SB Acoustics SB65WBAC25-4 - What to do?

mayhem13

Member
2008-09-22 4:37 am
You seem, subjectively speaking, like to appreciate distortion products, then.

I had them both, intended to be used in a multiway system. For me, listening to a sine-sweep, the SB was not perfect, but comfortably ok. The Peerless instead subjectively failed right away.

Measured with a NT passband filter (800Hz ... 3.5kHz) shows that under this specific condition, the SB is clearly superior to the Peerless:

SB (sine thd)
HD_SB_NT2_800-3500.png

Peerless (sind thd)
HD_PeerLess_NT2_800-3500.png

Under same conditions, SB produced 1% thd @ 1kHz, whereas Peerless produced 10% thd @ 1kHz.

SB (im multitone)
MultiTone_SB_NT2_800-3500.png

Peerless (im multitone)
MultiTone_PeerLess_NT2_800-3500.png

In Multitone test same picture - SB showed less IM poducts than Peerless


Make your choice ...

Hence my caution in adding 'subjectively speaking' LOL. I focused my listening on the driver as a fullrange unit and cue'd on off axis listening and found the Peerless superior and found the overall detail and balance superior as well......sometimes a biproduct of 2nd order HD.......can't slice that any farther than countless people who seem to prefer the organic sound of lower even order HD......and then there's the whole vinyl vs digital thing...LOL
 

stephdyn

Member
2019-03-06 4:56 am
I've done this enclosure for sb65wbac25 driver :)
 

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I'm wondering xrk971

xrk971 why not in a TABAQ or in a Martello ?
Buy the way, is it easy for you to "plot" this SB65....-4 like you did for DCR (I don't like 4 Ohms BUT) in the above mentioned boxes ?
Of course the device (as I understand) is not sensitive enough for a TABAQ but for close listening 2~3 meters/yards equilateral triangle between speakers and listener in comfortable level (let say 45 ~ 60 dB spl), maybe ideal (or not ? :confused: )
 
Nah, I wouldn't bother.

A TL would be too big for such a small speaker which could only deliver some bass at very near field.

The SB65's strength is not in bass output, but in the high reach and wide dispersion it delivers.
Asking it to put out meaningful bass will only detriment its strength.
 
normal conversatione level

According to some measurements (found on the net) a normal conversation is about 60Db. 65Db I believe is quite suficient for listening music (not for partying).


xrk in "Viva la Vifa" there is a curvy DCR for TC9 with 3 ports. In the proposed DCR here #5 you proposed 2 ports. The ratio between the 2 chambers is 2/1 ? The first (bigger chamber) has port only to the small ? Did you made any foam box to verify the given curves on "Here is corresponding max SPL" (80Db at about 80Hz ! Quite impressive). Is it possible (if I don't bother you) to post a sketch of the proposed DCR ?


Elias
 
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A DCR has two ports and volume ratio was 2:1 for upper vs lower chamber. I think my proposal was to extend this to a triple chamber reflex or TCR, but I never did that and don’t think much would be gained. The DCR provides better control of cone excursion and provides a nicer quality of bass as there are two chambers tunes to different frequencies. For the TC9FD, sensitivity was about 86dB and with a typical -5dB baffle step loss that is 80dB at 2.83vrms.

The SB65 is 82dB at 2.83v and with -5dB baffle step loss would be about 77dB at 2.83v. So indeed 65dB is very doable. I think a DCR would be a good alignment for this driver rather than a MLTL. I’ll work on that when I get some time.

Here was design for TC9FD DCR:
404866d1394457584-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-plan-png


Here was sound from DCR vs various ports and integrated sound. As you can see the sound falls off in bass so a baffle step compensation circuit is needed to shelve the higher frequencies. Probably a 0.5mH cool and circa 2-3ohm resistor in parallel.

404874d1394457660-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-1-meter-integrated-ports-no-bsc-spl.png


I made fancy curved walls to reduce diffraction and skinny slot ports but all that can be replaced worh prismatic box and round tubes.

404871d1394457584-viva-la-vifa-curvy-cabinet-dcr-tc9fd-dcr-vifa-photo-04.png
 
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DCR Design

Here is a pretty compact design for a DCR (dual chamber reflex) for the SB65WBAC25-4 driver. It really should not be used above 2.83vrms input (or about 2w of power) if you have much musical content below 50Hz. This will give you about 80dB SPL - good level for near field desktop listening.

These are inside dimensions so external will depend on your wood thickness.

3.5in wide x 6.5in deep x 10in tall (total). So if using 1/2in ply, add 1.5in to the height since there is a divider plus top and bottom. Each external vent is 1in dia (ID) tube x 3.5in long, the inter-chamber vent is 1in dia x 1.2in long. Needs a special BSC filter comprised of 3 components in parallel: 0.2mH air core inductor (20ga copper) + 3.3ohm 2W or higher resistor (use Panasonic ERX or KOA Speer BPR, or any metal thin film) + 3.3uF MKP film capacitor. Line inside of chamber with felt and add small amount of polyfill stuffing. Be sure to roundover the backside of the driver cutout to allow free air flow around the basket.

Here is predicted frequency response (4pi space - sitting on stand in middle of room):
attachment.php


Here is predicted cone excursion at 2.83v rms:
attachment.php


I think it will sound very good with bass extension down 57Hz (-6dB), although any bass below 200Hz will tend to have significant distortion due to the high cone excursions. But play around 70dB and you will be fine.

You can adjust the 3.3ohm resistor to taste. Smaller value for brighter sound. On front baffle, use nice 1/2in radius roundover to minimize baffle diffraction. Flush mount the drivers with a rebate as that helps improve imaging and reduces diffraction. Put the BSC filter on bottom chamber bottom wall to add weight to stabilize the speaker.
 

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OllBoll

Member
2010-11-22 11:24 pm
Those drivers are pretty nice, perform really well in a dipole setup too:

First is a single driver naked with EQ, and then in a small 4x setup half drivers inverted. First is without EQ and second with.
 

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OllBoll

Member
2010-11-22 11:24 pm
OB,
Very nice result. Never thought to use them bare as a dipole before.

What causes the sharp dip at 2.7kHz?

819238d1582420247-sb-acoustics-sb65wbac25-4-a-sb65-naked-90-180-png

My guess is something caused by the magnet structure on the rear. I have seen it on every driver where the magnet is large compared to the cone, and worse the bigger comparatively it is. A similar dip is present in coaxial drivers with large waveguides for the tweeter, like the RCF CX10N251.