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Multi-Way Conventional loudspeakers with crossovers

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Old 15th October 2018, 04:29 PM   #211
Paul Vancluysen is offline Paul Vancluysen  Belgium
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Again a long story, I did some analysis of the DI of both midrange and tweeter in the Monkey Box, both drivers without waveguide.
At first the comparison the DI of both drivers on infinite baffle and in the Monkey cabinet.
In the plots the most smooth DI is on infinite baffle.

midrange
DI midrange in cabinet and on infinite baffle.JPG

tweeter
DI tweeter in cabinet and on infinite baffle.JPG

For the midrange the DI in the cabinet is mapping on the infinite baffle DI (= no impact of cabinet) down to 1kHz and below 1 kHz the DI in the cabinet becomes higher due to the bafflestep of the cabinet. Applying a waveguide to it (like with the Volt VM752), probably the irregularity around 1.8 kHz will become better, and the DI will become a little higher above 1kHz. But the bafflestep boost below 1 kHz will not be changed by a waveguide.

For the tweeter the DI in the cabinet is mapping on the infinite baffle DI down to 3kHz. Below 3 kHz the DI in the cabinet has a dip at 2.5 kHz. This dip is related to the tweeter distance from the top of the cabinet, which is now 9 cm. Below 1 kHz the DI becomes higher also due to the bafflestep, just like the midrange. Applying a waveguide to the tweeter, probably the dip around 2.5 kHz will disappear. The bafflestep boost below 1 kHz also will not change. Above 3 kHz the DI will become higher.

By increasing the tweeter distance from top to 15 cm, the DI dip appears at a lower frequency, see in the plot below. Maybe a better match with the midrange can be obtained for a more flat combined DI with X-over.

tweeter 15 cm from top
DI tweeter in cabinet 15 cm from top and on infinite baffle.JPG

Looking to the combined DI with LR4 filter at 2500 Hz without waveguides.
DI combined LR4 2500 Hz.JPG

Adding a waveguide to the tweeter the dip at 2500Hz will be better. The dip around 1 kHz, I am afraid it will not disappear by a midrange waveguide like implemented in the Volt VM752, we have to check that with measurements on the Volt driver.
Applying the tweeter waveguide will increase the DI above a few kHz and decreasing the global power of the tweeter. I am afraid that maybe that power loss is not so good in combination with a 3 inch midrange. In combination with a larger midrange, it is different, now I have some doubts about the tweeter waveguide. I think we can evaluate that with IEC tests and simulating the global power of the design.
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Old 15th October 2018, 05:20 PM   #212
mbrennwa is offline mbrennwa  Switzerland
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Paul... This good stuff!

I guess we will have to see what the measurements say. In particular I believe the VM752 starts beaming quite a bit earlier than what Leap predicts for a conventional 3" driver. My goal would be to match the tweeter dispersion to that of the mid at xover, and have smooth dispersion above that.
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Old 16th October 2018, 06:19 AM   #213
KaffiMann is offline KaffiMann  Norway
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Originally Posted by mbrennwa View Post
... gofoundme campaign. If you want me to move ahead with building a first prototype for testing purposes, please support the campaign here. I you want to be included in the list of sponsors, please state your diyAudio user name in the comments of your donation.

For those of you who are actively participating in the design process or those who are interested in helping with fund raising, please send me a PM with your email address so that I can add you to the "team" of the gofundme campaign.

For those of you who are more into social media than me (i.e., most of you), please share the gofundme campaign so the project gets a bit more exposure in the right places.

Let's see how this goes.


P.S.: I guess I'll get both the Faital and the D.A.S. woofer so that we can compare them better.
Bumping this.
Looking forward to impressions of build quality on the drivers involved, as well as the results from measurements.
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Old Yesterday, 04:38 PM   #214
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by KaffiMann View Post
Bumping this.
Looking forward to impressions of build quality on the drivers involved, as well as the results from measurements.
The D.A.S. 12P woofers arrived today. I made a few photos and some first impedance measurements (attached). The build quality of the drivers looks good to me, and the impedance curves match nicely. The woofers are now breaking in (15 Hz sine at 10 Vrms over night). I will take proper impedance measurements after break in.
Attached Images
File Type: jpg DSC08544.resized.JPG (775.5 KB, 84 views)
File Type: jpg DSC08547.resized.JPG (838.7 KB, 83 views)
File Type: jpg DSC08546.resized.JPG (729.5 KB, 83 views)
File Type: jpg DSC08548.resized.jpg (206.3 KB, 85 views)
File Type: png DAS_12P_impedance_before_breakin.png (31.4 KB, 87 views)
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Old Yesterday, 05:01 PM   #215
Paul Vancluysen is offline Paul Vancluysen  Belgium
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Hi Matthias,

Super! We can already start with TSP check .
If you have the frd's of impedance responses, they are welcome.
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Old Today, 12:36 AM   #216
KaffiMann is offline KaffiMann  Norway
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Beautiful!
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Old Today, 09:24 AM   #217
mbrennwa is offline mbrennwa  Switzerland
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Quote:
Originally Posted by Paul Vancluysen View Post
We can already start with TSP check .
If you have the frd's of impedance responses, they are welcome.
The drivers first need some break-in to loosen the suspension parts. After a few hours of 15 Hz sine @ 10 Vrms this night, the resonance frequency decreased a bit from 52 to 48 Hz, and the impedance peak max. increased from 77 to 93 Ohm. This is not yet consistent with the datasheet says (42 Hz, 200 Ohm max.). I'll continue with the break in and see what happens.
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