Dig This People - B4 Plus Review

Dr. Spec

http://www.hometheaterhifi.com/volume_10_3/svs-b4-subwoofer-9-2003.html

This thing absorbed the full power of a bridged Crown K1 and asked for more. The amp gave out well before the sub did, shutting down several times. And Crown does not make **** amps, people.

He took ground plane THD measurements outside at 100 dB (no room gain) and the THD was incredibly low. It would be almost immeasurable inside with the benefit of room gain.

Except for the 15 Hz measurement which he took without the aid of a port plug (a big mistake IMO). 15 Hz is so far below the native tune (25 Hz) of the sub that THD skyrocketed as the woofs are quite poorly controlled at that frequency without the help of the port plugs to provide a lower tune point and the proper amount of restoring force inside the enclosure. Had he plugged a port or two, the THD at 15 Hz would have been far lower.

Doc

RuSsMaN

Still impressive, and 100% pure overkill and bang-for-buck.

Too bad you weren't the one that reviewed, and reviewed properly.

Cheers,
Rooster

dave shepard

Gees Doc I just bought the pb2+ and now you want to tempt me into the b4!!! LOL.

VR3

Forwarded this one to my Dad. That should ruffle his feathers! hahahahahha

tryrrthg

Doc,

What's with the review saying they may be selling through dealers soon?

the link is dead now so maybe the reviewer said something he shouldn't have...

EDIT: looks like hometheaterhifi's site is down so it may not just be the review...

Dr. Spec

Can't say about the dealer network; haven't heard a thing about that.

Doc Johnson really knows his stuff and puts a sub through its paces. I wish I had 1/10 of his testing gear.

But I really do feel like he made an error in judgement by testing the B4 at 15 Hz with all ports open.

The sub has variable tuning for a reason and feeding it a 15 Hz signal with all ports open was not envisioned by the designer.

While I have not seen an anechoic FR sweep, I would imagine the B4 is probably 10 dB (or more) down at 15 Hz with all ports open as compared to the 25 Hz level. It would therefore require 10 TIMES the power input at 15 Hz to achieve the same SPL at 25 Hz.

The port plugs are there for a reason and plugging two ports would have lowered the enclosure tune to about 16 Hz, provided far better woofer control, and substantially reduced the amount of power input required to achieve 100 dB at 15 Hz. THD would have accordingly been far lower.

Otherwise, a great review and the THD at all other frequencies within the intended operating range of the sub with all ports open is extraordinarily low.

The SPL he generated at higher frequencies at 1 meter outside at full power is staggering - in the 120+ dB region. Like he said, with room gain you are looking at 130 dB+ in a typical room and that's with 1500 watts of Crown power; the B4 can take even more.

Doc

HBombToo

Originally posted by Dr. Spec


Doc Johnson really knows his stuff and puts a sub through its paces. I wish I had 1/10 of his testing gear.

Doc

What the hell is this... "Audio Control Phase Coupled Activator. "

Sounds like it has a big cool factor! Help me decide to spend more money that I shouldn't:D

HBomb

Charles Rose

That thing would probably blow the roof off of my house...:p

VR3

Doc,
You think the B4 would be...like a good bed or something? Do you think it would cause structural(sp) damage to my room? Were talking 160+db in my room..my guesstament. I mean if it can hit 120 outside...lol. Holy crap! I am seeing shattered windows!!!!!

Dr. Spec

From the designer, Tom V. Like I said, when these guys talk, shut up and listen:

"The B4+ was measured in 25 Hz extension mode. So once frequencies drop much below the tuning point...THD is going to rise very quickly. Hitting 100 dB outside with 3% THD at 20 Hz isn't too bad considering that is already 1/3 octave below the tuning point of the enclosure. But you can see by 15 Hz the subwoofer isn't working optimally. One thing to remember, John Johnson measured the B4+ outside because he couldn't reach any type of output limits in his room...this is the first subwoofer that forced him to an entirely different measurement method.

In my experiences...going from ground plane to in room...you'll add about 4 to 4.5 dB per boundary (theory indicates 6 dB per boundary...but in the real world everything is "lossy"). So corner loading is going to add 8-9 dB...with another 1-3 dB for the ceiling depending on height and construction. So figure 10-12 dB just for the boundary effects.

"Room gain'' is something entirely different. That is a phenomenon that boosts the deepest frequencies in an enclosed or semi-enclosed listening area. In a typical North American 2500 cu-ft living area with a couple openings to other room areas...you might see 2-4 dB of *room gain* in the 16-25 Hz range. In smaller, well sealed rooms...you can see double that. In larger open rooms...nearly nothing.

So going from ground planing to corner loaded in a typical 2500 cu-ft room...you might see something like 12-16 dB of additional output for the same input levels.

When I was using the K1, the B4+ stayed very linear (low distortion) until the K1 reached its output limits...than the odd order THD suddenly skyrocketed and the combination could only manage another dB-ish. I remember John Kotches and I discussing this specifically a while back; his maximum output readings do seem to parallel closely to what B4+ owners measure in thier rooms with the most bass intense DVDs. Until he measures a few other subwoofers outside (if he ever does), it will be tough to gauge just how well the B4+ numbers are in some regards though."

goingganzo

hum i wonder if i get 2 more av15 if i can make a b4 clone. but that sub sounds awsome. or do you think just adding 2 more subs in a seccond box the same as the first strykeforce. i will have to work the numbers.

Dr. Spec

Bryan - just yank out those ports and shorten them to a 25 Hz tune and your sub will be able to play much louder without bottoming. Your 16 Hz tune is the culprit here.

burdette

Looking at the construction pics, doesn't look like he has that much length to work with to shorten... or are the pics deceiving?

Dr. Spec

Deceiving - his ports are rather long - PVC if I recall. At least some of his construction pics only showed the flared endcap, not the port itself.

A quick recalc and sawing off a few inches should do the trick. Cone excursion will be much lower, and resonator will take over sooner, and with room gain he'll still see an honest 20 Hz.

goingganzo

one problem if i retune i will get a 2-3 db hump at tune and 2-3 more output above and below tune.

Dr. Spec

If it's really an issue (and I doubt it will be), then buy a BFD for $120. It's cheaper than buying two more AV15's.

tryrrthg

Or you could throw some more bracing in the box to make less volume. that would get rid of that hump if you put enough stuff in there... just a thought...