Again, I've chosen 4" drivers because, as could be seen above, 6" drivers are beaming by about 1kHz. It takes a 4" to be good past 2kHz, which is what I'm shooting for.
The purpose of dual sealed enclosures it to remove the rear radiation from the acoustic output, while keeping the dipole action. Apparently, the magnet/frame structure causes a 90deg reflection of frequencies in the 1-2kHz range (wrt its rear radiation), disturbing the driver's 'ideal' dipole pattern. This causes excessive attenuation of off axis radiation between 1-2kHz, but then a spike in output at 90deg off axis, wrt the forward axis. This can be seen from the above data (dual 6" experiment), and will be shown again in this set of data.
So we'll start with looking at the cheap 4" poly driver (not a bad driver actually!):
Here is its nearfield response of the bare driver. Not bad, some problem at 3.3kHz:
Here is what happens on and off axis when used as a dipole with no baffle. Measured at 1m, rotated 0deg, 30deg, 45deg, 60deg, and 90deg.
What I'm interested in the above is seeing that the off axis polar irregularities have moved up to 2kHz (the 8" and 6" had them around 1kHz): excessive attenuation at 45deg and 60deg, then a spike at 90deg. I'm fairly sure one of the main causes of the frequency of the off-axis irregularities is the width of the magnet structure, but the frame ventilation makes a difference too as we will see. This suggests neo drivers may have some advantages when it comes to dipoles and regularity of the polar response.
Next is what happens when the driver is put into a small sealed enclosure (I'm guessing its about 50 in sq., plus there is stuffing inside). This was measured at 1m, but was measured out to 180deg off axis:
Looks pretty different than the no baffle dipole huh? What we can see is that it is basically a monopole up to 2kHz. Also, you can see the baffle step taking place between 1-2kHz. Not bad overall. I gave it a listen. More on that in a second.
Here is what happens when you put two of these back to back:
Yikes, that won't do. That notch/peak thing at 1.1kHz is classic dipole action. Really, the response looks like garbage from 800Hz up. The on center separation between the front cone and back cone was about 14", so to get the peak up well past 2kHz, the separation would have to be reduced to 4" or less. SOOO, long story short, there is pretty much no way one can get two drivers to cover 200-2000Hz, as far as I can see.
I listened to this configuration too, and it was kind of interesting (I did some digital EQing to try and roughly smooth things out). When used with a single driver and chamber, the presentation was classic 'box' sound: boxy. When switched into dipole mode, it became much more tonally neutral (despite a lot of other flaws). For me, the 'take home message' was that polar pattern matters. I did another experiment I'll write up that really emphasized this too.
The purpose of dual sealed enclosures it to remove the rear radiation from the acoustic output, while keeping the dipole action. Apparently, the magnet/frame structure causes a 90deg reflection of frequencies in the 1-2kHz range (wrt its rear radiation), disturbing the driver's 'ideal' dipole pattern. This causes excessive attenuation of off axis radiation between 1-2kHz, but then a spike in output at 90deg off axis, wrt the forward axis. This can be seen from the above data (dual 6" experiment), and will be shown again in this set of data.
So we'll start with looking at the cheap 4" poly driver (not a bad driver actually!):
Here is its nearfield response of the bare driver. Not bad, some problem at 3.3kHz:
An externally hosted image should be here but it was not working when we last tested it.
Here is what happens on and off axis when used as a dipole with no baffle. Measured at 1m, rotated 0deg, 30deg, 45deg, 60deg, and 90deg.
An externally hosted image should be here but it was not working when we last tested it.
What I'm interested in the above is seeing that the off axis polar irregularities have moved up to 2kHz (the 8" and 6" had them around 1kHz): excessive attenuation at 45deg and 60deg, then a spike at 90deg. I'm fairly sure one of the main causes of the frequency of the off-axis irregularities is the width of the magnet structure, but the frame ventilation makes a difference too as we will see. This suggests neo drivers may have some advantages when it comes to dipoles and regularity of the polar response.
Next is what happens when the driver is put into a small sealed enclosure (I'm guessing its about 50 in sq., plus there is stuffing inside). This was measured at 1m, but was measured out to 180deg off axis:
An externally hosted image should be here but it was not working when we last tested it.
Looks pretty different than the no baffle dipole huh? What we can see is that it is basically a monopole up to 2kHz. Also, you can see the baffle step taking place between 1-2kHz. Not bad overall. I gave it a listen. More on that in a second.
Here is what happens when you put two of these back to back:
An externally hosted image should be here but it was not working when we last tested it.
Yikes, that won't do. That notch/peak thing at 1.1kHz is classic dipole action. Really, the response looks like garbage from 800Hz up. The on center separation between the front cone and back cone was about 14", so to get the peak up well past 2kHz, the separation would have to be reduced to 4" or less. SOOO, long story short, there is pretty much no way one can get two drivers to cover 200-2000Hz, as far as I can see.
I listened to this configuration too, and it was kind of interesting (I did some digital EQing to try and roughly smooth things out). When used with a single driver and chamber, the presentation was classic 'box' sound: boxy. When switched into dipole mode, it became much more tonally neutral (despite a lot of other flaws). For me, the 'take home message' was that polar pattern matters. I did another experiment I'll write up that really emphasized this too.
Here is where the TB driver comes to the rescue:
This is the bare driver, no baffle, measured at 1m, at 0,30,45,60,90degs. This actually looks really promising. Looking at 2kHz, at 45 and 60deg, the level is much less attenuated wrt other drivers (even the 4" poly), and the 90deg measurement shows no great spike in output. The diameter of the magnets of 4" poly and TB are about the same, but the rear ventilation is much greater on the TB. My guess is that this leads to a much more regular polar response.
Just to compare, look at what the Eminence Alpha 6a was doing under the same conditions:
Much more irregular between 1-2kHz. Really, the TB maintains very good polar response out to 4kHz, which is great! Actually, the only polar response error below 4kHz is the bump at 2kHz, which I'm guessing is the baffle peak. There is no way to avoid this, but it doesn't look to be much of a problem. At least, it will be less of an error than with other drivers.
So here are the caveats - a small driver can't play as loud or as low, and it has a bit lower sensitivity (about 5dB), compared to the tweeter (Neo3PDRW). I did a bit of math cad sims though, and things may be okay - in terms of volume displacement, the driver isn't particularly limited with LR2 or LR4 crossovers between 250-300Hz. My woofers can handle the high XO point. But the big limitation is power handling - it might be maxing out with 50W in, which might be about 100dB/1m. In fact, virtually all 4" drivers are power limited for our needs.
In reality though, things aren't so clear. The amount of power the driver is dealing with depends on the bandwith. Also, Xmax based calculations don't really tell you when the driver will have excessive nonlinear distortion. A quick look at the driver's NLD showed acceptable but possibly problematic distortion levels. SOOO, only time will tell if the driver is power or NLD limited. Luckily, they aren't too expensive, so I don't mind burning one or two. There are a couple other affordable 4" drivers with possibly better power and NLD characteristics if I blow these.
I haven't gotten a chance to listen to them yet because I killed both my Neo3PDRW's due to switching transients 🙁 🙁 They developed a rasping buzz after an accident, but they actually might be easily fixable. We'll see.
An externally hosted image should be here but it was not working when we last tested it.
This is the bare driver, no baffle, measured at 1m, at 0,30,45,60,90degs. This actually looks really promising. Looking at 2kHz, at 45 and 60deg, the level is much less attenuated wrt other drivers (even the 4" poly), and the 90deg measurement shows no great spike in output. The diameter of the magnets of 4" poly and TB are about the same, but the rear ventilation is much greater on the TB. My guess is that this leads to a much more regular polar response.
Just to compare, look at what the Eminence Alpha 6a was doing under the same conditions:
An externally hosted image should be here but it was not working when we last tested it.
Much more irregular between 1-2kHz. Really, the TB maintains very good polar response out to 4kHz, which is great! Actually, the only polar response error below 4kHz is the bump at 2kHz, which I'm guessing is the baffle peak. There is no way to avoid this, but it doesn't look to be much of a problem. At least, it will be less of an error than with other drivers.
So here are the caveats - a small driver can't play as loud or as low, and it has a bit lower sensitivity (about 5dB), compared to the tweeter (Neo3PDRW). I did a bit of math cad sims though, and things may be okay - in terms of volume displacement, the driver isn't particularly limited with LR2 or LR4 crossovers between 250-300Hz. My woofers can handle the high XO point. But the big limitation is power handling - it might be maxing out with 50W in, which might be about 100dB/1m. In fact, virtually all 4" drivers are power limited for our needs.
In reality though, things aren't so clear. The amount of power the driver is dealing with depends on the bandwith. Also, Xmax based calculations don't really tell you when the driver will have excessive nonlinear distortion. A quick look at the driver's NLD showed acceptable but possibly problematic distortion levels. SOOO, only time will tell if the driver is power or NLD limited. Luckily, they aren't too expensive, so I don't mind burning one or two. There are a couple other affordable 4" drivers with possibly better power and NLD characteristics if I blow these.
I haven't gotten a chance to listen to them yet because I killed both my Neo3PDRW's due to switching transients 🙁 🙁 They developed a rasping buzz after an accident, but they actually might be easily fixable. We'll see.
And here is dessert:
I had a few cheap, small neo tweeter laying around, and when my Neo3s went out of commission, I thought I would give them a go.
These are two Dayton ND20FB, back to back:
And here is their polar response:
If you look closely, it is actually kind of problematic: it is only -3dB down at 60deg. Also, it goes to pot between 3.5 and 8kHz. It's on axis response is fairly uneven, although 30deg looks good. It also had asymmetrical side to side polar response, I don't know why. The Neo3PDRW looked a lot better.
So I redid my crossovers and got the dual dayton tweeter up and running, and gave it a listen - it sounded bad! Considerably worse than I had expected. Let me show you something else: the mid and tweeter combined polar response...
This is explains a lot of the bad sound, IMO. The mid is still the Alpha 6a - and between 1-2kHz, the off axis response is dropping too rapidly. This can probably be expected from any driver with a large magnet. Then, above 2kHz, the polar response rises way too much. Notice the on axis response is EQ'ed almost flat (the XO was LR4 at 1700Hz). It really sounded like garbage, very tinny. I think it is safe to say back to back tweeters won't work (on a large enough baffle, things might look fairly different. It would be interesting to see).
So what I did was put a mic out in the room, and measure the 'reverberant' field. It clearly showed the dip at 1.5kHz, and peak at 4kHz, (and a couple others in the lower midrange). I then roughly EQ'ed it to have a flat power response - and low and behold, it sounded much better, even on axis 1m in front of the driver. So the 'take home message': polar response matters a LOT!
Enjoy!...😀
I had a few cheap, small neo tweeter laying around, and when my Neo3s went out of commission, I thought I would give them a go.
These are two Dayton ND20FB, back to back:
An externally hosted image should be here but it was not working when we last tested it.
And here is their polar response:
An externally hosted image should be here but it was not working when we last tested it.
If you look closely, it is actually kind of problematic: it is only -3dB down at 60deg. Also, it goes to pot between 3.5 and 8kHz. It's on axis response is fairly uneven, although 30deg looks good. It also had asymmetrical side to side polar response, I don't know why. The Neo3PDRW looked a lot better.
So I redid my crossovers and got the dual dayton tweeter up and running, and gave it a listen - it sounded bad! Considerably worse than I had expected. Let me show you something else: the mid and tweeter combined polar response...
An externally hosted image should be here but it was not working when we last tested it.
This is explains a lot of the bad sound, IMO. The mid is still the Alpha 6a - and between 1-2kHz, the off axis response is dropping too rapidly. This can probably be expected from any driver with a large magnet. Then, above 2kHz, the polar response rises way too much. Notice the on axis response is EQ'ed almost flat (the XO was LR4 at 1700Hz). It really sounded like garbage, very tinny. I think it is safe to say back to back tweeters won't work (on a large enough baffle, things might look fairly different. It would be interesting to see).
So what I did was put a mic out in the room, and measure the 'reverberant' field. It clearly showed the dip at 1.5kHz, and peak at 4kHz, (and a couple others in the lower midrange). I then roughly EQ'ed it to have a flat power response - and low and behold, it sounded much better, even on axis 1m in front of the driver. So the 'take home message': polar response matters a LOT!
Enjoy!...😀
Hi Cuibono, your measurement shows similarity with my back-to-back tweeter measurement. Especially that massive drop.
back-to-back Hivi K1
I am convinced that the performance ceiling of typical dipole setup is the tweeter and we need to find an alternative to make it better (back-to-back waveguide i.e. Mige0...)
I wonder why SL argues against directivity of the tweeter.
I have 10" dayton waveguide and will see how it performs. I dislike to wander this way to unknown territory though.
back-to-back Hivi K1
I am convinced that the performance ceiling of typical dipole setup is the tweeter and we need to find an alternative to make it better (back-to-back waveguide i.e. Mige0...)
I wonder why SL argues against directivity of the tweeter.
I have 10" dayton waveguide and will see how it performs. I dislike to wander this way to unknown territory though.
Hmmm, back to back waveguides? Actually, a bare Neo3PDR is an excellent tweeter. Couldn't ask for more, really.
I agree though, the tweeter XO point plays a big part in how the rest of the system unfolds. I wish I could find one that would do 1kHz.
I agree though, the tweeter XO point plays a big part in how the rest of the system unfolds. I wish I could find one that would do 1kHz.
Neo 3 measurements
Do you have any directivity measurements of your open Neo3 before they died?
So, almost 2 months later, I finally gave up on PE getting the NEO3PDR back in stock, and went with Meniscus (got here quicker too!), and I'm back at it.
Here is what I've been getting at:
The Mids are the Eminence Alpha6a and the Tangband W4-656sc that were discussed above. I'm comparing them because of their differences in acoustic output off axis, particularly above 1kHz. I've added tweeters to each, and put together an crossover (with EQ) so that they are as close as can be, on axis at 30inches. They are XO'd to LR4 at 1700 acoustically (the overlay feature in Soundeasy makes it a cinch matching acoustic responses!) Here is an overlay of the final responses:
The magenta curve is the TB with Neo3, and the green is the Alpha6a with Neo3. On axis, they are almost identical. The differences come with off axis response, with the smaller, 4" TB driver maintaining regularity off axis, and the 6" Eminence not (see above posts).
I then did several days of listening to answer the big question: IS THERE A DIFFERENCE???
The answer - yes, a small one. On the first day, it was hard to detect. I couldn't do quick A/B comparisons, because my setup wasn't sophisticated enough, but I thought I could perceive a difference. On day 2, I listened to only the mids, without the tweeters, and I set up quick A/B switching - then the difference became very obvious - it was definitely interesting to hear. Then, day 3 I hooked the tweeters back in (and lost the quick A/B capabilities), but I could much more easily hear the differences now.
How were they different? The smaller TB driver sounded more natural and especially more coherent. The larger Eminence sounded a little 'hollow' in comparison - more like a speaker system. It was especially noticeable on acoustic guitar. The TB driver had slightly more ambience, and had clearer, fuller mid-highs. It sounded more balanced overall, and was easier to listen to. Also, walking around the room, the TB driver had less change in sound. All good stuff.
So was it worth it? Would I recommend it? I'm glad I did it - it is an improvement. Not as massive as the difference compared to moving to the bare Neo3PDR tweeters, but still a small but definite improvement in the 'naturalness' of the sound. I would recommend it to those trying to really craft their speaker - all in all, it is a modest but appreciated change.
Next is to see how it does with time - will it handle high volume situations without burning or sounding strained? We'll see.
As a final tidbit, here are two graphs of the in room, ungated, 1/3 octave spectrograph - the red bar charts in the images below (thanks to JohnK for teaching me how to do it!). It shows the differences in total output (on and off axis combined) of the two drivers - first the Alpha6a, then the W4. Although they are EQ'd to be the same on axis, notice how much more output the W4 has above 1kHz. I find these graphs correlate well to what I hear.
Thats all for now! Enjoy!
Here is what I've been getting at:
An externally hosted image should be here but it was not working when we last tested it.
The Mids are the Eminence Alpha6a and the Tangband W4-656sc that were discussed above. I'm comparing them because of their differences in acoustic output off axis, particularly above 1kHz. I've added tweeters to each, and put together an crossover (with EQ) so that they are as close as can be, on axis at 30inches. They are XO'd to LR4 at 1700 acoustically (the overlay feature in Soundeasy makes it a cinch matching acoustic responses!) Here is an overlay of the final responses:
An externally hosted image should be here but it was not working when we last tested it.
The magenta curve is the TB with Neo3, and the green is the Alpha6a with Neo3. On axis, they are almost identical. The differences come with off axis response, with the smaller, 4" TB driver maintaining regularity off axis, and the 6" Eminence not (see above posts).
I then did several days of listening to answer the big question: IS THERE A DIFFERENCE???
The answer - yes, a small one. On the first day, it was hard to detect. I couldn't do quick A/B comparisons, because my setup wasn't sophisticated enough, but I thought I could perceive a difference. On day 2, I listened to only the mids, without the tweeters, and I set up quick A/B switching - then the difference became very obvious - it was definitely interesting to hear. Then, day 3 I hooked the tweeters back in (and lost the quick A/B capabilities), but I could much more easily hear the differences now.
How were they different? The smaller TB driver sounded more natural and especially more coherent. The larger Eminence sounded a little 'hollow' in comparison - more like a speaker system. It was especially noticeable on acoustic guitar. The TB driver had slightly more ambience, and had clearer, fuller mid-highs. It sounded more balanced overall, and was easier to listen to. Also, walking around the room, the TB driver had less change in sound. All good stuff.
So was it worth it? Would I recommend it? I'm glad I did it - it is an improvement. Not as massive as the difference compared to moving to the bare Neo3PDR tweeters, but still a small but definite improvement in the 'naturalness' of the sound. I would recommend it to those trying to really craft their speaker - all in all, it is a modest but appreciated change.
Next is to see how it does with time - will it handle high volume situations without burning or sounding strained? We'll see.
As a final tidbit, here are two graphs of the in room, ungated, 1/3 octave spectrograph - the red bar charts in the images below (thanks to JohnK for teaching me how to do it!). It shows the differences in total output (on and off axis combined) of the two drivers - first the Alpha6a, then the W4. Although they are EQ'd to be the same on axis, notice how much more output the W4 has above 1kHz. I find these graphs correlate well to what I hear.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Thats all for now! Enjoy!
I've recently embarked on a similar adventure. Attachments show a sketch of my initial concept, a test jig to see how my midrange (Audax PR170M0) performed with no baffle, and the response curves (front and back, test jig rotated by hand so the angles aren't accurate or even). If I believe UPS my Neo3PDRs should be here Friday, so hopefully I'll get to play with them over the weekend.
I was concerned about diffraction problems around the 'nude' tweeter, and I see you used foam to address that. How much of a difference does that make, both audible and measurable?
Also, how did you kill your earlier Neo3s? Would be good to know what I shouldn't do 🙂 And were those PDR or not (the measurements shown in the other thread that you linked to)?
I was concerned about diffraction problems around the 'nude' tweeter, and I see you used foam to address that. How much of a difference does that make, both audible and measurable?
Also, how did you kill your earlier Neo3s? Would be good to know what I shouldn't do 🙂 And were those PDR or not (the measurements shown in the other thread that you linked to)?
Attachments
Last edited:
Hi Saurav,
I've always used Neo3PDR - I just don't always write out the name, I guess. I killed them either with too loud/long/low frequency test signals, or more likely, transients from switching interconnects/power plugs while the amps were on.
What I do now is put a cap in series with the driver, something like a 50uF electrolytic (film caps are expensive at that size!) to protect the driver. The foam around the edges smooths the raw response - I could do without them, they would just require more EQ (I use a computer with a lot of control for fine tuning). With the foam, they require very little EQ. In terms of audibility, I'm not sure the foam does that much. OB speakers are inherently devices with maximum diffraction - the back and front radiation intermixes almost immediately - and that isn't inherently bad. I guess the trick for OB is getting the two sides to interact as equally as possible.
Those measurements of yours look pretty good!
I've always used Neo3PDR - I just don't always write out the name, I guess. I killed them either with too loud/long/low frequency test signals, or more likely, transients from switching interconnects/power plugs while the amps were on.
What I do now is put a cap in series with the driver, something like a 50uF electrolytic (film caps are expensive at that size!) to protect the driver. The foam around the edges smooths the raw response - I could do without them, they would just require more EQ (I use a computer with a lot of control for fine tuning). With the foam, they require very little EQ. In terms of audibility, I'm not sure the foam does that much. OB speakers are inherently devices with maximum diffraction - the back and front radiation intermixes almost immediately - and that isn't inherently bad. I guess the trick for OB is getting the two sides to interact as equally as possible.
Those measurements of yours look pretty good!
Cuibono, does the foam help the on-axis dip and the curve crossing around 7-8K? From your and Michael's measurements, that seems like the biggest problem with the naked dipole Neo3-PDR.
Yes, it does help some, IIRC. The thing is though, my impression is that errors that high in frequency are less of a problem, so to me the 8kHz dip isn't to much of an issue.
I have measurements somewhere, I'll try and post sometime soon.
I have measurements somewhere, I'll try and post sometime soon.
Here are a couple of graphs of the Neo3PDR with and without foam edges. The foam is a nice little tweak - it does help the 8kHz notch, and at 30deg off axis, the response is almost flat and doesn't need any EQing.
I currently XO these LR4 at 1700Hz, but I'm tempted to go lower, just to see what happens. In theory, it might be a small improvement (wrt vertical lobing), but I suspect it wouldn't make enough difference. I'll probably try it sometime though....
I currently XO these LR4 at 1700Hz, but I'm tempted to go lower, just to see what happens. In theory, it might be a small improvement (wrt vertical lobing), but I suspect it wouldn't make enough difference. I'll probably try it sometime though....
Attachments
Great topic!
I am currently using a Visaton AL170 as an unbaffled midrange. The disadvantage with smaller drivers is that the magnet and spider are relatively large compared to the size of the cone. The AL170 has a relatively small magnet and spider and does better than any other 6.5" I've seen measurements of. See the pictures at Visaton - Lautsprecher und Zubehör, AL170
Maybe I should have used some smoothing here, as there are a couple minor reflections within the time window.
In my Unbaffled Dipole I am using the B&G Neo3W, not the PDR version. I decided on the Neo3W because simulations indicated that its beaming at higher frequencies would be of benefit in keeping the radiation pattern constant, but your measurements look nice too! I've got a pair of PDR's on the shelve, so maybe I should give them a try.
I am currently using a Visaton AL170 as an unbaffled midrange. The disadvantage with smaller drivers is that the magnet and spider are relatively large compared to the size of the cone. The AL170 has a relatively small magnet and spider and does better than any other 6.5" I've seen measurements of. See the pictures at Visaton - Lautsprecher und Zubehör, AL170
An externally hosted image should be here but it was not working when we last tested it.
Maybe I should have used some smoothing here, as there are a couple minor reflections within the time window.
In my Unbaffled Dipole I am using the B&G Neo3W, not the PDR version. I decided on the Neo3W because simulations indicated that its beaming at higher frequencies would be of benefit in keeping the radiation pattern constant, but your measurements look nice too! I've got a pair of PDR's on the shelve, so maybe I should give them a try.
Hi Keyser,
Nice graph. When I look at spider/magnet size, it is not so much about its size relationship to the cone, but more the width of certain wavelengths in relation to the spider/magnet. When things have certain dimensional relationships, sideways reflections are caused, which is undesirable from a constant directivity point of view. Ventilation around the back matters too, but that seems harder to predict.
I'd be very interested to see side by side measurements of a neo3 and neo3pdr - I figured things differently than you. I think this has been said in another thread, but to maintain a true dipole figure of eight pattern, the driver must be radiating to the sides (equally). Without the acoustic interference (difraction) on the sides, the figure of eight pattern cannot be formed. So I guessed that the Neo3PDR, which has a wider radiation pattern higher up in frequency, should maintain a more regular dipole pattern. But really though, I bet it doesn't matter too much.
It would be good to see though, especially with longer gate times (aka, higher resolution).
SOOO..... I hope nobody ordered any TB W4-656sc drivers. 😱 I've had four here so far, and they all buzzed. I don't know why, they do it right out of the box. It isn't super loud, but it is not too hard to hear either. Pretty obvious on music.
So, I went with what should be a better driver, but also $20 more, the TB W4-1320sj. It has a much smaller magnet, and much better rear ventilation, I've attached a picture. It also has shorting rings in the magnets, so it should have better nonlinear distortion performance. I'll get it on the bench tomorrow hopefully.
Nice graph. When I look at spider/magnet size, it is not so much about its size relationship to the cone, but more the width of certain wavelengths in relation to the spider/magnet. When things have certain dimensional relationships, sideways reflections are caused, which is undesirable from a constant directivity point of view. Ventilation around the back matters too, but that seems harder to predict.
I'd be very interested to see side by side measurements of a neo3 and neo3pdr - I figured things differently than you. I think this has been said in another thread, but to maintain a true dipole figure of eight pattern, the driver must be radiating to the sides (equally). Without the acoustic interference (difraction) on the sides, the figure of eight pattern cannot be formed. So I guessed that the Neo3PDR, which has a wider radiation pattern higher up in frequency, should maintain a more regular dipole pattern. But really though, I bet it doesn't matter too much.
It would be good to see though, especially with longer gate times (aka, higher resolution).
SOOO..... I hope nobody ordered any TB W4-656sc drivers. 😱 I've had four here so far, and they all buzzed. I don't know why, they do it right out of the box. It isn't super loud, but it is not too hard to hear either. Pretty obvious on music.
So, I went with what should be a better driver, but also $20 more, the TB W4-1320sj. It has a much smaller magnet, and much better rear ventilation, I've attached a picture. It also has shorting rings in the magnets, so it should have better nonlinear distortion performance. I'll get it on the bench tomorrow hopefully.
Attachments
I don't buy into that. I have done some measurements with three small FR drivers (Visaton FRS8, Fostex FF85K and FE 83). They are almost identical in outer dimensions (the FF85k having a somewhat larger magnet), but vary quite much in frequency response to the rear. Putting more width or depth to the magnets did change almost nothing.
For any effective reflection the reflecting surface would have to be much larger than the wavelength of the reflected wave. With my FR drivers the most significant differences between front and rear were around 2 kHz - even in a driver without baffle. This would need dimensions from 17 cm up to induce reflections. The largest "flat" surface on those drivers was 2 cm wide. Ergo: Any concept of reflecting waves does not apply.
That's the point! It is the Helmholtz resonators formed between the cone and the basket (and perhaps the mounting conditions) which make up for most of the backward peculiarities. Having a very open basket (like the AL170 and the TB 1320) surely helps. Opening up the driver cutout is beneficial too. But you really can't predict from a look at the basket, how it will behave.
Rudolf
The new Scan-Speak Discovery 10F/4424G looks interesting for a 'naked' mid. Frame under 4", nice FR and impedance curves and lower priced than most SS drivers.
Scan-Speak Discovery 10F/4424G, 4" Midrange from Madisound
Scan-Speak Discovery 10F/4424G, 4" Midrange from Madisound
Honestly, I don't know enough about the wave physics or the exact dimensions needed for reflections to happen - but there seem to be some basic relationships. The smaller the magnet, and the farther it is from the cone, the better, in terms of regular dipole response, at wide angles. Not really news, probably.
I'm guessing though, that there is a relationship between magnet/basket/spider size, and the reflection frequency - up till now, I've guessed that reflections occur at a frequency of roughly half wavelengths, wrt the magnet structure. IE, magnets are 4" to 6" wide, and the 90deg reflection abnormalities occur between 1-2kHz. Distance to the cone matters, but there seems to be an approximate relationship there.
Anyway, if I'm lucky, I'll get to take some measurements today, and post them.
I'm guessing though, that there is a relationship between magnet/basket/spider size, and the reflection frequency - up till now, I've guessed that reflections occur at a frequency of roughly half wavelengths, wrt the magnet structure. IE, magnets are 4" to 6" wide, and the 90deg reflection abnormalities occur between 1-2kHz. Distance to the cone matters, but there seems to be an approximate relationship there.
Anyway, if I'm lucky, I'll get to take some measurements today, and post them.
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