[Rudolf]

The damping materials would appear nearly non-existent to the lower frequencies, and they work as a low pass filter, for example, below 300-500Hz. So at those frequences, I expect the behavior to be the same as your modelling software. But at those frequencies we have no concern because they are below the first dipole peak. My target is to deal with the peaks and dips above the first dipole peak, and we are talking about possibly over 800Hz here.

Yes, you can do an acoustic low pass filter for the higher frequencies like that. And - in contrary to an electrical LP - you can do it for one side only. I`m not sure if you really need a doughnut shape or if just covering the backside would work the same. This may be worth the added effort I see compared to the electrical LP. You have to keep in mind that this single-side-filter will change the radiation pattern from dipole to monopole - whatever this means for the practical implementation.

The idea was for a fun, retro atomic look, and an asymmetric baffle.

Nice looking baffle indeed. "retro atomic" comes to the point. 
Did you know that asymmetric positioning of the driver on the baffle is no longer necessary if you choose the appropriate baffle width? On the contrary: Mounting the driver asymmetrically on a baffle of optimal width will change the radiation pattern to the worse again.

JohninCR (I've seen the photos) would be optimizing the power response as well as getting a good polar response with his symmetrical waveguides.
I really think that both parameters are very important.

Earl Geddes stated in one of his threads on DIYaudio, that, if he ever would build a dipole, it would look like a giant doughnut with the front and back opening as an OS waveguide.
While this would combine the space consuming attitudes of OBs and big horns at their worst, it is consequent in thinking.

[Rudolf]

How does this argument relate to other possible OB-types like Line Sources and Electro- and Magnetostatic panels ?

Erling,
the algorithms for computing OB radiation are very much the same in Boxsim as in EDGE. I only resorted to Boxsim because it does polar patterns at three angles and for left, right, top and bottom automatically and including driver specs. But Boxsim is restricted to rectangular baffles and circular sources.

So everybody could do those off-axis simulations in EDGE for linear sources and weired baffle shapes. It simply needs someone to begin with.

Rudolf

[Viridian]

Did you know that asymmetric positioning of the driver on the baffle is no longer necessary if you choose the appropriate baffle width? On the contrary: Mounting the driver asymmetrically on a baffle of optimal width will change the radiation pattern to the worse again.

this is very interesting. And how does one determine the "optimal" baffle width in order to take advantage of this?

Erik

[Rudolf]

And how does one determine the "optimal" baffle width in order to take advantage of this?

There is no lower limit for baffle size. But if you make the baffle too narrow the driver will run out of steam early.
The upper limit is defined by the highest frequency you want to emit with the driver. The baffle width should be less than the wavelenght of that frequency, because you want to stay below the dipol peak frequency. Look at this diagram from Linkwitz´ site:



You don´t want the off-axis SPL (30/45/60°) to become stronger than on axis. That will happen if you go past the dipole peak.
Someone could argue that in most cases the physical baffle width will be different from the effective baffle width -and that´s true. But if you don´t feel able to calculate the effective width of the baffle, the physical width should do well enough.

[scorpion]

Rudolf,

I don't think EDGE can do polar response, but you are right, I have some saved simus for B&G Neo8 with its rectangular form.
MJK's worksheet would be able to do simus like Boxsim's also for more unusual baffle shapes with 3 or 4 corners, like the one you propose.

/Erling

[panomaniac]

Did you know that asymmetric positioning of the driver on the baffle is no longer necessary if you choose the appropriate baffle width?

I have seen that playing with Edge.  Never did pursue it, though.  Maybe I should.
FWIW, you can sort of "cheat" of axis response in Edge.  Just move the mic off center!

Looking at Mr. Linkwitz graph, I see some of what I hear.  The off axis response tends to fill in the holes in the direct response.  At least in a typical room, it will.

[Rudolf]

I don't think EDGE can do polar response

Erling,
as Panomaniac already mentioned you can cheat it. I once made up a chart to help finding the right values:



If I recall Svante correctly he does not recommend to trust EDGE above 70°.

Rudolf

[Rudolf]

Looking at Mr. Linkwitz graph, I see some of what I hear. The off axis response tends to fill in the holes in the direct response. At least in a typical room, it will.

And this is exactly where people are drawing the wrong conclusions IMHO!
Because of that fill-in it could be easier to get a nice flat power response in room by designing past the dipole peak. But imaging will suffer. Imagine the side wall reflections being louder than the direct sound. That can easily happen, when the direct-radiated frequency is in the dipole dip and the off-axis response some 10 dB louder.
After I cut my midrange baffles smaller I believe imaging has improved.

Rudolf

[scorpion]

Yes, I see your point, I might have measured 10 degres off axis by accident sometimes  , Svante Granqvist is quite a nice fellow and should be trusted.
But with MJK's models you also actually simulate the real speaker and the real baffle.
In Edge you 'only' will have the baffleinfluence, which is of course what we are talking about.

/Erling

[scorpion]

Rudolf,

Commenting also on your latest answer. I think that combining bass H-baffles with smaller mid/treble-baffles, as we have discussed earlier, is a very
promising way to go.

/Erling

[JeffB]

What are V and D in the diagram? And where does 0.17 come from?

What is the calculation for the 680Hz.
Is it 1135 * 12/(2*D)?

[Rudolf]

What are V and D in the diagram? And where does 0.17 come from?

Sorry, I forgot to link to the corresponding website http://www.linkwitzlab.com/models.htm#A
I believe your answers are all readily in there - so no need to repeat it here.
For 0.17 you have to go to the end of chapter A.

[HiFiNutNut]

Rudolf,

I have a large U-frame speakers and have been playing with rear damping. When it is not stuffed (e.g. lightly filled) the response is simular to typical U-frame response with peaks and dips. When it is fully stuffed (packed and compressed) the response is basically the same as a monopole.

The interesing finding is that when it is partially stuffed, at higher frequencies the response is like the monopole and at lower frequencies the response is like dipole. This is of course due to the LP filter from the damping material. This is not unexpected.

But don't we want monopole response at higher frequencies? and don't we want to use dipole/U-frame below the first dipole peak? Yes we do. It is actually ideal. And that is the approach I am taking.

I always support the idea of using the correct baffle width (e.g. comparatively narrow, such as the ones in the Orion or NaO). But I realised that in order to do that the design is a lot more complicated with at least 3 way to achieve that. For diyers a two way with a full range driver argmented with a woofer is far more attractive for its lower costs and simplicity. But that requires a wider baffle. I was exploring the idea to make wider baffle work with damping materials applied to the baffle, an idea coming from the findings of my U-frame studies.

But I understand I am gradually moving off the topic so I think I should retreat now.

Happy DIYing.

Regards,
Bill

[HiFiNutNut]

I`m not sure if you really need a doughnut shape

I found one major drawback with OB speakers being severe diffraction. According to the discussions (Gedlee and others) at the diyAudio forum, OB speakers have twice amount of diffractions comparing to monopole. I have personally measured such effects and obviously don't like them.

A doughnut shape (whether it is made from timber or damping material) would substantially reduce the diffraction effects.

Regards,
Bill

[panomaniac]

I once made up a chart to help finding the right values:

Very nice, thanks!

[D OB G]

Rudolf,

Are you satisfied that a sloped baffle is optimum compared to a specifically stepped baffle for each driver (or even a sub-baffle), either via simulation or experimentation?

David

[gainphile2]

In regards to simulator, I have used JohnK's ABC Dipole with great surprise  . I had heard something wrong with my old 120x45cm baffle with eminence alphas (a "CS2 Clone") but not sure what it was. I measured it outdoor and got this. I was already suspicious that this has something to do with baffle width.



So, needing a tool I bought John's simulator. To my amazement this is the simulated plot 



So I have been using that software quite reliably for the "S7". Btw. I have yet to find independent measurement of Physics CS2, all the reviews seems to be positive talk only, keen to know.

[Viridian]

It has been mentioned and is possibly OT but just wanted to share as I think it is so cool. Edge diffraction is dealt with.

Erik

[Rudolf]

I have a large U-frame speakers and have been playing with rear damping. When it is not stuffed (e.g. lightly filled) the response is simular to typical U-frame response with peaks and dips. When it is fully stuffed (packed and compressed) the response is basically the same as a monopole.

The interesing finding is that when it is partially stuffed, at higher frequencies the response is like the monopole and at lower frequencies the response is like dipole. This is of course due to the LP filter from the damping material. This is not unexpected.

Indeed. While I have not tried stuffed frames myself, it all sounds very logical to me.

But don't we want monopole response at higher frequencies? ...

This is where we differ, I believe. I don´t want to make it a key requirement, because it very much depends on the individual room conditions. But in my personal situation I found adding backward tweeters to my dipoles very rewarding. They really helped to get the power response right.
Without the rearward tweeter I often felt the treble region to be too weak and not really integrated. But I could not raise the front tweeter SPL alone, because it immediately became screechy. Only when I added the rear tweeter I got a good balance.

... and don't we want to use dipole/U-frame below the first dipole peak? Yes we do. It is actually ideal. And that is the approach I am taking.

As I said, we seem to be of different minds in this regard.

I always support the idea of using the correct baffle width (e.g. comparatively narrow, such as the ones in the Orion or NaO). But I realised that in order to do that the design is a lot more complicated with at least 3 way to achieve that. For diyers a two way with a full range driver argmented with a woofer is far more attractive for its lower costs and simplicity. But that requires a wider baffle. I was exploring the idea to make wider baffle work with damping materials applied to the baffle, an idea coming from the findings of my U-frame studies.

The triangular baffle tries to solve that dilemma by giving every driver the baffle width it demands.
But there are many roads to dipole heaven, I believe.

[Rudolf]

Are you satisfied that a sloped baffle is optimum compared to a specifically stepped baffle for each driver (or even a sub-baffle), either via simulation or experimentation?

David,
I never have compared both approaches. It is just intuition that made me prefer a smooth transition from one width to another. Please keep in mind that each driver/baffle combination should not be designed for a specific frequency, but a range. And one range should connect seamlessly to the adjoining ones.

Otherwise: The Gradient Helsinki http://www.gradient.fi/helsinki15 prefers specifically stepped baffles for every driver and its designer is lightyears ahead of me WRT dipoles: