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Re: Mono "flanking sub" [message #81685 is a reply to message #81683]

Wed, 25 November 2015 16:12

jonone
Messages: 67
Registered: October 2015

Viscount

I just recently swapped av receiver and I think I had the " enhancer" mode engaged Embarassed

I think that what caused the thick vocals.
On a positive I let the auto setup decide the speaker distance and it's made the response flatter with just the mains on there own and even flatter still now I adjusted the delay to my mono flanking sub to create the flattest response across the three seats not " time aligned"
As far as I can tell the Bessel crossover is 12db which is 2nd order I beleive, is a linkwitz Riley 12db or butterworth 12db preferable?
Also I have been using pink noise in rew to measure the response/ adjust the delay is the the right signal to use?
Sorry if this has been covered somewhere.
Thanks

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Re: Mono "flanking sub" [message #81686 is a reply to message #81685]

Wed, 25 November 2015 18:08

Wayne Parham
Messages: 18786
Registered: January 2001

Illuminati (33rd Degree)

The phase differences in filter types are extremely subtle in comparison to the disparate phase relationships between reflections and direct sounds that we seek to address with multiple subs, both flanking and distributed.

The differences between filter types are very important to summing between point sources. But we're not talking about that here. We're dealing with dense interference. Rather than trying to combine two point sources constructively, we're blending a large number of reflections and direct sound sources with complex phase relationships.

So there is no "correct" filter type. It is actually non-sequiter to discuss filter type in this context. Basically, you want the slope that works best. You'll find that empirically. But don't expect much change between the filter types. The phase difference is tiny compared to the differences in phase between sound sources and their reflections.

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Re: Mono "flanking sub" [message #81688 is a reply to message #81686]

Thu, 26 November 2015 02:58

jonone
Messages: 67
Registered: October 2015

Viscount

Ok thanks again for the detailed response Wayne! Hopefully this will be helpful for other members.
So I can flick between filters to see if there is any change, but don't expect to see anything measurable because the reflection from boundary's have much more effect.
Is there a filter you use?
Also can you answer to if pink noise is the right signal to use to measure?
Thanks,
Jon

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Re: Mono "flanking sub" [message #81689 is a reply to message #81688]

Fri, 27 November 2015 16:23

Wayne Parham
Messages: 18786
Registered: January 2001

Illuminati (33rd Degree)

The signal type you use to measure in-room bass isn't too critical, as long as you use a method that doesn't gate out reflections. We're looking at the sound field, not trying to isolate the direct sound as a pseudo-anechoic measurement would. So white or pink noise are fine, as as are sweeps. Noise is broadband, while swept-sines are monotonic, but either signal type is fine provided we excite and sample over a long enough period of time to include the reflections from the room.

If we were measuring speakers, I'd suggest the exact opposite. I would want a reflection-free measurement. That's because I would want to know what the speaker does without influence from the environment it is used in. But in this case, we are measuring the speaker and room as a system, and we're looking at the behavior in the modal region. So we really need to see the room reflections and how they affect the sound field.

Measurement signal types

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Re: Mono "flanking sub" [message #81690 is a reply to message #81689]

Sat, 28 November 2015 11:29

jonone
Messages: 67
Registered: October 2015

Viscount

Brilliant detailed answer like normal! Cool

I will post more graphs when I receive my sub driver and Integrate it.
Thanks

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Re: Mono "flanking sub" [message #81691 is a reply to message #81624]

Sun, 29 November 2015 14:41

jonone
Messages: 67
Registered: October 2015

Viscount

I have an eq question, sorry Wayne ! Sad

My original plan is to have one channel of the 2x4 mini dsp for the flanking sub fed from the summed mains and the other channel for the nearfield sub fed from the lfe out but this means they have seperate eq channels also.

I have read you should eq multiple subs globally, I.e as one? so the only way I can think of to do this is to use a splitter before the minidsp so the summed out from the mains and the lfe from the av amp both go into input channel 1 of the mini dsp, I can then apply the appropriate crossovers to each output of 1( flanking sub)&2.(nearfield )

But this means the flanking sub will receive the signal from the summed mains and the lfe signal ( which is probably a good thing) and the nearfield sub will also receive the lfe signal and the summed mains signal but will be low passed by a circa 60hz crossover.

Will there be any weird effects because the subs are sharing both signals? Also it means there will be two crossovers applied to the nearfield sub, the crossover applied by the lfe out(say 80hz) and the mini dsp crossover to low pass it from the summed mains signal say 60hz, can I have a steeper crossover applied to the nearfield to help stop localisation or should that be shallow too?

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Re: Mono "flanking sub" [message #81692 is a reply to message #81691]

Mon, 30 November 2015 10:31

Wayne Parham
Messages: 18786
Registered: January 2001

Illuminati (33rd Degree)

Never apologize for asking questions here. That's what AudioRoundTable.com is for!

The thing is, flanking subs are a specialized type of multi-sub. Each flanking subwoofer is supposed to be placed two to three feet below, beside and behind a main speaker and be presented a low-passed copy of the exact same signal presented to the main speaker it is flanking. They are really intended to smooth the upper midbass and lower midrange by "filling in" the holes caused by self-interference from nearest boundaries. Flanking subs also tend to smooth the higher end of the modal region, above about 80Hz.

Distributed multi-subs are placed further away from the mains and are usually presented the LFE channel or a summation of all bass content in all channels. They can be equalized individually or globally, but the whole approach is to use several sound sources to create dense interference in the modal range, which tends to make equalization less important than location. The main benefit is derived by the number of sound sources and their distribution throughout the room.

Flanking subs are generally used with one or two distributed subs for best results. Flanking subs smooth the higher end of the modal region and the more distant distributed subs smooth the lower end.

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Re: Mono "flanking sub" [message #81694 is a reply to message #81692]

Mon, 30 November 2015 12:27

jonone
Messages: 67
Registered: October 2015

Viscount

Hi Wayne. I've got quite a good Handel on the approach now, and that's sums the technique up perfectly in a couple of paragraphs! Great for new members to the forum Cool

I realise I'm not actually using this technique and in fact what I'm doing is using two subs with one by the mains blended higher to help smooth the upper end of the modal region(which works as shown by my graphs) and overlapping the mains With the two subs for a total of four bass sources to smooth the lower modal region.
If I had the space and funds I would have four subs, two flanking , two distributed.

So maybe I should just call them my midbass and sub to be fair to your method as it's not true to it and realise it's not doing it justice.

I also understand eq is not required nearly as much as the smoothing effect from overlapping sources adjusted by delay does this.

But in an ideal world is it better to eq my midbass and sub globally or is separate ok?
Also is it better that the lfe signal and summed mains signal both get sent to the mid bass and sub?

It is probably easier for me to keep the midbass and sub on seperate channels of the mini dsp and the bonus is I get the option to add more delay to the sub if needed via the lfe distance setting inside the amp as the mini dsp only goes up to 7.5ms., The down sides are that way the the sub only gets the lfe signal and the midbass only gets the summed mains signal, they also don't share an eq block to eq them globally if that's even a problem?

Thanks, jon

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Re: Mono "flanking sub" [message #81697 is a reply to message #81694]

Tue, 01 December 2015 12:01

johnnycamp5
Messages: 354
Registered: June 2015
Location: NJ

Grand Master

jonone wrote on Mon, 30 November 2015 13:27

Hi Wayne. I've got quite a good Handel on the approach now, and that's sums the technique up perfectly in a couple of paragraphs! Great for new members to the forum Cool

Jon-

Not to repeat............... but I repeat..... Smile

I think you might be better off setting up your two subs as "flanking" the mains, instead of "one helper woofer, one lfe, distant woofer" approach.

I say this because I use a "single sub" (centered) technique, and I sometimes like it, but I also struggle with it.

For me, with just the one centered sub, (as Wayne has mentioned) stereo imaging can get smeared when crossed over high (above 80hZ), and localization becomes a problem.

If I turn down the crossover point to 50hZ, those factors diminish, but so does the midbass smoothing.

I have considered an eq for my system,
but personally, if I had a second (same as my first) sub, I would set it up "flanking", with no distant lfe sub, before I got wrapped up in Eq'ing things with a one-one (single helper/single lfe) set up.

Just don't want to see you put the cart before the horse here.
Apologies if I have mis-understood your system/set up. Perhaps you have already tried flanking both mains.

Regards!

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Re: Mono "flanking sub" [message #81698 is a reply to message #81697]

Tue, 01 December 2015 16:05

jonone
Messages: 67
Registered: October 2015

Viscount

Hi,I haven't tried flanking the mains with two, as I only have the "midbass" at the moment and my sub driver is not built yet.
They are quite different drivers so not the best match to make a stereo pair, I also don't have the space (or wife approval)to put the pair up front "flanking".
I don't seem to really suffer from smearing of the stereo image, and it's definitely not localisable on the same plane as the mains.
The driver is a very clean and can play up to 1khz off axis, my old sub that was regarded as "clean" would sound awful at 150hz, I personally think you need a different type of driver for flanking/helper woofers compared to distributed subs. Something to think about with your own system?

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