the B 200:
"Of course we have tested the B 200 with a phase plug too. There was no improvement, because the dust cap works as a radiating dome. At one time we even glued the silk dome of a tweeter on the voice coil. It wasn't better than the original."

I googled for B200 and phase plug, but couldn't find any measurements showing the different behaviour of the phase-plugged B200.
Do I have to resort to personal comments only?

Rudolf