[Wilseus]

I currently use my system for about 50% movies/TV and 50% music. My major problem is that it tends to sound muddled with complex/dense music (NIN, Devin Townsend) stuff like that.

To reiterate what it says in my sig, I have various sources (Arcam CD72T, Sony BDP S360 and Sky HD box) plugged into a Yamaha RX-V657 receiver and I am driving the front three speakers (Mordaunt-Short MS30) with a Rotel RB-976 6 channel power amplifier. I have the left and right bi-amped (my centre does not support bi-amping/wiring.) I also have the almost obligatory BK Monolith connected

When this system sounds good, it really can sound good, but it just seems to be a bit out of its depth with more complex music.It also lacks upper bass "authority" in my opinion, although I believe that is a characteristic of these speakers. What do you guys think is the weak point here? Is it my speakers?

[Mark.Yudkin]

As far as the hardware is concerned, the MS30 are the weak link. As far as the setup as a whole is concerned, the weak link is probably the (software) settings.

Since with those speakers you need a subwoofer for the bass and you have a Monolith but an upper bass problem, you ought to try tweaking your Monolith's and Yamaha's YPAO's settings. This test tones CD, in conjuction with a SPL meter should get you started.

[Arcam_boy]

As Mark has said try cutting in your sub a little higher if possible to bring a bit more impact/slam to your sound.

Have you got any budget in mind to upgrade the weakest item?

[Wilseus]

You have confirmed what I suspected about the speakers. I'll download that CD and have a play. I already have a sound level meter.

I've changed the crossover frequency from 80Hz to 120Hz, to see how I get on. If I start being able to localise the sub then I'll have to roll it back a bit. Unfortunately there's no room for the sub in between the speakers, so it's immediately to the left of my left speaker.

As for budget, I'm a bit skint at the moment but hopefully that will change soon. I was thinking along the lines of maybe £1000 for a stereo pair and then more for a centre and rears to match.

[Wilseus]

Changing the crossover to 120Hz seems to have helped a lot! There's quite a bit more authority now.

[Wilseus]

Listening to some more material, *some* sounded awful until I adjusted the phase on the sub. I wonder why that is?

[sergiup]

Originally Posted by Wilseus

Listening to some more material, *some* sounded awful until I adjusted the phase on the sub. I wonder why that is?

That could be because at certain frequencies you'll have constructive/destructive interference between the sub and main speakers' output? Just a guess. Tweaking the phase would move / change the points where this happens.

[Mark.Yudkin]

Here's an illustration of what happens if the phases are out by 180°:

and here's what happens if they're in phase:

The crossover / bass management in your Yamaha is designed with rolloffs for the speakers and sub so that the sum of the in-phase frequencies yields the original signal. If your sub is out of phase, they cancel, a shown above. Since your speakers and sub aren't producing the same frequencies, the cancellation is of course incomplete, but quite audible.

For completeness, I'll just add that the phase difference can be any angle:

but most subs only support 0 or 180°, as this covers the cases typically met in practice.

[Wilseus]

Oh yes, I understand all about phase and what happens when they interact.

I just thought it was slightly odd that when I crossed over at 80Hz one setting sounded best (about 90° - my sub has a variable adjustment) and at 120Hz it sounds best at 0°, although interestingly there's hardly any difference when I set it to 180°.

On a related note, no-one has ever managed to explain to me what actually happens to the subwoofer signal when the phase is set in between 0° and 180°. 180° can be seen as a complete inversion of the signal, which works equally for all frequencies, but as for setting it at any other "angle", I can't visualise how this can work.

[sergiup]

Originally Posted by Wilseus

Oh yes, I understand all about phase and what happens when they interact.

I just thought it was slightly odd that when I crossed over at 80Hz one setting sounded best (about 90° - my sub has a variable adjustment) and at 120Hz it sounds best at 0°, although interestingly there's hardly any difference when I set it to 180°.

On a related note, no-one has ever managed to explain to me what actually happens to the subwoofer signal when the phase is set in between 0° and 180°. 180° can be seen as a complete inversion of the signal, which works equally for all frequencies, but as for setting it at any other "angle", I can't visualise how this can work.

From the little electronic engineering that I remember, frequency filters will cause phase shift - how much depends on the circuit design, and I believe it will also vary depending on the frequency you set the circuit for. So if you change the crossover frequency, you will probably change the phase shift.

The variable phase shift simply causes the signal to be anywhere between 0° and 180° out of phase - imagine the blue signal in Mark's diagrams moving (horizontally) anywhere between where it is in the 1st and 2nd plots, if that makes sense...

[Mark.Yudkin]

The variable phase shift simply causes the signal to be anywhere between 0° and 180° out of phase - imagine the blue signal in Mark's diagrams moving (horizontally) anywhere between where it is in the 1st and 2nd plots, if that makes sense...

NO! Phase shift is not time shift, it is not the "moving" of a signal left or right. That is delay, not phase shift. Phase shift is a change in the y-value, not a shift in the x value. The confusion is caused by the equivalence when using a fixed frequency ("an infinitely long sinusoid") for the diagram, but is obvious as soon as you consider a real audio signal.

Here's a little diagram. The phase angle is the fixed angle between the lines on the left. The curves on the right show the effect on a sinusoid - the values arising from the values on the left having a fixed distance from the centre (magnitude) and a constant speed of rotation (frequency).

For those who haven't forgotten their trigonometry, here's a more formal definition.

[Alan Mac]

Originally Posted by Wilseus

On a related note, no-one has ever managed to explain to me what actually happens to the subwoofer signal when the phase is set in between 0° and 180°. 180° can be seen as a complete inversion of the signal, which works equally for all frequencies, but as for setting it at any other "angle", I can't visualise how this can work.

As you say, phase shift of 180 degrees at all frequencies is achieved by “inverting the amplitude”, ie. multiplying the amplitudes at each frequency by the factor -1 which is equivalent to phase shifting each frequency component by 180 degrees. But 180 degrees is of course a very special case.

A possible way to produce a constant, frequency independent, phase shift of any angle is to modulate a high-frequency carrier with the audio signal we want to phase shift, to give a single-sideband suppressed carrier (SSBSC) signal.

SSBSC modulation requires the use of an all-pass 90 degree phase shift network. Technically, the operation of Phase shifting by 90 degrees at all frequencies is known as “Hilbert Transformation".

We then demodulate this SSBSC signal using the original carrier frequency phase shifted by the phase angle we wish the audio signal to be shifted by. Phase shifting a carrier, which is a single frequency, by any arbitrary angle, is a relatively trivial operation.

The demodulated audio signal then forms the phase shifted version of the original audio signal.


Alan

[sergiup]

Originally Posted by Mark.Yudkin

NO! Phase shift is not time shift, it is not the "moving" of a signal left or right. That is delay, not phase shift. Phase shift is a change in the y-value, not a shift in the x value. The confusion is caused by the equivalence when using a fixed frequency ("an infinitely long sinusoid") for the diagram, but is obvious as soon as you consider a real audio signal.

Here's a little diagram. The phase angle is the fixed angle between the lines on the left. The curves on the right show the effect on a sinusoid - the values arising from the values on the left having a fixed distance from the centre (magnitude) and a constant speed of rotation (frequency).
image

For those who haven't forgotten their trigonometry, here's a more formal definition.

I stand corrected, I didn't express myself accurately enough. (fail)

[Mark.Yudkin]

Another way to do it is to convert the signal to digital, after which it's just a bit of computation. High end subwoofers such as the Velodyne DD+ series use this technique to support a variable phase shift in 15° increments. The ever-popular Velodyne SMS-1 add-on also offfers the same feature for those with other subwoofers.

[BlueWizard]

Within a given speaker, because of resistive, capacitive, and inductive components, the phase of a given speaker, and of the various drivers relative to one another is constantly changing depending on which parameter (res, cap, ind) is most dominant at any given moment.

Relative to resistance, which has no phase shift, capacitive or inductive load can be either +90° or -90° out of phase. What this means is that Current (amps) is either +90° or -90° out of phase with the voltage.

In a capacitor, we have in initial in-rush of current, almost as if a short circuit, yet the voltage does not appear until the capacitor begins to take on a charge. So, the flow current precedes the presents of voltage on the device.

When multiple currents are flowing at different phases, we combine them using vectors to arrive at the resulting current/voltage and the resulting phase angle. For example, if we have 4 volts at 0° and 4 volts at +90°, then the resulting vector is 5 volts at +45°.

This is one of the reasons that you see highly inductive motors rated in Volt-Amps rather than watts. Power is Voltage times Current, but that assume pure resistance. In inductive motors, the phase of voltage and current must be taken into consideration.

All this occurs with in a given driver. When drivers are combined into a speakers system and crossover networks are added, the phase relationship of the speaker system becomes even more complex because crossover are really just a collection of coils and capacitors. I've seen phase plot charts of speakers where the phase is rising from 0° and moving toward +90°, then suddenly it will completely flip to -90° and continue rising toward 0°. Remember this is the electrical phase of voltage vs current, not the mechanical phase of the speakers relative to each other.

However, all that blather aside, in our case, and relative to the placement of a Sub, it is all about distance and position in the room. If the Front speakers are in front and facing the back of the room, and the Sub is in the back of the room facing the front, then the Sub is 180° out of phase with the front. When the front bass drivers move, they move NORTH, when the Sub bass driver moves responding to the same note, it moves SOUTH; ie: 180° out of phase.

If the Sub is in the front but forward of the Front speakers, then there will be frequencies where that distance causes a phase error between the speakers. Fortunately, given the very narrow frequency range of the Sub, the area of overlap between the Front and Sub is very small. As you move above and below the crossover frequency, the front and/or sub become sufficiently attenuated, that any phase error doesn't matter that much. But in the area of the crossover, the position and distance between the front and Sub, can make a difference.

Next, the room itself can cause phase errors. If the Sub or Front send out low frequency waves, they will bounce off the back wall reflected back toward the front and intersect with new waves coming from the front. These overlapping waves can cause peaks and nulls in the room; point where those bass frequencies are exaggerated, and points where those bass frequencies are cancelled out.

In the case of the Phase control on a Subwoofer, the purpose is to delay the Sub woofer in an attempt to get its signal in sync with the front speakers. I say delay, because I think that is the only thing that is electronically possible. You can delay the Sub, but I don't see how you can push it forward in time, to do that, you would have to advance a signal that you hadn't received yet.

So, relative to a Sub and Front speakers, phase is a matter of timing, you want to adjust the Sub to get the Sub signals in sync with the sound coming from the front speakers. So, in that sense it is really a Timing Shift, but it is time shifted to get the common frequencies of the Sub in phase with the common (shared) frequencies of the Front speakers.

At least, that is how I see it. Though I'm more than happy to be proven wrong.

Steve/bluewizard

[Mark.Yudkin]

The phase control in a sub does not work by delaying the signal, that is done be setting the delay in the amp or the subwoofer, although the latter is not common. Delaying a signal will not resolve phase problems, as the amount of the delay is dependent on the instantaneous frequency. You studied physics, so you should have no problems with the formal definition: phase is the first derivative of the frequency response.

You should also have no difficulties appreciating the fundamental difference between impedance phase, caused by energy storage and release in inductors and capacitors, and acoustic phase, caused by the voltage transfer function.

As to how it's done, Alan has already given one technique. For DSPs, see FIR Filter Properties | dspGuru.com, which also links to the code.

[Wilseus]

Thanks guys, this is really interesting and you have pretty much answered my question (especially Alan!)
I also studied physics, although it seems it wasn't to quite the level of some of you!

As I see it, applying a (correct) delay to the subwoofer signal might very well prevent a possible cancellation at and near the crossover frequency but I agree there must be something cleverer than this happening in a real subwoofer, otherwise the 0-180° scale would be utterly meaningless, except at one, arbitrary frequency.

Even though I still can't visualise how it would actually change the "shape" of an arbitrary waveform, I have no problem accepting Alan's explanation at face value. Before his explanation of the process, whether done digitally or not, the only way of doing it I could think of was to use some kind of fourier analysis, pulling apart the signal into its constituent frequencies, applying a phase shift to each one (itself trivial) then summing them all together again. As I understand it, without the phase shifting, this is how MP3s work.

[Mark.Yudkin]

Originally Posted by Wilseus

Even though I still can't visualise how it would actually change the "shape" of an arbitrary waveform, I have no problem accepting Alan's explanation at face value. Before his explanation of the process, whether done digitally or not, the only way of doing it I could think of was to use some kind of fourier analysis, pulling apart the signal into its constituent frequencies, applying a phase shift to each one (itself trivial) then summing them all together again.

Here's an illustration of a 90° phase shift on a wave with two frequency components:

As Alan says, it's actually a Hilbert transform, which is indeed related to the Fourier transform, and his technique makes use of the limiting approximation.

[Wilseus]

Ah yes I see it now, thanks.

I suppose that it's the top two entries in this table that are important here. Also I notice in the section above that Euler's identity is involved. That seems to get everywhere!

[Wilseus]

Well, back to the original topic: I have a pair of Linn Keilidhs coming my way next week, which I got for a very reasonable price. Hopefully these will be a major upgrade from what I have currently

[Mark.Yudkin]

Originally Posted by Wilseus

Well, back to the original topic: I have a pair of Linn Keilidhs coming my way next week, which I got for a very reasonable price. Hopefully these will be a major upgrade from what I have currently

Let us know...

[WonkyEwok]

Originally Posted by Mark.Yudkin

As far as the hardware is concerned, the MS30 are the weak link. As far as the setup as a whole is concerned, the weak link is probably the (software) settings.

Just to add to this, the room is a damped, resonant system that's being driven by the amp and speakers. So maybe the layout of the room could also be improved : where you put the speakers will change their coupling with the room, and the soft furnishings will change its damping etc.

If your sound meter has an analog output (or even if not, but it's a pain then) you could try Room EQ Wizard (use google). Just using the tone generator and sweeping around the frequency range will show you whether there's a lot of boosting or cutting going on in the bass frequencies.

If you're prepared to spend a lot on an amp, the anthem mrx series has very good room correction : effectively changing the amount of energy that the system puts into the room at difference frequencies. I don't know whether it's any more clever than that - e.g. using phase as well as amplitude - but it seems to work. The latest audyssey (xt32?) might be equally good, and I'd liked to have been able to compare them. A demo might be worthwhile : a dealer near me was prepared to come and set one up on a Sat and leave it until the Monday. From what I've read about rooms in music studios though, it sounds better to fix the problem acoustically as much as possible (room, placement, speakers) and finish off with software.

[Wilseus]

Thanks for the advice. The thing is though, I have had these speakers for nearly 20 years and in that time I've driven them with numerous amps in numerous rooms. The one thing that has always stayed constant is the lack of upper bass slam. I don't think there's a response dip, I think it's more an overly laid back sound that these speakers have.
It's not that they don't go low, they do: they've got 8" drivers in a fairly large ported cabinet and easily do 40Hz. My original question was really rhetorical, as in my heart of hearts I always suspected that the speakers are the weak link. Setting the sub crossover point to 120Hz has gone some way to proving it. I strongly suspect that the very small voice coil has something to do with it:

[Wilseus]

Originally Posted by Mark.Yudkin

Let us know...

OK, I will!

I've had the Keilidhs (pronounced kay-lee) about a week now. I paid £250 for them, which considering they're pretty much immaculate, in their original double boxes and came with the highly desirable ku-stone stands, I think isn't too bad. They were a £600 speaker when they originally came out in 1992-ish, although these ones are somewhat newer than that. Like most of Linn's speakers they can be converted to active operation with the use of two (or optionally three) stereo power amps and an active crossover. However, for now at least, I am using them in passive mode. They are fairly sensitive (90dB I have been told) but are a 4 ohm load, so some amps may struggle to drive them.

As you can see from the photograph I have installed them in the only place they will fit: each side of my TV. They are toed in very slightly by a couple of degrees. I've mostly evaluated them integrated with my BK Monolith+ subwoofer (crossover at 80Hz for now) and Antimode, mainly because the very strong 50Hz mode in my living room makes the bass of any large speaker almost unlistenable. I spent a good while with a test disc and sound level meter getting this right.

My first impression after my first bit of serious listening was that the speakers sounded a trifle odd. I remember reading a review of them in a hifi magazine many years ago and the summary as I remember it mentioned, "awesome bass drive" and "sounds somewhat shut-in" rang true straight away. I also noticed at this point, when watching some TV that the speakers sounded somewhat "thinner" with dialogue. I wonder whether this is due to a lack of colouration, as the Mordaunts are a notoriously warm-sounding speaker.

I listened to quite a large variety of music. First off, Supertramp - Crime of the Century sounded OK enough, but at this point I was still reeling from the very different sound compared to my Mordaunt-Shorts. The Linns certainly have treble, and much more refined treble than the Mordaunts, but somehow it's veiled in a way I can't quite put my finger on. Perhaps I am looking for the "tizz" of the Mordaunts' metal dome tweeter which is just not there. Next up was Gabriel Faure - Requiem, which is one of my favourite pieces. Despite the "shut-in" issue mentioned above, this sounded "live" in a way that my MSs never could manage. Turning up the wick helped a lot with the sound, and helped them to open up, whatever the music.

After this I listened to Tim Smith - Extra Special OceanLandWorld of Cardiacs fame (or lack of it!) This recording usually sounds rather bright and suited the Linns well. So did my next CD, the "Lost Highway" soundtrack. The weird jazzy tracks by Angelo Badalamenti as well Barry Adamson's compositions sounded great here. I never liked this CD much on the Mordaunts, so the Linns get a big thumbs up here and they put a real smile on my face!:D "Rammstein (edit)" by Rammstein also rocked and had great power and authority. A lot of this material I had never listened to for a long time, and I suspect that that helped since I have no memory of how it sounded on the Mordaunts.

One of my favurite albums that I have not listened to for a while is Queen II which is an underrated prog-rock masterpiece in my opinion. Even though it's a pretty ropey recording (it's the original mix, I don't know whether the remaster is an improvement or not) it ROCKED! There was a magic with these speakers that I have not heard in any speaker before. I realised I was listening to the music and not the speakers. Also, I noticed that the soundstage extended outwards beyond the speakers, whereas the Mordaunts never had much of a soundstage at all. Staying with prog type material, I put on Andrew Lloyd-Webber - Variations which sounded great, and did not sound shut-in at all. Perhaps the Linns excel with certain recordings such as this one. Perhaps I was just getting used to their sound. Perhaps it's a combination of both! I noticed when listening to the jazzy bits of the album, as well as parts of Lost Highway that they seem to really like this style of music. I suspect that whoever designed them was a jazz fan!

With Tom Waits - Small Change I continued to be impressed, Waits' voice as well as the sax, double bass and strings had a realism that I have simply never heard before. Great! After this I listened to two Rush albums, Moving Pictures and A Farewell to Kings, both remasters. Both sounded very "live" and very good, especially Kings. However, the title track, "Eagle" from Abba - The Album was a disappointment, and sounded thick, congested, and sort of plodded along. Not good

Some industrial next, Front Line Assembly's FLAvour of the Weak did the honours here, and the Linns coped pretty well with the complex (and I mean complex) electronic breakbeats. There is also some extremely deep sub-bass in places in this album, that the Linns could not hope to reproduce even if I wasn't crossing over to the sub at 80Hz. This is the one album I own that my Mono struggles with in terms of bass "timing." Experimenting with turning off the sub, the Linns then made similar noises, so I guess it's not a sub issue per se, perhaps it's an issue with the material itself?

Last but not least was Cardiacs - A Little Man and a House and the Whole World Window", my favourite album from one of my favourite bands. Even though I must have listened to this a thousand times, I heard sounds I have not heard before. Their only "hit", "Is This the Life?" rocked and "R.E.S." sounded even crazier than ever and put a real smile on my face.

I understand that there's newer tweeter that can be retrofitted to the model I have. Going on the serial number, mine's the second of three tweeter revisions, and I have it on good authority that the later "three bar" tweeter is a vast improvement and goes at least some way to addressing the "shut-in" issue.

And that's about it. In summary I'd have to say the following:

What's good:
+ Great bass drive/timing
+ Magical "liveness" with certain recordings
+ Refined treble
+ Enveloping soundstage
+ Good looking speaker (IMO)

What's bad:
- Sounds rather shut-in with some material
- A 4 ohm load, which some AV amps may struggle to drive
- Need to turn the wick up to hear them at their best