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Feb. 2018
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A Harbeth centre channel speaker

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  • #31
    Re: A Harbeth centre channel speaker

    Alan,
    I really don’t think you need to worry too much on the physical size. Most of your prospective customers concern more about sound quality than cosmetic. There are already lots of ‘stylish’ speakers in market, those looking for ‘stylish’ solely won’t buy Harbeth anyway. Since sound quality is priority, we understand size can’t be too slim. As long as size is like a sideway lay P3 or M30, it should be ok.

    As a prospective customer, in order to simulate my purchase interest, the center should sound very like my LR channel speakers in terms of loudness/dynamic. Other wise the front sound field can’t be coherence. I understand Dolby and DTS recommend using same spk for Left, Center and Right channels. So it already dictates the center must use 8” bass unit for partnering with C7, SHL5, M30 or even M40.1. Personally I prefer a single 8” unit rather than double 5”.

    Comment


    • #32
      Re: A Harbeth centre channel speaker

      1x 8" is only 25% bigger than 2x 5".

      Comment


      • #33
        Re: A Harbeth centre channel speaker

        Alan
        In order to move this discussion forward i've done a quick trawl of the net to get some ideas about what others are doing.
        I chose to look at products from British manufacturers making conventionally dimensioned boxes (rectangular cuboids).
        Dimensions are HWD in mm.
        H W D
        450 180 297
        545 198 339
        510 175 220
        510 174 195
        583 291 225
        800 368 288
        290 155 234
        1025 325 200

        Although I appreciate that this is likely to represent Saturday morning frippery vs a cutting edge piece of consumer research I thought it may help.
        I noticed whilst trawling the sites that no forum like this was visible. I think that Mr. Shaws' dedication to this forum speaks volumes about the application that he has lavished upon the Harbeth brand, making a product that makes me smile every day.
        Jim

        Comment


        • #34
          Re: A Harbeth centre channel speaker

          To all-

          I think the breathe of Harbeths existing range would fulfill any level of performance for fronts or rears. A dedicated center would be amazing! Harbeths ability to "disappear" would make for an excellent home theater. The P3 range is a good place to start, given its ability to perform in close proximity to walls. I currently use Magnepans in my home theater and the center has to be at least 20" away from the wall! Not only that, but its performance when you are sitting off of center (either horizontally and vertically) leaves much to be desired. I believe that most consumers understand the importance of the center channel and would be willing to put up with size in exchange for performance. And when taking the P3 line into consideration, even if you doubled the size of one speaker to make the center, we aren't talking nearly as big as the Magnepan or most of the other high performance centers i have played with.

          Utilizing a 32" TV as the reference for sizing a center isn't too far off, but I would go a little bigger. I think that people that can afford a Harbeth home theater, more then likely can also afford a decent HDTV, which would be probably 40" or larger. (Especially given the standard of 1080P which isn't found too often in 32" TV's).

          In all of my experience in both selling equipment as well as setting up home theater systems, I have found that the center can make or break even the best of systems. I think that in a center there are 3 main things that most companies miss:

          1) A wide enough sweet spot to accommodate for the majority of homes seating situations, which might seat some viewers outside the desired listening angle.

          2) The ability to be placed in a cabinet without hampering too much performance. Half of the installations I have seen pop the center on a shelf in the entertainment center.

          3) Being able to do the above while still providing the impact, speed, and naturalness that movies need out of a center in order to keep you in the movie.

          If I were to switch things around here at home and were to utilize Harbeths for my home theater, I would more then likely use the Compact 7's for the fronts and P3's for the rears/sides. Both for budgetary and size constraints. Taking that into consideration, a center that would be a suitable match for the Compact 7 would be ideal as it would also be great for an all P3 system or a system incorporating M30's. I think there would need to be a different center geared for customers utilizing HL5's or M40.1's as a system designed around those speakers would warrant increased...everything?!?

          I would love to see a center from Harbeth! I am so pleased with my P3es2's, that given a suitable center, I might have shift things in my home theater.

          Thoughts?
          -wkatzir

          Comment


          • #35
            Multiple drivers - what's the surface area?

            Hi Garmtz,

            according to my maths a single 8" woofer has an surface area that is app. 21.9% larger than 2 woofers of 5". [Using the rule, surface area = pi x radius squared ...]

            The difference is 4 x 4 x pi - 2 x 2.5 x 2.5 x pi resulting in 16 pi - 12.5 pi which is 3.5 pi.

            pi is app. 3,14 so the difference is 10.99

            16 pi is 50.24 so 10.99 is app 21.9 %

            I hope this is correct. I left high school 31 years ago! But the internet provides help:

            http://en.wikipedia.org/wiki/Pi

            Here you find everything to calculate circles. The interesting thing would be to ask people not used to maths what they think is larger.

            For example you need exactly 4 woofers of 6' to have the same surface than a single 12"!


            Best regards
            Heiner

            PS: Don't get confused - listen to music!

            Comment


            • #36
              What is the true driver diameter?

              Good feedback, but one problem we should work through to check the consequences (the devil is always in the detail with audio designs) ....

              Contributors have made assumptions about the diameter (= 2 x the radius) of various drive units. They say 5 inch, 6 inch, 8 inch or 12 inch. In fact, the drive units do not have these exact diameters: these claimed diameters are really marketing words that do not agree with the real radiating or active area of a drive unit. Only the active radiating area of the cone + surround contribute to the measured loudness or spl of the drive unit. There are some 'rules of thumb' for estimating how much of the surround to include in the diameter measurement such as "half the surround" or "the inner third of the surround" but they are really only guesses.

              So, if you take a ruler to the full diameter if a drive unit and surround you will (almost certainly) overestimate the real radiating area. I know this because when designing the 5" RADIAL woofer for the P3ESR (and also modelling the 12" for the Monitor 40.1) it was clear that just placing a ruler across the drive unit did not show the radiating area. That was far too crude an estimation. The reason is that the rubber surround is not a fully active radiating part of the cone - it is a damping element, and only contributes a little to the cone's sound output but a lot to the total moving mass. So it acts as a brake. Hence, we have to remove from the estimation of diameter that portion of the surround that adds noting to the speaker's sound output. This is not obvious from visual examination.

              We must be cautious about measuring the active diameter of a drive unit. I'm no mathematician but we can approach the maths from another direction - we can use weight in lieu of diameter, and since we can weigh very accurately, we can then back-calculate the effective radiating diameter from the weight.

              I spent months on this aspect of the P3ESR woofer design*, and back in 2006 I looked carefully at the P3ES2 and LS3/5a woofers, since they had well known acoustic characteristic. See attached how I cross-correlated the diameter with the mass by dissecting the drivers. Attached are the two generations of LS3/5a woofers: the early SP1003 from the so called "15 ohm" LS3/5a and the later second generation, so called "11 ohm" (Harbeth) LS3/5a. You can see that even though these are both marketed as "110mm" woofers, the actual areas according to my calculations are 108mm and 100mm respectively and the total moving mass for that trimmed diameter is 11.0g and 10.2g.

              Now - surface area calculations for these two B110's:

              SP1003 (early Ls3/5a): Sd (surface area) = pi x r2 = pi x 0.054m x 0.054m = 91.6 cm2 (square centimetres)

              Sp1228 (later and all Harbeth LS3/5a): Sd = pi x 0.05m x 0.05m = 79 cm2

              So, even comparing these so called 110mm units, according to my calculations, there is a 16% difference in radiating surface area! But also note that there is a difference in moving mass ...

              SP1003 = moving mass 11.0g
              SP1228 = moving mass 10.2g

              That's a difference in moving mass of about 7%. So although the later SP1228 has a slightly smaller radiating area it's moving mass is somewhat lighter .... and, crucially, it's impedance is lower so it draws slightly more power from the amplifier. Taken together, the mass and the area and the impedance define the efficiency at some frequency (what frequency? That's another issue!) so we can't just pick one measurement; we have to see how they dovetail together.

              See how all these parameters work with or against each other? It's not possible then to be absolutely rigid in saying that two of this driver is necessarily a better solution than one of that diameter - there are many variables that can be adjusted. What is clearly bigger to the eye may not necessarily be louder or have the same bass response.

              * The entire design of the P3ESR and its all-new Harbeth RADIAL woofer is recorded in the daily Log Book from which I drew these photos. It was (is) essential that the P3ESR continues in the LS3/5a > P3 tradition of exceptional bass performance despite the diminutive cabinet size. This required a thorough, detailed analysis of the bass performance and the mechanical/acoustics of the small bass driver in the small enclosure. I approached the analysis with three different methods: an Excel spreadsheet of the interrelationships between the driver parameters (mass, impedance, area, compliance, magnetic force) and two commercial loudspeaker simulators. They all gave the same results within experimental error (say, 3%) so I'm confident about the P3ESR's astonishing bass, easy load and efficiency.

              You can read about the acoustic modelling process here (next post).

              >
              Attached Files
              Alan A. Shaw
              Designer, owner
              Harbeth Audio UK

              Comment


              • #37
                Acoustic modelling of woofers/cabinet combinations

                {Please go up one to check my previous post before reading this one}.

                From June 2005 (four years ago - time has passed very quickly) another example from the P3ESR Log Books shows the acoustic model of predicted bass response from these small 100mm (5") woofers in their shoe box size cabinets. This was an early stage of the software modelling process, and potentially much more sophisticated than the DOS-based system I'd pioneered in 1990 during the development of the original P3.

                To explain the graph: this shows the predicted nearfield (no crossover) bass response for a 110mm (5") woofer in a 4.5ltr box - about the size of a P3 or LS3/5a. On the left side we see an arbitraryY (vertical) axis, in dB, which shows us sound pressure level (let's call it loudness) and the X axis along the bottom shows frequency in the bass register. The coloured traces have a characteristic knee shape around 100Hz with falling output (diminishing Y axis dBs) as frequency lowers, as you would expect: loudspeakers, especially small ones, obviously cannot product deep bass at the same loudness as the middle frequencies. But the roll-off is smooth and the room will to some extent boost those lower frequencies.

                Step 1 > The blue curve is a real acoustic measurement imported into the graph. This is the 'control' data of a real, physical woofer of known parameters carefully sealed into the small cabinet of a P3ES2 and mounted in the usual way.

                Step 2 > The purple trace shows an early attempt at software simulation modelling that driver in that box: you can see that the model's prediction significantly overestimates the output (loudness, left hand vertical scale). If we could achieve this output we'd be very happy but we are deluding ourselves: the model is in error. We know this because we've measured a real driver (blue curve) and then back-fitted it's data into the model. So there is something wrong with the modelling: the blue line (actual measurement) and the purple line (modelled prediction) should overlay each other very closely if the software model accurately mirrors the real-world measurement.

                Step 3 > The orange curve now shows a revised, tuned model where I've slightly adjusted some of the parameters of the box, not the woofer. It seems that the air in the sealed cabinet behaves in an unexpected way not as a 'lump' and we have to train the simulator about that. [Note: solving this issue took weeks or months].

                Step 4 > (Not shown). Now we have matched the simulation to the actual woofer + cabinet characteristics, can we increase efficiency - move the orange curve upwards by adjusting any parameters of the woofer and/or the cabinet? What we can't adjust is the cabinet size (volume) ...... that's fixed. So what else can we tune - if anything - and still present an easy amplifier load?

                Someone recently asked here about alternatives to sealed or vented boxes and asked about 'transmission lines'. As I understand it, only recently has a simulator been marketed for TL speaker design. This concerns me: sealed/vented box simulators are really sophisticated now (as you've seen) and with care offer an excellent modelling potential following twenty years of refinement. Furthermore, the Thiele-Small maths behind those sealed/vented simulators was developed in the public domain some thirty+ years ago and thousands of loudspeaker developments have proven the accuracy of the TS maths models. There is no equivalent in-depth knowledge foundation underpinning loudspeaker 'Transmission Lines', hence, no knowledge pool to create software models from. Either TLs behave in an unpredictable, complex or non-intuitive way or modelling them is extremely difficult, inaccurate or there is no commercial interest in such models.

                But a software simulator allows the designer to seek out the very best possible driver/box combination, quickly and at low cost and fatigue. 'Cut and try' methods are exhausting and leave the question 'have I overlooked something'. I believe that reliable software modelling is, and has been for me since 1990 the only way to be sure that all the options have been fully expolored and that what the customer receives cannot be bettered.

                Does this cast any light on the design process? Can you see how if you design your own woofers 'from scratch' you can perfectly optimise the response? Conversely, if you buy-in the woofers (as most speaker companies do) you can never achieve optimum results. Off-the-shelf drive units cannot be optimised for a given box size.

                >
                Attached Files
                Alan A. Shaw
                Designer, owner
                Harbeth Audio UK

                Comment


                • #38
                  Re: A Harbeth centre channel speaker

                  One American speaker company, Zu, has negative things to say about the d'Appolito twin-woofer single-tweeter layout for a centre speaker, as they claim it causes "comb distortion". Instead, they use a single woofer with a tweeter at either end.

                  Which is better technically is beyond me, but it occurs to me that one benefit of their approach is that you end up with a smaller box, which I have to think is a plus. I wouldn't worry too much about the flatness of the enclosure, however: yes, the modern screens may be very thin, but there's usually a DVD player, satellite box, amplifier, what have you, that is considerably deeper than the screen anyway. I would say it's more important to keep the centre speaker as close as possible to the P3 in overall dimensions.

                  Comment


                  • #39
                    Re: A Harbeth centre channel speaker

                    Zu is correct in their findings that a double woofer causes comb filtering effects. This is easily tested with any center using such a configuration by putting on some pink noise and shifting your head from left to right in the listening seat or more close to the center speaker. You will definitely hear the sound coming in and out of phase at certain frequencies, something that is less of a concern with a single woofer.

                    Do remember however, REAL (vertical) D'Appolito systems have a very limited vertical dispersion. It's a known fact and design parameter of this type of speaker. In a center speaker, it will limit horizontal dispersion, a bad thing I think in a center speaker.

                    Comment


                    • #40
                      Re: A Harbeth centre channel speaker

                      I think the most important factor to consider when designing a new Harbeth centre channel speaker is that you will never create a loudspeaker that will please everyone. Please do not compromise the sound quality in favour of Gucci designs as I'm sure you wont. Your potential market will appreciate certain compromises in the visual realms in order to achieve superior sound quality. You will never have to compete with the ?200 "Sound Bar" speaker which consumers who place visual appearance over sound quality tend to buy. I would suggest that potential purchasers will already own Harbeth speakers and fully understand the "rules" relating to positioning. If their flat screen is mounted on a wall then they are likely to have speakers on stands away from the wall to either side of the screen. Consequently, a centre channel speaker mounted on a lower stand below the screen should not be a problem.
                      If the screen is placed on a unit, this unit is likely to hold some audio visual equipment and therefore will be of sufficient depth to allow placement either on top of the unit or on a shelf incorporated into the unit (with suitable isolating supports). For this latter reason I suggest that the width of the proposed speaker be no wider than the 44cm standard for components. If you need to increase the volume of the speaker, add depth and width up to the above mentioned limit. Hope my suggestions give you something to think about!

                      Comment


                      • #41
                        Re: A Harbeth centre channel speaker

                        Another idea would be to have a compensation switch for boundary placement (wall and/or on top of cabinet, or both). Chestiness is very easily obtained when the speaker does not compensate for the usual bad placement of the center.

                        Comment


                        • #42
                          Re: A Harbeth centre channel speaker

                          To me the most important factor is the height of the speaker, as almost invariably the centre speaker will be placed underneath or above the flat screen TV.

                          My friendly seller in Kuala Lumpur initially suggested a C7 as central speaker, but there is no way it will work in my living room, so we finally settled on a pair of P3. But even laying on its side P3 will need to be less than 150mm tall for it to not block my TV. As it stands I will need to raise my TV some 50mm.

                          I have no hesitation in buying the P3, as I can always use it for my bed room later. But I am concerned about how the placement will affect the tonal characteristics of the P3 - with one side resting against the TV bench/shelf. I hope it will not cause my TV bench to resonate.

                          I am still waiting for the delivery of my speakers. I will see how it goes.

                          My opinion is that a center speaker will greatly enhance Harbeth line of products.

                          Comment


                          • #43
                            Re: A Harbeth centre channel speaker

                            To elaborate on my previous post, I believe that form factor is very important for a home theater system. Most living spaces simply could not accommodate large speakers.

                            While I was choosing between Super HL5 and Compact 7 a couple of days ago, the deciding factor was the size of the speakers, rather than the subtle tonal characteristics between these two speakers.

                            Even Compact 7 is really too big to fit into my living rooms with the existing furnitures. I actually think that 5 P3's with a matching sub woofer would make a superb HT system.

                            Alan, do you have any plan to develop a sub woofer?

                            Cheers,
                            Yee

                            Comment


                            • #44
                              Re: Design specification for centre channel

                              Originally posted by A.S. View Post
                              I realise that the centre channel is important as it carries most of the dialogue (I'm told) but I think you are absolutely correct when you identify that you should aim to match the sonic characteristics of the P3s. This will not be easy: most (all?) contemporary speakers, including centre channel speakers, seem far to colored or aggressive for my taste so be careful.
                              The centre speakers carry more than dialog - depends on the nature of the DVD. I have a few musical DVD, and I found the centre speaker carry the solo instrument(s) or solo singer(s).
                              There is one particular set of DVD, "Claudio Abbado: Beethoven - Symphonies 1-9", where the center speaker is a continuation of the FR and FL speakers. I think this is true for all symphonic or choral music. This set of DVD is the one that I find most problematic.

                              My current setup is Compact 7ES3 for the front speakers, and a pair of P3ES2 as the center speaker. When I played the Abbado DVD's with 5.1 sound track the centre speaker is noticeably falls short of the of the front speakers in sound quality, to the point that PCM stereo actually sounds better than Dolby 5.1 .

                              For music DVD I actually think that the center speaker is MORE important than the front speakers. Harbeth dealer in Kuala Lumpur suggested that I purchase a third piece of Compact 7 as the centre speaker. That would have been ideal if my living room can accommodate it.

                              I had my Harbeth speakers for a week now. I am really enjoying every second listening to it.

                              Cheers,
                              Yee

                              Comment


                              • #45
                                Re: Design specification for centre channel

                                Welcome to Harbeth.

                                I think that the P3ESR with its RADIAL2? cone is going to give you a very close match in tone and timbre to your C7ES3s, which also have RADIAL cones. A centre P3ESR would be much easier to accommodate and considerably less expensive. You'd have no worries about bass either. That's definitely what I'd go for myself.
                                Alan A. Shaw
                                Designer, owner
                                Harbeth Audio UK

                                Comment

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