When to replace drivers.

Matt Harris

Freshman
Feb 17, 2011
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I have a set of sls960 that were made in 1999. They have over 1,000 shows on them since I bought them in 2004. My question is do you think I should replace diaphragms on the HF drivers? I can't say that anything sounds wrong but I'm sure something has had to change with 12 years on them.
 
Re: When to replace drivers.

Do an impedance sweep versus a new one.

I've found that the M200 mid drivers start to degrade over time, the VHF100s stay fine.

My experience with M200s was with my RS880s from 1996, where the brand-new M200s I got were not even close to the original ones. They still sounded about the same though. I ended up calling Dave Howden at Community for ideas, and it was probably just age that did it, whether the ferrofluid did something, or the mylar diaphragm was breaking down, or something else.
 
Re: When to replace drivers.

I did replace all the m200 drivers because I shifted a magnet on one. Here is a screenshot from Smaart comparing 2 of them. The phase in the HF varies.
trace.png
 
Re: When to replace drivers.

Do a simple measurement. I measured a turbo tq440-install today where the owner complained about a lack of hf. A simple transfer function found that the rig was down 12dB\oct from 6.5K, AKA blown hf-driver.

I would agree that a blow driver should be replaced. It shouldn't take a measurement to figure out a driver is bad-especially if it is not working at all.

Now if the parameters have changed-that is a different story.
 
Re: When to replace drivers.

I would agree that a blow driver should be replaced. It shouldn't take a measurement to figure out a driver is bad-especially if it is not working at all.

Now if the parameters have changed-that is a different story.

Parameters are more tricky yes, but in this case the customer could hear it, but didn't belive it. Some people needs the persuading power of squiggly lines on a screen :)
 
Re: When to replace drivers.

Should I be worried about the phase difference from 4k -16k in my boxes? I wonder if this is from age.
 
Re: When to replace drivers.

That is an unusual trace. The sudden deviation from the other driver is a concern. The downward slope at the limit of its HF response is also unexpected. There is no indication of scale, so I don't know how severe the effects are... I'd be much more concerned about the frequency domain differences. Phase differences of that magnitude can be due to a 1/2" difference in measurement mic location.
 
Re: When to replace drivers.

I did replace all the m200 drivers because I shifted a magnet on one. Here is a screenshot from Smaart comparing 2 of them. The phase in the HF varies.
trace.png

The frequency traces seem to correlate with my listening experiences. I have worked on several sets of these, as well as own a couple pairs myself. Having listened very carefully to each driver when servicing them - before and after, as a complete speaker system and exclusively driver by driver, I can say this represents the trend I heard. Not bad at all though, as the differences were very subtle and not noticeable to me with the other drivers running. To do this listening test, I also moved the same crossover from cabinet to cabinet to eliminate that as a variable (with the wires all dangling out of the back).

IMO, this was probably due to the magnet slowly losing its magnetism over a period of about 20 years or so. Replacing any M200 diaphram with a new one made absolutely no audible difference for me. On this graph, you can see the lower and upper extremes of the M200 roll off. I did hear this between the older and newer drivers (completete new assemblies), but really only when doing my critical listening tests when servicing them. But, as I said before, that was not even that noticeable to me in the grand scheme of things.

I don't really know what to say about the upper end of the phase trace.

P.S. Oops, now I see you were originally asking about the HF drivers (Silas's [post got me thinking about the m200's. Have you retried that test to see if might you come up different results?
 
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Re: When to replace drivers.

Hi,

the M200 is a midrange device, it does not work from 200Hz - 16000Hz
so what is the graph showing?
Phase trace indicates also some crossovers involved

as Bennet mentioned, graphs without scaling are not usefull

Re: when to replace drivers

we check HF devices for harmonic distortion

Uwe

P.S. Congrats to the new forum
 
Re: When to replace drivers.

These screen shots were taken a year ago. I hate I didn't grab the scale in my screenshot but Im pretty sure it was 3db per line. Also, 2 of my m200 have newer looking magnets and 2 of them have older looking ones. I think this shot may be one of each. I need to reshoot the measurements and post back when I get a chance.
 
Re: When to replace drivers.

In regards to the phase shift in the upper end it could either way. I don't know anything about these particular drivers but I can tell you this:

1 In individual drivers phase is in the spot is not of great concern within it's respective cabinet / system since that area doesn't have a strong relationship with the driver that is producing the mid range frequencies. This would not be the case if the phase shift happened at the crossover point between the mid and hi drivers. Of course this statement would be false if you added some wonderful super tweeters from the last decade.

2. Where it is important is that all of the drivers you are using have the same phase response. For instance if the two systems on your plot were a part of an active left vs. right or even placed side by side as a pair than you run the risk of cancellations. at certain frequencies.

Since neither of your phase traces are showing any one frequency a full 180 out than your PA might classified as "Phasey" but not a life threatening deal. It sounds like you replaced all of the drivers so hopefully they all have same response.

In a similar situation I just replaced once HF driver in a UPA because it was exhibiting symptoms of amplitude loss. It scared me to death that I was going to get a new driver from Meyer with a different freq or phase response. The new driver had a slightly different freq response, but the phase response was almost dead on. We know that changing the EQ of a driver changes it's phase response so I was fortunate that the differences were just subtle.

Here's a screenshot of the same UPA before and after EQ- see the phase shift on the top end and the actual reading of data on the low end where I added the 80-100Hz.

Now, how do you make screenshots full size. I clicked on it and choose full size but it didn't take?
 

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