[JohninCR]

Danny,

I'm an OB guy, so I don't even think about more than 20 degrees or so off axis. 

But it matters SOOOOOOO Much.  A Shame.

Not in my room because it's somewhat narrow, so with the speakers toed in, the only way to get more than 20 degree off axis at a reasonable listening distance is to put your head against the wall.  I build speakers for me, so forgetting about polar response makes things that much easier.  For listening significantly off axis or up and moving around, point source speakers don't come close to line arrays, so if it matters that much, why not go all the way?

[ekovalsky]

Just thought I'd chime in and say open baffle midrange rules 





System is a hybrid in the biggest way -- self contained ribbon tweeters and open baffle midranges in a short line array flanked by sealed metal cone woofers in an expanded array, separate subwoofers each with four separately vented subenclosures.

Speakers sound their best with the side and rear grill cloths removed. I have the front baffles of the main channels about 5' out from the rear wall.  Crossovers used in my DSP quad amp setup are 50hz, 400hz, and 2700hz via 24dB/octave, L-R type linear phase filters.

[JohninCR]

Just thought I'd chime in and say open baffle midrange rules 

As much as I love OB bass, it's hard to argue with that setup. Sweeeet!

[JLM]

Suprised that no one here has mentioned infinite baffles as a good compromise between the box and no box bass camps.  Just like O.B. bass multiple drivers and EQ are to be expected.

Some of those I.B. cult members are extremely devoted (and seem to know their stuff):

http://home.comcast.net/~infinitelybaffled/

[PaulHilgeman]

Danny,

I'm an OB guy, so I don't even think about more than 20 degrees or so off axis. 

But it matters SOOOOOOO Much.  A Shame.

Not in my room because it's somewhat narrow, so with the speakers toed in, the only way to get more than 20 degree off axis at a reasonable listening distance is to put your head against the wall.  I build speakers for me, so forgetting about polar response makes things that much easier.  For listening significantly off axis or up and moving around, point source speakers don't come close to line arrays, so if it matters that much, why not go all the way?

I was refering to how power response is what you hear off all surfaces and how little on-axis actually matters, espeicially in narrow rooms.

I am not quite sure what you meant by your last sentence.

For the most part, Hi-Fi speakers are made to be listened to from a single place, or a reasonable set of locations around a central sweet spot.  Even still, power response matters more than direct on-axis frequency response in this situation.  But as a result, speakers with even power response will sound better off-axis than speakers that dont.

-Paul

[Danny Richie]

I agree with Paul. Even if you never move from the sweet spot you are still listening to the over all room response and not just an on axis response. A limited off axis response will narrow the sound stage and close it in.

[JohninCR]

Danny and Paul,

More limited off axis response is one of the key advantages of OB in a similar way that the directivity of horns is an advantage.  Greater magnitude side wall reflections in my room...no thanks.  I want to move my side walls outward with lower magnitude and more diffusion.  I'd like it fine if they weren't there at all.  I understand the importance of a balanced off axis response, but again the inherent narrower dispersion of OB make that easier.  That's also where the advantage of OB bass lies, far less reflections to muck things up.

[Davey]

John,

I don't think I would characterize an OB has having "inherent narrower dispersion."  We're talking midrange pretty much here, correct?  Much depends upon the baffle construction, but open-baffle configurations can have a wider polar response relative to conventional systems.  If designed with that objective and in a certain frequency range....which is the whole reason for doing it. 

A semi-wide open-baffle can cause a widening of the polar response when the rear wave adds at off-axis angles with the front.  The reverberant field can become too bright...even though the on-axis response might be flat.  I believe this is the reason some poorly designed open-baffle speakers tend to have a "forward" quality to them that sounds good initially, but in the long-run doesn't please.

Adjusting baffle dimensions/construction is the essence of this type of design because problems created can't be corrected with EQ or crossover changes without changing the on-axis response.


In fact, one of my own designs from a few years ago is an illustration of this.

http://home.comcast.net/~dreite/Davey/Davey.htm

I compromised the polar response of the design (slightly) to allow usage of an extremely simple baffle/construction design.  I experimented during this process with some "wings" and some structural pieces on the back which yielded a somewhat smoother response, but required a more complicated construction.  Yet, even with this compromise the system sounds better than most conventional systems (regardless of price.)

Controlling dispersion is the key....not necessarily narrowing it.

Cheers,

Davey.

[JohninCR]

Davey,

I didn't mean "uncharted" in that OB speakers were new.  I meant that the design of the baffle itself has plenty of uncharted waters, and I don't mean just in looks.  Almost anything you do behind the front plane of the baffle makes an audible difference, and there's virtually no information available about how to manipulate the rear wave to your advantage with OB's.


Danny & Paul,
Maybe I'm not understanding something about polar response, but don't narrower dispersion, narrower polar response, and being more directive in nature all mean the same thing?  Linkwitz makes the point that the reduced reflections makes it so we hear a much greater percentage of front radiation compared to monopole speakers.  He also talks about polar response of dipoles being better essentially because of the cancellation at the sides for frequencies that would otherwise expand to free space.  Have I oversimplified something in the process of trying to fully understand SL's work ?

[JohninCR]

John,

I don't think I would characterize an OB has having "inherent narrower dispersion."  We're talking midrange pretty much here, correct?  Much depends upon the baffle construction, but open-baffle configurations can have a wider polar response relative to conventional systems.  If designed with that objective and in a certain frequency range....which is the whole reason for doing it. 

A semi-wide open-baffle can cause a widening of the polar response when the rear wave adds at off-axis angles with the front.  The reverberant field can become too bright...even though the on-axis response might be flat.  I believe this is the reason some poorly designed open-baffle speakers tend to have a "forward" quality to them that sounds good initially, but in the long-run doesn't please.

Adjusting baffle dimensions/construction is the essence of this type of design because problems created can't be corrected with EQ or crossover changes without changing the on-axis response.


In fact, one of my own designs from a few years ago is an illustration of this.

http://home.comcast.net/~dreite/Davey/Davey.htm

I compromised the polar response of the design (slightly) to allow usage of an extremely simple baffle/construction design.  I experimented during this process with some "wings" and some structural pieces on the back which yielded a somewhat smoother response, but required a more complicated construction.  Yet, even with this compromise the system sounds better than most conventional systems (regardless of price.)

Controlling dispersion is the key....not necessarily narrowing it.

Cheers,

Davey.

Davey,

No, I wasn't really talking about midrange only, but I'd like to discuss some of your points in more detail, because I've always ignored dispersion.  I've stayed away from wide or even semi-wide baffles for non-sonic reasons other than their black hole effect in the rear wave ambiance, ie close your eyes and you hear exactly where they are, because the rear wave reflections are missing from there.  For stability and asthetic reasons I try to keep the width in the range of typical boxed speakers.  Then I manipulate the rear wave primarily for bass extension, but along the way I've used a very visual approach to what's going on with the flow of the two wave fronts and I may have been addressing mid-range dispersion without knowing it.

Out of necessicity I've become a minimalist, using only full range and coax drivers with bass fill, and first order rolloffs at low points on the bass augmenters.  That's about to change though with a computer driven XO, so it's time to graduate to the next level and become more scientific.  I have plenty of wide range drivers and woofers to work with, plus a few compression horn tweeters.  It should be fun.

[JoshK]

Suprised that no one here has mentioned infinite baffles as a good compromise between the box and no box bass camps.  Just like O.B. bass multiple drivers and EQ are to be expected.

Some of those I.B. cult members are extremely devoted (and seem to know their stuff):

http://home.comcast.net/~infinitelybaffled/

   This is what I am doing...for sub territory.  I have a pair of Avalanche 15"s that I am going to mount under the floor in the basement firing up through a brass heater vent like grate.   Wife actually liked the idea, since there is no big box in the room.   

[Brad]

That's pretty cool Josh,

I actually sold the wife on the OB idea because the speakers won't be as deep 

I haven't brought up the point that it may take 2 pairs of Hawthorne Augies to make up the bass difference.

[markC]

Keeping it simple via infinite baffle...



2 x 15" in a crawl space 

Thank-You Carlman for the 101 on how to post photos!

[PaulHilgeman]

Hey,

Just thought I would poke my head in one last time here.

OB Dipoles really dont do much to the sound at 20 degrees off axis.  The range in the 0-20 degrees off axis is really all part of the on-axis sound field, and affects in here are usually refered to as beaming. 

The whole point of a speaker that has an open baffle midrange is to increase its directivity in the areas where it raidates equally to the front and rear, i.e. down low, say 200-1000Hz.

By increasing directivity I mean reducing output significantly at 90 degrees off axis, somewhat at 45 degrees off axis and almost no change at say 20 degrees off axis.

-Paul

[JohninCR]

Paul,

I don't know about it being the whole point, but it seems that polar response
kind of takes care of itself when you go fully dipole and don't use a wide baffle.
Then as you move toward U type shapes, you widen dispersion somewhat, but
still nothing like a box.

[PaulHilgeman]

Yes, not the whole point, rather "The whole point of dispersion with regard to midranges on open baffles is to control radiation at the extreme off axis"  This contributes in a LARGE way however to the sound of the speaker.

-Paul

[Danny Richie]

I agree with Paul,

Just have a look at his off axis responses.

http://www.nomad-audio.com/index_speaker.htm

If his mid-bass woofer were larger (like a 10" or 12" woofer) then you would begin to see a sucked out area in the off axis response in the 1 to 2kHz range as the tweeter would not play down low enough to fill the hole created by the limited off axis response of the large woofer.

Controlled dispersion is a good thing, but keeping that dispersion balanced will mean a more balanced room response.

Spectral decays are usually much cleaner with smaller drivers too as they have less stored energy and inertia due to lighter cone masses. This will give you what most call a cleaner or faster sound. How low the driver is allowed to play also is a factor as the lower it plays the more it has to move, but then again you don't want lower vocals covered to much by a large woofer either (or your low frequency driver/s), as it is having to cover the bottom end and is seeing heavier movement. It is a balancing point. I like seeing that crossover point in the 200Hz range or a little lower myself.

[JohninCR]

Thanks Danny.  Your original point about the detriment of larger drivers finally sunk into my thick skull.  I still want a 10" .7 Q coax though, and I'd think the designer would consider dispersion of the tweeter and woofer around the XO point for consistency.

[Danny Richie]

If you can cross the tweeter at around 1kHz you're home free.