Studio 101
Copyright 2009-14 Troels Gravesen

DRIVERS      CROSSOVER KIT     CABINET     CROSSOVER      MEASUREMENTS

 

This project has been on hold much too long, but here it finally is. A modest sized monitor from ScanSpeak 18W/8542-00 + SEAS 27TFFC. Some may find resemblance to a well-known commercial design, but the crossover here is not a clone of the original, rather a well-balanced network addressing a few problems not taken care of in the original.

Now, what makes a "studio monitor" different to any other "hifi" loudspeaker? Well, a true studio monitor is supposed to have a reasonably flat on-axis response combined with an even power response, allowing studio engineers to make the best possible mix of the recording before the final master. But shouldn't all speakers be suitable for this? I guess the term "studio monitor" was derived from well engineered speakers in contrast to most home audio speakers back in the Seventies, when domestic speakers certainly was a mixed blessing of drivers balanced by a few measurements or by the ear alone. Quite often this left a lot to be desired. Only a few speakers were well balanced like the BBC studio monitors, e.g. LS35A, BC1, etc., thus the distinction between home speakers and studio monitors. Besides this, good studio monitors were often made from drivers of considerable higher quality compared drivers in home audio speakers, thus quite revealing towards poor amps and poor source material. Studio speakers were often perceived as having a flat, forward sound with lots of detail. Consequently home audio speakers quite often had a "loudness" tuning, that is: Boomy bass and too much treble. ProAc speakers fall well into this category. What is needed when a potential customer enters the local hifi shop is something that immediately captures his attention, and lots of bass and lots of treble just simply sell. This may long-term create a lot of problems once the speakers are installed at home, but when we buy something we have often our minds set strongly on that particular product and may be reluctant to return the speakers - or we may too late realise that we were seduced by that tizz'n-boom tuning we heard in the shop.

The 18W/8542-00 driver is one of kind, unfortunately not often found these days: Long fibre paper pulp membrane and light-weight foam surround. Very much the same recipe used in the JA8008 driver from the TQWT and DTQWT designs. The wide acoustically transparent dust-cap used here is merely a design gimmick, creating some problems in the 5 kHz region, but targeting a point of crossover at ~2300 Hz, this problem is eliminated.

Cabinet volume is ~13 litres and we have F3 = 55 Hz. Should you have room for bigger cabs, 18 liters will make F3 = 49 Hz and from 22 litres F3 = 45 Hz. If you choose to make a larger cabinet, maintain cabinet width and upper placement of drivers; that is, extend front panel below bass driver. It won't change the midrange too much. Ultimately make a 1 meter high TL floorstander like the ATR25. Details below.

I had great expectations from this monitor due to the long-fibre paper pulp cone and I wasn't disapointed. My current workshop amps are the 5687 triode line stage driving a DC coupled Rotel amp. A heavily modded Rotel CD player delivers the music and a lot of times during crossover fine-tuning, the speakers are set up for audition.
Initially a series filter was tried and turned out very hard to fine-tune. The 8542 driver on a small baffle like this is not particularly easy to handle. The narrow baffle leaves the common midrange bump that must be removed and due to the wide acoustically transparent dust cap, a relatively low point of crossover is desired to eliminate some problems in the upper treble range. This simply didn't work from the series crossover, thus a parallel filter that is fairly easy to construct and most likely will render proper performance from all 8542 drivers. From my experience the 8542 drivers have wider tolerance levels compared to Revelator drivers, but the sound....
The sound from this paper cone with foam surround is just great. Lots of transparency, detail and responsiveness. Sensitivity is ~86 dB/2.8 volts, thus requires some 40-50 watts minimum, but this speaker can play loud and should perform very well with a suitable subwoofer, should the bottom octave be desired too. The 8542 in 13 liter net volume will not shake your guts, but compared to most 5" minis, this is far better due to decent driver Xmax and 155 cm^2 membrane area. Size matters - as always.

 

The Drivers
BACK TO TOP

Download data files: ScanSpeak 18W/8542-00, SEAS 27TFFC

The Cabinet
BACK TO TOP


You can place the port to the rear or front.
13 liter volume, Fb = 43 Hz, port = 50 (ID) x 143 mm (use port unchanged)
18 liter volume, Fb = 37 Hz, port = 50 (ID) x 140 mm (use port unchanged)
22 liter volume, Fb = 37 Hz, port = 50 (ID) x 110 mm (cut to 110 mm length)

TL floorstander for 8542/27TFFC


Click images to view large. Check
ATR25 for details on damping.


Studio 101 Crossover
BACK TO TOP


After initial measurements, this crossover was simulated in LspCAD.
The large bass driver on the small front panel calls for some midrange equalisation, thus
a notch-filter around 800 Hz. This is very much text-book practice and can be seen in the other
CSM constructions.
Combined resistance of R2031 and L2031 = 10 ohms +/- 1 ohm. The coil suggested below has DCR = 2.3 ohm, so R2031 = 8.2 ohm.

CROSSOVER KIT incl tweeter
BACK TO TOP

Complete kit with/without drivers available from contact@jantzen-audio.com

Kits can be bought w/wo drivers

Download Kit Presentations here (zip file):

All kit and component prices may be subject to change and are always to be confirmed by Jantzen Audio Denmark.

All technical questions to troels.gravesen@hotmail.com

 


Finished crossovers for Studio 101.


Possible crossover layout. The two holes are for terminals, having the board placed on rear panel.
The two "plus in" goes to the same terminal plus.


The board is actually large enough to take Superior Z-caps. And I'm serious. This speaker would benefit
from even better caps than those used in the finished crossovers.


Left: Crossover in place in cabinet. Silverplated copper in teflon cables used throughout.
Right: Folded piece of damping material on top of crossover and covering bottom of cabinet.


Measurements
BACK TO TOP


Left: SPL @ 1 meter, 2.8V from drivers mounted in cabinet.
Right: SPL from drivers driven from crossover. Point of crossover ~2300 Hz.


Left: SPL @ 1 meter, 2.8V with inverted tweeter polarity.
Right: Response merged with nearfield bass response at 250 Hz.
Blue = port response. This does look a bit optimistic in terms of bass extension, so, a grain of salt here.


Left: Final impedance of system. Minimum impedance is 6 ohms, making this a fairly easy speaker to drive.
Right: Cumulative spectral decay at 20 dB scaling.


Left: Horzontal dispersion @ 0, 5, 10, 15, 20 and 25 deg.
Right: Vertical dispersion up starting between tweeter and midbass @ 0, 5 and 10 deg. (red, blue and green).
Overall an excellent even power response.


Left: Vertical dispersion down starting between tweeter and midbass @ 0, 5, 10 and 15 deg.
Right: Step response displaying positive polarity for both drivers and clean decay from midbass driver.

Back to intro page