Considering a compact Coax with a 12" woofer whose breakup needs to be surpressed so a 1.2-1.3khz low pass is needed. The little SB seems up to the task for home use.
The Wavecor looked nice........but spec wise the SB looks like a better choice with a lower Fs and higher efficiency?
Not concerned with a directivity match in this design and the acoustic rolloff of the SB29 doesn't need the boost in output provided by a waveguide. Coaxially the WGuide approach doesn't work in this design.
I used the SB29RDC in a waveguide and a LR4 high-pass at 1300 Hz. Respective comparative distortion measurements of the SB29RDC crossed at 1300, 1700, 200 and 2500 Hz, respectively, are shown here - watch out, it's German, but the distortion measurements should be clear anyway.
In short: the SB29RDC worked fine crossed at 1300 Hz LR4 in a waveguide.
Regards,
Gaga
In short: the SB29RDC worked fine crossed at 1300 Hz LR4 in a waveguide.
Regards,
Gaga
Ignoring the directivity, the reason why I mentioned a wave guide is the boost directly reduces the strain on the tweeter around where you'd want to cross. The SB isn't capable down that low imo, Zaphs test show that, unless you do not wish to play particularly loud. A 12" has the capability to go really loud and you will need a tweeter that can keep up.
Linkwitz determined that the SEAS Millennium tweeter, with 0.5mm of one way xmax and 7cm2 of SD could cope with a 4th order at 1440Hz and reproduce the SPL peaks that he thought were necessary. The SB only has half the xmax, albeit with 9.6cm2 of SD. The volume displacement of the SB is lower than the SEAS and you can see that its motor is losing linearity quite a bit sooner than the SEAS as a result.
Low fs and high efficiency do not = capable of crossing over low. All the high efficiency does is mean that the tweeter will require less power to reach a given SPL. The max SPL it can reach before distortion is determined entirely by the linear volume displacement and also ultimately by how linear the motor actually is. Low fs helps, and in some cases is necessary, when you want to cross low but it's not mandatory. The XT25 tweeter is a very good example of this, it has a very low fs but it's motor and soft parts dictate that you really need to cross this over much higher than than would indicate.
I suppose a good question would be what is the system intended to do?
At the very least if you want a tweeter that could work better than most down that low then you want one with more than the 0.25mm of xmax that most tweeters seem to have. And one that doesn't show the type of rise in 2nd order that a lot of the ring domes seem to exhibit.
It's expensive, but as you can see here, this older SS tweeter has remarkable linearity down low and keeps it up even under duress.
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Not surprisingly perhaps it has 0.4mm of one way xmax and 8.5cm2 of SD.
Thanks for the detailed reply.....very helpful stuff of which I've pretty much considered also. Lol ..........just hoping for someone to agree with me for something other than a 1" CD and horn.
.....on that note. My own experiences have shown me that I don't find 2nd or even order HD objectionable when isolated as the value. Faaaaaar to often this is mistaken for cone breakup from the mid driver and nothing to do with HD. My mid of choice is smooth as silk in its intended pass band and I've been listening to it without a tweeter in its own sealed box for a few days now ( I disconnected the DE250 and lens sitting on top). My room needs a little something that wide dispersion domes give me over CD devices......a bit of air subjectively speaking. I thought maybe, just maybe I'd mechanically mount the SB29 over the dust cap of the mid and see how it goes........a rounded back bowl type mount I can turn on my lathe shouldn't effect the mid's response other than some mild diffraction.
Oh well......what to do, what to do?
.....on that note. My own experiences have shown me that I don't find 2nd or even order HD objectionable when isolated as the value. Faaaaaar to often this is mistaken for cone breakup from the mid driver and nothing to do with HD. My mid of choice is smooth as silk in its intended pass band and I've been listening to it without a tweeter in its own sealed box for a few days now ( I disconnected the DE250 and lens sitting on top). My room needs a little something that wide dispersion domes give me over CD devices......a bit of air subjectively speaking. I thought maybe, just maybe I'd mechanically mount the SB29 over the dust cap of the mid and see how it goes........a rounded back bowl type mount I can turn on my lathe shouldn't effect the mid's response other than some mild diffraction.
Oh well......what to do, what to do?
I used it crossed at 1600Hz here:
https://sites.google.com/site/audiosocietyofminnesota/Home/diy-projects/sb-acoustics-reference
https://sites.google.com/site/audiosocietyofminnesota/Home/diy-projects/sb-acoustics-reference
Mayhem: Despite the marginally higher efficiency and slightly lower Fs of the SB29RDC, the TW030WA13_14’s larger radiating area (Sd) and stroke (Xmax) suggest that it will have an easier time coping with the stress of a low crossover frequency (obviously the filter slope will also play a role).
SB Acoustics SB29RDC-C000-4 Sd = 9.6cm2, Xmax = +/-0.25mm, therefore max output at 1.2kHz calculates as 95.8295dB, at 1.3kHz is 97.2199dB.
Wavecor TW030WA13_14 Sd = 11.5cm2, Xmax = +/-0.65mm, therefore max output at 1.2kHz should be 105.676dB, at 1.3kHz 107.0665dB.
Maximum frequency-dependent SPL may be different in real life, but hopefully it is clear that the far greater Sd and Xmax of the TW030WA13_14 confer a substantial advantage.
SB Acoustics SB29RDC-C000-4 Sd = 9.6cm2, Xmax = +/-0.25mm, therefore max output at 1.2kHz calculates as 95.8295dB, at 1.3kHz is 97.2199dB.
Wavecor TW030WA13_14 Sd = 11.5cm2, Xmax = +/-0.65mm, therefore max output at 1.2kHz should be 105.676dB, at 1.3kHz 107.0665dB.
Maximum frequency-dependent SPL may be different in real life, but hopefully it is clear that the far greater Sd and Xmax of the TW030WA13_14 confer a substantial advantage.
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Given the off a is response of the Wavecor (wow), it does seem like a viable candidate over a CD/waveguide combo.
I've got a 120/60 horn coming to try that loads to 1khz so I'm gonna give that a listen and see if it brings some life back into my room first before giving the Wavecor a try. The 90/40 horn is just too narrow in the vertical for my room......but I worry about the discontinuity in directivity at 1.2khz also with the 12" woofer that will be narrowing a bit. I know Earl pushes his DE250 down to 900hz or so but some subjectively suggest it sounds strained that low.....haven't tried it myself. The BMS is favored by many below 1kjz but the top end response on paper is too ragged for my tastes.
That multi tweeter approach is really interesting but I'm not familiar with the XO topology to pull that off. I believe Dynaudio does something similiar as well. If I could figure it out and cross lower since using multiple HF devices, I can align everything horizontally and not worry about the vertical lobes.........maybe? I've only seen that done commercially from M-K in their theater systems.
The multi tweeter idea is a joke and a very poor idea from a technical point of view. Yes it will work if it's your only option but that's a big if. Most of the double tweeter rubbish you see from high end companies is simply a fad, it's distinctive and it stands out. The design engineers at Dynaudio should certainly know better.
But then you're going to get awful horizontal lobing. Vertical is the lesser of the two evils.
The above is a very rational approach, but it's based solely on MFG specs. I used to think this way, too. It would seem to be the way to evaluate a purchase, and without other data this is indeed a good way to compare two drivers.
Now I take a different approach - I look for harmonic distortion (IM too if available) for the driver at whatever SPL level(s) are available. Some DIYers have published their own measurements of various drivers for example. These tell the real story as far as I am concerned and would dictate (to me) where I can cross over a tweeter (e.g. how low I can go). The distortion levels do not typically follow the ranking that you would get from the MFG specs for Sd, Xmax, Fs, etc. For instance, I was very interested in a pair of 1" inverted dome tweeters in the typical 4" diameter faceplate and large Fe magnet type package. MFG claimed "low distortion motor design" and the specs looked good. But testing by a reputable guy showed that the distortion profile made the driver rather "uncompetitive" below about 2.5kHz despite the driver having a claimed 1.1mm Xmax! The Fs was around 1300, with Qts of 0.5 but distortion in the 1k-2k range was not good.
Now I know to find someone who has measured the driver, or to purchase one and measure it myself. Oh, and don't bother spending some stupid amount of money for a tweeter! Somewhere around $50 each is my pain threshold. Paying $250 for a tweeter that still has to be crossed over at 2kHz is just plain crazy.
CharlieLaub: fully agree that analysing the mfg specs should only be the first stage in the driver selection process. In the end, there is no substitute for measuring the driver candidates yourself, or having an experienced engineer make the measurements for you.
Although I don't have comprehensive measurements of the TW030WA13_14, a manufacturer friend with a Klippel looked at the TW030WA11_12 and thought that it could be suitable for a crossover frequency well under 1kHz (with suitably steep slopes).
Caveat: I'm OK with paying more for a driver if what I want it to do is unusual and the driver appears to have a good likelihood of meeting the performance targets. I'm also OK with acquiring a number of driver candidates for a given application, and discarding the less suitable choices.
Although I don't have comprehensive measurements of the TW030WA13_14, a manufacturer friend with a Klippel looked at the TW030WA11_12 and thought that it could be suitable for a crossover frequency well under 1kHz (with suitably steep slopes).
Caveat: I'm OK with paying more for a driver if what I want it to do is unusual and the driver appears to have a good likelihood of meeting the performance targets. I'm also OK with acquiring a number of driver candidates for a given application, and discarding the less suitable choices.
....but just one lobe, not like in a horizontal epic fail MTM. Crossing low goes even farther to avoid lobing in both the mid high and interference between the tweeters. The resulting null could be used to advantage with proper placement.
Liken it to the approach of a skilled engineer.......little to no eQ but mike placement is everything. Speakers operate in a very similiar principle.
......not textbook Toole, but that doesn't mean it won't work.
Stereophile's measurements of that speaker were actually fairly respectable. I was surprised enough to want to hear them.
The trick is that it uses multiple tweeters, but configuration is basically a 1.5-way. The outer two tweeters are lowpassed, though all three have a common highpass with the woofer.
I think "speaker dave" did the same thing on his McIntosh HT-1 design.
Agreed, a waveguide and a notch filter on Fs combined would be the best best.
This looks interesting: SB29RDC ON PELLEGRENE WAVEGUIDE
Cheers, Joe
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