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Feb. 2018
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M30.1 partnered with subwoofer theoretical calculations

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  • M30.1 partnered with subwoofer theoretical calculations

    For anyone interested in partnering their Harbeth M30.1 with a subwoofer, I've done some theoretical design simulations to see what sort of combined response might be achieved.

    The M30.1 has a quoted –3 dB low-frequency cut-off point of 50 Hz. For the purposes of the simulations, I have assumed that its low-frequency response follows a QB3 vented-box low-frequency alignment. A 2nd-order Butterworth high-pass filter response has been added to the "raw" response of the M30.1. This high-pass filter type is what is commonly found in AV receivers.

    The subwoofer is modelled as a system with a 2nd-order Butterworth high-pass filter with a –3 dB point of 20 Hz. A 2nd-order Butterworth low-pass filter with a –3 dB point of 200 Hz has been included in order to model the nominal high-frequency roll-off of the subwoofer's response. The 20 Hz low-frequency response seems to be attainable by a few subwoofers on the market today.

    A 4th-order Linkwitz-Riley low-pass filter has been applied to the "raw" subwoofer response. The Linkwitz-Riley filter type is typical of that to be found in subwoofers and AV receivers.

    After a few trial-and-error calculations, the –3 dB cut-off frequency for the 2nd-order Butterworth high-pass filter was chosen to be 58 Hz, while the –6 dB cut-off frequency of the 4th-order Linkwitz-Riley low-pass filter was set to 54 Hz. The subwoofer and M30.1 were connected with the same polarity. Owing to the effects of the low-pass filter, the output of the subwoofer needed to be raised by +1.2 dB to produce a smooth blending between the M30.1 and subwoofer. The resulting filtered acoustic responses of the subwoofer and M30.1 cross over at about 55 Hz at –6 dB. The combined low-frequency response is very flat, and the –3 dB point is at about 18 Hz. This is a very worthwhile extension of the M30.1's natural low-frequency cut-off point of 50 Hz or so.

    The computed frequency response plots are shown below:

    Click image for larger version

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  • #2
    Active Harbeth subwoofer?

    Witwald, many thanks for your detailed research, although much of it is beyond my comprehension. I'd be very interested if you could let us know whether you managed to apply this science practically. Did you use an active crossover to achieve good results with the M30.1?

    I briefly tried the Gradient SW63 dipole subs, which were made for the ESL 63 and have an active crossover, with a separate power amp for the subs. This system works extremely well, and I also tried it with my Harbeth P3ESR. This was also very promising, but visually absurd, since the Gradients were made to sit underneath ESL 63s. It got me thinking that I would love to try constructing a system with Harbeths and an active crossover to subs, and ideally with the Monitor 30.1.


    • #3
      Latest Gradient subs

      Elephant. Gradient's current SW dipole subwoofers sit vertically and are 30" tall. ( suitable speaker stand height)

      So your P3ESR could easily sit on top them.


      • #4
        Gradient combo

        Ok, now I look into it, that is the bass section from the Gradient Revolution, so that makes perfect sense. Gradient have actually shown the Revolutions at a show in the US with P3ESRs. I've heard from some people on the US forums that it was a stunning combination.

        Gradient are currently lacking much in the way of UK distribution and pricing is not at all clear.


        • #5

          I own both the Gradient Revolution and M30.1.
          My opinion is that system made of Gradient's woofer (dipole with two 12" units operating up to 200Hz) and Harbeth's speaker for mid/highs could sound excellent .

          The Revolutions are per se excellent speakers but couldn't quite match the quality of mid frequencies the Radial units reach. For that reason I 've bought the M30.1s!
          But pls have in mind that dipole woofer has differnt characterstics then mostly used sealed/ported units. With M30.1 I use sealed sw with amp/crossover inside, crossocer frequency is 40Hz. It integrates very well with the m30.1s.


          • #6
            BK sealed sub?

            Dragan, do you use 1 or 2 subwoofer(s) for bass extention to the 30.1s? - I have just picked up a new pair of M30.1s, which sound amazing ringt out of the box. I have been thinking that I might order a sealed subwoofer or two, for instance from BK Electric (quite inexpensive). Any advise on 1 vs. 2 would be appreciated.


            • #7
              Two subs?

              I use the JAMO 660! Two sw are better then one, but I am satisfied with one in the 60 m3 room!


              • #8
                Try without

                Thank you. Wow, that is a large listening space. I will listen more without sub, first, then decide.


                • #9
                  Never without dsp room equalization

                  The problem with subwoofers is that they produce such low frequencies that room modes become a real issue, generating unwanted peaks at certain bass frequencies, resulting in a veiled boomy sound. Using two subwoofers was the classic solution to reduce this problem. Two subs in different locations produce twice as many smaller peaks which is less unpleasant.

                  The modern alternative is to use dsp room equalization to reduce these peaks from room modes. I use the DSpeaker Antimode 8033 for this purpose and I could not be happier. It makes a huge difference, and my conclusion is that subs without room equalization are more trouble than they are worth.


                  • #10
                    Sub integration

                    willem, can you use the Antimode only for the sub, or do you have to route everything through it, hence converting all signals to digital? I couldn't accept my analogue sources being converted to digital for DSP purposes.

                    EDIT: Sorry, I've looked up the Anti-mode 8033 now and I see that this works purely for the sub. That sounds ideal to me. It means that so long as you find a monitor that doesn't interfere with your room modes you can get the lower bass integrated really well with a sub. It just leaves one question as to how you apply witwald's analysis above. Can the 8033 help in integrating the sub around the critical region of about 50Hz, where the monitor and the sub are likely to overlap?

                    Dragan, if you own both the Gradients and the M30.1 it would be fascinating if you did the experiment of replacing the top section of the Revolution with the M30.1. Please let us know what that sounds like if you try it. I don't know if it would work visually, but could be astonishing sonically. What is the crossover point to the dipole sub with the Revolution?


                    • #11
                      Subwoofer simulations only, no practical applications so far

                      Hi Elephant. No, I haven't applied these simulations to an actual M30.1 and subwoofer combination. Sorry. The aim was to show what might possibly be achieved with a reasonably good subwoofer, with regard to low-frequency extension, possibly using the filters that come with a typical AV receiver.

                      As others have noted elsewhere in this thread, room modes can become a bit of a problem when the low-frequency response is extended down to 20 Hz or below. Hence, some form of low-frequency room equalisation would likely be quite useful. A friend of mine has used this successfully with his two-way stand-mount loudspeakers and subwoofer. He found that a subwoofer added a new dimension to both music listening and movie viewing.


                      • #12
                        Sub integration, but not wise with vinyl replay

                        The Antimode 8033 works only with the sub. You connect it either to a pre-out connection, or at speaker level (with an attenuating cable). There is also a more expensive Antimode dual core that can also correct full range speakers or combinations of sub and stereo speakers. Such room equalization is at its most effective at the lower frequencies, however, so I decided that the 8033 was good enough for me.

                        I see you have a set of P3esr's. Combine them with a good sub and an Antimode 8033 and you have something that should sound really good. The Antimode will not help you directly in setting the crossover frequency of the sub and the level matching. Thus far I did this by ear, arriving at a lower crossover frequency than was theoretically indicated, and quite modest volume.

                        The Antimode comes with a calibrated measuring microphone, and I bought the matching MicAmp to connect it to a computer to measure frequency response and adjust from measurements rather than by ear. I have not had the time to try this, however.

                        As for digital vs analogue. This has me a little bit worried. First, I don't think there is anything wrong with digital. On the contrary, digital sources are far cleaner and have e.g. a much better frequency response. If you intend to use vinyl as a source, I suggest you should be very careful with a sub. There is no useful low frequency information on a vinyl disc, but only rumble. Sub's only really became a useful option with the introduction of superb cd sound with real low frequency information. See Alan's recent contributions on turntable specs on this forum.


                        • #13
                          Can't try

                          Elephant, it is not feasable for me to try Revolution/Harbeth combo because my Revolutions are passive version ie the crossover is inside of the speaker.

                          If it were active version - the one where the woofer part and mid/high part are "naked" and the crossover is box betwen the pre and two amps ( as it had been with ESL63 and SW63) I would try it.


                          • #14
                            Room correction essential

                            Witwald, your calculations seem to work pretty well. I use a pair of 30.1s with a BK XXLS400 subwoofer, which is equalised using an Antimode 8033. I was previously using a Meridian 568 as a preamp / DAC / crossover and using your figures the subwoofer integrated extremely well with the 30.1s.

                            Having played around with subs in 2-channel systems a fair bit, I would say that room correction for the sub is essential, or integration is just about hopeless. Unfortunately I ultimately decided that the Meridian wasn't for me and have moved to a separate DAC and preamp without a crossover. Setting the subwoofer levels manually gives an acceptable result, but of course there is still a full-range signal going to the 30.1s. I may play around with an external crossover at some stage, there are now a few interesting options available like the MiniDSP range or the Nadja board.


                            • #15
                              LP bass

                              Originally posted by willem View Post
                              If you intend to use vinyl as a source, I suggest you should be very careful with a sub. There is no useful low frequency information on a vinyl disc, but only rumble.
                              Willem, I've been using it since about the age of 7; that's a while ago. In my early twenties I bought a lot of 12" singles with bass information cd users could only dream of. Don't confuse the theory with the practice. We all know that cd is supposed to have greater dynamic range and frequency response, but the reality generally different in everything but classical music.

                              {Moderator's comment: we cannot agree at all with this post. The bass on vinyl is monophonic by intention during cutting and contains much non-musical scraping sounds. This is, like it or not, a technical fact and beyond refute.}