Another approach to matching directivity - AVS Forum
DIY Speakers and Subs > Another approach to matching directivity
fakamada's Avatar fakamada 07:27 AM 02-19-2014
I always had a feeling that matching directivity using big woofer (12"-15") and a waveguide has one disadvantage. Running big woofer so high in frequency makes midrange (circa 500hz-1000hz) less clear and detailed than it could be with for example 8" woofer.
So I think got an idea. How about making a simplest and cheapest possible waveguide for woofer, to match it's directivity with bigger waveguide? Any ideas how woofer's response might change?

PS. Dimensions are in milimeters, but I hope you get the picture. Woofer used in projest is Eminence Beta 8a

FOH's Avatar FOH 10:11 AM 02-19-2014
Interesting

I've often thought conventional wisdom would suggest the midband performance of typical 12" or 15" two-way loudspeakers may be an area whereby improvements could be implemented.

However, there's many examples of very high quality designs using such an approach; Gedlee, studio monitors from JBL, TAD, Augsburger, etc, all using 15" two-way designs without issue or need for higher resolution, clarity, or detail. They've employed .5 way approaches to off load excursion and add more capability in the bottom octaves, in some designs.

If one takes an overview of what's out there, the large two way is a solid and well vetted platform from which one can start a design. There's significant advances in materials and measuring capability since this platform began, there's just such inherent advantages with the large piston area (low distortion) combined with the directivity at the crossover region ... that you get with the 15".
I do feel there are possible areas for improvement for greater midband performance like some open back or IB technique that may help non-linearity issues, as the latent energy release thru the cone is no good, if it exists as a problem.
I believe
noah katz's Avatar noah katz 04:22 PM 02-19-2014
Interesting idea, may or may not work with the dimensions shown.

Maybe someone who knows Hornresponse can try it out.
Face2's Avatar Face2 08:02 PM 02-19-2014
Bill Fitzmaurice has posted a link to a dispersion simulator that displays how partially blocking off front of the woofer can be used to change directivity, I thought I bookmarked it, but can no longer find it.
noah katz's Avatar noah katz 09:10 PM 02-19-2014
I suspect it was widening dispersion, not narrowing it.
Face2's Avatar Face2 09:14 PM 02-19-2014
It's been a while since I've toyed with it, but I believe you could do either. I very well could be wrong too.
Face2's Avatar Face2 09:22 PM 02-19-2014
LTD02's Avatar LTD02 09:25 PM 02-19-2014
if i understand you correctly, what you describe is a good idea and is already in wide use.

the challenge is that the midwoofers that cover the 500-1000hz region a little better than 15" drivers just don't have what it take on the low end, so you end up with three way systems. here is an example of a mid-top that you might find in jbl's pro lineup for dance clubs. they have similar products for tour and theater, as do many other companies.


LTD02's Avatar LTD02 09:28 PM 02-19-2014
that is an interesting link face2 and jbl has a speaker out that does just that:

eon615. supposedly it sounds pretty good, but don't all new speakers?

anyway, that one is crossed up pretty high, around 2khz, so that will give it massive power handling and allow for a really cheap compression driver, but i suspect that it is not what most folks around here are looking for.


Face2's Avatar Face2 10:16 PM 02-19-2014
I've thought about doing something similar in place of the passive resistive cardioid enclosure I'm using now. The PRC's bandwidth is limited to 450hz in my application and I haven't had much luck raising it. Plus the aesthetics of this design has more potential than 12 2" holes drilled into the sides of an enclosure for a PRC. Now I have the motivation to experiment.

https://www.youtube.com/watch?v=vXhwPT0W3Ew

New? In this case of everything old is new again..or just tweaked.

Every time he says aperture, I thought of Portal. biggrin.gif
noah katz's Avatar noah katz 12:43 AM 02-20-2014

As far as I can tell that supports what I siad.

Directivity narrows with larger piston size through self-interference from all its radiating regions.

What's not clear to me and waht I was alluding to in my original comment is what it takes to make the added stationary area effectively radiating.
fakamada's Avatar fakamada 03:02 AM 02-20-2014
Quote:
Originally Posted by FOH View Post

Interesting

I've often thought conventional wisdom would suggest the midband performance of typical 12" or 15" two-way loudspeakers may be an area whereby improvements could be implemented.

However, there's many examples of very high quality designs using such an approach; Gedlee, studio monitors from JBL, TAD, Augsburger, etc, all using 15" two-way designs without issue or need for higher resolution, clarity, or detail. They've employed .5 way approaches to off load excursion and add more capability in the bottom octaves, in some designs.

If one takes an overview of what's out there, the large two way is a solid and well vetted platform from which one can start a design. There's significant advances in materials and measuring capability


I already build great sounding SEOS 12 design with 12" Faital 12PR300. In terms of power handling it's in my case a huge overkill. I'll be using 3-4watts for normal music listening. For now I don't have active subwwofers yet so I use Equalisation. Even after +20db of EQ on low bass I don't exeed 5mm xmax !!!!!!

As for advances in materials I don't think it works like that. Every driver at some point stops working as a piston. Then some detail smearing has to occur. The bigger the driver the sooner it happens. So while my 12" woofer based system sounds great I think there is some space for improvement. Therefore 8" woofer but with directivity matching maintained.

Quote:
Originally Posted by LTD02 View Post

if i understand you correctly, what you describe is a good idea and is already in wide use.

the challenge is that the midwoofers that cover the 500-1000hz region a little better than 15" drivers just don't have what it take on the low end, so you end up with three way systems. here is an example of a mid-top that you might find in jbl's pro lineup for dance clubs. they have similar products for tour and theater, as do many other companies.

Exactly. That's what I'm thinking. What I was trying to figure out is how to make ie easy and cheap.
As for low end - yes approach with 8" needs active woofers below 100hz.
Martycool007's Avatar Martycool007 03:35 AM 02-20-2014
Will a smaller 6.5" mid play the mid-range clearer, more detailed, and extend higher than a typical 15" mid/woofer that is commonly found in many 15" 2-way designs? Is it safe to assume that the small mids will do better in the 600hz to 1000hz area compared to a typical larger mid/woofer? With the draw back to using smaller mids being that the typically do not extend very low? Which will have the better directivity in the 600hz to 1200hz area, a typical 6.5" mid, or a typical 15" mid/woofer?
fakamada's Avatar fakamada 03:53 AM 02-20-2014
Quote:
Originally Posted by Martycool007 View Post

Which will have the better directivity in the 600hz to 1200hz area, a typical 6.5" mid, or a typical 15" mid/woofer?

That's what the idea is all about. To use smaller woofer with better midrange and simulate directivity behaviour of much bigger woofer by making a simple waveguide around it.
Martycool007's Avatar Martycool007 04:29 AM 02-20-2014
Quote:
Originally Posted by fakamada View Post

That's what the idea is all about. To use smaller woofer with better midrange and simulate directivity behaviour of much bigger woofer by making a simple waveguide around it.

So you are saying that, in concept, a larger mid/woofer, such as a 12" or 15" size, will have better directivity than a smaller mid?

I understand that your trying to come up with a horn/waveguide design for a smaller mid/woofer to give it better directivity, I just was unsure if directivity increases with driver size, or decreases with driver size?

I think this whole concept of using a type of horn/waveguide for a mid is an interesting design theory. I like the mid-horn that Wayne Parham sells that utilizes a 10" Eminence or 10" JBL mid. I personally prefer more hifi type mid drivers from the likes of ScanSpeak, Accuton, and Seas, in more of a 3-way setup with a dedicated woofer, over these large pro-woofer 2-ways.
LTD02's Avatar LTD02 06:01 AM 02-20-2014
"Exactly. That's what I'm thinking. What I was trying to figure out is how to make ie easy and cheap."

I see.


"As for low end - yes approach with 8" needs active woofers below 100hz."

that depends how loud you wish to run them and how much you wish to stress the midhorn driver, which is why you will typically see a pair of 15's rolled in around 300hz or so with most of these designs.

another approach is of course to build a horn around a coaxial driver like the danley sm60m:
http://www.danleysoundlabs.com/products/loud-speakers/molded-synergy-horns/sm60m/
LTD02's Avatar LTD02 06:02 AM 02-20-2014
marty, the larger the driver, the lower in frequency that it will start to beam and thus the lower in frequency you can get a good match to a horn. all other things equal.
fakamada's Avatar fakamada 06:06 AM 02-20-2014
Quote:
Originally Posted by LTD02 View Post

"Exactly. That's what I'm thinking. What I was trying to figure out is how to make ie easy and cheap."



another approach is of course to build a horn around a coaxial driver like the danley sm60m:
http://www.danleysoundlabs.com/products/loud-speakers/molded-synergy-horns/sm60m/

I'd love to hear those but unfortunately it's far from easy and cheap smile.gif

There's a program that simulates waveguides. I'll see what it shows:

http://www.randteam.de/_Software/AxiDriver_Demo/Download-AxiDriverDemo.html
LTD02's Avatar LTD02 06:23 AM 02-20-2014
i was only suggesting that as a model. for easy and cheap, something like this might work: http://www.parts-express.com/eminence-beta-8cx-8-coaxial-driver--290-500
coctostan's Avatar coctostan 10:17 AM 02-20-2014
AxiDriver is probably your best bet for simulating the directivity of horn and baffle profiles. There is a learning curve if you haven't used it prior.

The interactions between a driver that is 6-8" in diameter and its surrounding baffle is not as simple as a 1" driver and a similar horn. Horns are really just complex baffles...or maybe baffles are just very simple horns. Ultimately, the "gain" of a horn is simply boundary loading, no different than how any driver acts on a baffle. We just assume that a baffle is flat with squared off edges. Even rounding the edges impacts the directivity of a baffle.

It is more straightforward if the horn throat is smaller. Look at the simple conical horn in the 7Pi speaker. I believe it is a 4" square throat on a 10" driver. It also relies on wall proximity to control directivity lower.

What FOH said above is correct. Many excellent speakers use large drivers up to higher frequencies. How high is too high? It depends partly on the driver, but I wouldn't assume that a 6" driver is better at the mid frequencies than a 12" driver in the typical DI matched 2-way use. Much of that will depend on the drivers being compared and the crossover used. Remember also that putting the smaller driver on the angled baffle or horn will impact its response as well.

I do think there is a legitimate case for splitting a 2-way 12/15" woofer/horn speaker into 3-way with a horn midrange, but it is far tougher to pull off and the benefits are small.

LTD, that EON woofer aperature is interesting. It is clear that it allows JBL to get more SPL per $ out of their speaker without sacrificing pattern control. In the dirt cheap PA speaker market those are the only two criteria. They can use a $25 CD and a $25 woofer but still hit 125db+ with nice pattern control. All because of what is probably a $2 piece of plastic.
fakamada's Avatar fakamada 10:23 AM 02-21-2014
I've ran some tests and indeed it is more complicated. It's doable but complicated. Profile and depth have to be CAREFULLY designed to work properly.
zamboniman's Avatar zamboniman 10:31 AM 02-21-2014
Danley does something like this with at least one or two of their products.
Face2's Avatar Face2 10:34 AM 02-21-2014
Quote:
Originally Posted by zamboniman View Post

Danley does something like this with at least one or two of their products.
http://www.danleysoundlabs.com/products/loud-speakers/molded-synergy-horns/
Martycool007's Avatar Martycool007 05:24 AM 10-05-2014
Quote:
Originally Posted by LTD02 View Post
marty, the larger the driver, the lower in frequency that it will start to beam and thus the lower in frequency you can get a good match to a horn. all other things equal.
I just read this response after digging up this older thread, and what you said above is not making any sense to me.

Doesn't a larger woofer/mid start to beam the higher up you go in frequency, not the other way around?

More importantly, how does this beaming affect the directivity? I would guess that the larger woofer/mid drivers start to beam sooner than the smaller ones, and that would make directivity suffer, right? So would the smaller 6.5" to 7" drivers not have better matched directivity up top, and would having them in a horn loaded mid enclosure not be an ideal way to improve their directivity and pattern control?
Bill Fitzmaurice's Avatar Bill Fitzmaurice 06:58 AM 10-05-2014
Quote:
 Doesn't a larger woofer/mid start to beam the higher up you go in frequency
It does, but what he said was the larger the driver the lower the frequency where beaming begins.
Quote:
So would the smaller 6.5" to 7" drivers not have better matched directivity up top, and would having them in a horn loaded mid enclosure not be an ideal way to improve their directivity and pattern control?
A waveguide is a horn, and it will change both response and directivity. Predicting the response change is easy, just model it in HornResp. Predicting the directivity not so much, as that's determined by not only the mouth dimensions but also the throat dimensions and the horn flare, as well as the size of the diaphragm. To vastly simplify, high frequency directivity is primarily influenced by the throat dimensions, low frequency directivity by the mouth dimensions. That being the case you can make a horn loaded with a fifteen that has wider high frequency dispersion than a direct radiating eight.
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