Class A subwoofer...?
Righto.
So I now have one of these (currently languishing in my wardrobe):
And one of these:
(18 inch Goodmans bass driver...)
Got it for a tenner. I'm picking the cab' up in 10 days or so.
My thought is that I might somehow combine the 2 into some sort of ridiculous subwoofer.
This will simply be for the purposes of occasional amusement. It will not be for day to day use, or to be a serious piece of hifi kit.
My wonderings are:
1. How best to use both channels of the amp. Possibly this...?
2. What's the best way of introducing a volume control and bass roll-off...?
All advice welcomed... :-)
Yes. I know this is a bit silly. As I say, this does not need to be a seamlessly perfect device, just un petit accoutrement.
So I now have one of these (currently languishing in my wardrobe):
And one of these:
(18 inch Goodmans bass driver...)
Got it for a tenner. I'm picking the cab' up in 10 days or so.
My thought is that I might somehow combine the 2 into some sort of ridiculous subwoofer.
This will simply be for the purposes of occasional amusement. It will not be for day to day use, or to be a serious piece of hifi kit.
My wonderings are:
1. How best to use both channels of the amp. Possibly this...?
2. What's the best way of introducing a volume control and bass roll-off...?
All advice welcomed... :-)
Yes. I know this is a bit silly. As I say, this does not need to be a seamlessly perfect device, just un petit accoutrement.
Comments
Something like this...
See here.
It seems to have some volume facility too. Not sure about the finer points of the "impedence matching"...
Thank you.
What's the best way for me to know what frequency I want? (is this to integrate with the main stereo speakers?)
What about this preferred frequency Colin?
Earlier this morning I checked in some of the older threads to see if Paul (RFC) had posted any of his graphs of the frequency response form them when he re-furbed them. But I couldn't see any here.
I'll see if he has them on his PC.
They're not bass-shy. Nice 10 inch drivers, so a good deep and powerful as well as clean sound, especially from the SECA. As I say, this sub project is just a bit of fun really. :-)
Is.
A.
Bit.
Of.
Fun.
Here is the frequency response of the main RFC-modded Goodmans Goodwood speakers in my system. It's the dark blue trace that's relevant (thanks to Paul (RFC) for digging this one out for me.
And here's a trace for the 18 inch possible-sub Goodmans speaker:
I love it that the speaker was suitable for farigrounds.
I suppose what I'm wanting to do is to fill that gap area between 20Hz and 60Hz(ish) on the chart for the main speakers (top one).
A bit speechless really.
I will begin building up to giving this my best shot! :-)
I will be looking for guidance from someone, anyone, everyone, as I have never tried anything like this and so at present I don't really have any idea where to start with implementing that circuit diagram. But it is a question of when and not if! :-)
I noticed the batteries on the circuit diagram (my GCSE physics studies appear to have stuck). Is this cool device battery powered?
Hubba hubba. Check out the 18 inch Goodmans...
In time, Colin's design will be implemented, but for now I've stuck in a BK Electronics subwoofer amp...
And look, with a plant on the top, it's practically invisible. The wife won't notice it at all...
The sound is immense and hilarious.
Obviously one wants one sound waves arriving simultaneously.
Adding a sub adds sound waves that are unlikely to be eminating from a source the same distance from one's ears as are the main speakers.
My understanding is that the linear phase control on my sub amo adjusts the phase (0-180) of the crossover frequency, which according to what I've set *on the dial* (by ear) is about 65Hz.
OK first issue. The sub is 130cm away from my head (behind the sofa) whilst the mains are 330cm away. So the sub is 2m closer. Sound leaving it will arrive at me ears before the waves leaving the mains. So, I thought the phase control might be useful in holding back those 65Hz waves for a few miliseconds...
But, second issue, I read on this here paper that:
"since the sub is
always at least 8, 9, 10, 11 msec late [my reading is that this is due to the additional circuitry it passes through in comparison to the power amp for the main speakers]...It can be corrected in one of 2 ways only: you
can use some electronic means to ADD the same amount of delay to the top
(mains); or you can move the sub(s) closer to your body the correct number
of msec."
Now. If I take all this at face value...
My estimation is that if my sub amp is delivering signals 10 msec late, this (according to the speed of sound = 340m/s) equates to a 3.4m head start for the mainspeakers.
However, the sub, being physically closer has a 2m head start in terms of its distance from my lug hles.
So, that leaves a 1.4m advantage to the sub so far.
Now, at the crossover frequency, of 65Hz the wavelength is 5.23m. That means that if I set the phase to 180 it delays things by 2.615 metres at 65Hz. But I only need 1.4m, so I think that makes a phase setting of 96ish...?
Problem is, I'm sure it sounds best (most bassy most integrated) when the phase control is at zero...?
So if I trust my ears then the delay added by the sub can't be as high as 10ms. It must be that whatever the delay is, it is being cancelled out, pretty much exactly (by coincidence) by the subs physical proximity to me, relative to the mains. Which is 2m, so the delay added by the sub's circuitry must be adding a mere (2 / 340) 5.9ms of delay comaperd to the TOCA. So may be the TOCA has more bits and bobs packed in than a normal speaker, or the sub amp has less. Or my ears / calculations / research is wrong! :-)
I can't reread that to check if it makes sense as my mind has just melted....
Thanks Colin.
How is produced effect different from a continuous 0-180 phase adjustment...?
You almost give the impression of being someone who might know something about electronics design...
So now all I've got my list is:
Build class A amplifier.
Build subwoofer amplifier.
Build bucket brigade device.
Use a cad-like programme to design something.
I will be signing up for electronics and IT courses...
No. In fairness to me, I can do that one already. :-B
I wonder if one contributing factor here is the difference between what I believe (/know?) that I can currently do (in terms of electronics / computing) and your superlative aptitude for these things Colin. ^:)^
In any event, I am grateful to you for your high expectations. They are motivating: over the summer I will be looking into Veroboard and electronics in the hope of reaching a level of confidence where I can try your sub design.
However, in addition to the gratitude, I also feel fear that you are currently over-estimating where I am on this journey. That I can't yet possibly meet your expectations. I feel the threat of failure lurking... I feel like I have an elephant to eat. I can't eat it all at once...
MY responsibility / job is working out how to cut up this daunting elephant bite size chunks. And which to chomp on first. At the moment, and thanks to your suggestion, it does feel like the Veroboard.
It is very addictive to have this amount of bass on tap. Especially on tracks where there has been a clear intention to make deep bass a defining feature. E.g.
Beatie Boys "Don't Play no Game That I Can't Win"
There probably is a strong novelty value to this attraction at the moment.
What I want to work out is how much musicality I might be losing for the extra low-end, and to what extent that can be minimised by getting the sub's controls as right as possible
The good lady wife was kind enough to help out a bit last night.
I wanted to experience as accurately as possibly the difference made by altering the phase control. The problem I have is that I have to get up and move from my listening position to do so. Doing this I can detect broader differences (e.g. the bass is fuller towards the "0" end of the phase control than it is all the way over at the "180" end). However, I wanted to play around with finer adjustmenst (e.g between "0" and "45"), where any change to the sound is likely to be more subtle.
So Claire agreed to stand by the sub and adjust the phase control while I listened continuously. What a lovely lady I have. :-)
We didn't have long. It certainly confirmed that the bass drains away as the phase in increased. In fact the whole sound becomes more weedy and thin. Also a sense of congestion or smearing increases. So given where the sub is physically now*, phase needs to be towards the zero end. What I'm currently working on is whether the bass is fuller at zero, but the coherence of the sound is better (less congested or smeared) at around 30 (at a very slight trade of on bass weight).
Is this possible?
I'll be buying Claire some flowers later in the hope she will agree to a second session of knob fiddling...
*For cosmetic reasons, I tried it at the far end of the room (behind me) a couple of days ago. It was probably about exactly the same distance from my ears as the mains speakers are infront of me. At the listening position he bass was massively reduced, suggesting (I think) that at that distance things were very out of phase. With the sub tucked back just behind the sofa things sound waves from sub and mains give the impression of being closer together.
One of my favorite tunes.
Now it has yet another asset...!
The extended cowbell solo in the second half is the passage of music I have yet found for tuning the phase control on my sub.
The bass is now deep and controlled AND overall things are now as tight as a drum! Love it when one finds a sweet spot (reminds me of getting a cart setup right (that one time I managed to!
8-}
Paul, thanks very much for all the pointers there. I like the sense of clarity you convey. It certainly is helpful, though I may have to chat with you to compensate for my ignorance.
"the way to start is to treat the natural roll off as a 2nd order filter
with a crossover point 6dB down, so pick the point on the roll-off in
room which is 6dB down on peak and that becomes a good starter for 10."
You'll have to walk me through that. I have less technical nouce than I need.
The roll-off has settled on about 65Hz on the dial. Which was higher that I expected given that I suspect the roll off is not a brick wall, but based on fiddles to date it appears to integrate well there. Will be fiddling more over coming days.
Re. phase... Yes I've been learning about that with regard to subs over the past couple of days, and have been experiementing with the phase control on the sub-woofer amp that I've currently installed in the speaker cab. I made some progress with this earlier today, and am confident that in my listening position, the phase is close to where it should be (I think it's ended up at about 40). It's quite remarkable how much things snap into place as it gets close.
Main lessons are:
1. I hadn't realised how hard one has to work to integrate a speaker that is independent and physically separated of the main stereo speakers. (This physics stuff is complicated! It's almost as if you have to know what you're doing or something... :-B
2. It is very hard to go back to not having a reinforced bottom end once one has it on tap. Even when the mains are already as bass competent as the RFC/Goodmans.
3. The expertise and goodwill available on here (in this case from Colin and Paul) is heart warming. Thanks you.
Have been continuing to gently tweak settings (roll-off, gain and phase - they interplay with each other I suppose, so adjusting one can mean tweaking others accordingly), but increasingly less so - I think I'm nearly there.
When I first had it I wanted to "hear it" so cranked it up to obvious levels. Fun, but over time one notices all that is being masked / spoilt (e.g. soundstaging and midrange clarity). Getting the phasing right has been crucial, all else is really pissing in the wind otherwise.
Also finding the sweetspot of the product of gain and roll-off is an interesting challenge.
Anyway, now it's getting close to where I feel it should be, it's funny how little the sub needs to do. The RFC-Goodmans mains reach decently deep already! Basically if I turn the main Goodman speakers off the sub is just rumbling away somewhere near the earth's core. The sound is basically like standing outside a nightclub at 1am. But, turn the sub off and one notices the bottom end rolling-off as bass notes deepen.
The subwoofer is almost always doing something. The lower frequencies of the sounds of voices, snare drums, guitars, etc.,... can all be heard warbling through the sub. But, also revealed is how some tunes have loads of stuff going on down there (early Wailers stuff, most electronic music, well presented audiophile recordings (some of Dave's Ronin stuff has bass content of liver destroying levels)) and others almost nothing (more complicated / less well done mixes, most pop music).
Anyway. I like my sub. It's not Class A yet. But I think everyone should have a well-managed 18 inch driver somewhere in their system.
Not sure about taxi license. Will check.
You are always welcome here Colin.
Sounding fine though. 8->
Over the pas couple of weeks, I've really come to appreciate how important it is to get a sub to integrate with:
1. The main system.
2. The room. Or rather one's usual listening position in the room.
Finding the settings and the physical placement that achieve both of those satisfactorily has been difficult (but not impossible) as the two seem to inter-relate. I'm sure even the slightest movement of the sub (e.g. just 10cm along the side wall), or my ears (e.g. moving my ears just 20cm to the left) makes a significant difference. I can't quite understand why as the wavelengths of sound the sub is putting out (mainly <50Hz) are measured in metres. I suppose the extent to which the relating of the waves coming from the main speakers, the sub and the reflections of waves bouncing around all over the place is not an utter shambles must be detectable to the human ear.
Two telling points are that I am now listening to more dub music than I even have and; the more I tweak the sub's settings and position to my satisfaction, the less listening to the system without the sub satisfies.
Now listening to the system in 2.0 mode, I am wanting to voice that I'd forgotten how much bass energy the One4 > RFC-Goodmans can produce on its own. :-)
And more than that, it's highly possible that when in the past I've listened with the sub in place, some of the credit that I have mentally given the sub, has been unfairly allocated!