W18E001/JP3/NeoCD3 or W18E001/T25C003
The following project describes a 2-way floorstander of modest dimensions: 19 x 98 x 26 cm (W x H x D). As a follow-up to the 2.5 clone this project is targeting a better midrange, better treble, bass comparable to the 2.5 clone and a more moderate sized cabinet. Well, can all these requirements be accomplished in a smaller size construction? And from what drivers?
From the Point75 and Acapella projects the use of the SEAS W18 drivers seemed an obvious choice for a 2-way floorstander. And from the bass performance of the Point75 a smaller cabinet might provide similar or better qualities compared to the 2.5 clone. But you can never tell the bass quality until you've tried. What I also wanted to try in this construction was the use of a passive radiator and SEAS provides suitable PRs for 6" drivers. This PR proved to be a major disappointment, but more on this later.
Getting more bass out of a SEAS W18 design, the magnet obviously has to be smaller - or the cone must be heavier - compared to the W18EX001 driver used in the Acapella, hence the W18E001 was the one to look for. This driver has TS data suggesting a 24-litre cabinet to be suitable for some decent bass and a port/PR tuning of 34-38 Hz should provide a f3 at 40 Hz. The JP3 ribbon tweeter is described in the Acapella file and needs no further introduction here. This is a fine tweeter at a reasonable price. You may substitute the Fountek JP3 by the Aurum Cantus G2Si ribbon without changes to the crossover. I think the JP3 has a better faceplate compared to the AC G2Si despite being made from plastic. The JP3 plastic faceplate follows the curvature of the horn better and makes a good termination.
The prototype cabinets were made from 20 mm Baltic birch with 19 mm MDF front panel. Internal panels were added 4 mm self-adhesive bitumen pads (can be found in car accessory stores). All internal panels were damped with 10 mm polyester foam and behind the W18 driver 2 sheets of 4 x 15 x 20 cm MDM3 (Monacor) were placed. At the top and bottom of the cabinet more of this damping material was placed to reduce standing waves between top and bottom.
Much to often heavy front panels are produced without chamfering like seen on the picture to the right. This seriously prevents the air from having free access to the enclosure behind the driver. Remember, the amount of energy released from the rear of the driver membrane is exactly the same as from the front. Don't forget to chamfer the driver holes 45 deg. as seen on the picture to the left.
Left: TJL impedance curves: As can be seen
the port tuning is around 36 Hz. Vent 72 (ID) x 200 mm.
Overall impedance never falls below 7 ohm.
Left: TJL BM and T response. Point of crossover = 2600 Hz. Right: Blue = frequency response with reverse polarity of drivers. Red = frequency response with same polarity of drivers.
Left: TJL, cumulative spectral decay. Right: TJL, step response.
Sound of the TJL?
Initially I listened to the version with a
These magnesium drivers are revealing and improper recordings will be presented as such. The construction does not favour any particular type of music. Very often we read that a construction excels from simple acoustic music, jazz trios, etc., where large orchestral works fall apart. Not here. Of coarse there's a limit to the loudness due the size of the driver membrane, but it can play louder than most other 6" drivers I have tried. Very low distortion that is. I found the sound the best with some 70-90 cm from the front of the cabinets to the wall behind the speakers. For good reasons I haven't mentioned the treble from the ribbons. This you will find in the Acapella files. The JP3s in this set-up holds all the qualities from the Acapella. Given the simplicity of the construction and the modest size, I think the TJL handles all musical genres remarkably well.
Download cabinet drawing here.
*: 13-02-2006: The poor results from the passive radiator set-up may have been caused by the radiator simply being too far away from the bass driver.
It's been a long time since I've heard the TJL and comparing the TJL 2-way to the TJL 3-way was obvious. With the experiences gained from the Ekta and Zahra and carried through to the TJL3W from adding a small driver to handle the upper midrange/lower treble, the TJL doesn't have the dispersion in this area and will off-axis sound more closed and with a lack of presence as often heard from similar sized 2-ways. On-axis, this is less noticeable, but I would have liked you all to have the possibility of compared a speaker made from the same basic drivers, having similar sensitivity and amplitude profiles, but where one is a 2-way and the other a 3-way. The sound is very different. No surprise, the TJL3W is a better speaker, but it obviously comes at a cost. Should you decide to engage in a TJL project, I seriously recommend taking the 3-way into consideration.
The NeoCD3 and the JP3 are quite alike in their frequency response, but they are not compatible and the crossover will have to be modified to accommodate the NeoCD3 ribbon.
Polarity of NeoCD3: The NeoCD3 has it's positive terminal to the left when you view the driver from the rear and the terminals are up. Remember, the NeoCD3 - like the JP3 - has to be connected with inverted polarity.
So, the TJL was set up in the test cabinets again and this time I took the help of LspCAD to do most of the work. Actually the new measurements were so good I didn't have to change any component values to reach the target frequency and phase response. Great!
The "problem" with
re-visiting a construction you made a couple of
years ago is that what you have leaned since then makes
you reconsider the whole project. What are the strengths
and weaknesses of your construction? A few things here:
Some basics: The TJL uses a bass driver with a relatively small magnet (same situation as the 18W/8535 driver in the 2.5 Clone). This means relatively low sensitivity, but we get deep bass from a small cabinet - and the W18E001 really goes deep. It also means the frequency response of the driver is relatively flat, where a driver with a large magnet often has a steep rising response towards higher frequences. It also means the baffle step compensation has to be relatively small for the W18E001. To equalise the response of a driver on a narrow baffle we add a large coil to 1) provide baffle step compensation and 2) tilt the rising frequency response towards higher frequences. The result of this can produce several things: Quite often drivers have a bump around 800-1200 Hz due to baffle step loss and relatively high magnet strength (there are more to this, but these are two of the main factors). If we want a flat response we can do two things: 1) We can use a large coil to basically align the 1 kHz response with the lower midrange and 2) we can equalise less (use smaller inductor) and remove the bump at 800-1200 Hz by adding a notch filter for the same region. The benefit from the latter option is that we sometimes can avoid a dip around 400-600 Hz, which may be the result from simply using a large coil at the intro of the crossover to render a flat response at 1 kHz. The first option is to some extent the situation for the TJL.
With LspCAD at hand I decided to wipe the table clean and start all over again. From the merged nearfield and farfield frequency response profiles of the W18E001 driver we can see a phenomenal bass extension from a 6" driver. I have 10" drivers that will start to roll off from 80-90 Hz, but this little fellow goes down to 60-70 Hz before descending. The price for this - as said - is sensitivity. We're talking 83-84 dB/2.8V in the upper bass/lower midrange.
The TJL has a minor depression around 400-500 Hz (upper graph) to render a sonically optimal level at 1 kHz, so what if we tried to balance the 100-500 Hz region first, and then equalised the 1 kHz region with a notch filter = lower graph. What seems to be the result of this is 1) a flatter overall response, and 2) increased sensitivity in the midrange and treble. Well, we cannot increase system sensitivity from doing so. What the W18E001 can manage in the low bass is what determines the basic sensitivity of the construction. When we increase the response in the midrange and treble we sacrifice relative bass level, not extension but level. But the bass level of the TJL is so good that it may be worth sacrificing 1-1½ dB to get an apparently more sensitive speaker. How this will sound is a good question.
Next thing: Dispersion in the crossover region. Almost any 6-7" driver will have poor dispersion characteristics around 2-3 kHz where the point of crossover often is placed. Ribbon tweeters have (mostly) good horizontal dispersion and poor vertical dispersion, so the TJL is likely to have a reduced power response in the crossover region (read about the Acapella SEas experiments). It's a strange thing, because we can measure a 6" driver to perform well up to 3 kHz, but try a 4" driver handling the same upper midrange/lower treble region and you will hear a world of difference. To improve the power response in the crossover region we need a dome rather than a ribbon and thus the SEAS T25C-001 tweeter (Acapella SEas) was brought in again and inserted in the TJL cabinet and new measurements were performed with subsequent LspCAD simulations. To further improve power response, the point of crossover was taken down to approx. 2 kHz. Ideally I don't think a 6-7" driver should be taken much higher than 1.5 kHz, read SP38 file.
I have to say that what is
depicted here is highly dependent on proper
splicing of the two SPL graphs of the W18E001 response.
The near-field and far-field response has to be valid at
350 Hz for both readings. The far-field reading was an
average of 5 measurements at ½ metre distance to have a
lower reliable limit of approx 250 Hz and the near-field
measurement was an average of 5 measurements taken at 1
mm (one millimetre) distance to the membrane and with a
64 millisecond window to render a lower limit of 15 Hz.
Repeated measurements gave then same results.
Left: SPL from individual drivers without crossover attached. As can be seen, the response from the W18 is reasonably linear up to 400-500 Hz, then climbing some 5-6 dB up to 1 kHz. Last but not least, the horrific cone break-ups peaking at 5 kHz that has to be carefully suppressed by the notch filter. The T25 has a minor bump at 1700 Hz, but nothing that causes trouble in making the crossover work.
Summed response (red) with near-field bass response from 350 Hz. Now this is some smooth linear response and the sonic impact from this is not to be ignored. Blue = minimum phase.
Left: SPL from drivers with crossover attached. As can be seen the cone break-up from the W18 is thoroughly suppressed. Point of crossover is around 2300 Hz. (sorry for merging the tweeter also! Doesn't do much below 600 Hz)
Right: Impedance profile of TJL-T25. This is a relatively easy load on your amplifier.
The T25 Sound
So, what about the sound from this T25 version? Well, most of the new design criteria seem to be accomplished here. Right, the basic sensitivity of the construction hasn't changed - and yet the midrange/treble has been lifted some 1-1½ dB compared to the TJL-"Classic". And you really do not feel any lack of bass compared to the "Classic" despite the "brighter" voicing of the speaker. The upper midrange/lower treble is quite different from the "Classic" due to an improved dispersion in the crossover region.
To cut a long story short
you get a speaker with added presence from the T25
version. And you get an "easier-to-listen-to"
speaker due to enhanced dispersion. You also get a more
forward presentation and this may suit some, others may
prefer the more laid-back voicing of the TJL-Classic.
Comments from Andrej/Slovenia on the TJL
Here we go... This speaker is totally opposite of so called "lushness" sound. It is very detailed and can play VERY loud without noticable distorsion considering only 7 inch driver. My Proacs cannot even approach this volume level without severe distorsion. Imaging is very good. Due to more laidback voicing laying more behind speakers. Transparency is exceptional. This speaker with Fountek treble really excels where gitars and percussion plays major role. Just listen to Nils Lofgren's "Keith don`t go"...
It is really a great design (thanks of course to your great knowledge about speaker design!), but with my equipment it is not the best partner. I borrowed my friends good LP turntable and things got better. When I add a valve power amplifier things get more rounded and smoother with more enjoyable sound , but due low wattage, output dynamics suffer.
I chose this design because I really wanted to know what a good design with magnesium cones would sound like. I know now why Joseph audio loudspeakers are each time represented with big Manley valve power amps. Cause valves are great match to magnesium low distorsion cones. That's are my experiences from today's listening session. But with my equipment and CD collection it's just not the best match.
Because I've got nice TJL cabinets done, I decided to keep these boxes and choose between CNO or 8545 + 9500/9700 projects. I am targeting to some kind more forgiving sound compared to the Excel units. Some of my CDs sound great, but most of them sound less enjoyable with TJL JP3. I just wish to have more warm and smoother sound, like old Sonus faber designs. The Excel magnesium designs have great transparency, but I miss that some kind of "lushness" which give voices and instruments more natural and less edgy sound.
I could say goodbye to some deep bass and trasparency from TJL JP3 speaker to get little bit more sensitivity speaker with more relaxed sound. I've listened to Sonus Faber Electa Amator speakers which use 8545 driver paired to 19 mm tweeter from ScanSpeak. To my ears it sound marvellous...But I wish I could also hear the Seas 7 inch Nextel coated driver. Is there any major differences between these heavy coated units? If you got good a LP turntable in your system or valve preamp or valve power amplifier, than this system could sound magnificient. If you will pair it with all clean sounding solid state electronics than you might get a too transparent sound. Not agressive, just very revealing. Regards, Andrej
Andrej, thanks for your comments
to "the clone" and the TJLs. System matching is
a never ending story, but in comment to your mail, I
can't help mentioning that I a few days ago received the
latest recording done by John Atkinson at Stereophile: Attention
Screen/Live at Merkin Hall. This is what my
wife calls stress-jazz, but I like it and the recording
is excellent. Ordering CDs from the US I also included
all the Stereophile test CDs and here we find recordings
so good, that I started wondering if my LPs could ever
deliver something similar. Magnificent recordings! I was
in the process of fine-tuning a small mini-monitor in
replacement of the W11, a W12 Nextel construction: http://www.troelsgravesen.dk/W12.htm, and I couldn't
help thinking that some of our speakers are really better
than we think they are because most CDs really sound
crappy, when all of a sudden you're confronted with some