Philips AD5060/SQ8 vs AD 5061/M8
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The AD 5061/M8 is a whizzer cone speaker that has frequency response up to 18kHz on a good day, and a resonant frequency slightly below 100Hz
The AD5060/SQ8 is a midrange driver that has useable frequency response up to 5Khz and a resonant frequency of 220Hz.
The frequency response of both speakers is bound to be different, but considering that the 5" unit operates between 250 and 3000Hz in the Highboy, both will work.
The AD5060/SQ8 is a bit too close to its resonant frequency to my taste though.
The AD5060/SQ8 is a midrange driver that has useable frequency response up to 5Khz and a resonant frequency of 220Hz.
The frequency response of both speakers is bound to be different, but considering that the 5" unit operates between 250 and 3000Hz in the Highboy, both will work.
The AD5060/SQ8 is a bit too close to its resonant frequency to my taste though.
I have seen AD5060/SQ8 whizzer cone speakers. I have read that this speaker is sometimes preferred to the newer AD5061/M8 whizzer cone speaker. Also, there seems to be a common opinion that almost any good 8ohm midrange speaker will work quite well in the Rectilinear iii Highboy. No need to get hung up on original midrange speakers for this Rectilinear model. I don't know much about the AD5060/M8. Not all AD506* series are whizzer cone.
A follow-up to my initial post. I have 4 Rectilinear III Highboy speakers. One pair is a slightly different version - mainly the attachment of the woofer on the baffle and the size of the port. I have photos posted here somewhere. These were expertly restored to 'brand new' perfect condition in February 2025. All speaker components are original. The crossover was rebuilt and cabinet restored. Recently, one of the 2-inch super tweeters went silent. I don't know what the problem is. I started thinking that I better have original replacements ready for all of the separate speakers in the cabinet. I do not know what the model number is of the 4 Philips whizzer cone midrange speakers in my speakers. The tweeter is a Peerless MT-25. I do not know what the 2-inch super tweeter model number is. I just want to have spare original speakers or the best compatible new replacement speakers if/when another one goes bad. Some of these Philips and Peerless speakers are entering the realm of unobtanium. I am done now.
stickman
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In the Philips driver realm "M" means "Extended Range" while SQ is for "Squawker/Midrange" and W means "Woofer". The Dahlquist DQ-10 actually used a AD5060/W8 which is the only application I ever found for that particular driver.
The mids in Rectilinear III's were in early models AD5060/M8 and in later models AD5061/M8. The dust cap area inside the whizzer cones is smaller in the AD5060/M8 while there was not that much difference in voice coil diameters.
While the larger diameter Peerless cone tweeters were widely used by many speaker manufacturers in the late 1960's to mid 1970's (from Infinity to McIntosh to the Original Design Acoustics) the smaller diameter tweeters were not and are much more rare. People on Ebay are parting out Rectilinear III drivers all the time which is the typical source of the smaller tweeters.
The mids in Rectilinear III's were in early models AD5060/M8 and in later models AD5061/M8. The dust cap area inside the whizzer cones is smaller in the AD5060/M8 while there was not that much difference in voice coil diameters.
While the larger diameter Peerless cone tweeters were widely used by many speaker manufacturers in the late 1960's to mid 1970's (from Infinity to McIntosh to the Original Design Acoustics) the smaller diameter tweeters were not and are much more rare. People on Ebay are parting out Rectilinear III drivers all the time which is the typical source of the smaller tweeters.
Thanks for the information. I cannot find any specific information on the Peerless 2-inch super tweeters. I read somewhere that there is no specific crossover between the 2 1/2-inch and 2-inch tweeters. This is from the Rectilinear III brochure: The operating range of the woofer is between 20 and 500 Hz. Above this, the response is rolled off at 6db/octave to keep it out of the sensitive part of the midrange frequencies where coloration could become apparent. The midrange whizzer cone moves as a single rigid piston at lower frequencies. At higher frequencies, a decoupling takes place and only the whizzer cone moves. Below 500 Hz and above 3000 Hz, the frequency response of the midrange rolls off at 6db/octave. The 2 1/2-inch and 2-inch tweeters cover the frequency range of 3000 Hz and up. The larger tweeters contribute more up to 11k Hz, and the smaller tweeters contribute more above 11k Hz. There exists a virtual tweeter crossover at 11k Hz even though all 4 drivers (2 of each) are connected in series-parallel. What is that you ask? Well, a series-parallel circuit is one that consists of components that are arranged in both series and parallel configurations. I have not been able to locate a schematic diagram for the rectilinear III Highboy speaker. So, these 2 Peerless tweeters have overlapping frequency ranges that seamlessly blend together.
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