Four subs for smoother bass

As I mentioned in my other thread on the mini media-room system, I'm experimenting with using four subs to smooth out the bass in the room.

Well, even though I've yet to move what gear I do have to the smaller room, I decided to experiment and just place the four subs into the loft system and grab some measurements.

So I carted all four Dynamo's to the loft, good thing they are not too heavy

The loft is a medium-sized room, 20' long by about 14'wide with the 'left' side open to the stairwell, and the right open to an adjoining office.
It is also far from an ideal audio setup, so it presents some challenges.

The receiver I use is the Onkyo NR-818 with Audyssey XT32 room correction (lowest cost receiver I know of with XT32).

Mains are some old Mirage M-290 Bookshelf speakers with matching Mirage center and rear wall mounted surrounds.

Room is untreated stuco, so very reflective at all frequencies.


I brought up my measurement rig to the loft so I could tune the basic setup prior to running the room correction.

So that's the context, here come the tests and measurements.

I decided to go simple on locations, as this is a temporary setup, so I just plopped the subs outboard of the front left and right speakers and to either side of the couch we use to watch TV.

I measured each sub individually and then combined in various permutations to see if I could find any phase interaction problems. and sure enough, the combo of right side subs + left-rear sub point to a phase problem, so I flipped the polarity of the left rear and now had smooth responses from that set of three.
Sounds easy to say, but all that measurement and tweaking took the better part of an hour. But it pays off as we will see.

any one sub has huge variations in response due to room modes, to better see the contrast I overlaid all four individual measurements in the one graph:



as you can see, fairly lumpy, and each side has common room effects clearly visible.

Low end extension of these subs is limited of course, as they are just an 8" driver (that look smaller) with 75W driving it. But hey, not bad for $129/ea and easy to place (the fit between sofa and other furniture was perfect for these, any bigger sub and I'd have run into placement issues.

Rather than bore everyone with the myriad of other measurements, let's get to the punchline quickly.

Once all four were in place and basic setup confirmed, I ran the Audyssey room correction using five measurements taken across the couch used in this room.

I then re-measured using my measurement rig. and oh lordy! this combo is amazingly clean and smooth.

Here's the result of four subs + the left front Mirage from 20 to 200Hz at the main listening position:



Pretty amazingly smooth, no?

again, extension on the bottom is nothing to write home about, but four combined does give a bit more depth and a good bit more headroom.

So how does it sound?

have to say I was totally blown away when I played some music on this. My expectations had been low, as that setup never sounded 'good', it was OK for TV but not for any kind of music listening.
Playing some Porcupine Tree high-res multichannel FLACs via the network function of the receiver, it just rocked. No system this cheap should sound that tight. A big part of that is the Audyssey corrections, but the smoothness in the bass is the result of well-balanced room modes thanks to our four subs.

So bottom line, I highly recommend folks investigate the use of multiple subs over investing in one 'better' sub.

Really nice!
Multisub arrangement has obvious benefits and is often recommended. Just out of interest, do you have spectrogram measurement?

As a friend of mine always says, "I love it when a plan comes together."

Hola Jonathan. When I took the THX course at CEDIA, their configuration was as the same as that you are using now. Four subs, and they were cranking up a lot of demo movies, with heavy bass context that really, to me, did not gave me goose bumps. But, your point of view and settings are different. Seeing the graphics, I think that the best way is what you are doing now!. Thanks for your report! Happy listening.

JonFo said:

Rather than bore everyone with the myriad of other measurements, let's get to the punchline quickly.

Once all four were in place and basic setup confirmed, I ran the Audyssey room correction using five measurements taken across the couch used in this room.

I then re-measured using my measurement rig. and oh lordy! this combo is amazingly clean and smooth.

Here's the result of four subs + the left front Mirage from 20 to 200Hz at the main listening position:

View attachment 16493

Pretty amazingly smooth, no?

again, extension on the bottom is nothing to write home about, but four combined does give a bit more depth and a good bit more headroom.

Click to expand...

Does the low end extension come up if you collocate the subs 2 & 2? I would think you could still end up with pretty similar response and you might end up with a subwoofer combo that actually play subwoofer frequencies?

Hocky said:

Does the low end extension come up if you collocate the subs 2 & 2? I would think you could still end up with pretty similar response and you might end up with a subwoofer combo that actually play subwoofer frequencies?

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Unfortunately, the answer is no. Since the low-end extension is limited by the size of the driver (7.5") and probably a built-in high-pass filer in the sub itself (for protection).
Two subs co-located would let them play 3dB louder than as a single, and therefore EQ might have a chance of improving things, but at the end of the day, there is no replacement for displacement (as my auto-crazed buddies say).

For TV watching, and especially in the target much smaller room (where I can probably EQ it a bit more), it will be fine. If this was my primary system, I'd declare the experiment a success and go buy 4 15" subs.

MPS said:

Really nice!
Multisub arrangement has obvious benefits and is often recommended. Just out of interest, do you have spectrogram measurement?

Click to expand...

Yep, good control of modal decay is usual seen in multi-sub arrangements, but the basic quality of the sub(s) comes into play as well. And I have to say, for the price, these ML's are quite the bargain.



Note how most of the decay happens in the first 300ms. Not bad for an untreated room.

That looks really good, thanks.

MPS said:

That looks really good, thanks.

Click to expand...

X2

I've been considering using my ML Dynamo 1500X subwoofer for a coffee table in the center of my home theater system by installing a square piece of glass on the top of it. The sub can get very booming near the walls even with the PBK correction.

JonFo said:

So bottom line, I highly recommend folks investigate the use of multiple subs over investing in one 'better' sub.

Click to expand...

And what "better" subs that were properly placed and tuned have you compared it to?

I just want to remind people that 4 subs is 4 times the chances of hardware failure, 4 times the real estate and 4 times the power and tuning time and still won't get as low. A single better sub may be a better answer in some situations especially if they come with room correction already like the 1500x or the new 210/212. Although I was also thinking about putting two together and making a cofee table out of them to solve the space/aesthetic issues I have in my setup

#ZERO said:

X2

I've been considering using my ML Dynamo 1500X subwoofer for a coffee table in the center of my home theater system by installing a square piece of glass on the top of it. The sub can get very booming near the walls even with the PBK correction.

Click to expand...

Does the room correction make a noticable difference on the 1500x?

snyderkv said:

And what "better" subs that were properly placed and tuned have you compared it to?

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Well, I can walk downstairs to my custom AV room I built my house around, listen to my custom designed Infinite Baffle sub that measures and performs better than any commercial sub
Check out: http://www.jonathanfoulkes.com/Home_Theater/Speakers/IBSub.htm


So I'm rather on the picky side. Remember, I'm saying 'for the money', four cheap subs correctly placed can indeed deliver smooth frequency response, but no, they are not magic.

snyderkv said:

I just want to remind people that 4 subs is 4 times the chances of hardware failure, 4 times the real estate and 4 times the power and tuning time and still won't get as low. A single better sub may be a better answer in some situations especially if they come with room correction already like the 1500x or the new 210/212. Although I was also thinking about putting two together and making a cofee table out of them to solve the space/aesthetic issues I have in my setup

Click to expand...

Your are correct more subs = more gear to fail. However, it's also more opportunities to energize the room from different locations, and that's how one achieves smooth response.

If you want deep and clean, then you need to also use good quality and low-extension units. So four Dynamo 1500X with PBK applied individually, then Room correction (in the AVR) applied collectively will deliver better results than one single Descent-i any day of the week.

If getting two Dynamo's I'd not place them together, I'd place them at the mid-points of front and rear walls, that's been proven to deliver almost as good a result as four at the mid-points (see the Harman studies).

JonFo said:

Well, I can walk downstairs to my custom AV room I built my house around, listen to my custom designed Infinite Baffle sub that measures and performs better than any commercial sub
Check out: http://www.jonathanfoulkes.com/Home_Theater/Speakers/IBSub.htm


So I'm rather on the picky side. Remember, I'm saying 'for the money', four cheap subs correctly placed can indeed deliver smooth frequency response, but no, they are not magic.



Your are correct more subs = more gear to fail. However, it's also more opportunities to energize the room from different locations, and that's how one achieves smooth response.

If you want deep and clean, then you need to also use good quality and low-extension units. So four Dynamo 1500X with PBK applied individually, then Room correction (in the AVR) applied collectively will deliver better results than one single Descent-i any day of the week.

If getting two Dynamo's I'd not place them together, I'd place them at the mid-points of front and rear walls, that's been proven to deliver almost as good a result as four at the mid-points (see the Harman studies).

Click to expand...

Thnx for info

snyderkv said:

Does the room correction make a noticable difference on the 1500x?

Click to expand...

It makes a big difference and you almost can't use the subwoofer without it.

I've noticed the new Onkyo receivers are coming with 11.4 surround sound with four separate RCA pre-out channels for the subwoofers.

I'm not sure how the processing works yet but it's a real cool idea.

^^ yes, and if they have XT32 and Sub EQ HT, then they can correct for 2 subs, but it's still limited.

It only adjust delays and gains to the two subs, the actual EQ is global.

I maintain that one is better off with 2 or 4 subs that support PBK, adjust each one independently of the others, then run the AVR room corrector. In the case of AVRs with SB EQ HT, then let it adjust the delays and gains as well, so in my situation, the front subs would be paired on sub out 1, and the rear subs on sub out 2, as their delays would be the same.

#ZERO said:

It makes a big difference and you almost can't use the subwoofer without it.

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Cool thanks, I'm waiting for the BF210 as I'd rather have a better sub with pbk than 4 cheap subs without. I remember Peter saying they were suppose to be out already. Any know what the new ETA is?

great work Jonathan, thanks for sharing all the info !