Author Topic: 1 woofer or 2?  (Read 8274 times)

Offline sevenz

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Re: 1 woofer or 2?
« Reply #75 on: May 21, 2019, 17:54 »
So weird, after I set up 5.1, I did a mcacc calibration using my pioneer avr, the mid bass feel gone, left with lower bass. Generally not as strong or shiok before the calibration..

Have u tried rerunning MCACC to see if it yields the same result?

Try increasing the sub channel volume on the AVR till your midbass feels syok. Usually we need to bump the AVR sub channel volume after calibration to tweak to personal pref to feel the thumps. =)

Offline deadrick

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Re: 1 woofer or 2?
« Reply #76 on: May 23, 2019, 23:59 »
OK, I just shifted the sub more to the right and rerun mcacc, and connect the dspeaker, and now it feel much better. Haven't do my rew, but when I can find a pc to put in living room will test out.

Ran a frequency test, and find 51hz, 62hz, 73hz seems to have a null.

The 25to35hz does feels quite solid.

Offline sevenz

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Re: 1 woofer or 2?
« Reply #77 on: May 24, 2019, 09:41 »
Nice. Happy that it's sounding better for u now!  :) Enjoy the bass

Offline rayleh

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Re: 1 woofer or 2?
« Reply #78 on: May 24, 2019, 09:59 »
I tweaked with the time delay to improve the nulls. However, I also understand that decay is very important for bass, not just FR.

Offline ronildoq

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Re: 1 woofer or 2?
« Reply #79 on: May 24, 2019, 18:23 »
Actually nothing to tweak if there is only one sub, the delays will not solve the 51, 62 & 73hz issues he is facing, the only way is placement

But move it to another location, u will solve 51hz, but may have 35hz issue... and so on...

You cannot not have a null in a room from 20-100hz... hence the recommendation to go dual

Now that you have experienced first hand, u will understand why everyone recommends going dual sub, u r now back to square one, 1 woofer or 2?

You have your answer now....

Offline rayleh

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Re: 1 woofer or 2?
« Reply #80 on: May 24, 2019, 20:14 »
Thought he is running dual subs. Multiple subs is the way to go.

Offline deadrick

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Re: 1 woofer or 2?
« Reply #81 on: May 25, 2019, 10:50 »
Placement for 2nd sub is an issue. I'm curious if those dual sub in front, is it meant to boost more bass, or also help in reduce nulls and peaks too?
I'm guessing both sub in front, the rew measurement wouldn't be too different to cover the nulls and peaks or the other sub.

Because if I can add 2nd sub, its only beside the left speaker. Across the front wall is the walkway to bedrooms, a it obstructing to do dual sub across the room.

Offline rayleh

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Re: 1 woofer or 2?
« Reply #82 on: May 25, 2019, 13:12 »
My dual subs are exactly in the front to the left and right side. You are so wrong that they will not improve the bass. I use the miniDSP to cut the peaks and improve the nulls. Even without tuning, running dual subs is already better. This was validated using REW to measure.
« Last Edit: May 25, 2019, 15:06 by rayleh »

Offline ronildoq

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Re: 1 woofer or 2?
« Reply #83 on: May 26, 2019, 10:57 »
Thought he is running dual subs. Multiple subs is the way to go.

I thought I read it as 2.1 in living room, so impression was one sub only... yes if multiple subs , it’s the best !

Offline ronildoq

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Re: 1 woofer or 2?
« Reply #84 on: May 26, 2019, 11:39 »
Placement for 2nd sub is an issue. I'm curious if those dual sub in front, is it meant to boost more bass, or also help in reduce nulls and peaks too?
I'm guessing both sub in front, the rew measurement wouldn't be too different to cover the nulls and peaks or the other sub.

Because if I can add 2nd sub, its only beside the left speaker. Across the front wall is the walkway to bedrooms, a it obstructing to do dual sub across the room.

You are right, adding the second sub across your front wall  most likely is for the headroom and SPLs , doesn’t smoothen things. Ideally if the goal is to smoothen the response at the listening position, then spreading them out would work in your favour. When spreading, what you want is each sub handling specific frequency and they supplement each other. You don’t want both fighting for the same frequency

That’s why u must always look at the individual sub response first, what’s its frequency response at X location, so u can overlay them and see if they are complementing each other

Good luck in your subwoofer journey, no pain no gain !

Offline Djblackfm

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Re: 1 woofer or 2?
« Reply #85 on: July 05, 2019, 16:16 »
A good read to be shared.





USING MULTIPLE SUBWOOFERS TO IMPROVE (FLATTEN) BASS

One of the major problems in home audio listening setups is the likelihood of an uneven bass response throughout the room as discussed here. Note: It’s important you read and understand that article first. unfortunately, this is an inescapable fact in ‘small’ rooms due to how bass sound waves react in these rooms. Bass waves will bounce off walls and create peaks and nulls within the room, leading to areas where bass is either amplified or reduced. Don’t fret, though, because physics can be conquered with a few subwoofers and some elbow grease — you can smooth your in-room bass response by using multiple subwoofers strategically located in your room.

Why doesn’t just one sub work?

Because of the nature of standing waves and room modes in your room, what you hear for a given bass frequency could differ significantly from your guest who is sitting 3 feet from you — you may be sitting in a peak while he is sitting in a null. Below is an example standing wave running across your room’s width with two of you sitting side by side.

standing wave experience-peak and null
Why not just use Equalization?

Equalization, or EQ, might be able to tame peaks (and perhaps nulls) for ONE seating position in your room. But any changes you make via EQ at one seat will exacerbate any peak and null issues other listeners are experiencing at other seats. This might be ok for a home audio setup with one listening location, but won’t work for a home theater setup with multiple seats.

Before EQ is applied, you need to work on smoothing the natural response as much as possible uniformly throughout the room. Multiple subwoofers will help you do that.

Can’t I just use bass traps / absorbers instead?

Sure you can! If you’re willing to have traps that are several FEET in thickness. You’ll commonly read online or hear from acoustic panel retailers that all you need to do is add thick corner bass traps to smooth your response. That may be true for bass response above 150-200hz, but these panels won’t help you one bit in the important frequency ranges impacted by standing waves and room modes — even if you cover every corner in your room.

The wavelengths that we’re talking about for 20-120hz are 9 to 50+ feet long! Absorptive bass traps need to be about as thick as a quarter the wavelength to be effective in trapping that frequency, so you’re talking about traps that are 2.5-12.5 FEET thick (or that are thinner but stick out into your that far). See here for a view into how long bass wavelengths are. We don’t know about you, but panels that thick don’t fit into our home theater and home audio listening rooms.

Why multiple subwoofers help

Using additional subwoofers to improve bass response in your room is an effective way to tame room modes.  By placing subwoofers at strategic locations, they can be used to either excite or cancel room modes that your room’s dimensions naturally create. Without getting into deep physics lessons, just know that by placing a subwoofer in a null that exists because of your room’s modes, you will cancel out that room mode and its nulls, effectively smoothing out the response in room for that frequency.

You need to understand that a subwoofer placed in a specific location will have a unique reflection and standing wave pattern in your room. By placing subwoofers in various locations, you will create a unique reflection and standing wave pattern for each sub you add. These patterns of peaks and nulls will then sum together at your various seating positions.

Placed correctly, these different patterns will have peaks and nulls that occur at different locations and they will all add together and smooth out the individual peaks and nulls from any one subwoofer. As you add more subwoofers, the response should be even smoother since you benefit from a more diverse set of reflection and standing wave patterns. This will give you a more uniform listening response over a larger area rather than one optimized listening location with a single subwoofer.

So what do we mean by strategic locations? We generally mean the locations of nulls created by your room’s natural room modes. The nulls that create the biggest issues occur at 50% of your room’s length and width dimensions, followed by the nulls that occur at the 25% and 75% locations. These correspond to your primary and secondary room modes in the length and width dimensions in your room. More on that below.

Let’s take a real life example courtesy of MiniDSP, a manufacturer of digital signal processing hardware. We’ll focus on the frequencies up to 100hz because subwoofers are usually crossed over to the main speakers around 80hz.

Below is what a single subwoofer looks like at three different in-room seating locations. Notice how there are large variations (15dB!) in volume level between seats in 65-100hz frequency range. Individual seats (i.e each line) have very big peaks and nulls as well.

Now let’s see what happens when we add a second subwoofer to the room and look at the same three seating locations. Notice how much smoother the frequency response has become for each individual seat. Also notice that the gap in volume between seats has narrowed, especially in the 65-100hz frequency range.

Lastly, let’s look at what happens when a third subwoofer is added and properly integrated with the other two. Now you can see excellent uniformity in bass response not only for each individual seat (i.e. each individual line is relatively flat) but you also see exceptionally tight response ACROSS seats (i.e. the gaps between each line are very small).

In another real-world test in conducted by HomeTheaterReview.com, subwoofers were placed in the four corners of the room and the response measured from the listening position with one (green line), two (red line), and four (blue line) subwoofers. Just as above, you can see that as you add more subwoofers, the in-room bass response for a seat gets significantly smoother.

While the chart shows response up to 500hz, we are concerned with bass response below 100hz given where crossovers are typically set. This test showed marked improvement in smooth bass response with two subwoofers, and even further improvement with four.

So how many subwoofers should you add… and where?

So if four subwoofers are better than one, would six or eight be better than four? Research has shown that there is little benefit from adding more than four subwoofers.

Extensive and ground-breaking research was done by Todd Welti of Harman International on increasing numbers of subwoofers. In his research, both mathematical models and real-world testing was done to determine the impact of increasing numbers of subwoofers on flattening the bass response in a small room. The goal of the study was to find ways to minimize the variation of frequency response from one location to the next within a seating area while an additional goal was to maximize low frequency output of the subwoofers.

Both computer simulations and real-word measurements were done in a 20 foot by 24 foot room, with the number of subwoofers ranging from one to 18 and a listening area in the center of the room.

Both the computer modeling and real-world tests found the best and most cost-effective results by using four subwoofers.  Two subwoofers were almost as good though, so you’ll need to think through whether the added cost of two more subwoofers is worth it to you — that’s a personal decision we can’t help you with, though we still recommend 3-4 subwoofers if possible!

Best subwoofer configurations as found by Harman:

Symmetrical locations seemed to work the best.  One subwoofer in each corner had good low-frequency output, but does not perform quite as well as one subwoofer at each wall midpoint from the perspective of achieving the smoothest bass response. This can be explained by the fact that the walls’ midpoints correspond to the locations of the nulls created by the primary room modes!

So depending on your subwoofers’ capabilities, you should aim for either the corners or wall midpoints — if your subwoofers struggle to hit the output levels you need for your listening volumes, you may want to sacrifice some smoothness in your bass response for additional output and thus put your subs in your room’s corners.

Bringing it home
All the experiments and measurements discussed above point to multiple subwoofers as a very valid way to fix uneven bass response caused by standing waves or room resonance in home theater and home audio setups.  Due to the many variables of room size, seating locations, and furnishings, there is no single answer or formula for subwoofer placement, but you can use the experimentation above as a starting point and combine that with your own listening (and in-room measurements) to find your preferred locations.

(Source: Bringtheruff)

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