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Old 27th January 2010, 12:12 AM   #31
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Cuibono, does the foam help the on-axis dip and the curve crossing around 7-8K? From your and Michael's measurements, that seems like the biggest problem with the naked dipole Neo3-PDR.
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Old 27th January 2010, 12:31 AM   #32
cuibono is offline cuibono  United States
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Yes, it does help some, IIRC. The thing is though, my impression is that errors that high in frequency are less of a problem, so to me the 8kHz dip isn't to much of an issue.

I have measurements somewhere, I'll try and post sometime soon.
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Old 27th January 2010, 01:36 AM   #33
cuibono is offline cuibono  United States
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Here are a couple of graphs of the Neo3PDR with and without foam edges. The foam is a nice little tweak - it does help the 8kHz notch, and at 30deg off axis, the response is almost flat and doesn't need any EQing.

I currently XO these LR4 at 1700Hz, but I'm tempted to go lower, just to see what happens. In theory, it might be a small improvement (wrt vertical lobing), but I suspect it wouldn't make enough difference. I'll probably try it sometime though....
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File Type: jpg Neo3_wo_foam.jpg (135.2 KB, 1015 views)
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Old 27th January 2010, 05:15 PM   #34
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That's a nice improvement with the foam!
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Old 10th February 2010, 10:02 AM   #35
keyser is offline keyser  Netherlands
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Great topic!
I am currently using a Visaton AL170 as an unbaffled midrange. The disadvantage with smaller drivers is that the magnet and spider are relatively large compared to the size of the cone. The AL170 has a relatively small magnet and spider and does better than any other 6.5" I've seen measurements of. See the pictures at Visaton - Lautsprecher und Zubehör, AL170


Click the image to open in full size.

Maybe I should have used some smoothing here, as there are a couple minor reflections within the time window.

In my Unbaffled Dipole I am using the B&G Neo3W, not the PDR version. I decided on the Neo3W because simulations indicated that its beaming at higher frequencies would be of benefit in keeping the radiation pattern constant, but your measurements look nice too! I've got a pair of PDR's on the shelve, so maybe I should give them a try.
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Old 17th February 2010, 03:40 AM   #36
cuibono is offline cuibono  United States
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Hi Keyser,

Nice graph. When I look at spider/magnet size, it is not so much about its size relationship to the cone, but more the width of certain wavelengths in relation to the spider/magnet. When things have certain dimensional relationships, sideways reflections are caused, which is undesirable from a constant directivity point of view. Ventilation around the back matters too, but that seems harder to predict.

I'd be very interested to see side by side measurements of a neo3 and neo3pdr - I figured things differently than you. I think this has been said in another thread, but to maintain a true dipole figure of eight pattern, the driver must be radiating to the sides (equally). Without the acoustic interference (difraction) on the sides, the figure of eight pattern cannot be formed. So I guessed that the Neo3PDR, which has a wider radiation pattern higher up in frequency, should maintain a more regular dipole pattern. But really though, I bet it doesn't matter too much.

It would be good to see though, especially with longer gate times (aka, higher resolution).




SOOO..... I hope nobody ordered any TB W4-656sc drivers. I've had four here so far, and they all buzzed. I don't know why, they do it right out of the box. It isn't super loud, but it is not too hard to hear either. Pretty obvious on music.

So, I went with what should be a better driver, but also $20 more, the TB W4-1320sj. It has a much smaller magnet, and much better rear ventilation, I've attached a picture. It also has shorting rings in the magnets, so it should have better nonlinear distortion performance. I'll get it on the bench tomorrow hopefully.
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Old 17th February 2010, 07:55 AM   #37
keyser is offline keyser  Netherlands
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Quote:
Originally Posted by cuibono View Post
When I look at spider/magnet size, it is not so much about its size relationship to the cone, but more the width of certain wavelengths in relation to the spider/magnet. When things have certain dimensional relationships, sideways reflections are caused, which is undesirable from a constant directivity point of view.
Could you say a bit more about what you think are better or less good ratio's?
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Old 17th February 2010, 10:53 AM   #38
Rudolf is offline Rudolf  Germany
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Quote:
Originally Posted by cuibono View Post
When I look at spider/magnet size, it is not so much about its size relationship to the cone, but more the width of certain wavelengths in relation to the spider/magnet.
I don't buy into that. I have done some measurements with three small FR drivers (Visaton FRS8, Fostex FF85K and FE 83). They are almost identical in outer dimensions (the FF85k having a somewhat larger magnet), but vary quite much in frequency response to the rear. Putting more width or depth to the magnets did change almost nothing.

Quote:
When things have certain dimensional relationships, sideways reflections are caused, which is undesirable from a constant directivity point of view.
For any effective reflection the reflecting surface would have to be much larger than the wavelength of the reflected wave. With my FR drivers the most significant differences between front and rear were around 2 kHz - even in a driver without baffle. This would need dimensions from 17 cm up to induce reflections. The largest "flat" surface on those drivers was 2 cm wide. Ergo: Any concept of reflecting waves does not apply.

Quote:
Ventilation around the back matters too, but that seems harder to predict.
That's the point! It is the Helmholtz resonators formed between the cone and the basket (and perhaps the mounting conditions) which make up for most of the backward peculiarities. Having a very open basket (like the AL170 and the TB 1320) surely helps. Opening up the driver cutout is beneficial too. But you really can't predict from a look at the basket, how it will behave.

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Old 17th February 2010, 05:45 PM   #39
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The new Scan-Speak Discovery 10F/4424G looks interesting for a 'naked' mid. Frame under 4", nice FR and impedance curves and lower priced than most SS drivers.

Scan-Speak Discovery 10F/4424G, 4" Midrange from Madisound
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Old 17th February 2010, 07:36 PM   #40
cuibono is offline cuibono  United States
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Honestly, I don't know enough about the wave physics or the exact dimensions needed for reflections to happen - but there seem to be some basic relationships. The smaller the magnet, and the farther it is from the cone, the better, in terms of regular dipole response, at wide angles. Not really news, probably.

I'm guessing though, that there is a relationship between magnet/basket/spider size, and the reflection frequency - up till now, I've guessed that reflections occur at a frequency of roughly half wavelengths, wrt the magnet structure. IE, magnets are 4" to 6" wide, and the 90deg reflection abnormalities occur between 1-2kHz. Distance to the cone matters, but there seems to be an approximate relationship there.

Anyway, if I'm lucky, I'll get to take some measurements today, and post them.
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