# Your comments on my BFD filters please



## gperkins_1973 (Aug 25, 2008)

Hi guys,

I have done various heavy boosting as some of you may already know.

I have done another set of BFD filters with only 3db of boosting at 20hz instead of 14db. I have a steeper roll off from 20hz which is going to concern me as I love my bass and play alot of low end heavy bass music along with some normal stuff.

This first pic is showing the BFD filter set I am using at the moment which shows the 14db boost at 20hz and the graph to go with it.

The second one shows the BFD filter set with just 3db of boost but as I said a steeper roll off and the predicted graph to go with that.

The input I need from you guys is, will I notice a massive difference when playing say 10-20hz music between the two graphs.

I want to get the best from the sub.

cheers

Graham


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## Wayne A. Pflughaupt (Apr 13, 2006)

> The input I need from you guys is, will I notice a massive difference when playing say 10-20hz music between the two graphs.


Do you actually have music that generates stuff below 20 Hz?

Regards,
Wayne


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## lsiberian (Mar 24, 2009)

I can't suggest you pushing your sub that hard at 10hz. The distortion goes up and you will lose headroom were it counts. The best distortion reading I've seen on a sub shoots up like a rocket at 14-15hz. And that was an incredible sub. I understand the adrenaline rush of LFE extension numbers.

But this situation requires an ABX test to determine which is better to your ears. Without a controlled ABX test everyone will conclude the first graph is better. ABX testing can save you a lot of money and trouble.


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## gperkins_1973 (Aug 25, 2008)

Everyone I have spoken to have said that a 14db boost will damage my sub. My two FI Q18's have the BP upgrade on them and and have 2" of xmax ecursion. I have wired the sub up into 2400 watts rms 4ohms bridged. According to WinISD my sub is good for 103db at 10hz, 115db at 20hz and 125db 40hz onwards plus room gain. I don't know what that bares reference to the amount of headroom you can afford to loose to still gain good output at low hz.

Even at 10hz sine wave with the 14db boost I still don't that much excursion. 

Does cutting the 25hz frequency -12db counter act some of the boost I have applied to the 20hz region.

What exactly is ABX testing?

cheers

Graham


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## lsiberian (Mar 24, 2009)

gperkins_1973 said:


> Everyone I have spoken to have said that a 14db boost will damage my sub. My two FI Q18's have the BP upgrade on them and and have 2" of xmax ecursion. I have wired the sub up into 2400 watts rms 4ohms bridged. According to WinISD my sub is good for 103db at 10hz, 115db at 20hz and 125db 40hz onwards plus room gain. I don't know what that bares reference to the amount of headroom you can afford to loose to still gain good output at low hz.
> 
> Even at 10hz sine wave with the 14db boost I still don't that much excursion.
> 
> ...


There are several difficulties in reproducing 10hz. 

Distortion rises rapidly below your subs Fs. This can be seen on any number of sub measurements. So much so that by 10hz even at moderate volumes it will be noticeable. 

ABX testing is blind testing process that allows people to evaluate products based not on brand or psychological preference, but on actual performance. In audio this means electronics or speakers are switched without the knowledge of the listener. The listener then attempts to pick out the best speaker in a 1 on 1 battle. If the listener can't discern the difference between the two(less than 60% correct over several tests) Then there is no audible difference for the listener. 

ABX testing has been used to disprove/dispell/question a lot of myths in Audio. Including things like CDs sounding better than high bit rate mp3s, monster cable sounding better than coat hangers:R, solid state amps having differences that are audible.


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## gperkins_1973 (Aug 25, 2008)

Right guys,


Re did the EQ thing again tonight and I found that using the 80db on the spl meter gets me low levels and the only way to get good levels which don't cause any issues with REW is to put the spl meter to 70db.

Levels all fine so here are my new measurements and this time I only had to use a 4db boost at 20hz.

The first is my sub only un EQ'd graph
The second is my sub graph EQ'd
The third is my speakers and sub together.
The last pic shows the filters I used. I only had to use 8 this time.

I decided to go for setting the sub on 90hz and the speakers on 70hz which seemed to give the least dips. The other thing I noticed is that with still getting a flat graph the same as before, I could raise the sub trim level to 78db. 

The sub and speaker graph goes a little wobbly but I am not sure if that is ok.

cheers

Graham


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## Wayne A. Pflughaupt (Apr 13, 2006)

Here’s the electronic response of your first set of filters.







​

Here’s the electronic response of your second set of filters.







​

As you can see, they merely confirm what your in-room graphs show, that the first set better tracks the Target, while the second set goes for flat response.


















You’re simply going to have to decide for yourself which sounds better to you – we can’t tell you that.



> Everyone I have spoken to have said that a 14db boost will damage my sub.


People tend to make blanket statements like that without first qualifying them – i.e., not bothering to find out first what the size of your room is, the capability of your equipment, or your listening habits. E.g. it’s more relevant if you like to listen to pipe organ music at ear-bleeding levels than if you like chamber music at levels that would permit conversation.



> Even at 10hz sine wave with the 14db boost I still don't that much excursion.


That tells me you aren’t going to damage your subs. But lsiberian raises the issue of distortion; I’m not qualified to comment on that, except I would expect that it has to be audible to be a problem. That will only be an issue if your program material is generating something down there. A poorly-mixed rock CD that has the bass guitar falling like a brick below 125 Hz, it would never be an issue. Pipe organ music – may be an issue with something like that.

It would be inaccurate to say that your previous graph had a “14 dB boost at 20 Hz.” At 120/60 bandwidth, a filter that broad is merely _boosting the overall gain_ of the subwoofer. You could get pretty much the same effect by simply raising the amplifier’s gains instead. To see what I mean, here’s the electronic response of that filter. (If it were removed, electronic response would simply track the Target.)







​

If you compare electrical response of your first set of filters with and without the 20 Hz filter, it’s easy to see that it’s mainly being used as a level adjustment.














​

Regards, 
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

I love these graphs. :T They show the foolishness of people having a panic attack when they hear something like “14 dB boost at 20 Hz.” As your graphs show, you’ve boosted response below 20 Hz _with nothing but cutting filters._ Once again, equalizing requires additional and ample headroom, no matter if you’re boosting or cutting...

Regards,
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

By the way, why do you need so many filters above 80 Hz? Is there no bass management in your receiver? Or is that the way things are with bass management in place?

Regards,
Wayne


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## gperkins_1973 (Aug 25, 2008)

Wayne,

Thanks for that. I did notice that the 3 sets of filters I did yesterday, when I run measurements again today after taking another un EQ'd measure they came out like yours, where as yesterday they came out flat. So I guess you can take one un EQ'd measurement 1 day and EQ it, run another the next day and they will be different again.


I have just re run some new sub/speaker measurements and here are the best two.

I think preset 3 is better. That is with 14db boost but I have reduced the onkyo sub trim level to -13db to get 78db

Preset 4 is the 4db boost but the sub trim level on -2.5db.

Is is better to boost and then trim the sub down or boost very slight and up the sub trim. Does it matter what way you do it.

I have to say I do love the sound of my sub which is most important. It does sound very clean and with the power that the behringer 4000 gives out the two subs will eat that no problem especially with the BP power upgrade. 

cheers

Graham


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## gperkins_1973 (Aug 25, 2008)

Wayne

The reason I have made it flat to 100hz using the filters is because it sounds so much fuller. I don't get enough clout from the Monitor Audio RS6's from the onkyo 876 even though they are bi amped. You hear the upper bass much more. It kinda fills in the gaps if you know what I mean.

cheers
Graham


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## gperkins_1973 (Aug 25, 2008)

Wayne,

sorry here's preset 3. Its getting late here in the UK.

cheers
Graham


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## gperkins_1973 (Aug 25, 2008)

Wayne,

Here are the waterfall graphs for preset 3 and 4 EQ filters.

What do you think.

cheers

graham


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## Wayne A. Pflughaupt (Apr 13, 2006)

gperkins_1973 said:


> I have just re run some new sub/speaker measurements and here are the best two.


Hmm... Now you have a good-sized dip at 50 Hz. That wasn’t there before...



> Is is better to boost and then trim the sub down or boost very slight and up the sub trim. Does it matter what way you do it.


Makes no difference. The amp and drivers see it as the same thing, as far as the demands placed on them.

Regards,
Wayne


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## Wayne A. Pflughaupt (Apr 13, 2006)

gperkins_1973 said:


> Wayne,
> 
> Here are the waterfall graphs for preset 3 and 4 EQ filters.
> 
> ...


Amazingly good. :T

Regards,
Wayne


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## gperkins_1973 (Aug 25, 2008)

Wayne,

There has always been a dip at 50hz. Probably placement might help although there isn't any where in the room to put the 320lb monster. Preset 3 shows a much smaller dip which is the one I am using now.

I have to say it has been an interesting road building my sub. I have never built one before and my knowledge is pretty thin to be honest but I feel I have learned a few bits on the journey. I now have to veneer it and create some grills to finish her off. I must say that I feel it is a significant improvement over the PB13 I had previously. Music wise its a massive improvement. I really enjoy listening to different types of music now. Its not a perfect sub but what is, I could make two single 18's ported or sealed and maybe iron out the dips etc.. but that would mean getting rid of the last piece of furniture in the room and the other half hates me as it is with building the sub. I will be sorting out that annoying fan this weekend as I am sure that is making it sound pretty rubbish at low volumes. I must say though no hum from the BFD.

I did experience my first thump turning it on last night. Oops!

Thanks for your help Wayne.

You should check out my thread in the diy subwoofers sealed and ported when I veneer it and finish it.

cheers

Graham


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