SS 18W/8542-00 + 9500-9700
Copyright 2007 Troels Gravesen

9700 version      9500 version     CABINET 


ScanSpeak 18W/8542-00 + FD2905/9500-9700

Part I: 24 liter floorstander, 9700 option

Danny from Norway wrote me and asked if he should "eBay" his SS 8542 drivers, which I certainly think would be a very bad idea, so here we go. My 8542 drivers have been on the shelf much too long. This is one of my favourite SS drivers, long fibre paper pulp, foam surround, symmetric drive, etc. A driver you can listen to for hours and hours - that is if the tweeter is properly integrated.

Only bad thing about this driver is the dip at 6 kHz. I'm not sure what causes this problem. I had a suspicion on an un-damped polepiece, but by closer inspection it turned out the polepiece actually is damped. However, with a 2nd order filter this dip in response is way down and probably doesn't impact sonic performance.
The 8542 has been seen in studio-monitors and I'll later publish a construction in a 14 liter cab with the SEAS 27TFFC tweeter, as this is the classic set-up. But Danny asked for the 9700 tweeter option and this is where it will start, although not in the small cabs. I have pre-veneered, pre-cut panels for the mini, but later... The front panel used here is 190 mm wide and the 14 liter monitor version will have a 205 mm wide baffle and slightly different driver placement, so there may be changes to the crossover.

The Crossover


Crossover for 18W/8542 + 9700


Suggested crossover components from Jantzen Audio
Contact Jantzen Audio at: contact@jantzen-audio.com


The Cabinet

Basically this is the same as the TJL2W, only 240 mm deep. Construction details and damping materials can be found in TJL2W and SP38 files. Cabinet volume, front panel width and driver placement are the most important things to follow here.
Problem! Cabinet depth = 200 mm, vent length = 200 mm, won't work. (My test cabs a deep enough for a 20 cm vent). Use a 60 mm vent with a length of 12 cm, or make the vent towards the floor. Leave at least 40 room (spikes, etc.) for the vent to breathe.

8542 drivers, TS data, box simulation.


My measurements compared to the SS data, no major surprises.
Added mass method used.


LspCAD box simulation. From measured data: QB3 = 12.9 liter, SBB4 = 14.8 liter and SC4 = 13.8.
This looks fine for the 14 liter monitor version, but we can get deeper bass from this driver.
With a vent tuning of 45 Hz we have flat response down to 50 Hz - and it sounds good too.

Measurements

Left: SPL from 9700 and 9500 tweeter, red and green = 9500. As seen before the 9500 has higher sensitivity and the 9700, due to the symmetric drive feature, has a rising response towards higher frequences, thus needs equalising not to sound pointy.
Right: SPL from 8542 drivers and 9500 tweeters again. The dip at 5 kHz is sad, as this driver might have worked with 1st order filters had it not been for the design problems.

Left: impedance of all drivers, also displaying the spread in performance. This doesn't get much better.
Right: SPL from driver with crossover and summed response. Point of crossover is 2 kHz.

Left: Summed response at 1 m/tweeter height from same polarity (red) and reverse polarity (blue)
Right: Left and right speaker, one 8542 driver had a minor notch at 2 kHz making its way through to the final performance. However, hardly audible.

Left: Impedance of final system +/- mid impedance flattening circuit: 1 mH + 10 uF + 15 ohms across input terminals.
Right: Step response showing positive polarity of both drivers and a smooth decline from the 8542 driver. It also shows this speaker is not time-coherent.

Part II: 24 liter floorstander, 9500 option


Suggested crossover components from
Jantzen Audio

As always: Swapping tweeters can be major trouble and this one was no exception. The 9500 and 9700 are very different tweeters and the whole thing had to be worked over again. What made things worse was a minor difference in 8542 performance, which leaves you with task of making a crossover that will work for both drivers and hopefully for all 8542 drivers. I can only guess what the variation is. Worst case is a minor bump at 2 kHz, but I think one of my drivers is an exception.
Red = true resistors, "empty" resistors = resistance of coil. For the L1041, the total resistance of coil and resistor should be around 0.8 ohms.

Measurements

Left: This is what happens when we swap tweeters without fine-tuning the crossover for the new tweeter. Blue = 9500 option with 9700 crossover. Right: Here we can see the 9500 response (green) from the 9700 crossover. No further comments.

Left: Summed response (red) and response with inverted tweeter polarity. Measurements taken a tweeter height, 1 meter distance.
Right: Summed response and minimum phase.

Left: Impedance from system in 24 liter cabs. Red is with stuffed vent.
Right: Step response displaying same polarity of tweeter and bass and a smooth decline from the 8542 is seen.