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Old 22nd December 2012, 08:17 PM   #11
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by faija View Post
Hello streten and thanks for your comments.

I am sorry but I cannot understand what you mean. If the loudspeakers are placed
inversely they are still on the same vertical axis from the x/o point of wiev.
I don't believe that gravity would play any role here.

Best regards,

Jouko
Hi,

The x/o optimum axis is tilted up so the optimum axis is the tweeter
axis. Inverting the drivers tilts it down, nothing to do with gravity.

If your tweeters are still at ear height its not much of a problem,
but typically for inverted ear height becomes the bass/mid axis.

Inverted with bass/mid at ear height would be a different x/o.

rgds, sreten.
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Old 22nd December 2012, 09:10 PM   #12
system7 is offline system7  United Kingdom
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I can see this turning into the usual confusion already.

I don't think MarkK's SEAS Reed Cone + DXT design has much relevance here beyond some vague claims of being better than the Polycone Idunn on horizontal dispersion... I thought his filter was good on the Reed bass, but quite wrong on the innaccurate Fs tweeter notch. In any event the Fs notch makes it 4th order acoustic just like the Idunn.

Robin Marshall discusses dispersion at crossover:
Quote:
Marshall: I don't believe at all in the "let's get rid of the drive-unit as quickly as we possibly can" approach. Because if you're crossing over from a large unit into a small one, you've got a radiation pattern change straightaway. If you get this business where they're both rolling off extremely steeply so you've got a very fast change between two quite different polar patterns, that's very noticeable. The coloration generated by the off-axis performance of the speaker is going to be very noticeable. On-axis, it may measure as flat as a pancake; in theory, if you could listen to the speaker in an anechoic chamber, it might sound great. But once you put it into a real live room it's going to sound awful.
Robin Marshall: A Modicum of Genius | Stereophile.com

Inverted speakers have a splendid history, as illustrated by John DeVore's interesting Gibbon8 speaker. Let's see how it goes.
Attached Images
File Type: jpg MarkK_ER18DXT_Crossover.JPG (41.1 KB, 267 views)
File Type: jpg SEAS_Idunn_Crossover.JPG (30.9 KB, 238 views)
File Type: jpg DeVore_Gibbon8_speaker.JPG (20.5 KB, 245 views)
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Old 22nd December 2012, 09:14 PM   #13
faija is offline faija  Finland
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Hei Juha,
thank you for your informative remarks. I am still in the process of learning the
theory and terms of loudspeaker design Being retired I have more time but the transformation from a legal background to acoustics and related electronics will take some time.

I fully agree with the 2Khz boost based on the graphs and it is even more visible on the woofer graph of the manufacturer. I need to listen first and then come back to find out if there are ways to filter it out without spoiling the good sides of the consept. Again, looking at the graphs it paradoxically seems that the Idunn should sound best from a 30 degrees angle which the tweeter is able to handle pretty well.
Would be fruitful from my side to talk you more frequently in the future.

In the meantime I wish you hyvää joulua aswell.

Best regards,
Jouko
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Old 22nd December 2012, 09:25 PM   #14
faija is offline faija  Finland
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Hello tvrgeek and thanks for the comment. Your conclusion is a piece of philosophy. I will try to keep it in mind and trust my ears in the first place.
I promise to measure whenever problems arise. So far I don't feel like being burned but I'll be careful.

Have a merry xmas.
Best regards,
Jouko
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Old 22nd December 2012, 09:26 PM   #15
sreten is offline sreten  United Kingdom
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Hi,

Nothing against inverted driver speakers, except the seriously very crappy
Wharfedales, which I'm proud of not being able to remember the model of.

The classic budget model being of course the Mission 700's :

Click the image to open in full size.

The x/o doesn't work half as well the other way up.

rgds, sreten.
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Last edited by sreten; 22nd December 2012 at 09:30 PM.
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Old 22nd December 2012, 10:50 PM   #16
system7 is offline system7  United Kingdom
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BTW, Jouko, I had a look at crossover issues with inverted drivers here:

The logic behind the Focal Diablo Utopia's SLANTED SPEAKER DESIGN?compared to flat...

A 2.2 kHz crossover is a slightly different animal due to the longer wavelength at crossover, but tweeter phase inversion is still worth trying.
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Old 23rd December 2012, 06:49 AM   #17
Juhazi is offline Juhazi  Finland
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Guys,
I sort of cut the corners in my previous messages
I'm not expert enoght to desing speakers but this is what I have read:

The design axis is what the designer decides to use when he is measuring the spakers and he/she tries to make this on-axis measurement as good as possible. The position of mid and tweeter drivers( vertically and horizontally), the proportions of the baffle and the type of xo contribute to radiation pattern and directivity.

Typically a 2-way with 2nd order LR xo, the polar radiation tends to be tilted to the woofer's side. This is why many speakers utilizing this concept have the tweeter below. Like Mission above and many speakers of Harri Huuhkaja

The DXT has it's voice coil and membrane (the acoustic center) a little more back than conventional tweeters, and that makes it easier to make a LR2 xo with a tweeter above the midwoofer. John Krutke tells obout this in his TMM page Zaph|Audio

And finally here is Stereophile Magazine's story on measuring dispersion Measuring Loudspeakers, Part Three Page 7 | Stereophile.com

Jouko, I live in Jyväskylä but you can email me juha.sirkka(miukumauku)fimnet.fi

System7, thank you for your wise and nice writings here at diyaudio.com!

Merry Christmas to all of you!
Juha
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Last edited by Juhazi; 23rd December 2012 at 06:51 AM.
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Old 23rd December 2012, 07:35 AM   #18
Juhazi is offline Juhazi  Finland
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And here is Zaph's graph of vertical polar pattern that I wanted to show

System7, can you please specify the ER18DXT tweeter notch problem?. Mark says that he used the two notch circuits to achieve acoustic 2nd LR. XO is electric 1st order an drivers' own roll-off makes acoustic 2nd LR.

By the way I made Zaph's LR18 first but was not happy. Then I used that box and converted it to ER18DXT and now I'm happy (avatar pic). Zaph himself has said that MarkK's speaker is an upgrade to his SR71 which uses the same reed cone midwoofer. The L18 has conventional LR4 xo and a quite bad horizontal dispersion by today's standards.

Also I'd like to thank You sreten for your wise and nice writings here at diyaudio.com!

Juha
Attached Images
File Type: gif WaveguideTMM-minimalist-vertoffaxis-1400-3200-200step.gif (15.0 KB, 215 views)
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Last edited by Juhazi; 23rd December 2012 at 07:58 AM.
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Old 23rd December 2012, 10:51 AM   #19
system7 is offline system7  United Kingdom
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Juhazi, you are hijacking the thread with too much discussion of MarkK's ER18DXT project.

FWIW, MarkK and I had a heated and interesting discussion of the supposed advantages of his "First Order" DXT tweeter filter here:
Erse inductors in europe ?

In practise it turns out to model almost identically to the much simpler third order DXT tweeter crossover in the SEAS Idunn. That is when it is accurately and properly executed, which his IS NOT!

His filter and speaker is goodish overall, but not for the reasons he thinks. Too much Snake Oil in this game. It doesn't make me popular to point this sort of stuff out, but someone's got to do it.
Attached Images
File Type: jpg 3rdOrder_versus_1stOrderwithFsNotch.JPG (153.6 KB, 54 views)
File Type: jpg 3rdOrder_versus_1stOrderwithFsNotch_Phase.JPG (96.2 KB, 46 views)
File Type: jpg SEAS_Idunn_Type_Filter.JPG (23.9 KB, 50 views)
File Type: jpg MarkK_ER18DXT_Type_Crossover.JPG (24.9 KB, 51 views)
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Old 23rd December 2012, 11:00 AM   #20
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Juhazi View Post

Typically a 2-way with 2nd order LR xo, the polar
radiation tends to be tilted to the woofer's side.
Juha
Hi,

Not if you make the output purposely slightly assymetric
for both LR2 and LR4 acoustic to tilt the optimum axis.

Here is an example of assymetry to fix path length differences :
My RS180 MTM Design
Note the perfect phase wrap at the x/o point.

rgds, sreten.
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