Dr V's Twin Acoupower 18" Build

[vinculum]

This thread will chronicle the build of my subwoofer upgrade project using a pair of Acoupower 18" studio drivers. I also aquired a pair of 10" ports with spun aluminum flares. The flares are about 17.5" in diameters on the ends. They are quite intimidating to see. I can easily fit my head inside. The ports are so scary, I'm not really sure if I'm going to use them or go sealed! Build quality in general appears top notch. I have a lot more to write, but I know everyone likes the gratuitous pictures first, so I'll post a few to start and write more later on my goals, equipment, room, models, ect. I'm hoping to keep this a constructive and fun thread.

Dr V

[Mike P.]

Awesome looking subs and ports! How well do the subs model in ported?

[vinculum]

Here's my preliminary amplitude graphs @ 1250 watts (conservative)

Yellow - Sealed in 7ft.
Orange - Ported 16ft. Tuned to 21.68 Hz 10" port 25" effective
Purple - Ported 14ft Tuned to 15Hz 8" port 36.73" long (Ilkka's question from Buy in thread)

[Ilkka]

I would go with the purple one. Best balance between extension and deep bass output. Though the orange would sound subjectively the loudest, but probably you won't need all that extra output in 20-40 Hz area.

If you want to use those 10" missile silos... I mean ports, maybe something like 450 liters tuned to 18 Hz would work. The port length would still be around 35" which is doable when using a sonotube.

[Mike P.]

I vote purple. If I'm reading the graph right, it's 115db at 15hz. Wow!

[vinculum]

Green = 20cf, 18Hz tune 10" port 24" length

Sonotube ported isn't a great option for this driver due to the way air is pumped through the pot on the back. Think of it as an "air diode" or entrainment in fluid dynamics talk. It's simply going to blow right through the port! Carlos has gone to great lengths with the design of thermal considerations. Another reason this driver would work great sealed.

Dr V

[Ricci]

Awesome Vinculum! I bet you are excited hey? Heck I'm excited for you, and dang those ports are! I've got a little something coming in the mail for myselfnot Acoupower, but it should be interesting nontheless.

I voted for ported, but I'd really like to see you try both sealed and ported. You should definately use those ports too, so I vote for the orange box, or something similar.

[thxgoon]

Um... I'm scared

Purple all the way! Though with that much displacement if you had enough power you would get considerable output with a sealed design, LT would have lower distortion, higher output and some wicked looking ports! Impressive, what's the xmax on those drivers?

[vinculum]

thxgoon wrote:

Um... I'm scared

Purple all the way! Though with that much displacement if you had enough power you would get considerable output with a sealed design, LT would have lower distortion, higher output and some wicked looking ports! Impressive, what's the xmax on those drivers?

I should have made a color poll instead! Grrrr...

Its a hard choice isn't it? Carlos is hesitant to give an Xmax value for several reasons. For models, 30mm is a good value to use. He claims 100% BL to 18mm, and 35mm is when audible distortion becomes objectionable. If Ilkka gets his hands on one of these it will be very interesting. Underhung 6" voice coil with a neo magnet with over 90% of the flux lines in the gap. Considerable thermal dissipative properties. It might not be a perfect driver for all alignments, but it has considerable potential and build quality is top notch. They go through many tests before shipping, One of which was a free air 70 volt sine sweep from 20Hz to 500Hz.

Here's more chart candy..

[Kevin Haskins]

I'd vote for about a 17Hz tune. Man.... love those ports. You could loose a kid in your box though.

[funky_waves]

18-20cubes at 16hz.

[vinculum]

The flares give the ports a little extreme look. What they really bring to the table is the ability to run the air velocity a little higher than normal without chuffing. The fact that they are 6" deep also means that you get a lot more effective port length than what the tube itself is. The tube is actually 15" long, but with the flares, about 22-24" effective. I can get longer paper tubes, or play games with the distance to the back of the box for lower tunings.

Where does time go? I wanted to write more, but I have to go.

Oh yeah, the poll was changed to include additional tunings.

Dr V

[vinculum]

Ilkka wrote:

The port length would still be around 35" which is doable when using a sonotube.

I misunderstood this when i replied earlier. Sono is fine for the port tube, but not for the enclosure unless its sealed. 35" seems a little long for that tune, but I didn't run it through the program to check.

My max exclosure size is going to be 24"h x 48"w x 32? deep. Using 1" baltic birch for box walls and 2" for baffle, minus all the braces, port and driver volume I'll probably have about 16 cubes actual volume. Stuffing might get me close to 20 cubes effective. The driver and port will be on the same baffle, forward firing. One in each corner of the room. I'm going to build it and do a low level sine sweep of the port to determine actual tuning before buttoning it up for good. The sealed plan would be 24x24x30 or so.

I'm looking at Crown I-Tech 4000 for amplification, thats why you see 1250 watts in my models. If i did sealed, I'd be looking for more power. Might get more anyways? a Crown I-Tech 8000 and I'd consider it done. I was comparing them to the Crown Xti series. The I-tech puts out twice the power with the same AC current draw. Gotta love super good efficiency and networkable controllable DSP.

My system is mostly for concert DVD & studio music playback with the occasional movie. I'm not overly concerned with anything below 16Hz. The handful of chapters on a handfull of DVDs with anything lower just doesn't justify it in my mind. I want super transient capability with tremendous SPL overhead for lifelike reproductions.

Dr V

[Ricci]

I vote 20ft tuned to 18hz. It should get you down to 16hz just fine. I don't much care about output below 16 either. Since I already voted I couldn't vote again for the enclosure size.

You could get a used Crown CE4000 or 2 to power these with and save a little dough. But if you are going to pay for an I-tech you may as well get the 8000 and like you said "just be done with it".

[thxgoon]

vinculum wrote:

Stuffing might get me close to 20 cubes effective. The driver and port will be on the same baffle, forward firing.

If I remember right stuffing only increases the 'enclosure size' in a sealed design?? When porting you just need enough on the inside walls for dampening.

My system is mostly for concert DVD & studio music playback with the occasional movie. I'm not overly concerned with anything below 16Hz. The handful of chapters on a handfull of DVDs with anything lower just doesn't justify it in my mind. I want super transient capability with tremendous SPL overhead for lifelike reproductions.

Well, I beg to differ Those few scenes are a LOT of fun and deep bass is getting more and more popular in movies. Also, keep in mind that the lower the tune of the sub, the lower the frequency at which the port begins to play a role in the sound and the longer the system will act and sound like a sealed design.

[vinculum]

thxgoon wrote:

If I remember right stuffing only increases the 'enclosure size' in a sealed design?? When porting you just need enough on the inside walls for dampening.



Well, I beg to differ Those few scenes are a LOT of fun and deep bass is getting more and more popular in movies. Also, keep in mind that the lower the tune of the sub, the lower the frequency at which the port begins to play a role in the sound and the longer the system will act and sound like a sealed design.

Yes you could be right about that stuffing. I seemed to remember Carlos telling me to stuff it well to makeup for lost volume. I'll have to look over my old emails and ask him again. I could possibly go upto about 42" deep and that puts me at 21.74 cubes before port, driver & brace volumes. **** the box is getting big!

You make it sound like the ports output is diseased! If thats the case, the ports output is tainting the drivers output all the way through the range according to the FR graph.

Here's a look at a 7ft sealed box with some additional power. 2500 watts pushes the cone displacement to 32mm max, which is still acceptable.

30Hz = 118dB
20Hz = 113dB
15Hz = 108dB
10Hz = 102dB

Now lets add +6dB for 2 drivers, +12dB for 1/8 space placement and a +? for a little room gain. Of course I don't have to post the graphs on the phase responce, group delay because they are all superior to any ported alignment.

I'd have to think with those numbers, even sealed it would be a stellar performer in the SPL department, especially for music.

Just something to consider. How much is overkill is reasonable is a decision I have to make. Thats why I'm here for discussion!

Dr V

[thxgoon]

If those numbers for a sealed design are close to accurate, I'd say you have more than enough output to go sealed especially if max SPL is not your goal. It'd be easier to build and smaller, though I'd hate to see you give up that extra capability just because....

The port plays more and more of a role in the sound of the speaker the closer you get to it's tuning frequency. If you look at Steve's LLT Explained thread he goes through this in quite a bit of detail.

[vinculum]

I've been advised from the highest bass authority to consider the LLT/EBS alignment, so I'm going to reread Steve's LLT thread again to get up to speed and see what I can live with. I'd be curious to hear Steve's opinions with this driver and 10" ports.

Hey, If i didn't like it I could always plug the ports with a couple basketballs?

Dr V

[thxgoon]

vinculum wrote:

I'm going to reread Steve's LLT thread again to get up to speed and see what I can live with.

Can you live with some the most accurate, bone crunching bass imagineable? Lol! Good choice!

[Ilkka]

vinculum wrote:

I've been advised from the highest bass authority to consider the LLT/EBS alignment, so I'm going to reread Steve's LLT thread again to get up to speed and see what I can live with. I'd be curious to hear Steve's opinions with this driver and 10" ports.

Hey, If i didn't like it I could always plug the ports with a couple basketballs?

Dr V

Might that be Steve himself?

Sure, a large ported sub will give you more power down low, but it's not that two high power sealed 18" subs wouldn't be more than enough already. Depending on the amount of room gain, you might not need much EQ at all.

[Ilkka]

thxgoon wrote:

Well, I beg to differ Those few scenes are a LOT of fun and deep bass is getting more and more popular in movies.

Yes, but what is deep bass? Are you sure you can separate a 16 Hz tuned and a 12 Hz tuned subwoofer? Remember that in a room each will go at least 2-3 Hz lower than what the nominal tuning frequency is.

A low enough tuning frequency is a good thing, but at some point you are starting to get more negative than positive effects. And IMO usually this point is somewhere around 15 Hz. If there's output to spare, then you can go a little bit lower than that. Of course the parameters of the driver affect also.

Also, keep in mind that the lower the tune of the sub, the lower the frequency at which the port begins to play a role in the sound and the longer the system will act and sound like a sealed design.

It also means that the port is giving you less and less help with most of the material.