Speaker impedance, series/parallel, and
matching speakers with sound decoders.
by
We all assume
everyone knows about stuff when it is discussed... Seeing the odd question I
get the feeling that it might not be so in relation to speakers.
So... in case some list members are not familiar with speaker hook up
needs, perhaps its worth explaining a little about how
to connect multiple speakers. I will try to use simple words not jargon so
technically it may look imperfect, but practically the advice is good.
Hope it doesn't bore you... If you already know this stuff hit delete....OR
perhaps add a bit to help explain to those who need to learn about
"impedance" and its effect on the sound / life of the decoder.
About multiple speakers...
Simple answer - Sound decoders are designed to use one only, so use the
biggest single speaker of the correct impedance to make the best possible /
most efficient use of the built-in amp.
Longer answer, use two or more speakers if you need to, but be careful
about how you wire them up. Remember that the speaker is not an add-on
accessory - it is part of the amp circuit. So...
Speaker impedance is as important as any other component specification in the
circuit, and it its too far away from correct it will cause damage.
Some "ABC" speaker connection info...
Before we start - you can never just add a resistor to a speaker to make
the impedance right. Impedance is reactive and changes with frequency. At best
using resistors will waste power and result in really bad sound.
Basic speaker connection: (On lokSound (+) has a
red mark)
Series = daisy chaining the speakers. Two speakers in series would be: (-)
lead of amp to (-) terminal of speaker #1, (+) terminal of Spk
#1 to (-) terminal of speaker #2, (+) terminal of speaker #2 to (+) lead of
amp. When speakers are in series, just like with resistors, the impedance ADDS
(8+8=16ohms or in the case of loksound 100+100 =
200ohms)
Parallel = stacking the speakers. Two speakers in parallel would be: (-)
lead of amp to (-) lead of speaker #1 & to (-) lead of speaker #2, (+) lead
of amp to (+) lead of speaker #1 & to (+) lead of speaker 2 When speakers
are in parallel, just like with resistors, the impedance DIVIDES (8+8 = 4ohms
or in the case of LokSound 100+100 = 50ohms.
It is important to observe the + and - correctly. Doing this wrong will
cause cancellation of frequencies (out of phase speakers) and sound will get
thin and reedy. Example: swap wires on one of the speakers on your home hi-fi -
see how the bass disappears!!!
In the application of loco sound, we need to keep efficiency high. That
means not increasing the impedance of the load on the amp. We also need to look
after the amp, as lowering the impedance too much will damage it. This kind of
damage is obvious to a technician and would cancel any warranty cover! Ideally,
we need to keep the impedance of a LokSound as close
as is practical to the design level of 100 ohms, but you can vary it a little.
I would suggest that 50 ohms is the lowest safe limit. (2 speakers in
parallel... I've tested at this level and it gets warm but no damage). There
are + and - things that happen when you use multiple speakers.
Mulitiple speakers CAN help imaging (say
a small one up front to emphasise steam sounds, a bigger one on tender to
emphasise the general or lower frequencies) and they will also APPEAR to make
it louder. However be aware that by lowering impedance we exceeding design
spec, we are also increasing distortion a lot so it may not sound quite so
clean or sharp. This isn't too much of a problem in the example as experience
shows that most users lower the volume in an install like this and therefore we
re-balance the output a bit to keep close to spec, so it sounds good.
Using several speaker CAN work / be safe... for example if you take 4
identical speakers, make two pairs of 100 ohm speakers in series, then
parallel the two series pairs, you get back to the original impedance. Takes a
lot of space, though.
Also... using lots of speakers LOOKS like it would have the ability to move
more air BUT remember they each have "mechanical losses". This means
part of the amplifier power is used just to make the speaker start to move, so
less is available for making sound. Obviously several speakers will take
several times as much power just to start to "move", so even though
they have 4 times the cone area they will NOT make 4 times the noise...
Hope this helps... have fun and experiment with care - it’s the only way to
learn... BUT don't be silly and try 8 ohm speakers on a LokSound
- as Jason said, you'll damage it.
DCCconcepts
----- Original Message -----
From: "Jason McNair" <
To: <
Sent: Tuesday, August 09, 2005 7:45 AM
Subject: Re: [loksound] Difference between 4, 8,
32, 100 ohms speakers
I have to agree with Wolfram . . . the best speaker is the one that your
system is designed for.
For Loksound decoders, that speaker is the 100ohm
speaker - one of which is supplied with each decoder.
If you are designing your own system, then I guess it is up to you as to
which speaker you choose. Note that a higher impedance speaker will actually
require less power dissipation within the driving circuitry, and also will
allow for your amplifier to gain better control over the speaker coil, thus
producing a sharper and more controlled and accurate sound - something that is
readily apparent when comparing LokSound with other
sound decoders utilising 8ohm speakers.
The only difference between the various speaker values is the apparent
resistance and inductance that is presented to the system that they are connected
to. Mechanically, the higher the value, the larger the coil
and more powerful the magnet to compensate. Audibly, it is really up to
your ears to tell the story - there are vast differences between speaker types
of the same impedance value.
Which is best? That depends on what you wish to achieve. Higher impedance
speakers as already stated do allow for lower power dissipation with-in the
amp, thus allowing for cooler running, as well as greater control of the
speaker itself and lending for greater clarity. That does not mean that 8 or 4
ohm speakers are no good, as you can hear the results for yourself within the
hi-fi audio industry which uses 8 ohm speakers almost exclusively to produce
exquisite sound.
However, they have the luxury of larger speakers, enclosures and amplifiers
than we do in our trains - which is where minimum heat, lower power consumption
and greater control of the speaker diaphragm really does count and shine
through in the sound quality.
However, I do stress again that if you are purchasing an already built
system, then you do need to use speakers that match the impedance rating for
that system. Using an 8ohm speaker on a 100ohm system (such as a Loksound decoder) would be equivalent to placing a short
across the output - and instantly fry the audio output.
>
> Jason
> -----------------------
> Wolfram Steinke wrote:
>
>> The best is the one that the amplifier is
designed for. If there's a
>> mismatch
>> in the impedance for the speaker and the amplifier the maximum
sound and
>> it's quality will be affected.
>>
>>
>>
>> ----Original Message Follows----
>> From: "wakgrimes"
<wakgrimes@yahoo.com>
>> Reply-To:
>> To:
>> Subject: [loksound] Difference between
4, 8, 32, 100 ohms speakers
>> Date: Mon, 08 Aug 2005 12:36:32 -0000
>>
>> What's the difference between 4,8,32,100 ohms speakers? Which is
best?
>