A Look Inside the CT-62 Tweeter

[array]

I haven't posted on this website for a while but I do recall in the past I'd mentioned the intent of taking apart a CT-62 tweeter and examining it's innards. I can take a few photos and post results if a few show an interest.

[lennartj]

Yes, please do!
I use some CT-62, so I'm curious about the differenecs between it and MT20 and MT24.

[array]

Hello Lenn, I think you're the only one who cares to see inside these things! I find this surprising that no one else has shown similar interest especially because of this tweeters supposed bewildering mysterical popularity. I guess the language barrier on this website doesn't help though. Regardless, I'll upload the snapshots shortly for posterity's sake.

[array]

Ok, here we go. Some photos of the inside of the tweeter. I can't take anymore as I've thrown the sample out. I'll be updating this thread with the internal findings and assessment.

[Martin Dellstig]

Hi

Looking on the inside is fun for many I would say.
For me there is nothing new on the inside but most people have probably not seen this.

The way I see it there is nothing "magic" with the CT62 but it is a sound and well carried out design.
The low distortion and the plastic cone are probably the most obvious things to notice with it.

Regarding the language barrier, I would say that there is no such thing here, most people read and write english at a decent level here in Sweden.

Thanks for the interesting images.

Best regards

Martin

[momus]

As Martin writes, there is nothing special with this tweeter. The "tweeters supposed bewildering mysterical popularity" may come from that it was discontinued after a raher a short lifespan. The Obi-tweeter is, on the other hand, much, much better (and dearer to). I´ve heard two OA 116 with CT 62:s and they sounded harsh and unmusical. For me that was the end of an old love story.

[grafpro]

CT62 i said to be oil damped. Where is the oil?

[momus]

Yes, where is it?

CT 62 H 62 CT 13 40 PPB FF 8 ohm

Small cone tweeter with ferrofluid. This tweeter removes all doubts about using a cone tweeter in hi-fi systems. The voice coil is cooled and damped by magnetic oil, and this viscous damping eliminates the rise in resonance. The impedance curve is nearly linear and it is therefore very easy to make cross overs for this speaker. An absolute excellent tweeter for use in smaller hi-fi systems especially as tweeter in satellites.

CT 62 H
Thiele Small parameters:
Nominal impedance Zn (ohm) 8
Minimum impedance/at freq. Zmin (ohm/Hz) 6.6/2600
Maximum impedance Zo (ohm) 6.9
DC resistance Re (ohm) 6.1
Voice coil inductance Le (mH) 0.1
Resonance Frequency fs (Hz) 1500
Mechanical Q factor Qms 0.89
Electrical Q factor Qes 7.07
Total Q factor Qts 0.79
Mechanical resistance Rms (Kg/s) 3.01
Moving mass Mms (g) 0.28
Suspension compliance Cms (mm/N) 0.04
Effective cone diameter D (cm) 3.7
Effective piston area Sd (cm²) 10.8
Force factor Bl (N/A) 1.5
Reference voltage sensitivity
Re 2.83V 1m at 2600 Hz (Measured) (dB) 90
Magnet and voice coil parameters:
Voice coil diameter d (mm) 13
Voice coil length h (mm) 1.8
Voice coil layers n 2
Flux density in gap B (T) 1.0
Total useful flux (mWb) 0.1
Height of the gap hg (mm) 2.5
Diameter of magnet dm (mm) 40
Height of magnet hm (mm) 7.5
Weight of magnet (kg) 0.04
Power handling:
Long term Max System Power (IEC) (W) 100

Measuring methods and conditions are stated in Peerless Standard for Acoustic Measurements (PSAM)

[array]

Hi, it's a comforting thing to know in Sweden there is a high level of competency in English. But
speaking personally, I'm completely Swedish illiterate! It's good to see this thread's come alive with
everyones contributions.

To put any anxieties to rest, the ferrofluid is there alright, you can just make out some residue around

the polepiece in the one picture. I should've taken a shot of a slip of white paper wicking it up out of the gap.

Simply put, would I trade this tweeter for a Matsu? Not hardly. The CT-62 measured relatively smoothly
in terms of frequency response (as previously mentioned in the now defunct Matsu tweeter for sale
ad).

Others may have taken these apart before to see what's inside but like on the vast majority of audio
based internet forums, I've noticed members have little experience in driver design pragmatics and
therefore don't know how to observe precisely in detail what it is they are looking at. I do.

Some CT-62 design observations based upon experience;

It has a one piece formed poly diaphragm (which includes dust cap) with *very* slight curvature and
circumferential edge crimp.

Ferrofluid is present

Magnet is ceramic (not rare earth by any stretch).

The former used is aluminum and wrapped with round wire.

The pole piece is straightsided (i.e. non-focused geometry)

No inductance control is used.

The felt ring is not glued to the inside of the basket (it can flop around in there) with no
indication of adhesive residue for retention.

The sealed rear chamber is a relatively good size.

The tweeter does not use a spider to centre the coil. The stamped basket is a two piece press fit. The
combination of this and ferrofluid centres and maintains coil alignment in the gap in lieu of a
spider.

The adhesive used to attach the former to diaphragm is solvent tolerant (i.e. soft).

You think the published technical data is going to provide all those extra manufacturing design
details? It requires someone with experience who knows how drivers are put together and what makes
them sound the way they do. I won't bore the reader by going into the details but the above considerations are relevant.
When you have to obey all the laws of physics all of the time, the devil lies in the details.

Here is something only people who really know what they're talking about know. Notice the
voicecoil leads? Based on that glaring hint, let's see if a reader can determine another thing which makes the CT-62
a slightly cheaper tweeter than what it could have been.

As a final, take notice of the small divit on the back side of the cone. This is from a hot drop of
solder while taking the unit apart. Poly is not tolerant of heat. Imagine if your voicecoil heats up under high load?
I've seen poly go into meltdown at the former joint due to heat stress.

The CT-62 is not a super cheap tweeter, but not beautifully made either. But hey, that's business and
the bottom line. I commend the Peerless engineers for getting a product out there which not only does the job and
makes their bosses money too.

As for vintage audio, it's largely about getting the best and rarest for closest to free
as possible (and then of course bragging about it in an internet audio forum ;> ).
Given the chance, if the CT-62 were still made they'd outsell this new OBI(?) tweeter 10:1
due to price differential and we all know it.

[lennartj]

Thank you array!
Has anybody made comparable dissections of MT20 and MT24 (maybe I didn't search hard enough)?
It would be instructive to see what was carried over and what has been changed, especially with knowledgeable comments from array.
I guess nobody has blown an Obt tweeter and it costs a bit too much to dissect just for curiosity.