I'd think absorbers on the walls, extending say a foot or two from the speaker, would take care of most unwanted diffraction/reflection effects. Make them thick enough to absorb most everything above 500 or so.
I see much talk here of using a 90 degree dispersion, but I could see a benefit in making it 60 degrees. It would allow greater flexibility in furniture placement in a room, which I think is important enough, and especially considering my preference for stereo over HT.
Nothing so far that I've seen in this thread has suggested that narrowing the angle is detrimental from a waveguide functional point of view, save for something that Dr Geddes mentioned about 45 degrees possibly being optimal (although I don't think I understood why).
One problem would be the depth of the waveguide vis-a-vis time alignment, but I have a strange feeling there may be some issues with regards to the in room power response successfully creating all the late reflections that seem to be so coveted.
So, what would be the harm in going narrow?
Nothing so far that I've seen in this thread has suggested that narrowing the angle is detrimental from a waveguide functional point of view, save for something that Dr Geddes mentioned about 45 degrees possibly being optimal (although I don't think I understood why).
One problem would be the depth of the waveguide vis-a-vis time alignment, but I have a strange feeling there may be some issues with regards to the in room power response successfully creating all the late reflections that seem to be so coveted.
So, what would be the harm in going narrow?
There is not much downside performance wise, but narrower gets to be problematic in practice. People often forget the requirement that the woofer and the waveguide MUST have the same directivity at the crossover. A woofer which gets to 60 degress within its usable passband is almost impossible to find (I don't know of any). And, as you mention, the waveguide gets very long making the enclosure tougher to do. (My compression drivers are right at the back of the box now.) All this, and the performance improvements would likely not be that great, if at all. SO its not a "bad" thing, its just not a good tradeoff.
Dr. Geddes, Hello and warm regards from Florida! I recently found this forum and have read it from the beginning (whew!). A few questions for you...
On WG: What about narrowing the dispersion in the vertical plane?
On LF: Possibility of using the DCX to create a cardioid response pattern to control the LF directivity to lower frequency with a rear mounted driver?
On WG: What about narrowing the dispersion in the vertical plane?
On LF: Possibility of using the DCX to create a cardioid response pattern to control the LF directivity to lower frequency with a rear mounted driver?
A few woofers with extended usable passbands:
JBL 2226h stays pretty flat 'til its rolloff at about 1.6k (I'm using it that high now and it sounds very nice), the BD BD15 (though I've not seen third party measurement) is flat much higher, more like 5-6k, as is the AE TD15M.
I think that the advantages of time alignment are less important as you go further down in frequency.
If true, crossing at 1 kHz is less demanding than crossing at 3 kHz.
Can someone else confirm or deny that?
All of those drivers would meet the on-axis flat requirement, off-axis is another matter. I think the physics of the transducer diameter is the limiting factor with dispersion.
Lenard Audio explains this in this article. Look at section 2, Polar Response Dispersion.
I think if you look at the actual polar plots, depending on definition of contant directivity, you will find that the most constant region is actually in the 60deg (included angle) range. It depends on how you want to roll-off as you go off axis.
With a 90deg physical included angle, reflections from the mouth is reduced significantly. Making it narrower will require more care with the mouth termination.
You're not contextualizing well here. They're all well-behaved up into the region where they have narrower beamwidth, which is the matter under discussion. The doc is talking about taking them higher where they're narrower.
A 90 degree waveguide is not too dissimilar in depth than a 15" driver, off the top of my head, but a 60 degree waveguide might be five or six inches longer which is almost half a wavelength at 1kHz.
Im doing some measurements and XO sims right now on a waveguide design.
To match the directivity should pick the XO that will match the 45degree measurements of the woofer and waveguide?
I thought he was talking about finding a 15" woofer that has a 60° wide dispersion within its useable passband.
To my understanding the dominating the factor for dispersion of a cone type woofer is the woofer's size.
So, the 2226H's polar response should be similar to just about any other 15" woofer, I would think, but what am I missing?
This is the model for a JBL 2226H in a vented box.
An externally hosted image should be here but it was not working when we last tested it.
This is the model for a B&C 15 PS 40 in the same vented box for comparison.
An externally hosted image should be here but it was not working when we last tested it.
I was not expecting to see much difference (and I don't).
What I mean is that the requirement is for the woofer to be well behaved at the point where dispersion is nominally 60 degrees. We're agreed that size is the dominant factor in beamwidth, though cone design plays some role. But several drivers perform well higher in frequency, given the narrower beam is my point.
Badman, can you show me one of these several? I'm not trying to be argumentative, but I can't find any and I've asked/searched a few times before with no results. Seems very few people are paying attention to these metrics if anyone. Where can I even find a woofer polar response measurement out to 90 degrees off axis let alone one that measures well where its polar pattern is 60 degrees? It would need to be well behaved well above that for it to be useful. I've done quite a bit of looking. I'd even be happy with 15 degree steps, but out to 90 degrees at least would be adequate.
Thanks,
Dan
Thanks,
Dan
Having measured a lot of woofers, even two identical woofers are not as close as the data that you show. Two completely different drivers - no way - thats the same data, not two different drivers.
Size is the dominate factor, although cone angle is a factor as well.
It is the "control" that is the issue. You can see that a 15" woofer would have to go to nearly 2 kHz to be 60 degrees. No 15" woofer does that (real data only please not manufacturers claims!).
Size is the dominate factor, although cone angle is a factor as well.
It is the "control" that is the issue. You can see that a 15" woofer would have to go to nearly 2 kHz to be 60 degrees. No 15" woofer does that (real data only please not manufacturers claims!).