Midrange drivers

August 20, 2016
 by Paul McGowan

First, a quick note that John Darko published a terrific, insightful and informative review of DirectStream Junior.

Now, on to speakers and crossovers.

We've covered how tweeters and woofers get their sound isolated for proper operation in a 2-way loudspeaker. The crossover separates highs from lows and sends the signal to the correct driver.

Tweeters use a single capacitor in what is known as a highpass filter (all the highs pass through).

Woofers use a coil and a capacitor in what is called a lowpass filter (you can guess that one easily enough).

But what magic takes place when we move to a 3-way loudspeaker with a tweeter, midrange, and woofer?

This type of filter is known as a bandpass because only a narrow band of frequencies pass through.

How is that done? By combining the first two filters we learned about, the lowpass and the highpass (the woofer and tweeter filters), into a single filter for the midrange.

If you think about it, it's a pretty obvious solution. We don't want our midrange driver reproducing bass or treble - so we roll off the bass as well as the treble and leave a hole in the middle which we call midrange.

Most midrange drivers more closely resemble large tweeters than small woofers.

ScanSpeak Midrange dome

This is a picture of a SanSpeak 3" midrange dome, for example.

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16 comments on “Midrange drivers”

  1. Glad I just bought the DSJ ! Coming in next week (I hope).
    Not that I care a lot about other opinions in audio, but now I know that at least one other person likes the DSJ.
    Well, and of course Paul McGowan. and probably Ted Smith also.
    I'm not alone anymore.

  2. Paul, you just described the biggest dilemma in audio both analog- and digital wise : cutting the music into pieces and trying to mount the pieces finally together again hoping to get the original gestalt. No chance here to realise the ideal of HIFI. The best you can get is an artificial sound that resembles more or less the original sound. Henry Koss made already a similar statement in an interview some decades ago. Sound preferences are most different. Thus some look for powerful bass other for natural voices and other for just getting the rhythm right.

  3. Paul, sorry to disagree but IMHO I think you will find that far more 3-way speakers come with cone mid-range drivers. It's certainly the case with the models available here in the UK

      1. He's thinking cone vs dome, and in this case he has missed the mark. Aside from the preponderance of proprietary cones made by/for speaker manufacturers, on the open market it's a cone world. At Madisound, 32 of the 40 midrange drivers offered for sale are cones.

  4. Edgar Villchur (Acoustic Research) who invented the acoustic suspension woofer also invented the dome midrange and dome tweeter. The tweeter introduced in the AR2a around 1959 by adding it to AR2's 10" woofer and 2 Jensen 5" cone midrange drivers was incorporated into the 12" AR3 by adding it to his 12" woofer and a new dome midrange driver. Out of the box unequalized and with their volume controls set in the indicated dot positions this speaker had a lot of problems. The dots I eventually learned were not the flattest response, they were there to indicate the best position for what Villchur perceived as exaggerated high frequencies in contemporary recordings of the day. The flattest position was at max settings and AR3 still needed a treble boost. In this setup, AR3 produced some remarkable live versus recording demonstrations. But AR3 still had problems, the same problem everyone who designs a 3 way system faces. Three drivers cannot cover the full audible range well without extreme measures. In AR3's case, the problem was at the top of the woofer's range, 1 Khz. Some years later AR came out with a version having an improved dome tweeter and dome midrange called AR3a. The crossover between the woofer and midrange was pushed down to below 500 hz and the problem became the bottom of the midrange driver's range. Most other 3 way systems have a problem at the bottom of the woofer's range where the speaker simply can't produce deep bass. AR's solution of the day was LST, a souped up version of AR3a which incorporated 4 midranges to improve their bottom of the range power handling capacity and 4 tweeters. Unlike contemporary dome midranges and dome tweeters such as the midrange pictured above and the midrange and tweeter used in AR9 those midrange and tweeter drivers were designed for maximum dispersion. This shows the difference between efficiency and sensitivity. Efficiency is the percentage of electrical power converted into acoustic power. Sensitivity is the loudness of the speaker on axis at a given distance for a given amount of electrical power. Wide dispersion drivers with the same efficiency will have lower sensitivity than narrow dispersion drivers of the same efficiency. Today almost all tweeters are narrow dispersion on the theory that they produce better "imaging." The dome shape has other advantages. For its mass it is stronger than a flat cone of comparable mass and less likely to break up in harmonic modes. Most modern dome tweeters and dome midranges are recessed or have a hornlike structure (AR9) and the tweeters are not full hemispheres to restrict their dispersion and increase their sensitivity. The old AR domes were full hemispheres and were smaller, the tweeter dome being only 3/4" in diameter. It had a remarkable dispersion of being only 5 dbs down 60 degrees off axis at 15 khz. Designed by Roy Allison, it was the best dispersion tweeter I know of except for his own brand's tricky design he invented later. Nothing comparable being available today, its deterioration with age has made it impossible to fully restore these speakers to anything like new (I have a pair of the 8 ohm version used in AR2ax that still amazingly work.)

    In IRS, Arnie Nudelll used a large number of EMIMs to increase their power handling capacity at their low end. (There were other reasons as well of course.) But in IRS Beta, with few EMIMs he used the same solution AR used when it threw in the towel on the 3 way design and added a lower midrange driver turning it into a 4 way design. If you have a 3 way design that does not produce deep bass the way AR3 and IRS can and you add a subwoofer, you too now have a 4 way speaker.

    KLH model 6 was the first speaker I know of that used the crossover network to not only restrict the electrical bandwidth of the signal going to each driver but the first one to use the crossover network to passively equalize response. This was and still can be done by employing an active equalizer to get the desired response and then building its passive equivalent into the crossover network. Many modern speaker systems use massive passive equalization which makes them a nightmare load for all but the most robust amplifiers to handle. Example, the YG Acoustics Sonja 3.1 and 3.3. This is intended to eliminate the need for active equalization that audiophiles hate and would usually create havoc with because they don't have the ear training skill to use them.

  5. 3" midrange is for little old ladies listening to compressed Mozart on the radio. My tweeters have more diaphragm area. Also, the dome resonance is in audible range for a 3" which makes for some nasty side effects. Cone breakup can be just as bad, especially with Aluminum or high stiffness fiber reinforcement like Carbon, Fibreglas, Kevlar, etc. The breakup should show in both the fr and impedance curve of the raw driver and the finished system. Look for glitches in the midrange. If they are missing, they are probably smoothed out!

    The midrange is where the music is, and keeping crossover phase shifts out of this critical range means running the midrange from 300Hz-4KHz. At real acoustic music levels (let alone electric music or trap sets) you need at least an 8" driver, some 12dB more output for the same displacement, to handle peaks and control Doppler distortion. I use 10," 8" or dual 5" midranges with low inductance motors and treated paper or filled polypro cones.

    1. Metal driver cones whether stamped or machined out of billets with computer controlled milling machines and lathes have the same properties as you hear when banging an aluminum pie tin. They do not dissipate energy quickly, they ring. This is why they sound harsh and bright. Kevlar drivers also have sharp resonances and must be crossed over so that no excitation at their undamped resonant frequencies reach them. Not good choices. Surprisingly good is the right quality paper. Energy in the cone or dome is quickly dissipated by the soft pulp fibers. Villchur was particularly concerned with the quality of the paper used in his cones.

      1. you might also have a look on the Danish manufacturer Dynaudio. I use the old Confidence 5 with esotar midrange and tweeter. It's an ekseptional 3 dimensional performance by these speakers. IMO the new confidence series do not convince. It's a mess when a manufacturer has reached the climax where no more improvement can take place. From then there is only marketing.

      2. No mention of silk dome tweeters, which seem to have disappeared from the scene in recent times? What kind of insight can you give us about them, please?

  6. Here is a thought almost any headphone has no cross over . It has almost no low end acoustic issues that speakers have.
    So how come very good headphones driven by a good front sound good as good Asa premium speaker. ??

  7. My room is empty in the middle lol. Thanks for the reply
    I figured it has no cross over and only one driver and got no answer speaker people hate headphone people lol. Doesn't it count I have speakers tooooooo.

    1. I have both speakers and headphones, too, but I'm relatively new to headphones. My guess is that most of the people here are Old School, hence less likely to have expertise on headphones. It would be nice if I were wrong. Maybe you could get an answer at Headfi.org. Maybe some of the iem's have crossovers? They seem to have a lot of tiny drivers built into some of them. Amazing, in the true sense of the word.

  8. A while back I commented there is a small trend today of using an almost full range driver instead of a midrange, and capping it on the ends with a woofer crossed over low, and a tweeter crossed over high, leaving the full range driver to cover say 100Hz to 8-10kHz, thus keeping the crossover out of the critical midrange. As I often post late in the day, nobody seems to pick up this ball and run with it. Oh well.

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