TH-18 Flat to 35hz! (Xoc1's design)

Hi Crescendo,

Very well done (and a bit of envy)! Thanks for posting the pictures.

Please, head NEO Dan's warning, there is just no excuse for frying these wonderful drivers while testing. Also, keep the low cut (high pass) filter in place to limit the excursion at the bottom end.

How did the cone volume correction test turn out?

Regards,
 
I can see doing this for max voltage tests - good solution to my multi-meter problem. But for sweep testing, I would set voltage (2.83, 28.3) at the speaker terminals to take the voltage drop over speaker wire out of the equation.
The idea is to dial in the setup, without any noise or speaker related issues. If you are loosing voltage you might want to replace the offending wiring.

Of course - I don't see FR sweeps completing within 2 seconds.
Actually if you don't have a huge open area to test in you probably are best off with the 128k sweep, I use the 2 sweep average, it takes less than 6 seconds.

Let me know if there's any other equipment or specifics you're interested in.
How about the sound card mic preamp...


I'm also interested in your cone correction testing methodology and results.
 
Hi Crescendo,

Very well done (and a bit of envy)! Thanks for posting the pictures.

Please, head NEO Dan's warning, there is just no excuse for frying these wonderful drivers while testing. Also, keep the low cut (high pass) filter in place to limit the excursion at the bottom end.

How did the cone volume correction test turn out?

Regards,

Thanks, Oliver.

I guess I like to sometimes live dangerously. I suppose I can hold off anymore at-clip tests ;)

For shows, I have my HPF set to 27Hz/12dB LR. For 1W/1M & 100W/10M, I will have the HPF disengaged.

I'll post the test results below.


was there any benefit?

Indeed!


The idea is to dial in the setup, without any noise or speaker related issues. If you are loosing voltage you might want to replace the offending wiring.

I'm not saying I'm losing a significant amount of voltage. ANY wiring before the speaker will introduce some resistance and voltage drop. Some say to measure the resistance of the speaker wire and add that to the equation. My theory is: testing at the terminals will remove any and all of that out of the equation. Less math and as close to what the driver is actually receiving as possible.


Actually if you don't have a huge open area to test in you probably are best off with the 128k sweep, I use the 2 sweep average, it takes less than 6 seconds.


How about the sound card mic preamp...


I'm also interested in your cone correction testing methodology and results.

Sound card is the Echo AudioFire4


Brand new B&C 18SW100 loaded TH-18 (not broken in):
Without cone volume correction, with cone volume correction and, finally, corrected/calculated values to compensate for the meter's C-weighting, with cone volume correction.

Hz _ w/o _ w/cvc _ corr.
35: 117.1 / 118.1 / 120.6
37: 118.4 / 119.7 / ____
40: 120.8 / 121.7 / 123.5
45: 124.1 / 124.6 / 126.1
50: 125.4 / 125.7 / 127.0
55: 125.8 / 126.0 / 127.0
60: 126.0 / 126.3 / 127.2
65: 126.4 / 126.6 / 127.3
70: 126.7 / 126.8 / 127.4
75: 126.0 / 126.5 / 127.0
80: 125.7 / 126.5 / 127.0
85:
90: 126.98 / 127.3 / 127.6
100: 127.8 / 128.0 / 128.3

These tests were done outdoors, at 1M, over grass. Sine waves were played from my MacbookPro, thru my Serato ScratchLive software and interface, out to my Pioneer DJM-800 (mixer) - XLR outs to my dbx Driverack 260 (filters, delay, limiter and EQ off) and finally to my QSC PLX3402. Output was measured with the American Recorder Technologies SPL-8810.

**These tests were completed with only one side of the enclosure thoroughly screwed together with vinyl foam/tape in place of PL or glue.
 
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I don't use a controller. I use turntables (with Serato Scratch Live). A controller would be nice to have in college tho. I'd go with either the Vestax VCI-300 or the newer VCI-380 (both are compact; both use Serato Itch) or one of the Pioneer units (bigger); one integrates Serato Itch - the other, Traktor.

I was thinking of getting the Denon MC3000, and then adding on Traktor Kontrol F1's when I had the budget. I like tractor, and I see myself using one shots and cues much more than scratching
 
Thanks for the nudge.
I looked it up and it says, Bridged power of 3400 Watts into 4 Ohms @ 1% THD, 1 KHz. In that case, reaching mid 126, 127 db in a TH-18 is not much. The B&C 18SW100 rated at 3000W, 97db should reach the same SPL even in a BR enclosure.
What are we missing here?
Hi Samuel,

Your question is probably based on theoretical models instead of real world events. In the reality all enclosures and drivers suffer from system losses of all kinds:
A) Thermal Compression
B) Dynamic Compression (result of boundary effects, changing acoustic air properties ect)
C) Building errors (driver volume is not compensated in the S4 area, extra corner volume ect).

In reality basreflex do meet their predicted max level output (above a certain frequency) because the basreflex port starts to increase its stiffness (port compression) as power is increased. This is the result of the relative small bass-port. The effect is that the low end of the basreflex is less than predicted but the area above gains in level and does meet its predicted level. Often you will see the opposite in Tapped Horns and horns in general.
 
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