I certainly found this to be true with my Trilliums, which have the RS52s between the Seas DXT and a pair of RS225s. However, I'm not sure I'd recommend new designs with the RS52AN given what I've read about the current production.
I wonder how this driver would respond to a metamaterial termination like is done with the KEF Uni-Q? Something 3-D printed, perhaps?
It depends on what kind of performance you expect from the mid. If you want true high end performance and push the mid LP down into the sub 800 hz range, its important to modify Qts so you can lower THD in the resonance area and avoid pushing the dome into over excursion due to an under dampened system. Tighter VC control (up to a point) equates to higher max SPL, lower THD and greater mid clarity. In stock form, Qts is around 1.5 which is too high to operate the dome down into the Fs area. This is the case when crossing under 800 hz 3rd order with a 1 ltr chamber stuffed loosely with merino wool. If you want to retain the OEM felt, you have to place a 1 inch thick piece of acoustic foam right behind the magnet felt layer, followed by 10 - 15 g of roving merino sheep's wool.
@Paul Ebert It would likely respond very well to meta material dampening, but you still need flow restriction behind the magnet vents to lower Qts.
Profiguy: do have you measured T/S parameters of te SS/Seas 75 mm domes standard and modified, in order to verify to what extent Qts lowers in reality?
What is your reasoning one still needs flow restriction in order to lower Qts? That is not entirely clear to me: Qms modification -in my book at least- has only minor impact in comparison with Qes.
What is your reasoning one still needs flow restriction in order to lower Qts? That is not entirely clear to me: Qms modification -in my book at least- has only minor impact in comparison with Qes.
Can you demonstrate that in concrete and specific numbers regarding the midranges discussed here?
I did't know that specific numbers were wanted, and I have no direct experience with that midrange.
I can say that every aperiodic damping scheme I've used has lowered Qtc. It's no different than a woofer in a sealed box vs that same woofer and box utilizing a floor vent or drain packed with open cell foam. Qtc always goes down. That does not need numbers to gather results.
Adding bucking magnets can also favor a lower Qts on drivers. Added with same poles, Qts will go down. Reverse mount it and cancel electrical field like in shielding drivers and the Qts will go up.
I can say that every aperiodic damping scheme I've used has lowered Qtc. It's no different than a woofer in a sealed box vs that same woofer and box utilizing a floor vent or drain packed with open cell foam. Qtc always goes down. That does not need numbers to gather results.
Adding bucking magnets can also favor a lower Qts on drivers. Added with same poles, Qts will go down. Reverse mount it and cancel electrical field like in shielding drivers and the Qts will go up.
I do have saved results from TSP testing on the D7608s, but in an older PC with a crashed HD, so at this moment they can't be accessed. I did not focus on Qms or Qes separately, as my goal was to reduce Qts with flow resistance dampening. It has always worked for me and the D7608s were no exception. You can get their Qts down to 0.65 if you try hard enough with various dampening schemes. The most effective is with a 1" acoustic foam layer followed by sheeps wool or grille cloth loosely folded. The trick is to gradually slow down air resistance behind the dome. Abrupt changes will cause reflections and just raise Fs.
Of course there is no free lunch, so you have to accept some minor loss of sensitivity at Fs. Many self contained pre enclosed mids use a bump in Qts to increase sensitivity and it doesn't provide a good foundation for decent transient response having that overshoot just for the sake of output.
I know alot of people complain that the D7608 has no enclosure but thats actually a blessing in disguise, allowing you to adjust Qts and Fs (to a certain extent) to suit your needs. Being able to change sub enclosure design parameters allows this mid to sound its best.
If you look up the measurements on Hifi Compass about the D7608, you'll find the CSD is very clean in the pass band as well as excellent step response. This mid is a bargain for what it costs and the amount of flexibility you have to implement it correctly for your specific design.
The other cheaper Hivi and Tang Band dome mids aren't remotely as good and most have major inconsistency issues. Believe me, I've tried and listened to them all. They're not on par with the D7608 even though they cost a few dollars less. The Tang Band 1558SE was the best one, but the new SH version took a back seat in overall quality and performance. Not sure why they decided to go backwards with that one, perhaps due to cost cutting.
I have some saved impedance sweeps of my D7608 experiments on my current measurement setup, so if you can wait a bit, I can dig them up. Please understand I'm not that big on data collection with my designs and I understand why many on here love to see lots of graphs and numbers. I'm more focused on the end result than proving why something is how it is. I don't have the time or desire to throw up a bunch of measurements, just for others to bicker and argue over, oftenn contesting their validity. I just want results and knowing how I got them.
Of course there is no free lunch, so you have to accept some minor loss of sensitivity at Fs. Many self contained pre enclosed mids use a bump in Qts to increase sensitivity and it doesn't provide a good foundation for decent transient response having that overshoot just for the sake of output.
I know alot of people complain that the D7608 has no enclosure but thats actually a blessing in disguise, allowing you to adjust Qts and Fs (to a certain extent) to suit your needs. Being able to change sub enclosure design parameters allows this mid to sound its best.
If you look up the measurements on Hifi Compass about the D7608, you'll find the CSD is very clean in the pass band as well as excellent step response. This mid is a bargain for what it costs and the amount of flexibility you have to implement it correctly for your specific design.
The other cheaper Hivi and Tang Band dome mids aren't remotely as good and most have major inconsistency issues. Believe me, I've tried and listened to them all. They're not on par with the D7608 even though they cost a few dollars less. The Tang Band 1558SE was the best one, but the new SH version took a back seat in overall quality and performance. Not sure why they decided to go backwards with that one, perhaps due to cost cutting.
I have some saved impedance sweeps of my D7608 experiments on my current measurement setup, so if you can wait a bit, I can dig them up. Please understand I'm not that big on data collection with my designs and I understand why many on here love to see lots of graphs and numbers. I'm more focused on the end result than proving why something is how it is. I don't have the time or desire to throw up a bunch of measurements, just for others to bicker and argue over, oftenn contesting their validity. I just want results and knowing how I got them.
I just saw that there are two versions of that driver:
D7608/920010
and
D7608/920000
Seems the second one comes without front plate, is that correct?
@stv Yes thats the only difference. The slight WG of the 9200-10 makes the dome less sensitive to diffraction from slight baffle protrusions and helps time align the dome with other tweeters, not to mention provides a mounting flange. The D7608 doesn't benefit from a WG based on my previous experiments with trying to modify directivity response.
Here are some models for the D7608:
Legend: Black line- 2i SPL
Aqua line- Max SPL (excursion and/or power limited, whichever is lower)
In Scan-Speak's suggested 0.5L box:
In a slightly larger box of 1L, modelled with Qa= 5 ie. heavy fill eg. filled with fibreglass & Ql 10 - minimally leaky sealed box. Note the drop in Qtc:
Maximum SPL (assumes excursion limit of 0.45mm based on Voice coil height and gap geometry):
Here it is on mounted in a minimally wide box (160mm = 6.25") with 38mm (1.5") roundovers, the 4pi (anechoic) response, which mean it includes baffle step losses. Here @1m:
Is the 95dB SPL @1m a bit low for your liking? It is for me.
Well let's apply an electrical LR2 filter @ 400Hz. Now the excursion limited maximum SPL is of 103dB, with a Fc of 385Hz.
Legend: Black line- 2i SPL
Aqua line- Max SPL (excursion and/or power limited, whichever is lower)
In Scan-Speak's suggested 0.5L box:
In a slightly larger box of 1L, modelled with Qa= 5 ie. heavy fill eg. filled with fibreglass & Ql 10 - minimally leaky sealed box. Note the drop in Qtc:
Maximum SPL (assumes excursion limit of 0.45mm based on Voice coil height and gap geometry):
Here it is on mounted in a minimally wide box (160mm = 6.25") with 38mm (1.5") roundovers, the 4pi (anechoic) response, which mean it includes baffle step losses. Here @1m:
Is the 95dB SPL @1m a bit low for your liking? It is for me.
Well let's apply an electrical LR2 filter @ 400Hz. Now the excursion limited maximum SPL is of 103dB, with a Fc of 385Hz.
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What about the top end?
Based on Scan-Speak's IB response and the 0, 30 and 60 degree off axis charts, the -6dB beamwidth is 3KHz @ 45 degrees:
A skinny 6.25" wide cabinet with large round-overs would allow for wider dispersion.
How wide?
Based on diffraction modelling using just the on-axis SPL VituixCAD2’s approximation of off axis response out to 90 degrees:
It looks like you can take it out to ~3.8KHz.
Now is it a ATC SM75-150S beater? That's irrelevant because it's unavailable.
This D7608 is.
And I were to design a speaker with this, I'd be cautiously optimized about starting with an electrical LR2 high pass of 400Hz (and low pass 3.5KHz) and experiment with distortion testing, starting at 2.83V and stepping up to to 9V (...100dB)
Proceed with confidence my friends. Experiment.
This DIYourself audio, not Doubt it Yourself audio!
Based on Scan-Speak's IB response and the 0, 30 and 60 degree off axis charts, the -6dB beamwidth is 3KHz @ 45 degrees:
A skinny 6.25" wide cabinet with large round-overs would allow for wider dispersion.
How wide?
Based on diffraction modelling using just the on-axis SPL VituixCAD2’s approximation of off axis response out to 90 degrees:
It looks like you can take it out to ~3.8KHz.
Now is it a ATC SM75-150S beater? That's irrelevant because it's unavailable.
This D7608 is.
And I were to design a speaker with this, I'd be cautiously optimized about starting with an electrical LR2 high pass of 400Hz (and low pass 3.5KHz) and experiment with distortion testing, starting at 2.83V and stepping up to to 9V (...100dB)
Proceed with confidence my friends. Experiment.
This DIYourself audio, not Doubt it Yourself audio!
Last edited:
PS. My modelling was done with the current Scan-Speak datasheet.
Here’s a sample of the one with the faceplate
as tested by @ HifiCompass.
“Test baffle size – 1650x850 mm”
Yellow lines by me for emphasis of natural response on a quasi IB.
Yevgeniy measured it with 2nd order Butterworth high pass @ 500 Hz
As you know; a Butterworth filter has a -3dB at the cutoff point.
Reference:
https://hificompass.com/en/speakers/measurements/scan-speak/scanspeak-d7608/920010
If we need to play lower or louder we can use sleeper slopes…
@HiFiCompass
Dear Yevgeniy,
Do you recall testing this unit out of the box, or did you attach a small enclosure on the rear side?
Here’s a sample of the one with the faceplate
as tested by @ HifiCompass.
“Test baffle size – 1650x850 mm”
Yellow lines by me for emphasis of natural response on a quasi IB.
Yevgeniy measured it with 2nd order Butterworth high pass @ 500 Hz
As you know; a Butterworth filter has a -3dB at the cutoff point.
Reference:
https://hificompass.com/en/speakers/measurements/scan-speak/scanspeak-d7608/920010
If we need to play lower or louder we can use sleeper slopes…
@HiFiCompass
Dear Yevgeniy,
Do you recall testing this unit out of the box, or did you attach a small enclosure on the rear side?
@tktran303 That all looks pretty close to my findings. Thanks for posting this for us.
The test conditions SS used were with an infinite baffle and no chamber.
The practical HP cutoff is roughly 600 hz LR24, 700 hz BW18, 800 - 850 hz BW12 and 850 - 900hz LR12.
The practical max SPL before you can hear anything bad is mid 100s dB @ 800 hz LR12, which is pretty good IMO. I've used two mids with staggered LP and 650hz @ 18dB HP filters to get close to 110 dB max SPL with no discernable distortion.
The test conditions SS used were with an infinite baffle and no chamber.
The practical HP cutoff is roughly 600 hz LR24, 700 hz BW18, 800 - 850 hz BW12 and 850 - 900hz LR12.
The practical max SPL before you can hear anything bad is mid 100s dB @ 800 hz LR12, which is pretty good IMO. I've used two mids with staggered LP and 650hz @ 18dB HP filters to get close to 110 dB max SPL with no discernable distortion.
Sometimes 2 is better than 1 if you can accept the tradeoffs…..I’d be more inclined to us the Morel MD55 in this use case given the smaller size and closer C to C spacing obtainable. In these use cases, a ‘reasonable’ end user could/should employ a 19mm/.75 inch dome tweeter……around 3.5khz cross and you should see nice even dispersion out to +/-60 to 12khz or so.
That makes sense, but after having heard both the MDM55 and D7608 in various applications, the SS has the clear edge in terms of SQ and SPL capabilities. Don't get me wrong, the Morel is a very good mid, but it doesn't sound as detailed and open as the SS on vocals, strings or piano, despite being the smaller driver with a higher theoretical cutoff. The D7608 just sounds more agile and open overall. You can't cross the MDM55 as low either despite the claimed 2mm xmax. About 800 hz is the limit with a 12dB filter. Its better suited for small 3 ways with 8" LF drivers. They work very well in compact 3 way nearfield applications which need tight spacing to integrate drivers over a short distance. I still prefer to use the Morels in those situations.
A LP of 3.5k is optimal for mating the D7608 with smaller domes like the Seas 22TAF/G, SB 29RDNC and SB 26STCN. I've tried the good old Morel CAT378 with a 1st order filter along with the natural rolloff of the D7608 with good success, but the 10k peak of the SS needs to be notched out for that to work.
The most detailed metal dome which blends even better with the D7608 than the Seas is the pricier Audax TW025A28, but it only has a very slight edge. You wouldn't expect a metal dome to match the D7608 in harmonic character, but it does so more than most soft domes, likely due to the 2nd order HD profile around its upper rolloff.
The classic XT25 ring radiator also does well with the big SS dome, but it can't keep up in the dynamics department crossed with a 3.5k LR12 HP. You can hear the tweeter drawing attention to itself at higher SPLs and it begins to sound fuzzy.
The D7608 and Seas combo sounds effortless with acoustic, classical and string instrument music. Ribbons and planars work well too. The only major drawback is their narrow vertical dispersion can create an unnatural sounding off axis hole.
Theres a story behind my discovery of the D7608 which was purely by accident. The best combination I've tried came from a quick design using parts I already had thanks to a friend of a friend who didn't pay for parts he ordered and left me stuck with them. I came up with the idea to use a D7608 in a 3 way with the Audax TW025A28 and dual HM210C0 running in staggered LP (technically a 3.5 way). I used a bunch of left over crossover parts to throw a set of speakers together over a weekend, including the cabinets. I didn't even sim anything and just used a ton of clip leads, some white noise and my old Audio Control RTA to whip up a crossover in a few hours. I ended up living with these speakers for a few years in my main system.
I used to play Cello and believe to have a good ear for the instrument in a live setting - the above described 3 way played solo Cello so well, you could swear it sounded like the real instrument a couple of feet in front of you when closing your eyes. It was frightening how accurately proportioned the stereo image was.
Many years ago, a conductor friend of mine with a very picky set of ears auditioned the Audax/ScanSpeak 3 ways and gave me his critical feedback. He claimed it was the first time he could hear proper separation of string instruments in a full orchestra coming from non-elextrostat or planar speakers. He claimed the whole orchestra was correctly proportioned and balanced in the stereo image and couldn't believe the speakers were home made in a few days. This was coming from a man who owned the best Soundlab electrostats available at the time and was extremely critical when commenting on audio gear. He repeatedly said how clean and natural the mids sounded, even compared to his setup and he was even more surprised when I told him the type and cost of the drivers. I removed one of the D7608s and showed him what it looked like inside. His jaw dropped and he commented "how is that flimsy plastic frame driver making all that beautiful music?"...
The D7608 is that good compared to many other mids costing more, regardless of design. There's obviously nothing really special about it other than being a dome mid - no shorting rings or a fancy motors either.
If you insist on the Morel MDM55, the best tweeter match is the CAT378 for several reasons. The primary one is the perfect acoustic center alignment, but also the softer smoother character and the ability of the CAT378 to use 1st order filters without much drama.
For most people, the SPL capability of a single D7608 is more than enough for domestic use and even in a monitor application. I'm a bit more demanding when it comes to dynamic range, so running two SS mid domes with staggered filters is my preference as long as the CTC spacing isn't conflicting with the chosen crossover.
There are of course alot more choices in mid domes. The more expensive and exotic Bliesma mids are very nice, but also very expensive. A pair of silk or Alu M74s is over $800 here in the US. I can buy a pair of D7608s for just over $200, which are capable of 90 percent of the performance at that price. The lack of a rear chamber can be an advantage to the more experienced designer, so there are some benefits.
The people who claim a cone mid can do just as well or better likely haven't heard how good a well implemented large dome mid can sound. You'll be spending at least $200 on a cone mid that can come close to the harmonic capability of the D7608. No, its not perfect and it definitely is a difficult driver to work with, but its capable of reproducing very complex details an average cone mid usually can't.
Even the smaller MDM55 is a step above most cone mids. The only thing which can do better is a very well designed horn system, but those are even more expensive and tricky to work with. The SS dome has the right balance of detail and smoothness. When correctly implemented, it just disappears into the room. The FR curve looks ugly on paper, but it performs alot better in the flesh.
A LP of 3.5k is optimal for mating the D7608 with smaller domes like the Seas 22TAF/G, SB 29RDNC and SB 26STCN. I've tried the good old Morel CAT378 with a 1st order filter along with the natural rolloff of the D7608 with good success, but the 10k peak of the SS needs to be notched out for that to work.
The most detailed metal dome which blends even better with the D7608 than the Seas is the pricier Audax TW025A28, but it only has a very slight edge. You wouldn't expect a metal dome to match the D7608 in harmonic character, but it does so more than most soft domes, likely due to the 2nd order HD profile around its upper rolloff.
The classic XT25 ring radiator also does well with the big SS dome, but it can't keep up in the dynamics department crossed with a 3.5k LR12 HP. You can hear the tweeter drawing attention to itself at higher SPLs and it begins to sound fuzzy.
The D7608 and Seas combo sounds effortless with acoustic, classical and string instrument music. Ribbons and planars work well too. The only major drawback is their narrow vertical dispersion can create an unnatural sounding off axis hole.
Theres a story behind my discovery of the D7608 which was purely by accident. The best combination I've tried came from a quick design using parts I already had thanks to a friend of a friend who didn't pay for parts he ordered and left me stuck with them. I came up with the idea to use a D7608 in a 3 way with the Audax TW025A28 and dual HM210C0 running in staggered LP (technically a 3.5 way). I used a bunch of left over crossover parts to throw a set of speakers together over a weekend, including the cabinets. I didn't even sim anything and just used a ton of clip leads, some white noise and my old Audio Control RTA to whip up a crossover in a few hours. I ended up living with these speakers for a few years in my main system.
I used to play Cello and believe to have a good ear for the instrument in a live setting - the above described 3 way played solo Cello so well, you could swear it sounded like the real instrument a couple of feet in front of you when closing your eyes. It was frightening how accurately proportioned the stereo image was.
Many years ago, a conductor friend of mine with a very picky set of ears auditioned the Audax/ScanSpeak 3 ways and gave me his critical feedback. He claimed it was the first time he could hear proper separation of string instruments in a full orchestra coming from non-elextrostat or planar speakers. He claimed the whole orchestra was correctly proportioned and balanced in the stereo image and couldn't believe the speakers were home made in a few days. This was coming from a man who owned the best Soundlab electrostats available at the time and was extremely critical when commenting on audio gear. He repeatedly said how clean and natural the mids sounded, even compared to his setup and he was even more surprised when I told him the type and cost of the drivers. I removed one of the D7608s and showed him what it looked like inside. His jaw dropped and he commented "how is that flimsy plastic frame driver making all that beautiful music?"...
The D7608 is that good compared to many other mids costing more, regardless of design. There's obviously nothing really special about it other than being a dome mid - no shorting rings or a fancy motors either.
If you insist on the Morel MDM55, the best tweeter match is the CAT378 for several reasons. The primary one is the perfect acoustic center alignment, but also the softer smoother character and the ability of the CAT378 to use 1st order filters without much drama.
For most people, the SPL capability of a single D7608 is more than enough for domestic use and even in a monitor application. I'm a bit more demanding when it comes to dynamic range, so running two SS mid domes with staggered filters is my preference as long as the CTC spacing isn't conflicting with the chosen crossover.
There are of course alot more choices in mid domes. The more expensive and exotic Bliesma mids are very nice, but also very expensive. A pair of silk or Alu M74s is over $800 here in the US. I can buy a pair of D7608s for just over $200, which are capable of 90 percent of the performance at that price. The lack of a rear chamber can be an advantage to the more experienced designer, so there are some benefits.
The people who claim a cone mid can do just as well or better likely haven't heard how good a well implemented large dome mid can sound. You'll be spending at least $200 on a cone mid that can come close to the harmonic capability of the D7608. No, its not perfect and it definitely is a difficult driver to work with, but its capable of reproducing very complex details an average cone mid usually can't.
Even the smaller MDM55 is a step above most cone mids. The only thing which can do better is a very well designed horn system, but those are even more expensive and tricky to work with. The SS dome has the right balance of detail and smoothness. When correctly implemented, it just disappears into the room. The FR curve looks ugly on paper, but it performs alot better in the flesh.