Hi,
I purchased a pair of ATC speakers from USA recently - the PA75-260 8ohm, type STD, that were an experimental speaker made for EAW. They were never used in production and I now understand why.
I called ATC and they were amazingly helpful. At first they did not have anybody there who were old enough to know what they were. After sending them some pictures he found a specimen in the archive. He even made some on the spot measurements for me.
I was planning on making a SCM50 clone, using them with the SM75-150 and a nice tweeter, maybe 1" CD. The engineer recommended me to use them between 150-2kHz. At 1Khz, they are very shrieky, so I will probably use them lower than that. If I don't deem them as garbage.
Take a look at the attached diagrams and the letter from the ATC engineer, and tell me what you think!
I have the option of using active xo software or passive xo. Either way, I don't know where to begin even to fix the strange behavior of this speaker. Sometimes it is so clean and prestine, and sometimes it shrieks like the Nazgûl!
"Well, it seems you have somehow managed to obtain a very rare drive unit…in fact this was never built for production and is a prototype OEM driver intended for use in a EAW system (not sure which one). We have found one here in our archived driver store but sadly I don’t have any data on the Theile Small parameters. In order to assist you the best I can, I have taken a few measurements of our PA75 260, these are attached. Firstly please note that our drive unit here doesn’t sound very well, the glue on the spider platform is loose and causing distortion and it is likely other less obvious faults exist. Because this is the only unit available to me I cannot measure multiple drivers to gain a real idea of performance. The measurements I have carried out were performed quickly so I apologise for the lack of measurement accuracy.
1) Impedance measurements – I have included the raw data in a txt file for your processing (MatLab, Octave etc) and also a jpeg. Looking at the impedance curve I would recommend you use the driver as a mid-range from around >150Hz to <2kHz. It certainly has a rising voice coil impedance which will need compensating for in your xo.
2) Level and Distortion - Measurement taken without a baffle in non-anechoic conditions (data windowed to reduce effects of reflections). The bass extension would be improved greatly once in a box. The sensitivity of this drive unit seems exceptionally high at around 102dB at 1w/m, initially I thought my measurement method was wrong but upon checking a reference unit it seems 102dB it is. High 3rd harmonic may be due to drive unit fault or less than perfect test conditions." - ATC engineer
I look forward to hear what you can interpret from these diagrams.
Best Regards,
J
I purchased a pair of ATC speakers from USA recently - the PA75-260 8ohm, type STD, that were an experimental speaker made for EAW. They were never used in production and I now understand why.
I called ATC and they were amazingly helpful. At first they did not have anybody there who were old enough to know what they were. After sending them some pictures he found a specimen in the archive. He even made some on the spot measurements for me.
I was planning on making a SCM50 clone, using them with the SM75-150 and a nice tweeter, maybe 1" CD. The engineer recommended me to use them between 150-2kHz. At 1Khz, they are very shrieky, so I will probably use them lower than that. If I don't deem them as garbage.
Take a look at the attached diagrams and the letter from the ATC engineer, and tell me what you think!
I have the option of using active xo software or passive xo. Either way, I don't know where to begin even to fix the strange behavior of this speaker. Sometimes it is so clean and prestine, and sometimes it shrieks like the Nazgûl!
"Well, it seems you have somehow managed to obtain a very rare drive unit…in fact this was never built for production and is a prototype OEM driver intended for use in a EAW system (not sure which one). We have found one here in our archived driver store but sadly I don’t have any data on the Theile Small parameters. In order to assist you the best I can, I have taken a few measurements of our PA75 260, these are attached. Firstly please note that our drive unit here doesn’t sound very well, the glue on the spider platform is loose and causing distortion and it is likely other less obvious faults exist. Because this is the only unit available to me I cannot measure multiple drivers to gain a real idea of performance. The measurements I have carried out were performed quickly so I apologise for the lack of measurement accuracy.
1) Impedance measurements – I have included the raw data in a txt file for your processing (MatLab, Octave etc) and also a jpeg. Looking at the impedance curve I would recommend you use the driver as a mid-range from around >150Hz to <2kHz. It certainly has a rising voice coil impedance which will need compensating for in your xo.
2) Level and Distortion - Measurement taken without a baffle in non-anechoic conditions (data windowed to reduce effects of reflections). The bass extension would be improved greatly once in a box. The sensitivity of this drive unit seems exceptionally high at around 102dB at 1w/m, initially I thought my measurement method was wrong but upon checking a reference unit it seems 102dB it is. High 3rd harmonic may be due to drive unit fault or less than perfect test conditions." - ATC engineer
I look forward to hear what you can interpret from these diagrams.
Best Regards,
J
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Those are some serious bumps in the impedance plot, you'd have to measure your own units to be sure if they really exist or are the result of the driver under test falling apart.
The very high sensitivity will limit the bass extension and perhaps also a rather large cabinet might be required. The cone looks reasonably well behaved so that does sort of indicate that the resonances, as shown by the wobbles in the impedance, are coming from elsewhere.
Certainly not unusable but will require an application specifically tailored around them to get the most out of them. One also has to consider that as ATCs unit was falling to bits that maybe yours might end up that way in a few years, but that could have been because of poor storage conditions. If you cannot measure your own units then it might make more sense to go with a new part instead.
The very high sensitivity will limit the bass extension and perhaps also a rather large cabinet might be required. The cone looks reasonably well behaved so that does sort of indicate that the resonances, as shown by the wobbles in the impedance, are coming from elsewhere.
Certainly not unusable but will require an application specifically tailored around them to get the most out of them. One also has to consider that as ATCs unit was falling to bits that maybe yours might end up that way in a few years, but that could have been because of poor storage conditions. If you cannot measure your own units then it might make more sense to go with a new part instead.
I am planning to build a 3-way horn speaker, and these ATC would end up in the very large 100x70cm midbass horn. When building horns, sensitivity is everything, for some reason. The horn will hopefully extent the bass somewhat, and maybe affect its strange behavior positively. Guess we will see after I am done with the horn!
Romy the Cat used these Fane Studio 8M in his midbass horn. They also look a little strange, but he claims it sounds better than commercial alternatives. So I am hopefull! http://i307.photobucket.com/albums/nn281/AudioVoice/Fane_STUDIO-8M.jpg
Romy the Cat used these Fane Studio 8M in his midbass horn. They also look a little strange, but he claims it sounds better than commercial alternatives. So I am hopefull! http://i307.photobucket.com/albums/nn281/AudioVoice/Fane_STUDIO-8M.jpg
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