I was looking for these ones too Kex so I'll add it here. Really one should just buys what they likes. It's all too much of a headache. I go in and let the company prove their technology to me. It's designed to reproduce musuc and all the technobabble in the world can;t save them from the cold light of the listening room side by side comparisons. That is where truth is separated from advertising.

Dear John,
If you have been around for as long as you say then you should be able to remember that many of the self same designers that you mention were espousing different view on many matter 10, 20 or 30 years ago.

You may not recognise the fact that "low diffraction" and small narrow baffles are mutually exclusive, because this is governed by laws of physics that neither I nor anyone else can change, whether we like it or not.

You put your finger on it, being "in" with the latest fads helps little in this regard, as it changes nothing apart from creating the illusion that something important has been done and as you know fashion is only a fleeting "passion".

Not accepting the fact that narrow baffles have poor and very uneven dispersion behaviour is like denying that gravity exists, just step up on a roof and take one step forward and you will soon realise that whilst you may not believe in gravity, gravity certainly believes in you, then let me know which hospital you end up in and I shall send some flowers and a card wishing you a speedy recovery.

Whilst you are recovering may I again recommend reading Beranek, McLaughlin and Ohlsson, they tell you what you need to know about waveform propagation, you will then soon see that there is nothing old fashioned about wide baffles for starters, because there is no "moving on" from the fundamental waveform behaviour, nature sees to that.

All modern designers try to do is to circumvent the laws of physics in order to get an edge in appearance stakes, manipulation of the measurement techniques are widespread and are now more used as marketing tools than as guides to whether the speaker is actually any good.

I know that we are all working on creating an illusion with reproduced sound, but I never thought that the illusion goes as far as creating a belief system which is mightier than mother nature.

Sincerely,
Peter Qvortrup


Dear John,
Firstly, how many speakers have you actually designed and successfully marketed??

Since you are clearly a fully paid up member of current fashion club in speaker design, may I suggest that you go back and study two of the original works on acoustics and speakers, or perhaps 3,

a.) N. W. McLaughlin's Acoustics on McGraw-Hill, I believe it was issued about 1934, McLaughlin was probably the greatest mathematician who ever set foot in acoustics.

b.) L. L. Beranek's Loudspeakers.

c.) Any of Harry Ohlsons books.

These books contain the vast majority of what one needs to understand about sound propagation and acoustics, mostly forgotten knowledge as the industry has "progressed" towards commerciality with all its vagaries.

Now to comment a little on the rest,

1.) There several ways of achieving low frequency response and your contention that only a large diameter driver can do low frequencies is easily disproven, but rather than talk the talk you need to walk the walk and listen to a speaker which provides low frequency from a small woofer in a setting it was designed for.

2.) I don't understand why you would measure a speaker at 180 degrees and I have not measured or seen measurements on the NHT you mention, but I can tell you that I would have no real problem putting the 90 degree off axis response of any of our speakers up against any other forward radiating speaker, we would come out well there.

Remember here that 90% of all recordings are done with microphones that are not omnis and therefore the speaker dispersion at plus 90 and minus degrees is really all you need to "invert" the version picked up by the microphone.

Of all the products we make the speakers are not only the most villified but controversially the only ones which do well on conventional tests, see Hifi Choice's many tests for example.

3.) We go one better that simple time/phase alignment, we individually adjust and match the woofer's behaviour to the tweeter at the points where they both reproduce the same frequency, this is far far more important and sophisticated than the primitive practice of sloping the baffle a bit to "compensate" for the tweeters earlier and shorter response time.

The ear is far more sensitive to incorrectly matched start - stop anomalies than it is to minor static differences in frequency response, a fact which is neither well understood nor practiced by the loudspeaker industry.

We developed a way of measuring this behaviour realtime and ways of adjusting it as well over 15 years ago, and have been refining this since then.

To help you understand what I said in the next paragraph, basically in a 3 way speaker finding drivers which work together in such a way that it is possible to align their timing differences at two crossover points rather than one immense complicates the problem of adjusting the above behaviour.

4.) Again, I recommend that you listen to a speaker that achieves a response in a normal room size from 17Hz to 23kHz with good efficiency and ease of drive.

5.) Whilst I acknowledge that there is a lot still to learn (but not from current convention, I am afraid) I have much of the necessary experience, have you?

6.) The treble and midrange on the Lowthers was one of the best I have ever encountered, and I have owned pretty much everything over the past 35 years, from Voigt's field coil driven horns, Tannoy's original 1950's Westminster's, Siemens Klangfilm and WE cinema systems to B&W DM70s, stacked Quad 57's, Beveridge System 2's, Acoustats, to Hill's Plasmatronics, Heil's full range AMT, Snell A/IIIs you name it, I have at some time or another had them all and what they all has taught me is not insubstantial.

I rate the Lowther PM4 system and the Siemens systems as the best overall, but they are domestically almost impossible unless you live in a mansion, and very few of us do, so something smaller is needed.

Which is why we are here!

Sincerely,
Peter Qvortrup

Dear Greg,
Quite correct, which is why we cross over at below 2.3 kHz and use specially designed units to tailor their response to each other.

Like you say, there are VERY few tweeters who work this far down.
Sincerely,
Peter Qvortrup

They do not go above 14 Ohms either.

Impedance variation are in my experience not a great problem if it does not have a greater than 10 to 12 Ohm "window" and it does not go below 4 Ohms, but I think it is important to mention that a speaker's impedance is only one of several parameters that make up its general suitability to SET amplifiers.

Reflected load is a major problem in inefficient speakers when seen from the point of view of the amplifier, and whilst single-ended triode amplifiers without feedback have a high'ish output impedance they do not display any of the stability problems associated with feedback amplifiers, provided the circuit, power supply and output transformers compliment each other, the SET struggles with the combined "mass" of the drivers and crossover of inefficient speakers.

One parameter we "match" speaker behaviour to is the power transfer curve of a triode, because at the end of the day it is the end result that counts and we specifically design our speakers to have as flat an in room power response in the listening position as possible, when driven by a low power triode amplifier.

We design the parameters of all our drive units strictly with this in mind.

We also go to great length to make sure that both speakers in a pair have identical acoustic behaviour, in order to get decent stereo (or even mono) reproduction that is far more important than many of the highly touted "important" parameters used by other speaker makers.

It is a major advantage designing and making both "sides" of the "coin" because it allows you to gradually improve your understanding of what goes on between amplifier and speaker and slowly optimise the "match", unfortunately very few speaker or amplifier manufacturers are able to do this as they only design the front or back of the "coin".

The "specialist" speaker industry in particular appears to have very little understanding of what is best for a good amplifier, they have over many years relied on the premise that amplifier power solves all problems and squarely place the responsability for the end result of their poor understanding on the amplifier manufacturers' who have traditionally been forced to follow suit and make higher power amplification, which is a complex and poor sounding compromise

Dear RGA,
The market perception (supported by most magazines and manufacturers as it is) is that if there is "more" or "deeper" bass then you are getting something for your money.

This is not the case, in fact it is rarely the case that a sub qualitatively improves the music reproduction, generally the money would be better spent on bigger speakers or elsewhere.

The AN-E is probably the easiest to add a woofer to, the intention is to start at under 30 Hz and go down to around 12 Hz, it works pretty well, but having tried in different rooms the variability is too great in my view and positioning is very critical to get the right blend.

Single ended triodes is the only way to get proper bass, nothing else will do.


Dear TC,
The "leading" magazines certainly have a lot to answer for, imagine if they had had the courage to write what they REALLY thought about CD when it first came out, rather than just turn their back and bend over?

I spoke to many of the leading reviewers at the time(one advantage of being old is that you were there when it happened!) and what they thought privately was quite different from what they wrote in their articles.

Had they publicly said what they privately thought, it might have changed the course of CD and forced Philips and Sony to rethink their entire modus operandi.

Serious dereliction of duty and care to their readers, much like the stock analysts who recommend shares they privately denigrate.

Sincerely,
Peter Qvortrup

Dear Pat,
There are almost no speakers that have a flat off axis response at say 30 degrees either side.

It is interesting that you mention the average omnidirectional response, when did you last see one of these measurements in a modern audio magazine??

I never said power response was new, but almost no-one uses this today, and it is a good indicator of performance.

I think the reason we see neither of these measurements any longer is that modern speakers with their shallow deep cabinets and resulting poor and very uneven off axis response do badly when measured at listening distance.

50 inches is about 1 meter 25 centimeters, that is close enough to one meter, 2 - 3 meters are not really valid either, as you need to take into consideration the room reflections and their influence on the sound, as what you hear is always in the listening position, so why not measure where you sit?

Paul Messenger from Hifi Choice generally measures at a distance similar to listening distance and his overall measurements tell you more about the sonic balance of most of the speakers he measures.

I aim to make a speaker with a virtually perfect hemispherical dispersion behaviour, which is why I like wide shallow cabinets, in my view a speaker should have an even non jagged drop off as you move from 30 to 60 to 90 degrees off axis in all directions in order to be able to present the room with an even energy waveform.

Likewise, it is important that the speakers within the pair are acoustically identical, otherwise it is difficult to reproduce stereo.

Sincerely,
Peter Qvortrup