Auralex Subdude a MUST HAVE!! - Page 37

Bill, what do you mean a properly designed and constructed sub box does not vibrate withing the subwoofer frequency passband? / < 400hz.? I'm not trying to be confrontational, just trying to ensure I understand what you are communicating?

My personal experience with subwoofers dictates that every single subwoofer I've ever been exposed to, measured, or felt, vibrates the cabinet when playing --- IE - you put your hand on the outside of the sub box, you are going to know the sub is at work --- with the sole exception of dual opposed design. Horns do, bandpass do, even typical sealed subwoofer cabs do. By no means do I think the dual opposed design is the only proper subwoofer design - it is a good one, but just one of many 'proper' designs. I'm sure you understand this as well, so that's why I ask for the clarification on your statement.

While I agree with you that the subwoofer FR should not be changed by placing the sub on a isolation pad - if the cab's vibration is causing the floor, cabinets, shelves etc, in a home to vibrate at audible levels, then the isolation pad may have some function in helping to dampen those physical vibrations throughout the house. I do agree the isolation pad will do nothing to dampen or modify acoustic energy being dispersed by the subwoofer driver - it will only dampen the energy transferred directly from the sub cabinet to the wooden floor. I will say that transfer/vibration can be quite noticeable on a suspended wooden floor verses a basement with the same subwoofer. I've heard my caps in multiple rooms, and on a suspended wooden floor they are all the more tactile than on a concrete slab.

I popped into this thread to see what people thought about placing an isolation pad on top of a subwoofer to help eliminate physical vibration transmitting to a speaker sitting atop the subwoofer. In the case of my JTR ported Captivators they vibrate fiercely when given some power. The cab doesn't make a poorly built or improperly braced vibration noise, it is as sturdy a cabinet as I've ever been in contact with, but just the fact that an 18" high excursion driver is pumping back and forth makes vibrations physically shake the sub box. I'm on a concrete basement slab so I'm not worried about transmitting vibration down, but not sure if the vibration in the cab would affect speakers frequency response or sound characteristic if I set my speakers directly atop the subs. I understand that optimal placement might not be with the drivers for sub and mains in the same vertical plane - but I have measuring equipment with the omnimic and if it measure too poorly I'll buy L and R speaker stands. The reason this question has come up for me is that I typically have used tower speakers, but have recently been playing with eD and JTR high efficiency speakers which either need a stand, or to sit atop the subs to get to the proper listening height. At current I've just been setting them atop the subs with cheap foam spacer disks from home depot.

In the most basic terms, one that passes the knuckle test. When you rap a sub, or any speaker, with your knuckles it should make a high pitched knock sound, which indicates a panel resonance in the midrange or higher. If it makes a low pitched hollow sound the panel resonance is in the midbass or lower, indicating insufficient panel thickness and/or insufficient bracing. Should have gotten horns.
I assume the captivators are well made, so the panels aren't vibrating, but rather the entire box is moving in opposite reaction to the movement of the cones, Newton's Third Law of Motion at work. That's something that spikes can help with, by increasing the inertial resistance to that motion by more firmly grabbing into carpet. But you have to have carpet for them to work. Other methods of dealing with those forces include dual opposed drivers, which cancel out each others lateral vector forces, and horn loaded subs, which are so much more efficient than direct radiators that for a given output vector forces are far less. If the main vibrates atop the sub it should be isolated, though rubber feet or a resilient pad as thin as 1/8 inch is usually adequate. But the over riding reason not to put them there is that very rarely do subs and mains both work best within the same vertical footprint.

Interesting, I never heard of that. I just so happened to have my Omnimic out doing some measurements on amplifiers.

Using the real time spectrum analyzer of the Omnimic I did the knuckle test on my two Captivator cabinets. Mic placed at MLP. ~700-800hz peaks (most about 770hz from what I can tell) are what continually occurred during multiple tests on both cabinets with the RTA adjusted to slow and watching real time on the projector screen.

Interesting test...

So in regards to what these guys are talking about - the convo still feels a bit apples and oranges. IE Using my caps as an example - my caps aren't introducing rattle or bad noises in cab design that one might hope to remove with an isolation pad, but they could be introducing shake, feel, rattle noise from other things in the house that someone might want to eliminate in certain rooms or setups (assuming a wooden floor). I don't have any direct experience with a/b of isolation pads, but I can imagine a thick piece of spongy foam could dampen the physical vibrations transmitted directly to a suspended wooden floor in contact with on of my captivator cabinets. I'm fairly sure I could slosh water out of a glass sitting on the captivator cabinet with some high spl dubstep or WOTW where the same glass of water sitting in my seat would only ripple on acoustic energy alone. I think this same thought train would apply to the guys saying they stopped hearing their dishes rattle as much, or windows panes stopped rattling after adopting an isolation pad. It doesn't explain "tighter" bass however.


as to horns ---
I'm am perfectly happy with the Captivator's bass reflex design and having compared them directly to a couple different horns - a pair of Orbit Shifters in my room and a pair of F20's in HuskerOmaha's room --- I don't feel I'm missing anything in the SQ dept. Yes, the Orbit Shifters go to ludicrous volumes, but my Caps suffice for me at just ridiculous volume capability.


Edited by Archaea - 2/9/13 at 2:40pm

Possibly, but there's another factor to consider. Any movement of the cab requires the expenditure of energy. That energy which moves the cab does not produce sound. With a typical efficiency of only 3% to start with you don't want to be wasting energy making the cab dance. Foam may keep the vibrations of a dancing sub from being transferred to the floor, but it won't make the cab move less; in fact, it would allow it to move more. This is where a more rigid coupling to the floor works better. Things move about because the acoustic output of the sub causes the walls, floor and ceiling and large objects, like doors and windows, to vibrate. Smaller objects on or attached to those surfaces will then also vibrate. If you want to stop them from rattling either isolate them or secure them. It doesn't matter what the floor is made of, the walls and ceiling and other large surfaces will still vibrate. Even if the floor is soft it doesn't transmit low frequency vibrations to the walls. The maximum deflection of a floor will occur where it's softest, right smack in the middle. The strongest part of the floor, where it will not vibrate, is where it connects to the walls. Try hitting a drum some time, preferably a floor tom. The sound heard when you hit the head in the middle is totally different than that when you hit it near the edge.

Well, my HT is on hardwood floors in a second floor room. And I noticed that objects in the room stopped rattling as much (windows, doors) when I added Subdudes under my two SVS PB-13s.

However, I haven't drunk Kool-Aid since I was a kid and considering the fact that I have a Macbook loaded with the Beta REW and two new USB microphones, as soon as I get my room in decent order I'll do some A/B testing and find out for sure if my acoustics are improved with use of the Subdude. I'd prefer to have the subs directly on the floor as they are certainly prettier that way. However, I suspect that the room rattles minus the Subdudes are going to show up on the REW curves.

I think I'd need at least 2 layers of that to equal the Subdude. My existing carpet and pad is thicker than that Home Depot stuff, and not as effective. And I can actually SEE that the Subdude works - the vibration causing the picture on my screen to move at times is greatly reduced. That and additional bracing of my projector mount finally stopped the picture from vibrating.

As always, YMMV.

Craig,

 

As you have seen the (Obvious) benefit so have I.

 

And I know for a fact they greatly helped in stopping the vibrations in my HT.

 

No more dishes in the kitchen cabinets vibrating and rattling.

Door vibrating etc.

 

They are well worth the little they cost compared to the investment of a high end Home Theater.

 

Terry

If the foam allows the cab to move more, does that mean lower SPLs and help explain users' experience in reducing vibrating objects?

I suppose that's not impossible. But I doubt it. As is the case with claimed differences in the sound with everything from different cables to Magic Pebbles testimonials are never backed up by any real evidence. It's kind of like watching episodes of Ghost Hunters. If something really is happening it can be measured and identified. When I see those measured results and I can duplicate them I'll believe. But not before.

The metal spike feet on my L & R mains tended to send vibrations into my subfloor. My theater is in a bonus room built over a 2 car garage. My down firing cylinder sub did the same.

Anyway, the Subdudes look nice, and all 3 cost about what my projector mount cost ( and a tiny fraction of the cost of the projector itself ), so in the scheme of things, they are working for me in my setup.

Craig,

 

Makes perfect sense to me what you say.

 

My HT is the same way as I think yours is.

 

It is actually what is referred to as the Bonus room over the 2 1/2 car garage below.

 

Of course the room itself has been changed into the custom HT it is now.

 

And like you the floor is wood over the garage so the Auralex Pads in both our situations do what they are intended to.

 

Cost honestly is so little I cannot imagine all the on going conversation over their cost.

 

And I can't really get a grip on the fellow here that owns an Audio/Video Store and just completely dislikes the Auralex products.

Because he cannot (Scientifically) prove they are of any (Benefit).

 

Honestly if I was a customer and the A/V Dealer I was working with had that same attitude and I wanted to use those Auralex Pads.

I would not get into some lengthy discussion I would simply go and do Business where the A/V Dealer would be more (Flexible) and provide me with what I (Request).

If he or she believed in that product or not.

To me that is foolish and chasing away a customer because the owner does not believe in the product.

 

I should mention I was in Sales for way over Plus 20-Years and I can tell you I (Listened) to my customers.

If they wanted something I kept my (Personal-Opinions) to myself once I heard what they wanted.

Especially if they did not ask me my opinion.

Or if they did ask my (Opinion) and I stated it I still would tell them this.

(If that is your preference I would be tickled to get that for you and also if you like get it installed)

 

Terry

Edited by tigerhonaker - 2/12/13 at 1:25pm

A question for the gurus here . . .

My HT system is in the basement of my home. The flooring is carpet, with underlay, over concrete. Any point in using a GRAMMA or Subdude under my subwoofer? There is a gas firepace in the same room and it rattles quite a bit when the sub is really working. Just wondering if a GRAMMA or Subdude (or similar DIY solution) might help this.

None. No sub is going to cause a concrete floor to vibrate. The only thing that might work is to find which parts are vibrating and somehow tighten them up. The best way to find the rattling parts is to download a sine wave generator program to your PC (google it, there are a few and they're free), play it through the system and sweep the frequency until the rattling begins. There very well could be more than one resonant frequency.

Thanks very much for the advice!

While I absolutely agree with you from the acoustics point of view, I bought a Great Gramma for my sub and two Subdudes for my fronts exactly because they lift the speakers 2.5-3" off the floor and protect them from the vicious attacks of my Roomba.