Waveguide benefits/drawbacks - ongoing studies

[Mark Seaton]

Looks like Zaph has preliminary measurements for the 'new' PE waveguides, and the short answer is that they dont' seem to work as well as the MCM. The main aspect is increased HF oscillation - makes me wonder whether it might be (partially?) due to poorer matching of the tweeter to the throat. Otherwise, the 8 and 10" versions dont' seem to perform that much differently from each other.

When you say "HF oscillation" are you referring to polar/spacial lobing or something else?

[dwk]

When you say "HF oscillation" are you referring to polar/spacial lobing or something else?

No - I was just talking about some freq response ripples, mostly on-axis in the upper treble range. Could be from a couple sources. As indicated above, Zaph doesn't do any polar plots (although he does do off axis at 15 and 30). See the link here, down towards the bottom

http://www.zaphaudio.com/hornconversion.html

[JoshK]

To do polar plots do you have to do a whole bunch of varying degree measurements?

[JonMarsh]

Yes. To do properly, you need a turntable. Not one for vinyl, either.

[Paul H]

Yes. To do properly, you need a turntable. Not one for vinyl, either.

They're much cheaper than the ones for vinyl - a $10 lazy susan bearing and two pieces of scrap wood makes a nice turntable. I made one for my last project.

Paul

[Dennis H]

On-axis, top-octave ripples -- felt is your friend.

[jkrutke]

No - I was just talking about some freq response ripples, mostly on-axis in the upper treble range. Could be from a couple sources. As indicated above, Zaph doesn't do any polar plots (although he does do off axis at 15 and 30). See the link here, down towards the bottom

http://www.zaphaudio.com/hornconversion.html

Hello,

I still have these around and can do additional measurements. (in other words, I haven't thrown them out yet) Do you think 45 and 60 degrees might be worthwhile seeing? I'll throw it back on the baffle to see what it looks like.

I usually just do 0, 15 and 30 when testing on my infinite baffle. A little pre-configured mic arrangement makes it easy to zip through those. When testing speakers finished in a box, I use a 45" speaker stand mounted on a rotating TV tray with angle markings.

I'm not exactly sure where the top octave raggedness is coming from. I've seen it in a few "real" horns I've measured though. I've ruled out some sort of interference where the throat meets the tweeter face. I used various tweeters that fit my modded opening in various ways, but they all had the same results. The tweeters tested were as smooth as silk on a normal baffle.

I think AJINFLA was right about the coverage being a bit too narrow with these. Maybe if I cut them down further to reduce the throat angle.

[AJINFLA]

When the edge doesn't transition cleanly it can cause reflections back down into the throat, causing cancellation, roughening the response.

Cheers,

AJ

[dwk]

Hello,

I still have these around and can do additional measurements. (in other words, I haven't thrown them out yet) Do you think 45 and 60 degrees might be worthwhile seeing? I'll throw it back on the baffle to see what it looks like.

I wouldn't call it essential, but it would give an idea of how response falls off as you move outside the design angle. I'm somewhat surprised that these guys hang together as well as they do in terms of 'CD', given the noticable curve to the flare. Since falling response outside the design pattern is a goal of waveguides, it would be interesting to see how they do.

I'm not exactly sure where the top octave raggedness is coming from. I've seen it in a few "real" horns I've measured though. I've ruled out some sort of interference where the throat meets the tweeter face. I used various tweeters that fit my modded opening in various ways, but they all had the same results. The tweeters tested were as smooth as silk on a normal baffle.

I got my 8's and 12's last night, and after looking at them I'll throw my hat into the 'mouth termination' camp. The abrupt end to the flare at the rim of the waveguide can easily create the types of effects that are showing up. I suspect this isn't as much of a problem on the MCM due to the much shallower flare, and hence less abrupt termination of the horn.
Felt or acoustic foam on the baffle tightly surrounding the mouth would probably cut this down quite a bit. The 'right' answer is probably to build up a large-radius termination using bondo or something, although I'd guess this is a little outside the level-of-effort you're looking for on this.

I think AJINFLA was right about the coverage being a bit too narrow with these. Maybe if I cut them down further to reduce the throat angle.

For me, I like the narrow coverage. I'm in a small narrow room, and tight coverage is what got me seriously looking at waveguides in the first place. Mating this to the midbass cone driver might be more of a challenge, though. *IF* my Unity ideas actually work even OK, I'm hoping I can take the 12" down to maybe 500, which will make mating to a 12" easier. At first glance, these should be 'easy' to mount my mids to, but I'm not quite so sure that the mids will actually work as intended - the deviation from conical probably means that there isnt' as much low-end support from the waveguide which would be a problem.

[noah katz]

"I'm not exactly sure where the top octave raggedness is coming from."

There might be some funny business going on at the throat, since any deviation from smooth contours can cause reflections.

Maybe plop in some 30 ppi foam like Geddes uses

http://www.whalesale.com/filstar-foam-30-p-157.html?osCsid=bc518bf46c442b8198819730a20d4980

(not to say this is his source )

[JoshK]

Dr. Geddes mentioned it was like the fish filter but you can't actually use his foam insert for fish because it would kill them.

[cotdt]

Would the Dayton RS270 make a good waveguide? I know it's not a waveguide but you can rip out the cone and use it as a waveguide couldn't you? It wouldn't be too shallow or too deep wouldn't it?

[EdL]

Guys, if you dream up the "waveguide" profile you want to test, let me know. I'll make it. Including foam inserts. You test it with the understanding that results are posted. What could be easier?
I think the reference to polar response is important. Fleshing out the finer details of system response requires more attention given to the test method employed. I'm not the one to suggest the ground rules for such. I'll leave that to those with the gear and experience, though I like the discussion so far and think more would be wise so that results from different sources are relevant to each other.

[cotdt]

Guys, if you dream up the "waveguide" profile you want to test, let me know. I'll make it. Including foam inserts. You test it with the understanding that results are posted. What could be easier?
I think the reference to polar response is important. Fleshing out the finer details of system response requires more attention given to the test method employed. I'm not the one to suggest the ground rules for such. I'll leave that to those with the gear and experience, though I like the discussion so far and think more would be wise so that results from different sources are relevant to each other.

hello EdL, can you make a pair of 12" diameter waveguides that can withstand temperatures of around 800 degrees C?

[EdL]

cotdt asked:
can you make a pair of 12" diameter waveguides that can withstand temperatures of around 800 degrees C?

As the medium I have in mind is wood, the short answer is "NO", however bearing some research into making the reverse shape for casting in a moldable refractory , I guess it is possible to withstand temperatures around 1200 C.

Why the requirement for 800 C?

[cotdt]

cotdt asked:
can you make a pair of 12" diameter waveguides that can withstand temperatures of around 800 degrees C?

As the medium I have in mind is wood, the short answer is "NO", however bearing some research into making the reverse shape for casting in a moldable refractory , I guess it is possible to withstand temperatures around 1200 C.

Why the requirement for 800 C?

Yes that would be great. I am researching a tweeter made out of plasma that have very desirable audio properties and incredible frequency extension and transparency. It also glows with the music. While dome tweeters are improving, I want to take the next step in accurate reproduction. It is still in its early stages but will likely take a large waveguide to extend down to 1kHz evenly unless I make the flame very big (and power hungry). The flame tweeter will run very hot needless to say, but unlike in the past it will not generate poisonous byproducts, since it will be in a hot chamber that will decompose the poisonous gases. The ultimate goal is to cross it over at 200Hz with a subwoofer but that may or may or may not be realistic as the flame would have to be 5" or 6" inches.

[ThomasW]

Cool, your very own industrial strength ozone generator.....

[jdybnis]

No problem. He can sell it through Sharper Image and call it an air purifier.

[cotdt]

No problem. He can sell it through Sharper Image and call it an air purifier.

yeah and i'll pair it with this badass subwoofer:
http://kalecoauto.com/index.php?main...products_id=24
capable of antihertz!

that along with my earthquake generator will rock the house.

[JonMarsh]

I never had much luck with those air purifiers....


Wouldn't an Accuton diamond tweeter be a lot simpler way to get to basically the same place? Assuming you need 100 kHz reproduction for your SACDs- a lot of mine don't have much above 20 kHz.


~Jon

[JoshK]

Just a question, so don't shoot me.... but would a TMM 2.5 way make more sense than a MTM 2 way in the case where we are using a waveguide, due to the needed additional room that a waveguide requires?

[JonMarsh]

Just a question, so don't shoot me.... but would a TMM 2.5 way make more sense than a MTM 2 way in the case where we are using a waveguide, due to the needed additional room that a waveguide requires?

Oh, I think that's quite probably the case. I hear Evil Twin is already wondering if he can come up with a version of the Natalie P taking this approach... I mean, a black waveguide is "so Imperial"....

You're thinking along the right tracks, whatever way one winds up implementing it.

~Jon

[JoshK]

The dark side must be strong in me, cause that is exactly what I was thinking.

[noah katz]

"but would a TMM 2.5 way make more sense ..."

That's exactly what Zaph did with his TMM/waveguide.

[JoshK]

noah, yeah I know and what made me start thinking about it. but it is a good idea and nothing says you can't use a good idea because someone else used it already.

[jkrutke]

Just a question, so don't shoot me.... but would a TMM 2.5 way make more sense than a MTM 2 way in the case where we are using a waveguide, due to the needed additional room that a waveguide requires?

Actually, I think I'd prefer a MTM 2.5 way when using a waveguide. (even over a TMM, if system height isn't an issue) For a normal 2 way MTM, the massive size of a waveguide makes the woofer center to center quite large, moving the vertical lobing well down into the midrange.

[Mark Seaton]

I never had much luck with those air purifiers....

Funny you mention that Jon.

At CES Adire had on hand a simple proof of concept on a speaker based on the same concept that makes the Ionic Breeze that we see in Sharper Image catalogs work. Apparently the company who developed the technology had a faulty electronics in a unit, and suddenly it started producing a very audible 60Hz tone. After some investigation, the simple answer was that they were already able of creating air flow. Making sound just required modulating that air flow. It's quite a departure from normal speaker operation, but quite interesting with some apparent advantages and unique flexibilities.

Regards,

[oneoldude]

Hope no one minds my getting back to WGs.

Here is a pic of what I understand is a DIY speaker from Finland. Those folks are artists in wood!

This little speaker is supposed to sound very, very good. But that is all I know about it.

I will try to contact the poster to get some info on their research.

[Hank]

800 degrees C?? Flame tweeter???

I haven't checkd HTG since CES, and was about to feel at ease and at home, but unfortunately opened this thread first. :scareboo:

Although such talk matches Jon's avatar, YOU GUYS HAVE LOST IT! :rofl:

[ThomasW]

Somebody call the cops, Hank got loose again.....

[AJINFLA]

YOU GUYS HAVE LOST IT!

No. Codtd has this fascination with things that glow. I won't bother to rehash that young man's thoughts about vacuum tubes here. Just chuckle and move right along Hank. Nothing to see here. Over in scandinavia, it seems like they have it just about right with waveguides (both static and coaxial types) in terms of design trends. Now if they could just get them out of those boxes... :W

Cheers,

AJ

[noah katz]

oneoldude,

It's beautiful!

And they even managed to use the Seas w/hexagrid.

Any more info on it?

Thanks

[oneoldude]

Noah,

No more news on that speaker other than it appears to be made up of strips like butcher block somewhat like the Amphions.

I have written the poster but no reply yet.

It sure would be nice to know how they carved the guide and box. But its likely we will never know.

[ergo]

I know a little about this Finnish speaker ...

In Finnish magazine HiFi was a picture of the production unit. I was planning to post it as soon as I had time to "scan" it with my digital camera, but oneoldude beat me to it

First of all the design is made by Finnish speaker designer Anders Weckström.

The front plate is a separate piece and is milled out with a CNC machine.

The box is some kind of double chamber reflex.

I have not heared these speakers yet. Neither can I find any more info on these on net. So I know they presented the design in September 2005 in Finnish HiFI exibition, but are they actually selling in Finland I do not know.

Ergo

[technimac]

See More on Karoliina's Website

Here's Karoliina's home page: http://www.karoliinasalminen.com/

She seems to have the inside scoop on Anders Weckström's designs and has posted this link to several waveguide photos:

http://www.katix.org/gallery2/main.php?g2_view=core:ShowItem&g2_itemId=1643

....and here's two worth considering:

http://www.katix.org/gallery2/main.php?g2_view=core:DownloadItem&g2_itemId=1646&g2_serialNumber=2

Check out the quad with waveguide setup below - wonder how it sounds. Nice CNC work on those baffles!

Hopefully we'll hear more about these in the near future.

Cheers, Bruce

[mhelin]

http://www.weckstromspeakers.fi/

It is a transflex (as Weckstöm calls the combination of transmission line and bass reflex) speaker. The very same guy designed the Chorus (www.hifitalo.fi) waveguide and the Chorus line speakers and AW kits. The big one with 4 MW's (for controlling of directivity) uses compression driver in waveguide.

[ergo]

I did go to Finland yesterday and got few of the Chorus line WG-s. These are 29mm throat to 130mm mouth and a 140mm overall diameter WG-s. They are real nice and nice fit at least to 27TBFC/GTV tweeter.

[ergo]

I will try to make comparative measurement in a few weeks time.

I have panels ready for open baffle mid (W18NX) + tweeter (T29CF001). I will cut two more panels and instead of just tweeter these will use the Chorus WG + tweeter. I will try to mate the T29CF001 to this WG so it will be a fair comparison of tweeter with/without WG. I will remove the front panel from T29CF001 - we'll see how that works out.

By then I hope to have my DIY turntable ready so I can make many offaxis measurements also

Ergo

[ergo]

One more interesting fact - I also bought a Finnish book "Tee itse hifikaiuttimia" (translation - DIY loudspeakers) by Pekka Tuomela. Its a book about theory but also contains 41 speaker projects and their measurements.

Out of the 41 projects 19!!! are using either some sort of waveguide or coaxial speaker. As three projects are subs it means that more than half of the speaker kits use WG or coax. Finnish are really in leading role on this field it seems

From measurements in the book (all done in unechoic chamber in TKK Finland) it can be clearly seen that all the designs with WG have generally smoother power response around crossover.....

Ergo

[oneoldude]

ergo,

Thanks for the info. :T

They look really nice. :lol:

How deep are they along the central axis from throat to mouth?

By the way, did the book suggest rules of thumb for WG design in various applications?

Thanks,

[ergo]

It's 22mm deep.

No there is info on waveguides that they are good for equalizing the off axis behaviour between mid and high and allowing for smoother power response.

With some project there is a drawing of WG - I have attached one shot from book.

This is the basic shape that most of the finnish WG-s seem to use.

Ergo

[oneoldude]

Thanks :T

[ergo]

I opened the screws on T29CF001 to try to fit it with the WG.

T29CF001

Image not available

It appears that this also looses the plastic ring with the dome and contacts

front plate off

Image not available

dome assembly off

Image not available

But the T29CF001 without the frontplate is perfect fit for the Chorus WG - I just have to figure out how to fix the dome assembly without the front plate.

T29CF001 + WG

Image not available

Ergo

PS. Makes me want to try the Millennium like this. I own a pair of Millenniums also. It would be way interesting how the high end like Millennium will sound with WG 8O

[RonS]

ergo,

Can you post a clearer photo of that page from the Finnish book, the top of the page seems to show some dimensions.

Thx,
Ron

[ergo]

book page bigger

Image not available

not much there

130 - mouth diameter
24 - depth
39 - throat diameter

It seems this is one of older design where waveguide throat is much bigger and leaves a plain surface around tweeter.

Tweeter for this particular project is Seas H569 - 25TAF/DTV

Ergo