3-way OB

[Twisted85]

I'm still finishing my 2-way MTM project but I'm aldready planning my next project, which would be my first 3-way system.

I've been thinking of a using a open baffle midrange unit in this project. I've never made any ob speakers so I need some help and advices on this one.

I have something like this in my mind:

http://koti.mbnet.fi/twisted-/3way/model.gif

The front baffle would be tilted to compansate the acoustic center differences. I would use a 8" woofer probably in a reflex box. The midrange would be in an open baffle, the lighter gray in the picture is meant to be just a possible side brace (like a small U-frame).

At this moment actual issues would be to choose drivers, think appropriate placements for them in the baffle and chooce approximate xo point.

The woofer and tweeter are the easier ones, the midrange is more difficult. As a woofer I've been thinking maybe Peerless 830868 or 830884. I haven't had much thought with the tweeter, but ScanSpeak D2010 has been in my mind as an option.

I'd like to cross the midrange pretty high, somewhere around 3-5Khz, and midrange/woofer xo point would be around 400-500Hz.

Here's a simulation of Seas MCA15RCY in a baffle described above (without the side braces) as a possible midrange driver:

http://koti.mbnet.fi/twisted-/3way/response.gif

The Qts value is quite low, but if the xo point is around 400-500Hz this wouldn't be a problem, right?

Now questions about the OB that is unclear to me: How does it affect the driver sensitivity? Is the point where the frequency response starts to go down the same point where baffle step happens in a sealed box? above this point, is the sensitivity with OB and sealed box driver the same? If a driver would be set off axis (like in my scetch above) it would cause lobing to other side, is the effect similar with ob driver setup?
Why I've been thinking to cross the woofer/midrange around 400-500Hz is that this is the point where the midrange driver response starts to go down because of the OB. Is this a good idea?

Now about the midrange driver. Above I said that I'd like to cross the midrange/tweeter pretty high. I like the idea that one driver covers most of the midrange. The thing I've been thinking is the off axis response. Now let's take this driver as an example: Seas MCA15RCY. Let's say I would cross this driver at 4Khz. The on axis response is smooth, but the off axis responses are at lower level at this frequency. How does this affect in a open baffle design? Should I choose a driver and xo point where the response is smooth even measured from an angle (in an infinite baffle) or does this make a difference in a ob? If I would use the Seas driver mentioned, would it be more wise to cross it where the off axis is more at the same level, for example 3Khz?

All help, ideas and thoughts are appreciated.

[ttan98]

Last time I put my OB design here I got zero response.

If you get unsatisfactory response try this site there are many helpful people there.

http://www.audiocircle.com/circles/index.php?board=90.0

cheers.

[DougL]

I'd like to cross the mid range pretty high, somewhere around 3-5Khz, and mid range/woofer xo point would be around 400-500Hz.

I have a 3 way OB using am MCA15RCY. I cross it over on the low end at 320 Hz LR4, and currently have the high pass at 3000 LR4.Since I have a DCX2496, I have tried a wide range of values.
I really couldn't tell much difference crossing between 2 k and 4 k to a NEO3. My mid to woofer xo point was set by the desire to not excite the 2.1k resonance peak on my RS270 woofers, balanced with higher excursion at a low XO.
The size of your mid range baffle will also affect this.
I really think this driver works for an OB mid range, as long as you have a big enough baffle for your chosen XO point.

Doug

[Twisted85]

Originally posted by ttan98
Last time I put my OB design here I got zero response.

If you get unsatisfactory response try this site there are many helpful people there.

http://www.audiocircle.com/circles/index.php?board=90.0

cheers.

Thanks. I made a post to that site as well and waiting for replys.

If someone is willing to help I probably made my questions more clear at this another post so you could read this as well:

http://www.audiocircle.com/circles/i...?topic=48622.0

[DougL]

Now questions about the OB that is unclear to me: How does it affect the driver sensitivity? Is the point where the frequency response starts to go down the same point where baffle step happens in a sealed box? above this point, is the sensitivity with OB and sealed box driver the same? If a driver would be set off axis (like in my scetch above) it would cause lobing to other side, is the effect similar with ob driver setup?

The Short answer is No, an OB isn't as simple as assuming the sealed box model works, and at about the same point.

An OB affects driver sensitivity for about 4 octaves above "F Equal"
there will be a peak of around 6 db about 2 octaves above "F Equal", transitioning back to infinite baffle sensitivity above that.

Below "F Equal", the driver has a roll off of 6 db per octave.
Below Fs, an additional 12 DB per octave roll off occurs.
This assumes a Qts of .7 Drivers of lower Q will have additional roll off as they approach Fs.

There are several sites that explain the basics, and several inexpensive tools that predict LF dipole behavior. MJK and JohnK come to mind.

Now about the midrange driver. Above I said that I'd like to cross the midrange/tweeter pretty high. I like the idea that one driver covers most of the midrange. The thing I've been thinking is the off axis response. Now let's take this driver as an example: Seas MCA15RCY. Let's say I would cross this driver at 4Khz. The on axis response is smooth, but the off axis responses are at lower level at this frequency. How does this affect in a open baffle design? Should I choose a driver and xo point where the response is smooth even measured from an angle (in an infinite baffle) or does this make a difference in a ob? If I would use the Seas driver mentioned, would it be more wise to cross it where the off axis is more at the same level, for example 3Khz?

Its a trade-off, just like other designs And like other designs, your polar pattern will affect your power response. I personally can't hear much difference in my current design. However, I have drivers of a similar size so the affect may be less pronounced. As always, YMMV.

Doug

[navin]

Originally posted by Twisted85
I've been thinking of a using a open baffle midrange unit in this project. I've never made any ob speakers so I need some help and advices on this one...All help, ideas and thoughts are appreciated. [/B]

One of the advantages of OB is the dipole bass that a true fullrange OB provides. The dipole bass has a lot less BOOM than traditional sealed and ported boxes. So if you considering OB it might be worth while to consider OB for the bass section too.

For sometime I too have been contempalting building a speaker that will replace my circa 1994 Audio Concepts SUBs + Scanpeak MTM combo. It sems most likely that I'll end up making a 3 way based around a superb wide range with helper drivers to cover the extremes.

Since the wide range is the fundamental driver it is this driver that is most important to choose. Common choices are Jordan (Jx92), Fostex (16x and 20x), the Visaton B200, Supravox 165 and Veravox 7x drivers. One could also consider co-ax drivers like the Tannoy, Ciare, or Hawthorne.

One option I am toying with is 2 10" Hawthorne Augie drivers mated to either a Visaton B200 + tweeter option or a Hawthorne 10" coax.

The music I listen to encompasses classical, jazz, blues and a lot of the popular music from the 60s and 70s (rock, pop, metal, and punk). I enjoy the coherrence of fullranges but dont want to completely sacrifice SPL or the ability to occasinally play Led Zepp at "live levels". I would love to know more from the Gurus here.

[SamL]

Originally posted by Twisted85

I would use a 8" woofer probably in a reflex box. The midrange would be in an open baffle, the lighter gray in the picture is meant to be just a possible side brace (like a small U-frame).

The single open baffle mid SPL will not be able to match the 8" woofer in reflex box. Unless you use a very sensitive mid or a low sensitivity woofer. Alternatively You can use 2 mid to increase sensitivity or you can reduce the sensitivity of the woofer but this will require an active system.

rabbitz who is active in this forum and audiocircle have build something similar using SS9700, 18W/8531G00 in open baffle and Vifa M21WO-39-08 in ported box. He uses sub amp to drive the Vifa. Unfortunately his site is no longer there.
AndyG who is also active in this forum and audiocicle have build something similar call Blackwood. His post about it.
http://www.audiocircle.com/circles/i...?topic=38016.0

Have fun

[moray james]

http://www.t.kth.se/andzak54/speakersIntro.htm

[moray james]

http://www.digitalakuten.com/audio/o...ndorphine.html

http://www.lampizator.eu/SPEAKERS/Loudspeakers.html

[DougL]

The single open baffle mid SPL will not be able to match the 8" woofer in reflex box.

SamL, can you elaborate on this statement? The Seas MCA15RCY that is referenced has 90 db sensitivity, which should be sufficient to match an 8" woofer in any enclosure.

Doug