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Discussion Starter #1
24dB/octave Linkwitz-Riley crossover alignment is intended to sum driver response flat at the selected crossover point with no phase shift between the two. Why does Andy recommend shifting sub crossover frequency down 1/2 octave from the intended cross-over point? Is this an attempt to fight cabin gain?

Ge0
 

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Because most house target curves have a 10 DB increase on the low. Explains it pretty well in his article


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24dB/octave Linkwitz-Riley crossover alignment is intended to sum driver response flat at the selected crossover point with no phase shift between the two. Why does Andy recommend shifting sub crossover frequency down 1/2 octave from the intended cross-over point? Is this an attempt to fight cabin gain?

Ge0
Because the sub level is going to be several decibels higher than the mids, so that effectively changes the crossover point.

Basically, the higher output of the sub will push the point at which the slope crosses the midbass to a higher frequency, does that make sense?
 

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Discussion Starter #4
Because the sub level is going to be several decibels higher than the mids, so that effectively changes the crossover point.

Basically, the higher output of the sub will push the point at which the slope crosses the midbass to a higher frequency, does that make sense?
Yes. For those who want their sub level 20dB higher than upper midbass or midrange.

I was about to go outside and fart around with my new system. I was just wondering what was behind this rationale before trying it.

Ge0
 

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Discussion Starter #6
Smashing diagram sir. Thank you. I did see this towards the end of Andy's dissertation after E39 mentioned it. I guess I just didn't have the attention span to read the whole document :)

Ge0
 
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Discussion Starter #8
So here is an issue. I followed Andy's tuning guide to dial my bass in over the last fews days. Offset cross-over points, etc... However, my bass just doesn't sound right. On an RTA it looks perfect. But by ear the sub sounds a little weak and straining. Kind of like its fighting against something.

Then I ran across this article today (also by Andy) which seems to contradict what he mentioned in his tuning guide:

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First, we start out with the 80 Hz LR4 for both the high pass and the low pass and we set the gain for the subwoofer amp so that the bass is at the same level as the mids and highs.
276394


We measure with our tape measure and set the delays. Now our crossover is just about perfect.
276395


But we don’t have enough bass. Instead of just turning up the sub, which is where our last process went off the rails, what if we had one filter that would shape the low end without screwing everything else up? What if we could keep our phase relationship correct and just add bass? That would be pretty cool, right?
That’s what a shelf filter is for.
So, we choose a 2nd order bass shelf at 100Hz with a Q of about 0.7.

276396


276398


276399


There. Fixed. Everything works. Our midbass driver is happy. Bass is cohesive because everything is in phase and our tape measure works fine for measuring distance (since that’s what it’s supposed to do). The low frequency shelf should be applied to the subwoofer channel and the channels for the midbass. That keeps all of the phase intact and shapes our low frequency response. Now, when we get in to listen, all we have to do is set the level of the shelf filter.
***

This sounds very interesting and something I want to try. Is there a way in Helix software to apply the same Shelf filter to both midbasses and the sub at the same time? But, in the process, not screw up any of the other EQ settings that were already set for the individual drivers?

Ge0
 

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This sounds very interesting and something I want to try. Is there a way in Helix software to apply the same Shelf filter to both midbasses and the sub at the same time? But, in the process, not screw up any of the other EQ settings that were already set for the individual drivers?

Ge0
Sure - just define the same filter number as a shelf filter on both the sub channel(s) and the midbass channels. Then, with the channels linked increase the shelf filter until you get the bass level you want. That would increase the bass level on the sub(s) and the midbass at the same time.

The key though, would be to EQ the midbass and subs so that the bass response is flat first (most people have a 10dB+ gain for the sub and also a gain on the lower midbass freqs as well, so they integrate well with the sub).

Unless I'm misunderstanding the question (almost seems too straight-forward of an answer, so I have a feeling I'm misunderstanding something).
 

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So here is an issue. I followed Andy's tuning guide to dial my bass in over the last fews days. Offset cross-over points, etc... However, my bass just doesn't sound right. On an RTA it looks perfect. But by ear the sub sounds a little weak and straining. Kind of like its fighting against something.

Then I ran across this article today (also by Andy) which seems to contradict what he mentioned in his tuning guide:

*
First, we start out with the 80 Hz LR4 for both the high pass and the low pass and we set the gain for the subwoofer amp so that the bass is at the same level as the mids and highs.
View attachment 276394

We measure with our tape measure and set the delays. Now our crossover is just about perfect.
View attachment 276395

But we don’t have enough bass. Instead of just turning up the sub, which is where our last process went off the rails, what if we had one filter that would shape the low end without screwing everything else up? What if we could keep our phase relationship correct and just add bass? That would be pretty cool, right?
That’s what a shelf filter is for.
So, we choose a 2nd order bass shelf at 100Hz with a Q of about 0.7.

View attachment 276396

View attachment 276398

View attachment 276399

There. Fixed. Everything works. Our midbass driver is happy. Bass is cohesive because everything is in phase and our tape measure works fine for measuring distance (since that’s what it’s supposed to do). The low frequency shelf should be applied to the subwoofer channel and the channels for the midbass. That keeps all of the phase intact and shapes our low frequency response. Now, when we get in to listen, all we have to do is set the level of the shelf filter.
***

This sounds very interesting and something I want to try. Is there a way in Helix software to apply the same Shelf filter to both midbasses and the sub at the same time? But, in the process, not screw up any of the other EQ settings that were already set for the individual drivers?

Ge0
A shelf filter will affect all frequencies above, or below the filter, so you wouldn't need to set it for both the mids, and sub. Now, I am not very familiar with the Helix software, so you may need to link some channels together, or something, but I would think that adding a filter at the frequency you want should be enough.
 

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A shelf filter will affect all frequencies above, or below the filter, so you wouldn't need to set it for both the mids, and sub. Now, I am not very familiar with the Helix software, so you may need to link some channels together, or something, but I would think that adding a filter at the frequency you want should be enough.
Yeah, with the Helix, in order to cause the midbass channels and the sub channels to both go up by the same amount when you increase the shelf filter, you'd need to define the same shelf filter on both the sub and midbass channels (it's a "per channel" filter) - and link those channels so that when you increase the shelf filter on the sub, it also increases the same shelf filter by the same amount on the midbass channels.

However, the more that I think about this, you can only "boost" a filter (regardless of filter type) by 6dB in the Helix software, so if you have you midbass and sub tuned flat with the rest of the frequency spectrum like in Andy's example (lets' call it 0db, for example), I would think that this method would only allow up to a 6dB boost for the bass, which isn't enough (hell, my sub is like 20dB+ higher than my mids/highs!). So not sure how that would work. I think you'd need to EQ this midbass and sub channels so that they are "flat", but at a significantly higher level than the rest of the frequency spectrum before you applied the shelf filter.
 

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Discussion Starter #12
Sure - just define the same filter number as a shelf filter on both the sub channel(s) and the midbass channels. Then, with the channels linked increase the shelf filter until you get the bass level you want. That would increase the bass level on the sub(s) and the midbass at the same time.

The key though, would be to EQ the midbass and subs so that the bass response is flat first (most people have a 10dB+ gain for the sub and also a gain on the lower midbass freqs as well, so they integrate well with the sub).

Unless I'm misunderstanding the question (almost seems too straight-forward of an answer, so I have a feeling I'm misunderstanding something).
That is exactly what I mean. Start with a flat response 20Hz and up and a well blended cross-over. Then use the shelf filter to add low end boost.

What do you mean "define the same filter number as a shelf filter on both sub and midbass channels"?

Also, if I link the channels will only the changes made while I have them linked affect all three channels? I don't want to screw up existing settings. I've made that mistake a few times when I had channels linked by accident.

Ge0
 

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Discussion Starter #14
Yeah, with the Helix, in order to cause the midbass channels and the sub channels to both go up by the same amount when you increase the shelf filter, you'd need to define the same shelf filter on both the sub and midbass channels (it's a "per channel" filter) - and link those channels so that when you increase the shelf filter on the sub, it also increases the same shelf filter by the same amount on the midbass channels.

However, the more that I think about this, you can only "boost" a filter (regardless of filter type) by 6dB in the Helix software, so if you have you midbass and sub tuned flat with the rest of the frequency spectrum like in Andy's example (lets' call it 0db, for example), I would think that this method would only allow up to a 6dB boost for the bass, which isn't enough (hell, my sub is like 20dB+ higher than my mids/highs!). So not sure how that would work. I think you'd need to EQ this midbass and sub channels so that they are "flat", but at a significantly higher level than the rest of the frequency spectrum before you applied the shelf filter.
That thought ran across my mind. you can only boost 6dB. You would need to stack filters on top of each other to get enough boost. What kind of crazy **** would that do?

Ge0
 

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Minor hijack...
I'm confused by half an octave lower. If the midbass is highpassed at 80hz would the sub be lowpassed at 40 or 60hz?
 

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That thought ran across my mind. you can only boost 6dB. You would need to stack filters on top of each other to get enough boost. What kind of crazy **** would that do?

Ge0
Well, you can't even do that - because you can only define a single low-shelf filter. So it's not like you can define 4 low-shelf filters to boost by up to 24dB. :)

So I think you'd need to EQ the sub and midbass so that the low-end bass response is "flat", but like 15db-20dB higher than the mid/highs. Then you could use that single shelf filter to boost by up to 6dB from there. - or something like that. Not so sure this would work out so well with the Helix. :)

WHat I meant earlier was that you'd need to use the 1st filter on the sub and midbass channels as shelf filters (you can only use the 1st or last filters as shelf filters - the 1st one is a low-shelf filter and the last one is a high-shelf filter). You can't change any of the other filters to shelf filters.

So you would set the 1st filter on each midbass channel and the 1st filter on the sub channel as a shelf filter - with a freq of 100hz (just for example) and a Q of .7. Then when you link the sub and midbass channels together, any change you make to that 1st filter will actually adjust the shelf filter for all 3 of the channels (2 midbass and 1 sub). You could also just adjust the separately if you wanted to (without linking anything).

But yeah, that 6dB boost limitation would be an issue. Not sure what DSP Andy was thinking of when he wrote that article. Not sure if any of them would allow enough boost to go from perfectly flat to a full sub-level boost! It sounds good in theory, but not sure how you would do it in real life. :)
 

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Minor hijack...
I'm confused by half an octave lower. If the midbass is highpassed at 80hz would the sub be lowpassed at 40 or 60hz?
An octave is a doubling of frequency. So if your at 40 and you double it you get 80. Half octave would put you at 60.
 

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An octave is a doubling of frequency. So if your at 40 and you double it you get 80. Half octave would put you at 60.
Right but that's when you are going up. Where Andy's guide confuses me is that he says half an octave lower then the midbass. How does the math work if you're decreasing by half an octave?

Because our 12dB/octave bass boost has raised the crossover point, we can simply set the subwoofer crossover a half an octave below the midbass crossover.

Edit:
Nevermind. Sometimes I overthink.
 

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Discussion Starter #20
I ditched the idea behind the shelf filter for earlier reasons.

I've been playing with Helix auto tune and have been getting some favorable results. However, tonight I ran across a few gotcha's

1.) There appears to be a bug in Helix 4.65 software where the proper polarity of your sub does not load properly when you load a profile. You need to toggle the polarity back and forth to get it to work right. I tried this several times and results were repeatable.

2.) I have a very narrow and deep suck out at 50Hz that does not show up on an RTA unless you go to 1/6th octave resolution. There, it is just noticeable. Go to 1/12th octave and it turns into a sucking hole. It's like the 50Hz note is almost completely gone.

I played a lot of tunes tonight and was happy with my bass response until I listened to Beastie Boys Intergalactic. This song is comprised almost entirely of a 50Hz bass line. It was almost completely absent from the song. Weird...

Ge0
 
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