Announcement

Collapse

HUG - here for all audio enthusiasts

The Harbeth User Group is the primary channel for public communication with Harbeth's HQ. If you have a 'scientific mind' and are curious about how the ear works, how it can lead us to make the right - and wrong - audio equipment decisions, and about the technical ins and outs of audio equipment, how it's designed and what choices the designer makes, then the factual Science of Audio sub-forum area of HUG is your place. The objective methods of comparing audio equipment under controlled conditions has been thoroughly examined here on HUG and elsewhere and should be accessible to non-experts and able to be tried-out at home without deep technical knowledge. From a design perspective, today's award winning Harbeths could not have been designed any other way.

Alternatively, if you just like chatting about audio and subjectivity rules for you, then the Subjective Soundings area is you. If you are quite set in your subjectivity, then HUG is likely to be a bit too fact based for you, as many of the contributors have maximised their pleasure in home music reproduction by allowing their head to rule their heart. If upon examination we think that Posts are better suited to one sub-forum than than the other, they will be redirected during Moderation, which is applied throughout the site.

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 only, although HUG is really not the best place to have these sort of purely subjective airings.

The Moderators' decision is final in all matters and Harbeth does not necessarily agree with the contents of any member contributions, especially in the Subjective Soundings area, and has no control over external content.

That's it! Enjoy!

{Updated Oct. 2017}
See more
See less

Subwoofers - are two needed for hi-fi?

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Subwoofers - are two needed for hi-fi?

    This is a fork from the thread here concerning Harbeth's RADIAL™ cone material. This branch looks at whether subwoofers should be doubled-up, so that a home stereo system uses a pair of subwoofers, one connected to the left channel, the other to the right.
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

  • #2
    Bass frequencies responsible for 'air'? - No

    {Edited down from source thread above}

    Originally posted by Labarum View Post
    Piano? Ah yes. The the air around the instrument - a combination of the hall acoustics and the natural decay of the strings exploited by the skilful use of the damper pedal by the pianist. I am still thinking about your piano clips. The problem is that the "air" is the first thing to go as you move from a lossless format like FLAC to a lossy format like MP3 or AAC... I had thought the "air" was down to good bass extension capturing the ambience of the hall. (It is sometimes disconcerting to hear the hall aircon rumble!) But maybe I'm wrong about "air" and bass extension?...
    No - 'air' does not relate at all to the low frequencies contained in the hall or the recording. It's not 'air' as in air conditioning or 'air' as in stifling hot or 'air' as in a draught. That's an entirely separate but parallel issue. The enveloping recording atmosphere in the lower registers I think you're referring to is indeed a vital part of the overall feeling of 'being there' and has much to do with the selection of microphone types. The Peter Grimes thread is a good example of that all-important warmth and weight underpinning the live experience - omnidirectional mics of course. Personally, I would prefer some aircon rumble and a really solid, warm bass to a rolled-off anaemic bass free from rumble. The falling out of favour of omnidirectional mics with their very extended deep bass response (due to the increasing ambient noise in our modern world) has to some extent denuded modern recordings of the bass weight you hear in the hall.

    {See original post}
    Alan A. Shaw
    Designer, owner
    Harbeth Audio UK

    Comment


    • #3
      Thank you Alan for the Gulda demo with and without bass cut. I hear the effect well. (I made no confusion between metaphorical and literal air!)

      But I seem to be on the right lines suggesting that bass extension is essential to capture hall ambience, which, as you say is a separate issue. And am I right that the realism can only be heard if the bass is maintained in stereo - a mono sub will just not do it?

      Two effects then - capturing the lower bass as it interacts with the recording space, and capturing the detail of the natural decay of the sound of instruments at higher frequencies.

      You observe the RADIAL material does rather better than other cone materials with the latter effect. How much bass extension is required for the former effect. The SHL5 will clearly achieve more in the area that the P3.

      Comment


      • #4
        Dolby R&D

        {Edited from original post}

        Originally posted by Labarum View Post
        Thank you Alan for the Gulda demo with and without bass cut. I hear the effect well. But I seem to be on the right lines suggesting that bass extension is essential to capture hall ambience, which, as you say is a separate issue. And am I right that the realism can only be heard if the bass is maintained in stereo - a mono sub will just not do it?

        Two effects then - capturing the lower bass as it interacts with the recording space, and capturing the detail of the natural decay of the sound of instruments at higher frequencies.

        You observe the RADIAL material does rather better than other cone materials with the latter effect. How much bass extension is required for the former effect. The SHL5 will clearly achieve more in the area that the P3.
        Very astute observations. Let's take them individually:

        1) Dolby Labs invested much research effort into the reproduction of LF at home as a precursor to defining how many channels would be needed in a movie digital delivery system (DVD) for home use. They proved, and I'm sure they were right, that below about 120Hz, bass is sufficiently omnidirectional that it doesn't matter at all where in the room the bass radiates from: in front, behind, above, below, to the side - anywhere will do, or possibly even from the next room. Because of this omnidirectionality at low frequencies, there is no technical advantage to having two subwoofers as all LF soundwaves merge together. Furthermore, that omnidirectionality of LF at the recording means that bass, from whichever instrument, will be picked up almost equally by each and every microphone right across the orchestra, losing in the mixdown any sense of directionality or stereophony.

        All LP records have had to be mastered and cut with mono'd bass and nobody believes that there is stereophonic information at LF on vinyl do they? There can't be if 20 mins playing time per side is needed. No consumer would accept 10 minutes just to have stereo bass. The issue here is the same as the one Dolby investigated: there is no point using precious bandwidth, playing time or data to encode LF information that contributes nothing at all to the listening experience. That's first class engineering thinking.

        2) Yes, there are these two different but, in my opinion, defining components to a fabulous recording: warmth in the lower registers and simultaneously, the airiness and openness in the upper regions.

        {etc. etc.}
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • #5
          Subwoofers & stereo

          {Edited from original post}

          Originally posted by A.S. View Post
          Because of this omnidirectionality at low frequencies, there is no technical advantage to having two subwoofers as all LF soundwaves merge together. Furthermore, that omnidirectionality of LF at the recording means that bass, from whichever instrument, will be picked up almost equally by each and every microphone right across the orchestra, losing in the mixdown any sense of directionality or stereophony.
          Can we discuss this more? Dolby defends the received wisdom, but I do know an audio-pro who is adamant that two subs are essential in some circumstances.

          And there is this website, http://kenrockwell.com/audio/stereo-subwoofers.htm which I would consider less authorative.

          If a recording is made of acoustic instruments using a simple microphone arrangement, some audio-pros would seem to say there is directional information into the deeper bass that can be relayed by two subs or a pair of full range speakers. If, however, a more complex microphone arrangement is used, or a "stereo image" is contrived in a mixing desk there is nothing to be gained from stereo subs.

          And of course, if you are playing LPs the data is not there no matter how the recording was made.

          {etc.}

          Comment


          • #6
            Quarrying and subwoofers - and tweeter crossover frequency

            {Edited from original quote}

            Originally posted by Labarum
            Can we discuss this more? Dolby defends the received wisdom, but I do know an audio-pro who is adamant that two subs are essential in some circumstances. If a recording is made of acoustic instruments using a simple microphone arrangement, some audio-pros would seem to say there is directional information into the deeper bass that can be relayed by two subs or a pair of full range speakers. If, however, a more complex microphone arrangement is used, or a "stereo image" is contrived in a mixing desk there is nothing to be gained from stereo subs. And of course, if you are playing LPs the data is not there no matter how the recording was made.
            To be honest, my knowledge of subwoofers is so negligible that I can't contribute usefully to the debate. But if the wavelength at 30Hz is ten metres (say, 30 feet), far bigger than the even a very large home listening room. Are you really asking me to believe that I could expect to hear or reproduce directionality in the room (a container) a fraction of the wavelength of the sound we're attempting to reproduce which to fit the room, has folded itself around opposite and tangential surfaces already? Seems rather counter-intuitive to me.

            Within, I assume, a few miles of the Harbeth R&D centre tucked away deep in the countryside, there has been some sort of quarrying underway for months. I have often stood outside in the adjacent field, well away from obstructions asking myself from which direction that LF boom comes. I am unable to decide N, S, E or W - it's an occasional blast of repetitive 40Hz or so probably from earth moving equipment biting into a wall of rock with force. I really would like to take a look at the works, but I am none the wiser as to which direction to set off in.

            {etc.}
            Alan A. Shaw
            Designer, owner
            Harbeth Audio UK

            Comment


            • #7
              Superior knowledge

              I think I know the engineer that Labarum is referring to and he is adamant that when he's used subs in his recording work, he NEEDS two for stereo, even if the cut-off is at a low frequency making it theoretical that one sub should do. He swears that reverb and venue decay is adversely affected when "only" using one sub.

              I do fully appreciate that records have the low bass cut into them in mono, assuming it's not filtered out first, but the chap above (similar age to "us" Alan) has had many years in the AV/film sound industry and I do trust his judgements, while keeping my mind open to other viewpoints

              Comment


              • #8
                Bass directionality

                As always I bow to superior knowledge, but I'd very much like to know how the the recording engineers who have produced millions of discs over the last decades have managed without stereo subs.

                Here's a challenge then: I'll buy him lunch at a swanky pub nearby just for turning up ... I invite him to my field to hear the quarrying explosions or whatever they are. He can then point out, give or take 30 degrees, which direction we should head in across the fields to find the quarry. How about that eh?

                Alternatively, are there any research papers in the public domain that have examined this issue, perhaps the AES? I'm going to stick to my views on this, in line with academia until proven otherwise. Of course, it would be dead easy to prove or disprove with some DIY audio clips intended for headphone listening: I'll leave that to others!
                Alan A. Shaw
                Designer, owner
                Harbeth Audio UK

                Comment


                • #9
                  Stereo subwoofers

                  Originally posted by A.S.
                  Alternatively, are there any research papers in the public domain that have examined this issue, perhaps the AES?
                  There is stuff there Alan.

                  I just did a search on "stereo subwoofer". Try it, and you may have members access to see the whole text of the papers.

                  Just one:

                  https://secure.aes.org/forum/pubs/co...ns/?elib=13358

                  Comment


                  • #10
                    A DIY example of bass directionality - or not?

                    I've dreamed-up a way of perhaps demonstrating if there really is any sonic justification for the cost and inconvenience of using two subwoofers. Dolby's research suggests not. Wouldn't it be nice if we can judge for ourselves by listening?

                    It occurred to me at about 3.30am, wind howling, snow piling up at the windows, that I have an excellent example of a really wide, pinpoint stereo, surely recorded with omnidirectional microphones. I can see no reason to believe that the excellent stereo imaging is only restricted to the middle and upper frequencies. It seems logical that the stereophony would extend from the lowest to highest frequencies within the limitation of the recording equipment. What we can then do is progressively remove the middle and top frequencies until we are left with only the bass. We can then listen to those low frequencies, and hear for ourselves if there are any directional cues. We can also examine the low frequencies in a phase meter which will show us visually how much directional information is contained in the left and right signal at LF, if any.

                    I have a (somewhat) open mind on this matter, but I should caution you that I am not aware of any psychoacoustic research work these past hundred years or so that says that low frequencies are perceived as directional below a certain frequency.

                    Clips to follow this evening.
                    Alan A. Shaw
                    Designer, owner
                    Harbeth Audio UK

                    Comment


                    • #11
                      Two subs - a test

                      Originally posted by A.S. View Post
                      ...is there really is any sonic justification for the cost and inconvenience of using two subwoofers. Dolby's research suggests not. Wouldn't it be nice if we can judge for ourselves by listening?
                      It is indeed a widely held belief that bass is omnidirectional and therefore not worthy of handling in stereo. Now let's be careful that we are not confusing two concepts here. "Omnidirectional" implies that it radiates in all directions - demonstrably so unless we are dealing with large obstacles - large enough to cause the sound wave to be reflected rather than merely diffracted around the obstacle. The rule of thumb for sound wavelength is that 1kHz has a wavelength of 1 foot hence 100Hz has a wavelength of about 10 feet (3 metres).

                      The fact that LF sound radiates in all directions from its source (i.e. you hear the sound of a double bass nearly as well behind the instrument as in front) is not the same thing as saying that you cannot localize its point of origin. However (and this is paramount) it is much easier to do so in a large environment than a small one because, in a small space, the issue becomes badly confused because higher frequency components (in which the double bass is rich) will be handled, by the room, very differently from the lower ones. In short, the mid to high frequency clues used to localize the source become well and truly messed up in a small space. Some of the clues say "here", others say "there" while the fundamental is everywhere!

                      I've just done a very quick and dirty experiment, using the software I use for domestic listening, JRiver Media Centre (excellent in every particular) which includes some nice DSP functions, amongst which are low pass filters which we can configure to ditch everything above, say, 100Hz at up to 48dB/8ve.

                      So, I listen to the bass content only while fiddling around with the balance control. The question I'm asking myself is, "can a localize the image as readily as I can with higher frequency (i.e. normal) content?

                      The outcome is, "only partially". While the sound of male speech can be localized quite precisely wherever it is between the speakers - I have the speakers at roughly 60 and I think I can discern a simple mono speech source to an accuracy of about 10 - but with this low frequency stuff I reckon my ability to discern the position was really only hard left, centre, hard right - so my usual directional 'resolution' was much reduced.

                      So the conclusion, in my room, is that two sub-woofers would, in all likelihood, be a largely unnecessary luxury.

                      Comment


                      • #12
                        Studio techniques and LF

                        Originally posted by A.S. View Post
                        I'd very much like to know how the the recording engineers who have produced millions of discs over the last decades have managed without stereo subs
                        The 'sub' is a very recent concept born of the inability to accommodate speakers with inadequate LF capability for the job in hand*.

                        As a long-standing M40 user you might be pleased to learn that I've never felt a yearning for a 'sub', nor have most other engineers who have been privileged to sit in front of a pair of decent, full range, speakers.

                        * the 'job in hand' is, all too often these days, merely the reproduction of artificially enhanced low frequency effects. The correct name for the channel carrying the signal to be fed to the sub is, in fact, LFE - Low Frequency Effects.

                        Comment


                        • #13
                          Sickening sensational subsonic 'sperience

                          I've just recieved a fascinating and lengthy email from my engineering friend who had an hour or two spare this lunchtime to reply. He would be delighted to pop over to see you Alan when it's convenient and has much information to share on this subject I believe. Apparently, there's a point at which the body takes over from the ears - I dare not go further because it's not my expertise at all and I don't want to provide false second-hand information.

                          One suggestion though, is to look at the Cerwin-Vega produced? 'Sensurround' system from the mid 70's which helped to start this thing off I understand. Apparently recording practise for film is different in detail from recording purely music it seems and again, I feel a direct meeting with the source of all this info will prove most fruitful indeed.

                          On a slight tangent to all this, and mono-bass or not, I always thought that two sub systems in a domestic "AV" environment would be better than one because the room modes would be "driven" better. A long time since I read it up, so sincere apologies for not providing links to pages on this subject.

                          Me? I find that for most things, a pair of SHL5's have enough bass extension and of more than sufficient quality to hear low bass notes when there in recordings, especially the better recorded contemporary ones. I have too many memories of huge old IMF transmission-line speakers, able to dip well below 20Hz in-room, making me feel sick with pressure waves (the classic heart-beat sound on Dark-Side-Of-The-Moon played loudly from a Dolby-A master-tape copy springs to mind here).....

                          Comment


                          • #14
                            A counter challenge

                            The Audio-Professional whose name DSRANCE and I have been taking in vain has indicated he will take up your offer of a free lunch sometime Alan, but says he would fail your quarry test. As I thought, it's the wrong test.

                            He suggests:

                            Set up a 2.1 Harbeth system and a 2.2 Harbeth system using the same satellites and subs and see if you hear a difference with any true recording that hasn't been bass mono-fied during mastering for X.1. I suspect that Alan would hear the difference.
                            He may yet engage directly in this thread. Who knows?

                            Comment


                            • #15
                              Stoneage man

                              There is it seems to me the problem of the ear having a different perception to incomplete waveforms. (sinusoidal). On one post you placed tones separated by a small amount, and challenged us to determine which was higher in frequency.

                              I think that I did so reliably, but at the time also thought that it would be easier to do so on say a violin or piano waveform, because of the ears habituation over years of listening, and maybe also because of its evolutionary development; the superposition may have an effect on perceptive sensitivity.

                              Did the stone age people have sine wave generators?

                              {Moderator's comment: probably not but Alan doesn't have a violin, or piano handy! There is a limit to how far we can go!}

                              Comment

                              Working...
                              X