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In the Forum: Horn-Loaded Speakers
In the Thread: How to select mid/upper bass horn drivers.
Post Subject: How to select mid/upper bass horn drivers.Posted by Romy the Cat on: 8/25/2009
 Romy the Cat wrote:
A few years back I wrote somewhere that I “developed” a semi-mathematical formula according to which an acoustic system’s result might be absolutely objectively weighed up. I did not go very far with advisement of this equation of mine (because multiple reasons) but some of tangentially-derived conclusions from the equation are related to the subject of selected drivers for Macondo. So, if you guys take the subject of building your acoustic systems seriously then I might put some articles about “proper, meaningful and objective sound evaluation techniques” that I developed during the Macondo inventions.

If you have interest in this subject then before you continue I presume that you familiarize yourself with many threads at my site that covers the subjects of upperbass and midbass and horn loading. Just do a search and it will find a tone of them. I am not going to educate you how to select drivers for your midbass horns or upperbass horn – let presume that you have your own way to do it, you know what to expect from a midbass/upperbass channel and how to evaluate the drivers-candidates. What I am willing to do is to pay your attention to the few points that you most likely are not paying attention now. At least my conversations with different horn people and my listening of then different mid/upper bass horns suggest that some education is required. I do not pretend to post a complete drivers evaluation guide – I will stress just one very frequently overlooked point.

One of the major premises that you need to live with is the fact that in over 90% of all cases your horns will fuck-up sound of your mid/upper bass drivers. I did not use word “change the sound” but I used “fuck-up” as mid/upper bass horns mostly affect sound in a very negative way. In many ways horns destroy sound of non-compression drivers, primary it is because very seldom mid/upper bass drivers were made properly to work with given horns. Most of the drivers loaded into horns become dull and give up a lot of its d-i-s-c-r-i-m-i-n-a-b-i-l-i-t-y, presumable they had any to begin with….  A way how a horn modifies driver’s discriminability is the subject that I would like to talk about.

Let start saying discriminability of drivers is not a subject that is widely popular among audio people. The industry whores contaminated audio people with meaningless irrelevant vocabulary. Take for instance the meaning of “resolution”. The resolution of what? The industry whores claim that it is a “resolution of details” but in reality it has nothing to do with details (or the details connectivity) but it has to do with HF exuberance that the industry promote as their “quality”. Why do you think they do it? The answer is very simple – because the plugged in the industry idiots have the ONLY one motivation –to sell, and the “resolution” is a most comfortable commodity/tool to do sale.  Resolution is quantifiable, it is demonstrable, it is “wrappable” in anything you wish, it permits a person who do sale and a person who buys to be Morons – which mostly are the cases. That explains why “resolution” is very much on radars of each audio-fool but not something like “discriminability”. The question would be, why the discriminability of drivers not being used widely? Because “discriminability” as a notion, is IMPOSABLE TO SALE.

Discriminability is in many ways is not a characteristic of driver but rather a characteristic of a listener expectations, listener esthetic evolvement and listener own reference points. You can’t wrap it up, package and ship those things – they come from different source and the industry whores can’t cash out on it.  So, the discriminability of drivers is hidden from attention of hi-fi Morons who value only what was sold to them. However, discriminability is one of the primary keys in sound of any driver. Somebody who does not know what discriminability is would ask me: the discriminability of what? Well, I would live this answer outside of the scope of this article – when you learn then you will not ask. Let juts pretend that a driver has own discriminability that fits the listener definition of “acceptable”. Let pretend also that driver is not a compression driver. There are very few bass compression drivers out there and they are controversial in my view. Anyhow, now the mean thing happen – your driver has pleasing you discriminability loaded into a horn most like will lose a lot of discriminability – this is a main indication that ether your driver is used wrongly with your horn or you use a wrong horn for the driver.

People who talk about horns seldom make sense. Most frequently horn topology is widely abused and misused - there are reasons for it but it is not the subject now. Also, most frequently horn topologies are evaluated from a completely wrong perspective. If you wiling to wipe out all evaluation criteria for sound of the driver via hone and leave ONLY the discriminability then a few point you might consider: There is a delta between discriminability of driver operating in open air and the driver loaded into a horn. A properly implemented horn-loading for a given driver must INCREASE the discriminability of a channel. Changing the loading patterns (mechanical or electrical damping, etc) affect discriminability of a channel. The best solution is the one that offer higher discriminability along with higher amplitude of horn EQ. A discriminability of a channel and the channel TTH characteristics are NOT related. Learn how to differentiate them. The drivers with low discriminability in air but high discriminability in a given horn are better candidate for the hor. Discriminability exists at tonal, dynamic and accent levels, it might wary across dynamic range but it dynamic variations are greatly affected by driver amplifier.

I do not pretend that I know where the discriminability of the non-compression drivers comes from. There is a lot in the material of diaphragm and the material of suspension.  Those things are absolutely not measureable and no test equipment and not T/S specification would give any indication about discriminability. Loaded into a horn the discriminability changes.  How, does it change is very hard to say. Thinking about the cone mass, cone’s damping, primary resonance is fine but it to a larger degree would impact the macro picture of the horn performance and would hardly indicate how a given channel will be able to discriminate minute tonal and contrast fluctuations of sound. A properly made horn for a given driver must act not only as LF amplification devise but also as discriminability amplification devise.  If it not happen then ether your driver is wrong, or it was wrongly used in your horn, or your horn is too weak.

Ok, what happen with mid/upper bass channels when a horn reduces the discriminability of drivers?  The channel begins to output semi-identical sounds within it’s band pass and there is nothing worth then this. In my view this is how most of mid/upper bass horn out there sound like – a big, generic, fat slab of non-specific sound that the Morons call horn-bass. Let me give you a radical example but it will set your mind in the necessary direction.

In the second part of 1950s Mercury recorded Doráti with Minneapolis playing the Tchaikovsky 1812 Overture. The recording was “spiced” with firing of French period cannon which Mercury borrowed from at West Point Military Academy. The recording is widely popular and considered by audio Morons as some kind of gold standard. I hate this recording.  Leaving aside a relatively weak play of Minneapolis orchestra and relatively boring Doráti’s reading of the work I would say that the most devastating thing in the recording are the shots of those damn cannons. There are 16 shots in the score. I am not a big fun of the idea to have the cannon shots in there to begin with but if to do it then it would worth to pay attention that Tchaikovsky wrote use of 5 cannons making 16 shots. Why, because the shots fire at different moments while the music is being played they need to be differently-sounding guns. Tchaikovsky wrote the overture in 1890s and the very slow re-lording muzzleloading cannons were in his time a long history. He can go away with 2 or 3 cannons but he insisted 5. Listed the Overture and you clearly heard a need for 5 notes. Doráti however went for one canon, recorded multiple times. Now, listen what Doráti end up with. In the second part of the cannons introduction, where the orchestra introduces “God Save The Tsar!” thyme, there are a barrage of the cannons shots. The orchestra is crashing through the anthem, ending up with fucked up by Doráti tuba’s thyme of “warning” and while they do all of it this stupid carbon-copy sound of the same cannon is being presented. This absolute lack of differences in characters between all those cannon shots is some that turn me off very aggressively from this performance. With the same success they can instead of the cannon’s sound bring 16 fragments of telephone dial tones…

Anyhow, the expressivity of those Mercury’s cannons is how most of mid/upper bass horns sound out there. To make your channel to lose discriminability of drivers by screwing the driver discriminability with inappropriate horn-loading is a very common mistake. Do not do it. If you horn-loaded channel does not improve the discriminability of your driver then stay with direct radiators.

Romy the Cat

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