Do drivers shake their mounting boards? - Page 3 - diyAudio
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Old 30th December 2010, 11:03 PM   #21
anatech is offline anatech  Canada
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Hi Nigel, sreten,
I can't disagree at all.

Speaker "box" design is still an engineering trial, for the cost and weight. Anyone can make something pretty darn good is cost is not an object, but once you have to sell the design, everything changes. A budget appears out of nowhere.
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Old 31st December 2010, 12:39 AM   #22
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Hello all,

To go In the same way than Planet (and to give a little temptation to c2ct), I can give you a real life advice:

the enclosed dipole push pull is worth the try in some cases.

I could compare it with the same 15" mounted in 2 H-frames.

First great improvement, all the distorsions in the 20/30 Hz area are gone. And with steel baskets drivers, these distorsions can even be described as aerodynamic noise, it's very annoying.

Second great novelty, as I came from H-frames, no more very big dipole peak. Even properly equalized, a king of harmonics always stayed, here, it's cleaned.

As a trade off, efficiency is 6 dB down, but the power handling increase is more than 6 dB.

Absolutely no pressure in the box, as I removed the dust caps on vented drivers, it's still more obvious.

Of course, as the drivers are out of phase, there is no mechanic cancellation, but with a heavy box it's not a big issue at domestic levels.


I use this with massive EQ ( 20 Hz +15 dB, Q=4 with low shelving 6 dB starting at 50 Hz, no LT here), but the head room is just limited by the rattle of the house.

Since 3 years I use this, it's no way that I could be back to open dipole.
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Old 31st December 2010, 12:44 AM   #23
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I think it's all about forces, and the forces are created by the bi-directional cone movement acting against the speaker frame. Imagine the cone in the most inward position, and then it starts the movement towards the other extreme. What is it that stops the cone from leaving the box? The attachment with the surround and spider, who in turn is attached to the frame. So, when for example, the forward motion of the cone is stopped by the surround and spider, forces are acting on the frame and propagates to the box. That is why some builders recommend that you use rubber grommets when attaching the driver to the box. That's more or less how a tech paper I have at home explains this phenomenon, at least as I recall it.
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Old 31st December 2010, 01:12 AM   #24
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Ooops, I'm back on-topic, prior to the introduction of that engaging push-push discussion.

If it is all so obvious and Newtonian why an OB baffle shakes, just why doesn't a sealed box do the same thing since the cone, basket, magnet, and board and assorted pendulums are there? (Sealed boxes have vibrating panels but the box doesn't shake, does it?)

Maybe it has to do with the way the rear wave exits my OB. The giant board is mounted 90 mm from the wall and parallel to it. Perhaps there are no feelable consequences till the frequencies get down to whole-assembly resonance territory and then the whole assembly starts shaking. Or course the area where the sound "exits" the cone is nearly 200 sq inches and increases with distance outwards - so not a high pressure.
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Old 31st December 2010, 01:15 AM   #25
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Quote:
Originally Posted by MisterTwister View Post
I don't think push-push will work on open baffle. There will be no bass at all.
Both drivers must move synchronously in the same direction, push-pull.
Push-push drivers are wired so that they both push at the same time and pull at the same time. Acoustically they act like any other pair of drivers wired in phase. To get no bass at all you'd have to wore them acoustically out of phase -- that would be a wiring error.

dave
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Old 31st December 2010, 01:18 AM   #26
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Quote:
Originally Posted by anatech View Post
Are they open to the sides Dave? Top and bottom also? Because you have a pair of baffles so close together, I'm not sure it acts the same way as the classic open baffle design. You have some acoustical passages there.
At the LF frequencies involved it would be effectively the same as a flat baffle. the entire mass of air in the slot would act as one large radiator

dave
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Old 31st December 2010, 01:21 AM   #27
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Quote:
Originally Posted by bentoronto View Post
just why doesn't a sealed box do the same thing since the cone, basket, magnet, and board and assorted pendulums are there? (Sealed boxes have vibrating panels but the box doesn't shake, does it?)
But they do. Panels tend to be smaller and better braced in a sealed box than an OB. So they shake at higher frequencies... you have heard (or seen) subwoofer boxes "walk" haven't you?

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Old 31st December 2010, 01:27 AM   #28
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Quote:
Originally Posted by planet10 View Post
But they do. Panels tend to be smaller and better braced in a sealed box than an OB. So they shake at higher frequencies... you have heard (or seen) subwoofer boxes "walk" haven't you?

dave
No, I have never heard of that - maybe I've been living isolated in carpeted environments - but I do not doubt your word. But a speaker with vibrating panels might walk due to panel vibration, not whole-box vibration which I think is something quite different.

Someone earlier suggested things like that happen with cheap woofers. I thought it was churlish of him to suggest my speakers might be cheap ones and I would never say that to any owner of walking boxes, but what if his theory is right?
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Old 31st December 2010, 03:26 AM   #29
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Last edited by MisterTwister; 31st December 2010 at 03:55 AM.
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Old 31st December 2010, 04:37 AM   #30
anatech is offline anatech  Canada
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Hi Dave,
Okay, around what frequency will the design depart from something like an OB type speaker. What I find attractive is that the out of phase rear wave looks like it's not as important. Since I haven't played with anything even close to this, I'm somewhat at a loss as to it's character.

I do like the idea.

-Chris
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