Poor Man's Strad Excel
Copyright 2010 Troels Gravesen

CROSSOVER     CABINET     MEASUREMENTS     SPEAKER KIT

SEAS W22EX001 + W15CY001 + 27TFFC

This will be a short presentation of the PMS-EXCEL as most info on design considerations is available at Poor Man's Strad.
Here the relatively small W15 midrange (75 cm^2 membrane area) has all the acoustic support needed from the wide baffle and from a point of crossover around 350 Hz a good integration with the W22 bass is achieved. The slightly modified 27TFFC is doing so well that I left it in place from the PMS set-up. No need for more expensive tweeter although I'm sure that some will believe the 27TFFC cannot match tripple priced tweeter. It can. This tweeter is used in well-recommended Britisk speakers from ProAc and Spendor.

The Cabinet: Go to PMS file.
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The W22EX001 fits well into the 38 litre cabinet and the vent tuning of ~33Hz was maintained.


The Crossover:
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The W15 was modified around 2000 as can be read here:
http://www.troelsgravesen.dk/SEAS_5INCH.htm
- thus a small change to the mid notch filter.


The speaker kit
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The crossover for the EXCEL variant takes a few more components compared to the paper-coned version. No wonder, the midrange driver's cone break-up has to be carefully suppressed to render a clean treble. However, the 2nd order filter between bass and mid could be maintained from the PMS with a few modifications. The mid low-pass section is 3rd order + a notch filter and the tweeter maintains a 3rd order filter similar to the PMS.

Complete speaker kit available from contact@jantzen-audio.com

Please all technical questions at troels.gravesen@hotmail.com


Sound of PMS-EXCEL

This is the part I really hate because describing sound is impossible. We are extremely sensitive to any negative comments on performance. We can take any high-end speaker and start lining up what this speaker is not good at, because no speaker does it all. But we rarely read reviews like this in magazines. The magazine would very soon run out of speakers offered for reviews. A review is meant to sell speakers and we have to carefully read between the lines to try to find any reservation from the reviewer - in case there are any. Mostly it's "bla...bla... this is the best speaker I have had in my system, etc." Useless!

Thanks to the internet we are seeing more critical reviews although a lot of "amateur" reviewers try to copy the style and language of their professional colleagues.
Before I go to the sonics of the PMS and PMS-EXCEL, a few comments on drivers. The high sensitivity of the PMS is derived from the use of drivers with lightweight paper cones. Paper, when done right, can provide a speedy, transient sound and usually the break-up of the paper cones is of an ear-friendly kind. The sound simply gets muddled when the speakers are driven too loud. Not necessarily so with the hard-cones. These EXCEL drivers use magnesium membrane material, which is extremely hard and work as a piston in the range where the driver is intended to perform, but outside this area, they break-up and produce some very nasty peaks that has to be carefully removed in the filter. Despite the low weight of magnesium the cones are heavier than the paper cones and the EXCEL drivers generally have 3 dB less sensitivity compared to the paper cones and the sensitivity of the EXCEL version is ~3 dB lower than the PMS. Very much as expected.

The reduced sensitivity of the PMS-EXCEL was immediately recognised when the first speaker was compared to the PMS. Going from 88 dB to 91 dB/2.8V makes a difference and the 150 wpc amp in my workshop has to work harder to render the soundstage of the PMS. Next thing was that the EXCEL drivers are low-coloured compared to the paper cones and at the same time I warn you to put too much into this. Every driver colour the sound due to the materials used in driver construction. I'm sure that some will favour the paper version due to speed and transient attack and others will favour the ECXEL due to the more cool and clean sound. It's a matter of taste. Another thing is that higher sloped crossover usually provides a "cleaner" sound as the drivers don't try to do things in the neighbouring area where it may not be best performer, and the blend of the sound from two drivers sharing a certain frequency band will always be a mixed blessing of different sounds.

The PMS can be driven from small amps where the PMS-EXCEL gets better and better the more watts you put behind. The EXCEL drivers can grow with the task of larger amps, where the PMS really doesn't need a whole lot of power to perform the best. This doesn't mean the EXCEL can't be fully enjoyed from an e.g. 50 wpc valve amp, which is what I'm running right now when this is written. The Copland CTA 505 does very well with the EXCEL set-up - as it does with the Acapella SEas. All depends on how loud we play.
All this to say that I wouldn't choose between the PMS or the PMS-EXCEL purely based on cost. One version may hold qualities that will suit a particular set-up better than the other.


Measurements
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Left: Impedance of drivers in cabinet without crossover. Vent tuning for bass is around 33-34 Hz. Vent tuning for mid = 70 Hz, not a big issue as the point of crossover is around 350 Hz. Stuffing the mid vent does very little to the sound.
Right: Impedance of the whole system with crossover in place. Impedance in the 100-300 Hz region stays around 6 ohms. No deep dips here and an overall amp- friendly performance.

Left: For those interested, the individual response of drivers with no crossover. Please notice the humongous peak (cone break-up) from the bass driver at around 5 kHz. This is some 15 dB above average level! However, crossing over at 350 Hz can be done 2nd order without further fine-tuning.
The W15 is doing great here, flat from 200 Hz to 4.5 kHz. Peaks are well above intended point of crossover to the tweeter. 27TFFC really is a sensitive tweeter. 93 dB/2.8V is no problem and it makes it suitable for the
C17 construction where an overall level of 95 dB sensitivity is achieved.

Right: Displaying the overall SPL response is tricky due to the gating technique of the CLIO measuring system. The graph above is made from three measurements and merged at 200 and 700 Hz. Basically the speaker is flat from 500 Hz to 20 kHz and I would have to take the speaker outside to get a better picture of performance below 500 Hz.

Left: The mid low-pass section was tried with a 2nd order + notch filter (blue graph), but after some days of listening there was "something" to the treble that wasn't right. A 0.33 mH was added to the mid and the shunt cap increased from 10 uF to 13.3 uF and the green graph appeared. Result: Clean treble. Only shows the importance of suppressing these resonances more than 20-25 dB, which is often seen from e.g. the SEAS kits.

Right: Step response showing inverted polarity of tweeter and mid.

That's it!

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