Announcement

Collapse

HUG - here for all audio enthusiasts

At its inception ten years ago, the Harbeth User Group's ambition was to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless, independent of the observer and can be replicated. However, we live in new world in which objective facts have become flexible, personal and debatable. HUG operates in that real world, and that has now been reflected in the structure of HUG.

HUG has two approaches to contributor's Posts. If you, like us, have a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual Science of Audio sub-forum area of HUG is your place. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be readily understood by non-experts and tried-out at home without deep technical knowledge.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings area is you. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area. From Oct. 2016, Posts in the Subjective Soundings area will not be spell checked or adjusted for layout clarity. We regret that but we are unable to accept Posts that present what we consider to be free advertising for products that Harbeth does not make.

The Moderators' decision is final in all matters and Harbeth does not necessarily agree with the contents of any member contributions and has no control over external content.

That's it! Enjoy!

{Updated Jan. 2017}
See more
See less

How do you determine the impedance of a speaker system?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • How do you determine the impedance of a speaker system?

    Hi Alan

    I have often been intrigued by how you determine the specific impedance of Harbeth speakers? Taking an example, the SHL5 has a 6 ohm officially published impedance. The impedance is very important since it determines how much power is needed from the amplifier to suitably drive the speakers. Generally speaking, a 60 watt amplifier (at 8 ohms) would be 90 watts at 6 ohms and 120 watts at 4 ohms. When I study the impedance chart (or at least try to), the impedance is represented as a curve which rises and dips across the frequency spectrum. Do you take an average across the board or is there any possibility to "massage" the figures in order to get the 'right' numbers? As a speaker designer, I would appreciate your thoughts on this question of impedance and of how manufacturers can determine the imepdance depending on the parameters they consider important.

    Best regards
    Dennis

  • #2
    A complex question

    Originally posted by denjo View Post
    Generally speaking, a 60 watt amplifier (at 8 ohms) would be 90 watts at 6 ohms and 120 watts at 4 ohms
    Denjo - what you have written would be precisely accurate if impedance and DC resistance were one and the same thing. I think, before your question is answered, we need a short discourse on the nature of AC and the relationship between AC voltage and current and what happens when the frequency in question is near a crossover point.

    What a can of worms :)

    Comment


    • #3
      Measuring impedance

      The simplest way to do it, is to use a signal generator on the speaker input that generates a 1 V signal and let the generator sweep the signal from 20 Hz to 20 kHz and measure the resulting current on a large number of points, which you then can calculate back to impedance with Ohm's law (U = I * R, or R = U / I, where U = 1 V, so R = 1 / I).

      Well, this is theory, I haven't really tried something like this in practice.

      Comment


      • #4
        SHL5 - an easy electrical load (analysis)

        Originally posted by denjo View Post
        I have often been intrigued by how you determine the specific impedance of Harbeth speakers? Taking an example, the SHL5 has a 6 ohm officially published impedance. The impedance is very important since it determines how much power is needed from the amplifier to suitably drive the speakers. Generally speaking, a 60 watt amplifier (at 8 ohms) would be 90 watts at 6 ohms and 120 watts at 4 ohms. When I study the impedance chart (or at least try to), the impedance is represented as a curve which rises and dips across the frequency spectrum. Do you take an average across the board...
        Firstly, the doubling of power output from an amplifier with a halving of the resistive load is a theoretical ideal. It takes a very good amplifier with a strong power supply to even approach that sort of behaviour.

        Taking a look at the SHL5 electrical impedance curve, it can be seen that the minimum impedance is about 5.9 ohms in the vicinity of 150 Hz, although it does drop as low as 5.2 ohms at 20 kHz. The minimum at about 150 Hz has a phase response of about 0. This indicates that the speaker is behaving more or less like a pure resistance around that frequency, and that is a relatively easy load for any competently designed amplifier to drive.

        Keep in mind that there is usually quite a bit of sound energy in the 80 Hz to 500 Hz frequency range, so having a relatively moderate impedance of around 6 ohms in that range makes for an easier load for any amplifier. Outside that frequency range, the impedance of the SHL5 is usually greater than 6 ohms, so that means that the amplifier will need to supply relatively less power to the loudspeaker at those frequencies for a given sound pressure level. The maximum phase shift in the electrical impedance of around 40 also helps to make the SHL5 an easier load to drive as the impedance is not very reactive in nature.

        Comment

        Working...
        X