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Testing my new sub

post #1 of 16
6/23/12 at 10:15pm
Thread Starter 
I see you guys post these cool graphs and data.
I'm bringing my DIY sub home tomorrow to try out before i finish it
how do i test it?
ive got radio shack SPL and a computer
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post #2 of 16
6/24/12 at 12:22am

http://www.hometheatershack.com/roomeq/wizardhelpv5/help_en-GB/html/gettingstarted.html#top

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post #3 of 16
6/24/12 at 7:25am
Thread Starter 
i was affraid it was REW
hhhh
i'll get started lol
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post #4 of 16
6/24/12 at 10:50am

You could do it manually. Grab some test tones from 20-80hz and write down the spl number at each frequency.

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post #5 of 16
6/24/12 at 7:46pm
Thread Starter 
ah, good idea, do i just keep it around my regular listening volume?
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post #6 of 16
6/24/12 at 8:45pm

Doesn't really matter, I would just measure at 75db.

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post #7 of 16
6/25/12 at 7:09am
Thread Starter 
OK, So got my SPL on 80, c, slow
to what do i set the vol on my avr and sub amp?
I'll read more into REW. there is too much i dont understand
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post #8 of 16
6/25/12 at 10:36am

Play some pink noise and raise the volume till you hit 75db, then start measuring.

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post #9 of 16
6/25/12 at 7:39pm
THX Reference Level is pink-noise at 85db A-weighted from each speaker and 95db C-weighted from each sub.

This is what is referred to as "0db Ref".

This gives peaks of 105db(120-20khz) from each speaker and 115db(20-120hz) from each sub.
Which is quite a lot to ask out of most systems, or any system for that matter.

I have 17 discrete channels of power hooked up to 7 speakers and 9 subwoofers, and I can barely approach this spec (in the subwoofer region).
Most people that "say" they listen at 0db Ref or have experienced it properly, is probably lying to you, that or... they just don't know any better.
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post #10 of 16
6/25/12 at 8:11pm
Quote:
Originally Posted by BassThatHz View Post

THX Reference Level is pink-noise at 85db A-weighted from each speaker and 95db C-weighted from each sub.
This is what is referred to as "0db Ref".
This gives peaks of 105db(120-20khz) from each speaker and 115db(20-120hz) from each sub.
Which is quite a lot to ask out of most systems, or any system for that matter.
I have 17 discrete channels of power hooked up to 7 speakers and 9 subwoofers, and I can barely approach this spec (in the subwoofer region).
Most people that "say" they listen at 0db Ref or have experienced it properly, is probably lying to you, that or... they just don't know any better.

HUH? how is it possible you can barely reach reference with all your gear? I can hit reference all day long with just 2 subs, let alone the whole flock of them. Do you have some sort of giant room??
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post #11 of 16
6/26/12 at 6:38pm
Quote:
Originally Posted by N8DOGG View Post

HUH? how is it possible you can barely reach reference with all your gear? I can hit reference all day long with just 2 subs, let alone the whole flock of them. Do you have some sort of giant room??

I don't know why. Maybe it does do it but my CM-140 SPL meter is lying to me? My room is 4000 cubic feet, large, but not ungodly large.
Even with two bridged EP4000's into the two 21's and an IT8k into the LMS-18, each on a dedicated circuit breaker. With everything near max excursion, it struggles to hit those figures at the LP 12ft away at any frequency.
With all 9 going it only measures 110-115db average with peaks approaching 130db; which according to a THX Ref standard... I should be hitting as you said, much louder...
So I'm not sure why that is confused.gif
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post #12 of 16
6/26/12 at 7:53pm
humm thats really strange. Seem like everything may not be coupling and you're getting some cancellation? I dunno, you should be able to laugh at reference, even in a room your size. I regularly play at 8dB's over reference when I demo my system, though at that loud, I usually wear ear plugs, it's just to show off the subs and how clean the speakers can play at high volume.
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post #13 of 16
6/26/12 at 9:50pm
Quote:
Originally Posted by BassThatHz View Post

I don't know why. Maybe it does do it but my CM-140 SPL meter is lying to me? My room is 4000 cubic feet, large, but not ungodly large.
Even with two bridged EP4000's into the two 21's and an IT8k into the LMS-18, each on a dedicated circuit breaker. With everything near max excursion, it struggles to hit those figures at the LP 12ft away at any frequency.
With all 9 going it only measures 110-115db average with peaks approaching 130db; which according to a THX Ref standard... I should be hitting as you said, much louder...
So I'm not sure why that is confused.gif

Funny thing is when you measure a system that is distorting, the SPL reads higher than it would seem, compared to measuring a system with vanishingly low distortion at the same levels, at least that's what I have found, either that or I 'broke' my meter. Anyone else find this phenomenon? I wonder if it's because the meter is an integrator.... thoughts?
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post #14 of 16
6/27/12 at 11:30am
Quote:
Originally Posted by michael hurd View Post

Funny thing is when you measure a system that is distorting, the SPL reads higher than it would seem, compared to measuring a system with vanishingly low distortion at the same levels, at least that's what I have found, either that or I 'broke' my meter. Anyone else find this phenomenon? I wonder if it's because the meter is an integrator.... thoughts?

I haven't been able to see this for myself with my subwoofer, but it makes perfect sense assuming that the meter loses sensitivity at lower freqs. As for other possible reasons, I don't know. My mains use 12s with PRs (low excursion drivers) that should reach 115dB at my LP ignoring power/other compression, yet I've read 118dB at my LP at full power in the bass (maybe with room gain, not sure). I looked at the recorded waveform and it was a bit distorted (past xmax), which might explain the reading. Eh.
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post #15 of 16
6/28/12 at 12:03am
Quote:
Originally Posted by michael hurd View Post

Funny thing is when you measure a system that is distorting, the SPL reads higher than it would seem, compared to measuring a system with vanishingly low distortion at the same levels, at least that's what I have found, either that or I 'broke' my meter. Anyone else find this phenomenon? I wonder if it's because the meter is an integrator.... thoughts?

I took one 21" outside yesterday and tested it anechoically, definitely not a phase/room issue, I got 115db at 40hz 3ft max excursion with some bassotronics tracks, at 9-12ft it was down to 95db BUT... I then walked 60ft away at a 90 degree angle and it was still ~93db which could still be easily felt. No distortion I could hear. I'm still puzzled, I'll have to re-try this whenever I pull the trigger on that FP14k just to make tripple sure its not a power thing.
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post #16 of 16
6/28/12 at 9:52am
Quote:
Originally Posted by BassThatHz View Post

I don't know why. Maybe it does do it but my CM-140 SPL meter is lying to me? My room is 4000 cubic feet, large, but not ungodly large.
Even with two bridged EP4000's into the two 21's and an IT8k into the LMS-18, each on a dedicated circuit breaker. With everything near max excursion, it struggles to hit those figures at the LP 12ft away at any frequency.
With all 9 going it only measures 110-115db average with peaks approaching 130db; which according to a THX Ref standard... I should be hitting as you said, much louder...
So I'm not sure why that is confused.gif

Looks like you're hitting reference just fine. *Peaks* should hit a maximum of ~121db. Average (sustained) volume should *NOT* be 110-115db. You want a system that is capable of hitting the peaks cleanly but not blazing along at 110-120db all the time. That's why we can listen with peaks that seem extremely loud, because they are brief. Listening to a music concert at 105db sustained is extremely loud and will damage your ears quickly since the volume is sustained, whereas hitting 125db peaks in movie LFE is no risk at all.
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