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Discussion Starter · #1 ·
OK, here is the dilemma.
I just measured my sub response with CM140 that Sonnie sent me (Major Thanks) and discovered that i also have huge 60Hz dip, like many people here.
I don't have a BFD yet, wanted to see if i need it at all.
My plate amp has selectable Bass Boost at 14,20,28Hz and damping selection (Low,Mid,High). I always knew that high damping factor is better in the amp so originally i set the damping to be High. But now that i can actually see the response i noticed that when i switch the damping to Low the response moves up and straightens out.
I also played with Bass Boost freq. but these are the best settings i attained.
On the graph RED=High Damping, PURPLE=Low Damping. Which one to select?
Tomorrow my Visaton B200 arrive and i already have baffles for them. Will this lower damping integrate with OB? Or am i forced to keep it at high?


I think choosing lower damping the response is almost flat leaving me to trim only 2 peaks (16 and 50Hz). It's kind of redundant to Bass Boost 14Hz on the amp and then cut them with BFD. Will it compress the dynamic range?

Another idea i had since i only use 1/15th of the power of the amp i could just cut ~10-15dB and make the whole graph ruler flat (eliminating 60Hz dip) and just turn the gain knob on the amp way more.

In case someone is interested here is the whole system response, DIY Bob Brines FE167E MLTL + "My-own-design'' Lambda Acoustic 12" MLTL sub.


The sub level is a little high due to my 'calibrations' lol, ignore that. And don't mind strange SPL figures, i measured at night.

FE167E seems WAY too bumpy (look at all the +-10dB hills) considering i copied Bob's design word for word and his response is much flatter +-3.5dB.:huh:
Both speakers already have BSC circuits but look at the midrange peak.:wits-end:
http://www.geocities.com/rbrines1/Pages/FT-1600_MkII/Design_Details.html
 

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Welcome to the Forum!

Tomorrow my Visaton B200 arrive and i already have baffles for them. Will this lower damping integrate with OB? Or am i forced to keep it at high?
What’s a Visaton B200?

Another idea i had since i only use 1/15th of the power of the amp i could just cut ~10-15dB and make the whole graph ruler flat (eliminating 60Hz dip) and just turn the gain knob on the amp way more.
How would you do that, since you don’t have an equalizer? Turning down the amp’s gain won’t fix that 60 Hz depression.

It's kind of redundant to Bass Boost 14Hz on the amp and then cut them with BFD. Will it compress the dynamic range?
If by that you mean “Will I loose headroom,” the answer is any equalization exacts a headroom penalty, so you have to have enough to spare going in. It appears that you do, based on your “1-1/15th” statement.

FE167E seems WAY too bumpy (look at all the +-10dB hills) considering i copied Bob's design word for word and his response is much flatter +-3.5dB.
The only way to duplicate Bob’s figures is to use the same measuring technique with the same measuring instruments and equipment in the same environment he measured in. Change any one of those and you won’t get the same results. What you’re seeing there is room interactions, coupled with the response of the mic you measured with. I’m not sure the CM140’s mic is accurate all the way out to 20 kHz. Did you use any smoothing? That will make a difference in the way the graph looks.

Regards,
Wayne
 

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Discussion Starter · #3 · (Edited)
Thanks for the welcome Wayne,
1. Visaton B200 is very popular driver among Open Baffle enthusiasts
http://www.audiocircle.com/circles/index.php?topic=19253.10 (Here is ~100,000 views thread :dizzy: )
http://www.6moons.com/audioreviews/roadtour5/roadtour5.html (This is what the speakers may look like)
The reason i mentioned it within the context of damping question is because Open Baffle speakers usually have shorter transients -> they are 'fast' (even though i hate to call it that), hence it's tricky to integrate 'regular' subs with them (they seem 'slow' = low system Q, delay), sometimes requiring OB / IB / TL subs. I was worried if i use Low Damping Setting (because it looks flatter) the woofer would be looser and less accurate.

2. I actually mean to buy BFD and 'cut ~10-15dB' with BFD to bring the whole response curve to the lowest level of 60Hz dip, making it smother and then increase gain on the amp to make up for the EQ cut. I'd loose efficiency but make the response flatter. Is it worth it?

4. I used the calibration file for ecm8000 which is +-2dB from ideal while Sonnie is making one for CM140. I also used 1/3 octave smoothing to approximate the response. I understand that the conditions are not the same, i guess i'll need to build some acoustical panels since i can't use EQ for higher freqs.

Thanks
 
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