Harbeth Monitor 40 domestic specific

[A.S.]

I have not been able to give my full attention to the User Group for several weeks. This is because of my commitment to the final stages of the design of the new Monitor 40. Now that I have virtually finished, I would like to take a short holiday. After I return, I will listen again and if I am completely satisfied, we can set a production start date for as early as possible.

This project has been underway for over a year and has ranged through every single aspect of the design. The original objective was quite narrow; to replace the abruptly discontinued VIFA bass unit with a Harbeth designed, Harbeth made woofer. However, as the months progressed, I became deeper and deeper involved with the minute details of the design, and this led to numerous small improvements. So the bass unit is completely new - a 12" first for Harbeth and the midrange driver is a new version featuring a 9 ohm voice coil to keep the system impedance nice and high: a very easy load indeed.

Unfortunately, the changes are so extensive that there is no practical upgrade path from the original model.

You may be interested in my reasoning behind the overall system balance of the new M40.1. I believe that in the 10 years since production commenced we have filled most of the professional installations that demand a true-BBC monitor. Also, most BBC installations are Active, and this allows great flexibility in tuning the speaker to the studio acoustics which is not possible with the passive version as used at home. This has resulted in some users deciding to invest in room-EQ systems when I would like to save them the cost, trouble and inconvenience by making the M40 even more universally usable in ordinary rooms.

The working life of a Harbeth is 15-20 years (or more) so the best potential for sales growth for the M40 is the domestic non-studio market; that is, ordinary rooms in your homes. With this in mind, I have decided that as the Active version offers whatever adjustments the pro user demands, I should concentrate on making the new M40 100% domestic friendly. That means, in the same size classic-BBC three-way box as the previous model ...

1. A tighter, dryer bass thanks to the cast-chassis plastic-coned Harbeth-designed and made 12" woofer (compared to the pressed chassis, paper coned VIFA unit)
2. Higher electrical resistance (and easier load)
3. Even smoother frequency response by attending to micro-details in the response,
4. Better on and above-axis response integration so less height critical due to complete redesign of the crossover (which uses less components)
5. New 8" RADIAL midrange driver with 9 ohm voice coil and long-throw high-flux magnet

and ....

6. Overall system is noticeably more sensitive. About 4dB more sensitive than the original model so nearly the same sensitivity as the C7ES3. That's an astonishing increase in efficiency.

Needless to say, it sounds 100% true to the Harbeth philosophy. What astonishes me is just how huge and unconstrained the sound stage is: as if the sound stage curves around the speakers and along the side walls. It must be related to the extremely well integrated responses.

We have many back orders to complete so please order soon if you expect delivery in 2007. More details to follow: look out for the August 07 News & Views newsletter with pictures of the (grey box, pro-cabinet) prototype being tested recently by Derek and myself in the BBC anechoic chamber. Normal domestic veneers are and remain Cherry and Eucalyptus. Picture of my prototype crossover - fewer components than the original model. I will try and make time to design a new PCB on my laptop.

Am I allowed a short holiday now - please?!

>

[Peter Jacobsen]

Hi Alan,

since you're in the process of re-designing the M40, have you considered reversing the positions of the tweeter and the mid on the domestic model? This would bring the tweeter down about 8 inches, thereby allowing listeners to raise the entire speaker to get rid of those bass reflections we've been hearing about.

I understand that changing the position of the units will (slightly) alter the sound, but this might be alleviated through design of the crossover.

After all, people don't sit on a high chair at home like the professionals do in a studio (at least I don't).

On a related note, how would turning the entire speaker upside down affect the sound?

Enjoy your holiday,

Peter, Shanghai

[Will]

Thanks for keeping us updated Alan... sounds very promising. I can't wait to audition it.

Enjoy your well-deserved vacation!

[A.S.]

Hello Peter,

You raise interesting points. Actually, now that my ears have rested I will start listening again to the prototype M40.1 (provisional name) tomorrow, and if I am still satisfied with the listening we will commit to production. As for the measurable in-room technical performance, this simply can not be bettered: the M40.1 measures as an astonishingly flat line in my quite ordinary listening room at the Cottage (described here before). So, I think - subject to a final listening test - that we can say that the design is now complete.

Every step of the path has been documented painstakingly in my Log Book complete with graphs, hand written notes, calculations, cut-and-pasted printouts and photographs and extends to over a hundred pages which, in time, I will share with you. Not only have I been acutely aware of the importance of doing a good job but of leaving a documented trail as I go in keeping with the legendary status that has followed the Mobitor 40 and of which even I, the original designer, am in awe of.

Now, you asked a couple of questions. To answer them:

Q1. Reversing the position of the tweeter and woofer?

A1: I considered this and quickly dismissed it again for the very same reason as when deciding on the original M40 layout some ten years ago. Forgive me if I make the point again: a good speaker should mimic what we hear in nature. I mean by this that as we walk about in our ordinary lives we are exposed to sound. Evolution has programmed us such that low sounds (like growling) make us instinctively look downwards to identify predators, and of course, dogs. Conversely, high pitched sounds are associated with height - bells and specifically birds in flight and in trees. If we place the tweeter at the top of the cabinet this natural order is maintained, but if we move the tweeter to the middle of the cabinet these is some subconscious stress - some confusion - as to the size and vector of the sound. This may or may not be noticeable on-axis at the sweet spot but it will be exacerbated off-axis. We can not assume that any of our listeners are sitting rigidly at the sweet spot! So, I strongly believe that the tweeter should be at the top of the cabinet.

Q2: Raise the speaker upwards by 8" (200mm) or so ....

A2: As we say in the User Guide, the Harbeth owner has a duty of care to members of his family to mount his speakers so that they can not topple over and injure anyone or damage the speakers. I do not think that it would be wise to put the heavy M40 on very tall stands unless they are of 'studio' industrial strength and the speakers screwed or strapped to them as they are in the studio. If they fall over off inappropriate stands they could seriously injure a child or animal.

Actually, the point that you make in Q1 and Q2 are at odds with each other. If the tweeter is at the top (as it is in the M40) then this allows you to use a low stand - ideal from the consideration of stability and safety.

Q3: Reflections from the floor ...

A3: As for bass reflections from the floor which are an inevitable part of listening to any speaker in any real domestic room - believe me you can not eliminate these unless you listen in an anechoic chamber. Fortunately, the ear is remarkably tolerant of these reflections which typically fall in the 150-300Hz region.

In the M40.1 design I have carefully adjusted the optimum crossover frequency of the bass to midrange unit to take into account the floor bounce.

[Eric Pitschmann]

Dear Alan,

Thanks for shedding some light on the redesign of the M40. As one who ordered a pair earlier this year, I'm very excited to see that the new version will soon become reality! I hope you don't mind a few additional questions:

1) Since it appears you've taken the floor bounce into the equation in the M40.1, is there a specific stand height (or range of height) that you would consider to be optimum in most rooms?

2) In the 7ES3, the surround on the RADIAL driver was changed. Was this also done for the M40.1?

3) I noticed in the prototype that the tweeter guard was missing. Will the guards be left off in the production version as well? Leaving them off may be OK in a domestic environment, where the speakers will be more stationary, provided owners leave the grills on as instructed.

Eric

[A.S.]

Hello Eric,

To answer:

1) This is an interesting question, because it follows the new design approach which I 'pioneered' with the Compact 7ES3 and clearly has been a great sonic (and commercial) success. Basically: the designer has to pick some point on the baffle from top to bottom which he considers to be his 'reference axis'. There is no textbook rule as to where this should be - it could even be near the bottom - and indeed that would be an ideal place to set it if the listener habitually lay on the floor (in a state of inebriation of stupefaction perhaps?). Normally though the reference axis will be in the upper half of the baffle, typically just below, on or just above the middle of the tweeter's dome. There are a number of factors to be taken into account before deciding where to chalk-mark the baffle; one concerns the best phase-match between the midrange and tweeter. Another concerns the likely position of the listener's ears when sitting in a normal chair.

In the studio - and I've measured this many times over the years - the listener's ears are always about 124cms above the floor when sitting at the mixing desk in a good roller chair with proper posture to avoid RSI and back problems. This rule does not apply at home - the domestic listener is sitting much lower - probably slouching in a soft chair so what may be the best design reference axis in-studio may not be suitable for home use. One advantage the studio user has though is that he can rake the speakers downwards, and we've made metal stands to do exactly that.

Now, in the case of the C7ES3 and again with the M40.1, I've been using a new version of my crossover/time alignment simulator which is about 10 times faster than the previous generation. That extra speed allows the calculation of electrical network components for the best possible integration on the reference axis to be made very quickly: not in itself a big deal. What I can do now though is to use the processing power to explore millions of other component/circuit possibilities to engineer as wide a vertical listening arc as possible on and above the reference axis that knits together the mid and HF driver's phase-tracking.

What this means in practice - and the C7ES3 proves this - is that the speaker is remarkably unfussy about stand height. You can listen just below, on or (10-15cms) above the reference axis and the driver integration is seamless. The same applies to the M40.1 so you can probably get great results (depending upon your ear height of course) in stands from, say, 12 - 20 inches. But I can't give you a rule that will apply in all rooms because I don't know about your ears, your chair or your seating posture!

2) Yes: the M40.1 uses the same surround as the new C7ES3's driver.

3) Currently the tweeter guards are off. I am advised that despite the risk from little fingers - and the substantial costs involved in replacing tweeters at the user's expense - that certain users seek what they consider to be the ultimate performance. My fear is that unprotected, there will be a risk of customer-damage. We will have to (reluctantly) draw a line at the point of manufacture and pass the duty of responsibility to the user as these tweeters are extremely expensive.

[Eric Pitschmann]

Alan,
Thank you for the very detailed reply - good news on all three counts! Personally, I would prefer the tweeter guards off, but never attempted this with my M30's.

[Will]

A.S. wrote :

"We will have to (reluctantly) draw a line at the point of manufacture and pass the duty of responsibility to the user as these tweeters are extremely expensive."

Please excuse my ignorance, but I don't understand the sentence. Does it mean the grills will be on, off, or easily removable?

Personally, I'd prefer the safety and peace-of-mind of having grills. The new, more "transparent" grill in the C7-ES3 would seem ideal to me.

[A.S.]

What it means is this ....

"As users have requested that the tweeter's protective grille be removed the user must be aware that deletion of the grille at the manufacturing stage may result in user damage. The Harbeth factory can not be held responsible for the consequences of misuse by users".

At this final stage of the M40.1 development, the tweeter grilles have been deleted from old-stock M40 tweeters and the frequency response adjusted in the crossover network.

[A.S.]

Personally, I would prefer the tweeter guards off, but never attempted this with my M30's.

Noted. Please do not attempt to remove the tweeter guards from existing M30 or M40 speakers.

The magnetic field is very strong and it is almost impossible to prevent the half-off, half-on grille being pulled by the magnetic field into contact with the diaphragm. This would be a very expensive mistake for the user as even the slightest crease of the delicate diaphragm will disturb the tweeter's performance.

[kevint]

Dear Alan,

Will M40.1 replace tri-wire with single-wire connector like C7ES3?

Also please reconsider the possibility of offering existing M40 users upgrade service to M40.1, I really don't want to sell my beloved M40. But having learnt there is an improved version, especially with better home friendliness, it is really hard to resist the temptation of upgrade.

Kevin

[A.S.]

Will M40.1 replace tri-wire with single-wire connector like C7ES3?
Also please reconsider the possibility of offering existing M40 users upgrade service to M40.1 Kevin

My plan is to fit the M40.1 with one pair (red, black) of connectors. This is simple, and it allows me to design the network with complete confidence about the electrical load as seen by the amplifier.

Upgrade: this really is not financially viable. Not only is there the logistics of returning the speakers to us (you will need fresh cartons, caps etc.) there is the risk of damage in transit, and the time and effort here to dissassemble and then reassemble. I guess that you'd end up with a bill for 75% of a new pair and the worry about transit damage to/from us.

As for upgrade kits, our priority is to restrict the availability of the Harbeth-made drive units and to prevent those drivers removed from original M40 being used elsewhere.

[markus sauer]

Remind me to tell you of my experience in Japan when I was invited to be one of the first visitors to the new Stereo Sound listening room an couple of years ago! Again .... the wonderful SHL5.

After your return from your well-deserved holidays, would you please be so kind and share that anecdote with us?

Also, can the Monitor 40 domestic be ordered in grey paint? I like that colour and actually prefer to have a technical object like a loudspeaker look like an industrial item instead of a piece of furniture. But I don't like the transport handles that one sees on the pro version.

[A.S.]

The new, more "transparent" grill in the C7-ES3 would seem ideal to me.

Will: we have discussed in the office this morning your suggestion of using the hex grille from the C7ES3 on the M40.1. It's a very good idea and would simultaneously solve the issues of maximum acoustic transparency and protection from 'little fingers'.

I've just made an experiment to see if I can fit the hex protective grille to a stock M40 tweeter: almost, but not quite. That means we will either have to tool-up to make a hex-grille specifically for the M40 (with potential for stock mix-up with the C7ES3's grille) or we have to redesign the M40 tweeter faceplate to take the C7ES3 grille. Either way, I feel much more comfortable with the tweeter protected.

Thank you for an elegantly simple and eminently practicable solution.

[Groovetracer]

Alan, There's speculation/rumour that the new M40 will cost more in the USA than current pricing. Can you comment on this at this time?

[Will]

Thank you for an elegantly simple and eminently practicable solution.

You are very welcome!

[A.S.]

Here is a close-up of the hex grille. This photo is from the C7ES3. As you can see the grille is almost all air.

[A.S.]

I'm now at the final stage of approving for production the new M40.1 (provisional name). I have played many different types of music from my collection - and I've run out of ideas. Perhaps you can suggest what music/tracks/artists you would use if you were auditioning the M40.1 at home or by appointment at a dealers. I would like to be sure that I've thought of everything!

My opinion thus far is that listening to music on these speakers at home is most alike inviting the musicians around for a private performance. But that always has been the uniqueness of the Monitor 40.

[ronaldg]

The album "Naked Songs" by Rickie Lee Jones is an exceptional live album in both fidelity and musical quality. The crowd noises are also very realistic and give you the sense that you are there.

Regards,
Ron

[TNIC]

I found the following 2 tracks exercise the M40 and benefit from the full size presentation. Both tracks are high quality recordings, well balanced not over emphasized in any way, yet they capture and release every zero and one of the performance (at least my CD player does) in great detail - but are not offensive. These are red book CDs (not SACD etc).

The M40s really blossom with these recordings (in my opinion). I have not heard the other tracks on these recordings. I am usually so happy listening to these two recordings I can stop there and enjoy the rest of the day fully satisfied.

Sample 1 – Full track is 8 plus min (8 well spent min) and includes soft delicate as well as raucous lively sections. The entire orchestra gets a chance to shine together and as individuals. The M40s present every instrument clearly. On my systems you sound like your not too far behind the conductor enjoying fully balanced mostly direct sound.
Sample 1- http://www.amazon.com/gp/music/wma-p...am_wma_001_003

CD 1 http://www.amazon.com/Smetana-Short-...7529568&sr=1-2


Sample 2 - Full track is over 7 min long min (7 well spent min I might add) and includes soft delicate and raucous lively sections. The entire orchestra gets a chance to shine together and as individuals and the M40s allow you to pick out ever instrument clearly. On my systems you sound like your not too far behind the conductor enjoying fully balanced mostly direct sound.
Sample 2 - http://www.amazon.com/gp/music/wma-p...070675-5778064

CD 2 http://www.amazon.com/Ports-Call-Hug...7529843&sr=1-1

These tracks (particularly Finlandia) often leave my guests, and me speechless. For some of us they touch something deeper inside than our ear drums. Your listening experience and preferences in music may be different of course.