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Help pick sub locations

Denon545

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Jan 25, 2021
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Hello All,

I am trying a couple of locations for my subwoofers that give me the best overall output. They are located on my front wall and flank my center speaker. After a lot of measurements, I have found the two best locations but I cannot decide which is best.

This is the combined response of both subs, at the locations that have the flattest response. Yes I know that neither are particularly flat. This is no smoothing or EQ or anything. I have a Denon 3600 and plan to EQ with MultEQ-X, but I need to try and get something it can work with easily from the start, so that it isn't trying to boost nulls etc.

I would be crossing over to the mains around 80hz. The black trace gives more output at 70-100hz but falls off very jagged. The orange trace doesn't seem as good, but has a much smoother rolloff at the upper end.

If you had to pick between these, which would you recommend? Is one any better than the other? With EQ would they practically be the same?

Edit- the 65hz dip is due to a room mode that I can't fix without different placement or more subs- neither are in the cards.

Sorry for all the questions- just wanting to learn!

90 vs facing.jpg
 
I would rather have worse response elsewhere than that 10-12 dB dip at 65 hz. That is too big to fix with EQ and it is low enough to be below the subs crossover frequency while still above where instruments actually play. Are the test locations away from the back wall? Did you try to measure with the sub all the way in the corner?
 
Hello All,

I am trying a couple of locations for my subwoofers that give me the best overall output. They are located on my front wall and flank my center speaker. After a lot of measurements, I have found the two best locations but I cannot decide which is best.

This is the combined response of both subs, at the locations that have the flattest response. Yes I know that neither are particularly flat. This is no smoothing or EQ or anything. I have a Denon 3600 and plan to EQ with MultEQ-X, but I need to try and get something it can work with easily from the start, so that it isn't trying to boost nulls etc.

I would be crossing over to the mains around 80hz. The black trace gives more output at 70-100hz but falls off very jagged. The orange trace doesn't seem as good, but has a much smoother rolloff at the upper end.

If you had to pick between these, which would you recommend? Is one any better than the other? With EQ would they practically be the same?

Edit- the 65hz dip is due to a room mode that I can't fix without different placement or more subs- neither are in the cards.

Sorry for all the questions- just wanting to learn!

View attachment 379895
If you are crossing at 80hz, I'd definitely go with the black trace. As a rule of thumb you can EQ peaks but not dips. So you basically just want to find the curve with the fewest dips in the frequency range you're interested in.
 
I would rather have worse response elsewhere than that 10-12 dB dip at 65 hz. That is too big to fix with EQ and it is low enough to be below the subs crossover frequency while still above where instruments actually play. Are the test locations away from the back wall? Did you try to measure with the sub all the way in the corner?
The subs are behind an acoustically transparent screen in a home theater set up. See picture below with the screen removed- I am limited to these placement options. The deep at 65hz is due to 9’ ceiling height. If the Umik is held on the floor, that dip goes away.

IMG_1374.jpeg
 
Does it impact the bass response to turn the subs sideways so the drivers are closer to the wall?
 
Does it impact the bass response to turn the subs sideways so the drivers are closer to the wall?

Yes, facing the room like shown in the photo is the worst response. I didn't include that in the original measurements as it was much worse.

The black trace above is with them facing each other. The orange trace is them turned facing the outer walls. Sounds like the black trace is what I should go with.
 
I was looking at phase and impulse alignment between my subs and center channel in REW using the alignment tool. I am not sure if this is the correct procedure, but I was thinking that it would give insight on the best crossover point to use for the center crossing over to the subs.

If I align them at 90hz it gives me a message that the phase has to be flipped- they have opposite polarity. But if I align them at 80hz it doesn't give me that message. Everything is set at zero phase on the subs, so I am curious as to why it would be like that. I was probably going to use 80 crossover anyway, so would there be any issues? I seem to remember reading somewhere that you want the phase and impulse to match an octave above and below the crossover point. If that is the case, then perhaps 60hz would be the better crossover point? I did not receive the polarity warning there either.

Some additional notes- I used the aligned sum of each sub together compared to the center channel in the example below. I get the same polarity notice in REW when I used an LFE sweep of both subs combined and aligned to the center as shown below.

90hz-

1720620160734.png



80hz-

1720620146057.png
 

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did you try the baby boom sub bass configuration 1977

5screenTHX.jpg
 
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Well the subs are Rythmik FV18's which weigh about as much as I do. So unless you have a crane you could loan me, I don't think elevating will be possible. But I won't rule it out.

All kidding aside, any thoughts to using the 80hz crossover if we know at 90hz a polarity switch is needed for proper alignment? Or, would something lower like a 60hz crossover be better? I don't fully understand the downstream consequences of it.
 
You have 2 subs correct? if so you might try a Rythmic 10" as the one to elevate.
 
Well the subs are Rythmik FV18's which weigh about as much as I do. So unless you have a crane you could loan me, I don't think elevating will be possible. But I won't rule it out.

You don't have to. Use REW's room simulator and elevate the subs with your mouse. If it looks like it might solve your problem, then you can go hire a crane.

All kidding aside, any thoughts to using the 80hz crossover if we know at 90hz a polarity switch is needed for proper alignment? Or, would something lower like a 60hz crossover be better? I don't fully understand the downstream consequences of it.

The problem with subs is that the phase continuously rotates, so flipping the polarity may not do much. The phase should be aligned at the crossover point.

As for the choice of the XO point, measure your main speakers and see where they roll off. Also look for distortion. You may want to choose a higher point if your mains distort at low frequencies.
 
OP, do you have access to an extra speaker (of any kind) that's reasonably competent at 65Hz? If so, you could use that to experiment with sub placement without having to pick up your 18" monsters. It can be literally any kind of $20 particle-board Craigslist flotsam -- the laws of physics don't bend for cheap speakers and we're not looking for any particular response or phase curve here. We just need to find a spot where 65Hz isn't nulled at the listening position.
 
Geddes runs his subs as mono fiven the wavelenghts below 1000Hz in a small room phase will typically not be noticeable. Size for the 3rd sub doesn't have to be great the way the subs are used is to remove nulls and peaks, so active eq doesn't have to do the heavy lifting.
 
Hello All,

I am trying a couple of locations for my subwoofers that give me the best overall output. They are located on my front wall and flank my center speaker. After a lot of measurements, I have found the two best locations but I cannot decide which is best.

This is the combined response of both subs, at the locations that have the flattest response. Yes I know that neither are particularly flat. This is no smoothing or EQ or anything. I have a Denon 3600 and plan to EQ with MultEQ-X, but I need to try and get something it can work with easily from the start, so that it isn't trying to boost nulls etc.

I would be crossing over to the mains around 80hz. The black trace gives more output at 70-100hz but falls off very jagged. The orange trace doesn't seem as good, but has a much smoother rolloff at the upper end.

If you had to pick between these, which would you recommend? Is one any better than the other? With EQ would they practically be the same?

Edit- the 65hz dip is due to a room mode that I can't fix without different placement or more subs- neither are in the cards.

Sorry for all the questions- just wanting to learn!

View attachment 379895
The black line would be the one I'd choose, but it really depends where your crossover point is and how well the mains handle the 70-100hz region. A lot of bass happens in that region, so I'd rather that smoother and sacrifice a bit on the low low end. Whether you can actually hear the dip is hard to say since it's quite narrow.
 
OP, do you have access to an extra speaker (of any kind) that's reasonably competent at 65Hz? If so, you could use that to experiment with sub placement without having to pick up your 18" monsters. It can be literally any kind of $20 particle-board Craigslist flotsam -- the laws of physics don't bend for cheap speakers and we're not looking for any particular response or phase curve here. We just need to find a spot where 65Hz isn't nulled at the listening position.

I have two HSU VTF2-MK5's that the 18's are replacing. I suppose I could sit one of those on top of the 18's and see if that cleans up the null at 65hz. In order to make that work, I would have to use an RCA Y-adaptor of some sort. My Denon 3600 AVR has two sub outputs which I am currently using. I guess I could split the 18's on one output and put the HSU on the other to test. Assuming that works, I would then need to try and get one of the 18's up to similar height, right?

You don't have to. Use REW's room simulator and elevate the subs with your mouse. If it looks like it might solve your problem, then you can go hire a crane.



The problem with subs is that the phase continuously rotates, so flipping the polarity may not do much. The phase should be aligned at the crossover point.

As for the choice of the XO point, measure your main speakers and see where they roll off. Also look for distortion. You may want to choose a higher point if your mains distort at low frequencies.

The mains roll-off around 35hz, I haven't checked for distortion yet. I would guess anything between 40 to 80hz could be used for XO points.

The mains have a similar dip at 65hz. Here's the subs- blue line, and the center ran full range in REW- gold line.

1720711273576.png
 
One trick is to try crossing them over right at 65 hz. That way you get effectively a 4-way bass array at that frequency. May help or may not depending of woofer heights in the mains. If anything, gives more moving diaphragm area to EQ out the null. Perhaps a down-firing sub would help?
 
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