I've been working on my speakers today!
I built Graham Maynard's T-bass circuit, which has added some bass extension and power, whilst seemingly reducing the upper bass peak.... the difference between hopelessly coloured and really quite a good speaker.
I then relieved the midrange driver of bass with a 1st order high pass at about 250hz. So far so good. I then found the treble was a touch too loud, which 1.5R cured nicely.
The midrange still has a slight upper emphasis, which is intended to be reduced by a 1st order filter. As I don't have those parts yet I tried a zobel/impedance compensation network on one speaker, but I'm undecided on the usefulness of it so far.
I've attached a schematic of the work in progress so you can see how I've wired things. Really I did it to keep track myself!
Simon
I built Graham Maynard's T-bass circuit, which has added some bass extension and power, whilst seemingly reducing the upper bass peak.... the difference between hopelessly coloured and really quite a good speaker.
I then relieved the midrange driver of bass with a 1st order high pass at about 250hz. So far so good. I then found the treble was a touch too loud, which 1.5R cured nicely.
The midrange still has a slight upper emphasis, which is intended to be reduced by a 1st order filter. As I don't have those parts yet I tried a zobel/impedance compensation network on one speaker, but I'm undecided on the usefulness of it so far.
I've attached a schematic of the work in progress so you can see how I've wired things. Really I did it to keep track myself!
Simon
Attachments
SimontY said:
Ehem,
sorry. No i am not suggesting that ...
I see, there is some explanation missing.
I simulate the "true" and the mirrored baffle in the horizontal
plane, because this way you can place them easier in the
"edge" design window.
The floor of the listening room goes vertically through the
design window, separating the "real" and the virtual baffle
created by the floor reflections.
In the example design, the "real" baffle has 6 drivers and
is assumed to be the left one. The right half of the design
represents the 6 virtual sound sources created
by the floor reflections.
It does not matter for the simulation, how the baffle is
oriented in the design window, as long as the
virtual microphone is placed correctly in relation to the
"real" baffle.
The baffle is only oriented horizontally because it is more
practical with "edge".
Just a trick.
Best
Hi Simon,
A couple of quick suggestions.
Re LF drivers and the series-parallel connection. If you join the neg wires from the top two drivers together you have two drivers in parallel in series with another two drivers in parallel instead of two series chains connected in parallel. This averages the mechanically induced coupling effects prior to series connection, instead of leaving any loading differences between series connected pairs to mutually influence each other.
You could have both lower drivers facing rearwards, no 1 in parallel with no3 and 2 with 4 before connecting these pairs in series. Might improve lower mid clarity.
I have a Zobel across my LF drivers - try 10R and around 47uF, plus another series choke after the transformer output to match the driver. This choke removes some LF-mid driver interaction when the mid has a series capacitor. Do keep readjusting all of your T-bass values as you shift the relative level balances elsewhere within the project.
When a tweeter is used it can be better to take some hf from the mid using a low value series inductance (>200uH), or, if the network has a series divider (like yours) by fitting a Zobel across its terminals (8R + <470nF)
A simple C to a tweeter can still induce fundamental resonance which increases harshness of overall reproduction. It can be better to fit a parallel damping resistor across the tweeter (try 8 to 22 ohm).
Sometimes the tweeter series C with a parallel damping resistor can behave like a Zobel for the mid, but this depends on overall system/connections.
As you say - 30cm wide is not going to give you much bass, and I don't know whether you or a parntner is setting dimension limits, but if you want to improve bass without re-introducing the cabinet-like sound you have escaped from, then can I suggest that you find some carpet offcuts, roll these into pipes, and set these against each side of your baffle.
I would need to leave fixing arrangements and roll dimension up to you, but carpet reduces baffle edge induced effects and significantly increases the length of the front/back path, which reduces LF radiation loss without causing the pressure reflections which can so impair enclosure bass.
The rolls can be drawn towards each other behind the drivers too, so that their contribution to the overall width might be no more than 3" either side for 6" rolls, and there is no way that wooden wings can create this kind of improvement. 6" dia rolls are like 18" extra baffle widthe !
Cheers ....... Graham.
A couple of quick suggestions.
Re LF drivers and the series-parallel connection. If you join the neg wires from the top two drivers together you have two drivers in parallel in series with another two drivers in parallel instead of two series chains connected in parallel. This averages the mechanically induced coupling effects prior to series connection, instead of leaving any loading differences between series connected pairs to mutually influence each other.
You could have both lower drivers facing rearwards, no 1 in parallel with no3 and 2 with 4 before connecting these pairs in series. Might improve lower mid clarity.
I have a Zobel across my LF drivers - try 10R and around 47uF, plus another series choke after the transformer output to match the driver. This choke removes some LF-mid driver interaction when the mid has a series capacitor. Do keep readjusting all of your T-bass values as you shift the relative level balances elsewhere within the project.
When a tweeter is used it can be better to take some hf from the mid using a low value series inductance (>200uH), or, if the network has a series divider (like yours) by fitting a Zobel across its terminals (8R + <470nF)
A simple C to a tweeter can still induce fundamental resonance which increases harshness of overall reproduction. It can be better to fit a parallel damping resistor across the tweeter (try 8 to 22 ohm).
Sometimes the tweeter series C with a parallel damping resistor can behave like a Zobel for the mid, but this depends on overall system/connections.
As you say - 30cm wide is not going to give you much bass, and I don't know whether you or a parntner is setting dimension limits, but if you want to improve bass without re-introducing the cabinet-like sound you have escaped from, then can I suggest that you find some carpet offcuts, roll these into pipes, and set these against each side of your baffle.
I would need to leave fixing arrangements and roll dimension up to you, but carpet reduces baffle edge induced effects and significantly increases the length of the front/back path, which reduces LF radiation loss without causing the pressure reflections which can so impair enclosure bass.
The rolls can be drawn towards each other behind the drivers too, so that their contribution to the overall width might be no more than 3" either side for 6" rolls, and there is no way that wooden wings can create this kind of improvement. 6" dia rolls are like 18" extra baffle widthe !
Cheers ....... Graham.
Hi Graham,
Wow, that was more than a couple of "quick suggestions"!
I've now got some more parts and can respond a bit better. I'll try changing the way the bass drivers are wired when the crossovers are next disconnected. I find the idea of rewiring them quite daunting if I'm honest.
Changing which way drivers face could be done at the same time, but it'd certainly create even more spaghetti.
I might try a zobel on the woofers but I've just connected 3.3mH / 1.75RDC in series to attenuate and it's doing a pretty good job... of course it's also affecting other parameters, and yep, as hoped for the bass is coming on nicely.
Regarding the tweeter / mid crossover... I previously forgot to order the coils (0.22mH iirc) so I've done that today. I also ordered coils (0.39mH) to complete a 2nd order filter on the tweeter, to see if this is any better than 1st order here.
Now when I added the coils to the woofers the sound got a bit weird, sort of better but lacking midrange, strangely in the area I'd call lower midrange. I remedied this partly, firstly by adding a zobel network across the mids (8R / 3.2uF) to bring the upper mids down a touch. This helped but there was too much treble now... added 27R across the terminals and bingo! The sound changed a lot and is rather good now.
I still have an upper midrange peak, which the coils I ordered are for. I can also try rolling this off 2nd order, as I think it would need ~10uF caps, which I have knocking around.
Lastly, my baffles are now 40cm, NOT 30! This is a big difference, and they can't actually be any wider at all in this room, there isn't space physically. I'm in a tiny box room here
I can't even add several inches of carpet, but I can add some wings, which I hope to do at the weekend.
I'll report back when I add the wings or progress the crossovers some more.
Appreciate all the interest and help so far.
Simon
Wow, that was more than a couple of "quick suggestions"!
I've now got some more parts and can respond a bit better. I'll try changing the way the bass drivers are wired when the crossovers are next disconnected. I find the idea of rewiring them quite daunting if I'm honest.
Changing which way drivers face could be done at the same time, but it'd certainly create even more spaghetti.
I might try a zobel on the woofers but I've just connected 3.3mH / 1.75RDC in series to attenuate and it's doing a pretty good job... of course it's also affecting other parameters, and yep, as hoped for the bass is coming on nicely.
Regarding the tweeter / mid crossover... I previously forgot to order the coils (0.22mH iirc) so I've done that today. I also ordered coils (0.39mH) to complete a 2nd order filter on the tweeter, to see if this is any better than 1st order here.
Now when I added the coils to the woofers the sound got a bit weird, sort of better but lacking midrange, strangely in the area I'd call lower midrange. I remedied this partly, firstly by adding a zobel network across the mids (8R / 3.2uF) to bring the upper mids down a touch. This helped but there was too much treble now... added 27R across the terminals and bingo! The sound changed a lot and is rather good now.
I still have an upper midrange peak, which the coils I ordered are for. I can also try rolling this off 2nd order, as I think it would need ~10uF caps, which I have knocking around.
Lastly, my baffles are now 40cm, NOT 30! This is a big difference, and they can't actually be any wider at all in this room, there isn't space physically. I'm in a tiny box room here
I can't even add several inches of carpet, but I can add some wings, which I hope to do at the weekend.
I'll report back when I add the wings or progress the crossovers some more.
Appreciate all the interest and help so far.
Simon
Hi Simon,
Always do original work in 'rough' and then tidy if/when satisfied. A single AA cell sits amongst my chokes and capacitors to check that the polarity of driver wiring matches what is intended.
Changing lower driver facing is not essential, but is a simple way of moving lower cones slightly forward without additional cabinet work.
3.3mH / 1.75RDC. If this is the dcR of the choke then it will have considerable effect with OB mounting. There will be audible loss circa 30Hz and lack of damping above.
The transformer bass circuit is not a substitute for LF crossover, but can reduce the number of degrees cut subsequently necessary.
Yes a plain resistor or Zobel network across driver terminals can make a big difference. With these observations in your ROM you will be able to process sound/component aspects as if second nature.
My baffles are 18" wide, but now taller in order to populate with decent cone area.
Cheers .......... Graham.
Always do original work in 'rough' and then tidy if/when satisfied. A single AA cell sits amongst my chokes and capacitors to check that the polarity of driver wiring matches what is intended.
Changing lower driver facing is not essential, but is a simple way of moving lower cones slightly forward without additional cabinet work.
3.3mH / 1.75RDC. If this is the dcR of the choke then it will have considerable effect with OB mounting. There will be audible loss circa 30Hz and lack of damping above.
The transformer bass circuit is not a substitute for LF crossover, but can reduce the number of degrees cut subsequently necessary.
Yes a plain resistor or Zobel network across driver terminals can make a big difference. With these observations in your ROM you will be able to process sound/component aspects as if second nature.
My baffles are 18" wide, but now taller in order to populate with decent cone area.
Cheers .......... Graham.
Good call re. AA battery, I'll try one on mine just to be sure!
I may try a lower RDC coil later on but I thought it wise to keep the parts cost down at this stage. There's no hope of achieving 30hz bass in this tiny room by the sounds of things so far anyway.
I did read the piece you once linked to that claimed to debunk the myth of dipole speakers being unable to reproduce frequencies lower than the lowest axial room mode. I can't comment from personal experience yet but I'll crack out some test tones soon and see what happens.
What's a ROM in this context?
18" wide baffles must be good
Oh I realised something I've done wrong, or rather not altered to take account for a new change I made.... Now that I've rolled the bass drivers off above about 260hz, the midrange crossover of about 350hz leaves a gap!! I need to put another 30uF or so on there - next thing I'll try. I have bought some Mundorf bipolar 'lytics for this task.
Simon
I may try a lower RDC coil later on but I thought it wise to keep the parts cost down at this stage. There's no hope of achieving 30hz bass in this tiny room by the sounds of things so far anyway.
I did read the piece you once linked to that claimed to debunk the myth of dipole speakers being unable to reproduce frequencies lower than the lowest axial room mode. I can't comment from personal experience yet but I'll crack out some test tones soon and see what happens.
What's a ROM in this context?
18" wide baffles must be good
Oh I realised something I've done wrong, or rather not altered to take account for a new change I made.... Now that I've rolled the bass drivers off above about 260hz, the midrange crossover of about 350hz leaves a gap!! I need to put another 30uF or so on there - next thing I'll try. I have bought some Mundorf bipolar 'lytics for this task.
Simon
Well, well, well.... I swapped the cap bundle (~75uF) in series with my mids for a fairly cheap 100uF Mundorf "Elko Rauh" and hit something of a milestone. I played my new Eleanor McEvoy disc and was shocked at the dynamics, naturalness and bass. Certainly could enjoy that quality all night. The lower mid response seems fairly correct now.
The cheapo Wharfedale tweeters I found on Ebay are perhaps showing their (lack of) quality now, as they tend to make the same noises on every CD, though it isn't generally distracting to be honest.
The upper mid still needs taking down, might even try winding some coils DIY-style to get some improvement before the Mundorf coils arrive.
Played some Chris Rea (Road to Hell) and found something a little lacking, probably due to the baffles causing smearing.... the 6mm? MDF vibrates like mad at almost any volume
The bass response is now rather good, but again, is suffering from a smudged quality, perhaps due in part to the high DCR of the series coil and/or non-optimised T-bass components. 100VA transformers might be on the low side for the reasonable output levels I enjoy.
I now have on Bad by Wacko Jacko and can honestly say I've not owned a pair of speakers before that could unravel the layers in the busy sections like this. The bass, in particular, is propulsive in a way I've not heard with boxed speakers, particularly the ported variety.
The smudged but enjoyable bass output I can now hear reminds me of transmission lines somehow... anyway, for the parts and cr@ppy baffle it sounds stupidly good!
More tweaking tomorrow...
Simon
The cheapo Wharfedale tweeters I found on Ebay are perhaps showing their (lack of) quality now, as they tend to make the same noises on every CD, though it isn't generally distracting to be honest.
The upper mid still needs taking down, might even try winding some coils DIY-style to get some improvement before the Mundorf coils arrive.
Played some Chris Rea (Road to Hell) and found something a little lacking, probably due to the baffles causing smearing.... the 6mm? MDF vibrates like mad at almost any volume
The bass response is now rather good, but again, is suffering from a smudged quality, perhaps due in part to the high DCR of the series coil and/or non-optimised T-bass components. 100VA transformers might be on the low side for the reasonable output levels I enjoy.
I now have on Bad by Wacko Jacko and can honestly say I've not owned a pair of speakers before that could unravel the layers in the busy sections like this. The bass, in particular, is propulsive in a way I've not heard with boxed speakers, particularly the ported variety.
The smudged but enjoyable bass output I can now hear reminds me of transmission lines somehow... anyway, for the parts and cr@ppy baffle it sounds stupidly good!
More tweaking tomorrow...
Simon
I went on holiday and was busy with work so progress has been quite slow.
I've listened a lot and realised some issues with the sound. It takes time with no measurement setup.
I realised the tweeter needed padding down more (+1R = sorted) and I shorted the 1R resistor that attenuates the T-bass gain. It's hard to tell a difference, but there's perhaps a bit more weight down there now, which is welcome.
The sound overall is reasonably integrated now, but there's still a peakiness in the mids and upper bass. I think the simulated hump is a part of it, and I will attempt to remedy this in two ways:
1 - by literally cutting corners i.e. removing a strategically shaped section of baffle from each speaker from near the tweeter and mid driver.
2 - by increasing the series coil L for the woofers. It's 3.3mH and I'll experiment by adding another in series.
Thirdly, I think big colouration is coming from using a cardboard-thin baffle, which is seriously easy to resonate! I'll get some thicker test baffles built up ASAP.
Watch this space.
Simon
I've listened a lot and realised some issues with the sound. It takes time with no measurement setup.
I realised the tweeter needed padding down more (+1R = sorted) and I shorted the 1R resistor that attenuates the T-bass gain. It's hard to tell a difference, but there's perhaps a bit more weight down there now, which is welcome.
The sound overall is reasonably integrated now, but there's still a peakiness in the mids and upper bass. I think the simulated hump is a part of it, and I will attempt to remedy this in two ways:
1 - by literally cutting corners i.e. removing a strategically shaped section of baffle from each speaker from near the tweeter and mid driver.
2 - by increasing the series coil L for the woofers. It's 3.3mH and I'll experiment by adding another in series.
Thirdly, I think big colouration is coming from using a cardboard-thin baffle, which is seriously easy to resonate! I'll get some thicker test baffles built up ASAP.
Watch this space.
Simon
Just had a quick skim following the link you gave me on the T-Bass thread. First, your 4 drivers gains you 6dB sensitivity, you were right with 3dB for each doubling of cone area. I'm interested in this project as I've been wondering how well OB can work in our typical British smaller rooms with speakers pushed into corners or near walls. I too have a stash of drivers in the loft 
richie00boy said:Just had a quick skim following the link you gave me on the T-Bass thread. First, your 4 drivers gains you 6dB sensitivity, you were right with 3dB for each doubling of cone area. I'm interested in this project as I've been wondering how well OB can work in our typical British smaller rooms with speakers pushed into corners or near walls. I too have a stash of drivers in the loft
Well put it this way... I have pretty good sound out of this on cr@ppy baffles, including good quality, tight and informative bass down to reasonably deep notes.
I have a tiny room, speakers close to walls and I can keep turning it up - due to OB bass it NEVER, EVER booms or loads the room up. It simply punches harder in the drums and bass guitar.
Believe it or not, it actually plays stuff like trance really well too!!
As ever, simple acoustic music shows things off nicely.
I think you need to hear some OBs to know if it's for you or not. I'm finding there's a little trade-off sometimes. Tracks where I'm used to the bass pressurising the room don't have the same appeal but this is generally over-compensated for by increased detail (due, it seems, to lack of time-smear).
Simon
I forgot to say, I also added 0.22mH in series with the small Audax driver - this instantly made the match between mid and top more harmonious. The top to mid transition probably won't get much more "correct" on a 1st order crossover.
It's worth noting that unless I sit as far back as my small listening space allows the drivers don't gel properly. This is expected.
Simon
It's worth noting that unless I sit as far back as my small listening space allows the drivers don't gel properly. This is expected.
Simon
Hi Simon,
Hope you have the mid and tweeter dust caps at the same distance from your listening position.
Often a damping resistor across mid and tweeter voice coils can clean up thier responses. This is because series capacitor leave the voice coils floating at higher impedance, and thus resonances can intrude. This will waste amplifier energy, but if it sounds better ...
You might also care to try a rear tweeter.
Cheers ......... Graham.
Hope you have the mid and tweeter dust caps at the same distance from your listening position.
Often a damping resistor across mid and tweeter voice coils can clean up thier responses. This is because series capacitor leave the voice coils floating at higher impedance, and thus resonances can intrude. This will waste amplifier energy, but if it sounds better ...
You might also care to try a rear tweeter.
Cheers ......... Graham.
Graham,
Yes, tweeter and mid dome and dustcap are at good heights, each roughly the same distance to my ears.
Mid & tweeter each have a parallel resistor forming an L-pad, this works well.
When I find the schematic I drew (I seem to have lost it) I'll amend it to show the full setup as it currently is.
I'd considered rear tweeters. I have more of these cheap Wharfedale 1" domes so it's not a problem to add some
Ta
Simon
Yes, tweeter and mid dome and dustcap are at good heights, each roughly the same distance to my ears.
Mid & tweeter each have a parallel resistor forming an L-pad, this works well.
When I find the schematic I drew (I seem to have lost it) I'll amend it to show the full setup as it currently is.
I'd considered rear tweeters. I have more of these cheap Wharfedale 1" domes so it's not a problem to add some
Ta
Simon
SimontY said:
Hi Sy,
I wonder how many readers picked up on that post ?
No box storing amplifier output energy and returning it in its own time.
No monopolar pressurisation making the room floor/ceiling/walls store energy and return that in their own time.
The limit is set by the cross sectional area of your drivers. Double up again for one channel, and the taller the cleaner is what I have found for LF, irrespective of width.
See if like me you can get to the point where you actually prefer to not add a sub.
(If you do try a different transformer you will need to re-select all your component values again.)
Cheers ........ Graham.
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