Hi all, I usually post on Audiokarma, but I think this fits better on this forum.
I got Altec 605a's about a year ago in roughish shape. I ended up having SRP remagnatize and recone the LF, and given one HF diaphragm was blown so I bought replacements from GPA. I put these in 620 cab replicas (~9cuft) and hooked them up to simple markwart time-aligned crossovers. Now, as we know, 605a's usually get a bad reputation for how they did in the market, the smaller magnet structure, lower efficiency, onward and onward. Others say the 605a's sound up to snuff with 604e's, probably have better phase coherence due to the smaller distance between the HF/LF structures, and better bass response in a smaller enclosure.
I make no claims as to whether the 605a is as good or up to performance as 604's, but I have enjoyed them quite a bit and always wondered what their frequency response curves really look like. There are not really any measurements on the web, and there really aren't many for 604's either. I recently got a UMM-6 dayton measurement mic and wanted to see what it looks like.
My measurements are not super scientific: they were performed in an untreated room, with the mic propped up on a plastic stand, 1M from the drivers, at ~5mW (0.3 VAC into 16 ohm, a typical listening volume for me, did not want my ears bleeding), from a 2a3 custom built amp. Speakers are pretty much up against the wall (speaker placement is a bit non-negotiable with my wife).
Now, surely the 700hz dip is a floor reflection. Potentially the peak ~70hz a room issue. I also like my mid highs a little bit hot (4-8khz). I could lower that a bit with the L-pad at the cross-over, but after much experimentation I like it here in my listening position. I'm sure you could get flatter with some treatment. But, It does show I'm getting decent response from ~35 hz to ~13 khz. Cross-over is at 1500 hz.
I also did quite a few measurements at my listening position, 8ft back from the speakers, speakers are separated by ~7 feet. Middle of the room.
Red is right, black is left. These are averages over 9 measurements from around my listening position. Given the right speaker is the corner, and the left speaker has an open passageway next to it, the low bass responses are quite a bit different. I also applied an EQ via REW to try to fix this.
Red is right, black is left, 1/12 octave smoothing. The bass response could be trimmed further from the right a bit still. I have some work to do. I really like the sound of this so far. But it's encouraging that I can get a reasonably flat response from these to their HF and LF limits in a badly set up room.
One day I'll have to convince my wife to let me tinker with the speaker positioning etc, but for now I'm a little stuck where I am. Overall, I really like these drivers in these cabinets. Now, if you are dying for that 20-35 hz, and need the sparkle above 15khz, these are not the speakers for you!
I'm pretty new to this measurement thing, so let me know if there are things I should do or ideas you might have. Again, the impetus of this was just to get more data out there for folks given that there is literally none. Maybe this will be helpful to someone as they think about using these speakers.
I got Altec 605a's about a year ago in roughish shape. I ended up having SRP remagnatize and recone the LF, and given one HF diaphragm was blown so I bought replacements from GPA. I put these in 620 cab replicas (~9cuft) and hooked them up to simple markwart time-aligned crossovers. Now, as we know, 605a's usually get a bad reputation for how they did in the market, the smaller magnet structure, lower efficiency, onward and onward. Others say the 605a's sound up to snuff with 604e's, probably have better phase coherence due to the smaller distance between the HF/LF structures, and better bass response in a smaller enclosure.
I make no claims as to whether the 605a is as good or up to performance as 604's, but I have enjoyed them quite a bit and always wondered what their frequency response curves really look like. There are not really any measurements on the web, and there really aren't many for 604's either. I recently got a UMM-6 dayton measurement mic and wanted to see what it looks like.
My measurements are not super scientific: they were performed in an untreated room, with the mic propped up on a plastic stand, 1M from the drivers, at ~5mW (0.3 VAC into 16 ohm, a typical listening volume for me, did not want my ears bleeding), from a 2a3 custom built amp. Speakers are pretty much up against the wall (speaker placement is a bit non-negotiable with my wife).
Now, surely the 700hz dip is a floor reflection. Potentially the peak ~70hz a room issue. I also like my mid highs a little bit hot (4-8khz). I could lower that a bit with the L-pad at the cross-over, but after much experimentation I like it here in my listening position. I'm sure you could get flatter with some treatment. But, It does show I'm getting decent response from ~35 hz to ~13 khz. Cross-over is at 1500 hz.
I also did quite a few measurements at my listening position, 8ft back from the speakers, speakers are separated by ~7 feet. Middle of the room.
Red is right, black is left. These are averages over 9 measurements from around my listening position. Given the right speaker is the corner, and the left speaker has an open passageway next to it, the low bass responses are quite a bit different. I also applied an EQ via REW to try to fix this.
Red is right, black is left, 1/12 octave smoothing. The bass response could be trimmed further from the right a bit still. I have some work to do. I really like the sound of this so far. But it's encouraging that I can get a reasonably flat response from these to their HF and LF limits in a badly set up room.
One day I'll have to convince my wife to let me tinker with the speaker positioning etc, but for now I'm a little stuck where I am. Overall, I really like these drivers in these cabinets. Now, if you are dying for that 20-35 hz, and need the sparkle above 15khz, these are not the speakers for you!
I'm pretty new to this measurement thing, so let me know if there are things I should do or ideas you might have. Again, the impetus of this was just to get more data out there for folks given that there is literally none. Maybe this will be helpful to someone as they think about using these speakers.
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