Just thought I'd share the build of my latest loudspeaker venture here on this thread. For a long while, I've wanted to design and build a small-ish 2-way ported loudspeaker that will work well in small to medium sized rooms and perhaps include part of the magic of a few famous designs of the 1970's....enter stage left the Reference Rhapsody speakers.
They will be a 50 litre enclosure housing an 8 inch mid-bass and a 25mm soft dome tweeter. Cab will be tuned for 35Hz.
I'll add photos as the build progresses. For now, the driver units have been chosen but I'd rather keep under wraps what these are as this will probably become a commercial venture in the future.
Reference Rhapsody
#2
These are coming along nicely now with cabinets in construction. I'm using Baltic Birch for all but the corner framing which is an integral structural part of the design as well as aesthetic framing.
Cabinets are extremely heavily braced for minimal panel resonance plus a few of the panels are double thickness....all resulting in over 30Kg per box before drivers even fitted! (just a shade under 700mm high for scale)
A sketch render:
Bass tuning (compared against the Reference Fidelios) and modelled group delay: (Fidelios are thinner of the two lines)
Crossovers are designed in their initial stages. I'm using second order with an impedance flattening Zobel for the bass and an LCR for the treble so that a fairly flat system response is the targeted end result.
I'll fit the drivers to the cabs in a week or so and measure each individually for TS parameters and actual impedance curves and fine tune the crossovers as required.
Cabinets are extremely heavily braced for minimal panel resonance plus a few of the panels are double thickness....all resulting in over 30Kg per box before drivers even fitted! (just a shade under 700mm high for scale)
A sketch render:
Bass tuning (compared against the Reference Fidelios) and modelled group delay: (Fidelios are thinner of the two lines)
Crossovers are designed in their initial stages. I'm using second order with an impedance flattening Zobel for the bass and an LCR for the treble so that a fairly flat system response is the targeted end result.
I'll fit the drivers to the cabs in a week or so and measure each individually for TS parameters and actual impedance curves and fine tune the crossovers as required.
#4
All finished now
A few tweaks needed to the crossover.
Whilst I used an impedance flattening Zobel, I didn't use an LCR in the bass filter (only in the tweeter filter); I noted very slight upper mid distortion close to crossover point, which whilst 1KHz lower than published cone break-up, could either be the new drivers needing bedding in (perhaps 50 hours or so) or the filter may benefit to a slight lowering of the shunt cap value to roll the woofer off more quickly.
Measured cab tuning is within 0.5% of calculated at a shade under 34 Hz and tweeter response is lovely and flat out to almost 20KHz (measured semi-anechoic ally) but could do with a slight lift close to the crossover point. A little blending close to crossover needed but all in all a very fine sounding pair of (substantial) stand mounters. The front baffle on these is 40mm Birch Ply and internally they're very heavily braced hence the 30Kg per cab.
A few tweaks needed to the crossover.
Whilst I used an impedance flattening Zobel, I didn't use an LCR in the bass filter (only in the tweeter filter); I noted very slight upper mid distortion close to crossover point, which whilst 1KHz lower than published cone break-up, could either be the new drivers needing bedding in (perhaps 50 hours or so) or the filter may benefit to a slight lowering of the shunt cap value to roll the woofer off more quickly.
Measured cab tuning is within 0.5% of calculated at a shade under 34 Hz and tweeter response is lovely and flat out to almost 20KHz (measured semi-anechoic ally) but could do with a slight lift close to the crossover point. A little blending close to crossover needed but all in all a very fine sounding pair of (substantial) stand mounters. The front baffle on these is 40mm Birch Ply and internally they're very heavily braced hence the 30Kg per cab.
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Dave the bass
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#5
I keep waiting for the tweeter to blink at me!
Nice build Mr Reffc, well done.
Nice build Mr Reffc, well done.
"The fat bourgeois and his doppelganger"
#6
Thanks Dave. Yes, it is a little Cyclops-like isn't it?!
Having examined the woofer filter measurements and the free air (and non-filter) impedance and SPL plots again, the break-up area is very benign indeed, so that isn't the cause of the resonance and slight distortion at around 2Khz. Scratching my head now but can only ascribe this to the very stiff driver suspension needing much longer break-in. I'll leave the values as they are until more break-in achieved.
Having examined the woofer filter measurements and the free air (and non-filter) impedance and SPL plots again, the break-up area is very benign indeed, so that isn't the cause of the resonance and slight distortion at around 2Khz. Scratching my head now but can only ascribe this to the very stiff driver suspension needing much longer break-in. I'll leave the values as they are until more break-in achieved.
#7 Update on Rhapsody Project Progress
Some more recent pictures of the completed speakers and stands.
For now, here's the latest pictures: Stands are rock solid and very heavy.
Stands are solid Beech wood, 75mm sqr. All joints are proper Mortice & Tenon...no biscuit joints here! These are exceptionally rigid and strong.
Cleaned up Grilles in place. Stands exactly match speakers which are designed to sit 5mm over the front of the stands to help break up the visual bulkiness. In the flesh, the result is quite elegant:
Without Grilles:
24K Gold plated adjustable feet supplied with matching floor protectors for use on bare floors:
Fit of grilles: They overlap the frame by 2mm all round leaving the walnut frame on show which accentuates the speakers visually from the front:
For now, here's the latest pictures: Stands are rock solid and very heavy.
Stands are solid Beech wood, 75mm sqr. All joints are proper Mortice & Tenon...no biscuit joints here! These are exceptionally rigid and strong.
Cleaned up Grilles in place. Stands exactly match speakers which are designed to sit 5mm over the front of the stands to help break up the visual bulkiness. In the flesh, the result is quite elegant:
Without Grilles:
24K Gold plated adjustable feet supplied with matching floor protectors for use on bare floors:
Fit of grilles: They overlap the frame by 2mm all round leaving the walnut frame on show which accentuates the speakers visually from the front:
#8 Re: Update on Rhapsody Project Progress
The only way!Reffc wrote:
Stands are solid Beech wood, 75mm sqr. All joints are proper Mortice & Tenon...no biscuit joints here! These are exceptionally rigid and strong.
lurvelly!
There's nowhere you can be that isn't where you're meant to be
#9
Some 30 degree off-axis frequency plots taken in-room (mic equi-distant from both speakers and pink noise used for measurement). A slight tweak on the crossovers needed but these are looking (and sounding) pretty good now. Semi-anechoic results were flatter so there's a little room interaction here:
#10 How did you measure?
Looks like an awful lot of averaging in the response plot for a real room, two speakers and off access.Reffc wrote:Some 30 degree off-axis frequency plots taken in-room (mic equi-distant from both speakers and pink noise used for measurement). A slight tweak on the crossovers needed but these are looking (and sounding) pretty good now. Semi-anechoic results were flatter so there's a little room interaction here:
Whenever I feel blue, I start breathing again.
#11
Hi
Its pretty standard 1/3 Octave smoothing...no averaging other than that but a little misunderstanding as it was one speaker...I'd just meant that both were measured the same way.
I've since modified the crossovers/internal damping and this is the on-axis plots measured from a little further back (2m) with the speakers placed well out into the room.
Again, 1/3 Octave smoothing applied. This time it is left plus right channels on-axis, grilles on. They're now sounding great and the response is about as good as I can get them. Personally, I'm pretty chuffed with the outcome.
[/img]
Its pretty standard 1/3 Octave smoothing...no averaging other than that but a little misunderstanding as it was one speaker...I'd just meant that both were measured the same way.
I've since modified the crossovers/internal damping and this is the on-axis plots measured from a little further back (2m) with the speakers placed well out into the room.
Again, 1/3 Octave smoothing applied. This time it is left plus right channels on-axis, grilles on. They're now sounding great and the response is about as good as I can get them. Personally, I'm pretty chuffed with the outcome.
[/img]#12 physics has been beaten?
Can you let us know how an 8" woofer can have flat response down to 20 Hz in a modest bass reflex box (tuned to 34Hz). That tuning is 4th order and that means below cutoff the box unloads and output drops at around 24dB/8va. The output from the vent eventually cancels out the output from the woofer. A real room measurement should also have a "hole" in the frequency response between 120Hz and 200Hz.
Magazine reviews measure the woofer and port separately and then sum. It makes for a pretty picture, but it is so far from reality..........
In a sealed box, we can use EQ to extend response, with the loss of maximum output.
I think there are a lot of people that would love this type of bass response. I don't get it in my system and room and have 3 15" low frequency modules in sealed boxes with EQ.
Magazine reviews measure the woofer and port separately and then sum. It makes for a pretty picture, but it is so far from reality..........
In a sealed box, we can use EQ to extend response, with the loss of maximum output.
I think there are a lot of people that would love this type of bass response. I don't get it in my system and room and have 3 15" low frequency modules in sealed boxes with EQ.
Whenever I feel blue, I start breathing again.
#13
The lower response is a little odd, but it is not flat to 20Hz (look again). It should shelve off steeply from 30Hz and I'm looking into the mic calibration files to see if there's an anomoly there, as I suspect that is where the optimistic results close to 20Hz stem from. As for the rest of it, it is what it is and measures the way it does, and I'm more than happy with the end result. Holes in response depend entirely on room dimensions for null points and also on any diffraction anomolies or internal damping anomolies (as you are aware, a ripple in response can be an indication of slight under damping or a problem with internal cabinet dimensions). The reality is though that these are a very fine sounding pair of loudspeakers 
Last edited by Reffc on Tue Jul 08, 2014 5:00 pm, edited 2 times in total.