More Bass....

Gary, you are a bad, bad man for posting that link. You've set my feverish little engineer brain working overtime!!!

DIY speakers with big bass drivers :slayer:

Wooden floorboards

Massive underfloor crawl space :rds2:

Hmmmmmmmmmmmmmmmmmm :torkmada:

 

Mmm, some people - not most. I have had the pleasure of using a setup flat to 20hz and it is anaemic. Surely due to the ears lack of sensitivity, and inconsistant amounts of room gain, we need to have the bottom end raised up a notch or two at typical domestic listening levels?

I never said that GTM! Many things come into play here but it is only with drive units claiming to exhibit low THD that I have been able to hear into the bass and detect fully formed instrumentation. Maybe you could offer an alternative explanation mate, as I have tried sealed, vented, bandpass and isobaric loading, along with crossovers from 40hz to 500hz and still come back to low distortion drive units being essential for the bottom two octaves.

Of course with the DD series it is feasible to slacken off the servo control and effectively increase the THD (although I cannot see what else this would acheive). Sadly it is not possible to generate Rel levels of distortion, even on the minimum setting.

 

Surely recording engineers have human ears too, though, and would thus compensate for any lack of bass in the mixing stage, long before it reaches our flat-to-20Hz monitors..?

Or indeed anywhere near REL levels of distortion......

Dunc

 

Not being an engineer I can't comment Dunc, but they should assume some room gain.

Having said that, their interpretations do seem to vary, and with most modern recordings being so heavily compressed, it seems difficult to boost the bottom end above digital zero.

The point is that your flat to 20hz speaker array will be anything but in the typical room, and I think GTM is suggesting that room gain will cause the bottom octave to be bloated if the speaker measures flat in an anechoic chamber. My experience with Tact would suggest otherwise - and that most modern recordings rely on boost at the lower frequencies via room gain or EQ to attain an "accurate" spectrum at normal domestic listening.

I imagine that if the recording is mastered with LF at say digital zero, it would be possible to keep the midrange at somewhat lower levels and produce satisfying bass levels in a domestic enviromment. The "problem" is that the recording then sounds quieter and less immediately impressive on radio and cheap players. The ultimate quality is however IMHO far better. Good examples in my collection are the early Underworld CD's, Leftism and even Rumours. To many engineers seem to heavily compress stuff these days, effectvely mastering at max levels in the midrange.

Anyway, I'm sure someone will come along with a lot more knowlwdge than me to tear that apart

 

Now you be careful out there, Chris.

It's a great idea to use all that space but you have to make sure your floorboards don't resonate. Also the 'baffle' must be airtight, if you're going IB.

Another thing to watch is driver cone excursion, if you don't have the restraining influence of a smallish box.

In the old days I saw some designs in 'Speaker Builder' magazine which used a box with a port opening into a much larger enclosure (such as a car boot or underfloor cavern). That's another interesting approach.

 

Resonating floorboards eh? They do that alright! I think a layer of suitable underlay followed by laminate flooring might reduce that somewhat though

Not for this house I don't think. But for the next one...

Something to bear in mind

 

I've built 3 IB subs, initially starting with a single 12" driver, then a single 15" driver and finally a pair of 15" drivers. In terms of performance, an IB sub is pretty impressive, the most obvious thing that is apparent is the quality of the bass due to the lack of cabinet colouration. In my case, the only location I had for the sub was in the ceiling which caused problems with resonance, something I was never able to cure so I've reverted to a traditional (big) sealed box. If you are able to accomodate an IB sub, then, in terms of performance, there's not much available commercially that can touch it.

Regards
Gary

 

But at least an anechoic measurement is a level playing field – with in-room figures who knows what sized room they used? It’s useless as a comparison – the only way it could work would be if a standard room could be agreed upon and I can’t see that happening somehow, especially with the differences between the average UK and US room.

I’m also struggling to see how making a sub that will play flat to 20Hz with no room loading is a bad thing – why should a sub that does this be any worse than one that will only play flat to 28Hz? Okay, so maybe if there is a big room peak at 20Hz then the latter sub will create less of a problem but who says the peak will be at 20Hz? Surely the peaks will vary depending upon the room in question (and various other factors) so it would be impossible to a sub manufacturer to anticipate this and therefore going for a flat response has to be the best bet?

I guess the ultimate integrated solution is the inbuilt EQ system in the DD12 sub that Merlin’s trying out – I think that one plays flat to something like 18Hz anechoic but , unless I’m mistaken, it also analyses its in room response and then adjusts its output (and phase) at various different frequencies in order to produce a flat in-room response – bloody clever stuff.

Agree with this – I don’t think a lot of people could hear a difference between 1% and 10% distortion at the lower frequencies. However, my understanding is that it’s not unusual for certain popular subs to produce 30% or more distortion when attempting to produce the low frequencies at a reasonably high volume level.

Play a movie with some really low bass through one of these lesser subs and then swap to a low distortion model and the difference is more than noticeable. I tried this on ‘The Haunting’ DTS – my old REL Q200 had convinced me the film had ridiculously bloated, over the top LFE content – when I got my Velodyne HGS15 I gave it another try and it sounded as clean as you like – very deep but no distortion.

One other point on THD figures – it’s interesting to note that THX (who I think it’s fair to say know a bit about reproducing movie bass) now stipulate some pretty tough requirements for subwoofers. To obtain THX Ultra II certification I understand subs have to be able to reproduce 20Hz @ 105dB with no more than 4% distortion. I don’t think you’ll find many subs that can do this – no doubt many manufacturers whose subs aren’t up to this will simply claim that they are not willing to spend the money on THX certification.

Finally – and this ties in the THX bit with what Dunkyboy was saying – I guess even if all manufacturers used either anechoic or ‘same sized room’ –3dB measurements (and provided distortion figures) then this wouldn’t could for a lot unless they quoted output levels in dB too i.e. I presume it’s a fair assumption that getting a sub to play flat in room to 20Hz with little distortion is a lot easier at 80dB than it is at 95dB.

Matt.