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Ok, last resort (subwoofer tuning)


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Background ;

Having just bypassed my preamp and gone straight into mono amps from my DAC.

The problem is that I need pre out to my active subs in addition to line out to the fronts.

I do not want a split-cable solution, so what I do is to use both RCA and XLR out from the DAC.

So far so good, but the fact that single ended output (RCA towards sub) uses one side of the balanced transformer, we get 6dB lower output than the XLR fronts. The load the RCA output observe is 47kohm, so it is high enough to not pull down the signal on the outputs. Rout of DAC is 1,5kOhm.

My idea was to adjust the volume locally on subs to compensate for -6dB level difference, which should work .

There is no scale for the volume, moreover, the gain adjustment scale is not directly transferable to experienced SPL .

Fronts has 2 pieces. 12" woofers and sub ​​has 1ea. 12" .

On this basis, I isolated the front left and entered a 45Hz sine (XO at 50Hz , 24dB / octave ) with 80dBc SPL in the sweet spot . Then I muted fronts and adjusted sub to the same SPL as the fronts .

Did the same for the companion channel.

Result: Too hot reproduction <50Hz.

In the next test I adjusted the subs so they matched fronts, i.e. I measured the fronts and stopped raising the volume bar for the subs when I saw a level elevation of 1/2dB.

Result: Missing depth, impact and substance as fronts dominate <50Hz.

Finally, here comes the question for counseling;

Is it possible to calculate how to adjust this based on measurements?

When the speaker membrane surface area increases (moves air) , so does the SPL.

What I am looking for is a approximate number that I should adjust the subs, based on the given SPL from the fronts.

For example, if the fronts provides 80dB at 45Hz, what level should we expect when the subs engage (e.g. '83'dB)?

An auto calibration (mic setup) won't work this late into the loop because subs and fronts play simultaneously, but there is not only one of the signals that need to be adjusted.

 

I guess putting my room properties into a DSP software and simulate the response won't do the trick.

 

But a DIY calculator was actually the solution I had hoped for.

 

Anyone?

If no response I guess the only remedy is listening.

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Frankly, it may not be possible without a LP filter depending on the LF FR of your main speakers.

Thanks, Kal.

Actually I have to correct one thing.

The fronts are open baffle with XO from ribbon to woofer at 400Hz, so the info above is for the subs.

The front LP is 2nd. order (40 dB/decade or 12 dB/octave) slope. My room mode is restricted to 40Hz (4x4m) so there is little sound reproduced below 35Hz without closed servo subs.

image.jpg

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You could run two Dspeaker anti mode 8033 for left and right subs.

I have one of those and the Antimode 2.0, but what is it that I achieve?

My main speakers must also work during calibration or it won't make any sense when trying to adjust a seamless transition between the two.....

I have the means to adjust it (EQ and volume control on my sub) but my problem could simply be solved by the answer to the question 'to what level should the sub be set?'

Could it be adjusted from an equation, measurement or must I throw in the towel and just trust my ears?

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Thanks, Kal.

Actually I have to correct one thing.

The fronts are open baffle with XO from ribbon to woofer at 400Hz, so the info above is for the subs.

The front LP is 2nd. order (40 dB/decade or 12 dB/octave) slope. My room mode is restricted to 40Hz (4x4m) so there is little sound reproduced below 35Hz without closed servo subs.

 

actually, I mis-typed and meant to say that you need an HP filter for the mains.

Kal Rubinson

Senior Contributing Editor, Stereophile

 

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actually, I mis-typed and meant to say that you need an HP filter for the mains.

But how will this affect the volume balance between the mains and subs? This is the core of my problem.

It is not the crossover itself that poses a problem (and neither the means of adjustment available to me).

Either you all did not catch the problem the way I described it or it is me that don't understand the replies......

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But how will this affect the volume balance between the mains and subs?

""..................?....

Either you all did not catch the problem the way I described it or it is me that don't understand the replies......

perhaps. My understanding is that you are not rolling off the LF of your main speakers with a HP filter. If so, balance with an overlapping sub will always be a problem.

Kal Rubinson

Senior Contributing Editor, Stereophile

 

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perhaps. My understanding is that you are not rolling off the LF of your main speakers with a HP filter. If so, balance with an overlapping sub will always be a problem.

OK, Thanks - I got your point.

My speaker designer is concerned that the 'punch' in the music might suffer if HPF is used.

The integration works very well when the levels are equal.

I think I have to use the 'foot-tapping' gut feeling and adjust when playing some real music in my system. I reckon one guy in the sweet spot and the other one adjusting could work (procedure: ‘stop adjusting when the bass gets dominant/or missing').

The baseline prior to sub calibration will be flat (current setting).

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Even Jim Smith from Get Better Sound book and Dvd recomends to use your ears for final judgement. First set your mains correctly and the start playing with the subs. If you are happy with crossover and location is just a matter of playing with the volume. Sorry if I am misunderstanding the issue. But I am intrigued. Hope you find the solution and keep us updated

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My speaker designer is concerned that the 'punch' in the music might suffer if HPF is used.

 

"Punch" is excess energy around 90-ish Hz, which is just what you will get if you don't roll off your mains and just add a sub anyway. As the owner of Rythmik subs says, "We don't make punchy subs".

 

To integrate your sub, you have to measure the sub by itself and the main by itself, both full range, to match the levels. Then you add the XO's and measure the LP sub and HP main by itself. Then you can do a combined measurement and tweak the polarity and delay of the sub to match. If the XO freq is near the natural roll-off of the mains anyway, you may need to make some extra adjustments to the HP slope, or add a Linkwitz xform, or etc. It is more complicated.

 

One other trick you can do is to play both the sub and the mains at the same time at the XO frequency, purposely invert the polarity of the sub and tweak the delay until you get a null. Then flip the polarity back and you should be good to go.

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  • 6 months later...

Just wondering how you got on with this in the end, and which DAC you were using? I'm thinking to do similar running a single sub off the RCA sockets of an Audiolab MDAC, with the main speakers running off the same's Balanced XLRs.

Mac Mini > RME ADI-2 DAC > Hypex Ncore monoblocks > ATC SCM-11 speakers & C1 subwoofer

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Hi, occamsrazor.

My preamp has both pre out and line out via the volume control, so I am using this solution and not the PS Audio DirectStream DAC dual outputs.

After endless attempts, I found that the only remedy was to listen. The measurement results did not match well because I use the system both for 2 channel and home cinema. I am quite happy with the settings now.

 

Hope it helps.

 

Dist

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