# New Sub: Monolith Response, any thoughts?



## 3ll3d00d (Jun 6, 2006)

Hi

I have upgraded to the BK Monolith from its little brother (XLS200), a fine sub for its size but I felt something meatier was required :bigsmile: 

I was using quite a few filters on the old sub to massage its response into something sounding good but initial impressions (on a brand new hence not run in) sub shows that the monolith needs less work. 

The Monolith is running at 80Hz crossover with B&W602S2 fronts and a B&W CC6S2 centre.

I've attached 3 graphs 

1) unfiltered sub only
2) filtered sub only
3) filtered sub with mains

Now it looks like it has the basis of a reasonably natural house curve with the exception of a peak-trough and a trough-peak combo. The former is in the 40-55Hz range, the latter around ~90-105Hz which has a particularly massive dip.

I can also hear one problem which is that the sound has a certain (difficult to know how to describe this) 'hollow' quality to it, the low end is fine for those big hits (much much cleaner then the old sub, now I realise I was hearing the old sub distort when pushed) but the mid bass range is not so good.

I have tried to tame the peak at ~42Hz but have found it difficult to do without driving down the trough at 55. 

I did try boosting the big dip at ~95Hz but that must be a room null as nothing seems to help there. Interestingly (or curiously) adding the mains pushes the trough out by about 7-8Hz, is this significant? Perhaps changing the phase would have an impact?? Can you see phase issues in a response graph??

I have forgotten to note down the filters I settled on for a 1st pass (I'm at work) but I recall there were 4 of them;

a cut at about 40
a boost around 50
a boost around 90
a cut at bout 102

Any thought/comments on any of this would be welcome.

Cheers
Matt


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## brucek (Apr 11, 2006)

> the mains pushes the trough out by about 7-8Hz, is this significant? Perhaps changing the phase would have an impact?? Can you see phase issues in a response graph??


The effects of phase differences between common frequencies of the mains and sub are directly shown as response changes. Since the common frequencies are at the crossover, then that's where the response is modified. You can play with the phase of the sub and attempt to get the best graph results in that area ~60Hz-100Hz.

I think your graphs look good. Hopefully you didn't add too much gain. You might try increasing the wholesale volume of the sub (at the sub amplifer) to bring it above the mains level.

brucek


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## 3ll3d00d (Jun 6, 2006)

> I think your graphs look good. Hopefully you didn't add too much gain. You might try increasing the wholesale volume of the sub (at the sub amplifer) to bring it above the mains level.


thanks, I didn't boost too much, just a little tweak in those two dips to try and counter the side effect of the cut next door.

I will remeasure through all the different phase settings and see what works best, I did have a quick test at 0 & 180 and 180 looked better but I must revisit it. What do phase problems sound like? 

Cheers
Matt


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## brucek (Apr 11, 2006)

> What do phase problems sound like?


In a single speaker, they don't produce any effect.
But when two speakers produce signals at the same frequency at 180 degrees out of phase, they cancel. When in phase, they add.

Around the crossover frequency of your system, there are frequencies produced by your mains and sub that are the same and as such can cancel or add to each other producing dips and peaks.

Use REW and try and set the phase of the sub to produce the most even response around the crossover.

brucek


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## Ayreonaut (Apr 26, 2006)

3ll3d00d said:


> I didn't boost too much, just a little tweak in those two dips to try and counter the side effect of the cut next door.


Right on. Go ahead and use a little more boost to avoid attenuation at your existing dips. As long as you aren't applying any _net_ boost from the BFD there is no problem.

Here's mine as an example. There is no net boost, but no added attenuation at the dip either.


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## 3ll3d00d (Jun 6, 2006)

Ayreonaut said:


> As long as you aren't applying any _net_ boost from the BFD there is no problem.
> 
> Here's mine as an example.


Hi

I see and get what you mean about the net boost however I'm not 100% sure what you have selected in that graph, filters & target response & measured?

After watching a film tonight (5th Element, the added low end definitely bought a smile ) I had a pass at playing with phase and varying the meter across different listening positions. This demonstrated that the big dip 95Hz was somewhat illusory as the effect is at its peak in the middle of the sofa, a foot or so either side (i.e. sitting at one end or the other of the sofa) tones down the dip a lot. I also settled on about 45degree for the phase as the optimum position based on the graphs. These changes led to another as the filters as per the attached, definitely looks better, now I just need to listen to and let it bed in for a while.



Cheers
Matt


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## Ayreonaut (Apr 26, 2006)

3ll3d00d said:


> I see and get what you mean about the net boost however I'm not 100% sure what you have selected in that graph, filters & target response & measured?


The top line was my unfiltered response, the bottom line is my filters, and the middle line is the corrected response.

Your response looks great!


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