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Old 19th September 2008, 01:35 PM   #1
MJK is offline MJK  United States
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Default 20 Hz to 20 kHz Dipole Speaker System

I have been busy the past couple of months designing, building, and testing a new two way dipole speaker system. The resulting speaker has an efficiency of 88 dB/W/m and covers the full spectrum from 20 Hz to 20 kHz. You can find pictures and the documentation of the design on the Projects page of my web site.
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Old 19th September 2008, 01:54 PM   #2
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Hi Martin,

Apart the obvious compliments, particullary for excellent calculated Vs measured data, I have two question:
1) How is imaging with such large baffle?
2) How bad are the vibes ?
Excuse for my rude english, I found your work always accurate and scientific.

Cheers,

Paolo
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Old 19th September 2008, 02:18 PM   #3
MJK is offline MJK  United States
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Quote:
Originally posted by inertial
1) How is imaging with such large baffle?
2) How bad are the vibes?
Hi Paolo,

Imaging is very good, as good as any of the other systems that have been in my room.

I assume you are asking about cabinet vibes. To be honest I have not spent much time investigating cabinet vibes. In the future I am going to add mass using a large piece of stone iwhich should be a step in the right direction. But I am not sure it is required.
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Old 19th September 2008, 02:22 PM   #4
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Thanks Martin,

Paolo
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Old 19th September 2008, 02:32 PM   #5
infinia is offline infinia  United States
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Hi Martin
I like your work esp. correlating theory with measurements.
I quote you from your project paper



"The use of an active crossover really makes the system work. Levels and
crossover points can be adjusted to optimize performance. Crossing low maintains the
full range driver sound while removing the demand to produce bass from the Jordan.
The system comes together really well, deep dynamic bass and clear crisp response
from approximately 20 Hz to 20 kHz. But be warned, at 88 dB/W/m it does take some
power to make them really sing their best. At the end of an evening of enjoyable listening
at decent volume levels, my amps are warm."


1) How do you choose the crossover frequency and order of the active filters? I realize this is partly based on the excursion tradeoffs of the fullrange driver and the want to cross low. But there is alot more that comes to play here... yes?

2) Can you discuss the highpass boost to the H frame woofer in more detail?

3) Are you going to publish circuitry details for 1) & 2) ?
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Old 19th September 2008, 03:51 PM   #6
MJK is offline MJK  United States
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Quote:
Originally posted by infinia
1) How do you choose the crossover frequency and order of the active filters? I realize this is partly based on the excursion tradeoffs of the fullrange driver and the want to cross low. But there is alot more that comes to play here... yes?

2) Can you discuss the highpass boost to the H frame woofer in more detail?

3) Are you going to publish circuitry details for 1) & 2) ?
1) My first cut at crossover frequencies and slopes is done using MathCad simulations. I have found that 2nd order filters connected in phase work well for the style of dipole designs I am focusing on. I revisit these calculations when I have measured SPL response data for the individual drivers in the system. Then adjustments are made by ear, I am using a dBx Driverack PA digital crossover so you can change setting on the fly and hear the results immediately. Simulations get me most of the way and the final small tweaka are done by ear.

2) I just applied a 2.5 dB boost, I tried other values to see what sounded most balanced and it came down to between 1.5, 2.0, and 2.5 dB settings. I settled on the 2.5 dB value for now.

3) The only thing I build are the speakers. The amps and crossovers are all off the shelf purchases. I have no interest in electronics design and construction.
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Old 19th September 2008, 04:05 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

Another excellent and informative article.

to address some points in this thread and the article :

The c/o point selection principles are in the other articles.

For all things active see http://www.linkwitzlab.com/

The sensitivity and gain adjustment indicates a bucketload of drivers
would work in this design, if they are flat or passively EQ'd flat.

The Tangband-W4-1337SA (with some form of treble disperser ?)
springs to mind for 86dB/W, just reduce the bass gain a little.

Regarding the need for or lack of a treble driver :

Off axis response does matter and is perceived at the listening
position by the ratio of reflected to direct sound, how much ?
YMMV but off axis starts going off at around 3KHz.

Adding a tweeter would bring in a lot more driver possibilities.

The Tangband W5-704D + tweeter would certainly be cost effective.

/sreten.
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Old 19th September 2008, 05:30 PM   #8
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Martin,

What is the excursion like on the goldwood in the h-baffle around resonance?

Sean
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Old 19th September 2008, 06:14 PM   #9
britbug is offline britbug  United States
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Excellent article!
I prefer the JX92s to the Lowthers I have (DX2)
But, the wife & kids don't agree so I am gonna take the Jordans to the office & re-set up the lowthers in OB
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Old 20th September 2008, 12:52 AM   #10
tinitus is offline tinitus  Europe
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Active highpass so a 2-way active speaker is that very important
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