Powered sub-woofers - is it just me?

[RojDW48]

This follows on from my previous thread - https://www.vintage-radio.net/forum/...d.php?t=139513. I was just about to order bigger chokes and think about knocking up a nice reflex cab when I visited my local auction house and found a KEF PSW2000 subwoofer going for virtual pocket change.

I have always had an aversion to these things based upon no evidence at all other than the feeling that I don't want someone else's electronics interfering with the output of my chosen amp. Nevertheless, I thought it must be worth a try (at that price!) with my Tripletone amp and the little Decca satellites.

Now here's the thing. In a lot of ways this set-up sounds a lot like my big Radford T-lines. Much more bass than needed - but it's adjustable to an appropriate level - and a sweet sound from the little Deccas, but...........I don't like it!

Is it my imagination? Am I a frightful old traditionalist......or is there something intrinsically 'wrong' with the sound of these PSWs? Please discuss.

[Nuvistor]

I thought those sub woofers were to get the realistic cinema sound effects on the large screen TV sets.
Lots of sound effects and poor dialogue and speech reproduction don't do much for me. Probably why I don't like many modern films.

[joebog1]

What Nuvistor said!! I have a surround system on my TV, MOSTLY because the TV's origional sound was total rubbish, and I couldnt hear anything.
My surround system has an electronic graphic equaliser built in, so I have tailored it so I can hear. Subwoofers ?? most are class D, and I dont know if its just me or not, but it seems to get a resonance at some frequencies making it very harsh and overblown bass even though I have it wound back by 9dB. ( graphics are +/- 9dB ). I find the worst to be bluubbly gardio ( AKA Dolby Audio) I can hear the ant walking around as far as effects go, but speech is garbled beyond recognition.

Joe

[unitaudio]

I know what you mean. A friend of mine has such a system and although he's got it set up correctly and there doesn't appear to be anything missing from the sound, something about it just doesn't sit right. Works well enough with movies but it's not great for music. It's not cheap rubbish either, Mordaunt-Short subwoofer and late model Wharfedale Diamonds fed from a Yamaha surround amp. We've messed with the settings on the amp a lot but nothing seems to make it "right".

Regards,
Paul

[Radio Wrangler]

There's an issue called 'one-note bass' where a sound reproduction system has a bass response with a significant peak in it.

On sound effects as mentioned above it adds more clout to toneless sounds which go "thud" or "boom" It makes Hollywood's explosions sound more dramatic than without the peak. It acts as a substitute for a flat bass response which extends lower in frequency. Some pop music ha a toneless bass line which is just a drum thumping away and speakers with peaked bass try to convince listeners that they produce deep bass. It fools enough of the people enough of the time to help sales, and many people think that modern progress allows deep bass at high levels to come out of small speakers.

The trick comes unstuck on music containing bass sounds which have different notes like tuned drums, pedal stops on pipe organs and bass guitars provided the listener knows that there should be a tune played in the bass line. The peaked speakers just give their series of thuds, but with the volume falling off rapidly on notes away from their peak. It sounds wrong.

The peaked bass trick was done on a lot of small speakers which tried to be impressive. If you know what bass should sound like, they sound wrong... fatiguing.

The TV surround system subwoofers play this trick at frequencies a bit lower than shoebox speakers did. They make dramatic sound effects somewhat more dramatic.

Now, there are good systems with subwoofers, but they were carefully designed so that the subwoofer response fits together with the main speaker low frequency response without a hole between them and without the subwoofer being exaggerated in level or peaky.

Most subwoofers were designed for the big boom and thud market, and just getting one to add to completely unrelated speakers is likely to give a very poorly managed transition. If you're used to a decent pair of speakers with extended rather than exaggerated bass response, you won't like the result.

When most people hear my hifi system, they think it's bass-light. Most people look at the big transmission line speakers and expect them to produce a lot of bass all the time and to just generally be very loud simply because they're big. It takes a bit of explanation to get them to understand that quiet sections of music get reproduced quietly, that they can reproduce bass, but only when there is some in the music.

It's amazing how prevalent misconceptions about sound reproduction are in the general public. It's not their fault, it's what they've been exposed to.

David

[Diabolical Artificer]

I think it depends what your listening to, what mood your in and what your normal hifi and stereo speakers are like.

If I'm feeling a bit lively (not very often these days) and am really digging the music I'm listening too it's nice to crank the music up a bit. Some music like reggae loves being played loud on a system that has oddles of bass response. Most reggae doesn't need a good hifi, just big bass speakers; a lot was mixed with the big sound system's in mind. However a bit of Bob on the deck calls for a system with capability to reproduce the whole audible sound spectrum, with good stereo separation. The mixing is brilliant on Rastaman Vibration and Survival - you can hear someone tinging a triangle right in the corner on some tracks - subtle.

Obviously other types of music are the same to a certain degree, depending on the mix, mood etc. But on the whole unless your into modern dance music or making/mixing it, or like to skank around the living room to some tasty dub beats, you don't need a subwoofer if your hifi setup has a good flat response and your stereo speakers can reproduce low frequencies without distortion.

Andy.

[Craig Sawyers]

For a treatise on integrating a non-booming sub with a speaker system, this http://linkwitzlab.com/thor-intro.htm (and Linkwitz's site in general) is well worth a read.

[Pilot Mariner]

I also agree with the OP, I bought the minx sub that goes with my Cambridge Audio 1 system from Richer Sounds. All I am greeted with is a load of one note boomy bass, although set up in the conservatory, not a patch on my lounge IPL acoustic transmission line speakers.

Mark

[paulsherwin]

I have quite a good Yamaha subwoofer hooked up to the main system, but I rarely use it. If configured properly it does extend the bass of the main speakers (B&W DM560s) but it adds little to most material. I actually dislike the low frequency thumps added to so many Hollywood movies.

[Nickthedentist]

I agree with the general gist of these comments too.

For the telly - no thanks, just a pair of halfway decent bookshelf speakers is more than good enough. I want to hear the dialogue, not feel the sofa wobble.

When listening to most music - a pair of biggish speakers will do the job perfectly.

And as Andy says, for reggae, dance music etc. with a strong bassline and designed to be played in clubs or a "sound system", then a subwoofer is a nice thing to have and stops one's main speakers being damaged by cranking up the bass control too far.

N.

[mhennessy]

A good sub really can add something to a good stereo setup. The key word there being "good". Sadly, they are few and far between - as already noted, there is no shortage of poor ones out there.

Coupled to that, it's actually quite hard to set them up. Room positing is extremely critical - though the usual advice is "throw it down anywhere - bass is omnidirectional, so it doesn't matter". It's not that simple. Then there is an array of adjustments to get right - all far too difficult for a non-technical person to understand. And even if you do have a good understanding of what's going on, how do you measure the results? Ever tried measuring bass in a real listening room? It's just about impossible. Sure, you'll see lots of graphs from folk on AV forums, but interpreting the results is key. Counterintuitively, a flat response at the listing position in a typical room is not what you want.

The effect of a sub should be very subtle indeed. A good rule of thumb is "you shouldn't hear it until it's taken away". It is not intended to add bass; rather it's there to extend the low frequency response. Not everyone understands the difference. As a result, most people set the crossover frequency too high, so the output from the sub is adding to the output of their stereo speakers before the stereo pair has started to roll away. It would be easier and cheaper to just turn up the bass control slightly.

A good sub will have been engineered to have a good transient response. That's actually more important than how flat the frequency response is (although that's easy enough), as the room will make a mess of that. What matters is that it stops and starts when it should - this makes a massive difference for many types of music. If you want to do that, you need a sealed box with a Q in the 0.5-0.7 region. However, this results in a resonant frequency that is higher than you'd like, and below that the response falls away at 12dB per octave. So your amplifier needs to include equalisation for that (although "room gain" helps). But the upshot is that you need a massive amplifier, and a motor assembly that can cope with the heat - normal speakers are inefficient enough, but driving them below resonance is much, much worse (obviously, every 3dB is a doubling of power). But done well, the results can be incredible. I did it many years back with a cheap 10" JBL car sub and a 1 cubic foot MDF box. It went all the way down to 25Hz - lovely! It was quite loud enough for my small listening room, and that was just using a 50W amp - I never got around to building the 300W amp I had planned, as a change in speakers meant I no longer needed it. But, it was great. I bought a another drive unit (they were on sale for just £30), and would have built 2 (much easier to place 2 in a room than 1). Perhaps I will, eventually...

I built that because my experience of commercial subs (plus the obvious "no-brainer" technical arguments) convinced me that was the best way for domestic use. Of course, PA is different. But for a manufacturer, it's an expensive way to do it, so that's why there are so many ported units out there. Some of those can be great as well, but there are many more variables to juggle, and so many more ways to cock it up. Especially if you go for bandpass rather than simple ported or ABR... But in general, these tuned resonant boxes are much more efficient than the closed box solution, which is why manufacturers prefer them. If you tune them appropriately, they are very efficient at a narrow range of frequencies, which is great in a way, but this what leads to the "one note bass" that is so common with these designs.

And that's before you add transient response into the mix. Resonance implies energy storage, so when you look at the output of one of these cheap subs, you can see the envelope rise slowly at the start of a transient as everything gathers momentum, and you see it decay over many milliseconds rather than stopping instantly (most function generators have a "gated" mode, so this test is very, very easy to do). There is an easy analogy with car suspension (compare a Ford Cortina to a Ford Focus). So ultimately, it's no surprise these things are muddy and annoying, even if they are set up as well as they can be given the available user controls.

Luckily, the DIY route is very easy indeed - I'd never buy a sub. Have a look here for more information and ideas: http://sound.whsites.net/project48.htm

[stevehertz]

It doesn't sound 'right' to people often because they are not used to live sound; for example the sound of a bass guitar bottom 'E', the fundamental note of of a bass drum, or the really low notes from an organ or a synth. Never mind surround sound and cinema stuff, the sub has a very valid use in a bog standard hifi system to lift these missing notes to where they should be in the mix. If you don't like that, that's fine, no-one can say that you have to have your hifi set up in a certain way. But make no mistake, few 'full range' speakers are able to reproduce the really low notes that I mentioned. So, that's where the sub comes and in, and yes they do have to be set up with care, knowledge and a good ear. Those controls being cut off frequency and level. It's not easy to get both of those right, I know, I'm a musician with considerable studio mixing experience and one who has listened to hundreds of live bands, not to mention my own over the years.

Also, one doesn't need to worry too much about distortion levels at these 'sub' frequencies, our ears can tolerate (are unable to distinguish) distortion levels into single figures, unlike the very critical mid range where voices sit and we know from listening to human voices all day long what they should sound like.

In my opinion subs can play a very important part in enhancing a hifi system up by adding the missing very low frequencies. If you don't like those sounds, leave them out, that's fine, but live and in the studio, they're there.

[stevehertz]

Originally Posted by Radio Wrangler

There's an issue called 'one-note bass' where a sound reproduction system has a bass response with a significant peak in it.

That's true, but that phenomena - like it or not - can actually be part of, be present, in the original mix due to a hump in the amplification or equipment being used by the musician. They may have tuned a graphic equaliser to get that very effect. Who knows? how can you tell? Begs the question doesn't it? do you like listening to recordings how they were made and mixed, or would you rather change it? And last but not least, is that effect due to a wrongly adjusted sub (user error) that is causing the one note effect? Like I said in another post, setting up a sub correctly is difficult. For example, say you feel the system is bass light, it needs a tad more bass. Do you increase the sub level, or do you allow the sub to reproduce more 'higher bass'? Because to the untrained ear, both can 'appear' to have a similar effect, but one may well give rise to a frequency hump or one note effect. Although I'm very pro properly set up sub woofers, probably, unless you know what you are doing it is better not to bother with them due to the negative effects of setting them up wrong.

[Craig Sawyers]

They may have tuned a graphic equaliser to get that very effect. Who knows? how can you tell? Begs the question doesn't it?

Listen on very high quality headphones. That'll tell you if it a feature of the recording or not.

[Radio Wrangler]

There are many, many more subwoofers out there than there are people who even know that they need careful setting up, never mind than people who can set one up.

OK if done right, Awful otherwise.

The problem with listening to a recording and wanting to hear it 'as intended' is that you don't get told what sort of equipment characteristics it was intended to be heard through and whether or not someone has tried to compensate for what instead they think it will be heard on.


For anything which has been through a mixing desk, there never was a real performance you could have been present and heard. Maybe fidelity is a mirage and we should just twiddle for maximum happiness?

David

[parlourtw73vs]

"Maybe fidelity is just a mirage and we should just twiddle for maximum happiness". Sounds like a flippin' good life plan to me David.

[stevehertz]

If that suits anyone, I agree with it entirely. Life is about being happy, not perfect or rich.

[RojDW48]

Clearly it isn't just me - which is reassuring. Lots of really useful information - thanks. I tried a comparison with the same source and there was no doubt that the transmission lines were obviously more focused and accurate in the bass. However I shan't give up just yet. The ability to control parameters on the Kef isn't terribly sophisticated. 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?

As the source for this set-up is my computer, I guess it would make sense to download a tone generator to help with getting the response as flat as possible - any suggestions?

[AC/HL]

An easy one here: https://www.vintage-radio.net/forum/...ad.php?t=98197

[RojDW48]

Just the ticket, Bill - many thanks - I shall have a play.