Pressure Bass, Displacement Bass, You Need Both - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 16 Old 01-22-2019, 11:02 AM - Thread Starter
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Pressure Bass, Displacement Bass, You Need Both

I've been playing with four sealed Ultimax 18" subs this year in my basement home theater. They are on casters to make them easy to reposition.

Setting:
The theater area is 19ft x 24ft. All seven channels are 8ft from the ref listening point. The walls/celing all have at least 7" of Ultratouch denim sound adsorption covered with 95lbs/dozen moving blankets and different airspacing for each wall. Some areas have 36" air space behind the blanket/ultratouch with lots of clothes on hangars and cardboard boxes filled with pink fluffy fiberglass.Two corners have 7ft x 32" x 32" pink fluffy bass traps in the 36" air space. the screen is on a 19ft wall in front of a blanket/7"ultratouch wall with 4" airspace. Two 8' soft walls make the stage area 12ft wide. The back wall is also soft and has 50" air space with lots of clothes on hangers in the air space. Bass response is tight with no spikes/suckouts above 50Hz.

In this room I tried many subwoofer positions and EQ'd them with Yamaha YAOP in the preamp. The 3000w crest amps do not clip except at painfully high SPL. The subjectively best woofer placement in terms of emotional excitement has been with all subs in a line along the screen wall even when compared to very close placement of the subs as coffee tables around the seats.

From these experiments it seems there must be more than SPL that determines emotional response one gets from thier bass. I think it might be the air displacement causing individual hairs to move.

If you surround yourself with subwoofers the bass you get less tactile impact because the air displacement of woofers on opposing sides of the LP cancel each other and you only get the pressure variation. To get the full

So in conclusion: To maximize the bass experience, put all your subs in one direction from the LP and expose as much skin as possible..... How's that for a pick up line? It's the new millenim nerds version of "Wanna go back to my place and check out the sound system?" I bet it works just as well too....
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post #2 of 16 Old 01-22-2019, 11:56 AM
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You should look around on the forums a little bit in the threads talking about Vibs. There's a lot of discussion about impactful bass, both physically and emotionally impactful, and what makes it happen.
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post #3 of 16 Old 01-22-2019, 12:33 PM
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Quote:
Originally Posted by artsci2 View Post
I've been playing with four sealed Ultimax 18" subs
You need to take a look around this place

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post #4 of 16 Old 01-22-2019, 01:38 PM
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Nicely done on treating the room so thoroughly.

Very interesting observations. The pressure discussion goes way deep here at AVS...look up the vibesensor thread for a months good reading.

Thr 2 most impressive rooms i have heard have lots of subs (8 or more BIG PORTED ones) and cones point in every direction, very much at each other.

Im not disputing your situation, in fact i like the observation that coffee table subs didnt do the job as well. It could well be that with 4 subs the wall is giving you a 5 or 6db boost, maybe even 10 or 12 at a corner that impacts you harder even at a distance.
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post #5 of 16 Old 01-22-2019, 03:59 PM
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Originally Posted by johnson636 View Post
You need to take a look around this place
In his defense he has put a significant amount of effort into his treated room. Im curious if the clothes on hangers are available for wardrobe or just old stuff that wasn't given to Goodwill.

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post #6 of 16 Old 01-22-2019, 04:02 PM
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Quote:
Originally Posted by mushroommunk View Post
You should look around on the forums a little bit in the threads talking about Vibs. There's a lot of discussion about impactful bass, both physically and emotionally impactful, and what makes it happen.
I think in the Vibsensor thread someone was dressing in underarmor type gear to avoid the distraction of flapping clothes. Perhaps the full nuddy is required for optimum sensation?

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post #7 of 16 Old 01-22-2019, 04:14 PM
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Originally Posted by Pradeep2 View Post
In his defense
No need to defend him because I wasn't attacking him. Kudos for his work with the treatments.

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post #8 of 16 Old 01-23-2019, 04:35 AM - Thread Starter
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.... just old stuff that wasn't given to Goodwill......
yes
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post #9 of 16 Old 01-23-2019, 04:47 AM - Thread Starter
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Quote:
Originally Posted by Pradeep2 View Post
I think in the Vibsensor thread someone was dressing in underarmor type gear to avoid the distraction of flapping clothes. Perhaps the full nuddy is required for optimum sensation?
Yeah that is the new millenium pick-up line for yah....

But seriously:
I did search using "Vibsensor" and it's unclear which thread you are referring to. Is it "Nearfield Ported MBM for Increased Mid-Bass Tactile Response" or something else? I'm starting on down through that thread btw.

EDIT:
OK I found"The VibSensor Accelerometer Test Thread"

EDIT2:
In the "Nearfield Ported MBM for Increased Mid-Bass Tactile Response" thread it seems that the greater cone excusion below tune (compare to sealed at the same spl) is bein disregarded. That greater cone excursion is a more plausible explanation for couch shaking than "sound intensity".
Also even at the port tune frequency, the first cycle has greater excusion than sealed because the box-port system is not resonating yet.

Last edited by artsci2; 01-23-2019 at 06:49 AM.
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post #10 of 16 Old 01-23-2019, 10:16 AM
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I hate to say it, but I'd like to see the measured response from each of the different sub arrangements. I wonder what the difference is, and how that translates to what you enjoy.
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post #11 of 16 Old 01-23-2019, 02:20 PM
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I agree, we need both

I too run 4-sealed um18's but mine are all mounted in one large sealed cabinet with around 26ft3 net air space constructed with braced 1.5" thick plywood walls. It's powered by a QSC powerlight 3.4 running 4-ohm bridged.
I'm also running a JBL 4642 which is a ported dual 18 pro cinema sub that I've upgraded with dual 18" 2242 woofs. It's running off a QSC plx2602 at 4-ohm bridged with a 20hpf to protect the woofs.

You would think there is no place for the JBL along side the massive UM array but you'd be wrong...the tactile feel that the JBL gives, especially when playing high spl music, is something that the UM array can't quite match. It brings the music to life in way the UM's just can't. The JBL is tight sounding and lightning quick in response and I honestly feel an upgraded 4642 like mine could give a lot of high-end diy and commercial subs of similar size a run for it's money above 20hz when it comes to sound quality and would hang in the spl department to.

Now if i want to do structural damage to my home...sure the UM array is my weapon of choice. When pushed, it can literally shake that end of the above 2nd floor to the point I fear real damage could be done to my home. Stuff falls off the walls, lamps dances off of end tables, etc. I actually cracked the drywall on a second floor wall after pushing the UM's a little bit.

I started out with dual SVS CS Ultras back in 2001-2 when SVS was really just starting out as a company. At the time they were considered, and rightfully so, one of the better performing music/ht subs you could get...especially at their sub $2k price point. With that said, I don't know if it's a high excursion driver thing in general but I noticed a similar comparison in feel between the SVS's vs the JBL then as I do my UM's vs the JBL now. Even near field, and at similar moderate spl's...the Ultra's didn't have that tactile "feel it in your chest" excitement that I craved and so that's how i ended up with the JBL a few years latter. For awhile I ran both the SVS's and JBL together and compared them head to head and while I knew the SVS's wouldn't hang spl wise...I was shocked at how much better the JBL sounded in general at all volumes.

Maybe this is the reason why some folks with these modern "high excursion infrasonic bass monster" subs are looking to add MBM(mid-bass modules) and the like to their systems. Sub 20hz bass is great and all but don't underestimate the importance of the 40-80hz stuff. I've found getting that right makes all the difference.

btw..I also run Aura Pro bass shakers in all my seating to add that little extra "feel" to movies.
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post #12 of 16 Old 01-23-2019, 03:05 PM
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I think the other issue is that as we introduce more ULF capability into a system, that can tend to drown out mid bass detail. So one also needs to ensure adequate response in the higher bass.

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post #13 of 16 Old 01-24-2019, 08:35 AM - Thread Starter
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Quote:
Originally Posted by KenWH View Post
...4-sealed um18's...QSC powerlight 3.4...4-ohm bridged
...JBL 4642...QSC plx2602...4-ohm bridged
... higher frequencies the JBL gives..something that the UM array can't...
That's easy to explain. Looking at 50-100Hz range:
Four 88.6dB sensitivity drivers in series-paralell gives 94.6dB/watt.
The JBL 4642 is rated at 100dB
You need more than 3x the power to get the same SPL out of Quad Ultimax.

However down below the box tune frequency of the JBL the cone area and xMax of the um18 allows the quad's output to beat the JBL.

So you have a sweet "horses for courses" set up. Have you tried running the um18 lowpass ~40Hz and the JBL highpassed ~40?

Last edited by artsci2; 01-24-2019 at 08:42 AM. Reason: corrected SPL of um18 Quad
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post #14 of 16 Old 01-24-2019, 08:48 AM
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Originally Posted by KenWH View Post
I too run 4-sealed um18's but mine are all mounted in one large sealed cabinet with around 26ft3 net air space constructed with braced 1.5" thick plywood walls. It's powered by a QSC powerlight 3.4 running 4-ohm bridged.
I'm also running a JBL 4642 which is a ported dual 18 pro cinema sub that I've upgraded with dual 18" 2242 woofs. It's running off a QSC plx2602 at 4-ohm bridged with a 20hpf to protect the woofs.

You would think there is no place for the JBL along side the massive UM array but you'd be wrong...the tactile feel that the JBL gives, especially when playing high spl music, is something that the UM array can't quite match. It brings the music to life in way the UM's just can't. The JBL is tight sounding and lightning quick in response and I honestly feel an upgraded 4642 like mine could give a lot of high-end diy and commercial subs of similar size a run for it's money above 20hz when it comes to sound quality and would hang in the spl department to.

Now if i want to do structural damage to my home...sure the UM array is my weapon of choice. When pushed, it can literally shake that end of the above 2nd floor to the point I fear real damage could be done to my home. Stuff falls off the walls, lamps dances off of end tables, etc. I actually cracked the drywall on a second floor wall after pushing the UM's a little bit.

I started out with dual SVS CS Ultras back in 2001-2 when SVS was really just starting out as a company. At the time they were considered, and rightfully so, one of the better performing music/ht subs you could get...especially at their sub $2k price point. With that said, I don't know if it's a high excursion driver thing in general but I noticed a similar comparison in feel between the SVS's vs the JBL then as I do my UM's vs the JBL now. Even near field, and at similar moderate spl's...the Ultra's didn't have that tactile "feel it in your chest" excitement that I craved and so that's how i ended up with the JBL a few years latter. For awhile I ran both the SVS's and JBL together and compared them head to head and while I knew the SVS's wouldn't hang spl wise...I was shocked at how much better the JBL sounded in general at all volumes.

Maybe this is the reason why some folks with these modern "high excursion infrasonic bass monster" subs are looking to add MBM(mid-bass modules) and the like to their systems. Sub 20hz bass is great and all but don't underestimate the importance of the 40-80hz stuff. I've found getting that right makes all the difference.

btw..I also run Aura Pro bass shakers in all my seating to add that little extra "feel" to movies.
JBL is no doubt a top choice for a pro type sub. Many here are now pairing their UM18s with Dayton PA460s, which are a very cheap version of your JBLs...for exactly the same purpose.

The discussion goes exactly as you described....a high sensitivity lower mass lower excursion driver designed for pro use provides better tactile and pressure, while the high excursion high xmax higher mass drivers handle the low end and any tactle and pressure related to say under 40hz.

in my situation, i have tried separating the subwoofer ranges with a crossover, but i personally find that i prefer to blend them using them full ranges as i get more cones moving through the full range and have the benefits of all the subs spread out in different positions.

how did you choose to integrate yours?
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post #15 of 16 Old 01-24-2019, 09:38 AM - Thread Starter
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Back to the hair swaying:
It takes about 5500cm^3 displacement to get 125dB at 50Hz , 1m, free space.
The surface area of a 2m sphere is 4Pi*100^2=125,664cm^2
So the air is moving +-0.44mm 100/second at the 1m radius.
The peak speed of this motion is Amplitude*2Pi*Hz= 0.44mm*6.28*50/s=138mm/s
If I wave my hand back and forth 5" every second, I can feel that.

A thought occurs... maybe we are feeling the cooling of our skin with the motion of the air....
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post #16 of 16 Old 01-24-2019, 11:02 AM
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Quote:
Originally Posted by artsci2 View Post
That's easy to explain. Looking at 50-100Hz range:
Four 88.6dB sensitivity drivers in series-paralell gives 94.6dB/watt.
The JBL 4642 is rated at 100dB
You need more than 3x the power to get the same SPL out of Quad Ultimax.

However down below the box tune frequency of the JBL the cone area and xMax of the um18 allows the quad's output to beat the JBL.

So you have a sweet "horses for courses" set up. Have you tried running the um18 lowpass ~40Hz and the JBL highpassed ~40?
Yep...I have sort of the best of both worlds right now when it comes to subs. But even level matched the sound quality difference between them is still noticeable on music especially with the JBL besting the UM's. Sealed, the UM's are no slouch in sound quality mind you but JBL knew what they were doing when they designed the venerable 2242 woofers all those years ago. One reason I'm so high on the JBL is that I actually use my theater a little more for music than movies...if it were the other way round I would be perfectly happy with just the UM's.


Quote:
Originally Posted by RoboAVS View Post
JBL is no doubt a top choice for a pro type sub. Many here are now pairing their UM18s with Dayton PA460s, which are a very cheap version of your JBLs...for exactly the same purpose.

The discussion goes exactly as you described....a high sensitivity lower mass lower excursion driver designed for pro use provides better tactile and pressure, while the high excursion high xmax higher mass drivers handle the low end and any tactle and pressure related to say under 40hz.

in my situation, i have tried separating the subwoofer ranges with a crossover, but i personally find that i prefer to blend them using them full ranges as i get more cones moving through the full range and have the benefits of all the subs spread out in different positions.

how did you choose to integrate yours?
Never tried cascading them...both subs are low-passed at 80hz with no other filters other than the 20hz hi-pass on the JBL. I used to run a BFD to eq my subs but pulled it awhile back and just let the pre/pro's room correction handle it for now.

My theater room is roughly 24'x22'x8.5'h with a small additional "L" shaped lobby/equipment rack space in one back corner so one side wall is closer to 30'. The 24' wall is my front/screen wall.

As to locating these two in the theater so they play nice together...I've tried corner loading, co-locating in corners and along the same walls etc. ,etc. I've found the "sweet spot" is having each sub located roughly mid-way down opposing side walls. Though not the best locals for ultimate spl(co-located corner placement), this mid-wall placement best smooths out the room response and improves the tactile "feel" at the main seat which trumps chasing maximum spl. Having these two in the same room is a luxury as worrying about adequate spl is really not an issue.

I also have at times run two additional JBL 4645(single 18's) for a total of 8-18's all at the same time. It was fun but really overkill so I have since moved the 4645's to a dedicated 2ch. setup.

If you can't tell, I really love the big JBL pro cinema gear. In addition to their subs, I also run the speakers in my avatar across the front. The center is semi custom to fit under my screen and I also use them as the side surrounds. I recently switched over to JBL 9300 on-walls for rear surrounds and I have a pair CT-321's waiting to go in the ceiling when I move to Atmos. I was fortunate to be able to buy most of my JBL gear used and at great prices from a nearby commercial theater supply dealer in Memphis. They thought i was a bit "nuts" putting all this stuff in my home. Back years ago when i first started with the JBL pro cinema gear, I think only one or two other guys here on AVS were using similar pro gear. Now it's kinda caught on and is not quite as radical as it was when I started.

It's hard to argue with having the effortless full-range sound that these big speakers have...if you have the room and no waf to deal with that is.
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