mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 Check the vertical scale of this graph in relation to the one I posted - the curves are very close to the same. My comment on the relative performance below 40 Hz for the THT and the KPT-1802 are basically unchanged. Huh? Your scale drops about 13db between about 30-45Hz. On this graph between 22Hz-45Hz the drop is only 7db. In the graph shown, it would be very very simple to attenuate 40-50Hz down a bit and have a decent curve to 150Hz, excluding the -10db notch right at 85Hz. Quote Link to comment Share on other sites More sharing options...
Chris A Posted September 15, 2014 Share Posted September 15, 2014 (edited) Same graph, but with a vertical axis to proportion showing the FR more usefully...10 dB down is about 30 Hz. Compare this to the KPT-1802's minus 10 dB point: ~21 Hz--conservatively. This isn't a very smooth FR plot, and says to me that there are actually some design issues with the THT that weren't iterated in order to get good performance out of the basic design. The harmonic distortion plot also got my attention, but I don't see the output level (dB) at which these harmonics were measured. Edited September 15, 2014 by Chris A Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 I see what you mean Chris, but the slopes start at different positions. Yours starts at 45Hz, and has a -10db pitch. The Green graph starts at 22Hz, and is a much steeper -24db slope. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 The green curve is not unlike this DTS-10 curve from Data-bass only the slope starts at about 14Hz on the Danley: Quote Link to comment Share on other sites More sharing options...
Chris A Posted September 15, 2014 Share Posted September 15, 2014 (edited) The same plot for a TH-SPUD DIY: Edited September 15, 2014 by Chris A Quote Link to comment Share on other sites More sharing options...
jason str Posted September 15, 2014 Share Posted September 15, 2014 (edited) I too was interested in distortion measurements of the THT and found the results. Measured information located at the top of page 11 HTS page 11 Edited September 15, 2014 by jason str Quote Link to comment Share on other sites More sharing options...
Turbox Posted September 15, 2014 Share Posted September 15, 2014 Hey Turbox, FYI, I think the KPT-1802 is the awesomest sub out there. I am definitely not trying to poo-poo them. I was just bored, and had this idea. No disrespect taken at all. no worries. 1 Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 (edited) Here are my measurements. 24" wide THT's, Pink Noise, 1 meter, internal iPhone 5S mic 19" from the floor, 2.83V as measured by my Extec Instruments 430 True RMS Multimeter. I tested average on each of three for 35 seconds each. Sub 1, Sub 2, and both subs at the same time. This demonstrates that in this test, the subs start to roll off at about 24.5Hz. Here is the graph with 12.2Hz highlighted: 24.5Hz highlighted: 50Hz highlighted: 83Hz highlighted: 122Hz highlighted: Edited September 15, 2014 by mustang guy Quote Link to comment Share on other sites More sharing options...
Chris A Posted September 15, 2014 Share Posted September 15, 2014 Where did you take the measurements? Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 (edited) FYI, sub 1 was slightly louder than sub2. I'm not sure what caused this, but it was the inside sub, and sub 2 was the outside sub. The measurements were taken in my shop. The closest wall is 60' away. The ceiling height is 24' at the eves. Edited September 15, 2014 by mustang guy Quote Link to comment Share on other sites More sharing options...
Chris A Posted September 15, 2014 Share Posted September 15, 2014 So your room volume is something like 72000 cubic feet, and the subs are in the middle of the room on the floor, with the objects you show in the picture in the close field? Quote Link to comment Share on other sites More sharing options...
jason str Posted September 15, 2014 Share Posted September 15, 2014 Thank you for taking time out to measure your sub(s). Its possible one sub may have a small air leak causing the discrepancy in output. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted September 15, 2014 Share Posted September 15, 2014 A 20 dB drop from (roughly) 85 to 25 Hz or am I reading this incorrectly? Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 So your room volume is something like 72000 cubic feet, and the subs are in the middle of the room on the floor, with the objects you show in the picture in the close field? No, the room volume is closer to 130,000 cf. Here are some pics that may put it in perspective: Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 A 20 dB drop from (roughly) 85 to 25 Hz or am I reading this incorrectly? Depending on which of the 3 measurements from 83-24.5Hz it's 22.4db, 24.1db and 24.4db. That's roughly 24db drop. Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 Thank you for taking time out to measure your sub(s). Its possible one sub may have a small air leak causing the discrepancy in output. Not sure, but the curves are pretty close, and I always thought air leaks cause distortion mostly. Any way, it's not that different, and it is nice to have 2 subs to corroborate the measurements from. When I built these subs, there were no air leaks at all. If there is one now, it has developed over time. Quote Link to comment Share on other sites More sharing options...
jason str Posted September 15, 2014 Share Posted September 15, 2014 Mostly loss of output from air leaks, even a pinhole size leak will cause loss. Lets not forget this is not the full size THT, the 3 ft wide model is dam near flat to 25 Hz. Quote Link to comment Share on other sites More sharing options...
Chris A Posted September 15, 2014 Share Posted September 15, 2014 (edited) Assuming that your T60 is about 0.8 (i.e., a very live room), that puts the Schroeder frequency at about 30 Hz. I assume that you're using upsweeps to test? Oops: you mentioned that you're using pink noise. Right? Chris Edited September 15, 2014 by Chris A Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 (edited) Right pink noise. Here are some calculations with the numbers plugged in. The second sub adds about 6.1db. I am extrapolating what a third sub looks like in column H: Edited September 15, 2014 by mustang guy Quote Link to comment Share on other sites More sharing options...
mustang guy Posted September 15, 2014 Author Share Posted September 15, 2014 (edited) Mostly loss of output from air leaks, even a pinhole size leak will cause loss. Lets not forget this is not the full size THT, the 3 ft wide model is dam near flat to 25 Hz. I will test for leaks. Pretty easy, right from the build sheets... Will report back in this post.. #40 Results: No leaks. These speakers are 100% tight. These are 24" wide THT's. Together, they are 48" wide, and dual drivers. Should result in flatter curve than a 36 with a single driver. Am I wrong? Edited September 15, 2014 by mustang guy Quote Link to comment Share on other sites More sharing options...
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