Speakers, headphones, Ohms, ipmedence…

[tadka]

Not strictly computer stuff but it is hooked up to my PC so here it goes.

I have studio monitors Alesis M1Active 520USB. They connect to my PC via USB and have an internal Amp and a headphone jack socket.

I just bought new headphones Beyerdynamic DT 990 Pro 250 OHM.

They work okay but I have a nagging feeling something is not right. As if the sound is a bit week or something. I did a bit of googling and apparently there is something called impedance and that might have something to do with that. Tried reading about it but as always anything electronic is a bit of a struggle for me. Also tried googling to find out how many ohms are put out by the headphone jack on those monitors but no luck.

Any idea regarding this? Am I just imagining things or are those headphones too powerful for my speaker output?

[doctoryorkie]

The speakers may well just use passthrough for the headphone jack.

Plug the ‘phones directly into your sound card / MB output.

If the volume is still too low, you might need a headphone amplifier.

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[RSB]

Just an idea. Have you got the option of going over the Max headphone volume “Boost I think” in the sounds control pannel. If not try and search google to enable it. I use it often in windows and linux to.

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[tadka]

Maybe it’s just my imagination. If I turn the volume on the studio monitors way up I can physically feel the vibrations from the headphone drivers hitting my ears. But it’s just that for some reason I feel like there is something missing from the sound but I don’t know what. Maybe I feel that way because my previous headphones had smaller drivers and more high frequencies and now the lower frequencies of my new headphones makes it look like something missing. I don’t know. I think I thought that lack of Ohms is struggling to generate those high frequencies. Probably just paranoia and ignorance on the subject talking here  🙂

[Alan Wood]

This is an extremely complicated subject and difficult to explain to a non-electronic person. Basically the rule is that the impedance of the headphones must match the output impedance of the amplifier it is plugged into. Unless this is met then the maximum power transfer does not occur. Any mismatch results in a reduction in power transfer.

There is a further complication. Resistance (ohms) is the relationship between the voltage applied and the current (amps) that flow through the circuit. The relaionship is expressed mathematically as Resistance(R in Ohms) equals Voltage divided by Current or R=V/I where I represents current in Amps.

If a voltage is applied to a purely resistive circuit then this relationship holds true. This rarely the case however as most circuits involve the use of inductance (L in Henries) which is associated with a coil or magnetic effect and Capacitance (C in Farads) which is associated with electricity storage between conductive surfaces separated by an insulating material.

In these circuits the reactance (equivalent of resistance) varies depending on the frequency. Reactance increases with frequency in an inductive circuit and decreases in capacitive circuits ie the opposite effect. Most circuits comprise components containing inductance and capacitance, so the circuit as a whole is frequency dependent, Impedance (Z) is again the overall equivalent of resistance when the circuit contains inductance and/or capacitance and is therefore frequency dependent.

 

Applying this to the question, the output impedance of the amplifier must match the input impedance of the load circuit for maximum power transfer. Any mismatch therefore has varying effects depending on the frequency which could result in progressive loss of higher or lower frequencies depending whether the load is inductive or capacitive.

In this case the possible resistive  mismatch could be causing the loss of volume and the possible loss of high frequency by an impedance mismatch.

Unfortunately Tadka does not give the output impedance spec of the amplifier so it is not possible to give a definitive answer bearing in mind that headphones have impedances ranging from as little as 8 ohms and he is using 250 ohm headphones.

Impedance matching is important as if the mismatch is large, then the power dissipated in the output device (which should have been transferred to the load device) can rise above its rating causing overheating and eventual burn out failure.

This is a very simplistic explanation to explain the basic idea behind the situation and I appreciate it hard for a non electrical engineer to fully comprehend.

[Ed P]

@Alan, I thought that you did a great job of explaining it!

About the only thing you could perhaps have emphasized is that obviously the ‘sound’  being amplified consists of many different frequencies so if the impedences are not matched then some frequencies will get boosted and others muted so giving an overall lower sound quality.

[tadka]

Thanks for the replies. AW lost me on the second sentence in that post. The rest was just like… what?..

Still, judging from those end sentences it sounds like I probably bought headphones with too many OHMs.

I do like the headphones tho so will look into the amplifiers and if they are not too expensive and can work with my setup then I will get one.

[JayCeeDee]

If you can get into the manufacturer’s support page – internet first, then Facebook or Twitter might be a way to try, – you need to find out the output impedance that is on the headphone socket, coming from the speaker’s inbuilt amplifier.

This will give you the necessary information to either swap your new headphones for the same model, (but with different impedance) or some form of impedance matching transformer or piece of kit, that will allow you to match them correctly.

Some manufacturers like Beyerdynamic have 2-3 different impedances for the same model, which they list for different sources.

Above quote from HERE – { advice:) just take the quote, the rest of the info lost me and I have a basic/general understanding of it albeit from a good few years ago!!}

 

EDIT – I’ve just seen that ALESIS have a support forum HERE. That may be the best place to find the impedance details you need.

[Alan Wood]

Ed P wrote:

About the only thing you could perhaps have emphasized is that obviously the ‘sound’ being amplified consists of many different frequencies so if the impedences are not matched then some frequencies will get boosted and others muted so giving an overall lower sound quality.

Quite correct, I should have summed it up with this conclusion.

 

I like the explanation in the link by JayCeeDee but thought it a bit too technical for Tadka who professes to be non technical in this area.

[JayCeeDee]

I like the explanation in the link by JayCeeDee but thought it a bit too technical for Tadka who professes to be non technical in this area.

 

Hence the “{ advice:) just take the quote, the rest of the info lost me and I have a basic/general understanding of it albeit from a good few years ago!!}” comment??

[Alan Wood]

Hey I finished college in 1972 at the ripe old age of 30 so it is digging up issues I have not had to look at for over 40 years but then again the basics never leave you once fully understood. It is the detail which eludes me now. I used to love circuit analysis in real time using Laplace transforms on servo mechanisms but now I can only just remember what a Laplace transform is, never mind how to manipulate the maths of it. There again at 73 and retired I no longer need to do so but it is nice to know that if needed I could go back and use them I have the capability to do so. Lets hope never.

[JayCeeDee]

Alan Wood wrote:

Hey I finished college in 1972 at the ripe old age of 30 so it is digging up issues I have not had to look at for over 40 years but then again the basics never leave you once fully understood. It is the detail which eludes me now. I used to love circuit analysis in real time using Laplace transforms on servo mechanisms but now I can only just remember what a Laplace transform is, never mind how to manipulate the maths of it. There again at 73 and retired I no longer need to do so but it is nice to know that if needed I could go back and use them I have the capability to do so. Lets hope never.

 

I know – it’s great. There are still times when my memory of Elementary Telecommunications Practice ( City & Guilds ) from the late 60’s amazes my son  with a Computer Science degree!! He didn’t think the old man was that smart!!:) But it was all basic principles that apply today, just as they did then.

[Wheels-Of-Fire]

Ah yes Mr Ohm. Didn’t he date a girl called I V Whatts ? ?

On the question though I had a problem with a pair of old Boston Accustics digital speakers that had something “missing” after upgrading to W10. It turned out that although I had told windows that my speakers were only stereo it was still outputing 5.1 sound. My speakers only decoded the front stereo pair so I lost the center channel along with most of the mid bass. I can’t remember exactly how I fixed it but it involved pluging a pair of headphones into the PC and setting them as the only speakers with the main ones unpluged. After pluging the digital speakers back in and some messing in windows sound settings things started working properly.

[Wheels-Of-Fire]

Oh and Mr Kirchoff drove me loopy for a second with his law ?

[Alan Wood]

Wheels-Of-Fire wrote:

Oh and Mr Kirchoff drove me loopy for a second with his law ?

 

If In remember he postulated 2 laws.

 

At any node the sum of currents in equals the sum of currents out.

In an circuit the EMF (Applied voltage) equals the sum of the individual potential differences in the circuit components.

.

Common sense really as you can’t just lose voltages or currents.

[Ed P]

A major divert but (sort of) but computing related. When I was at college, digital computers were mega expensive, hard to program (assembler) and quite limited. So we turned to hydraulics to emulate electrical behaviour – it was quite amazing how fairly complex circuits could be emulated by fluids (though sometimes with a little cheating when it came to things like triodes! fluidics link

[edit] I should perhaps have said that fluidics was bleeding edge at the time and thought to have much more potential than digital with its limited accuracy and round-off problems!

[Alan Wood]

Yes I remember that too. Fluidics were reliant on surface tension and stiction. We constructed logic circuits using them. At the time their potential was in fire risk locations in the petro chemical industries. I guess it never really materialised as the inherent problem was that they were much slower than conventional electronic gates etc.

[Wheels-Of-Fire]

By the time I went to collage we had the TI 7400 series logic gates. Hours of fun with truth tables and Boolian algibra if i remember rightly.

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