I was going to centralize my findings on my google site but hey... put it here, the content is protected to just the users here and I get another point for posting! (I might just move my RX-DT680 restore info here as well)...
So anyways, I read this forum and stereo2go and I get a majority saying that the DT680 has 'most' bass of the RX-CT and RX-DT series... so I decided to do a little test here.
I have done this process for my HT setup, not to mention I had friends do something similar in car audio soundoffs back when I was younger. Still, it ain't a definitive guide. I could have missed something, or not done something right. Did this experiment to the best of my knowledge. Here goes!
Equipment Needed:
a)My laptop that is running a program called TrueRTA http://www.trueaudio.com, real time analyzer for tuning audio gear. The free version will do for this test.
b)The mic is from my Onkyo Integra 5.9, it comes with all the Onkyo/Integra units for auto calibrating your soundstage
c)RX-DT680
For the microphone, I had to go into windows and turn off mic boost and set its level to 50. In TrueRTA, I had to setup input to L channel only, and in 'Spectrum Analyzer' I chose 'hold peak' as this will result in the program reading only the highest output levels and not show a fluctuating graph. So in a silent (seriously... as in no ceiling fan running, most electronics off, windows closed...) room, running TrueRTA yielded the following curve (no other adjustments was made beyond plugging in the mic and fixing the boost)
Now to setup the test environment. There are two scenarios, I will explain each one:
1. Solid Ground
In this instance, we test 2ft away with the unit sitting right on the floor. Having it sit right on the floor introduces some things, but in a nutshell - putting a speaker in direct contact with solid dense ground without any decoupling of any sort can amplify sound! (maybe that's what some want...) The mic is isolated from the ground, as you probably listen to the unit with your ears toward it and not your ears touching the ground...
2. Isolated Ground
This scenario is identical to the previous one, except the RX-DT680 is now placed on a damping material (a blanket). Simulates putting your box on grass or other surface that will absorb a good chunk of the energy from the speakers.
3. Test Source
a. Downloaded a pink noise mp3 file (VBR, 13MB) and burned it to CD. http://www.archive.org/details/TenMinutesOfWhiteNoisePinkNoiseAndBrownianNoise
Pink Noise is audio recorded within the range of 20-20KHz (simple explanation)
b. using the unit, recorded the pink noise onto a cassette (Fuji DR90 Normal Bias). WHY? Simple - doing this in theory will record the pink noise at the frequency range of the heads within the unit, so we can get a feel of the frequency response of the tape heads.
Testing Procedure
IMPORTANT: S-XBS setting to 0, equalizer settings are FLAT.
a)For the CD, I pressed play, hit 'Go' in TrueRTA, and ramped the volume from 0 to 2.5 max, held it for 20 sec.
b)For the cassette, I pressed play, then in TrueRTA pressed 'Go' (avoids registering the clicking of the tape mechanism), and ramped the volume from 0 to 2.5 max, held it for 20 sec.
I did both these tests for each scenario, for a total of 4 tests.
Results (Solid Ground)
CD:
Cassette:
Results (Isolated Ground)
CD:
Cassette:
Conclusion
Midrange performance was better when you put the unit straight on the ground. Then again, I think most boomboxes back in the day were positioned that way. Notice the dropoff in midrange performance when you isolate the box. As far as the high end response, I didn't tweak that part that much, pretty much most mics I plugged into the soundcard of the laptop cut off at around the same point, but if you follow the existing curve before the sudden dropoff you can see that the CD has better high end response than the cassette (duh). For the cassette, the dropoff is around the 10KHz mark.
In all the charts above, we see that there is a peak that occurs around 120Hz.
All things being equal(that is, if your boombox amplifier is still ok, your model has 4x4PDS, S-XBS, and is rated 30W in the Platinum Collection Catalog), the better bass on the 680 is due to, not surprisingly, the speakers. The peak also demonstrates that the speaker enclosure (bass reflex) is tuned to resonate around that given frequency (Note:The mic graph without any noise shows the sound level go up around the same point; so it appears there was some resonance from the room or mic or both, that occurred in that range. Nonetheless, the test graphs shows the bass response increasing at around 250Hz, which means that the tuned frequency of the box may have peaked at around 120Hz or lower..)..
It is possible that the tweeter on the 690 ruined the setup, as the port on the 690 is skewed compared to the port on the 680 (bass reflex enclosures are finicky about ports, them being too short/long/elongated/misplaced can have adverse or positive effect on bass output of a given speaker.)
See pictures to compare the ports (the pics aren't mine, just using to illustrate the difference in ports):
Assuming the speakers are the same, then internally the volume should be the same as well as the port cubic space, which it appears isn't quite true, as the 690's port is bigger than the 680.
So perhaps if you ran the speakers on the DT680 on the 690 you would get the same result, and again, all things equal, the other models sharing the same speakers as the 680 will, for the most part, sound just as good as the DT680..
I hope that sheds light on things, and again... this isn't a definitive test! Trust your ears - if they are happy, then so is the listener
So anyways, I read this forum and stereo2go and I get a majority saying that the DT680 has 'most' bass of the RX-CT and RX-DT series... so I decided to do a little test here.
I have done this process for my HT setup, not to mention I had friends do something similar in car audio soundoffs back when I was younger. Still, it ain't a definitive guide. I could have missed something, or not done something right. Did this experiment to the best of my knowledge. Here goes!
Equipment Needed:
a)My laptop that is running a program called TrueRTA http://www.trueaudio.com, real time analyzer for tuning audio gear. The free version will do for this test.
b)The mic is from my Onkyo Integra 5.9, it comes with all the Onkyo/Integra units for auto calibrating your soundstage
c)RX-DT680
For the microphone, I had to go into windows and turn off mic boost and set its level to 50. In TrueRTA, I had to setup input to L channel only, and in 'Spectrum Analyzer' I chose 'hold peak' as this will result in the program reading only the highest output levels and not show a fluctuating graph. So in a silent (seriously... as in no ceiling fan running, most electronics off, windows closed...) room, running TrueRTA yielded the following curve (no other adjustments was made beyond plugging in the mic and fixing the boost)
Now to setup the test environment. There are two scenarios, I will explain each one:
1. Solid Ground
In this instance, we test 2ft away with the unit sitting right on the floor. Having it sit right on the floor introduces some things, but in a nutshell - putting a speaker in direct contact with solid dense ground without any decoupling of any sort can amplify sound! (maybe that's what some want...) The mic is isolated from the ground, as you probably listen to the unit with your ears toward it and not your ears touching the ground...
2. Isolated Ground
This scenario is identical to the previous one, except the RX-DT680 is now placed on a damping material (a blanket). Simulates putting your box on grass or other surface that will absorb a good chunk of the energy from the speakers.
3. Test Source
a. Downloaded a pink noise mp3 file (VBR, 13MB) and burned it to CD. http://www.archive.org/details/TenMinutesOfWhiteNoisePinkNoiseAndBrownianNoise
Pink Noise is audio recorded within the range of 20-20KHz (simple explanation)
b. using the unit, recorded the pink noise onto a cassette (Fuji DR90 Normal Bias). WHY? Simple - doing this in theory will record the pink noise at the frequency range of the heads within the unit, so we can get a feel of the frequency response of the tape heads.
Testing Procedure
IMPORTANT: S-XBS setting to 0, equalizer settings are FLAT.
a)For the CD, I pressed play, hit 'Go' in TrueRTA, and ramped the volume from 0 to 2.5 max, held it for 20 sec.
b)For the cassette, I pressed play, then in TrueRTA pressed 'Go' (avoids registering the clicking of the tape mechanism), and ramped the volume from 0 to 2.5 max, held it for 20 sec.
I did both these tests for each scenario, for a total of 4 tests.
Results (Solid Ground)
CD:
Cassette:
Results (Isolated Ground)
CD:
Cassette:
Conclusion
Midrange performance was better when you put the unit straight on the ground. Then again, I think most boomboxes back in the day were positioned that way. Notice the dropoff in midrange performance when you isolate the box. As far as the high end response, I didn't tweak that part that much, pretty much most mics I plugged into the soundcard of the laptop cut off at around the same point, but if you follow the existing curve before the sudden dropoff you can see that the CD has better high end response than the cassette (duh). For the cassette, the dropoff is around the 10KHz mark.
In all the charts above, we see that there is a peak that occurs around 120Hz.
All things being equal(that is, if your boombox amplifier is still ok, your model has 4x4PDS, S-XBS, and is rated 30W in the Platinum Collection Catalog), the better bass on the 680 is due to, not surprisingly, the speakers. The peak also demonstrates that the speaker enclosure (bass reflex) is tuned to resonate around that given frequency (Note:The mic graph without any noise shows the sound level go up around the same point; so it appears there was some resonance from the room or mic or both, that occurred in that range. Nonetheless, the test graphs shows the bass response increasing at around 250Hz, which means that the tuned frequency of the box may have peaked at around 120Hz or lower..)..
It is possible that the tweeter on the 690 ruined the setup, as the port on the 690 is skewed compared to the port on the 680 (bass reflex enclosures are finicky about ports, them being too short/long/elongated/misplaced can have adverse or positive effect on bass output of a given speaker.)
See pictures to compare the ports (the pics aren't mine, just using to illustrate the difference in ports):
Assuming the speakers are the same, then internally the volume should be the same as well as the port cubic space, which it appears isn't quite true, as the 690's port is bigger than the 680.
So perhaps if you ran the speakers on the DT680 on the 690 you would get the same result, and again, all things equal, the other models sharing the same speakers as the 680 will, for the most part, sound just as good as the DT680..
I hope that sheds light on things, and again... this isn't a definitive test! Trust your ears - if they are happy, then so is the listener