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Old 19th October 2012, 12:00 PM   #21
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Perhaps you could float the centre baffle board...
Reverse two diagonal drivers as suggested before, for both weight distribution and distortion.
Suspend from top of cabinet and fill gap with soft flexable filler.
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Old 19th October 2012, 06:14 PM   #22
DrBoar is offline DrBoar  Sweden
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zmyrna have you seen OBL11
I have the same 10" drivers as you, and 8" cloth suspension as well as many of those 1.5" cone tweeters. My plan is to build something like the OBL11 but use the 4x 10" instead of the 15" and merge with the xover of BLACKCONES

I built a H-frame for the 10" units and noticed a lot of vibration to my surprise. Spending a thought on the problem it obvious that the pressure differences across the frame is as high as in a closed box ( above high pass) and as much motion induced vibration and this into a structure that has less intrinsic bracing than a box structure. So when I will build the baffle mass and braces will be prominent!
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Old 22nd October 2012, 08:25 AM   #23
zmyrna is offline zmyrna  United Kingdom
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Here is the background of my speaker building story and my goals:
I have severe tinnitus and am very sensitive to upper mid and HF distortion / ringing.
Several years ago when I first put my hands on an Oskar Heil Syrinx by chance, it was a big revelation. The dipole AMT tweeter was cleaner, more open and more dynamic than the dome tweeters I have had before.
Since then, the dipole AMT kept growing on me while the shortcomings of the slow 7" woofer became more apparent.
I became convinced that the openness and dynamics need to be extended to mids and bass.
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Old 22nd October 2012, 09:00 AM   #24
zmyrna is offline zmyrna  United Kingdom
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@DrBoar
I am so glad to hear that you have the same drivers and plan a similar design.
I really love those blackcones and my initial plan was to build an all blackcone dipole.
10" Seas 25TVs are very well regarded (Dynaco A25). But after having them up and running on a prototype, I think they are not efficient and dynamic enough for my build.
They might bland well if you go active with Eq and combine them with rubber surround mids (as in Nao Note and Orion).
Each 25TV is around 90dB/1w. Two would make 93 and four 96dB/1w. We need 8 per side to reach 99dB/1w. Correct me if I am wrong.
To start with a 90dB woofer on a passive OB is a loosing proposition.
One can get 99dB with just one pro 15" woofer.
Two 15"ers even better: higher eff plus second woofer on top would lift the center of bass higher (closer to mid driver and ear level).
My next prototype will use two cheap 15" pro woofers per side.
At 98dB each, they would make 101dB in series.
It would also make a 4ohm load and add another 3dB in total eff (104dB). Again, correct me if I am wrong.
I also plan to move to U baffle instead of H. Resonant peak of U baffle would be easier to deal with. You pay for the additional freq extension of H baffle by a further reduction in efficiency anyway.
Good that you mentioned OB11. I also plan to use a similar lowpass filter to that of Troels'. Visaton NoBox crossover is another example. I did not know that a 1st and 2nd order filter can be used in tandem until recently. I think it is a very elegant solution to the falling bass response of dipoles. But it requires massive efficiency in a passive bass set up.
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Old 22nd October 2012, 09:13 AM   #25
zmyrna is offline zmyrna  United Kingdom
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As I have mentioned earlier, I am becoming more suspicious of high excursion, rubber surround, heavy coned mid or bass drivers (most modern drivers).
I think even a light paper cone becomes too heavy to operate with a rubber surround.

For good dynamics, large diameter and light paper cone with fabric surround is probably the way to go.

Unfortunately large vintage alnico drivers are a few and not easy to find (hence the high price).
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Old 22nd October 2012, 09:19 AM   #26
zmyrna is offline zmyrna  United Kingdom
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@ Stig & Silent
I am thinking with soft suspension we run the risk of turning the whole panel into a diaphragm.
I will try mass and dampening first.
Sand or plasticine (think playdough) or both.
Plasticine can be used to both dampen the panels and fill the corners and angles (less parallel surface to resonate).
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Old 22nd October 2012, 09:24 AM   #27
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Quote:
Originally Posted by zmyrna View Post
@ Stig & Silent
I am thinking with soft suspension we run the risk of turning the whole panel into a diaphragm.
Look at the weight ratio between the moving mass of the loudspeakers and the weight of the baffle. If we have a 1:100 ratio, then the baffle - if completely suspended - will move 1/100 of the speaker cone. Or -40 dB. Not a big problem in my opinion.
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Old 22nd October 2012, 02:37 PM   #28
DrBoar is offline DrBoar  Sweden
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The good thing about the Seas in OBs is that they are quite! If you send a 20 Hz sinus thrugh the Seas unmounted it simply swings back and fourth say +/-3-5mm making no sound. Doing the same with quite a number of drivers will make you listen to strange hummings and buzzing sounds probably from the rear suspension acting up.

I might get hold of four additional seas10" drivers so that I will have 6 per side...

Some years ago I listened to the HFN &RR garage door track on the Audiotronic Megatrend that had 18 KEF B200 8" per speaker in open baffles roughly two meter high and perhaps 0.8 m wide. The sheer power of 36 eight inch drivers slamming was an experience. Something like mating Quad ELS with the impact of Klipsch corner horns.
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Old 22nd October 2012, 03:13 PM   #29
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zmyrna: one driver 90db, two in parallel 93db, four in series-parallel 93db also. Series wiring liberates zero gain in efficiency. If anything this makes the case for a single high efficiency woofer much stronger.

These reasons are why i have considered a Mivoc 18, fs 38hz, xmax 4mm, 98db/W. I wanted to ensure i had enough headroom to eq the bass without xmax excursions.

Even better, two 18s in ripole or slot loaded OB, total of four 18s. 101db/W plenty headroom
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Last edited by mondogenerator; 22nd October 2012 at 03:26 PM.
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Old 22nd October 2012, 07:51 PM   #30
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Ah... two drivers in parallel means +6 dB voltage sensitivity, at the cost of half the impedance. Two drivers in series means no gain in voltage sensitivity, but double the impedance. Four in series-parallel is +6 dB voltage sensitivity and the same impedance as one driver.
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