[Bloodstain]

Hi,

I started a thread at diyaudio.com and someone told that I could get more help at this dedicated OB forum.

I'm planning my first 3-way design and I've been thinking to use the midrange driver in a open baffle. I made the design by myself but unexpectedly someone at this forum had made a 3-way very close to what I was planning for.

Referring to this:

http://www.audiocircle.com/index.php?topic=44431.0

This is what I'm going for:

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

The dimensions aren't final, but something to begin with. The front baffle would be tilted back to get the acoustic centers more aligned, the midrange driver is off the center for better response and the tweeter is on the same line with the midrange. The lighter grey in the pic are only meant to be side braces.
I've been planning to probably use the ScanSpeak D2010 as a tweeter, but I'm not sure what midrange and woofer to use yet. Probably 8" woofer from Peerless or Seas in a reflex box. As for the midrange, I've been thinking of using the Seas MCA15RCY. (at this point I don't really have any alternatives in my mind)

But as I have never made any OB speakers, there are some things I'd like to ask.

First thing I'd like to discuss is the off axis responses. As I've understood in a typical 2-way sealed speaker, the off axis response should be smooth at the XO point even when measured from 45-60 degrees angle. If the XO point is very high, the woofer's response begins to fall down at 45 angle and there will be a drop in the frequency response before the tweeter response. This isn't supposed to be a good thing.
Now back to open baffle designs. If the midrange is in a open baffle, the off axis responses are at lover level as there is more directivity. How evenly this directivity hapens in the midrange (~500-3khz)? Now what happens to tonal balance if the midrange works in a open baffle, it has more directivity than the tweeter and when measured from 45 angle the tweeter level is more higher than midrange?

Other thing I'm thinking at this point is the sensitivity. Does this change in a open baffle system? My plan is to cross the woofer/midrange where the midrange response begins to drop.

This is what I simulated with MCA15RCY:

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

So I would use xo point around 400-500Hz.
Now If I would use a sealed box for the midrange, the baffle step would affect in this same point in a 40cm baffle. Using the same xo point I could use 90dB sensitivity woofer, and match this with a midrange with sensitivity 6dB lover or anything above it, as the baffle adds 6dB to the midrange driver response. Now is this the same case with this open baffle design I'm planning?

Any help, comments and advices are appreciated!

[grantnsw]

Hi,
I hope its ok to do this, but this thread: http://www.pinkfishmedia.net/forum/showthread.php?t=8135&page=3
uses the MCA15rcy in OB. I just thought it might be of interest to you.
grant

[zipidachimp]

how about this one:

http://www.lampizator.eu/SPEAKERS/PROJECTS/P19/P19%20alnico%20open%20baffle.html

ran across this site awhile back. can't vouch for accuracy. looks like a neat 3-way though.
cheers!

[Rudolf]

I'm planning my first 3-way design and I've been thinking to use the midrange driver in a open baffle. I made the design by myself but unexpectedly someone at this forum had made a 3-way very close to what I was planning for.

Referring to this:

http://www.audiocircle.com/index.php?topic=44431.0

This is what I'm going for:

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

Any help, comments and advices are appreciated!

I really don´t understand why somebody would want to combine a 360° monopole radiation pattern in the bass with a 360° dipole pattern in the midrange and a 180° monopole pattern for the tweeter.
You simply can´t get a flat on axis response AND a comparable in-room response this way. Regardless how you try. Grant, at least you should follow "zipidachimp"s proposal to dipolize the bass area too.

[johnk...]

I really don´t understand why somebody would want to combine a 360° monopole radiation pattern in the bass with a 360° dipole pattern in the midrange and a 180° monopole pattern for the tweeter.
You simply can´t get a flat on axis response AND a comparable in-room response this way. Regardless how you try. Grant, at least you should follow "zipidachimp"s proposal to dipolize the bass area too.

There are arguments on both sides for monople woofers combined with dipole mids. It depends on mid/woofer crossover point, room size, woofer cut off frequency and other design objectives such as power matching between mids and woofers.

[JoshK]

I agree with Rudolf & JohnK.  However, I side with Rudolf and think you really should try to go dipole bass unless your current situation and/or design constraints rule it out for the reasons he stated.  I've heard it argued that the region from 80hz up to ~300hz is probably where dipole radiation does the most good (arguable). If that is the case, then dipole bass should be considered heavily. 

Using a monopole sub below your lowest room mode also makes sense to ease the demands on the dipole woofers. 

[mcgsxr]

Sounds like good advice, though in practice, is it not hard to split the bass two ways?

Sounds like a 2 way Xover from mains to dipole woofers, and then again onto a sealed sub?

I use dipole bass, and use a 2 way Xover from mains to sub, and EQ the sub to sound as though the lower bass is represented.  I have no measurement tools, so I am tuning by ear etc.

[richidoo]

Bass is easiest to crossover, because ear is less sensitive to tone down there, and sub amps phase can be adjusted to match. I like the idea of putting in a sub below lowest mode, then the monopole radiation will not excite any trouble.

[Rudolf]

There are arguments on both sides for monople woofers combined with dipole mids. It depends on mid/woofer crossover point, room size, woofer cut off frequency and other design objectives such as power matching between mids and woofers.

My main concern was about changing the radiation pattern TWICE. And after reading your http://www.musicanddesign.com/PowerMatching.html considerations a couple of times I find crossing from dipole woofers to monopole mids (above the baffle step) even more attractive than otherwise. I very much think along the line of JoshK.

[jeffreybehr]

Well, I'm not sure I'm following the this-pole-bass and the that-pole-midrange and the next-pole-treble arguements, but I know I sure do like the sound of open-baffle (even if not technically dipole) bass and OB midrange from my systems.


The rear of the bass/MR drivers, eight Sonic Craft 65s, and the 2 woofers, Sonic Craft SCC300s, are completely open...


Properly equalized, the sound is BIG and spacious but also with excellent image focus and soundstage-center focus, just the way I like it.  The quality of the bass is excellent, with high degrees of tightness, control, extension well into the bottom octave, etc.

Both Roger Modjeski, who has heard my system, and Jeffrey Glowacki, who has not but who has advised me often during my long journey, have recommended building sealed bass systems for my final, good-looking versions, but those new systems, too, will feature OB bass.  The new bass system will have slightly shallower wings but I'll add a top this time*.  The main (tower) portion's wings, too, will be shallower and of course will require more equalization to get the warmth I require from my speakersystems.

The system is triamplified and uses a dbx-brand DriveRack PA digital speaker-management system.  The bass low-pass filter point is 45Hz; the Bass/MR high-pass FP is 30Hz while the low-pass FP is 2KHz; and the treble HP FP is 2KHz.  All slopes are 4th order except the 30Hz HP on the B/MR drivers.

* still with NO parallel surfaces

[johnk...]

My arguments would be in favor of dipole or OB mids properly matched with monopole woofers. Dipole or OB mids remove cabinet resonances and re-radiation through the cone from the critical midrange. The arguments for dipole bass are usually with regard to room mode excitation. However, the idea that fewer room modes are excited is really a mixed bag. If the dipole axis isn't aligned with a room axis then the fewer room modes argument doesn't really pan out. What you often have is a power mismatch with dipole mids coupled to dipole woofers. What you have to look at is what modes are excited and by how much. If a monopole and dipole woofer excite the same mode to the same level then it will take the same time to decay. On the other hand there is also the school that argues for exciting as many modes as evenly as possible. This generally means corner woofer placement which is not possible with a dipole woofer.

The single advantage that I would perscribe to dipole woofers is that, being a velocity source, they can not over power a room below the room fundamental. Put a 20 Hz dipole woofer in a room with a 40 Hz fundamental and there isn't any problem, so to speak. Put a 20 Hz monopole woofer in a 40 Hz room and chances are that the deep bass response will boom and be ill defined. But given a large room efficiency and power arguuments swing towards monopole bass.

[JANDG]

I have just ordered a pair of SEAS MCA 15RCY for some OB experiments. I will be using a high quality 12" FR of high eff. below this & the SEAS mid on a very small baffle of 10"x16" bolted to the 24"x24" baffle the 12" resides in. Now I must find a tweeter that will work nice with the MCA 15RCY, my hunt is also on. If I have to run a quad of tweeters forward & rear fire so be it..I support via a pair sealed subs from 80hz down 4th active via BASH plates ran right next to main baffles. Very Intested in how your turn out

[HiFiNutNut]

John,

Quote: "My arguments would be in favor of dipole or OB mids properly matched with monopole woofers"

OB mids to what frequency? 300Hz? 200Hz? 100Hz?

My new speakers will be crossed at about 150Hz between the "mid" and "bass" woofers. I am struggling on the choices of OB or monopole bass from 65Hz to 150Hz. It will be monopole below 65Hz.

Regards,
Bill (HiFiNutNut)

[johnk...]

I think you are on target. I x-o to OB mids around 120 to 150 Hz.

[Andy G]

I agree with John  (for a change    )  .. Hi John 

Have a look at these as  OB mid + vented woofer implementations.  Both cross mids to woofer around 160-180, which give 5" or 4.5" mids plenty of breathing space. 

http://members.optusnet.com.au/~gradds55/ARGOS/blackwood.html
http://undefinition.googlepages.com/diy-aethers

[ttan98]

Bastani, a commercial system uses a sealed box as bass and dipole, mid and compression driver high with good effect.

I believe it is crossed fairly low, possibly or 100-150hz or below. go to Bastani site to find out

[Bloodstain]

I thought I should make a little update about the situation of the project.

I read a lot about OB from here, diyaudio.com and various other sources and found out how complicated it is to design a good open baffle speaker, so I decided to postpone my OB project to later time. But I got a lot of good info about ob speakers and one day I will deifinitely experiment with ob speakers 
Instead of the original plan, I am going to make a similiar 3-way floorstander with tilted front baffle, using sealed and reflex boxes.

[zipidachimp]

Are you sure you aren't making this more complicated than it is? with my simple OB project, I've got diana krall sitting next to me singing her heart out, same with the late pavarroti, sonny rollins, bill monroe and a whole slew of others. come on in, get your feet wet, you'll be amazed what an OB can do, even a simple one. start with the mjk project and go from there. 

http://www.quarter-wave.com/General/OB_Design.pdf 

[ttan98]

Are you sure you aren't making this more complicated than it is? with my simple OB project, I've got diana krall sitting next to me singing her heart out, same with the late pavarroti, sonny rollins, bill monroe and a whole slew of others. come on in, get your feet wet, you'll be amazed what an OB can do, even a simple one. start with the mjk project and go from there. 

http://www.quarter-wave.com/General/OB_Design.pdf 

All our comments(many different ideas) seem to frighten him off. If he is concern, get a simple 2-way going first, once he has more confidence then go for more complicated OB project.