Dual SVS 20-39 PC+ question

**Vader** · **07-12-06, 10:35 AM**

First, a little back history: I have been wanting an SVS ever since I started reading the reviews on HTF, and I finally got one in February 2006: a 16-46 PCi. The problem was that I jumped in without doing my homework (ie. emailing Ron & Tom with my room specs). Turns out that, as hard as it is to bring an SVS to it's knees, my 3200 ft^3 HT room did just that: it came very close to bottoming (port noise, compression) at even modest volume levels (I listen at around 10-15 dB below reference typically). After a great deal of troubleshooting, and patience from Ron, Jim and Erik at SVS (I can't thank you enough!), I ended up with a pair of 20-39 PC+ cylinders. Right now, I run both in 20Hz tune, and regularly go over to the neighbors to straighten their pictures after watching a movie(!)

However, now I am paranoid about sacrificing any of the headroom I gained (the full 6dBs) by using the 16Hz tune, and bottoming the 20-39's out. I get fantastic bass on the 20Hz tune (greater than or equal to the 16Hz tune down to about 18Hz anechoic), but I do miss some of the really deep stuff I was getting with the 16-46 cylinder Is there anyone out there with Dual 20-39 PC+ cylinders and an even larger airspace that can tell me if I am worrying for nothing?

**Josuah** · **07-13-06, 06:58 PM**

I guess you're just running them really loud. I've got a pair of 16-46PC+ subs, separately placed so I guess +3dB from doubling up. And I've only bottomed them out when trying to, not from any content. I sit about 11' away from the center of their drivers, room is >5000ft^3 open to the rest of the house. Bottom out will happen at absolute levels 105dB <20Hz, 110dB > 20Hz at my listening position, which means I can run at -10dB reference max.

What is the max SPL you can hit at your listening position with the two 20-39PC+ subs?

**Vader** · **07-13-06, 09:13 PM**

Josuah,

A single 16-46 PCi sub (ISD driver) was what nearly bottomed (as determined by compression, and loud port chuffing) running 12 dB below reference. After lengthy troubleshooting by Ron and I, we determined that my best bet was a pair of 20-39 PC+ cylinders (12.3 drivers). I have not gotton anywhere near the physical limit of these using the 20Hz tune, and still fear for the safety of my foundation (not to mention the sanity of my dogs). I just know that I will lose a couple of dB headroom in the 16Hz tune, and don't want to bottom these at the same listening levels. I know I am comparing apples and oranges here, as I have upgraded the drivers, amp power, port space, etc., but I am the paranoid type....

Edit: based on everything I've read about the performance of other PC+ subs relative to room size, I am really starting to wonder if I would peel the paint off the neighbors house before bottoming two PC+ drivers in a 3200 ft^3 room. And in another review here on the shack, Wayne Pflughaupt was unable to bottom an single PB10 ISD in a 6200 ft^3 room! Maybe my wife is right; I worry to much, and when I don't have anything to worry about, I usually create something!

**Josuah** · **07-14-06, 02:59 PM**

Oh, PCi, not PC+.Oops. Room size isn't always applicable. If you're sitting 1' away from a sub, the room size isn't going to affect your max SPL so much as your ears exploding.

I'd say give it a try and see where you can go.

**Vader** · **07-14-06, 03:08 PM**

Quote:

If you're sitting 1' away from a sub, the room size isn't going to affect your max SPL so much as your ears exploding.

Been there. Done that. Got the T-shirt.

**UNICRON-WMD** · **07-18-06, 03:50 AM**

Dual PC+ subs will bottom sooner or later but you should be able to hit 115-116db in 16hz tune in a 3,000 cu ft room.

I say watch WOTWs at the loudest you would ever tune up your system. If the subs don't bottom out, you should be fine with anything else you play at or below that level.

Also, the PB10 has a limiter in it that won't let the sub bottom out. The other SVS subs don't use this same limiter and will sooner or later bottom out.

**Vader** · **07-18-06, 11:59 AM**

Unicron-WMD,

When Ron and I were troubleshooting a single 20-39 PC+ cylinder (remember, 3200 ft^3), we found that compression started to set in around 106-107dB (listening position about 12 ft away) using the "tripod emergence" sequence in WotW; any louder and I feared for my own safety (and the structureal integrity of the house). So, as co-located duals would give approx 6dB additional headroom, that would be in the ballpark of your figures. I am thinking that once I get a BFD and upgrade my soundcard, I can raise the lost 3-4dB SPL back to flat safely. I thought WotW bottomed the single 20-39 PC+ cylinder, but now am not so sure that is what I heard. The sound is described as a loud "clack", but is it obvious it is not part of the soundtrack? I had mistaken a loud "crack" (during the rocket launch in "The Incredibles") for bottoming, but Ron told me that many do, and for that reason they don't use that particular sequence for testing. I just don't want the subs bottoming because I am oblivious to what is happening.

**Tom Vodhanel** · **07-20-06, 10:37 AM**

>>>Also, the PB10 has a limiter in it that won't let the sub bottom out. The other SVS subs don't use this same limiter and will sooner or later bottom out.<<<

That is correct---sort of..

They use the same limiter circuitry, but with different overall settings(and interaction to the settings)

Setting the limiters in a subwoofer is a complex process of "give and take". You have to decide how much performance you are willing to trade off, to make the subwoofer acceptably "bullet-proof" (and I suppose you also have to define “acceptably” while you are at it).

Another issue that factors in is the capabilities of the subwoofer in general. For example, our new “B4” design (and our old B4 design for that matter) really doesn’t need any limiters. It is so powerful that in the vast majority of domestic venues…you won’t reach the driver limits.

Tom V.
SVS

**subwoofer_boy** · **07-22-06, 10:24 AM**

Quote:

snip...For example, our new “B4” design (and our old B4 design for that matter) really doesn’t need any limiters. It is so powerful that in the vast majority of domestic venues…you won’t reach the driver limits.

Tom V.
SVS

Tom can you elaborate on the new B4 design? Can we expect it this year? Will this top an PB12/Ultra2?

Any pricing? I can't wait to see this puppy!!!

**lienly** · **02-17-07, 07:15 PM**

any updated info of new B4? will it carry new 13.5" driver x 4 with 3000w power?

Quote:

Tom Vodhanel wrote:

For example, our new “B4” design (and our old B4 design for that matter) really doesn’t need any limiters. It is so powerful that in the vast majority of domestic venues…you won’t reach the driver limits.

Tom V.
SVS

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