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Old 23rd Sep 2017, 7:11 pm   #21
Radio Wrangler
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Default Re: Powered sub-woofers - is it just me?

The phasing is simple. You want the subwoofer to be in phase with the main speakers as it takes over, so that it reinforces the sound coming from them. Get the phasing wrong and it will cancel their output and you'll get a bad dip in the response. You won't hear the dip of course unless what you're listening to has some content near that frequency.

It's the same matter as getting the phasing in agreement between a stereo pair of speakers... except in this case instead of having two ways round for a pair of wires, you have a variable phase control because the phase lag in the main speakers will be changing quite a bit as they cut-off.

You may have to compromise depending on where you place the three speakers. Ideally your ears should be the sme distance from both main speakers, and it helps if the subwoofer is equidistant from the mains. The lower your subwoofer crossover frequency the less subwoofer position matters, but the crossover depends on how low you can use the mains.

The subwoofer phase control compensates for the phase shift in the subwoofer and its
crossover, for the phase shift as the mains roll off and for the difference in distance of your ears to the mains compared to the subwoofer. So it helps a bit if things are symmetrical because you will only compensate one difference in distance at once.

You need to twiddle it with a sweeping bass tone, at a low enough level to not overheat things or drive yor neighbours up the wall.

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Old 23rd Sep 2017, 8:18 pm   #22
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Default Re: Powered sub-woofers - is it just me?

David, no, it's not simple at all. What you WANT and how to achieve it are two very different things!

What's the actual, blow by blow procedure to achieve that? I'm experienced, and I couldn't set the phasing switch from that description/procedure. I'm not being rude now, just realistic.

Like I said, setting up a sub woofer is not a thing for the beginner or inexperienced meddler. It's probably best not to bother with a sub in some cases as a poorly performing one (as posters have clearly eluded to) sounds worse than not having one. I've set up just two sub woofers, and after much twiddling and changing settings, both now sound very nice; nice, deep, extended bass with no lumps. Getting phasing right is not a simple matter in my opinion, as is cross over frequency and level. A veritable minefield of sonic trip wires. And all inter-reactive..
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Old 23rd Sep 2017, 9:02 pm   #23
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Default Re: Powered sub-woofers - is it just me?

Sorry, my fault. What I was hoping to convey was that understanding why someone would want to adjust the phase of a subwoofer is easy. Actually adjusting one to get a smooth transition with the main speakers is a right pig of job, and isn't necessarily successful.

The best cases of systems with a subwoofer is where the whole thing was designed to go together. Getting brand X speakers and getting a brand Y subwoofer and trying to integrate them involves possibly an overdose of enthusiasm.

I've heard only one subwoofer system that I liked the sound of, and a large number I wouldn't live with. Going for a seriously big pair of speakers that do their own subwoofing is the easy way out!

It's not only the crossover frequency, level and phase that needs to be got right, there is also the order of the roll-off to be accommodated.

Sorry
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Old 23rd Sep 2017, 11:43 pm   #24
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Default Re: Powered sub-woofers - is it just me?

Thanks David and Steve. My rudimentary understanding of phasing extends to making sure that the cones are all moving in the same direction at the same time in a stereo system. All I am trying to achieve with this slightly bizarre mix of 50s and 90s(?) technology is a stereo output with a central woofer. I was confused by the concept of adjustable phasing. Is that only relevant for multi-channel 'cinema' sound or is it significant in the simple stereo set-up I am trying to achieve?
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Old 23rd Sep 2017, 11:47 pm   #25
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Default Re: Powered sub-woofers - is it just me?

The vast majority of subs don't have adjustable phasing, just a switch to invert it. The easiest way to set it is to turn the cutoff frequency control to maximum and try both positions. The one that sounds best is the right one. Once the phasing is set you can reduce the cutoff frequency and adjust the level.
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Old 24th Sep 2017, 3:11 am   #26
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Default Re: Powered sub-woofers - is it just me?

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Originally Posted by RojDW48 View Post
There's a x-over frequency control 80 - 120Hz, an input level control and a phase adjust - hopefully someone can tell me why I would want to adjust the phasing?
The faze is fer when ya listen to Black Sabbath at 78 speed man!!

I have the subwoofer setup for movies, I still have my 1968 Tannoys for my modest 7 watts per channel stereo music box ( home made), STILL with a faded Garrard 401, SME 3009,
and of course the almighty Shure V15 MR cartridge. All set up on concrete, with a sloping roof 11 feet high one side 9 foot 6 the other side, 12 foot wide and 18 feet long. CERTAINLY doesn't need a sub woofer, and in any case, I don't have an amp to drive one. Seven watts being obtained from PP 6BW6's.

ESSENTIALLY the only surround system I have ever heard that worked properly was Walt Disney's "Fantasia" set up in Sydney many years ago using origional 30 watt Westrex amplifiers. ALL done by a bunch of oldies ( like us ) with a true appreciation of sound

Joe

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Old 24th Sep 2017, 5:58 am   #27
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Default Re: Powered sub-woofers - is it just me?

It's applicable if the subwoofer is added to any other speaker arrangement.. mono, stereo, or however many channel surround.

The more channels, the more difficult setting it up becomes.

Getting the amplitude and phasing right for a smooth transfer between different drivers is something that the designer of a crossover has to do for a normal multiway speaker. Some basic attempts don't make a good attempt at synchronising the arrival of sound waves from different drivers at your ears. Some speakers have stepped baffles or top mounted mid-range and tweeters stepped back a bit to use distance as a time delay to compensate goings on in the crossover network. Other designs have more elaborate crossover designs to do phase/delay compensation... The Harwood/BBC designs are examples. The designer of a speaker crossover has a lot of advantages over the designer of a subwoofer adjustment unit:

He knows exactly which drivers he is driving
He knows their relative positioning.

These allow him to do a much better job than a subwoofer designer can. Even so, there are enough problems left in ordinary speaker crossover design. drive unit impedances vary all over the shop and complicate crossover design, and some crossovers include fixes for uneven frequency responses (in those BBC crossovers again) and on top of this, the components in the crossover have to handle high power, and then the speaker drive units react to the source impedances presented by the crossover. It gets messy.

One way to reduce the problem is to treat each speaker driver to its own personal amplifier and do the crossing-over at low power before the amplifiers. At a stroke each driver now gets driven from a nice, controlled, low impedance and damping factors go up. Each speaker becomes isolated from interactions with the impedance variations of its colleagues. Crossover components become a lot less imperfect than the high power ones. Active circuitry can do the job without needing inductors.

Consequently a lot of professional speaker development went down the multi-amplifier active crossover route. Some domestic stuff went the same way (Linn/Naim, Meridian...) and in home built speakers, Seigfried Linkwitz has already been mentioned. And sometimes purpose designed separate woofers are in these systems.

Meanwhile in mass-market consumer domestic equipment, subwoofers are everywhere. Tellies have to be ultra-thin to comply with modern fashion, and their audio sections are rubbish. The manufacturers want you to pay more and buy a surround system to go with it (or at least a 'sound bar' which is only marginally less awful than the token speakers in the set) Modern fashion in decor dictates that the surround speakers must be tiny, tall and thin, so no bass there then. So the need for some thump is met by a subwoofer, to be hidden in a corner or behind the sofa. All told, these surround systems fit in with what Hollywood are doing to their sound tracks. I think it's just coincidence that there are so many adverts for headache cures on TV, there used to be plenty of those in the days when TVs had wooden cabinets and a single 6x4 speaker.... or maybe they were for line whistle back then?

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Old 24th Sep 2017, 7:34 am   #28
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Default Re: Powered sub-woofers - is it just me?

No, it's not an easy job setting up a sub or indeed any speakers to achieve a flat (or anywhere near flat) response in a given room. That's why I have bought and now use a Behringer Ultracurve Pro DEQ2496 24-Bit Mastering Processor to check and adjust the output of my speakers to match the room. Even that is not perfect and can never be for complex reasons too much to go into here. However, when you first start the test procedure you can clearly see how flat (not!) your existing speakers/room match is in the Behringer's display. Then after a few minutes of analysing, the processor has completed it's corrective actions and the display and (obviously) the sound are light years better, flatter. You wonder how you could have listened to it before, honestly. But that's the problem; you get used to 'bad sound'. My current speakers are Tannoy Revolution XT6Fs and the bass is pretty good so I'm not currently using a sub with those, but I am using a sub with some bookshelf speakers in another room. It took me a few days to get that set up right, listening to lots of different kinds of high quality music at different levels.

Messing around with frequency responses to get good sound has fascinated me for years ever since I built a (copy) pair of Spendor BC1 alikes in the 70s. The art of being able to hear and identify what frequencies are dominant, lagging etc etc must be one of the most difficult arts on the planet. At the BBC and in top studios there are (or were) technicians who were capable in the art of performing 'sweetening techniques'. In simple terms that's the art of identifying speaker/room anomalies and making adjustments to get the sound more natural. In all modesty I'm only reasonably good at that, and being a musician I have spent hundreds of hours fiddling around with graphic equalisers to help me identify what different frequencies sound like when boosted or cut. Even then, it is far from easy to make these adjustments yourself, which I why I bought the Behringer processor. You wouldn't knowingly buy speakers with +/- 10 or even 15dB response anomalies would you? So why would you listen to such a bad frequency response in the average room that creates that situation? The flattest speakers in the world can sound terrible in the 'wrong room'. Now, I know that what I'm listening to has a reasonably (pretty darn good actually) flat response.
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Old 24th Sep 2017, 7:46 am   #29
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Default Re: Powered sub-woofers - is it just me?

This is left and right responses of my LX521 Linkwitz speakers at 2 metres (so in the listening position). The big hump at around 60Hz is the main room resonance. Measured using an XZT room analyser https://www.xtz.se/product/room-analyzer

No Sub, but the resonance hump at least shows how difficult it is to integrate a sub-woofer, since its response is significantly modified by the listening room modes.
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Old 24th Sep 2017, 7:59 am   #30
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No Sub, but the resonance hump at least shows how difficult it is to integrate a sub-woofer, since its response is significantly modified by the listening room modes.
Exactly. You're showing a maximum frequency response anomaly of +38 to +60dB, that a whopping 22dB difference. An intelligent room processor would automatically iron that out to be more or less flat.
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Old 24th Sep 2017, 8:09 am   #31
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Default Re: Powered sub-woofers - is it just me?

No - the average level is about 48dB and the average hump is about 58dB. Or a 10dB hump, not 22dB. A room processor would in any event only EQ for one listening distance, with the door closed/open, windows closed/open etc. The only real way to deal with room interaction is via significant use of traps; I flew that option past my better half - her reply involved words like "over my dead body".
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Old 24th Sep 2017, 8:22 am   #32
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Default Re: Powered sub-woofers - is it just me?

I was going to ask about listening position in the room or if another piece of furniture is brought into it. Craig has answered that point.

Is this all not getting into listening to the sound and ignoring the music, sit back and enjoy, it will never sound like live music whatever you do.
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Old 24th Sep 2017, 8:39 am   #33
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Default Re: Powered sub-woofers - is it just me?

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Is this all not getting into listening to the sound and ignoring the music, sit back and enjoy, it will never sound like live music whatever you do.
Agreed. Certainly with the LX521, its total lack of box and EQ'd response down to 15Hz I get totally lost in the music, and find it easy to overlook the single low-Q longitudinal room resonance at around 60Hz.

And since they are dipoles, the do not excite the other two room modes at all.
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Old 24th Sep 2017, 10:25 am   #34
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Default Re: Powered sub-woofers - is it just me?

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The only real way to deal with room interaction is via significant use of traps.
Precisely - anything beyond simple bass rolloff to compensate for wall or corner proximity is doomed to failure because tweaking the excitation will simply screw up the direct sound without fixing the acoustic problem. And it doesn't matter what the analyser says - it can't distinguish between the two. That's why speakers are measured in anechoic conditions. It took the pros a long, long time to work this out...
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Old 24th Sep 2017, 10:29 am   #35
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Default Re: Powered sub-woofers - is it just me?

I said earlier that a flat response at the listening position is not what you want. Such a setup results in a sound that is unnaturally bright, because high frequencies are absorbed in a room. The human hearing system is amazing good at separating out the room from the sound source, and so attempting to remove the room from the sound is unnatural. Why? Because an equaliser - no matter how clever it is - can only affect the frequency response. It can't affect the time-domain response. We respond to time-of-arrival as well as level. If anything, we get more cues about a sound from time-domain information than frequency-domain. So when we enter a room that is relatively "dead" - a typical lounge, for example - then we - without consciously realising - are expecting sounds to be slightly duller than they would be if we were in a kitchen or bathroom.

Luckily for us, our hearing system is also good at dealing with the bass end too. Again, we sub-consciously map out the acoustic space, and largely ignore small changes in bass level with frequency. If the bass speakers have a good transient response - as explained earlier - then we are much more forgiving of the room nodes. Luckily, once ideally situated in the room - which makes a big difference - then attempts to equalise those can be relatively positive, given a "fast" source. If you have a typical ported boom-box, no chance!

I'm a firm believer in setting up the loudspeakers so that they measure flat under anechoic conditions. Such a speaker stands a fighting chance of sounding good under a wide range of listening environments - experience (not just mine) has demonstrated this time and time again. It's really simple - people don't equalise their voices as they walk from one room to another. When an estate agent shows you around a house, you don't question why they sound different as they describe each room! But, if you'd made an audio recording of the tour, the playback would sound very odd indeed - without the visual and acoustic cues you get when in the same space yourself, then the brain is unable to adapt automatically, and amplifies the differences.

In short, mild and broad (low-Q) equalisation (say, +/-3dB) is one thing, but if you need more than that, you're trying to apply a sticking plaster to a bad loudspeaker (of which there are many because speakers with a flat frequency response don't sell in a typical showroom dem scenario) in a bad room (of which there are many - not least because of the current fad for "minimalism" and bare wooden floors).

I'm constantly surprised that people think nothing of spending small fortunes on new kit, cables, etc, in an attempt to improve their sounds, but wouldn't consider acoustic treatments. I've yet to hear any hi-fi setup that wouldn't be significantly improved by some simple (and very cheap) acoustic tweaks. These sorts of things aren't all that effective at the bass end, but as I say, it's not really needed down there, providing the speakers are clean and fast and have been positioned optimally in the room.
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Old 24th Sep 2017, 11:45 am   #36
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Default Re: Powered sub-woofers - is it just me?

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I'm constantly surprised that people think nothing of spending small fortunes on new kit, cables, etc, in an attempt to improve their sounds, but wouldn't consider acoustic treatments. I've yet to hear any hi-fi setup that wouldn't be significantly improved by some simple (and very cheap) acoustic tweaks. These sorts of things aren't all that effective at the bass end, but as I say, it's not really needed down there, providing the speakers are clean and fast and have been positioned optimally in the room.
That's all very well Mark if the person knows what to do with these "acoustic tweaks".

Like I say, I've used a digital processor to make adjustments in my listening room (that is on the dead side of middling in terms of liveliness) and I'm very pleased with the results. I did also say in my original post that I recognised that such a process is not perfect for a number of complex reasons, one of them being the listening/testing position. But hey ho.
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Old 24th Sep 2017, 1:56 pm   #37
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Default Re: Powered sub-woofers - is it just me?

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I'm constantly surprised that people think nothing of spending small fortunes on new kit, cables, etc, in an attempt to improve their sounds, but wouldn't consider acoustic treatments.
You're forgetting all those little tuning dots the gullible buy and stick in magically determined places on their walls and vindows (-and record player arms and fuseboxes and speaker cones and probably the loo seat as well)

The buyers think they're acoustic treatments....

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Old 24th Sep 2017, 2:02 pm   #38
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Default Re: Powered sub-woofers - is it just me?

Anyway, the definitive answer to the original question is:

No, it's not just you, Roj. The rest of us seem to agree that the majority of subwoofer setups are ghastly.

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Old 24th Sep 2017, 2:40 pm   #39
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Well yes demonstrably, but in my case I agree only on the basis that it is difficult to get right. That aside, no-one can deny that a hifi system where the full range of recorded notes are reproduced at the correct level (for example, audible) can only be applauded. On the other hand, there are those who simply don't like the sound of those ultra low notes. All fine by me. After much tinkering I have been very happy with the two subs that I have installed in my home. But when I first hooked them up though, the sound was 'lumpy', it took a lot of tinkering and thought, analysing, to get it right. So yes, not a simple 'plug and play' solution to getting your hands on low bass.

Variables being:
Cut off frequency
Rate/slope of cut off
Level of sub
Phasing of sub

That's a lot to play around with a get wrong! especially at bass frequencies where it is not always easy to hear or interpret what's going on when you make changes.
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Old 24th Sep 2017, 3:17 pm   #40
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Default Re: Powered sub-woofers - is it just me?

This thread may have gone a bit esoteric for the non crtical application the OP has in mind. Given the little 3 + 3 watt Tripletone and 2 x 8" x 5" (Celestions?) Decca satellites, I would have thought that any Budget Sub would do (e.g. Gale) as long as you can trim the crossover frequency.
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