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The best sounding HF driver you have ever met

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Teunos View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Teunos Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 10:20am
Originally posted by Steve_B Steve_B wrote:

One thing that has not been mentioned in this thread is the distortion caused by the horn.

Before anyone makes claims for or against any particular drive unit be aware that this is acoustic distortion.

For an exponential horn the % 2nd harmonic is:

D = 1.73 x f/fc x √IT x 10-2

f = frequency reproduced
fc= horn cut off frequency
IT= intensity in watts per square metre

The throat area for a 2” compression driver is 4 times that of a 1”, therefore for a given output power the % 2nd harmonic distortion is double that of a 2” drive unit.

Say you use a horn with a 1KHz cut off frequency (this is a characteristic of the flare rate not the crossover).  A 7KHz signal with an intensity of 4W/cm2 will be producing over 20% 2nd harmonic distortion.

4w/cm^2 is a lot of noise.  Actually you would be deaf at 166db of noiseLOL
Best regards,
Teun.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ray666 Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 1:37pm

Beyma is good, but there is no way to line these. they will sum up only up to 7 khz. Then single cab all the way - x @ 1.1 khz beyma in the middle and two pd 122-s on the side. 

thanks for helping out.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 2:12pm

Some rough calculations. I’ll assume a flat surface area rather than spherical cap that the sound is radiating into.

The area of a 1” compression driver throat is:

Πr2 --- π x 0.01272 =  0.0005 m2

The actual area of the openings in the phase plug could be less.

Say the driver is fitted to a round 60˚ horn.

At 1m out (from the throat) the radius of the cone is Tan30 =0.577

So the area is π x 0.5772 = 1.04 m2

That is a difference of 1.04/0.0005 = 2094.

According to this thread, some 1” compression drivers are capable of keeping up with three 12” drive units. Winisd calculates three 12” PD drivers (mentioned in the first post) will produce 132dB @ 1 m.

132dB-sil works out at 16W/m2 divide by 10,000 to get to W/cm2 then multiply by 2094 to calculate the intensity at throat and it comes out at about 3.5 W/cm2

Some manufacturers are claiming up to 140dB peak levels which means the intensity at the throat is 20W/cm2.

 The graph on page 276 of Acoustics by Beranek, which shows the amount of 2nd harmonic distortion for a given power density and frequency relative to cut off, tops out at 10W/cm2 even at that level, using the same frequencies I used previously gives 40% 2nd harmonic distortion.

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Tony Wilkes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 2:24pm
The only thing that I will add is that the audibility of 2nd Harmonic Distortion in Compression Drivers has been under discussion for a while now and I suspect that IM distortion is the real culprit in bad sounding drivers.

Tony
www.forteaudio.eu - BMS - db-Mark Processors - Lexon (SAE)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Steve_B Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 3:18pm
Tony, I'm not actually on about the driver. This is distortion produced by the non linear compression of the air in the horn. The more rapidly the horn flares out the less distortion there is, hence the ratio of frequency to cutoff frequency. Conical flares will have less distortion while hyperbolic horns will have more.

By default the exit of the driver is an extension of the horn, but to a large extent the make of the drive unit is irrelevant. Whether it is BMS, JBL, etc, etc the sound wave is still being squeezed through a small hole.

I brought a similar topic up years ago on a well known pro-sound forum, but ended up getting harassed because I disagreed with the then designer of a large loudspeaker manufacturer. Basically he said the problem was one for drive unit manufacturers rather than cabinet designers. I felt he was being pedantic.

As materials and drive units improve I think that we are running into the physical limitations of what the air can do. One advantage of line arrays is that the ratio of cones to compression drivers has reversed, so the power density at the throat is reduced.

I know that many here try and wring the last upper KHz out of their systems which means using 1" drivers, but a 2" offers  four times the throat area which means lower power densities.

I'd be very interested to hear what some of the compression driver designers think about this topic.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snafu Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 4:24pm
A 2" comp taking it easy sounds better than a 1" being driven hard, you get a lot of sound for your money.
And when the going gets heavy you can always turn a 2" up.
About 10 years ago when looking for hf drivers for my concert system I investigated the stage accompany ribbon drivers, I was very impressed but at a grand apiece they were out of my reach.
They gave pro sound output flat from 500hz to 20khz.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 5:01pm
@ Steve_B  Sorry mate mis-read you :)

Tony
www.forteaudio.eu - BMS - db-Mark Processors - Lexon (SAE)
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Marko View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Marko Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 5:08pm
well, I have totally different experience
after reading, mostly on this forum, how good bms drivers are I decided to give them a go and buy 2 x 4544 for a 12"+1" box.
Horn was B&C ME 20 and I wanted to cross them at 2K but there was a lot of distortion in sound below 4K. That was with active 4th order high pass filter and with passive 2nd order the situation was a lot worse.
Then I got the RCF HF 101 horns, which are bigger, and better load the driver at lower freq. but with them I lost a little bit of top end, gain a lot of pattern control but distortion below 3,5K - 4K was still there.
Then I got Faital pro HF 140 with horns from Martin F 15 cabs (1,4") and when crossed at 2K 4th order they sound good. But lower than 2K not anymore.

So, what I doing wrong?
Which horns you guys recomend with 4544?
I even start to doubt that my BMS comps are original since I read somewhere that there are some copies
from China are around.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 6:00pm
Marko, BMS drivers have a big bump at 3-4Khz in its frequency response and you need to have a very good passive crossover to tame that bump. Once they get flat they sound extremely good even down to 800Hz.

Marjan Milosevic
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TENSiON Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 7:31pm
4W/cm2 for a 1" exit comp on a 60/40 horn equates to about 133dB@1m. Anyone expecting or running their 1" comps at such levels does well deserve all the distortion they can get Tongue

On another note, 3rd harmonic distortion is a lot more defining in terms of how good (or bad) it will sound, as the 2nd is less perceivable due to being more "harmonic".
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Post Options Post Options   Thanks (0) Thanks(0)   Quote _djk_ Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 7:38pm
The size of the driver exit is not the throat of the driver.

The throat of the driver is the slots in the phase plug.

Most drivers have a 10:1 ratio between the diaphragm area and the area of the slots in the phase plug.
djk
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Post Options Post Options   Thanks (0) Thanks(0)   Quote thepersonunknown Quote  Post ReplyReply Direct Link To This Post Posted: 23 January 2013 at 10:11pm
sorry to bring this up again, but what do we think of using some of the newer 'linearay' waveguides in a pointsource box.

my idea is to use two comps to keep up to a particularily loud midrange horn in the upper high range 4k+, but withought thrashing the hell out of a single driver, and coupling as best a posible, much like a line array cab, but using just 2 waveguides mated to a flare which allows around 90horizontal by 30 vertical (20down 10up) dispersion.


They keep telling me life is short, but its the longest thing ive ever done!!!
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