Old tweeter behaviour

[davidsrsb]

I acquired a pair of 15 year old TDL T-Line 3s with original drivers. These have a 30mm metal dome tweeter with 25mm coil. They sounded tizzy and Holmimpulse showed very strong output from 5 to 10 kHz and very weak from 2 to 3 kHz, one much worse than the other. Harmonic distortion was also poor at the low frequencies.
I dismantled the bad tweeter and found the ferrofluid was solid, sticking the voice coil on one side. Cleaning out the ferrofluid got a fairly flat response and low distortion, so I did the other tweeter as well and now the two tweeters are closely matched.

I was surprised that the drying ferrofluid actually increased sensitivity at the high end. Has anyone else seen this?

[DrBoar]

Many drivers have complicated resonaces in the upper spectrum. Getting the coil stuck can have shifted something that make it resonate at the top.

[flavio81]

Originally Posted by davidsrsb

I acquired a pair of 15 year old TDL T-Line 3s with original drivers. These have a 30mm metal dome tweeter with 25mm coil. They sounded tizzy and Holmimpulse showed very strong output from 5 to 10 kHz and very weak from 2 to 3 kHz, one much worse than the other. Harmonic distortion was also poor at the low frequencies.
I dismantled the bad tweeter and found the ferrofluid was solid, sticking the voice coil on one side. Cleaning out the ferrofluid got a fairly flat response and low distortion, so I did the other tweeter as well and now the two tweeters are closely matched.

I was surprised that the drying ferrofluid actually increased sensitivity at the high end. Has anyone else seen this?

There's a page from Roger Russell dedicated to McIntosh speakers and he mentions several times that this is one of the problem with ferrofluid-cooled tweeters.

[davidsrsb]

I am thinking that ferrofluid thickens quickly, even in the showroom - I have seen the same demo speakers in the shops for 5 years+ and is the cause of metal domes reputation for harshness