Waveguide shootout - part 2

[paulspencer]

Hi guys, some of you will have seen the results of our previous shoot out where we measured and listened to various popular waveguides and compression drivers in one day.


http://www.diyaudio.com/forums/full-range/181253-waveguide-shootout.html

Here is part 2.

Who is we? A small group of Aussies into DIY who are building speakers with waveguides and compression drivers. Previously we changed more than one thing at a time, but here we wanted to get a bit more nitty gritty.

We found that the Selenium titanium compression driver used on the Econowave was quite harsh. We used both times some torture tracks intended to reveal any harshness. It's not subtle - you hear it and wince. We wanted to know if the waveguide or the compression driver were to blame.

This time we found that when we put a better CD on the waveguides, the harshness was much less. Put the B&C DE250 on the Econowave style JBL clone and it will play very loud and clean without that harshness.



Here is how it measures:



Does that look good or does that look good?!

Full details here:
http://redspade-audio.blogspot.com/2...ide-gtg-2.html

[gedlee]

The ARTA polar maps always look so heavily smoothed compared to what I get. Do you have any idea what smoothing is used? With a polar map there are two dimensions that can/should be smoothed so just knowing the frequency one is not enough. I never see anything as smooth as what you are showing above and I've seen a lot. I know exactly how much smoothing I use and ARTA always looks like a lot of smoothing.

[mayhem13]

Great Job guys! The B&C again proves it's overall superiority as CD. IMO the best $$$ to donuts option available.

[paulspencer]

First reply comes form Mr Waveguide himself!

I don't know how much smoothing. One of the other guys was running the measurements both times - learning how to drive Arta properly is on my to do list. But as you say it does look smoothed. Also keep in mind that you are seeing a normalised plot, which makes it look better. We want to see there what the directivity would look like relative to a perfectly flat response.

What do you use to measure, Earl?

I like to see both, although I also keep in mind that with axi-symmetric guides, I might want to see the non normalised plot if I'm going to toe them in to avoid the axial dip Earl talks about. That particular one is the JBL clone shown in the picture above it.

Mayhem,
The B&C was as good or better than the BMS 4550 and Faital pro HF100TX. I want to do more comparisons, but my feeling is at this point that those other two are quite comparable where the response is the same. The B&C is smoother on the top end than the Faital and appeared to give a better response overall. The BMS has some extra efficiency in the mid band, it appears they went for as much as they could get, but could not maintain it over the full range. That means you have to do some extra EQ to pull back the midband, but the B&C needs less work to get flat. In fact, in my little 6" oblate waveguide, if measured at the mouth, it's ruler flat as if it were a good dome tweeter measured in an anechoic chamber!

One of the perks of hosting this GTG is that some of the guys left some of their bits with me. I've had a chance to do some more comparisons of my own.

One of the things we have learnt, which was not too surprising, is that a good polar plot does not necessarily mean it sounds better. The Selenium compression driver for example yielded by far the worst sounding results. From memory, it measured exceptionally well on the Dayton 10" waveguide, which has a profile that I don't quite know what it is. We found though that this waveguide and the Selenium driver were the worst sounding. By that I mean, they had the most harshness.

When I figure out how to cut it, I'll be putting foam in 3 of the waveguides.

[gedlee]

Originally Posted by paulspencer

What do you use to measure, Earl?

I use HolmImpulse to take data at the polar angles, but the analysis techniques and plotting that I use are all custom software. This is how I know how important the smoothing characteristics can be. Yes, I did not realize that the data was normalized, that too makes everything look better. I don't like normalization because it wipes out resonances. And it will make an axial hole look completely unrealistic. Unnormalized is what you are listening to so thats what you should look at.

[pos]

Very interesting test, thank you Paul!

from the conclusion page:

If you already have the Selenium driver, the good news is the sound can be improved a great deal.

Could you please elaborate?

It would be interesting to add some "vintage" titanium compression drivers like the JBL 2416H (screw-on budget CD used in the 4425 studio monitor) and 2426H (used in the 4430 studio monitor, and has an integrated adapter to fit both screw and bolt horns) to the test, to see if the problem with the selenium driver is purely due to the fact that it is titane.

[paulspencer]

Could you please elaborate?

Replace the Selenium with the B&C! That's what I meant. It isn't expensive.

It would be interesting to add some "vintage" titanium compression drivers like the JBL 2416H (screw-on budget CD used in the 4425 studio monitor) and 2426H (used in the 4430 studio monitor, and has an integrated adapter to fit both screw and bolt horns) to the test, to see if the problem with the selenium driver is purely due to the fact that it is titane.

The problem I see with this is anything vintage usually has an inflated price because of the perception of having some kind of magic. These drivers get viewed through rose coloured glasses. I had a look the other day at an Altec 1 3/4" CD ... huge! (As they all are at that size). The designs haven't changed much from what I can see.

A new driver like the B&C is cost effective with no premium added for some vintage aura of magic. You simply pay for something decent and well designed.

I'd like to spend some time comparing to the other drivers, I think they are probably quite comparable. The other two have annular diaphragms.

I have photos of them as well on the blog:

Red Spade Audio: Introducing B&C DE250

[MunkeyQ]

Have you looked at the 1" Celestions yet? I'm running a CDX1-1745 (as used in the QSC HPR152i) and it sounds very nice now I've managed to sort out the CD EQ. That same 1.4" diaphragm is used in the 1731 and a couple others too.

[6.283]

Originally Posted by paulspencer

I don't know how much smoothing. One of the other guys was running the measurements both times - learning how to drive Arta properly is on my to do list.

The smooting is adjusted upon creation of the polar map (in the Window where you load the .pir files).
Arta offers 1/1, 1/3, 1/6, 1/9 and 1/12 Oct. 1/3 Oct. seems to be the default.

[gainphile]

Smoothing was 1/3 octave. Gating 5ms.

This was outdoor but with heavy wind. Otherwise I normally don't gate. Distance is 200cm.

Selenium's harshness is due to 12khz resonance. This is effectively mitigated by notching that frequency.