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Multi-Way Conventional loudspeakers with crossovers

Yet another 6+1 construction: SB17MFC35-8 + SB26ADC-C000-4
Yet another 6+1 construction: SB17MFC35-8 + SB26ADC-C000-4
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Old 25th August 2016, 04:59 PM   #1
DIYBras is offline DIYBras  Brazil
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Default Yet another 6+1 construction: SB17MFC35-8 + SB26ADC-C000-4

Hello fellows from DIYAudio,

Oh... my first thread, after one year of participation here

Here is my new construction using polypropylene cone speaker and aluminum tweeter of the SB Acoustics. This is not anything new. Designers like Troels Gravesen have done their versions.
This project was born of a need and a curiosity: I was curious to know the results so acclamed about the high Qm speakers***, and so I chosen this SBA. Also chosen why I had not yet experienced playing with polypropylene speakers, and maybe it was the kind of sound I was looking for ...
I already had a pre-assembled box, only missing the front. Time to apply the speakers! I decided to imitate Troels using stepped baffle and LR-2 crossover. The point is that Troels no longer publishes the crossovers values, and rightly so, given the circumstances that occurred to him. And their project do not match 100% with my project, which differ in dimensions. Time to learn more about crossovers!
Soon I publish some measurements and the resulting crossover after some iterations. But I advise here: I'm a newbie about acoustical measurements, and my apartment is small, so everything below 1kHz or so is a disaster... but at least the cross point is higher than that.
And is a working in progress: if knowledge permits, some refinements are in order

***but I have much fear about power compression, due to lack of the inherent "heatsink" in this fiberglass former, in comparision with the more common aluminium VC former.
Attached Images
File Type: jpg 20160824_130437.jpg (66.4 KB, 1211 views)
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Last edited by DIYBras; 25th August 2016 at 07:51 PM.
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Old 25th August 2016, 05:18 PM   #2
DIYBras is offline DIYBras  Brazil
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Some measurements, starting with the resulting impedance
The box is ported but at moment I have at work and don't remember the resulting dimensions.
Interesting is: the crossover point is 2.5kHz, but the impedance hump occurs at 1kHz (well, several projects have same resulting Z, anyway...)
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File Type: png MFC+AL 3.png (48.7 KB, 1185 views)
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Old 25th August 2016, 05:31 PM   #3
DIYBras is offline DIYBras  Brazil
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WARNING : Some acoustical measurements, for some tries

"Almost all" using 1/6dB smooting and some 6~7ms gating

For the 7th figure (last figure), with portuguese inscriptions, note the higher measurement, is the most flat response I can obtain until today. +/-3dB or so from midrange up is not tooo bad, but is only at WOOFER axis ("nível do AF"). At this point, the midrange/low treble response with most music are basically neutral.

For the 5th figure, various vertical angles. Maybe the cross point are not yet well matched, since the vertical response changes too much (even considering the stepped baffle, I think). maybe need some refinement.

For the 6th figure, is to check the horizontal dispersion. The purple/blue (what a color...) is a extreme angle, so the tweeter HF suffers, but obviously the cross response is OK here (relative to not change with angle).

The first other figures are the first attempts, and I love to use too much the overlays Some show the attempts to match the desired response per driver/to match the L-R 2 target.

Since this is work at progress, tomorrow will have some new measurements, including HD sweep
Attached Images
File Type: png MFC+AL 1.png (60.0 KB, 1130 views)
File Type: png MFC+AL 2.png (63.6 KB, 1092 views)
File Type: png MFC+AL 4.png (59.7 KB, 1078 views)
File Type: png MFC+AL 5.png (63.8 KB, 145 views)
File Type: png MFC+AL 6.png (53.1 KB, 119 views)
File Type: png MFC+AL 7.png (49.7 KB, 113 views)
File Type: png MFC+AL 8.png (62.6 KB, 149 views)
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Last edited by DIYBras; 25th August 2016 at 05:34 PM.
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Old 25th August 2016, 08:02 PM   #4
DIYBras is offline DIYBras  Brazil
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About the "polemical" thing, the sound...

Like I said, is well balanced at woofer axis. And respectable outside that, but maybe some refinement is required.
But I don't noted sooo much difference in "resolution" (relative to high-Qm fame), instead I noted since first time a strong, more "resonant" bass, if compared, for example, with the Mark K ER18+DXT. In MarkK the bass is more lean but more true to original (this from memory; the MarkK-based is with a friend now). In these SB, the bass is more perceptible but have a little tendency to booming. Of course, very different drivers, but here is the results.
In fact, is fun to listen bass-heavy in these SB, like some electronic, reggae, and "bass noise disc testers". You can listen easily 36Hz notes even without EQ and with electronic music with strong vocals and midrange content etc.
About my results with ER18+DXT, see: Mark K's er18dxt
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Last edited by DIYBras; 25th August 2016 at 08:06 PM.
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Old 26th August 2016, 02:20 AM   #5
system7 is offline system7  United Kingdom
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I saw this project: SBAcoustics-61-MFC

It's a fairly useless low inductance polycone, IMO. Most 6" polycones rolloff faster, and don't have all that hash around 6kHz!

Makes hard work with crossover, especially time-aligned, where LCR (What? 3.9uF/0.2mH/2.2R for 6 kHz?) notches don't work so well. Maybe a ca. 0.5mH coil after the shunt in the bass filter, third order would help?

I found the quick and dirty crossover looked OK. I think I'd start there. Just don't know if the 6kHz breakup will be annoying. I didn't get reverse polarity on the tweeter for some reason. I added a Zobel, because metal tweeters sound better with them IMO.

I don't like this one, TBH. It seems to all work better on flat baffle.
Attached Images
File Type: png SB Acoustics Style Time Aligned.PNG (7.3 KB, 297 views)
File Type: png SB Acoustics 2nd order FR.PNG (17.5 KB, 311 views)
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Old 26th August 2016, 11:44 AM   #6
DIYBras is offline DIYBras  Brazil
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SB Acoustics SB17NAC35-4 measurements!
In fact, the poly version is not better than the metal version... for some, is worse

system7, I considered using another crossover order, and cut the tweeter lower, but the temptation to get the LR2 was big (and to experiment with stepped baffle). Personally I'm about to give up the decision, because the response does not behave well at vertical, although the end user of this box (which is a friend of mine) is already amazed with the current results. For him I already declare terminated the project. He is used to listen mini-systems and micro-systems, and this is already a revelation for him. And for serious listening, the window is comfortable large (far larger than full ranges, for example).
By the way, at this time will be difficult to change the box front, so I'm stuck with stepped baffle...

Follow the resulting crossover, for now. The component quantity is based on Troels project . The tweeter notch is made oversized, to cut down the response at tweeter resonance (is awful sounding) and to match the 100µF elcap.
By the way, even the Troels solution has some response anomaly near cross point.

I don't used speaker crossover simulator to obtain the values. I played with component values, starting from some other LR2 projects, and arrived here.

A remark about vertical response: It gets worse as it rises above the tweeter level, and not much worse towards the speaker down. My preferred solution? Use the box upside down! Is easier than try to mess with crossover... But results ugly aesthetically... Or use a stand to match the woofer a little higher than ear level.
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File Type: jpg 20160825_194916.jpg (59.8 KB, 297 views)
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Last edited by DIYBras; 26th August 2016 at 11:46 AM.
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Old 26th August 2016, 11:58 AM   #7
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Some measurements with box upside down only to confirm the inversion of low/high vertical response (not noted in graph, but confirmed in practice)
The resulting actual crossover Z, with some zoom. Note some glitch at near 400Hz; maybe need more stuffing
The HD stepping with 2.83V. For sure that SB distorts more than the Seas ER18 in bass department (now I need to find my ER18+DXT measurements...)
Attached Images
File Type: png MFC+AL 9.png (50.2 KB, 221 views)
File Type: png MFC+AL 11.png (46.6 KB, 81 views)
File Type: png MFC+AL 13.png (50.7 KB, 82 views)
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Old 27th August 2016, 02:46 AM   #8
system7 is offline system7  United Kingdom
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I've never liked second order with 6" bass. You can't get steep slopes on the bass, and so you hear breakup IMO.

I was looking at SB Acoustics EKA design, below. Add 18mm offset for time alignment, tweeter recess, by all accounts, which seems about what Troels and you did.

4 ohm NRX woofer: 6" SB17NRXC35-4 :: SB Acoustics

8 ohm bassier but less efficient MFC woofer with far less breakup: 6" SB17MFC35-8 :: SB Acoustics

Anyway, it's the design that seems to line up phase nicely. It's third order in effect, but phase aligned. I like the look of it. Conversion to 8 ohm is just a question of adding 50% or so to coils and resistors, and reducing caps by a third. My own sim slightly disagreed, but I was using a higher inductance bass.

But what's not to like? 25dB down at 5kHz electrically, so no nasty breakups. Sort of thing I'd build and tune by ear. Tweeter level particularly. 10 ohms seems a lot! I'd suspect it could be smaller. But it's near enough the old KEF tweeter filter adjusted to 4 ohms.

So, IMO, this EKA filter is the right concept here. Just needs tuning. See with low inductance bass, you often add back some inductance and it then behaves like high inductance with second order to give you overall third order.
Attached Images
File Type: png SB Acoustics EKA.PNG (19.4 KB, 236 views)
File Type: png SB Acoustics Rough Sim Circuit.PNG (8.1 KB, 242 views)
File Type: png SB Acoustics Rough Sim.PNG (14.9 KB, 244 views)
File Type: png SB Acoustics Rough Sim Phase.PNG (15.4 KB, 163 views)
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Last edited by system7; 27th August 2016 at 02:50 AM.
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Old 29th August 2016, 12:50 PM   #9
DIYBras is offline DIYBras  Brazil
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Quote:
Originally Posted by DIYBras View Post
Some measurements with box upside down only to confirm the inversion of low/high vertical response (not noted in graph, but confirmed in practice)
The resulting actual crossover Z, with some zoom. Note some glitch at near 400Hz; maybe need more stuffing
The HD stepping with 2.83V. For sure that SB distorts more than the Seas ER18 in bass department (now I need to find my ER18+DXT measurements...)
OOPS; ERRATA: the last graph are not the HD sweep. Here is it:
Is not bad; in fact, at this power level, the higher-order HD from midrange up is almost absent. And sounds smooth and "round". Comparing with some others measurements I have made, this is a good result. Even the ER18+DXT have more high order grunge than this (except in bass department).
Attached Images
File Type: png MFC+AL 12.png (59.5 KB, 152 views)
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Last edited by DIYBras; 29th August 2016 at 12:57 PM. Reason: Additional info
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Old 29th August 2016, 01:13 PM   #10
DIYBras is offline DIYBras  Brazil
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Quote:
Originally Posted by system7 View Post
I've never liked second order with 6" bass. You can't get steep slopes on the bass, and so you hear breakup IMO.

I was looking at SB Acoustics EKA design, below. Add 18mm offset for time alignment, tweeter recess, by all accounts, which seems about what Troels and you did.

4 ohm NRX woofer: 6" SB17NRXC35-4 :: SB Acoustics

8 ohm bassier but less efficient MFC woofer with far less breakup: 6" SB17MFC35-8 :: SB Acoustics

Anyway, it's the design that seems to line up phase nicely. It's third order in effect, but phase aligned. I like the look of it. Conversion to 8 ohm is just a question of adding 50% or so to coils and resistors, and reducing caps by a third. My own sim slightly disagreed, but I was using a higher inductance bass.

But what's not to like? 25dB down at 5kHz electrically, so no nasty breakups. Sort of thing I'd build and tune by ear. Tweeter level particularly. 10 ohms seems a lot! I'd suspect it could be smaller. But it's near enough the old KEF tweeter filter adjusted to 4 ohms.

So, IMO, this EKA filter is the right concept here. Just needs tuning. See with low inductance bass, you often add back some inductance and it then behaves like high inductance with second order to give you overall third order.
Very interesting propositions! And I like the "external" coil, since most speakers varies the inductance with displacement, even this MFC/NRX/NAC line (the Satori varies almost none). So is good to put it out of equation, or reduce the contributions magnitude. By the way, the VC inductance value is not a guarantee of linearity: The JA-8008 I have in Troels TQWT have almost zero inductance change, measured by John from Zaph Audio, despite high VC inductance.
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