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Old 28th June 2008, 02:08 AM   #1
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Default RAAL special high efficiency Ribbon

Aleksandar from RAAL makes a special high efficiency Ribbon model. The main difference to the standard 140-15 is sensitivity.

more info's and pictures at my forum

Click the image to open in full size.
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Old 28th June 2008, 02:14 AM   #2
agent.5 is offline agent.5  United States
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I thought the regular RAAL already is TOO efficient?
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Old 28th June 2008, 02:20 AM   #3
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it depends how you will use it. If you want to combine it with horns, then higher efficiency is certainly welcome.
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Old 15th July 2008, 01:27 AM   #4
Richard is offline Richard  Australia
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Hi Angeloitacare,

Thank you for posting this information. I'm interested in this model and have a couple of questions.

What impedance is this high efficiency model?

You also indicate that it sounds very much the same. On the frequency response plot you posted there appears to be a bit of a dip between 16 42 Khz.

Have you been able to compare the high efficiency model to the original 140-15D?


Richard
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Old 15th July 2008, 01:38 AM   #5
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Default Re: RAAL special high efficiency Ribbon

Looks the same as the one a good friend of Alex(of RAAL) had made. I presume its a 210-10 ie. 21cm x 1cm ribbon element?

If that's the case then the radiating area is equal to 140-15 at 21sq cm The trade is higher sensitivity but worse vertical dispersion.

Nice that Alex allows tailoring to suit the application.
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Old 15th July 2008, 10:31 AM   #6
VHF man is offline VHF man  Australia
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The on axis response cetainly looks a lot different to the published graphs of the 140-15.

Efficiency is probably a misleading term in this context. A better way of describing the measured on axis spl would be - on axis gain. As one who works with radio propagation models I can see a direct analogy to radio antenna gain. Antenna gain by nature implies a cardioid polar response that is the result of summing the power of antenna dipole elements in either the horizontal or vertical plane. In essence you don't get something for nothing and it's the same with ribbon tweeter design. All you have done is focus the power over a defined beamwidth that is inversely proportional to the length and width of the radiating element.
In RF we use an imaginary (theoretical) point source antenna called an Isotropic radiator as a gain reference.
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Old 15th July 2008, 12:00 PM   #7
Richard is offline Richard  Australia
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Hi ShinOBIWAN & VHF man,

Thank you for bringing that info to light. Your right about all the trade offs.

Apart from biamping with an active (or passive line level) crossover, is there any way to increase the efficiency of the 140-15D by about 2-3db?
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Old 15th July 2008, 12:46 PM   #8
VHF man is offline VHF man  Australia
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Hi Richard,

What is it that you are contemplating with the Raals? I gather you are thinking of building a 2 way system with high efficiency paper cone drivers or a horn loaded mid etc.
There's really no silver bullet but if your power budget is tight then active or dsp crossover would be the way to go. The q loss of typical passive crossovers can reduce efficiency by up to 2 dB.
The other advantage of an active crossover is that the tweeter power amplifier is only amplifying the tweeter voltage and is not exposed to the higher low and mid frequency voltages that occur at music fundamental frequencies. This will allow you to use a very low power tweeter amp (eg. SET) and to perform gain matching via global feedback adjustments or a simple attenuator at the amplifier input.
FWIW I am not a member of the high efficiency camp. I actually prefer large voltage SS amps and speakers with a wide power bandwidth and a nice wide horizontal dispersion.
Each to his/her own I guess.

Cheers
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Old 15th July 2008, 12:53 PM   #9
VHF man is offline VHF man  Australia
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Richard,

I forgot to add that if you do intend to use a passive crossover then bigger is better. You can't eliminate Q loss but you can minimise it so if every dB counts then go with the lowest loss caps and inductors you can house (and afford).
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Old 15th July 2008, 01:21 PM   #10
Richard is offline Richard  Australia
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Hi VHF,

I playing around with a Philips Ad5200 in a JE labs open baffle arrangement, but the highs need to be tamed/supplemented. I have tried an Eminence APT 80 (105 db) tweeter with a passive 1st order corssover, which was ok but Im after something a bit better. The Philips is a 12 99db full range.

I wanted a suitable tweeter to match the Philips, but reconsidered the (210-10?) custom Raal after seeing the price. The 140-15D is an attractive option as I know I will use it other projects, but am I losing sleep with this 4-5 db difference?

Rich
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