Philips 9710/M01, 8 ohms
Copyright 2005 Troels Gravesen
       

- go to chapter II
- go to chapter III, coating
- go to chapter IV, dissasembling of a 9710 driver.


Download scan of original Philips 9710/M8 brochure here. 370 KB.
Thanks to Darryl for not throwing out this Philips brochure like I did many years ago.


Philips 9710 M/01 alnico version

 

Measurements

First of all impedance of the two drivers: Nice! Both having a Fs of around 44-45 Hz. The coating of surround works fine and I hadn't expected to hit the same Fs for the drivers. Remarkably there's only a minor increase in impedance towards higher frequencies. This is usually only seen from symmetric drive (SD) speakers where the pole piece is covered by thin copper. As can be seen from the TS data sheet below, the induction at 10 kHz is low.

Since I wrote the above notes I found this on a website from Holland:


Philips 9710 with the pole piece covered with copper.
So, indeed Philips used "symmetric drive" long before Scan Speak.
No wonder the impedance curve is so flat.
Nothing new under the sun - only evolution.

TS-data:

TS-data. Note that calculated sensitivity is 91 dB.

 

Calculating a box for the 9710 isn't that easy as math dictates an excessively large cabinet. More than 100 litres closed for a Qtc of 0.7.
A 40 litres vented cabinet of 40 litres only provides a F3 of 56 Hz. If we had had the Fs = 35 Hz and Qt = 0.4, we would get an F3 of 43 Hz from a 40 litres cabinet. We'll see if the drivers change over time. Usually Fs decreases and so does the Qt. Philips recommends a 40 litres cabinet and this it's likely to be.

Frequency response at 1 metre distance from microphone to front panel. Both drivers shown. Disregard what's below 300 Hz due to gating. This looks pretty good in terms on drivers' consistency. Same SPL response from drivers. The peak at 3 kHz is certainly to be heard when listening to music. On-axis it's severe, but the strange thing is that it's an ear-friendly kind of peak. It's excessively loud, but it doesn't shred your ears the same way the 18W/8535 did in the 2.5 clone at 2 kHz. The FR is clearly consistent with the Philips measurements seen below.

Left: Philips 9710 anechoic response. Right: Philips' claimed response in living room conditions. Now, this all of a sudden almost looks too good to be true. Taking the speaker into your living room all has suddenly changed for the better, and +/- 3 dB from 70-12000 Hz isn't bad at all. If I extend my measuring window to 320 milliseconds and add some heavy smoothing, I can simulate living-room conditions and it looks like this:

It appears that the Philips claims are not all that wrong and what's depicted above can take any shape depending on actual placement in your living room. If I put the speaker close to the wall, I would probably get even more response in the bass and lower midrange area. My workshop has a severe dip at 60-70 Hz, so this will account for lack of response in this area. However, it doesn't relieve the 9710 of having a severe peak at 3 kHz.


Impulse response. Hmm...some peaks and in all directions. Probably not that unusual from a twin-cone driver.


Step response. Two major peaks; I guess the second one is from the whizzer cone.

Equalisation of 9710 - LspCAD:


A single coil and a series LCR network to reduce the 3 kHz bump should make the 9710 perform
like seen above. And so it does as seen below.
This makes the upper treble week and I added two old 4 ohms Peerless cone tweeters connected in series and
driven from a 2nd order network consisting of 1.5 uF + 0.1 mH to ground and ended up with this FR:


Quite some dips and bumps, but it sounds better than you would think.
The tweeters were simply placed on top of the cabinet, thus the irregularities in upper treble.
This sounds good on vocals, the tweeter balance is fine and this will be my first set-up in the test cabinets.


- if only I could find some more of these...

Nov-05: Finally got some of these Peerless cone tweeters, the CT62H.


February 2006, Chapter II
The Peerless CT62H option

It's very much time to take another look at the Philips 9710 fullrange drivers. One of the drivers has been at the corner of my workshop in a 30 litre test cab. Two of the Peerless cone tweeters were floating on the top, spewing treble in all directions and making enjoyable noise when doing other project. A simple 1st order network was connected to the drivers.
A pair of 37 litres cabs were constructed and I very much enjoyed making a pair of old-time cabs again - close to how I did more than thirty years ago - except for the driver rebating. I didn't have a router then - much too expensive. And we didn't have MDF either. Chipboard was the menu of the day.


Left: First time set-up, the 9710 with two Peerless cone tweeters, CT62H. Right: preliminary crossover, V2.

Cabinet, basic dimensions:


Cabinet made from 19 mm MDF.
300 mm (W) x 550 mm (H) x 319 mm (D), net volume ~ 37 litres.
Vent = 73 mm (ID) x 110 mm length.

 

Measurements

Above is seen the frequency response of the 9710 driver alone with no crossover attached.
I've recently had a mail exchange with a fellow running two 9710s in series on an open baffle and I'm still wondering how he can live with this. The open baffle may sound very different from what I hear from my boxed 9710s, but it won't remove the peaky treble. The frequency response of the 9710 not only looks awful on paper, it sounds awful too - to my ears. 10 dB peak at 3.5 kHz! Exactly where the ear is most sensitive! I honestly don't get it. As said previously, it's not an ear shredding kind of peak, but this is by any standard low-fi. I'll call it amplitude distortion as it surely changes the way instruments and voices sound.
I did survive this in the late Sixties having the speakers at the corners and on the floor of my room, where on-axis listening was impossible unless I was lying on the floor. And my B&O amp had tone controls... I don't recall if I used to lower the treble. However, the 9710 didn't last long and in came Peerless 3-25 kits, fitted with 12" bass drivers, 5" midranges and cone tweeters. Much better. Well, my hifi story some other time. Had I been able to make a crossover as seen below, my hifi career might have looked very much different. But we didn't have personal computers, CLIO and LspCAD back then.

 

Frequency response of individual drivers. The Peerless tweeters are connected in parallel and the FR is measured right between the tweeters at 1 metre distance. Placing a pair of tweeter on a horizontal axis has its problems as we will see later.

Impedance of drivers. Note the remarkably flat impedance of the two Peerless tweeters in parallel. Blue and yellow is phase. Vent tuning is 43-44 Hz.

Here's the final system impedance (crossover V4) from LspCAD. 6.3 ohms minimum where it hurts and a minimum of 4.5 ohms at 3 kHz. This is a dream for every low wattage valve amp.

 

Crossover version 4. Producing a linear response from the 9710 proved much more difficult than anticipated and quite some tweaking had to be tried before rendering what is seen above.
Every large 8" driver - and the 9710 is a large driver - will start to sound honky when it has to handle the upper midrange/lower treble. BUT, honkyness is not only a matter of dispersion, but also on level and not having an elvated level at 750-1500 Hz is of paramount importance. My V2 crossover ran for some time and I thought there wasn't much to do about it, but bypassing the first 1 mH coil with a 47 ohms resistor and bypassing the second coil with (2R7 + 1.5 uF) helped smooth this troublesome area and surprisingly the forwardness and slight honkyness was much reduced. Maybe we really can have an 8" running everything up 2.5 kHz... Well, it's never going to be like what a 4" can do, but possibly something we can live with.
The tweeters took a little equalisation too, hence the 0.1 mH paralleled by 2R7 at the entry.
Phase tracking may not be the best I seen, but I value amplitude higher than phase tracking here. The 9710 is lively cousin, and if you don't treat it right it'll shred your ears.

So how did the modelling fit with reality? Very good indeed as depicted above. Now the overall response is basically flat and vocals have improved compared to previous crossover versions. Red = FR, blue = minimum phase.
A guy visiting me brought along an MingDa MC34-A integrated amp (EL34 pp) and we ran the 9710s from this amp and don't say hifi can't be simplistic: An amplifier like this and a decent pair of 92 dB/2.8V speakers. Try Chris Minh Doky: "Listen Up", the intro track, and you'll jump in the seat when the drummer hits the snare drum hard. And try an old Garrard 401 turntable + the Denon 103 cartridge and you have a system that we could have listened to some 40 years ago. Amazing.
System sensitivity is 92 dB/2.8V based on average midrange response.

Vertical dispersion. Very good indeed.
Red is at 1 metre distance at a height between 9710 and tweeters. The other graphs at +/- 10 and 20 cm from this position corresponding to +/- 30 and 60 cm at 3 metres listening distance.

 

Horizontal dispersion. Very bad indeed.
No surprise, placing two tweeter on a horizontal axis will produce this picture. Red = on axis, yellow = 10, purple = 20 and green = 30.
But it's not as bad as you may think. This is what a single, tiny microphone capsule picks up at a specific position, not similar to what our two ears perceive at different locations. But obviously it's not the perfect solution .


March 2006, Chapter III
The Fountek NeoCD3 option


Fountek NeoCD3 ribbon tweeter

Let me say that the 9710s are great fun! It may not be the end of your search for the sound, but they may provide some very enjoyable hours in front of your "stereo".
These speakers are discriminating. They will leave some of your CDs and vinyls on the shelf, but from not too poor recordings they can provide a wide soundstage, a vastly enhanced transparency compared to running the drivers fullrange and an overall balanced sound that make the saxophone of Paul Desmond sound even better than ever. They provide a 92 dB/2.8V sensitivity and an easy load on your amplifier. Low-wattage valve amps will love the 6-7 ohms impedance.
I have a range of 9710 drivers, three with the common whizzer cones and two without. The whizzer cone only has some impact above 8 kHz and removing it doesn't change the huge bump at 4-8 kHz, much to my surprise. The three whizzer cone drivers leave one for experimentation and the 9710 is easy to take apart. Three screws holds the basket in place and by removing these you can lift off the basket with cone and voice coil.
Check images
here and preliminary writing.

 

The crossover

Crossover for 9710 and Fountek NeoCD3 ribbon tweeter.
This is a pretty straight forward 4th order filter and if you think 4th order filters destroys transient attack, try this!
And please don't confuse severe peaks in frequency response with good transient performance. This is very often the case.



Frequency response of system (red) and individual response from drivers.


Vertical dispersion from 1 metre distance.
Green = between treble and bass.
Red = + 20 cm, blue = +10 cm, yellow = -10 cm, purple = -20 cm.

Read also:
Disassembling the 9710 driver.


Removing whizzer cone and coating of 9710 cone.

Chapter III

Removing the whizzer cone has the effect seen above. Red = un-modified and blue = whizzer cone removed and rubber "phase plug" inserted. The whizzer cone is mostly active above 6-7 kHz and the response is reasonably linear up to 16 kHz. Not bad for an 8" driver. It also means the bump above 2-2.5 kHz is smoother and the response declines nicely above 7 kHz.

Coating of the 9710 cone is a serious matter. What type of coating should be used? If it doesn't work there's no way back. I don't have a whole range of coating materials - and not a whole range of 9710 drivers as well - so to cut a long story short, I chose to use the DAMAR coating. The 9710 cone is rather soft and the DAMAR will most likely make the cone more rigid. This may have several consequences: One is that the cone will operate more like a piston and the other is that rigid cones tend to break up - somewhere. Hopefully not in the area where it's supposed to operate. Thirdly the coating material will add weight to the cone and reduce efficiency.
Actually the DAMAR coating worked rather well on this cone, where I in other cases have seen serious cone break-ups around 2.5-4.5 kHz, just where the point of crossover is supposed to be. Seen below is the response from the 9710 before (red) and 7 days after one DAMAR application (blue).

Red = un-coated 9710 without whizzer cone. The frequency response is here merged with the nearfield response at 350 Hz.
What can be seen is an approx. 1-1.5 dB loss in sensitivity due to the coating but also that the steep rise in response above 2 kHz has moved some 4-500 Hz up. Good.

Green = un-treated cone. Red is 5 min. after application of DAMAR. Some serious loss in sensitivity, but most of the "DAMAR" is solvent that will evaporate over time.
Green is after 30 minutes. The response after 7 days is seen above.

Without doing further modifications to the crossover, here's the response of the 9710 + NeoCD3 before and after coating of the 9710.
Red = after coating. Blue = without coating + whizzer cone.

Summary:
1. removing the whizzer cone removes the response above 7 kHz, but leaves the area where I want to use the driver mostly un-affected.
2. Applying DAMAR coating reduces the sensitivity by some 1-1 dB and moves the bump above 2 kHz up some 4-500 Hz.

So what about the sound?
The sound changes very much.
Getting rid of the whizzer cone immediately makes a more clean sound. The 9710 used as a "common" midbass driver really do not need a whizzer cone but I have a feeling that some will miss the more colourful sound of the original.
Adding a single thin layer of DAMAR coating makes yet another powerful impact on sound. Now this set-up really starts sounding like hifi - so take great care! - but it doesn't relieve the 9710 of having a sound much dictated by the very deep and conical cone.
The DAMAR coating greatly enhances the level of transparency and it is obvious that the very soft paper cones smear a lot of detail.
The 9710 still has "something" that the Monacor SP200X is short of. The sense of speed and sparkle.
Monacor.
The transient attack of the 9710 is very hard to find elsewhere, but it comes at a price.

It has been great fun reviewing the 9710s here. I've enjoyed it a lot getting my old Sixties' drivers back and finding out what it was I was listening to back then.
The 9710s are not the end of story and I'm sure we can find better drivers today built from the same concept of a very lightweight 8" paper cone and maybe I should take a look at those
Supravox drivers and find out what they can do.

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