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SB Acoustics SB65WBAC25-4 - What to do?
SB Acoustics SB65WBAC25-4 - What to do?
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Old 19th April 2015, 12:05 PM   #1
xrk971 is offline xrk971  United States
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SB Acoustics SB65WBAC25-4 - What to do?
Default SB Acoustics SB65WBAC25-4 - What to do?

I now have a pair of these really cute 2.5in drivers - they seem to have some nice specifications on paper. They look very well made and superb fit and finish - I am impressed by the quality from SB Acouatics. I have heard some great recommendations of this little guy - great HF extension almost aluminum dome tweeter like. Oh wait, it is about the size of an aluminum dome tweeter.

The neat thing is that with an xmax of 5.3mm and a moderate Qts, it can reach sub 100Hz in the right enclosure. Sure, if I run this in a FAST XO at 400Hz it would work very well. But given the huge xmax, I want to see what creative uses we can all come up with. Does anyone have experiences of good boxes that they have tried?

Click the image to open in full size.


SB Acoustics :: 2 1/2" SB65WBAC25-4


My first thought is to make a small BLH for it. Maybe a hybrid BVR type BLH... Like a mini Decware DNA.
Attached Images
File Type: jpg image.jpg (87.3 KB, 1478 views)

Last edited by xrk971; 19th April 2015 at 12:22 PM.
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Old 19th April 2015, 12:34 PM   #2
zman01 is offline zman01  Bangladesh
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SB Acoustics SB65WBAC25-4 - What to do?
xrk971,

Specs are nice...have you simmed anything yet? What about a mini-mini-Karlsonator?

Given the limited cone size, would the driver be able to go sufficiently loud while being pushed low? Maybe good for nearfield/DT usage? How about Labyrinth TLs?

BLH or BVR would be big?
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Old 19th April 2015, 01:37 PM   #3
xrk971 is offline xrk971  United States
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SB Acoustics SB65WBAC25-4 - What to do?
Initial sims of DNA scaled to 0.5x look promising with 80Hz bass extension and no BSC necessary. 4in wide x 6in deep x 14in tall box.
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Old 20th April 2015, 01:07 AM   #4
xrk971 is offline xrk971  United States
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SB Acoustics SB65WBAC25-4 - What to do?
Default DNA mini (0.45x scale) with SB65WBAC25-4

Before I describe the sim, I figured out how to memorize this driver's long name: SB 65 (mm nominal dia) Wide Band Aluminum Cone 25mm (voice coil) - 4 (ohms).

Ok, so if we take this design, nominally for a 5in driver, and cut the size down by about half and use it for a 2.5in driver that should be OK, right? Well, not quite and luckily for us, the DNA is not a true horn so the tuning frequency is set more by the chamber and vent size which forms part of the hybrid bass reflex part of the DNA, the other half being a rear facing "horn" that provides impedance matching of the BR duct to the environment.

Here is a rendering of the DNA (from website):

An externally hosted image should be here but it no longer works. Please upload images instead of linking to them to prevent this.


Here is my reverse engineered dimensions of the full scale DNA:

Click the image to open in full size.

If we scale this drawing by 0.45x (easy to apply in the existing Akabak model). The true size is about 3.6in wide (internally) x 12.375in tall (externally) x 5.75in deep (externally). That is a tiny rear-firing hybrid-BR-horn speaker. Then add a 1.7in dia x 6in long vent tube between the driver chamber and the first segment of the horn. This is what you get in 4pi space with diffraction and reflection turned on but walls are far away. The sensitivity is not good but at least the bass levels are high enough to overcome baffle step losses:

Click the image to open in full size.

Here is the corresponding cone displacement at xmax:

Click the image to open in full size.

And this is the SPL output at xmax with 6v of drive:

Click the image to open in full size.

So it seems that it is really excursion limited and you won't get much SPL out of this. However, for near field use, probably OK. The result of using such a tiny driver to get bass is problematic as we can see. A better true horn loaded design will enable this to go to much higher SPL's.
Attached Images
File Type: png DNA-plan-Rev-Engr.png (612.1 KB, 1345 views)
File Type: png DNA-SB65WBAC25-4-Displ-2.83v.png (8.4 KB, 70 views)
File Type: png DNA-SB65WBAC25-4-Freq-1m.png (39.6 KB, 1322 views)
File Type: png DNA-SB65WBAC25-4-Displ.png (8.6 KB, 1310 views)
File Type: png DNA-SB65WBAC25-4-Freq-1m-max-SPL.png (15.6 KB, 1312 views)

Last edited by xrk971; 20th April 2015 at 01:19 AM.
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Old 20th April 2015, 11:54 AM   #5
xrk971 is offline xrk971  United States
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SB Acoustics SB65WBAC25-4 - What to do?
Default A Tiny 62Hz DCR?

This is a very easy build and certainly not as fancy as the mini DNA, but achieves a remarkably flat, albeit lower sensitivity system. For near-field monitors or PC soeakers, the lower sensitivity may not be an issue.

The box is 4in wide x 6in deep x 12in tall (quite small). The slot vents are 4in wide x 0.4in high x 4in long. The interchamber vent is 1.6in dia round tube that is 1.33in long. A BSC circuit was used to balance lows and highs as follows: 0.3mH + 4ohm + 3.3uF all in parallel. The result is truly an amazingly flat response. If the driver tracks this, it could be a mini monitor.

Here is predicted SPL at 2.83v and 1m away in 4pi space:

Click the image to open in full size.

Here is corresponding cone displacement at xmax (5.3mm) reached with 6,5 volts of drive:

Click the image to open in full size.

Here is corresponding max SPL:

Click the image to open in full size.

Here is Impedance of system:

Click the image to open in full size.

Note that higher SPL's can be achieved if high passed at say 55Hz.
Attached Images
File Type: png DCR-SB65WBAC25-4-Freq-1m.png (17.4 KB, 1673 views)
File Type: png DCR-SB65WBAC25-4-Displ.png (8.3 KB, 1290 views)
File Type: png DCR-SB65WBAC25-4-Max-SPL-1m.png (15.9 KB, 1304 views)
File Type: png DCR-SB65WBAC25-4-Impedance.png (8.3 KB, 1290 views)
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Old 20th April 2015, 12:18 PM   #6
IG81 is offline IG81  Canada
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It appears SB specifies Xmax as a peak-to-peak value though, so it's more like 2.65mm, assuming symmetry of whatever factor they specify Xmax upon. Neat nevertheless, though the 4" to 5" range is more of a sweet spot for me when it comes to small FR drivers.
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Old 20th April 2015, 12:28 PM   #7
xrk971 is offline xrk971  United States
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SB Acoustics SB65WBAC25-4 - What to do?
IG81,
Thanks for pointing the xmax out - in the case of 2.6mm it is like a TC9FD but not so sure any vented design makes sense given the low sensitivity. I might make it for grins but seems like this is best for a FAST high passed above fs. Probably where it shines is to act like a mid tweeter. The 1im aluminum dome dustcap probably sounds a lot like a good dome tweeter as it goes above 20kHz.
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Old 20th April 2015, 12:36 PM   #8
IG81 is offline IG81  Canada
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Been there. I was looking at the SB16PFC25-08 for a simple 2-way design a while back and thought it was weird Xmax was 9mm for a 6", until I went back to the spec sheet and noticed the "(p-p)" I had missed the first time around.
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Old 20th August 2015, 01:32 AM   #9
jeshi is offline jeshi  Japan
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I originally posted this over on the thread A Subjective Blind Comparison of 2in to 4in drivers - Round 3, but I thought it would be worth reposting here....

Quote:
Originally Posted by jeshi View Post
I Decided to order the SB65WBAC25-4 after this listening test. It was my top pick (H), the measurements and specs are good and I have great experience with SBacoustics drivers in the past.
It arrived and I am very impressed!!
Tiny little thing, but it is definitely fullrange.
Click the image to open in full size.

It is actually quite dynamic and has a delicate detailed treble like a dome tweeter. Even though this is just first impressions, but I think I like it better than the fe83en and ff105wk that I currently have (still waiting for EuropeAudio to ship my 10f/8424 grrr).
The SB65 really has a beautiful clarity and purity to them, but also have a surprising dynamic punch in the midbass. Almost sounds like a 3" or 4" driver but with a dome tweeter like clarity.

And mine actually measures even flatter than the one XRK shows here!
I made measurements here at 90db at 0.5m, which I think is higher than XRK's tests. At this level the drivers are quite loud. I am not sure how to measure the voltage (AC across the speaker terminals?). Maybe the voltage ranged from 1.3-1.8volts during the sweep. My measurements are fullrange and yes I did put 30hz into that little driver (poor thing), but the xmax on this thing is amazing (5.3mm p-p) for such a tiny driver.
Click the image to open in full size.
Click the image to open in full size.

compared to XRK's measurement (with the 350hz XO to RS225)which I believe are at a lower output level than my measurements
Click the image to open in full size.

here is a measurement at 12cm when it first arrived, and fitting it to a target curve with a bass rolloff of 12db/oct at 145hz.
This is super flat with most of these bumps at 2-3db (no eq of course, just the raw driver in a sealed box)
Click the image to open in full size.
Unfortunately the local distributor only had 1 left, but when they get more, I am very tempted to pick up more (maybe do a small line array). But I should probably wait till the 10f arrive before I get too caught up in yet another driver purchase.
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Old 20th August 2015, 01:54 AM   #10
jeshi is offline jeshi  Japan
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I need to wait for more drivers to get back in stock at the local distributor in Japan (shipping is almost too much for these little drivers from US or EU). But I am thinking about putting 2x or 3x into a line array on the edge of a slot-loaded open baffle woofer.

something like this but where the 20cm (8") woofer is not forward firing but a single pair is slot loaded. A folded W version of Nelson Pass's SLOB The Slot Loaded Open Baffle Project Article By Nelson Pass.

In Nelson's design he uses 6x 8" woofers in each slot but he is planning for these to be big room filling speakers. My aim is more a high quality, low distortion near-field monitor.
Click the image to open in full size.
SB Acoustics SB65WBAC25-4 - What to do?

This would make a small (for OB) approximately 30cm x 40cm x 30cm open-backed box (folded OB) which could be used near-field or in a room. The reason I am leaning toward a small line-array is that the drivers max SPL does seem a bit limited if we want to keep distortion under control.

Something similar to this in basic design and end result http://www.atcloudspeakers.co.uk/pro...rs/scm25a-pro/ but with OB woofer and line array of mid/tweets (SB65)
SB Acoustics SB65WBAC25-4 - What to do?
Attached Images
File Type: png sb65-linear-array-SLOB.PNG (16.6 KB, 1156 views)
File Type: png sb65-linear-array-SLOB-edge.PNG (81.6 KB, 42 views)

Last edited by jeshi; 20th August 2015 at 02:19 AM.
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