TH-18 Flat to 35hz! (Xoc1's design) - Page 103 - diyAudio
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Old 23rd September 2012, 02:36 AM   #1021
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hi all,
Is this a better responce ?
Thanks,
NS
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File Type: jpg RTA Both rings in.jpg (178.4 KB, 453 views)
File Type: jpg Spec ARTA lower rings in.jpg (145.2 KB, 439 views)
File Type: jpg Sweep both rings in.jpg (133.0 KB, 427 views)

Last edited by noSmoking; 23rd September 2012 at 02:43 AM.
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Old 23rd September 2012, 03:25 AM   #1022
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I noticed voltage fluctuation (+/- 0.5v) during two different frequency sweeps I have. Is this normal? Has anyone measured voltage at the amplifier during an REW or Smaart freq sweep? Does voltage fluctuate (+/- 0.5v)?
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Old 23rd September 2012, 04:04 AM   #1023
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by noSmoking View Post
hi all,
Is this a better responce ?
Thanks,
NS
I dunno it looks funky with the squiggle in there, can you e-mail the REW file?
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Old 23rd September 2012, 05:12 AM   #1024
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by CRESCENDO View Post
I noticed voltage fluctuation (+/- 0.5v) during two different frequency sweeps I have. Is this normal? Has anyone measured voltage at the amplifier during an REW or Smaart freq sweep? Does voltage fluctuate (+/- 0.5v)?
The sweep is a sweep and if you are using a multimeter to measure the sweep you are subject to it's averaging accuracy, thus using a sweep to set a level is not recommended due to the variable nature of the signal/meter combination. If you are not measuring at a large level of power these sweeps should not cause the amp output to sag. At high output levels you could monitor the DC supply rails in the amp to see if they sag much. But generally speaking if the amp 2kw+ amp is sagging at 100w or something like that just find a dumpster for it and get a real amp.

Measurement sweep setup suggestion:
  • Attach multimeter to amp terminals or wire ends, speaker is not attached at this point.
  • Use the REW generator to play a 60Hz sine wave and set amp output voltage, 4Ω: 2v/1m, 10v/5m, 20v/10m. Note the REW generator output level setting, and do not go higher than -12 to avoid digital clipping. Ensure there is no clipping elsewhere in the signal chain.
  • Start measurement sweep dialog, set output level to the same value previously used in the generator, set frequency of sweep to 20-300Hz and select the shortest/128k sweep length and set the number of sweeps to 2.
  • Click the start measuring button, if you have too much or too little input signal make corrections at the mic/input level side only.
  • Look at impulse response and adjust IR windows to 25ms left and 150ms right, then click Apply Windows
  • Now look at FR and phase.

Note:
If you use a C-weight SPL meter to calibrate your setup with the 60Hz sine wave the actual level is ~.9dB higher than indicated due to the roll off of the C-weight filter.

If one is to be able to make valid comparisons to other anechoic measurements it is important to measure outdoors well away from large reflective surfaces and use appropriate time windowing on the measurements to produce an accurate response.
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Old 23rd September 2012, 05:51 AM   #1025
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by noSmoking View Post
hi all,
Is this a better responce ?
Thanks,
NS
Quote:
Originally Posted by NEO Dan View Post
I dunno it looks funky with the squiggle in there, can you e-mail the REW file?
Hi NS,
I was not paying attention, I see the input level is low @ -75dB. Your mike missing it's phantom power?
The source of the squiggle is something late in the impulse response and a little noise possibly.
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Old 23rd September 2012, 06:21 AM   #1026
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Quote:
Originally Posted by NEO Dan View Post
The sweep is a sweep and if you are using a multimeter to measure the sweep you are subject to it's averaging accuracy, thus using a sweep to set a level is not recommended due to the variable nature of the signal/meter combination. If you are not measuring at a large level of power these sweeps should not cause the amp output to sag. At high output levels you could monitor the DC supply rails in the amp to see if they sag much. But generally speaking if the amp 2kw+ amp is sagging at 100w or something like that just find a dumpster for it and get a real amp.
Was using a multimeter to measure very low voltage (>2v). I was under the assumption the sweep swept thru frequencies at the same level - that's what raised this question. I wasn't using the frequency sweep to set level.

Quote:
Originally Posted by NEO Dan View Post
Measurement sweep setup suggestion:
  • Attach multimeter to amp terminals or wire ends, speaker is not attached at this point.
  • Use the REW generator to play a 60Hz sine wave and set amp output voltage, 4Ω: 2v/1m, 10v/5m, 20v/10m. Note the REW generator output level setting, and do not go higher than -12 to avoid digital clipping. Ensure there is no clipping elsewhere in the signal chain.
  • Start measurement sweep dialog, set output level to the same value previously used in the generator, set frequency of sweep to 20-300Hz and select the shortest/128k sweep length and set the number of sweeps to 2.
  • Click the start measuring button, if you have too much or too little input signal make corrections at the mic/input level side only.
  • Look at impulse response and adjust IR windows to 25ms left and 150ms right, then click Apply Windows
  • Now look at FR and phase.

Note:
If you use a C-weight SPL meter to calibrate your setup with the 60Hz sine wave the actual level is ~.9dB higher than indicated due to the roll off of the C-weight filter.

If one is to be able to make valid comparisons to other anechoic measurements it is important to measure outdoors well away from large reflective surfaces and use appropriate time windowing on the measurements to produce an accurate response.
Thanks for the notes. Sorry for the short/quick reply. More later
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Old 23rd September 2012, 07:57 AM   #1027
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by CRESCENDO View Post
Was using a multimeter to measure very low voltage (>2v). I was under the assumption the sweep swept thru frequencies at the same level - that's what raised this question. I wasn't using the frequency sweep to set level.
Gernerally I think unless you have a "high end" HP or Agilent meter and a perfectly flat output on your sound card you should expect the meter to waver on a sweep.

If you look at the loopback calibration for your setup you can see how much correction was applied to flatten the response. Obviously this is a correction of the cumulative deviation of both the input and output, but the early rolloff of a sound card would be a good reason to see the meter waver during a sweep, but not at a fixed frequency.

Don't sweat the meter, the calfile covers anything in the the loop at the time it's made... Leaving the mic, amp, speaker, and envrionment. You can cal with the amp in the loop if you take care with the voltage, but the amps noise floor may intrude. Probably better to just check the amps FR with your setup, remember to turn off the HPF You might want to lookup the curve for your mic though
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Old 23rd September 2012, 10:38 AM   #1028
ODougbo is offline ODougbo  United States
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Let me know if you need a stack of disks; just pay for the shipping

Quote:
Originally Posted by noSmoking View Post
Hi Oliver,
Interesting ,so do you think in the case of using a 18 " speaker that the disks would react differently as apposed to the stub that goes across the whole camber or if the stub was shorter what difference in responce would that have,
To all of you guys Nice work on cone corrections ,I am beginning to figure it out ,Got REW setup and working just got to get the hows and whys to correctly figured, to hopefully have a correct response curve,!
Have A GREAT Day!
ns
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Old 23rd September 2012, 09:00 PM   #1029
Xoc1 is offline Xoc1  United Kingdom
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Quote:
Originally Posted by NEO Dan View Post
I'm really curious as to where fudging S2 via an inflated cone correction became a good idea? The 18SW115 is really not going to make it to 60mm p-p without dammage, in fact it is hard to drive to 40mm p-p, and that's with HUGE amounts of power.
Hi Dan
S2 compression ratio is currently about 3:1 but this includes the cone correction volume. I'm still unsure about if to stick with this value or reduce the compression ratio. If I can I might reset the geometry for a bigger S2 value but leave enough space for users to be able to fit a double packing piece if needed, to reduce S2 for those users who have the most robust drivers.
What would you think is an optimum S2 compression ratio for budget and top end drivers?
.
Please note that nothing is completely set yet and I am still tweaking the design. I felt that it was time to post the work in progress and get some collaborative input.
Regards
Martin
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Old 24th September 2012, 06:03 AM   #1030
NEO Dan is offline NEO Dan  United States
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Quote:
Originally Posted by Xoc1 View Post
Hi Dan
S2 compression ratio is currently about 3:1 but this includes the cone correction volume. I'm still unsure about if to stick with this value or reduce the compression ratio. If I can I might reset the geometry for a bigger S2 value but leave enough space for users to be able to fit a double packing piece if needed, to reduce S2 for those users who have the most robust drivers.
What would you think is an optimum S2 compression ratio for budget and top end drivers?
.
Please note that nothing is completely set yet and I am still tweaking the design. I felt that it was time to post the work in progress and get some collaborative input.
Regards
Martin
Hi Martin,
IIRC I went from ~2.4 to 3:1 and it was very noticeable with the 18SW115, but I didn't have the large S1. The increase in compression brought flatter LF response but the sound was compressed in nature, I immediately recognized the difference at any output level. This is really critical to the sound quality in the octave above the box FB. I'm sure your new large S1 will reduce the effect to some extent as will the more open taper you are looking at now.

The problem with the drivers we are using is that they are at the very top of what's available WRT the available force per area. When someone else comes along and puts in an average driver in the box the effect of the compression becomes even more pronounced and it becomes a source of heat induced failure caused by the stalling of the driver motor near FB.

Adding to the list...
Code:
15SW115-8   202.43
15NW100-8   179.8
PD1850-8    160.49
15TBW100-8  153.8
21SW152-8   150.89
15TBX100-8  149.12
18SW115-8   146.00
15SW100-8   141.94
PD2150-8    131.56
18NW100-8   127.05
18PZB100-8  112.48
PA380-8     112.10
18TBW100-8  108.68
2269H       107.35
18SW100-8   106.22
18TBX100-8  105.37
21SW115-8   100.07
4018LF       99.13
2242H        96.38
2226H        83.78
PD2450-8     83.47
PA460-8      80.93
4015LF       76.96
IMPERO 15a   79.26
2268H        68.73
2241H        59.95
2245H        58.49
IMPERO 18a   56.97
Looking at the PD1850 datasheet reveals that the claimed 11.05mm X max is possibly X var as the coil is 28mm long and the gap is 12mm, leaving the real X max at 8mm. The displacement limit is listed as 34mm p-p, that would leave the coil still 3mm in the gap with 25mm hanging below/above. Is the slice of magnet only 25mm thick? They must be make a killing on recone kits
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