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Old 19th March 2007, 12:02 PM   #41
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THD.

Same method, 125mm etc. But instead of changing levels, we change frequency - 100dBSPL was chosen.

First 1KHz- the lower the frequency, the greater the demand on the tweeter.

D30 :

Click the image to open in full size.

That looks like high THD - 1.325% - but it is dominated by the 2nd.

HDS:

Click the image to open in full size.

Yes, the THD is lower, but look closely. In D30 the 2nd is greater than 3rd whereas HDS 3rd is greater than 2nd. This makes the Total Harmonic Distortion figures misleading.

Let's go onto 2KHz.

D30:

Click the image to open in full size.

Still dominated by 2nd, but 3rd is just noticeable and higher suppressed.

HDS:

Click the image to open in full size.

Lower 2nd but higher 3rd.

Now 4KHz.

D30:

Click the image to open in full size.

Nicely cascading - a good sign a la Jean Hiraga.

HDS:

Click the image to open in full size.

Pretty much a draw here.

OK, where does this get us? Note that in every set of plot HDS measures lower? Yes, THD is misleading, only by breaking the figure into individual harmonic components can we see the real picture.

The winner. Curiously that every THD favours HDS, yet as above D30 is a narrow winner.

What do you think?

Joe R.

Next: IMD Tri-Tone Tests.
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Old 19th March 2007, 12:58 PM   #42
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IMD Tri-Tone Tests.

This is the last 'chapter.'

The Tri-Tones will be centered around 1KHz, 2KHz and 4KHz. Two out of three adjusted to 100dBSPL @ 125mm.

1KHz

D30:

Click the image to open in full size.

HDS:

Click the image to open in full size.

2KHz

D30:


Click the image to open in full size.

HDS:

Click the image to open in full size.

4KHz

D30:

Click the image to open in full size.

HDS:

Click the image to open in full size.

The winner? This time you tell me. The calculated IMD figure overwhelmingly favours HDS - what do you think?

So there you have it. Spend some time analysing the graphs, maybe you noticed something I didn't? I have tried to keep running comments to a minimum, only guiding where I feel appropriate. Where I have discussed a so-called 'winner' it is only to point that summed distortion figures - and hence into a single figure - can be misleading. This alone should be discussed.

Other factors: If you are assembling a 4 Ohm speaker system and don't mind paying the extra money, then you should consider the D30. But if you are aiming at a sensitive speaker system and 8 Ohm, then HDS is for you. If cost is a consideration (Madisound lists a 3.7:1 price ratio), then the HDS is made for you!

The final thing that stands out is in relation to D30: The shelved 2nd order distortion. There seems to have been made a conscious decision to trade off greater 2nd harmonic distortion for a lower level 3rd. This alone strikes me as the single overall most important conclusion regarding its behaviour and maybe why these two samples here measure differently than earlier 2006 samples (these are definitely 2007).

Over to you guys!

Joe R.
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Old 19th March 2007, 02:37 PM   #43
Zaph is offline Zaph  United States
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Quote:
Originally posted by Joe Rasmussen
The winner? This time you tell me. The calculated IMD figure overwhelmingly favours HDS - what do you think?
Thanks for the tests, Joe. It's good to see this level of thoroughness.

The calculated IMD% number, like THD, is heavily weighted by 2nd order products. A good way to compare these is to just drop one on top of the other to compare the whole spectrum. We'll call that Mark K style, since he's the only guy I see doing that. Praxis has it built in, but if I want to do it in SE, I have to use an image editing program.

Your results are actually very close to both mine and Mark's, done on 2006 tweeters. The SPL of the 6600 seems to be the same, and the only real difference seems to be minor variations in the top octave.

Unfortunately, there's minor variations in the top octave for all the 6600's from 2006. I've tested 4, my own pair and another pair, and just about every one had a mildly different top octave. Peak at 20kHz (2), dip at 12kHz with a plateau above (1), and perfectly flat out to 35kHz (1). I don't put a lot of value in the top octave response, as long as it's somewhat there. The important part of the response curve starts at the low end, IMHO.

Thanks,
John
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Old 19th March 2007, 10:51 PM   #44
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Quote:
Originally posted by Zaph

Thanks for the tests, Joe. It's good to see this level of thoroughness.

I'll take that as praise.

Quote:

The calculated IMD% number, like THD, is heavily weighted by 2nd order products. A good way to compare these is to just drop one on top of the other to compare the whole spectrum. We'll call that Mark K style, since he's the only guy I see doing that. Praxis has it built in, but if I want to do it in SE, I have to use an image editing program.

I have SE V13, but I don't, have not, used the data acquisition part of it (I've had various versions down to V1 - that virtually made me a beta-tester). I supposed you have pestered Bohdan about it. He only lives down the road from me, the road is called the Hume Highway. OK, it's 1000K but it's still down the road.

But is this what you are looking for:

Click the image to open in full size.

The maroon line tracks the Total Harmonic Distortion, but is totally dominated by red, the 2nd harmonic. This proves your point.

You are saying that Praxis does this and SE not? This is ClioWin 7.03 (very latest) and is a dodle.

Quote:

Your results are actually very close to both mine and Mark's, done on 2006 tweeters. The SPL of the 6600 seems to be the same, and the only real difference seems to be minor variations in the top octave.

I don't put a lot of value in the top octave response, as long as it's somewhat there...

In these two samples, the top averages out flat in the top 10-20KHz octave off axis. This is a plus with me and an advantage over both XT25 and HDS. Yet to hear D30 but I suspect it will have some 'sparkle' and I mean that in a nice sense. But I am very familiar with the sound of HDS - it's a terrific performer. What is of concern is D30's sample variations from a manufacturing point of view and as the company I am associated with is considering using this in a design.

Quote:


The important part of the response curve starts at the low end, MHO.



I didn't quite nail that in my FR plots, my baffle not large enough. But the depression is common in all three FRs and you can see past it on that basis. My baffle needs to be closer to IEC size.

Re bandwidth: The HDS is further down @ 1KHz but can be pushed hard to bring it up to matching measurement level of D30. To match this level is emphasizing 3rd a bit in some of the plots? As I have used the HDS in a system, I have used 1st order down to 1500Hz approx (from 3KHz) but engineered a response 4-5 order below that. It's about a controlled low end of the bandwidth to get lowest distortion. This may well help cancel out some of the higher 3rd, compared to D30?

John, did you ever look at a tweeter response when not flush mounted. YIKES!

Joe R.


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Old 19th March 2007, 11:41 PM   #45
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Hi John

I just realised that I misunderstood you, you were speaking re the IMB multi-tone graphs and that Praxis can do overlays. But the THD sample shows that ClioWin can do overlays as well, both THD and IMD.

The last overlay always sits on top and the is what Mark uses to advantage.

Joe R.
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Old 20th March 2007, 12:30 AM   #46
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Hi,

For Windoze users out, the quick way I like to do overlays, is in MS Paint.

Start -> Accessories -> Paint

Paste your first picture in. (use Paste or Edit->Paste From...)

On the left panel, click on the Image Overlay icon. (see attached image #1)

Then paste your 2nd image in.
(see attached image #2- 1.3KHz comparison-HDS blue, D30 red)

Then quickly tap <Ctrl>-<Z> (Undo) <Ctrl>-<Y> (Redo) to get a feel for the differences.

And, yes, I'm sure there's an easier way to do it in OS-X, but meh.
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Old 20th March 2007, 12:40 AM   #47
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Default 1.3KHz comparison- HDS blue, D30 red.

An example-
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Old 20th March 2007, 05:01 PM   #48
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Yup, that's a similar thing that I have to do with SE to show one IMD on top of another like this. Otherwise I can only show one driver at a time. Praxis does a lot of things that SE can't but for the price I can get by with SE. Hell, I could probably get by with the Arta demo and SW for $0.

I've got a pair of 2007 6600's on the way soon to compare to the 2006 version, but based on Joe's results I'm not expecting major differences.
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Old 20th March 2007, 09:23 PM   #49
dlr is offline dlr  United States
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Default To throw in some more measurements

I've got the 6600 from Mark for testing. I've done all of the measurements and tried a small tweak, of limited to no use, but haven't put up a page yet.

Click the image to open in full size.

One of the benefits of the 6600 is supposedly to have the increased output down low (which it does) while having the dispersion of a 3/4" tweeter (which it doesn't). I finally set up and measured a bunch of drivers at 90 degrees recently. The 6600 is 3db lower than the OW1 at 7K and continues to lose ground above that until about 12K, at which point it does exceed the OW1. It's too late at that point in my book.

Curiously, at 90 degrees the RS28 is about an even match in absolute terms. My plan is to set up a bunch of graphs to show the 90 degree response normalized to the drivers own on-axis response as something of a dispersion indicator.
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Old 1st April 2007, 03:47 AM   #50
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Default Waveguide

Hi Guys

Just as an afterthought, come back to the earlier posted posted graph that shows the family of OFF axis of Scan-Speak D30 (RED), new Peerless HDS (BLUE) and Vifa XT25 (GREEN):

Click the image to open in full size.

It's the XT25 that is of interest here. Now note below the same tweeter that I have measured with a square waveguide used in my Elsinore Project speakers:

Click the image to open in full size.

Both are calibrated dBSPL measurements and 25 degrees OFF axis.

Ignore the rise below 3KHz (that is caused by the waveguide). It's higher up that interests me. Compare the XT25 being -20dB at 20KHz and the results when using a waveguide. The OFF axis response does not seem to drop off anywhere near as when it is flush mounted to a largish flat rectangular baffle.

Any comments on this? Has anyone else observed something similar? I suppose, what I am asking, does a waveguide bolster the OFF axis, in this case 25 degrees (the wave guide is much shallower than that).

There was a review of the Lipinski L707 speakers in December 2005 Stereophile that also used a waveguide (staggered foam) with XT25 tweeter. The technical side of the review showed surprise that the off axis was that good since it was using THAT tweeter. "Unusually for a ring radiator tweeter... doesn't get as directional at ultra-sonic frequencies as other designs I have measured."

Any thoughts?

Joe R.
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