Hello Everyone,
I may introduce my latest speaker project to you:
Name: Edelstoff (german for "precious stuff" and also a beer brand from munich)
Type: 2-way constant directivity vented compact speaker
Impedance: 4 Ohm (> 2.7 Ohm @ 300 Hz)
Sensitivity: ~86dB @ 2,83V @ 1m
Response: 60Hz ... 30kHz +/- 1 dB, -6dB @ 47 Hz
Tuning: 10l gross / 8,5l net @ 45Hz
Crossover: Quasi-Linkwitz/Riley ~4th order @ 2.2 kHz acoustically
Cabinet: Birch plywood 18 mm, MDF 19 mm black colored, wax oil
Damping: 3.5 mm bitumen pads + 8 mm wool felt, Isobond WLG 040
Dimensions (w x h x d): 18cm x 33 cm x 27 cm
Tweeter: Seas 27TBCD/GB-DXT
Woofer: SB Acoustics SB15NBAC30-4 with additional neodymium magnet N42 d70/30x10 mm
Tube: Intertechnik Highpower BR/HP 50/180, drilled in the center for standing wave control (research state)
Drivers within the enclosure were measured in the garden on a tripod with turntable at a distance of 1m, mic 1-2 cm below the acoustical axis from the tweeter.
1)+/- 60° horizontally and +/- 40° vertically on a very slim speaker stand (see above in the first picture),
2) again +/- 60° horizontally placed onto the other speaker without gap (extension of the baffle downwards "to infinity", use case is e.g. placement on subwoofer or at front on lowboard/sideboard).
Single drivers in enclosure on slim stand:
Frequency response with crossover simulation in VirtuixCAD:
Comparison of placement on slim stand (solid) and onto the other speaker (dashed):
Frequency response hor +/- 60° on slim stand:
Frequency response hor +/- 60° on the other speaker:
Power response and directivity index hor +/- 60° (solid) and hor +/- 60° plus ver +/- 40° (dashed):
Phase and group delay:
Electrical filter response:
Speaker Impedance:
Crossover Network:
The 0° responses were merged with nearfield responses of woofer and vent (and baffle simulation):
I pimped the woofer with an additional fat neodymium magnet to push the data in the fundamental somewhat and to increase the stability of the magnetic field at lower frequencies by further saturation of the rear pole plate, the untreated SB has a weakness there.
According to my TSP measurements, the force factor increases by approx. 7-8%, which has a positive effect on the overall tuning according to simulation:
My mic distorts with a lot of k2, but here is a Farina sweep of the woofer in the box in 0,5m distance with the added magnet:
I may introduce my latest speaker project to you:
Name: Edelstoff (german for "precious stuff" and also a beer brand from munich)
Type: 2-way constant directivity vented compact speaker
Impedance: 4 Ohm (> 2.7 Ohm @ 300 Hz)
Sensitivity: ~86dB @ 2,83V @ 1m
Response: 60Hz ... 30kHz +/- 1 dB, -6dB @ 47 Hz
Tuning: 10l gross / 8,5l net @ 45Hz
Crossover: Quasi-Linkwitz/Riley ~4th order @ 2.2 kHz acoustically
Cabinet: Birch plywood 18 mm, MDF 19 mm black colored, wax oil
Damping: 3.5 mm bitumen pads + 8 mm wool felt, Isobond WLG 040
Dimensions (w x h x d): 18cm x 33 cm x 27 cm
Tweeter: Seas 27TBCD/GB-DXT
Woofer: SB Acoustics SB15NBAC30-4 with additional neodymium magnet N42 d70/30x10 mm
Tube: Intertechnik Highpower BR/HP 50/180, drilled in the center for standing wave control (research state)
Drivers within the enclosure were measured in the garden on a tripod with turntable at a distance of 1m, mic 1-2 cm below the acoustical axis from the tweeter.
1)+/- 60° horizontally and +/- 40° vertically on a very slim speaker stand (see above in the first picture),
2) again +/- 60° horizontally placed onto the other speaker without gap (extension of the baffle downwards "to infinity", use case is e.g. placement on subwoofer or at front on lowboard/sideboard).
Single drivers in enclosure on slim stand:
Frequency response with crossover simulation in VirtuixCAD:
Comparison of placement on slim stand (solid) and onto the other speaker (dashed):
Frequency response hor +/- 60° on slim stand:
Frequency response hor +/- 60° on the other speaker:
Power response and directivity index hor +/- 60° (solid) and hor +/- 60° plus ver +/- 40° (dashed):
Phase and group delay:
Electrical filter response:
Speaker Impedance:
Crossover Network:
The 0° responses were merged with nearfield responses of woofer and vent (and baffle simulation):
I pimped the woofer with an additional fat neodymium magnet to push the data in the fundamental somewhat and to increase the stability of the magnetic field at lower frequencies by further saturation of the rear pole plate, the untreated SB has a weakness there.
According to my TSP measurements, the force factor increases by approx. 7-8%, which has a positive effect on the overall tuning according to simulation:
My mic distorts with a lot of k2, but here is a Farina sweep of the woofer in the box in 0,5m distance with the added magnet:
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Both breakup resonances of the woofer and tweeter were treated with series notches according to https://purifi-audio.com/wp-content/uploads/2022/03/220211_R05-Notchfilter.pdf to decrease pre-echoes of the resonances in the distortion profile.
Tweeter notch frequency response:
Tweeter notch impedance:
Tweeter backwards source impedance (solid line, with additionally connected driver = dashed):
Woofer notch frequency response:
Woofer notch impedance:
Woofer backwards source impedance (solid line, with additionally connected driver = dashed):
Circuitry for backwards source impedance analysis:
I'm waiting for the last missing parts of the crossover to get everything running, until then I'll be fighting with the standing wave in the vent tube.
Actual state:
A bit better with the additional resonator (anyhow, 6dB is half power), will decide if further measures are needed after final integration and listening...
Best regards
Peter
Tweeter notch frequency response:
Tweeter notch impedance:
Tweeter backwards source impedance (solid line, with additionally connected driver = dashed):
Woofer notch frequency response:
Woofer notch impedance:
Woofer backwards source impedance (solid line, with additionally connected driver = dashed):
Circuitry for backwards source impedance analysis:
I'm waiting for the last missing parts of the crossover to get everything running, until then I'll be fighting with the standing wave in the vent tube.
Actual state:
A bit better with the additional resonator (anyhow, 6dB is half power), will decide if further measures are needed after final integration and listening...
Best regards
Peter
Lovely!
Such careful attention to all aspects of the design. Looks great, and pushes the limit of SB15NBAC of what the it's capable of, as a mid-woofer.
Can you tell us the genesis or story of this design? What were your goals?
Please run some 96dB@1m distortion sweeps, if possible.
PS. Do you think the ultrasonic notch for the tweeter is required, or optional?
Such careful attention to all aspects of the design. Looks great, and pushes the limit of SB15NBAC of what the it's capable of, as a mid-woofer.
Can you tell us the genesis or story of this design? What were your goals?
Please run some 96dB@1m distortion sweeps, if possible.
PS. Do you think the ultrasonic notch for the tweeter is required, or optional?
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A couple clarifications, parallel notches placed in series are called "parallel notches", and -3dB is half power, not -6dB. The program is VituixCad, seems a lot of people want to put an R in there....
That said, this is a very thorough design! I've recently had to do the additional magnet regimine as well. In my case was just to get it to meet specs as it fell short. I hope you used adhesive to attach it to keep it from moving. The magnetic pull will keep it attached, but not from moving under a sudden impact to the cabinet.
I really like the aesthetics of the cabinet with the Valcromat black (wish we could get that over here) and the mitered BB ply. Can I ask what the radius of the baffle is? It almost looks like a thumbnail/table edge router bit with the not constant varying radii. I've used those myself too.
I like the gradual bass alignment to get better in room extension too. Seems most of my PR designs that I shoehorn into a box aspire to this arrangement of highish F3 and low F10.
Keep us posted on the port study, I like your application process there.
That said, this is a very thorough design! I've recently had to do the additional magnet regimine as well. In my case was just to get it to meet specs as it fell short. I hope you used adhesive to attach it to keep it from moving. The magnetic pull will keep it attached, but not from moving under a sudden impact to the cabinet.
I really like the aesthetics of the cabinet with the Valcromat black (wish we could get that over here) and the mitered BB ply. Can I ask what the radius of the baffle is? It almost looks like a thumbnail/table edge router bit with the not constant varying radii. I've used those myself too.
I like the gradual bass alignment to get better in room extension too. Seems most of my PR designs that I shoehorn into a box aspire to this arrangement of highish F3 and low F10.
Keep us posted on the port study, I like your application process there.
I can only agree with this for reasons that are certainly well known.
Many greetings,
Michael
Btw.: I can't use smilies on my end. Does anyone know the reason?
Xovers:
Rough Measurement in 0,5 mm distance, no gate:
A bit of the Tweeter resonance still remains; here in Vituixcad with better application of the mic calibration curve:
But pre-echoes in the distortion response are completely surpressed:
(The 90dB is correct, measuring distance approx. 30cm. The k2 comes from the mic...)
Here the modded woofer alone, without xover:
(The SPL is correct, measuring distance approx. 30cm. The k2 comes from the mic...)
Woofer nearfiled resonse & distortion (uncalibrated, but much less than 90dB):
I drilled out the 6 holes in the reflex tube to 4mm and optimized the damping minimally.
(a little thinner plucked where the gap is narrower, before that it was somewhat stuffed):
That's sufficient for me for now.
First impressions: This is a really serious, linear and noise-free story; the 3k€ active speakers just behind it are a little ashamed of what can go with detail resolution and spatial imaging. The fundamental is quite strong through the almost complete bafflestep compensation (at least if you're used to much wider baffles), and in the bass there's also power; the small SB punches so neatly that I'm thinking about a more stable stand, on the wobbly ones I'm using currently the bass sounds minimally "soft" (I know the effect, had therefore once a stack of paving stones as LS stand in the past...)
I've never had heard such a real and pleasing reproduction of Sara K's "Tell me I'm not dreaming" within my own walls before, very nice!
Very dense and dynamic music (e.g. Metal, Piano concert with whole orchestra...) is reproduced surprisingly clean and transparent up to a certain spl level, but of course some pressure and "kick" is missing due to the limited cone area and overall displacement of the speaker (3k€ active speakers regaining some self-confidence...)
No router bit, did it free hand with sandpaper...
Best regards
Peter
Rough Measurement in 0,5 mm distance, no gate:
A bit of the Tweeter resonance still remains; here in Vituixcad with better application of the mic calibration curve:
But pre-echoes in the distortion response are completely surpressed:
(The 90dB is correct, measuring distance approx. 30cm. The k2 comes from the mic...)
Here the modded woofer alone, without xover:
(The SPL is correct, measuring distance approx. 30cm. The k2 comes from the mic...)
Woofer nearfiled resonse & distortion (uncalibrated, but much less than 90dB):
I drilled out the 6 holes in the reflex tube to 4mm and optimized the damping minimally.
(a little thinner plucked where the gap is narrower, before that it was somewhat stuffed):
That's sufficient for me for now.
First impressions: This is a really serious, linear and noise-free story; the 3k€ active speakers just behind it are a little ashamed of what can go with detail resolution and spatial imaging. The fundamental is quite strong through the almost complete bafflestep compensation (at least if you're used to much wider baffles), and in the bass there's also power; the small SB punches so neatly that I'm thinking about a more stable stand, on the wobbly ones I'm using currently the bass sounds minimally "soft" (I know the effect, had therefore once a stack of paving stones as LS stand in the past...)
I've never had heard such a real and pleasing reproduction of Sara K's "Tell me I'm not dreaming" within my own walls before, very nice!
Very dense and dynamic music (e.g. Metal, Piano concert with whole orchestra...) is reproduced surprisingly clean and transparent up to a certain spl level, but of course some pressure and "kick" is missing due to the limited cone area and overall displacement of the speaker (3k€ active speakers regaining some self-confidence...)
No router bit, did it free hand with sandpaper...
Best regards
Peter
Got it from ebay (Germany): https://www.ebay.de/itm/291279095939
Here the magnets's effect on TSPs which I measured (fixed math method to tie as much other parameters):
Furthermore, I have drilled out the 6 holes in the vent tube each to ~8mm. Have measured and calculated everything that the total area of the holes approximately corresponds to the cross-sectional area at the inlet position of the little resonator. Here is the actual near field measurement on the vent tube of both speakers:
All disturbances are now <=20dB below normal level, so I'm very happy for the minimal effort and don't plan any more optimizations at this point!
Measured impedance curve of both speakers:
The minimum impedance is at quite low 2.7 ohms at 300Hz as simulated, but with hardly any phase shift (~pure resistive load). Nevertheless, this is a speaker for modern Class A / B or digital amps that prefer to deliver current than voltage - less for tube amps....
So far, the speakers were operated on a Yamaha R-N303D as well as on an old Sony F210 without any problems, even at permanently high volume. My recommendation would be an amp with 50W "nominal power capability" and 100W "music power capability" into 4 ohms.
Here is another FR measurement (gated, without room influence) at a distance of about 80cm, mic just below tweeter axis:
Note the scaling....
In addition, I had noticed by "hand" that the plastic front panel of the DTX resonates at certain frequencies and higher volume. To counteract this, I applied aluminum butyl sheet to the back of the rear chamber and in the cavities at the mounting flange (see e.g. here https://www.speakerdesign.net/seas/tweeters/dxt/images/dxt_motor_coil.jpg); now nothing vibrates anymore, which has audibly calmed the reproduction somewhat and made it a bit more transparent.
The bass reproduction still slightly soft / spongy, which I put down to the very wobbly speaker stand. I have now ordered material cutting for new stands from mechanical engineering aluminum profile as well as spikes - goal is: as stiff as possible and thereby as little sound radiating outer surface...
Best regards
Peter
Here the magnets's effect on TSPs which I measured (fixed math method to tie as much other parameters):
Furthermore, I have drilled out the 6 holes in the vent tube each to ~8mm. Have measured and calculated everything that the total area of the holes approximately corresponds to the cross-sectional area at the inlet position of the little resonator. Here is the actual near field measurement on the vent tube of both speakers:
All disturbances are now <=20dB below normal level, so I'm very happy for the minimal effort and don't plan any more optimizations at this point!
Measured impedance curve of both speakers:
The minimum impedance is at quite low 2.7 ohms at 300Hz as simulated, but with hardly any phase shift (~pure resistive load). Nevertheless, this is a speaker for modern Class A / B or digital amps that prefer to deliver current than voltage - less for tube amps....
So far, the speakers were operated on a Yamaha R-N303D as well as on an old Sony F210 without any problems, even at permanently high volume. My recommendation would be an amp with 50W "nominal power capability" and 100W "music power capability" into 4 ohms.
Here is another FR measurement (gated, without room influence) at a distance of about 80cm, mic just below tweeter axis:
Note the scaling....
In addition, I had noticed by "hand" that the plastic front panel of the DTX resonates at certain frequencies and higher volume. To counteract this, I applied aluminum butyl sheet to the back of the rear chamber and in the cavities at the mounting flange (see e.g. here https://www.speakerdesign.net/seas/tweeters/dxt/images/dxt_motor_coil.jpg); now nothing vibrates anymore, which has audibly calmed the reproduction somewhat and made it a bit more transparent.
The bass reproduction still slightly soft / spongy, which I put down to the very wobbly speaker stand. I have now ordered material cutting for new stands from mechanical engineering aluminum profile as well as spikes - goal is: as stiff as possible and thereby as little sound radiating outer surface...
Best regards
Peter
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Tell me more about the port. Is there just a small gap between the port and the grey sleeve, and in the gap is that damping material? And the sleeve is sealed at both ends? It would be interesting if you could do harmonic distortion and chuffing testing of the this port vs a standard port. My experience is that HD and chuffing get worse and I haven't found a way around it. Sort of makes sense that these would get worse when there are discontinuities in the port wall, and a small air mass vibrating back and forth in the holes. I think this must create some eddy currents on the surface, and these eddy currents have been shown in other research to be the source of chuffing.
If I may, I can say something about it: yes, the description fits roughly. I had once made a sketch with MS Paint:
It's basically a kind of tube resonator, tuned to the frequency of the first longitudinal resonance of the bass reflex port.
First question: what does the term "chuffing" mean? My translation program doesn't seem to know it either.
Apart from that: I imagine that effect takes place on the resonant frequency of the tube resonator, but that the openings towards it behave relatively inconspicuously away from this frequency.
The alternative would be to make the BR port so small that the longitudinal resonance is outside the intended frequency range of the bass-midrange driver. But then you would possibly have severe problems with flow noise.
Or you could use a passive radiator instead of a port. But then the group delay in the bass is higher, because the high-pass filter formed by this would be of a higher order. In addition, this solution is also more expensive.
It would certainly be a good idea to make comparative measurements. In the end, however, loudspeaker construction is always a collection of compromises.
Many greetings,
Michael
Translated with some help from DeepL
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Port noise caused by excessive air velocity, or turbulence. "Chuffing" is an onomatopoeia. It's like heavy breathing or blowing through a tube depending on the port.
Thanks, Michael, for the drawing!
(Michael poited me to this idea in german diy-hifi-forum, so - thanks again, Michael!)
The idea is to couple a resonator to the pressure maximum of the half-wave-resonace of the tube to suck it's energy out. This is done by a quarter-wave-resonator which then has half the length of the tube. Alternatively a Helmholz-Resonator may also be used - or even a design which combines and adds both effects.
My solution is a quaterwave-resonator with some compromises due to the simple, pragmatic construction:
1. It's tapered from zero to ~2,7 mm annular gap
2. The inlet/boreholes are not at the beginning, but at ~30% of the length (length is approximatly equal to the vent tube's half length)
Of course the boreholes in the tube are a source of turbulence, but i assume the effect of chuffing is much higher at the tube inlets where is much more discontinuity?
I did no 1by1 comparison or distortion Measurements at the port. But after modding the vent I percieved no differences in Low frequency reproduction, but clearer mids.
Of couse the port is chuffing at very high excursion and frequencies below the tuning frequency, but you have to force it to make that audible (e.g. with "Amplifer - the Octopus" Track 5 - theres only infrasonic rumbling in the intro - and level then set near to woofers xlim). This was the case before and after applying the boreholes, could not notice that chuffing sets in significantly earlyer after the mod.
I also thought of a passive radiator, an 5″ x 8″ SB15SFCR-00 will fit very well in my simulations. But beside the increased group delay the much higher mechanical losses (Qm=2,7 vs. 10-15 of a port) will cost me some Hz and/or dBs at the lower cutoff frequency. As this is not a speaker to sound a party or home cinema, but relaxed "living room level" I decided to keep the port...
Best regards
Peter
(Michael poited me to this idea in german diy-hifi-forum, so - thanks again, Michael!)
The idea is to couple a resonator to the pressure maximum of the half-wave-resonace of the tube to suck it's energy out. This is done by a quarter-wave-resonator which then has half the length of the tube. Alternatively a Helmholz-Resonator may also be used - or even a design which combines and adds both effects.
My solution is a quaterwave-resonator with some compromises due to the simple, pragmatic construction:
1. It's tapered from zero to ~2,7 mm annular gap
2. The inlet/boreholes are not at the beginning, but at ~30% of the length (length is approximatly equal to the vent tube's half length)
Of course the boreholes in the tube are a source of turbulence, but i assume the effect of chuffing is much higher at the tube inlets where is much more discontinuity?
I did no 1by1 comparison or distortion Measurements at the port. But after modding the vent I percieved no differences in Low frequency reproduction, but clearer mids.
Of couse the port is chuffing at very high excursion and frequencies below the tuning frequency, but you have to force it to make that audible (e.g. with "Amplifer - the Octopus" Track 5 - theres only infrasonic rumbling in the intro - and level then set near to woofers xlim). This was the case before and after applying the boreholes, could not notice that chuffing sets in significantly earlyer after the mod.
I also thought of a passive radiator, an 5″ x 8″ SB15SFCR-00 will fit very well in my simulations. But beside the increased group delay the much higher mechanical losses (Qm=2,7 vs. 10-15 of a port) will cost me some Hz and/or dBs at the lower cutoff frequency. As this is not a speaker to sound a party or home cinema, but relaxed "living room level" I decided to keep the port...
Best regards
Peter
Basically one can use either a Helmholtz Resonator (notch) or a acoustic lowpass;If I may, I can say something about it: yes, the description fits roughly. I had once made a sketch with MS Paint:
View attachment 1104669
It's basically a kind of tube resonator, tuned to the frequency of the first longitudinal resonance of the bass reflex port.
First question: what does the term "chuffing" mean? My translation program doesn't seem to know it either.
Apart from that: I imagine that effect takes place on the resonant frequency of the tube resonator, but that the openings towards it behave relatively inconspicuously away from this frequency.
The alternative would be to make the BR port so small that the longitudinal resonance is outside the intended frequency range of the bass-midrange driver. But then you would possibly have severe problems with flow noise.
Or you could use a passive radiator instead of a port. But then the group delay in the bass is higher, because the high-pass filter formed by this would be of a higher order. In addition, this solution is also more expensive.
It would certainly be a good idea to make comparative measurements. In the end, however, loudspeaker construction is always a collection of compromises.
Many greetings,
Michael
Translated with some help from DeepL
See; https://en.wikibooks.org/wiki/Acoustics/Filter_Design_and_Implementation
(there are better sources, but this is enough to show the idea and physics behind it)
Just some holes would suggest an acoustic highpass, although maybe some coupling with the actual cabinet might be happening.
"Just some holes" has the disadvantage that the boreholes couple directly to the cabinet. Tired this before the approch with the closed concentric resonator tube:
Blue: Without holes
Green: With holes open to the inner cabinet; The tuning frequency increases (virtual tube length decreases), and a lot of midrange dirt goes through them.
Red: With holes, but tube is wrapped with isobond acoustic felt + Gaffa Tape; a lot better, but the mechanical losses of the port are increased and so the output level decreased by ~ -1dB.
Blue: Without holes
Green: With holes open to the inner cabinet; The tuning frequency increases (virtual tube length decreases), and a lot of midrange dirt goes through them.
Red: With holes, but tube is wrapped with isobond acoustic felt + Gaffa Tape; a lot better, but the mechanical losses of the port are increased and so the output level decreased by ~ -1dB.