Tim Gillett wrote:So harmonic distortion from the horn driver. Tha's a lot more targeted than just mention of "harshness".
Equating technical descriptions with underlying causes has always been a problem. But it seems natural to me that harshness = distortion. If it had been a simple EQ problem I would have commented on it being bright, or maybe forward sounding.... But to me, those old JBL studio monitors sounded 'harsh', meaning they introduced audible HF distortions.
I understand JBL invested heavily in R & D with compression horns.
They needed to -- along with every other manufacturer of horn drivers -- but I understand reducing distortion in compression drivers was a very difficult nut to crack because of the inherently non-linear behaviour of modulating air as a sound medium at high pressures.
That's why I was so surprised and impressed with what Meyer had achieved when I first heard the X10 in the run up to Christmas 1999.
...but precious little about the horn, as if he was basically using standard horn technology of that time. If Meyer had been doing something new with the horn it seems strange nothing was said about it in the article.
Meyer had used standard JBL compression drivers in a lot of their PA speakers up to the late 90s, as there wasn't really much alternative. However, his company often rebuilt them to improve their performance, and learned a lot about the technology in the process.
But when Meyer was commissioned to build a PA system for an Opera House it became clear that these existing horn drivers just weren't good enough for the job, and that's what started John down a development path to build a fundamentally better compression driver of his own design.
The compression driver in the X10 was essentially his second-generation design, so he really wasn't using 'standard horn technology'. And it's not really strange that the information is limited: I had to sign NDAs when I first went to see and hear the X10 prototype, and I continued under those NDAs when I was subsequently commissioned to write up a lot of the public-facing and internal company documentation on the project. It was all genuinely pioneering stuff that involved a lot of commercial secrets.
In brief, and within the bounds of what I can say about it publicly, John and his R&D team managed to create bespoke innovative compression horn drivers that produced well below 0.2% THD at 90dBSPL -- directly comparable to dome drivers -- but these drivers were able to maintain very low distortion levels even at continuous SPLs far beyond the capabilities of any dome tweeter.
For comparison, typical compression drivers (at that time, anyway -- I don't know how the technology has been advanced by other manufacturers over the last 20 years) produced around 1.5% THD at 90dBSPL. That kind of distortion might be acceptable when working at PA levels with the driver pushing out 130dB plus, but it clearly isn't in a quality studio monitor that probably spends most of its time working around 85dB SPL or so (in large professional control rooms).
The Meyer R&D team spent two years developing their compression driver, starting with a 3-inch unit because they had the facilities to stamp the complex diaphragm shapes and had suitable magnetizers on site. The final design involved an innovative alloy and bespoke shape for the diaphragm, as well as a clever hybrid suspension which was much quieter and introduced massively less distortion than conventional solutions.
They then scaled this driver design up to a four-inch model which had a greater bandwidth and could be coupled to a 15-inch bass driver in a two-way design. (The 3-inch couldn't go low enough to achieve a viable two-way crossover with a 15-inch bass unit, and was generally used with 12-inch bass drivers).
Much of the driver's performance gain, though, was down to the design of the compression throat feeding into the horn, and John worked with the Jet Propulsion Lab as only they had the technology and experience to analyse the behaviour of air at high pressures in confined spaces!