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Discussion Starter #1 (Edited)
Optimal Tune & Port Frequency/Velocity for UXL-18?

I’m planning to get four UXL-18’s with the pending AVS group-buy to build four slot port Marty type subs for a 10,000 cf room. While I wait for drivers, I’m trying to find the optimum Port Resonance and Port Velocity at the lowest efficient Tuning Frequency for my build. As I play around with WinISD and try to get a feel for different tuning and port options, I’m finding it hard to meet all the various member recommendations that appear in AVS.

SUGGESTIONS

Most people have said to push port resonance above 150 Hz to keep it out of the pass band. They have also recommended keeping the port velocity below 25 m/s to minimize chuffing. However, if I keep resonance above 150 Hz, the velocity rises above 31 m/s or more. If I push the velocity below 25 m/s, the resonance drops below 100 Hz or more. Each of these values change slightly when I adjust internal volume.

I have also read that the slot port design I’m planning to use (like the Marty subs) are much more forgiving than round ports; that a BFD or notch filter can attenuate a port resonance in the audible range without affecting the sound; and that a port velocity around 32 m/s is usually masked by the rest of the LFE in movie soundtracks. Lastly, people recommend flaring the port openings inside and outside to reduce turbulence, but this mostly relates to round ports and I don’t see how this can be applied to a Marty-style slot-port other than routing out a radius in the ¾ plywood at either end.

PARAMETERS

The theater area is open on two sides to a 10,000 cf open floor plan, so I can’t expect much room gain until about 6 Hz. Therefore, all four subs will sit behind the LP for maximum near field response. To fit my space limitations, the four UXL’s are going into two right/left rear subs at approximately 32"h 27"w 24"d and two center rear subs at approximately 32"h 32"w 21"d.

I know the UXL-18 likes between 9-12 cf to really perform, but space limitations keep me around 8 cu ft . Although the UXL-18 is rated at 1200w RMS, most people feed it 2000w RMS and using a HPF to keep cone excursion below the UXL-18’s Xmax of 45mm. LTD02 has recommended that I build all four subs at the identical tune. He also wrote that as long as the port area, port length and box internal volume remain the same, different cabinet configurations will match at the same tuning frequency.
 

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Discussion Starter #2 (Edited)
PORT AREA

First, I modeled several port area combinations between 40.5 in^3 and 51.56 in^3 in WinISD keeping the volume near 8 cubic feet. I found the optimum combinations for 150 m/s resonance were between 40.25 in^3 and 45 in^3 port area. When I tried combinations below 40.25 in^3 port area, the port velocity jumped to 60 m/s or more. When I tried combinations above 45 in^3 port area, the port resonance dropped below 120 Hz or more. The signal for each comparison was kept at 2000w with a 2’nd order Butterworth HPF around 13 Hz. Each enclosure was kept at 32” high and had the width adjusted to match the relative internal volumes between the 21” and 24” deep subs:

(1)

Volume: 7.81 cf
Tuning: 17.17 Hz
Area: 41.25 in^3
Resonance: 150.28 Hz
Velocity: 32.74 m/s @ 16.24 Hz

32”h x 27”w x 23.625"d
Ports: 2" x 6.875" x 45” (x3)

32”h x 33.5”w x 19.5"d
Ports: 2.5" x 5.5" x 45” (x3)

(2)

Volume: 8.05 cf
Tuning: 17.21 Hz
Area: 42.5 in^3
Resonance: 150.34 Hz
Velocity: 32.23m/s @ 16.35 Hz

32”h x 24”w x 24.375"d
Ports: 2" x 7.125" x 45” (x3)

32”h x 31.75”w x 21"d
Ports: 2.375" x 6" x 45” (x3)

(3)

Volume: 8.2 cf
Tuning: 17.17 Hz
Area: 45 in^3
Resonance 150.36 Hz
Velocity: 31.86 m/s @ 16.35 Hz

32”h x 26.25”w x 25.5"d
Ports: 2" x 7.5" x 45” (x3)

32”h x 32.5”w x 21"d
Ports: 2.5" x 6" x 45” (x3)

(4)

Volume: 8.25 cf
Tuning: 17 Hz
Area: 45 in^3
Resonance 150.71 Hz
Velocity: 31.7 m/s @ 16.65 Hz

32”h x 27.5”w x 24.375"d
Ports: 2" x 7.125" x 45” (x3)

32”h x 33.375”w x 21"d
Ports: 2.75" x 6" x 45” (x3)

(5)

Volume: 8.5 cf
Tuning: 17.49 Hz
Area: 45 in^3
Resonance 150.71 Hz
Velocity: 31.7 m/s @ 16.65 Hz

32”h x 27.125”w x 25.5"d
Ports: 2" x 7.5" x 44.875” (x3)

32”h x 33.5”w x 21"d
Ports: 2.5" x 6" x 44.875” (x3)
 

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Discussion Starter #3
TUNING FREQUENCY

Second, I picked the best port combination at 150 Hz resonance, then modeled various tuning frequencies between 16-19 Hz. Port combination #5 had the lowest velocity and largest volume, but at 25.5” deep it’s a little large to accommodate easy access for cleaning. Port combination #4 is fairly close on velocity, maintains a lower 17 Hz tune at 150 Hz. and fits the location slightly better for clearance. However, when I take the #4 configuration and adjust tuning frequency and port length, the port velocity remains between 30 -36 m/s while the port resonance swings widely from 132 – 191 Hz:


Tuning: 16 Hz / 51.25”
Resonance 132.01 Hz
Velocity: 30.43 m/s @ 15.09 Hz
HPF: 12.8 Hz

-3 db: 33.65 Hz
-6 db: 17.01 Hz
-9 db: 14.72 Hz

30 Hz: 118.59 db
25 Hz: 118.02 db
20 Hz: 117.22 db
17 Hz: 115.90 db
13 Hz: 108.51 db


Tuning: 16.5 Hz / 48”
Resonance 140.93 Hz
Velocity: 31.5 m/s @ 15.59 Hz
HPF: 12.9 Hz

-3 db: 31.73 Hz
-6 db: 16.87 Hz
-9 db: 14.91 Hz

30 Hz: 118.79 db
25 Hz: 118.31 db
20 Hz: 117.58 db
17 Hz: 116.04 db
13 Hz: 107.79 db


Tuning: 17 Hz / 45”
Resonance: 150.33 Hz
Velocity: 32.49 m/s @ 16.12 Hz
HPF: 13.05

-3 db: 29.32 Hz
-6 db: 16.91 Hz
-9 db: 15.13 Hz

30 Hz: 118.90 db
25 Hz: 118.60 db
20 Hz: 117.92 db
17 Hz: 116.00 db
13 Hz: 106.90 db


Tuning: 17.5 Hz / 42.325
Resonance 159.84 Hz
Velocity: 33.49 m/s @ 16.67 Hz
HPF: 13.05 Hz

-3 db: 25.58 Hz
-6 db: 16.97 Hz
-9 db: 15.37 Hz

30 Hz: 119.20 db
25 Hz: 118.90 db
20 Hz: 118.25 db
17 Hz: 115.97 db
13 Hz: 106.08 db


Tuning: 18.02 Hz / 39.75”
Resonance 170.23 Hz
Velocity: 34.45 m/s @ 17.26 Hz
HPF: 13.3 Hz

-3 db: 21.43 Hz
-6 db: 17.5 Hz
-9 db: 15.63 Hz

30 Hz: 119.40 db
25 Hz: 119.25 db
20 Hz: 118.53 db
17 Hz: 115.70 db
13 Hz: 105.25 db


Tuning: 8.51 Hz / 37.5”
Resonance 180.38 Hz
Velocity: 33.45 m/s @ 17.8 Hz
HPF: 13.35 Hz

-3 db: 20.38 Hz
-6 db: 17.32 Hz
-9 db: 15.85 Hz

30 Hz: 119.68 db
25 Hz: 119.58 db
20 Hz: 118.77 db
17 Hz: 115.39 db
13 Hz: 104.25 db


Tuning: 19.02 Hz / 35.376”
Resonance 191.23 Hz
Velocity: 30.46 m/s @ 18.37 Hz
HPF: 13.35 Hz

-3 db: 19.99 Hz
-6 db: 17.51 Hz
-9 db: 16.12 Hz

30 Hz: 119.90 db
25 Hz: 119.94 db
20 Hz: 118.90 db
17 Hz: 114.90 db
13 Hz: 103.67 db
 

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Discussion Starter #4
TRANSFER FUNCTION MAGNITUDE

As I change tuning, the Transfer Function Magnitude shows wide swings in response. Above 18 Hz tuning, this combo is way more efficient and maximizes SPL between 20 – 30 Hz. Below 18 Hz tuning, you loose a lot above 20 Hz but gain a lot between 13 – 17 Hz. However, when I graph SPL, the losses and gains are much more minor keeping between a 2 db range from 16 Hz to 19.5 Hz tuning. For comparison, when I graph it at 19.02 Hz tuning in WinISD, it comes closest to the Mini Marty in overall performance.

JBrown found that Four UXL-18’s at approx.. 2000w each, will gain +12 db in SPL over a single sub. I modeled this in WinISD by multiplying the number of drivers, ports and volume by a factor of 4 and found it to be true. LTD02 suggested tuning all four subs at 16 Hz and making up the loss with the extra 12 db from multiple subs. However, when I look at Transfer Function Magnitude, it seems like I’m loosing over 13 db between 20-30 Hz just to gain 1.48 db at 17 Hz and 5.5 db at 13 Hz. If that’s true, then the extra 12 db is a wash over 20 Hz and I’d be building four subs just to pick up 1-5 db below 17 Hz.

BEST OPTION?

Most of the Marty subs variants and the majority of AVS recommendations I’ve seen for UXL-18’s in 8 cu ft stay around 19 Hz. There must be a reason why everyone settles around this tuning for maximum efficiency. However that may only apply to a single sub. I'd like to have the tactile feel of 16-17 Hz tuning without sacrificing too much above 20 Hz. Multiple subs may mean I can have both 120 db SPL and 16-17 Hz extension. However in such a large 10,000 cf room, maybe I'm chasing a pipe dream (even near field 12” to 60” from the LP). Some people have suggested using tactile transducers to augment the “feel” of deeper extension to make up the difference, but I examined my sofa and can’t find a spot to mount a But Kicker without lots of fabrication or needing to purchase three sets of Crowsons and raise all the seating to similar height.

Based upon the above models, which would be the best tuning-resonance-velocity combination to provide a real punch without audible chuffing from near field subs in such a large room? What is more important for movie soundtracks anyhow? Does more of the in-your-gut punch of special effects occur mostly between 20-35 Hz? Or, will I give up too much above 20 Hz to chase after 13 Hz in 10,000 cf room even accounting for close proximity of the subs?
 

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Discussion Starter #7
Are you considering the impact of a high pass filter on the port airspeed?
Yes, I used a HPF between 12.9 Hz and 13.2 Hz on all WinISD simulations depending upon what it took to keep the cone excursion under 45 mm which is the Xmax for the UXL-18 driver
 

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Yes, I used a HPF between 12.9 Hz and 13.2 Hz on all WinISD simulations depending upon what it took to keep the cone excursion under 45 mm which is the Xmax for the UXL-18 driver
That's certainly not how I would set the HPF. The driver doesn't have 45mm of usable travel.
 

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Discussion Starter #9 (Edited)
Simple answer to all that: Make the box bigger...that's it.

With a bigger box, the port resonance rises and the airspeed can come down by adding area to the port.

Because this is a living room HT rather than a dedicated HT, I have some size limitations that can't be avoided. I can't go any deeper than 24" and 21" without blocking access to clean behind the seating (we have dogs). I can't go higher than the 32" seating height because of artwork on the wall. There are two large potted plants and an air conditioning return vent that dictate width be kept to about 27" for the right/left subs and 64" combined (32" each) for the center subs. That leaves me with about 8-8.5 cf maximum interior volume.

The question is, within the size parameters I have to live with, what's the best combination of tuning vs port resonance and velocity?

Which has more impact, port tune below 150 Hz or velocity above 25 m/s? I can tune them at 16 Hz to get more extension but it will drop the resonance to 132 Hz. Can that be tamed by a notch filter? At 16 Hz the port velocity peaks at 30.4 m/s at 15 Hz - is that even audible? If 16 Hz is feasible, does this give up too much SPL efficiency above 20 Hz to get a couple of extra db below 15 Hz? Will the 12 db gain from multiple subs more than compensate for the loss? Which is more important on most movie soundtracks anyway?

I've never built one of these. I was hoping that someone with more experience on how these changes in parameters affect how it actually sounds could give some perspective so I don't build a mistake. I guessing that 150 Hz resonance and 31 m/s velocity at 17 Hz tune is probably OK as a starting point based upon some of the other successful builds I've seen in AVS like the Marty Cube and Marty Mini variants. But how far can I push this in either direction to get more extension or more SPL efficiency without creating audible chuffing or boomy bass?
 

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The UXL-18 has an XMax of 34mm as listed on the product page here: http://www.istonline.ca/mach5_uxl_18.html


I would double check all the sims you ran in WinISD and adjust accordingly with the proper XMax plugged in to WinISD. Big diff b/t 34mm and 45mm. "Big difference", as in "dead driver" big. :eek: Granted you'd probably hear the coil slamming against the backplate first, but why chance it?


I'm in a similar situation as you, but my room is 1/3rd the size of yours and is a sealed room for all intents and purposes. I'm trying to find optimal box size for two of these drivers (in separate boxes) and am encountering the same hurdles as you. Lower port velocity and 1st port resonance drops too. It's physics....you just can't win; you must find a compromise...a happy medium.
 

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Because this is a living room HT rather than a dedicated HT, I have some size limitations that can't be avoided. I can't go any deeper than 24" and 21" without blocking access to clean behind the seating (we have dogs). I can't go higher than the 32" seating height because of artwork on the wall. There are two large potted plants and an air conditioning return vent that dictate width be kept to about 27" for the right/left subs and 64" combined (32" each) for the center subs. That leaves me with about 8-8.5 cf maximum interior volume.

The question is, within the size parameters I have to live with, what's the best combination of tuning vs port resonance and velocity?
Since aesthetics are more important than audio in this build...

Calculate and set your enclosure volume. Don't forget to subtract the port volume including the divider panel, the bracing volume, and the sub volume.

Then keep adding port area till the port velocity comes down to 22ish M/s.

Keep raising the tuning frequency till you get about a 40" long port at 150-160hz resonance.

At that point your box is tuned as low as it can be, you get what the sim says. Maybe a 22hz tune, but if you want to lower that the box needs to be bigger. There is a reason they are called Large Low Tuned subs.
 

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It seems like you are fighting too many constraints and have to budge on something, and your wall space doesn't seem to be very well utilized. Perhaps you need to mix two types of subs. Can't you do two smaller subs in the middle behind your couch (say for example sealed), and two tall enclosures behind the two plants (large ported box or a tall horn like the HzHorn or LTD's NOTHORN) on either side?
 

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Discussion Starter #18
After playing around in WinISD some more, I came up with the following:


CENTER SUBS #1 and #2 :

Box: 32h x 32w x 21.75d

Port: 2.75 x 6.25 (x3)
Port Area: 51.563 in^2
Port Length: 46"
Port Tune: 17.84 Hz

Internal Volume: 8.801 ft^3 (net of port)
Resonance: 147.12 Hz
Velocity: 25.27 m/s
Signal: 1,000w per sub
EQ: HPF @ 10 Hz


RIGHT/LEFT SUBS #3 and #4 :

Box: 32h x 29.5w x 22.625d net

Port: 2.5 x 6.875 (x3)
Port Area: 51.563 in^2
Port Length: 46"
Port Tune: 17.84 Hz

Internal Volume: 8.832 ft^3 (net of port)
Resonance: 147.12 Hz
Velocity: 25.27 m/s
Signal: 1,000w per sub
EQ: HPF @ 10 Hz


With 4 subs at 1000 watts each I get:

-3 db: 17.64 Hz
-6 db: 15.86 Hz
-9 Db: 14.64 Hz


30 Hz: 130.68 db
25 Hz: 130.40 db
20 Hz: 129.67 db
17 Hz: 127.10 db
15 Hz: 122.94 db
13 Hz: 117.01 db
10 Hz: 105.69 db


WHAT DO YOU GUYS THINK?

147.12 Hz resonance
25.94 velocity

The UXL-18's can take 2,000 watts, but not in these enclosures.
Any reccomendations on an amp @ 1,000 wpc?
 
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