Since this is my thread, I thought I might add some political commentary about 3" dome midranges.
The disadvantages of a 3” dome compared to a 4” or 5” cone midrange.
The dome has higher Fs and lower Xmax. This pushes the high pass crossover up to a higher frequency. Even the very best 3” domes need to have a crossover no lower than 500 Hz, and higher is better. The cone mids can easily be crossed as low as 300 Hz. This lower crossover frequency makes it easier to choose a woofer, especially if you want to use a big woofer. The upper end limit of a dome is not necessarily higher than a cone mid, particularly the 4” class. They both start to become highly directive above 3.5k, and this means the usable bandwidth of dome mids are less.
The dome has an Fs of 300 to 500 Hz and this means there will be an impedance hump very close to the crossover frequency. A cone mid will have an impedance hump at 70 – 100 Hz, which is well below the crossover and easier to deal with.
The dome is more expensive to manufacture, and this is reflected in the retail pricing. For the same kind of frequency response build quality, dome mids seem to be about 50% more expensive than a cones. When it comes to 3” dome mids, there are only a few options available for DIY purchase, and the two which I would consider for future projects are the Volt series and the Bliesma series. These are expensive drivers no matter what sort of budget one has.
The advantages of a 3” dome mid
Sensitivity, power handling and maximum SPL. Not every design needs this kind of capability, but if the design calls for it, the few really good 3” dome mids can deliver (Bliesma and Volt). Other options might be a line array of cone mids, or a large horn with a 1.4” compression driver. But nothing else really delivers this kind of high SPL performance from a point source direct radiator in a relatively small faceplate.
Another advantage is that some listeners report that dome mids have subjectively better resolution of fine detail. Let’s assume that the subjective comparisons are made at reasonable SPL where a cone mid is not at a disadvantage. The subjective assessment may be true, or it may be a result of better system design… Since 3” dome mids are expensive, they tend to be used only in expensive systems, and expensive systems tend to be more optimized and refined. It would be hard to make a real apples-to-apples comparison. Nonetheless, this is what some experienced users have reported.
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So, my opinion is that when comparing a 3” dome to a 4” or 5” cone midrange, cost and SPL capability are the deciding factor. If my budget for a midrange driver eliminates the Bliesma and Volt from consideration, then that is it… the mid driver will be a cone mid. On the other hand, if the maximum SPL capability requirement is higher than what a cone mid can deliver, than I will consider the Bliesma and Volt drivers, no matter the cost. In my case, I would like to build a future system around the Bliesma M74A, not for the high SPL capability per se, but to see if I like the sound.
j.
The disadvantages of a 3” dome compared to a 4” or 5” cone midrange.
The dome has higher Fs and lower Xmax. This pushes the high pass crossover up to a higher frequency. Even the very best 3” domes need to have a crossover no lower than 500 Hz, and higher is better. The cone mids can easily be crossed as low as 300 Hz. This lower crossover frequency makes it easier to choose a woofer, especially if you want to use a big woofer. The upper end limit of a dome is not necessarily higher than a cone mid, particularly the 4” class. They both start to become highly directive above 3.5k, and this means the usable bandwidth of dome mids are less.
The dome has an Fs of 300 to 500 Hz and this means there will be an impedance hump very close to the crossover frequency. A cone mid will have an impedance hump at 70 – 100 Hz, which is well below the crossover and easier to deal with.
The dome is more expensive to manufacture, and this is reflected in the retail pricing. For the same kind of frequency response build quality, dome mids seem to be about 50% more expensive than a cones. When it comes to 3” dome mids, there are only a few options available for DIY purchase, and the two which I would consider for future projects are the Volt series and the Bliesma series. These are expensive drivers no matter what sort of budget one has.
The advantages of a 3” dome mid
Sensitivity, power handling and maximum SPL. Not every design needs this kind of capability, but if the design calls for it, the few really good 3” dome mids can deliver (Bliesma and Volt). Other options might be a line array of cone mids, or a large horn with a 1.4” compression driver. But nothing else really delivers this kind of high SPL performance from a point source direct radiator in a relatively small faceplate.
Another advantage is that some listeners report that dome mids have subjectively better resolution of fine detail. Let’s assume that the subjective comparisons are made at reasonable SPL where a cone mid is not at a disadvantage. The subjective assessment may be true, or it may be a result of better system design… Since 3” dome mids are expensive, they tend to be used only in expensive systems, and expensive systems tend to be more optimized and refined. It would be hard to make a real apples-to-apples comparison. Nonetheless, this is what some experienced users have reported.
--- --- ---
So, my opinion is that when comparing a 3” dome to a 4” or 5” cone midrange, cost and SPL capability are the deciding factor. If my budget for a midrange driver eliminates the Bliesma and Volt from consideration, then that is it… the mid driver will be a cone mid. On the other hand, if the maximum SPL capability requirement is higher than what a cone mid can deliver, than I will consider the Bliesma and Volt drivers, no matter the cost. In my case, I would like to build a future system around the Bliesma M74A, not for the high SPL capability per se, but to see if I like the sound.
j.
In other news, I have two different midrange drivers on their way to me for evaluation. The first is the SB15CRC30-8, and the other is the SB12MNRX2-25-4.
As I mentioned earlier, my feasibility simulations showed that I would need to use an 8 Ohm mid to keep the impedance above 3 Ohm. The SIG225-4 woofer will have net sensitivity of 85 dB after accounting for the baffle step. Most small 8 Ohm midwoofers have a sensitivity in the range of 85 dB, so this works well.
The smaller SB12 unit is 5 dB more sensitive than the SB15. In theory I will need enough series resistance such that the overall speaker impedance will be acceptable.
I intend to evaluate both drivers. The SB15 unit is 60% more cost than the SB12, so it will be interesting to see what kind of performance the higher cost brings to the table.
j.
As I mentioned earlier, my feasibility simulations showed that I would need to use an 8 Ohm mid to keep the impedance above 3 Ohm. The SIG225-4 woofer will have net sensitivity of 85 dB after accounting for the baffle step. Most small 8 Ohm midwoofers have a sensitivity in the range of 85 dB, so this works well.
The smaller SB12 unit is 5 dB more sensitive than the SB15. In theory I will need enough series resistance such that the overall speaker impedance will be acceptable.
I intend to evaluate both drivers. The SB15 unit is 60% more cost than the SB12, so it will be interesting to see what kind of performance the higher cost brings to the table.
j.
Another observation about dome midranges: They use to be more common, as @b_force commented in post#51.
I remember hearing both A/D/S speakers and Canton speakers in early 1990's that sounded really good, with 2" dome mids. At that time, Vifa, Audax, Morel, Dynaudio, they all had 2" or 3" dome mids available for DIY. I think the reason they were more common is that tweeters back then were limited. Most tweeters had an Fs of about 1k, and most worked best above 3k. It was rare for a tweeter to be able to work well (low distortion) down to 2k. The few that could do it (like Dynaudio) were quite a bit more expensive than the more typical Peerless, Vifa, and Audax models.
Eventually, affordable tweeters became available with large back chambers, lower Fs, and bigger Xmax... and then it became much more feasible to cross them at 2k or so... and with that, the need for a 2" dome mid started to diminish...
That is my theory ... 🙂
I remember hearing both A/D/S speakers and Canton speakers in early 1990's that sounded really good, with 2" dome mids. At that time, Vifa, Audax, Morel, Dynaudio, they all had 2" or 3" dome mids available for DIY. I think the reason they were more common is that tweeters back then were limited. Most tweeters had an Fs of about 1k, and most worked best above 3k. It was rare for a tweeter to be able to work well (low distortion) down to 2k. The few that could do it (like Dynaudio) were quite a bit more expensive than the more typical Peerless, Vifa, and Audax models.
Eventually, affordable tweeters became available with large back chambers, lower Fs, and bigger Xmax... and then it became much more feasible to cross them at 2k or so... and with that, the need for a 2" dome mid started to diminish...
That is my theory ... 🙂
I personally think the reason is pretty simple.
Everyone wanted to go smaller, 2-way systems.
Which introduced a whole set of other compromises and difficulties.
But yeah that put pure mid-ranges (domes but also cones) out of fashion very quickly.
Everyone wanted to go smaller, 2-way systems.
Which introduced a whole set of other compromises and difficulties.
But yeah that put pure mid-ranges (domes but also cones) out of fashion very quickly.
Oh sorry, and as for pros vs cons between dome vs cone.
Very much simplified, it's sensitivity (= max SPL) vs lower frequency.
There are some additional nuances and differences, but those are basically just secondary to that. (As in, a result of).
Crossing lower than 500Hz isn't so easy in a passive filter to begin with btw.
Very much simplified, it's sensitivity (= max SPL) vs lower frequency.
There are some additional nuances and differences, but those are basically just secondary to that. (As in, a result of).
Crossing lower than 500Hz isn't so easy in a passive filter to begin with btw.
It would be nice if there would be some modern combo of 50 to 75 mm midrange dome and 13-19 mm dome tweeter. Something like Visaton G50FFL and G20SC tweeter. Or DSM series. But in more modern package with lower tweeter fs....with equal look and very wide dispersion to above 10 kHz.
Sweet dreams are made of these...nobody will probably ever again produce so small tweeter.... 🙂
Sweet dreams are made of these...nobody will probably ever again produce so small tweeter.... 🙂
I don't follow, almost every brand has a 19-22mm tweeter?
Some are even capable of doing 2kHz no problem.
Some are even capable of doing 2kHz no problem.
The Dynaudio, Scan Speak and mainly Vifa series stem from begin to mid eighties. Units like the D26TG35 then offered practically what a good affordable 25mm dome offers nowadays, including low fs and high power capacity. Personally, I think not much has changed in 40 years. Bart is right imo, 3-ways got out of fashion.
From the same days the Vifa 76mm dome also rocked the boat. We had quite a famous three way design with it over here which was virtually a no-brainer between the available designs then. That same 76mm is still for sale…
Production quality and precision mostly, as well as patents that have expired.
Leading into (sometimes better) copies of the same idea for a better price and higher quality.
The biggest change has been more the common knowledge, which has been further build upon.
Leading to some more well defined improvements.
Although I still see many approaches that a lot of manufacturers are still stuck on.
I well remember the Vifa drivers. A few years ago I dismantled an old design of mine from 1992, and the only driver I kept was the tweeter. I re-used it in a speaker for my workshop.
The D25AG35-06 was a real game changer, along with the silk dome version. It was less than half the cost of a comparable Dynaudio or ScanSpeak unit.
A little discussion about driver spacing.
My current practice for driver spacing originates with this post by Kimmo, and the following discussion.
https://www.diyaudio.com/community/threads/vituixcad.307910/post-6538511
Among the recommendations, there are two that pertain to the baffle design: (1) minimize baffle area around tweeter (2) CtC spacing between of about 1.2 x WL, although the actual recommendation is between 1.0 and 1.4 x WL. These two baffle constraints are equal in importance in my experience. Doing one without the other will give some benefit, doing both gives the most benefit.
Since being alerted to this important design consideration by @fluid and others, I have designed, built, and tested 3 non-waveguide and 1 waveguide systems using this guidance. In those four speakers, I have achieved my goal of good Power&DI performance along with good on-axis performance.
Maintaining good DI performance through the crossover region is one of the more challenging aspects of 2-way and 3-way non-waveguide systems. This means a DI curve which either steadily increases with frequency or remains flat through the crossover region until the tweeter directivity naturally starts to rise. In addition to the Kimmo guidelines, I use baffle diffraction simulation to help me decide the crossover frequency the approximate crossover frequency early in the design, and this process has typically driven me to a fairly low crossover frequency.
A low crossover requires a wide spacing, and it can look strange, particularly with a small midrange or midwoofer. At higher crossover frequencies, the 1.2xWL spacing is easy to achieve, and is often achieved by accident just by placing the drivers close together. Waveguides often force the CtC spacing to be wider, and this can be an unappreciated benefit to waveguides.
If a standard 105 mm flange tweeter is placed very near a midrange or midwoofer (5 mm separation), the chart below shows the crossover frequency where CtC spacing is 1.2xWL. As shown, a 4” driver could cross to a tweeter at 3.5k with the drivers almost touching, and the CtC distance would be 1.2xWL. For a 6” driver, the crossover frequency would be 3k. I think this is on the high side, but still reasonable.
I also show the results for a separation of 25 mm and 50 mm.
There has been a lot of discussion over the years about the audible effect of crossover frequency. There have been comparisons made and conclusions reached. However, most of these comparisons involved changing the crossover frequency while keeping the driver spacing constant. Thus, there are two effects changing, the crossover frequency and the wavelength effect on vertical polar response, which then affects the Directivity Index, Power Response, Early Reflection response, etc. The only fair way to isolate the effect of changing crossover frequency is to keep the CtC wavelength distance constant.
With this current design, I am using a small waveguide tweeter. The waveguide, although small, controls the directivity down to about 3k, as I showed in post # 6. This allows the crossover to be in the 3k range, which of course shrinks the necessary spacing between the drivers.
j.
My current practice for driver spacing originates with this post by Kimmo, and the following discussion.
https://www.diyaudio.com/community/threads/vituixcad.307910/post-6538511
Among the recommendations, there are two that pertain to the baffle design: (1) minimize baffle area around tweeter (2) CtC spacing between of about 1.2 x WL, although the actual recommendation is between 1.0 and 1.4 x WL. These two baffle constraints are equal in importance in my experience. Doing one without the other will give some benefit, doing both gives the most benefit.
Since being alerted to this important design consideration by @fluid and others, I have designed, built, and tested 3 non-waveguide and 1 waveguide systems using this guidance. In those four speakers, I have achieved my goal of good Power&DI performance along with good on-axis performance.
Maintaining good DI performance through the crossover region is one of the more challenging aspects of 2-way and 3-way non-waveguide systems. This means a DI curve which either steadily increases with frequency or remains flat through the crossover region until the tweeter directivity naturally starts to rise. In addition to the Kimmo guidelines, I use baffle diffraction simulation to help me decide the crossover frequency the approximate crossover frequency early in the design, and this process has typically driven me to a fairly low crossover frequency.
A low crossover requires a wide spacing, and it can look strange, particularly with a small midrange or midwoofer. At higher crossover frequencies, the 1.2xWL spacing is easy to achieve, and is often achieved by accident just by placing the drivers close together. Waveguides often force the CtC spacing to be wider, and this can be an unappreciated benefit to waveguides.
If a standard 105 mm flange tweeter is placed very near a midrange or midwoofer (5 mm separation), the chart below shows the crossover frequency where CtC spacing is 1.2xWL. As shown, a 4” driver could cross to a tweeter at 3.5k with the drivers almost touching, and the CtC distance would be 1.2xWL. For a 6” driver, the crossover frequency would be 3k. I think this is on the high side, but still reasonable.
I also show the results for a separation of 25 mm and 50 mm.
There has been a lot of discussion over the years about the audible effect of crossover frequency. There have been comparisons made and conclusions reached. However, most of these comparisons involved changing the crossover frequency while keeping the driver spacing constant. Thus, there are two effects changing, the crossover frequency and the wavelength effect on vertical polar response, which then affects the Directivity Index, Power Response, Early Reflection response, etc. The only fair way to isolate the effect of changing crossover frequency is to keep the CtC wavelength distance constant.
With this current design, I am using a small waveguide tweeter. The waveguide, although small, controls the directivity down to about 3k, as I showed in post # 6. This allows the crossover to be in the 3k range, which of course shrinks the necessary spacing between the drivers.
j.
I am evaluating two drivers as candidates for the midrange, although I may evaluate others in the future… The first is the SB15CRC30-8. I have a lot of experience with the sister drivers, NBAC aluminum and CAC ceramic/aluminum, and those drivers are excellent…so I am very curious about this composite cone. The second is the SB12MNRX2-25-4. It is a smaller driver (4”), with an Sd of only 50 cm^2. It has a paper cone that I would describe as semi-stiff. It is not a soft paper cone, but neither is it a hard paper cone. The price is very attractive at $60.
The first thing I do when I get any driver is take an impedance sweep of the bare driver sitting on a block of thick foam. Most defects can be discovered this way, and none of the 4 drivers showed anything unusual.
The FR scans were made in my prototype test baffle. I made a small 2.5 l box with two removable face plates, one for the SB15CRC and one for the SB12MNRX2. I then modified the XPS foam test baffle to accommodate the 2.5 l box. The tweeter hole was filled with foam and covered with tape, although my photos don’t show this. I cut the recess for the SB12MNRX2 slightly too large, so I filled the gap and covered it with tape. I got the SB15CRC recess cut right the first time...
The FR scans were made at about 1 Vrms, at a distance of 1 m, 0 – 180 degrees, in increments of 15 degrees. The far field polar scans were merged with the near field scan. The NF scan was adjusted to the baffle shape, in accordance with VituixCad instructions.
The first thing I do when I get any driver is take an impedance sweep of the bare driver sitting on a block of thick foam. Most defects can be discovered this way, and none of the 4 drivers showed anything unusual.
The FR scans were made in my prototype test baffle. I made a small 2.5 l box with two removable face plates, one for the SB15CRC and one for the SB12MNRX2. I then modified the XPS foam test baffle to accommodate the 2.5 l box. The tweeter hole was filled with foam and covered with tape, although my photos don’t show this. I cut the recess for the SB12MNRX2 slightly too large, so I filled the gap and covered it with tape. I got the SB15CRC recess cut right the first time...
The FR scans were made at about 1 Vrms, at a distance of 1 m, 0 – 180 degrees, in increments of 15 degrees. The far field polar scans were merged with the near field scan. The NF scan was adjusted to the baffle shape, in accordance with VituixCad instructions.
I didn't like the SB Rohacell drivers when I heard them. Could been the cabs or design I suppose, but I didnt.
Here I show the Power and DI for the drivers.
The burst decay plots were made from the 0-degree polar scan (1 m, 1 Vrms).
The distortion measurements were made as ground plane scans. The mic distance for distortion testing was 30 cm, and the SPL was measured at 1m. I raised the gain until I got 97 dB at a distance of 1 m. I used test tones between 1k and 2k to set the level. To convert the ground plane SPL into an equivalent free field value, I subtract 6 dB from the measurement. So these scans are equivalent to 91 dB at 1 m.
I ran the SB15CRC from 100 to 8 kHz. The SB12MNRX2 is a midrange driver, not a midwoofer, so I ran it from 200 to 8 kHz.
The burst decay plots were made from the 0-degree polar scan (1 m, 1 Vrms).
The distortion measurements were made as ground plane scans. The mic distance for distortion testing was 30 cm, and the SPL was measured at 1m. I raised the gain until I got 97 dB at a distance of 1 m. I used test tones between 1k and 2k to set the level. To convert the ground plane SPL into an equivalent free field value, I subtract 6 dB from the measurement. So these scans are equivalent to 91 dB at 1 m.
I ran the SB15CRC from 100 to 8 kHz. The SB12MNRX2 is a midrange driver, not a midwoofer, so I ran it from 200 to 8 kHz.
I see you have the same 5db dip in the response of the SB12MNRX2-25-4 that I have. I lived with it when I ran it passive but I flattened it out when I went active. Honestly I'm sure if it made all that much of a difference in the sound.
SB12 has strange D2 peak, what is causing that? Did you get that too mtidge?
It's on-axis dip at 2kHz comes from high profile surround I guess, cavity interference/mode
It's on-axis dip at 2kHz comes from high profile surround I guess, cavity interference/mode
I didn't do any distortion measurements and the consensus at the time was the large surround was causing the dip at 1.5khz. There is a good chance that the surround would also cause the distortion too. Maybe it would be better if SB used an accordion style surround instead, but then that might lower the efficiency to much. Maybe an inverted surround would be better or just use a Purify type surround.