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Old 5th May 2021, 10:18 PM   #21
SoundRight is offline SoundRight  United Kingdom
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Old 6th May 2021, 10:58 AM   #22
SoundRight is offline SoundRight  United Kingdom
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Join Date: Jul 2010
Ok, time has come. Firstly, why bother? Simple, I'm sick of reading misguided unsubstantiated nonsense from "gurus" that many appear to hold in high standing, hanging on to every bit of subjectivist nonsense they spew out...

Let's be clear, no loudspeaker is perfect, no audio component is perfect, and sorry to burst bubbles but brand name is meaningless and the amount you pay has no relation to performance. Science doesn't work that way.

If you want credentials, because I am not one of the "designer gods", I started my interest in 1972, was involved in live audio with an EV horn based PA system (EV Sentry IV's, SM500 horns, etc)..built my own VOTT's. At the other end of the scale, and domestically, had stacked QUAD electrostatics, my own design 2 x 15 sub and Kelly Ribbon tweeters...an active system (TEAC) in 1975!! Taking a leap to the future(!), one of the first to design studio monitors around DSP (BSS366) which were reviewed in the UK and put in the same class as ATC, PMC and Genelec. This design was innovative in that it had 18" drivers in a Linkwitz Transform bass and a 12" coaxial for mid and treble.

So when I approached this project I set some targets. Certain criteria had to be met for substantially good audio performance, and many seemed obvious and elementary.

Ideally I wanted a driver to cover a wide bandwidth to avoid the requirement for "tweeters"..limited compromises could be made here, putting any anomalies in response or "break up" above 10khz where there is little information may suffice. The majority of tweeters fail this test anyway unless their diaphragms are 19mm or less, and most seem content with that. Ribbons may avoid this problem, but they have other issues!

Response must be flat to "monitor" standards and +/-2dB throughout the bandwidth of interest seemed appropriate.

No point having a flat response just on axis so they must perform equally well on and off axis.

Distortion must be low, in particular odd harmonics.

No point having a "flat response" if it is made up of resonances..so, critically, the response must produce clean Burst Decay and Cumulative Spectral Response plots..these, as I'm sure you all know, reveal if there are any problems and how audible they will be. No loudspeaker is perfect, and I'll say again, no loudspeaker is perfect, but it is a case of how audible the anomalies are.

Right..that set the targets. How to go about achieving the result..(bored yet)..it took me a year of development so have some patience!

The loudspeaker is only part of a circuit of course (making cable arguements the total BS they are). The easier the load in terms of flat impedance and phase angle the more your amp will love you. You will note from the plot this design achieves 6 ohms throughout from DC (shown from 100Hz) to 20khz and a 0 deg phase angle. The amp is basically seeing a 6 ohm resister. Easy, and you wont need a "high end" BS amp to drive it..a cheap one will do ..or a load sensitive one. This is almost designed with Class A SET valve amps in mind. It is also designed for those that like passive crossovers..theory 6 ohm designs will work perfectly.

The particular loudspeaker chosen has a falling HF response from around 3.5Khz and this has been dealt with by implementing a "cutting" passive eq circuit, which you will note achieves the desired flat response. It also reduced the efficiency of the device to around 100dB/watt but that' ok...

Both circuits had to work together of course to provide the target result..flat impedance and flat response..

So you will probably have guessed its a horn and CD driver we are talking about!!

The choices here..I put constant directivity and even dispersion above beaming at HF, a performance characteristic of all other horn types. I eschewed the nonsense about all CD horns "shout" or have a characteristic sound (only in their even power delivery)..and put faith in Don Keele who's designs superseded all other horn types for good reasons.

As I said at the beginning, no loudspeaker is perfect, but it was my belief that ensuring maximum damping will ensure the diaphragm of the CD driver is optimally controlled. A decent sized throat will reduce distortion, which we know now is a heating effect..and a 3" diaphragm will push break up/resonance to above 10khz.

Cost although not a critical factor, was factored in..but science and a "different" approach to problems were more important than fancy high end arguments. The passive components are not cheap but one could argue they have to offer value given the outcomes which I think you will have to agree put many far more expensive alternatives to shame. The plots are unequivocal. (Of course the circuit boards are also "generic" and other drivers/horn combinations could have circuits derived for them..)

And now, the component choices. All passive components are Janzen, a mix of air cored and ferrite (for the RCL's) and 1% resisters. Unfancy (read no BS) Polyprop caps as one can see.

The horn is a P.audio 4525 90 x 40, 2" throat...AKA the Goldwood PB450 on your side of the pond. This was chosen as it is the only horn that performs like a CD horn but has the "dual" throat, a combination of slot and circular entrance.

The driver comes from a company I hold in very high regard having worked with many of their superb drivers..Beyma from Spain. The CP750ti is a well built 2" throat 75mm titanium diaphragm device with mylar suspension providing it with extension, damping and a design goal of theirs, an extended HF.

So there you have it, the plots don't lie. Consistent even coverage over a wide angle, low distortion, flat response and lack of resonances. And guess what, they sound great...well, they almost don't sound at all as colourations are reduced to a minimum....
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Last edited by SoundRight; 6th May 2021 at 11:02 AM. Reason: spelling
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Old 6th May 2021, 05:49 PM   #23
Lampie519 is offline Lampie519  Netherlands
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I was close but did not expect a horn here. Interesting indeed !
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Old 6th May 2021, 07:36 PM   #24
SoundRight is offline SoundRight  United Kingdom
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Join Date: Jul 2010
Yes, indeed
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Old Today, 06:35 PM   #25
SoundRight is offline SoundRight  United Kingdom
diyAudio Member
Join Date: Jul 2010
Never mind....I'm enjoying them, and if one trusts physics over snake oil and would appreciate how this new approach to old problems might benefit in terms of clarity and lack of colouration you can always get in touch...

Last edited by SoundRight; Today at 06:43 PM.
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