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Old 28th December 2004, 06:47 AM   #1
akunec is offline akunec  Canada
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Default Building new dipole system, need comments

I want to build some speakers and I would like to here what you guys have to say baout it. I want to build a 3 way fully active system with a vifa tweeter covering 10000-20khz, four or 6 tang band 3 or 4 inchers to cover 300-10000hz, and a pair of 8 inch tang band subwoofers for the bottom end. The drivers will be mounted on a baffle that is curved so that all the drivers are equidistant from the sweetspot. Im still not sure if I want to make the subs open baffle cause im not sure ill get all the output i desire. I chose such a high crossover frequency as i want to try something different, and many people argue that a xo at 2000hz is not good idea as our hearing is very sensitive in that range.

Any comments?

Thanks
Alex
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Old 28th December 2004, 08:39 AM   #2
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Hi Alex

Unless your room is small, a pair of 8 inch is too light for dipole bass, where the smaller SL dipole (Orion) bass uses a pair of 10 inch, with *12.5 mm Xmax for sufficent Vd.
Have you read www.linkwitzlab.com - allow a lot of time!

A curved baffle is quite a bit of work Ė may not be necessary. If listening distance is (guessing) more than 5-6 feet, benefit may be small.

Multiple drivers can cause lobing, but others know far more about that than me.

Cheers
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Old 28th December 2004, 03:03 PM   #3
Bill F. is offline Bill F.  United States
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If your baffle is quite large, a pair of high-excursion 8" drivers *might* get down to 50Hz at realistic levels, but with little/no headroom, IMO. Linkwitz recommends crossing his Phoenix dipole bass (2 x 12") steeply to a sealed sub at 40Hz, and I don't believe even that is a very high-output solution.

When it comes to bass driver displacement on OBs of reasonable size, I recommend figuring out how much sealed box displacement would meet your bass needs, then quadrupling it for an OB.

The dipole bass mantra: Displacement, displacement, displacement!

I have a smallish listening room, and I run a pair of 3' x 4' OBs down to 35Hz with 21" drivers (about 3-3.5 times the displacement of two eights per channel), and it's not hard to drive them into over-excursion. I am planning to add sealed subs in the future.
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Old 28th December 2004, 05:08 PM   #4
adason is offline adason  United States
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hi,
i have been experimenting with open baffles for a long time
and i can say that guys are right
for good open baffle bass, the bigger the baffle and larger the cone area the better
i have arrived at four 15" woofers total with intimidating size of baffle
and i love it
sound is free of boxiness if there is such word
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Old 29th December 2004, 08:10 AM   #5
akunec is offline akunec  Canada
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I think it would be in my best interest to make the 8 inch drivers sealed then. I know some of you guys really hate boxes, but im only 20 an feel that i need a lot of output down low.

Alex
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Old 29th December 2004, 11:35 AM   #6
adason is offline adason  United States
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Quote:
I think it would be in my best interest to make the 8 inch drivers sealed then.
there is no shame in making it sealed box, many famous speakers are like that, sealed sub, open baffle midrange and up.... alon, genesis....
just make it as two separate parts, so you can redo it later
good luck
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Old 29th December 2004, 01:40 PM   #7
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Quote:
Originally posted by adason


there is no shame in making it sealed box, many famous speakers are like that, sealed sub, open baffle midrange and up.... alon, genesis....
just make it as two separate parts, so you can redo it later
good luck
Thats what mine is like.

I did post a response but for some reason it didnt get added to the thread? DIY audio then went down so maybe it got lost in the wires getting to the DIY servers

Anyway what I was asking was, with H baffles, if you have a baffle that is 12" wide with flaps that are 6" wide all over that means you have an overall 24" wide baffle right? the 12" from the main panel and 6+6=12 from the wings.

So then that gives you extension down to about 130hz, which is then about 10dB down at 40hz, this doesnt seem like a lot of EQ to get appreciable bass.

With all that in mind I tried it! , thank god my brother got a big moniter for christmas, lots of cardboard. See pic.

Now as you can see behind is the sealed box the XLS works in normally, this requiring EQ anyway. This is about 8dB per octave working from about 100hz, which is where my makeshift openbaffle starts to need EQ, so ive got about 2dB more per octave of EQ then is required.

Anyway to cut a long story short they sounded really good some of the most tuneful, and to my surprise, forceful bass I have ever heard.

Now I use the KX drivers on my computer which allow you to build digital xovers with the DSP so I added a 4th order highpass at 40hz to protect the driver from over excursion.

I dont really understand where you guys are coming from with the running out of excursion, this driver played just as loud in the open baffle as it did in the sealed box, OK it lost a little bit of SPL but nothing major. I also know that the sealed XLS with EQ is not designed for high bass SPL either, but if you are only interested in playing music you dont really miss the 20-40hz range, and in a small room you dont run out of level. This was a single pair of XLS playing in a 3*4 meter room and I certainly didnt require more level.

I will now be making Hbaffles and seeing how they perform.
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Old 29th December 2004, 05:10 PM   #8
adason is offline adason  United States
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Quote:
With all that in mind I tried it! , thank god my brother got a big moniter for christmas, lots of cardboard. See pic.
that bring us to the question what is the best material for making open baffles? should it be light and stiff or heavy and stiff? does it have to be one type of material only or the middle should be heavy and stiff and wing can be light and stiff? how stiff does it have to be? i have seen phy-hp mount their driver on small brass plate and this attach to a big wooden baffle
than other project, i lost the link, had ultralight balsa wood laminated....how about you guys, what do you use besides cardboard? /just kidding, i once mounted a fullrange on small board in the middle of the carpet and hang it from the ceiling in the middle of the room....impressive sound, very low gaf/
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Old 29th December 2004, 08:58 PM   #9
Kensai is offline Kensai  United States
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If its about displacement, then how about using something like:

http://www.partsexpress.com/pe/showd...number=295-455

Models pretty well for OB and has a very large Xmax. Way out of my current price league (especially assuming I'd have to build some seriously sturdy now baffles to mount these suckers, too), but not all that pricy compared to drivers alot of folks are using in their subs or even as mids for pairs of speaks.

Or, how about even this:

http://www.partsexpress.com/pe/showd...number=290-268

Cheaper, with nearly 3x the Vas. Slightly lighter weight driver, but even more surface area and baffle size needs.

Kensai
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Old 29th December 2004, 10:17 PM   #10
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I think that accordion surrounds are not suitable for dipole (canít recall why).
The Dayton would be good.

Remember that many otherwise very drivers make chuffing noise through the vent when used in dipole bass, and canít be used eg the Adire Shiva.

The newish TC Sounds TC2+ 12 inch has knocked off the champ of 12 inch dipole, the XLS. With similar very low distortion, itís Xmax is 56% higher then the XLS.


Richard
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