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Old 7th November 2005, 03:00 PM   #1
Puggie is offline Puggie  United Kingdom
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Default hornloading a ribbon

Anyone done this? I have a pair of Fountek Neo CD3s and I'm looking at fitting a waveguide of sorts. Anyone done this or similar? any advice? by how much is this likely to lower my potential crossover point?

also what is the limiting factor for powerhandling on this unit, the transformer or the ribbon?
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Old 10th November 2005, 03:47 AM   #2
el`Ol is offline el`Ol  Germany
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There are some companies from the pro audio sector that do so:
http://www.alconsaudio.com/site/index.html
http://www.slsloudspeakers.com/proaudio/rla_ls9900.html
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Old 12th November 2005, 04:39 PM   #3
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You can try... generally speaking what happens is that the flatness of the freq response will be disrupted. It may not be, of course, but it often happens.

You'll likely not get much extension below the nominal F3 point of the ribbon, some but not much. The reason is that the ribbon is rather excursion limited mechanically, so the "lift" that a good horn (waveguide) may provide is going to be offset by the limitation of the diaphragm. Imho.

You might achieve 1/2 octave improvement - the biggest benefit would be in terms of power handling at and below the F3 point - but again there may be a hump produced in that region, and some ripple above depending on how effective the loading to the diaphragm is by the horn that is added... +/- sidewall reflections and termination reflections...

The pro drivers use the waveguide for "LF" dispersion control and to improve the power handling (headroom) at the xover point...

Ymmv, of course.

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Old 12th November 2005, 05:05 PM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
what if one is not looking for an extension in the low frequency response, but instead just trying to improve the sensitivity within the normal pass band of the ribbon.

Does the ribbon have a strong enough motor system to drive the horn up to the highest audible frequencies?

Should one match the throat to the width of the ribbon or produce a bit of compression by reducing the throat width to something less than the ribbon width?

If the ribbon can drive the horn through say two octaves from it's normal lower limit how far above two octaves will it go? to three or to four octaves? or even wider? 1250Hz to 20kHz is already four octaves. Most ribbons are renowned for an extended upper frequency response making a target of five or even six octaves. Is this feasible? 1kHz to 32kHz might make a first target to aim at.
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Old 12th November 2005, 05:07 PM   #5
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Decca did it with good results. The Londons were a revelation in my youth....

Click the image to open in full size.

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Old 12th November 2005, 07:51 PM   #6
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Quote:
Originally posted by AndrewT
Hi,
what if one is not looking for an extension in the low frequency response, but instead just trying to improve the sensitivity within the normal pass band of the ribbon.

Does the ribbon have a strong enough motor system to drive the horn up to the highest audible frequencies?

Should one match the throat to the width of the ribbon or produce a bit of compression by reducing the throat width to something less than the ribbon width?

If the ribbon can drive the horn through say two octaves from it's normal lower limit how far above two octaves will it go? to three or to four octaves? or even wider? 1250Hz to 20kHz is already four octaves. Most ribbons are renowned for an extended upper frequency response making a target of five or even six octaves. Is this feasible? 1kHz to 32kHz might make a first target to aim at.

In general terms, imho, you can't simply plunk a horn onto a given driver and increase the sensitivity across the band.

The way that horns work is as acoustic transformers that have a frequency dependent aspect. That is they "transform" more/better as the frequency decreases down to the flare rate (frequency) and mouth size (larger is required to keep it flat down to the lower freqs).

So, what this seems to mean in practice is that you design a driver with relatively rotten LF response and very wonderful but not particularly good at direct radiation as it goes low. Mostly very narrow gaps, big magnets where the sensitivity is very high, but the excursions small BUT very strong - ie. controlled by the VC/flux combo quite well. Then you take this short strong motion and convert it into much weaker longer motion via the horn...

In the case of the compression driver the phase plug makes the HF response better by providing a non-interfering equidistant path to the throat from the diaphragm (or as good as is possible).

Viewed independently from the horn, the compression driver looks like a driver with a rising output, going from LF to high, with the maximum output all the way at the top of its intended operating range.

At that frequency, a typical HF larger high quality compression driver probably has the nominal sensitivity of ~109db/1w... say at 14kHz approx.

That's for a compression driver.

Take a regular non compression driver and strap it onto a horn and it behaves similarly but not as "effectively" since it doesn't load the horn as well... Generally speaking the best results have been with drivers that have a rising freq response... (again depending a bit on what ur trying to do, and the application...)

The Decca ribbons are a good example since they work fine without a horn on them. Levinson used them that was in his HQD system:

Quad ESL
Decca sans horn
Quad ESL
Hartley 24" Subwoofer

Driven with an ML-2 25watt class A amp was fairly impressive in ~1974 or so...

But without the horns they don't go as low.
The horns were mostly to "pick up" the lower octave of potential response from the ribbons... iirc the "Kelly" version used a larger horn than the Londons and went a little lower as a result...

If you go and try to load ur Founteks into a horn and manage to acheive some compression, the problem is likely to be that the response is no longer flat - unlikely that the *entire* spectrum will be equally lifted in sensitivity or efficiency.

The best bet is to gain some LF extension and/or LF polar response control...

It will be difficult to actually get any significant compression if the sides of the diaphragm are not sealed to the rear of the driver... and the diaphragm material may or may not stand up to real compression loading, if you could make it happen.

2 octaves below the present F3 is unlikely... but nothing lost by trying and seeing what you get!

_-_-bear
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Old 12th November 2005, 09:46 PM   #7
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Quote:
Originally posted by bear iirc the "Kelly" version used a larger horn than the Londons and went a little lower as a result...
Other way around -- the Kelly (aka DK30) has a smaller horn and goes to 2.5K (IIRC) and the londer to 1k (althou the "standard" XO was at 1.5k)

dave
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Old 19th November 2005, 09:59 PM   #8
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darn facts and details!!

they always get in the way...

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