Single vs Multiple driver loudspeakers...

There are some single driver systems that very nearly cover the entire 20 Hz - 20 KHz range with reasonable linearity. The drawback here is that they typically lack sensitivity and are SPL challenged. If one can provide them with suitable quantity and quality of power and aren't too bothered by a lack of "raise the roof" volume levels, the things that they do well can many times more than make up for the things that they don't do. I know that my perspective changed quite a bit when i heard my first "full range" single driver system several years back. Then again, these aren't really conventional or even planar type drivers, so there might be something to that aspect of presentation too. Sean
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PS... Sounds like you're taking for granted that "single driver" means Lowther or Fostex type drivers according to much of what you wrote. They aren't the only game in town.

Twl: By the way, Nelson's comments about this being "the best sounding speaker he's ever heard" has a LOT to do with the linearity of it. After he was done combining equalization and amplifier loading characteristics, that speaker was VERY close to being "flat". While he did comment on the lack of bass, he's taking care of that in his next article. That is, he's going to bring in "El Pipe-O", which is a HUGE vertical pipe housing a sub that he built a while back. Sean
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El: You should start studying Walsh "Bending Wave" technology. It doesn't suffer from all of the problems that most conventional dynamic drivers that you have described do. No whizzers yet you can get very reasonable high frequency extension, excellent horizontal dispersion, gobs of surface area for good low frequency extension, etc... Using this approach though, one is still limited in SPL range though.

As to more conventional designs, Nelson Pass' latest DIY speaker effort is published in AudioXpress this month. Making use of a Lowther DX55 in each HUGE and highly technical cabinet, the results are staggeringly non-linear and completely lacking in bass. After applying equalization circuitry and running a completely out of the ordinary amplifier design that is the reverse of what is commonly bought and used, the end response doesn't look bad at all. The fact that it took someone like Nelson Pass, a huge cabinet, custom built electronics and this much work to get the speakers to flatten out says gobs about where this type of driver is at in the grander scheme of things. Sean
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Nelson is now marketing limited edition products specifically suited to the FR ( Lowther / Fostex ) crowd. As such, this was not only "research" for his products, but also the chance to have some fun and experiment at the same time for him. As you know, he's more of an "electronics man" than a "speaker man", so i'm sure it was a nice change of pace for him. The fact that he'll end up making money derived from the research and results that came out of this "fun time" probably doesn't hurt him either : ) Sean
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Twl: I've heard Lowther's, but not to any great extent. I've also read the entire article that Nelson published. I've seen the response curves and have at least a decent idea of what it took to get that driver to do what it is doing. I can pretty much guarantee that there's nobody other than Nelson Pass in the entire world that is getting that type of response out of those drivers. That is, unless there's someone else out there using similar equalization circuitry and an amp that has an output impedance that is appr EIGHTY ohms.

Even with all of that and a horn mouth that is 5 feet wide and 6 feet tall connected to a cabinet body that is 9.75' tall and 4.5' deep, the speaker is still -3 dB down at appr 48 or 49 Hz. In Nelson's own words "I have been extremely pleased with the results, but i must smile when i see that all of this effort barely gets us below 50 Hz".

Other than that, i have 104 dB horns and have driven them with as much as 400 wpc SS and 35+ wpc tube. Two watts isn't enough power for a speaker, even at that efficiency level. That's because 104 dB's @ 1 meter becomes appr 95 dB's at a 10' listening distance. While this is pretty loud for most people, it is nowhere near the levels that one hears at a live orchestral performance if sitting reasonably close to the performers. This is not to mention a live jazz, blues or rock show either.

Besides the spl levels, with only 2 watts, one is pretty much guaranteed to run the amp into compression and clipping on a regular basis. On top of that, feeding that much steady state power into an excursion limited Lowther is going to create dynamic compression and introduce other forms of distortion into the equation. This is why, even though he had a GIANT horn doing all the work and keeping the driver properly damped and loaded at low frequencies, Nelson Pass stated "Still, they play loud cleanly in a manner that Lowther owners don't usually encounter, and the cones are barely moving". Without the aid of a horn this size, there is just no way that the Lowther can produce ANY type of bass and / or high spl at the same time.

As a side note, Nelson provided the readings as taken from a Lowther in a standard sealed box. Using the output at 1 KHz as a reference point ( industry standard ), this driver is down appr -15 dB's at 100 Hz. By the time we get to 40 Hz, we are down almost -30 dB's. That's why he couldn't squeeze ANY deep bass out of the driver, even in that phenomenally LONG and HUGE horn.

Needless to say, i DO like some of the advantages of a single driver, but i also realize that, at least at this point in time, none of them do everything well. If you want extension, you give up efficiency. If you want efficiency, you give up extension. They are all a trade-off, some to a greater extent than another. Sean
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I am NO fan of "sterile" sounding audio systems, regardless of how well they measure. Music is neither sterile or boring and in order to reproduce it as it was recorded, a system needs to maintain a high level of accuracy. Combining the two aspects of reproduction ( musicality and measurable accuracy ) gives us "musical accuracy". Sean
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Gregm: According to the chart that Nelson Pass had published in that article, the Lowther DX55 showed a gradually dropping slope below appr 700 Hz. As compared to the average output levels in the upper midrange & treble regions, output was down appr -4 dB's at 500 Hz and appr -13 db's at 200 Hz. As such, without some type of equalization circuit, the usable bandwidth of this specific driver is much narrower than what you've described.

For those of you that are "into" the full-range driver approach, AudioXpress recently had an article about modifying a small Tang Band driver. After modifications, it was FAR more linear than any Lowther i've ever seen and even had greater bass extension and linearity. The fact that it is only a 3" driver severely handicaps the ability to achieve the spl's and / or dynamics of the much larger Lowther drivers. Once again, we come back to the fact that there are trade-offs with ANY loudspeaker design and they become even more complicated as one reduces the number of drivers used.

It's too bad we can't find some way to make a plasma driver both more efficient and wider bandwidth. This would solve all of our problems. Well, that and getting rid of the excess ozone that they generate : ) Sean
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The article was published in the January 2005 issue of AudioXpress, complete with photos, text and test results. It is no joke as can be seen by the end result. Sean
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I've never seen very much on the Manger's although the design intrigues me. John Curl has made some very positive comments about these drivers and their potential, but once again, they are limited in terms of spl and extension. The articles that i have seen have suggested using multiple Manger's to get around this problem, which somewhat defeats the purpose of using a full-range driver. That is, the point source radiation pattern is lost with more potential for phase related cancellation issues. Sean
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