Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.
HUG has two approaches to contributor's Posts. If you have, like us, a scientific mind and are curious about how the ear works, how it can lead us to make the right - and wrong - decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual area of HUG is for you. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and can be easily understood and tried with negligible technical knowledge.
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Questions and Posts about, for example, 'does amplifier A sounds better than amplifier B' or 'which speaker stands or cables are best' are suitable for the Subjective Soundings area.
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I was in Hong Kong a few days ago and discussing the delivery situation. We have a substantial back-order from Hong Kong. We are duplicating the PCBs now. Unfortunately, our production manager broke his arm just before I left the UK and it has not healed. As I write, he is in hospital having a metal plate fitted across the break. He is key to us starting production.
It is our intention that we make the first few pairs next week and that includes some stock for Hong Kong.
A very gifted sound engineer (with a large broadcast organisation) has, at his own initiative and with just basic data from me, found a way to program a multi-channel off-the-shelf digital filter box to precisely clone the crossover of the passive M40.1. This dramatically cuts the development time of a marketable active M40.1 solution, just requiring the programed filter box plus six channels of amplification (bass, mid, tweeter x 2).
We discussed today making time between Christmas and my trip to CES2008 to get together and verify that the DSP works as we expect and to measure and listen to this low-cost active solution v. passive. If it does sound OK, then we will endorse his solution. Whether he is willing to make it available to all customers I can't say, but we are treating this project very seriously indeed.
We don't publish frequency response curves, because there are so many variables in the measurements that comparisons are impossible. Each brand develops its own methodology and refines it until their measurements convey enough information to them, which somehow correlates with what they hear. Most of us use mathematically manipulated in-room frequency responses (various smoothing techniques) to arrive at a believable quasi-anechoic curve with mental allowances for the known features of the room, according to our long term experience. Unless you could differentiate the room from the measurement the curves would be useless.
What I can say in that in-room (which is what really matters) the M40.1 is, under my measurement conditions and even more importantly, to my ear, exceedingly neutral, balanced and exciting. There are no oddities in an otherwise commendably flat response, and certainly no 'BBC dip' which has never been a feature of Harbeth speakers and about which there is much misunderstanding.
You are correct: what measurements would reveal is that the overall mid/top measured response is very similar between M40 and M40.1 +/- 1dB or so but the M40.1 is measurably and subjectively dryer and tighter in the bass in my rather sparsely damped listening room. What you really need is an outside quasi-anechoic curve, but I'm sorry to say that it's too cold outside to take one. For that we need to get up to 20 degrees C or more or an expensive re-visit to the BBC anechoic chamber, which I do not myself need now I am completely happy with the design.
Designer's options e.g. Monitor 40.1 low frequency curves (generalised)
I found a picture on the internet which shows a generalised situation concerning the low frequency response of most speaker systems, sealed or vented. This is not at all specific to the Monitor 40 or M40.1 (all details are different) but it shows the general idea of the designer's options.
Note that there are a number of frequency response (sound pressure) curves that have been overlaid. Each one represents a choice for the designer who will eventually optimise the speaker system to behave as one and only one curve. Note that all curves pass through a point which I call the 'pivot point' at, in this generic example, 60Hz. You can see that if the designer wants some more output above the pivot point this can achieved done but the trade-off is that there will be less output below that point. In other words, he can trade extension for output around the pivot frequency.
Although the designer will fix the parameters of the bass unit unit and/or enclosure to whatever his marketing dept. tell him is the low end sound needed by the customer, if the box is vented (ported) the user does have a small ability to swing the changes around the pivot frequency. He can stuff the port(s) with socks or similar which will have the effect of reducing output above pivot frequency and increasing below ..... but he will reduce power handling and he will probably change the sonic quality in the middle frequencies as the box can no longer 'breath'.
The relevance of this discussion is how it relates to the M40 and M40.1. In general terms you could say that the M40 and M40.1 have approximately the same pivot frequency, and the M40.1 has been tipped in favour of extended bass, a lower Q, and hence more compatible with typical untreated domestic rooms. The original M40 was specifically designed to mimic the BBC LS5/8 and work in traditional BBC-style control rooms where the deep wall-lagging is tuned to suck-out lots of sound in the 50-100Hz region.