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Headphone
specs and advertising
by Rick
Viola
Impedance.
Basically, you get the most power to
the speakers when the headphone impedance matches the machine. Not
only this, but you will have higher efficiency and draw less battery
current. What
is the machine impedance? Well, it varies with the manufacturer.
Many machines are 150 ohms and a few are about 300 ohms. However,
advertisers seem to often claim 150 ohm headphones. Well, that may
be the impedance of the speakers used, but unless you are
swinging a true stereo machine (there are very few) your headphone
speakers are in parallel. This makes your so called 150 ohm
headphones really 75 ohm headphones. There are also so called 100
ohm headphones that, you guessed it, are really 50 ohms when you
connect to a typical machine. The further away you get (up or down)
from the machine impedance, the less volume you get. This will most
likely affect distortion, making the sound you hear
further away from the sound that was intended.
Here is a scan of impedance
through the entire audio range of so called 150 ohm headphones with
the usual speakers. Impedance numbers are on the left. This measures
69 ohms at 1000 hertz.
Here's Ratphones. More constant
though the entire audio spectrum:
Then there is Minelab. Their machines working better on low
impedance headphones is not really correct. They ship Koss UR-30
phones with some machines that say they are 100 ohms. Well since
they are stereo that means each speaker is 100 ohms. Minelab machine
jacks connect stereo phones in series. That means you are connecting
200 ohms to the machine. So where is the low impedance? The newer
Minelabs have better circuitry, but the X-Terra's have a slight hum
in the mid tones. This can be heard with any wide response phones.
The X-Terra has an output impedance of 230 ohms, so Ratphones are an
excellent match. But you may want the Sov mod installed to clean up
this noise in the X-Terra.
Here is an impedance plot of Koss UR-30 headphones as connected to a
Minelab machine:
So it seems they ship 250 ohm headphones with their machines!
New Ratphones Max impedance graph:
However, impedance matching alone does not make a good sound. This
mostly optimizes volume. Other
features such as the speaker efficiency, magnets, materials
and durability are also important. The final judge will be your own
ears. Some customers actually like a loud distorted screech!
KNOWN
OUTPUT IMPEDANCES (OHMS):
Here is some machine impedances we have verified by either
schematic or testing:
FISHER:
1260: 220
1210: 100
CZ-70: 470
F-75: 274
ID Edge: 500
TESORO:
(Most all 150)
CUTLASS II/BANDITOII uMAX: 150
SILVER SABRE PLUS: 150
Silver saber: 150
GOLDEN SABRE: 150
ELDORADO (NON-uMAX): 180
GOLDEN uMAX: 150
TROY:
SHADOW X2: 150
SHADOW X3/X5: 277
Minelab
Xterra: 230
NAUTILUS
150 ON HIGH CHANNEL, 47 ON LOW CHANNEL.
WHITES
6000DI: 470
3900: 300
GM III: 168
CLASSIC I: 220
MXT: 230
So let's review a few
points:
1) To get the highest
volume and efficiency, match the headphone impedance to the machine impedance.
2) Mono detector phone speakers are in parallel. So 150 ohm speakers
will make 75 ohm phones, on ANY machine.. Minus a little (or a lot)
wasted by the controls.
3) If you use true stereo phones, this is a special case. The
speakers STILL end up in parallel, however the manufacturer will
spec the impedance in ohms per side. On machines other than Minelab
or Garret, 100 ohm per side stereo phones will end up at 50 ohms
seen by the machine. But on Minelab and Garret, the wiring in the
machine puts stereo phone speakers in series. In that case, 100 ohm
per side stereo phones will now become 200 ohm phones.
Ratphones use 600 ohm speakers resulting in true 270 ohm total impedance delivering
more power to the speakers and match a wider range of machines. They
have less distortion and higher clarity. They will be 270 ohms on
ANY machine. (300 minus a little for the controls).
Speakers. And frequency response.
As you are searching though the specs, see how many 150 ohm
(actually 75 ohm as discussed above) have a frequency response of
200 to 3200 Hz. Sound familiar? Well, most of the major brands that
I took apart have the exact same speakers! Why not, they have been
around a while, they seem to hold up. Yes they have been around
because they were developed for telephones. We all know how bad
telephones sound. Sure, nice and loud, but a bit distorted.
Engineers in those days had the attitude that if the human voice was
in that range then that is all the frequency response you need.
Maybe for Alexander Gram Bell. Not for today’s
electronics. We want to hear every nuance of the sound from soft to
loud!
It’s also interesting how
some headphones are “specially made” for a certain type of detector
but have the same speakers. Making phones that only work with
machine “x” or "y" by removing the compatibility switch, does not
make it optimized.
Ratphones frequency response is 20 Hz to 20KHz which is the full
spectrum of human hearing. Believe me, you will hear it! Since
Ratphones do not need a switch, the failure rate is greatly
decreased, not to mention the replaceable cord. Since the cord is
reversible to make them compatible with all machines, there is no
need for a switch or to produce a “special” version, except stereo,
or maybe a single volume. If you want something different, just let
us know.
DB
ratings
Don't
put too much stock in db ratings. Headphone manufacturers are at the
mercy of the speaker manufacturers on that one. There are many ways
to test this as there are standards. But let me say this, you can
take the loudest headphones and make them twice as loud. But if the
sound is not clear, you gain nothing.
Ratphones will allow you hear your machine better. That's what is
important.
Ear muffs.
Many headphones we see use
three basic styles. They are excellent for metal detecting. No metal
parts, comfortable and look stylish. There are two typical ways that
earmuffs are rated, NRR (noise reduction rating, North American) and
SNR (single number rating, European). They are just different
standards based on different test procedures. The SNR is always a
little higher that the NRR., so you will hear that number more often
in advertising. The original type that appeared has SNR rating of 28
db. The ones with the added an additional plastic piece is 29db. To
put that in perspective you need 2 or 3 db to notice a difference.
Then there are the “lighter” cups you see that are 24 db. Do they
feel lighter on your head? I don’t think anyone would really notice.
You may notice the slightly more hollow sound due to the thinner
plastic. Well, they cost less and are almost as good.
But that’s the three major
designs. 29, 28 or 24db. That’s all. No matter what the ad says.
Some like the super light home stereo phones also, which sound good,
but are uncomfortable and not really made for outdoors. In the
end, it's a personal preference. I'm just saying, if they look the
same, they are.
Ratphones use the popular 28 db NRR version in a gloss dark green. They are professional looking and cartoon picture fee. (Well,
just the little RAT logo). The new Pro-Form leather cushions have
increased the rating to the more stringent NRR spec. Not to mention
greater comfort! The new Pro-Leather ear pads conform to your
head for excellent isolation and unlike the older vinyl type, bounce
back like new and don't become brittle for a longer time.
Limiters.
This is a “circuit” that tends
not to affect the lower volume sounds and prevents the loud sounds
from being too loud. If you have a modulated audio machine that has
weak and loud sounds, some users like this. Some machines (many
Whites) have too much dynamic range in the audio, where if you turn
up to hear deep, the shallow targets are way too loud.
Recently I tested the Whites
MXT. This machine needs a limiter on many headphones. It's much too loud on shallow
targets. Our limiter will work just right and will not affect your
deep signals. The medium volume signal will decrease slightly and
the loud blasts just a little louder than the medium ones. It is a soft knee limiter that still allows you to
tell the difference but with much less of a blast. It also generates
even order harmonics rather than odd which would make the sound
harsh or distorted. Also, if you are not using full range headphones
on an MXT, you are really not hearing that machine as intended.
Ratphones will sound clearer at all volumes so you don't need to
turn up as high to hear the deep targets. But if you think you
still need limiting, we
will gladly insert our limiter circuit for low cost. It has a softer,
more natural limiting effect.
Volume Controls.
Volume controls, also called
potentiometers or "pots" can be a very important component in
headphones. Pick the wrong value and the max volume will be too low or the
adjustment range will not be smooth. Most
important, if you choose the wrong wattage, there could be too much
current through the control and it will be damaged or become
scratchy over time.
Let's say for example you have a 1K pot that is 0.2 watt and 150 ohm
speakers. This is used a lot on competitor headphones because they
cost less than a buck. The maximum current allowed though that pot will
calculate to 14 mA. With those speakers connected to a Whites MXT
the current can be as high as 22mA.
A Nautilus cam be over 40 mA That is a failure waiting to
happen! After about a month or so, the controls will burn out and
become scratchy from dead spots in the carbon element.
You can see why we changed to 1 watt pots.
From then on, we never follow the competition. Detents (clicks) are
not needed here. They have just the right feel for continuous
adjustment to get the exact setting you want. Plus we added an
o-ring for an even tighter feel. Our low inductance speakers also
have the same tone for the entire range of the volume control. So
you don't have to turn the volume all the way up to get a crisp
sound.
Switches.
Hey, who doesn’t like switches?
Sometimes they are necessary to turn features on and off or to make
headphones compatible with different wiring schemes of the machines.
They will increase the failure rate. The better ones that fail less
are very costly (and rarely seen).
Ratphones don’t need a switch. If you request a feature switch, we
use splash proof epoxy and internal o-ring sealed switches. No protection boots are
needed.
Volume
Are Ratphones the loudest? No. But you will actually hear more.
Limiting factors of volume on detectors are headphone output short
protection, component ratings, battery capacity and battery time. So
you can only deliver so much to the headphones. Then there is the
volume controls in the headphones. If you want a smoother range when
you turn the control, you will sacrifice volume. If you want full
audio range, you sacrifice volume. We think we have achieved just
the right balance. We understand that the clarity of the sound
is most important. If you just want the loudest beep, no mater what
the target, you should
look elsewhere. Then replace the speakers on your home stereo with
bull horns!
Circuitry
OK, let's call volume controls,
speakers and wires circuitry. Is there much engineering here? In our
case, yes.
Ratphones controls are industrial
sealed and cost 6 times more than the
typical low cost carbon commercial control. They will not be
affected by moisture, dirt or other elements and the rotation life
of these controls is much-much longer. Rated at one watt, makes them
unprecedented and just not found in the industry.
The max input voltage is 8.8v rms (4.4v single volume version), where the
typical competitor is 2v or 1v for single volume models. We
like a little more headroom than that because many machines deliver
1vac rms during battery test tone! Please note that these maximum
voltages do not correspond to the battery voltage. The duty cycle
(how long the pulse is on) and the output impedance plays a major
role in determining the actual machine output voltage.
Our wiring is military/aerospace
grade adding even more to the value and dependability. The Teflon
insulation can endure longer soldering time to insure proper solid
connections and resist stress. We even thread our own cross wires
with the same wire to insure the quality. No compromises!
Ratphones…something new….really.
Manufactured
with a lot of care and thought by Detect USA.
No hype needed.
Satisfaction guaranteed.
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