Connecting Headphones in Parallel With a Speaker

[mg]

If you are hooking up to more than one speaker, realize that the
negative speaker terminals are usually not common, and cannot be
connected together.

You can get a 'speaker pad' to do the level adjusting, they are
available in a number of different impedences.

I was giving the speaker-pad idea some serious thought since it's
something that I can buy off the shelf and I'm really not all that
anxious to go buy a box and start soldering wires and resistors.
However, I did happen to stumble across something that looks like it's
designed to do exactly what I want to do. It's called the "HeadTAP
Headphone Tap" and it's available at the following URL:

http://tinyurl.com/26pjt4
http://img3.musiciansfriend.com/dbase/pdf/spec/180628.pdf

 

[mg]

You don't have to get sound in only one ear - just parallel the left and
right phones. The impedance will be half, but take that into account for
your attenuator.

Cheers!
Rich

Great idea. I'll probably do that.

 

[mg]

It is better to use a circuit like this:

150 Ohm
-- R1 -----------
from |
amp R2 10 Ohm headphones
|
-----------------

I would have never guessed that the best way to do it is with two
series resistors instead of simply using one, but then I don't know
anything about audio. I did manage to find something off the shelf and
it has the two-series resistors design. The only difference is that
the second resistor is a potentiometer. So, I suppose if you went to
the end of the adjustment, you would only have one resistor, but
otherwise there would be two. I've decided to buy it. It's called the
"ART HeadTap Headphone Tap" (#180628) and is described at:

http://tinyurl.com/26pjt4
http://img3.musiciansfriend.com/dbase/pdf/spec/180628.pdf

 

[mg]

"mg" < wrote ...




Similar things have been done perhaps since before you were born.


3K is very high for this application. You don't really need
any series resistance to prevent overpowering the headphone
since it is such high impedance already (compared to the
speakers). However resistance on the order of 100 ohms
(or higher, up to 1K for modern higher-impedance headphones)
is frequently used as a form of attenuation. Most power amps
are rather noisy, but you don't hear the noise because you
don't listen to speakers with you ear against the grille. But
when you directly connect headphones to the power amp
output, you will likely hear this low-level noise. Attenuating
the audio with a series resistor is a cheap way of dealing
with this issue.

Thanks Richard. As soon as I read your first sentence the lights
turned on and I realized the 3K would be to high. I did find something
available off the shelf, by the way, that I believe will suit my
purposes. It's at:

http://tinyurl.com/26pjt4
http://img3.musiciansfriend.com/dbase/pdf/spec/180628.pdf

 

[StickThatInYourPipeAndSmokeIt]

You don't have to get sound in only one ear - just parallel the left and
right phones. The impedance will be half, but take that into account for
your attenuator.

Cheers!
Rich

Headphones are not 8 ohms.

 

[Arny Krueger]

"Arny Krueger" wrote ...

I think we have lost track of what "damping factor" is.

The most compliant headphone element is extremely stiff
compared (on a proportional basis) to even an average
modern LF speaker driver.
I agree with Arny that throwing a (relatively) large
series resistance in the line will just exacerbate the
frequency-response roughness (because of varying
impedance). But that is a different phenomenon than
"damping factor".

If you say so.

I agree that it is desirable to feed headphones (or most
anything else, for that matter) from a low-impedance,
flat (freq-resp) source.

Same reason why it is desirable to feed just about all loudspeaker systems
from a low-impedance source.

Discussions of damping factor focus on bass driver performance, but the
actual audible effects of driving a speaker system from a high impedance
source are very often more audible in the midrange.

But "damping factor" needs a low
impedance load as well, else you can't "control" the
position of the transducer.

Whether it is headphones or a loudspeaker system, the disease and the cure
are often almost exact analogs of each other.

It is more likely that you'll find headphones with a fairly flat impedance
curve than speakers. I'm not sure why that is, but it is possible that the
explanation could be as simple as a shunt resistor.

 

[Arny Krueger]

I have seen plenty of speaker curves, but I'm lost as far
as headphone Z curves.

http://www.headphone.com/technical/product-measurements/build-a-graph/

 

[JANA]

On both the left and right side feed, put a 160 ohm / 1 Watt resistor. The
ground is common. This is standard.

If you connect your headphones directly across the amplifier output, you
will damage them.

--

JANA
_____


I would like to connect some headphones in parallel with a single
speaker. The amplifier powering the speaker is a 110-W, Sony STR-DE997
A/V, surround-sound receiver. The speaker has an 8-ohm impedance. The
headphones are Sennheiser model HD 580 (open air) with a nominal
impedance of 300 ohms and a "load rating" of 200 mW.

I'm sort of guessing/figuring that a 3K-ohm resistor in series with
the headphones ought to work. The 3K ohm resistor in parallel with the
8-ohm speaker would yield a net resistance of about 7.9 ohms to the
amplifier. And if power divides the same way current does, that should
provide a maximum of about 300 mW to the headphone. There would only
be a signal to one side of the headphone, of course. I would also put
a headphone volume control in the cord.

As anyone ever done anything like this before? Does anyone know of any
reason it wouldn't work?

---------------------------------

The reason I want to do this, incidentally, is to try to clear up a
problem that I have with hearing dialog in TV movies, etc. The
headphone would be connected to the center speaker of my surround
sound system. The center speaker typically carries the speech part of
the audio, while the other speakers carry mostly the sound effects.
The fact that I would only get sound in one ear probably wouldn't
matter at all since one of my ears is really, really bad and the other
one is only sort of bad.

 

[Don Pearce]

http://www.headphone.com/technical/product-measurements/build-a-graph/

Unfortunately this bunch appear not to have understood the measurement
they are making. They have used a dummy head with ear canals and a
microphone at the bottom of them. So they are measuring the response
of both the headphone and the outer auditory system - which is exactly
what is not wanted. It is the ability of the phones to deliver a flat
response at the outer edge of the pinna that is the measure of the
quality of the headphones. The first bit of the head's auditory system
has to unflatten the response to whatever degree the rest of the
internal system needs.

d

 

[Jan Panteltje]

I would have never guessed that the best way to do it is with two
series resistors instead of simply using one, but then I don't know
anything about audio. I did manage to find something off the shelf and
it has the two-series resistors design. The only difference is that
the second resistor is a potentiometer. So, I suppose if you went to
the end of the adjustment, you would only have one resistor, but
otherwise there would be two. I've decided to buy it. It's called the
"ART HeadTap Headphone Tap" (#180628) and is described at:

http://tinyurl.com/26pjt4

Yes, that is the same circuit, note 'input impedance 150 Ohm'.

http://img3.musiciansfriend.com/dbase/pdf/spec/180628.pdf

Right, and they use a potentiometer for R2, with the headphone
on the tap, so even lower drive impedance for low volume ;-)


And use 2 circuits.

45$ is a lot of money, I can buy a DVD player for that IIRC,
but anyways, if you are not into DIY, then it is a good solution.

Regards
Jan

 

[Arny Krueger]

Unfortunately this bunch appear not to have understood
the measurement they are making. They have used a dummy
head with ear canals and a microphone at the bottom of
them. So they are measuring the response of both the
headphone and the outer auditory system - which is
exactly what is not wanted. It is the ability of the
phones to deliver a flat response at the outer edge of
the pinna that is the measure of the quality of the
headphones. The first bit of the head's auditory system
has to unflatten the response to whatever degree the rest
of the internal system needs.

Note that I cited this source as a reference for impedance curves. ;-)

 

[Don Pearce]

Note that I cited this source as a reference for impedance curves. ;-)

Did they have those too? I didn't bother moving on after the amplitude
nonsense.

d

 

[Arny Krueger]

Did they have those too? I didn't bother moving on after
the amplitude nonsense.

Impedance curves was the context in which I mentioned them...

 

[GregS]

http://www.headphone.com/technical/product-measurements/build-a-graph/

Its my guess, its good to stay away from driving Z's 1 to 3 times the nominal
headphone Z. Lower and you get constant voltage, and much higher
you get constant current feed. This I am thinking will minimize impedance
responce errors.

greg

 

[Don Pearce]

Impedance curves was the context in which I mentioned them...

OK - wasn't even half concentrating.

d

 

[Arny Krueger]

Its my guess, its good to stay away from driving Z's 1 to
3 times the nominal
headphone Z. Lower and you get constant voltage, and much
higher you get constant current feed.

I have the impression that headphones are designed to work in range from no
higher than matched impedance to constant voltage. Hi-Z phones tending more
towards constant voltage, and Lo-Z phones more like matched impedance.

In the case of HD-580s, I am comfortable with source impdances from about 80
ohms to 16 ohms to minimum.

 

[GregS]

I have the impression that headphones are designed to work in range from no
higher than matched impedance to constant voltage. Hi-Z phones tending more
towards constant voltage, and Lo-Z phones more like matched impedance.

In the case of HD-580s, I am comfortable with source impdances from about 80
ohms to 16 ohms to minimum.

There is a lot of variation among the Z plots from that web page. i'll have to study
them some more.

greg

 

[mg]

Yes, that is the same circuit, note 'input impedance 150 Ohm'.


Right, and they use a potentiometer for R2, with the headphone
on the tap, so even lower drive impedance for low volume ;-)

And use 2 circuits.

45$ is a lot of money, I can buy a DVD player for that IIRC,
but anyways, if you are not into DIY, then it is a good solution.

Regards

I actually missed the 150-ohm input impedance spec. It must be old
age, I guess. Back in my younger days, I used to do a lot of DIY
projects. In fact, I think I still have some Greenley chassis punches
out in the shed someplace. I also have an old Tektronix, 200 MHz scope
laying around and a couple of multimeters. Years ago, though, before I
retired, I discovered that if I applied my efforts to the stock
market, I could make more money in a few days in the stock market than
what I could save in a lifetime of DIY.

Thank you for the help Jan. I really appreciate it.