Over the years, I've dissected a handful of mostly blown tweeters. The ones with lower Fs are all equipped with a rear chamber. Basically the center portion of the magnet structure inside the voice coil/slot is a hollow tube that goes right through the magnet structure. The backside is closed by a (usually) plastic cap which enlarges the air chamber and seals it behind the dome. Sometimes, these spaces are filled with damping -- poly fiber, foam, etc. -- which appears to lower the amplitude and Fs, if only a touch.
The SB Acoustics SB26ADC is a current DIYAUDIO darling for its good performance & modest price. Equipped with a small rear chamber, my sample of this tweeter has a Fs of 590 Hz with a peak of just 6 ohms ( double the 3 ohm norm). Xmax is rated for1.2mm (p-p), high in comparison to most other tweeters, even larger ones. The Wavecor TW030WA11, for example, a 30mm dome with Fs of 440 Hz, is rated for Xmax 0.4mm (0.8mm p-p).
Here are pics of a disassembled SB26ADC.
Unlike the 29mm series, the 26mm dome/coil appears to be user-replaceable. Clearly visible in the magnet structure is the copper ring inside the slot for the VC/former, the hollow within, and a cone on the inside of the plastic back cover. That cone is probably to reduce standing waves between the dome & the back. No damping material.
This pic shows the back cover; the total depth of the air space behind it might be 4-5mm.
It seems pretty obvious that if the total rear chamber space was enlarged, Fs would drop. Would this allow operation to a lower frequency, especially with a 6" Augerpro waveguide?
I'm want to cross as low as 1200 Hz. The high Xmax of the SB26 might make this safe enough? Or at least 1500 Hz.
The main benefits for me are... better power response in 2-way xover with 8" (or even bigger) woofer, improved dispersion/power to higher frequencies. Plus all the positives we already know about the SB26.
The mod itself looks like it should not be difficult: Pry the plastic back cover off and replace it with a half ( or smaller) portion of a hard plastic ball of suitable size. Fill it with poly or wool fibers to control resonances. I'm tempted try but would prefer not to destroy the back cover.
Thoughts anyone?
The SB Acoustics SB26ADC is a current DIYAUDIO darling for its good performance & modest price. Equipped with a small rear chamber, my sample of this tweeter has a Fs of 590 Hz with a peak of just 6 ohms ( double the 3 ohm norm). Xmax is rated for1.2mm (p-p), high in comparison to most other tweeters, even larger ones. The Wavecor TW030WA11, for example, a 30mm dome with Fs of 440 Hz, is rated for Xmax 0.4mm (0.8mm p-p).
Here are pics of a disassembled SB26ADC.
Unlike the 29mm series, the 26mm dome/coil appears to be user-replaceable. Clearly visible in the magnet structure is the copper ring inside the slot for the VC/former, the hollow within, and a cone on the inside of the plastic back cover. That cone is probably to reduce standing waves between the dome & the back. No damping material.
This pic shows the back cover; the total depth of the air space behind it might be 4-5mm.
It seems pretty obvious that if the total rear chamber space was enlarged, Fs would drop. Would this allow operation to a lower frequency, especially with a 6" Augerpro waveguide?
I'm want to cross as low as 1200 Hz. The high Xmax of the SB26 might make this safe enough? Or at least 1500 Hz.
The main benefits for me are... better power response in 2-way xover with 8" (or even bigger) woofer, improved dispersion/power to higher frequencies. Plus all the positives we already know about the SB26.
The mod itself looks like it should not be difficult: Pry the plastic back cover off and replace it with a half ( or smaller) portion of a hard plastic ball of suitable size. Fill it with poly or wool fibers to control resonances. I'm tempted try but would prefer not to destroy the back cover.
Thoughts anyone?
Last edited:
A 6" waveguide will lose pattern control and gain long before 1200hz. Still I think your idea has merit. You should look at the work of @Patrick Bateman. He printed a resonator array and replaced the back plastic with it. I don't remember what the impact on Fs was, but I do recall the distortion was better.
Probably Xmax and THD increase are first limiters to filter it at 1200 Hz, not Fs.
But make bigger chamber for test and measure THD.
Not always: both moving mass and compliance may determine Fs: 590 Hz is already pretty low.
I also had good experiences with Vifa's, but lowering Fs from 1000-1100 Hz with a bored polepiece and damped rear chamber to some 800 Hz is the easy part: below that the trick is not so easy anymore.
But hey, there is little to lose, so try it!
Wow, I had no idea!! Metamaterials, indeed.
I heard for myself the blurred effect of the drive'rs back wave coming through the cone in a Tannoy coax installed in a factory-recommended ported box. It was well braced & built, measured close to spec, but it just didn't sound great, and I could not put my finger on why. This was a couple years after living with self-built Orion dipoles. It took only one return back to the dipoles to realize I was hearing internal reflections through the cone. With the Orions, I had got used to them not being there. Big ah-ah.
Why didn't it occur to me that this could happen with domes the same way?!
Patrick Bateman's report of reduced sb26 distortion with metamaterials makes perfect sense: less pressure on the back of the diaphragm would do it.
Obviously, lots of reading needs to be done here... but my immediate thought is to build 2 stand-atop tweeter boxes with waveguides for these sb26s, with huge back chambers in each. Open up the back of just one tweeter, and experiment with stuffing, drinking straws, etc & leave the other tweeter stock as reference.
The resonance also is there to obtain a flat response. And you need the excursion anyhow to reach the desired level: distortion likely remains there, even if you lower fs.
Mostly it is a nuisance because of the electrical behavior combined with a passive crossover. Rather use a notch (IIRC it has a bump) to flatten the impedance and you can cross it at 1,2k.
Mostly it is a nuisance because of the electrical behavior combined with a passive crossover. Rather use a notch (IIRC it has a bump) to flatten the impedance and you can cross it at 1,2k.
This is where measurements meet the end of the road and listening takes over. The fatal flaw of pushing dome tweeters so low is power compression. Tone bursts will only tell you part of the story where complex content playback reveals the confusion of the wavefront the closer you get to Fs of the driver. Loading a dome with a waveguide only adds to the problem by adding more power compression to the system……..excuse the metaphor but all you’re doing is squeezing a lemon to get more juice.
I would suggest another cheap experiment while you’re at it……..pick yourself up a pair of 3” Tecton BMR drivers and build some quick and dirty test boxes and cross those to your 8” woofers at 800hz or so. Let your ears decide what works best on that larger baffle required to support a 6 or 8” compression loading waveguide. Be forewarned though…..when you hear pristine, uncompressed upper midrange detail and clarity, you‘re forever spoiled. Add in the reduced center to center spacing and the cohesive nature of the system becomes even more apparent as now the point source behavior through the telephone passband is extended.
Waveguide loaded dome tweeters developed popularity in the studio monitor realm for one important reason…….the confusion of the critical passband makes everything sound better when you mechanically ‘compress’ the signals…..when you’re all out of plugs ins and outboard electronics that just can’t bring those transients to bear. Folks tend to think it’s improved directivity that merits the attention……but in a well treated mix or mastering room, the increased directivity in the nearfield doesn’t matter. Don’t get me wrong……waveguides are great for what they do but at heart, they are nothing more than a compromise And when you have all of that baffle real estate to work with, the better solution reveals itself upon deeper examination.
I would suggest another cheap experiment while you’re at it……..pick yourself up a pair of 3” Tecton BMR drivers and build some quick and dirty test boxes and cross those to your 8” woofers at 800hz or so. Let your ears decide what works best on that larger baffle required to support a 6 or 8” compression loading waveguide. Be forewarned though…..when you hear pristine, uncompressed upper midrange detail and clarity, you‘re forever spoiled. Add in the reduced center to center spacing and the cohesive nature of the system becomes even more apparent as now the point source behavior through the telephone passband is extended.
Waveguide loaded dome tweeters developed popularity in the studio monitor realm for one important reason…….the confusion of the critical passband makes everything sound better when you mechanically ‘compress’ the signals…..when you’re all out of plugs ins and outboard electronics that just can’t bring those transients to bear. Folks tend to think it’s improved directivity that merits the attention……but in a well treated mix or mastering room, the increased directivity in the nearfield doesn’t matter. Don’t get me wrong……waveguides are great for what they do but at heart, they are nothing more than a compromise And when you have all of that baffle real estate to work with, the better solution reveals itself upon deeper examination.
mayhem> I used the 46mm Tectonics BMR for a center channel, where each was flanked by two Dayton RS100. I had high hopes but I did not feel the treble was at all refined. It needed a tweeter. YMMV.
Agreed.....sorry if that was presumed by my response. What i 'meant' to say was that an 8" woofer is much better served in a 3 course/piece meal. The BMR is the cheap option/introduction for those who doubt the concept and pretty easy to integrate.......2 and 3 inch domes take some work and are more expensive
So little 49 bucks bugger has copper ring inside, that is really amazing...
Just thinking, would small TL tube in the back help with damping all the back energy at Fs. Something Nautilus-like...it would be easy to install it...
It would not play lower, but maybe would lower distortion even further in area from Fs to 2-3 kHz...
Just thinking, would small TL tube in the back help with damping all the back energy at Fs. Something Nautilus-like...it would be easy to install it...
It would not play lower, but maybe would lower distortion even further in area from Fs to 2-3 kHz...
Hi, subscribed.
Two or three things always stop me to buy a pair : all the sb26, Be line included, show not good waterfaall behavior below 2500 hz circa. Second is the little peak around 5/6 k where the sound can be too much shiny (false details as well). I prefered to go to the hybrid Seas 22 TAF/G cause at the end this one can be used till 2 k hz and have the spl patern of a cheap Be. The last is the small Qts... all the good teeter seems to have stronger motor there, nearer to 0.4 to 0.5 Qts but I could be wrong !
BUT (and it's a big one, blah) the SB26 line, especially the ADC and CDV are showing excepional distorsion behavior related to the price and in paar with very expensive tweeter. And of course the beautifull Xmax.
Meta material ? My understanding is ypu need to know what to tame as it is an helmotz resonator certainly calculated on specific measured peaks on a specific unit. I am not sure anyonne did that diy.
There is maybe something to do with the back chamber to trade off the waterfall vs the DHT. But (a small one... but) due to the pedigre of the men behind that design, task is certainly a challlenge
Thanks to all the contributors!
As described earlier, I know the absence of internal reflections coming through the cone is a major reason for my preferring open baffle speakers. So thinking through, perhaps a better mate for the RS225 is a GRS PT2522 magnetic planar in its own substantial sub-enclosure -- like the conical or pyramidal "Dagger TL" in XRK's FAST. Even though @Patrick Bateman reported no improvements on a BG Neo 3 with 3D printed metamaterial, experimenting with this in a large asymmetrical back cavity could result in better monopole behavior. But low-end excursion <2kHz will probably still be a problem esp. if the xover is not active. 🤔
My local library runs a small FabLab with both 3d printers & lasers. Mostly free for small things. I had a couple of Augerpro 6" SB26 WGs 3d printed for a $40 donation. I can see another visit happening very soon.
You mean instead of trying to mod the rear cavity?
I have to admit I didn't quite understand your first post re WGs in studios etc... but I have certainly played with and appreciate small full-range drivers: The ScanSpeak 10F is one of my all-time favorite drivers, though I've only used it open baffle (LX521/NaO Note inspired 4-way OB) or full-range in a cardboard box. 😉 In fact, my original intent for the Dayton RS225 was to build XRK's FAST with the 10F. My only hesitation is the narrow off-axis output at higher frequencies. After studying the RS225, I thought it might be worth running it up to 1.5 kHz with a good tweeter to go that low. Hence this post.
As described earlier, I know the absence of internal reflections coming through the cone is a major reason for my preferring open baffle speakers. So thinking through, perhaps a better mate for the RS225 is a GRS PT2522 magnetic planar in its own substantial sub-enclosure -- like the conical or pyramidal "Dagger TL" in XRK's FAST. Even though @Patrick Bateman reported no improvements on a BG Neo 3 with 3D printed metamaterial, experimenting with this in a large asymmetrical back cavity could result in better monopole behavior. But low-end excursion <2kHz will probably still be a problem esp. if the xover is not active. 🤔
My local library runs a small FabLab with both 3d printers & lasers. Mostly free for small things. I had a couple of Augerpro 6" SB26 WGs 3d printed for a $40 donation. I can see another visit happening very soon.
I never understood no one made a WMTM with the 10F, like a better Kef 104 ref clone for illustration !
I’ve been literally sitting on this same thought.
I have the drivers sitting here, but I just keep coming back to dispersion.
Since I bought the drivers for this build, I have learnt how much I like controlled directivity and a wider dispersion so I’ve just not committed to actually putting it together.
The 10F is a gorgeous little driver though. I keep wondering how it’d go put through a 1.4” adapter into a horn and run down to 500hz.
I’d be really keen to find a way to cross the SB26 to the rs225 as well. I think that would make a fantastic “budget” bookshelf speaker if it could be done.
Yes, presuming you go passive. Lowering Fs isn’t worth the trouble. Better damping of the cavity might help though.
It has kept up me up some nights! 😆
An aside: One solution is to add a supertweeter with a 1st order passive at 7~8 kHz. Dayton's PTmini-6 comes to mind, since I have a couple & they actually do work in this role. Main question is whether to add it above the 10F in a line or beside it like so many 3-way studio monitors. It's cheap and so small & shallow that it can be put into a router-cut slot on the front baffle, not even penetrating into the enclosure. The air, sparkle & total power response should improve, but unsure of detriments.
You’ll hate that GRA planar……my measured response looked nothing like the published data on two samples.
As for dispersion in your room and the 10f……maybe the narrowing of the wavefront above 2.5khz or so is advantage out to your use case…….and I wouldn’t concern myself with HF dispersion beyond 12khz…….even painted drywall will soak that up and diminish any first reflections worth considering. Take that 10f right up to the edge of a naked 3/4” dome though at 5khz or so and now you‘ve got one hell of a revealing speaker…….but if you understood my earlier anecdote, bad recordings sound BAD with a proper 3way no matter but good recordings can’t be outperformed by any two way……..sadly the reality though is that just about everything sounds ‘ok’ with a two way……hence the popularity
Last edited:
Hmmm... I have measured it -- not nearly as smooth as claimed, but then I measured it w/o baffle in dipole mode. IIRC, the original FR was done with drive mounted on a large baffle. I'd have to mount it on the intended baffle and use a small traffic cone to absorb as much of the back radiation as possible.
I did use it recently on another LX521-style variant, and it worked well -- crossed ~4kHz.
But you're right -- "maybe the narrowing of the wavefront above 2.5khz or so is advantage". I could just build X's FAST, set in the intended room & listen & measure there. If it doesn't work well enough, mod or move on. That's a practical approach, I guess.