# Need Advice: 20-39PC-Plus - Push to the limit without bottom out



## media2368 (Apr 19, 2006)

Hi all gurus,

I need some advise from you about calibrating my 20-39PC-Plus using 12.3 driver.

As commonly know that "Flight of the Phoenix" (FOTP) has some of the loudest bass measured in the 20-35hz range. And I am trying to push my sub to the limit but without bottom out when it play FOTP.

And in addition to the low bass, FOTP also has lots of upper bass in the 40-60hz region. 

The 12.3 do a little better in the upper bass (since many have commented the lack of mid bass punch from SVS for 12.2 driver). As a result, it reaches its limit faster. 

- My usual listening volume is 65db (-15 on AVR master volume (At ZERO on AVR master volume, it was calibrated to 80db for reference)). 
- BFD House Curve is 20hz~32hz + 8db, i.e. 20~32hz will play at 73db when I watched a movie.
- Subwoofer Gain is in between 10 o'clock and 11 o'clock, i.e. 10.5.
- 20-39pc+ is tuned to 16hz (with one port plugged)
- Room Size: 24' (L) x 14' (W) x 8' (H)

My questions are:

1) Is it safe to use the BFD to calibrate/push the Freq 20~32hz (using house curve) to 80db on the Subwoofer when I play at my usual listening volume (65db)?
2) Should I adjust the Freq 40-60hz down slightly from the BFD to avoid the 12.3 driver reaches its limit? How much should I adjust?


----------



## lalakersfan34 (Oct 31, 2007)

Do you mean to ask if it's ok if your sub hits 80dB peaks, or if you listen at reference? Reference level is probably a bit too loud considering it's a single 20-39 PC+ in a decent sized room and you're running it in the 16hz tune. I'd guess your sub should be able to handle peaks of around 105-110dB at your LP before you run into problems. Of course this depends on your room acoustics, subwoofer and seating positions, etc. What did you use to calibrate your system to reference level? I know DVE is 75dB, and Avia is 85dB. What source did you use that sets reference level at 80dB?


----------



## media2368 (Apr 19, 2006)

lalakersfan34 said:


> Do you mean to ask if it's ok if your sub hits 80dB peaks, or if you listen at reference? Reference level is probably a bit too loud considering it's a single 20-39 PC+ in a decent sized room and you're running it in the 16hz tune. I'd guess your sub should be able to handle peaks of around 105-110dB at your LP before you run into problems. Of course this depends on your room acoustics, subwoofer and seating positions, etc. What did you use to calibrate your system to reference level? I know DVE is 75dB, and Avia is 85dB. What source did you use that sets reference level at 80dB?


Thanks for your reply but I am sorry that I have edit my message just to make it more clear.

By the way what is "LP"?

I didn't use Avia or DVE. I just sets the reference level at 80db using an SPL meter for 6 channels.

My usual listening level is 65db.

For the subwoofer, I have introduce a house curve using the BFD to calibrate the 20hz~32hz to play at 8db hot (i.e. 73db).

As you said: my SUB can handle peaks of around 105-110dB so is it safe to calibrate the freq 20hz~32hz to play at 35db hot (i.e. 100db)?


----------



## drdoan (Aug 30, 2006)

LP=listening position. Dennis


----------



## Ed Mullen (Jul 28, 2006)

If you are using the AVR test tones for calibration, use 75 dB (C-weighted / Slow) for every speaker channel, and use 73 dB for the subwoofer. Due to the C-weighted filter, the RS meter reads ~2 dB low on the typical subwoofer test tone. 

AVR test tones are designed to play at approximately 30 dB lower than a normal Dolby Digital 5.1 DVD. So (for example) if your calibration level is 75 dB at master volume 0.0 (hereafter referred to as Reference Level), then listening to a real DVD at Reference Level (master volume 0.0) will result in bass peaks of ~105 dB from any speaker channel (redirected to the subwoofer), and 115 dB bass peaks from the LFE channel (since the processor boosts that channel 10 dB upon decoding). A combined bass peak in several speaker channels and the LFE channel can require over 120 dB from the subwoofer at the listening position. 

Most people typically listen at -15 to -10 Reference Level.

Most mid-size rooms will show some natural level of room gain below ~30-35 Hz. While the subject of a "house curve" and the Fletcher-Munson effect will likely remain evergreen, if you want the most headroom from your subwoofer, run it in the 20 Hz tune, adjust the FR for a flat response from 20-80 Hz, and calibrate it to 73 dB with your AVR test tones (with the speaker channels at 75 dB). 

If you hear port noise, woofer farting, or outright bottoming - you are overdriving the subwoofer and you should back-off the master volume a few dB on that passage and note the master volume setting for future reference to avoid trouble on that DVD. One or two instances of bottoming should not hurt the woofer, but repeatedly overdriving it will eventually ruin the driver. 

If your preferred playback level is inconsistent with the clean/linear/uncompressed limits of a single PC+, then you should either double-up to colocated dual PC+ (for a 6 dB increase in headroom), or step-up to the PC-Ultra (which will provide 4-5 more dB of max output than a single PC+).


----------



## media2368 (Apr 19, 2006)

Thank you Ed, nice to hear from you here.

Anyway, I have tested the FOTP this morning and I managed to hit the LFE at 115db for the plane crash scene without bottom out.


----------

