If you know how in some optical systems imagery get destroyed when an aperture getting closed to F64 or even smaller, then you understand what happens in compression driver when frequency get higher and spaces smaller. Yes, the proximity of wavelength to the geometry of driver’s cavities and the signs of Sound’s “liquefying” are clearly detectable in context of some phase-plugged compression drivers. Different drivers, in one or another degree, fight with the problem more or less successfully, however the result not particularly follows a brutal engendering logic.
Most of the contemporary common magnet structures (later Altecs 900 and others) suck sonically, big time suck. If the ceramic magnets perform more or less OK at LF drivers then at mid-range they sound like “taste of cotton candy” and at HF they sound like “dreck”. The drivers with electromagnetic magnet sounds sometimes too soft at lower midrange and this effect dynamically progresses across the frequency range: the lower it does the softer it sound. The exotic neodymium and Supermendur magnets are too exotic to say anything defiantly. If you heard one driver and the driver was bad then does it mean that the entire family of those drivers is impotent? Defiantly not! For instance the TAD does neodymium magnet and TAD’s drivers sound like synthetic caramels…Is it because of the neodymium magnet? Certainly not or possibly not? Have you heard many others midrange compression drivers with neodymium magnets? How many One or two/ I hoe you understand where I am doing with it…
Most of the diaphragms for compression drivers suck or do not perform well in context of it’s driver. The design a diaphragms and it’s surrounding that perform well within a given driver, within a specific plug, within a specific loading and many other thing is VERY complex and no one does it PREDICTABLY good. If some diaphragms do work well then it is more or less accidental. I do not even mention that none of known to me drivers has a civilized mechanism for a diaphragms alignment and as a result most of the diaphragms out there are not properly aligned. A non-aligned diaphragm is a big, completely moronic secret of the compression driver industry and even some of the manufactures with whom I spoke are totally clawless about the effectiveness of a correct alignment. With some compression drivers by tightening of those ugly alignment bolts I was able to move a octave of a tone (!) or was able to reach the harmonic distortion of 25%! In all extreme position the diaphragm was “perfectly aligned” and the coil did not scratched the walls of the gap. Practically none of the drivers offered any inelegant way to secure or mark the correct alignment. Anyhow, the paper diaphragms do not work well in compression drivers. Beryllium sounds too tacky and glycerin like. Titanium is too zippy, aggressive and too hi-fi. Plastic (mostly Phenolic) is more or less OK in tweeters but is not good in midranges and has no tonal respect. Aluminum is less problematic, but it has problem with structure integrity when a midrange driver used too low (that should not take place to begin with). Also, the Aluminum diaphragms require very accurate and “smart” damping with surrounding. Altec tried to do something like this in this Symbiotic diaphragms but the result was quite bad. Once again, it is VERY difficult to make/find a good sounding diaphragm… and to build a properly sounding driver around it. BTW, all that I said about the diaphragms is also applicable to the situations when people use none-compression or ultra-low compression mid-range drivers.
Dose it sound like fan to you so far? Let go further…
Another quite unpleasant thing in the world of midrange horns drivers is the frequency slot where is utilized. Some, primary Japanese manufacturers, suggest to use 2-3 midrange drivers, each of them running in own octave. This is quite foolish and totally unnecessary sonically, although it helps to sell more drivers with a tag of $5K-$6K for each driver. Yes, it is NOT DESIRABLE to make a midrange horn ultra wide bandwidth and the nature of horns loading suggests that it should not be pursued. ~3 octaves is a maximum that a horn can handle well. The first thing that kills sound when a horn try to cover wider range is a low frequency region. Let me explain a little: Usually horns made a half-wave of crossover point. The fun part that in order a driver/horn tandem be able to reproduce a frequency with a necessary harmonic richness) of course a channel much use a first order explicitly) the driver/diaphragm should be able to handle at least one octave below it’s crossover point. The compression drivers do not have any long tail belong this LF boundary and usually drop there practically vertically, therefore, a desire to use the compression drivers closer to it’s LF boundary make them sound not at thier best force a driver loose it’s LF overhead. Besides it forces to build larger more “waohwy” sounding horns and consequentially have more HF attention due to the horn depth. I think the deception came from the complete foolish specifications on the most of the compression drivers where the manufactures suggested the ultra low crossover points (that coils might handle electrically) but those crossover points are not proven sonically as the compression drivers rolls off right after it’s primary resonance very fast. Anyhow, most of the horn guys, as a result, are running across the audio world like wounded in ass antelopes and looking for the driver that go down to 200-300Hz but this peruse is totally unnecessary. The size of the horn logarithmically get target with the frequency go down. The 2000Hz horns and 6000 horn are not very different, however the 1000Hz and 300Hz horn are very different animals. Mid range horn should handle the mid range only. The upper bass 150Hz-600Hz is the MOST important frequency for audio reproduction and it MUST be handled by ANOTHER DRIVER and it is a mistake if a mid range driver to go there. There is a reason why first violins do not play in orchestra viola or cello parts and there are reasons why viola and cello were introduced in orchestration to begin with. Under-stressed midrange compression driver with removed form it’s horn LF ingredient usually delivers way more interesting result but unfortunately very few people in the horns world understand, hear or use it.
The greatest problems pf all compression drivers are their troubles to handle the dynamic contrasts and to mountain tonal integrity and color richness. Nope, you read correctly: the dynamic contrast is the problem. Nope, not of normal direct radiators even remotely approach in thier dynamic discrimination to what most of the compression drivers can do; however, the compression drivers are still not there where they should be. The “dynamic blindness” at MF is still the biggest problem, even with horns. If you take a dozen of the similar drivers and listen them in the same application that you will detect that all of them defiantly recognize and render the dynamic contrasts and map colors to each level of contrast. This is the most critical quality of a compression driver. The better driver should have most DYNAMIC DISCRIMINATION with minimum tonal influence and maximum saturation of original color. The total tonal influence might be in some way influenced by the horn but I will cover is in the next par when I will be talking about the MF horns. It is possible to find a good combination between the tonal idiosyncrasy of MF driver and a matching horn material but it is too fastidious process. I would stick to the drivers that can handle the tone themselves without seeking help from a horn. I intentionally do not name which driver is dynamically tedious or alive and which is color wise interesting or dull. This is not a driver selection manual but a general observation…
A good MF compression drivers should not be able to handle a lot of power. Lot of power means a lot of voltage across the coil, a lot of heat and consequentially a lot of dynamic compression. The fluided drivers are kind of strange sound while they handle complex or “fat sounds”, the “kinky-vented” drivers are also very rare, or at least I did not see and good one. Most of the pro old compression drivers and all-contemporary drivers meant to be use with 70W-100W amplifiers and they have “strangely-durable” coils. Perhaps this explains why all color-wise dull and monochromic. This is totally unnecessary for home audio: a lot of power handling. Unfortunately very few compression drivers presumed that they would be driven by 5W-12W amps and those drivers that were designed for the low power do sound significantly more interesting.
Most of the compression drivers have very strange, not to say very stupid mounting mechanism. The profile of the driver’s mouth is not always friendly to accommodate a horn. Generally the drivers that have a long pathway inside the driver and have throat far from a diaphragm do sound mach better. The continuation between driver and horns should be very smooch and without a step in the profile of curve, or anything else that creates a feedback Any micro-steps at the “meeting place” (between horn and driver) creates problems. It looks the further the “steps” into the horn’s curve the lessen problems are.
Probably a few words should be said about the Lowther-like drivers or about that army of those Fostexes, PHY, AERs and many others. They do have some interesting quality at midrange but in the very narrow midrange only. Unfortunately most of people use them as wide-range driver and this is a huge mistake that makes the system built around the Lowther-like drivers sound like crap. The Lowther-like drivers should not be used below ~350-400Hz and should be very accurately used at it’s upper mid range and they have very fuzzy HF. If you lock a Lowther-like between ~400 and 6000kHz then it might be OK. However the larger size of the through in those horns is always do something to me that bothers me sonically. The Lowther-like works way more interesting as the direct radiator in the 3-4 ways systems where they used as a narrow mid-range driver. It would be important mention that, a Lowther-like full range driver, operating as a direct radiator at mid range and as a back -loaded driver at upper bass is probably the worst topological result you can get out of audio. Do not try to explain or convinced to the back-loaded Lowther-like community anything: they (audio-wise) are complete Morons and thier famous klan-enthusiasm is juts a comical ignorance and self-assured audio-virginity.
From what I said it is easy to see how much “fun” the horn people have and how much coral reefs the horn people face while they build thier horn installations. The next section will be: THE PROBLEMS WITH HORNS: MID-RANGE HORNS.
Romy the Cat
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche