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Old 1st August 2011, 07:19 PM   #21
keyser is offline keyser  Netherlands
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Quote:
Originally Posted by doug20 View Post
There was a good discussion about this on HTguide.com when Augerpro was building a two. I will try and find it. We also rear mounted our woofers to try and get the AC closer together.
I considered rear-mounting of the woofer and I actually started building the speaker with such a configuration, but I didn't like the way it looked (heck, I've even got a picture of it!), so I built a new baffle with the woofer on the front.

It was indeed a bit more difficult than usual to get the crossover right, but I think in the end it turned out pretty well.

I'll have a look at the thread at HTGuide!
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Old 1st August 2011, 09:10 PM   #22
doug20 is offline doug20  United States
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I used a 3/4" round over to make it look a little better.

btw, Great pictures, Great build! Its nice to read that you had some experienced listeners over for a listen and they liked it! Its important for others to listen. Im stuck with friends and family that do not really care about differences in audio. They tend to say, "Yep, that sounds great"
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Old 1st August 2011, 10:39 PM   #23
boris81 is offline boris81  United States
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Originally Posted by keyser View Post
Last saturday I threw a party to celebrate my birthday.
Congratulations! Sounds like you gave yourself an awesome birthday present.

Are you running the open back 12" down to the lowest frequency? May I suggest you explore having a regular monopole sub at the bottom. The cardioid response already has a wide dispersion that looks like it may transition well to a monopole. I don't know if this will work, I'm only suggesting. A sub should give you enough power on the low end to not worry about the 8dB gain.
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Old 1st August 2011, 10:50 PM   #24
keyser is offline keyser  Netherlands
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Hi Boris,

Thanks!
The front speakers are highpassed at 100 hz and I'm already using multiple subs. They are a combination of passive radiator subs and a closed one. They match pretty well with the fronts. I think directivity doesn't matter much anymore below about 300 hz and I could probably get away with a higher crossoverpoint for speakers and the subs that stand right beside each one of them. That way I could increase dynamic range. But to be honest, I don't think that's necessary. The system already goes crazy loud!
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Old 1st August 2011, 11:23 PM   #25
Tytte71 is offline Tytte71  Norway
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Cool project that will be very interesting to follow

Q1: Can the design be concidered as a OB with a low pass filter for the higher back radiating frequencies?
Q2: Do you gain any increase in capacity at the lower frequencies compared to a normal dipol mount?

Best Regards
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Old 2nd August 2011, 10:16 AM   #26
keyser is offline keyser  Netherlands
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Originally Posted by Tytte71 View Post
Cool project that will be very interesting to follow

Q1: Can the design be concidered as a OB with a low pass filter for the higher back radiating frequencies?
Q2: Do you gain any increase in capacity at the lower frequencies compared to a normal dipol mount?

Best Regards

Hi Tytte71,

In this picture you can see the woofer response a 0 degrees and 180 degrees (gated, 1/24 oct. smoothing).

Click the image to open in full size.

It's difficult to say exactly what's going on, because several mechanisms are at play here.

- Driver directivity.
- Baffle- and box-shape influences.
- Interference of front- and rear-radiation
- Low-passed rear radiation of the woofer due to motor-structure.
- Low-passed rear radiation of the woofer due to damping material.
- Delay of the rear-wave due to damping material.


Click the image to open in full size.
Directivity Sonogram, ungateda 1/6 oct. smoothing.

It is evident that the damping material still has some effect at lower frequencies. Between 100 and 200 hz it looks a bit like a super-cardioid. Between 200 and about 500 hz things look a bit messy while the dispersion widens a bit, but at least directivity is greater than that of a similarly sized closed box. At higher frequencies things don't look much different than a conventional box, although there may be slightly greater directivity.

What is gained compared to a closed box is the less rapidly changing and thus more constant directivity. Compare to for instance the Gedlee Abbey (currently considered the state of the art by many):

Click the image to open in full size.

Is the better controlled directivity in the lower midrange of my speaker audible? I'm sure it doesn't hurt, but I don't know if it sounds better.

This greater directivity comes at the cost of efficiency. Efficiency in the lower frequencies is probably not much different than if it were a dipole, but the radiation pattern is. I haven't done a direct comparison between with and without the damping material, so I can't tell you for sure.
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Old 2nd August 2011, 04:22 PM   #27
Tytte71 is offline Tytte71  Norway
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Thanks that was very informative.

Looking at the songram and its irregularities between 200-500Hz, could this have something to do with the perforated cabinet that you use (caused by reflections and diffractions)?

Have you tried using the same damping material wrapped around the back of a nude driver to see if this create a more uniform response? And would this lead to loss in any properties below 200 and above 500Hz?

Best Regards
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Old 2nd August 2011, 09:59 PM   #28
Tytte71 is offline Tytte71  Norway
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Sorry, forget the above questions... it is already answered for
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Old 3rd August 2011, 11:36 AM   #29
Tytte71 is offline Tytte71  Norway
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Hope you will excuse me for nagging, but it would be very nice to also see a sonogram for vertical axis and impuls respons for the mid
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Old 4th August 2011, 07:31 PM   #30
_Wim_ is offline _Wim_  Belgium
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Fantastic thread! Now I really want to cut holes in the sides of my Abbey clones...
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