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Old 13th June 2012, 03:38 PM   #11
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Marks ER18DXT design uses an LR2 @ 1500Hz and he performed stress measurements to make sure that the tweeter could cope and found that it could. As his blog was hacked a while ago I think those measurements might have ended up being lost.

Both the ER18 and U18 have shorting rings in the motor and offer lower distortion as a result. The U18 appears to have a slightly cleaner upper midrange compared to the ER18, which has slightly cleaner bass/lower midrange. The ER18 does not show the small blip in the second harmonic like the woven poly cones do.

I would expect any competently designed loudspeaker based around the ER18 or U18 to be superior to a design with the U16. The DXT is robust enough so that it can be crossed over low enough such that any off axis issues associated with the larger driver size are a non issue.

Marks design, as far as I recall, has better off axis curves compared to the SEAS Idunn, mainly because of the lower xover point.

Apart from the wave-guide, half of the point of using the DXT is to take advantage of its ability crossover low without hassle.
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Old 13th June 2012, 03:44 PM   #12
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Originally Posted by boris81 View Post
It will be interesting to compare the off-axis response to other designs. The Application Notes on the DXT Technology show excellent results with a 4" woofer. It seems that the DXT tweeter can be made to work well with a good range of midwoofers without compromising it's great directivity.
The design compromise in choosing a midwoofer would be that larger drivers will give better low-end extension while some smaller ones might offer lower distortion in the upper midrange.
Well the DXT should be crossed around 3.5kHz to a mid/bass of the same diameter as the tweeter if you want to get a decent directivity match. This pretty much means you need to use a soft cone of good design.

If you're going to crossover lower, then you really need to do so at a frequency before where the DXTs small wave-guide starts to control the directivity and also before the mid/bass shows any signs of beaming.
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Old 13th June 2012, 05:49 PM   #13
gornir is offline gornir  Sweden
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Originally Posted by sreten View Post
Hi,

Its obviously different :

with a more complex c/o and a lower c/o point :

The x/o is not near LR2 acoustic as used here.

rgds, sreten.
Yes, it looks like an asymmetrical fourth-order LR to me. The great thing with the “Prestigious Two – Monitor DXT” setup is that the relative acoustical off-set between the driver units coincides well with a symmetrical LR2 topology without the need for a slanted/tilted baffle or a time delay circuit to get a perfect phase behavior between the tweeter and mid-woofer at a listening range between 2.5-3m.

I think SEAS purposely trying to hide the frequency response above 20kHz.

Here is how it looks like above 20kHz (Picture1).
Click the image to open in full size.

This hard dome break-up is crazy!

Quote:
Originally Posted by tomewing View Post
Nice crossover on the tweeter, remarkably simple! One inductor and two caps per channel - beautiful! Have you ramped up the SPL and to see how the tweeter retains its composure in the crossover region at high volumes?
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Originally Posted by chlorofille View Post
Excellent job Goran! I'm also curious to know if the tweeter will hold up at louder volumes.
Perhaps the X-max of the woofer will run out before the tweeter starts getting harsh.
Thanks!
It’s not a problem at the listening levels I use, but yes, the tweeter will be the limiting factor in this design at very high listening levels.

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Originally Posted by martinbls View Post
Very interesting project!
Please keep us updated about the sound and the values of the crossover components, if you don't mind (as well as cabinet size, port length and so on).
Since there already is a project with the DXT tweeter and the ER18RNX woofer, what do you think is the main sonic signature of the U16RCY? Did you also try the ER18?

Thanks!
Martin
Yes, the full design will be published at www.audioexcite.com, hopefully within a couple of weeks. I still fine tuning the tweeter level padding and a system impedance correction circuit as well as compiling all the measurement data etc.

Yes, I have used the ER18 in the ZA-SR71 design see review ZaphAudio ZA-SR71 Review!

The U16RCY has a light-dark midrange character and doesn’t have the micro-detail and resolution as ScanSpeak Revelator or AudioTechnology drivers and that goes for the ER18 as well.

It’s in the bass area that I think the U16 excels over the ER18. The U16 is much quicker, alert and powerful in its character compared to the ER18, even though it can’t be driven as hard as the ER18 with its larger cone area and displacement. I think two U16 would do great as bass in a small narrow three-way.

Picture 1-4 shows control measurements done at 2m at tweeter height and the measurements are valid down to 400Hz. The design is optimized for the 15deg off-axis frequency measurement and at a listening distance of 2.5-3m.

Picture1: On-axis. Blue=Left speaker, Red=Right speaker.
Picture2: 15deg off-axis. Blue=Left speaker, Red=Right speaker.
Picture3: 15deg off-axis frequency response.
Picture4: 15deg off-axis frequency response, with tweeter reverse polarity.

Note! Picture4, nice deep and even reverse null at the cross-over point. It’s even deeper at 2.5-3m, indicating a good phase behavior at the cross-over frequency.

Regards

/Göran
Attached Images
File Type: jpg Picture1.jpg (134.5 KB, 1062 views)
File Type: jpg Picture2.jpg (134.2 KB, 457 views)
File Type: jpg Picture3.jpg (137.8 KB, 455 views)
File Type: jpg Picture4.jpg (140.3 KB, 454 views)
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Old 13th June 2012, 07:05 PM   #14
gornir is offline gornir  Sweden
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Quote:
Originally Posted by 5th element View Post
I would expect any competently designed loudspeaker based around the ER18 or U18 to be superior to a design with the U16. The DXT is robust enough so that it can be crossed over low enough such that any off axis issues associated with the larger driver size are a non issue.
I would say it depends on personal preferences and design philosophy.

Yes, with a larger woofer you hopefully get a deeper more powerful bass that can be played louder, but at the cost of a larger enclosure, less good upper-mids/lower treble behavior and a tweeter that has to be crossed-over lower and often steeper, with less dynamic headroom.

Even though the mid-woofer off-axis dispersion is a non-issue when crossed-over low enough, the tweeters ability to play mid-range is a limiting factor. Sonically, I think a well behaved mid-woofers ability to play upper-mids is superior to a tweeters ability to do the same. If you like me prefer low-order filters you also get a larger “comfort zone” for the tweeter to work in.

To generalize, it depends if you prioritize bass performance or mid-range performance in a small to medium sized 2-way stand-mount.

As you realize I’m not a huge fan of 2-ways with a mid-woofer larger than 6.5”, but that doesn’t mean there aren’t great sounding 2-way designs using woofers larger than 6.5-7” out there. As always each design has its pros and cons and design goals and don't forget that most people has their own taste and sound preferences.

Regards

/Göran
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Old 13th June 2012, 09:12 PM   #15
Starre is offline Starre  Sweden
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Gornir, the "Tired2way" use a 8 inch Seas paper woofer and it works well, so do not dismiss that config. since it can work (like you wrote). Nice speaker you made, anyhow.

Last edited by Starre; 13th June 2012 at 09:20 PM.
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Old 13th June 2012, 11:59 PM   #16
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Quote:
Originally Posted by gornir View Post
I would say it depends on personal preferences and design philosophy.

Yes, with a larger woofer you hopefully get a deeper more powerful bass that can be played louder, but at the cost of a larger enclosure, less good upper-mids/lower treble behavior and a tweeter that has to be crossed-over lower and often steeper, with less dynamic headroom.
I would tend to say that the main reason behind going for a 6.5" unit is that it generally gives you a system with a higher end sensitivity. Now providing that the 6.5" unit is crossed over appropriately to the tweeter then the mids should not be compromised in any way. Of course one does have to make sure that the tweeter is capable.

I do agree that a 5" + 1" set-up hits a nice sweet-spot, generally because it allows you to cross over high enough (even with metal cones, most of the time) such that a less robust/expensive tweeter can be used.

Quote:
Originally Posted by gornir View Post
Even though the mid-woofer off-axis dispersion is a non-issue when crossed-over low enough, the tweeters ability to play mid-range is a limiting factor. Sonically, I think a well behaved mid-woofers ability to play upper-mids is superior to a tweeters ability to do the same. If you like me prefer low-order filters you also get a larger “comfort zone” for the tweeter to work in.
Well if you prefer low order filters, then low xover points and stiff cones are out by their very nature. I think it very much depends on what tweeter you are using. Sure, normal 1" domes tend to struggle a little when xovered too low, but when you've got a wave-guide, even just a small one, added into the mix it changes things.

The DXT, due to the wave-guide is capable of handling a 2nd order 1.5kHz xover. I believe Mark K was unsure of if the DXT would be able to handle this in his ER18DXT, so he tested it with his usual multi-tone measurement up fairly loud and found it coped admirably. It's a shame that his blog was hacked and the measurements were lost. I too was surprised at how well the tweeter coped.

I agree with you though that 8" mid/bass drivers aren't really suited to 2 ways. You can make them work if you pick your drivers carefully or use a wave-guide, but there's very little room for compromise.

Quote:
Originally Posted by gornir View Post
As you realize I’m not a huge fan of 2-ways with a mid-woofer larger than 6.5”, but that doesn’t mean there aren’t great sounding 2-way designs using woofers larger than 6.5-7” out there.
I am not a huge fan of 2 ways period! I think they can be great if all you want to do is listen to music at lower levels in a small room. But for serious listening even at modest SPLs, if you prio midrange then you should really go with a three way.

I too think that the U16 would be excellent as a dedicated bass driver in a small form factor three way. A pair of them + something like the scanspeak 10F + the DXT would make for a very nice compact three way. Some might think the DXT wasted in such a design, but I'd want it just for the small region of constant directivity that it provides.

Have you tried experimenting with larger wave-guides Goran?
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Old 14th June 2012, 05:57 PM   #17
gornir is offline gornir  Sweden
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5th element,

I agree with you in almost every aspect.

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Originally Posted by 5th element View Post
Now providing that the 6.5" unit is crossed over appropriately to the tweeter then the mids should not be compromised in any way. Of course one does have to make sure that the tweeter is capable.
This is interesting. I usually evaluate new drivers using my DEQX system in an active cross-over configuration. With it I test different cross-over points e.g. 1.5, 2, 2.5 and 3kHz etc. with the exact same cross-over slopes and frequency response. With this configuration I can swap between cross-overs with a simple press on the remote control while sitting at the listening seat. This is a very good way to judge mid-woofer/tweeter integration and I promise you that e.g. a 2kHz cross-over sounds different than a 3kHz, even though the frequency response is the same.

What I’m trying to say is that I usually prefer a smaller mid-woofer crossed-over at the 2.5-3.5kHz rather than a larger mid-woofer crossed-over at 1.5-2.5kHz, just because the tweeter sound better this way when it doesn’t need to play mid-range, even if distortion isn’t an issue. However this is not always the case, since it depends on which drivers or driver combinations are used.

Quote:
I am not a huge fan of 2 ways period! I think they can be great if all you want to do is listen to music at lower levels in a small room. But for serious listening even at modest SPLs, if you prio midrange then you should really go with a three way.
I agree, but my comments earlier referred to different sizes of mid-woofers in two-ways.

Quote:
I too think that the U16 would be excellent as a dedicated bass driver in a small form factor three way. A pair of them + something like the scanspeak 10F + the DXT would make for a very nice compact three way. Some might think the DXT wasted in such a design, but I'd want it just for the small region of constant directivity that it provides.
Aaaaah, you stole my idea…. Just kidding, but I have sketched exactly this configuration before, but I haven’t had time to realize it.

Quote:
Have you tried experimenting with larger wave-guides Goran?
Yes, I actually have one medium sized wave-guide on the drawing table, but I haven’t done any detailed measurements yet. The idea is to use it in a large two-way together with a 7” or perhaps an 8”, if I can find a suitable one. I also have some sketching done about an “omni” directional loudspeaker, but other projects have higher priority right now.

Here is an average of the 0, 15, 22.5, 30, 45 and 60deg off-axis frequency response @ 2m. I kind of a simple power response for the "Prestigious Two - Monitor DXT".
Click the image to open in full size.

Regards

/Göran
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File Type: jpg PT-MDXT power response.jpg (123.8 KB, 556 views)
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Old 14th June 2012, 08:42 PM   #18
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Quote:
Originally Posted by gornir View Post



This is interesting. I usually evaluate new drivers using my DEQX system in an active cross-over configuration. With it I test different cross-over points e.g. 1.5, 2, 2.5 and 3kHz etc. with the exact same cross-over slopes and frequency response. With this configuration I can swap between cross-overs with a simple press on the remote control while sitting at the listening seat.
I too have this capability although not via the DEQX, it can be quite interesting. I assume that you use the DEQX to dial in perfect (ie non asymmetric) acoustic slopes and then phase align each of the designs using time delay before auditioning the different designs.


Quote:
Originally Posted by gornir View Post
This is a very good way to judge mid-woofer/tweeter integration and I promise you that e.g. a 2kHz cross-over sounds different than a 3kHz, even though the frequency response is the same.
My experience in doing this kind of thing is rather limited only to a single design, but the subtle changes that I've experienced I've usually been able to attribute to the slight differences in the off axis performance. This is mainly because neither the mid or tweeter are over taxed in any of the configurations and the axial frequency response of each was virtually identical. The changes I've experienced are all subtle changes in the tonal balance rather then anything pleasant/unpleasant, they are just different.


Quote:
Originally Posted by gornir View Post
What I’m trying to say is that I usually prefer a smaller mid-woofer crossed-over at the 2.5-3.5kHz rather than a larger mid-woofer crossed-over at 1.5-2.5kHz, just because the tweeter sound better this way when it doesn’t need to play mid-range, even if distortion isn’t an issue. However this is not always the case, since it depends on which drivers or driver combinations are used.
Well indeed, if a woofer/tweeter combination is capable of being crossed over higher, rather then lower, then it would stand to reason that it would sound better for it too.


Quote:
Originally Posted by gornir View Post
I agree, but my comments earlier referred to different sizes of mid-woofers in two-ways.
Mine really was too, but only meant to go a little further in saying that if you really prio midrange go for a three way

Quote:
Originally Posted by gornir View Post
Aaaaah, you stole my idea…. Just kidding, but I have sketched exactly this configuration before, but I haven’t had time to realize it.
I've been eyeing those SEAS drivers with the increased SD for a while now for a three way, but also haven't had time to do a three way with them. Hopefully I will get around to doing that at some point, the trouble is that there isn't a huge demand for three way designs. At least not when almost every room in the house has a pair of loudspeaker in it already ;/

Quote:
Originally Posted by gornir View Post
Yes, I actually have one medium sized wave-guide on the drawing table, but I haven’t done any detailed measurements yet. The idea is to use it in a large two-way together with a 7” or perhaps an 8”, if I can find a suitable one. I also have some sketching done about an “omni” directional loudspeaker, but other projects have higher priority right now.
I've found that when using larger wave-guides that the treble becomes clearer and more 'tangible' if you like. Describing how things sound is never an easy task!

Matching a 7" wave-guide to a ~7" driver would be a very good idea, it's what I do myself. If you crossover at around 2.5kHz you get a nice directivity match, but it does rely on you having a mid driver with a soft cone.
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Old 15th June 2012, 04:08 AM   #19
ttan98 is offline ttan98  Australia
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Hi,

Gornir and 5th Element, good discussions, keep them coming.

Question:
a std 5 1/4 " midrange/mid woofer driver e.g GR research M130 assuming it be crossed as high as 3kHz, would this be suitable to use with DXT tweeter in order to ascertain constant power directivity from 600Hz to 20Khz?
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Old 15th June 2012, 04:14 PM   #20
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I don't even think that Geddes largest speaker has controlled directivity down to 600Hz.

Think of it this way, when placed on an infinite baffle (in this case I really do mean an infinite flat plane), all drivers radiate sound into a hemisphere at low frequencies. Then as frequency increases there comes a point where the driver starts to beam and it now radiates its sound out into a cone. As frequency increases further the size of the cone continues to get smaller and smaller until it only outputs sound directly on axis.

The rate at which all this happens is largely dictated by the diameter of the drivers cone/dome. If we take a standard 6" + 1" two way and cross it at 3kHz what we get is just above 1kHz the 6" driver starts to beam ever so slightly and it starts to radiate sound into a cone. By the time the driver has handed over to the tweeter it is beaming quite a bit, but because the dome tweeter has a small diaphragm it is radiating into a hemisphere at this frequency.

A design like this basically emits sound hemispherically at low frequencies, then starts to emit into a cone as the mid/bass starts to beam, then transitions back into a hemisphere as the tweeter takes over and finally ends up radiating into an ever decreasing cone as the tweeter starts to beam. This creates an uneven set of off axis curves which at one point transition quite abruptly from one extreme to another and at a frequency where our ear happens to be most sensitive.

The main issue with such a design are the abrupt changes in how the loudspeaker radiates sound as it hands over from the woofer to the tweeter, this is one thing we want to get rid of.

Now as you well know, you can get rid of these changes by crossing over the tweeter at a much lower xover frequency, this does however put a large demand on the tweeter so isn't always appropriate and you are still left with the tweeters own off axis profile that starts off very wide and then starts to narrow with increasing frequency.

The other option is to use a wave-guide loaded tweeter. Now in this case what we want is a wave-guide that is roughly the same diameter as the driver. Why? Because the rules that dictate when a mid/bass starts to beam also dictate when a wave-guide will start to control it's directivity and this is a good thing. Now once the wave-guide has started to control it's directivity it transitions into a region of constant directivity, where no matter how high you go in frequency, the off axis response is held constant. This is half of the point of using a wave-guide as it dramatically reduces the amount of energy radiated at the walls compared to what is radiated at the listener, reducing the effects of the room and giving you a wider sweet spot.

Now if you take the 6" driver and the 6" wave-guide and compare their off axis curves you will find that they match up fairly well. In other words both drivers start to beam at the same time, but whereas the 6" driver continues to radiate into an ever narrowing cone, the wave-guide transitions into constant directivity. Because both drivers start to beam at the same time it means that there is a region of overlap between the two where their directivities are roughly the same. This is what it means to match the directivity of the wave-guide to the mid/bass. In this case because the match is good at a fairly high frequency, say around 2.5kHz, it means you can cross over to the wave-guide loaded tweeter at quite a high frequency and still have a smooth set of off axis curves.

As you can see, the size of the wave-guide, compared to the size of the mid/bass is important in getting a good directivity match. If you use a tweeter such as the DXT with a 6" driver, the 6" driver will start to beam way before the DXT starts to control its directivity, so you don't get a good match. In this case you have to cross over the mid/bass to the DXT at a low frequency, that is before the mid/bass starts to beam. This means you get a smooth set of off axis curves, as you would with a low crossed standard dome tweeter, but as you're using the DXT you still get a small region of constant directivity.

Now of course with this kind of thing there is a great amount of flexibility into what may or may not be considered optimum. The optimum set up is to use a flexible well behaved mid/bass with a wave-guide of a similar size. This gives you the best directivity match, allows you to cross where the mid/bass has started to beam and reduces the demand placed on the tweeter.

If you're using a wave-guide smaller then the diameter of the mid/bass, then the optimum thing would be to put the crossover frequency low enough so that the two crossover before both the mid/bass start to beam, as this pushes the transition from omni>constant directivity entirely within the bandwidth of the tweeter and keeps the transition smooth.

Naturally you can crossover higher if you like and the set of curves will still look very nice, but ideally you'd keep the xover at or lower then where the mid/bass starts to beam.
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