Understanding low-frequency reproduction....room or speaker

First of all you need to look at the way speakers need to be supported correctly on the floor or if they are on stands.

Never spike a speaker (floor stander)or (stand mount) into a suspended floor, as you only make that floor a sound board for the low frequencies, and that will muddy up or ruin your bass. The speaker need to isolated from a suspended floor.

The only times a speaker (floor stander or stand mount) should be spiked into the floor, is if that floor is a cement slab, and not be able to act like a sound board. Start with this first, then positioning.

Cheers George  

I can think of two things that may cause your wife's trinkets to shake in response to the low frequencies output by your speakers  

The first is room gain or boundary reinforcement as mentioned by "nonoise" ... below your room's transition point (Schroder frequency) the wave lengths of the frequencies' below the transition point will no longer fit within the room's dimension and these frequencies below the transition point will pressurize the room ... unfortunately this pressurization is not even through out the room with the four corners and the mid point of all walls having higher pressure than the rest of the room   

If your wife's trinkets are placed in or on a corner Hutch and placed in the corner of the room they will be experiencing higher pressures due to the wall's reinforcing and boosting of those low frequencies in the corners  ... this excessive build up in the corners during low frequencies passages may be just enough to shake the trinkets and is also the reason why you place your Resistive Bass Traps in the corners of the room to reduce the extra energy created by the corner walls  

Also you room no matter what the dimensions are will have higher pressurization at the mid points of all the walls including the ceiling and floor ... if your wife has her trinkets placed on a free standing book case and that book case is placed right at the mid point of the front/back or side walls they will also experience higher pressurization like in the corners and this can be the cause of the shaking during low frequency passages 

Placement of trinkets on a free standing book case or hutch which is placed at the mid point of any wall or in the corner may experience enough pressure from the wall's boundary reinforcement to cause them to shake when low frequencies below the room's transition point are present   

But I don't think that is what is causing your problems 

One of the biggest misconception in audio is that the speakers can produce enough vibrational energy that the cabinet's coupled to the floor can cause the walls ceiling and floors to vibrate 

If the speaker had that much energy to shake the room violently they would probably come apart at the seams and the stuffing would fall out into the room  

Here's the second reason I believe your wife's trinkets are being shook 

Your wall are excited and vibrate in sympathy with your speaker's low frequency response when the speaker produces a frequency that is equal to your wall's Primary Resonate Frequency 

Based on the length of the dimensions of the room each wall (length .. width .. and height )  has a primary resonate frequency dictated by it's actual length that will cause the wall to vibrate when that frequency is excited by the speakers low frequency response  

You can calculate this P/Resonate Frequency mode by dividing 562 ( the speed of sound divided by 2) by the walls length  

In your case 562/16 Width  = 35.125HZ's ... for the room's length 562/17 Length = 33.05HZ's  and for the 8 ft ceiling height (I'm guessing) it would be 562/8 Height or 70.25HZs  

When ever your speakers reproduce one of these low frequencies ... 33HZ .. 35HZ or 70HZ ... the wall whose primary resonate frequency (based on it's length) is close or a match to that frequency being produced by the speaker will vibrate in sympathy with the speaker which is pressurizing the room again below the rooms transition point 

You should be able to see that when your speakers produce these low frequencies that match the wall's Primary Resonate Frequencies' based on it's length  ... the wall or walls will vibrate violently shaking anything attached to them such as a shelf with trinkets on it or pictures hung on the wall or recessed lighting fixtures along with any Deer Head or Fish trophies attached to the wall  

Speaker produces low frequency that excites wall ... wall shakes in sympathy to speaker exciting it at it's P/R/Frequency and wife's trinkets on shelf attached to wall shake 

Also take  note  that because your room's dimension are very close (16x17) that the room's P/R/F points are very close also and will reinforce each other causing additional boost or gain  

You will also get additional reinforcement because your 8 foot ceiling height is a direct multiple of your 16 foot wall dimension in a 2 to 1 ratio ... Happy Birthday  

Most Home Theater low frequency punch is around 30 to 35HZ and seldom goes into the mid or low 20's .... this punch or slam is right at your room's dimensions (16x17) Primary Resonate Frequency excitation point ... so I feel the low frequency content in the 30 to 40HZ range is exciting your walls and shaking the wife's trinkets  

An easy way to check this out is to run a test disk ( like any of the Stereophile test disks)  with 1/3 octaves from 200HZ down  

As the 1/3 octaves play down to the lower frequencies the bass tones will be clear and distinct ... when you hit the octave on the test disk that matches your wall's Primary Resonate Frequency point ...   the walls and room will shake violently and it will be clearly audible ... once the test tones are out of the range that excites the wall ... the bass test tones will become clear and distinct again  

I'm just guessing by your room's dimension that your walls will vibrate audibly between 30 and 40HZ and also around 70 or 80HZ

bcgator ...  you got it ... walls by their dimensions have a natural P/R/Freq, ... when your speaker produces this frequency the wall will resonate and vibrate in sympathy with the speaker

This is very hard to cure as it is based on your rooms dimensions that you can't  change ... you're more or less stuck with the walls vibrating at their P/R/Freq point

If there is any solace in this ... at least you know exactly what the problem is ... where it is occurring  and what is causing it ... this way you are not making yourself crazy trying to figure it out

The other issue not related to the walls vibrating is the peaks and nulls created by the rooms dimensions which can be very easily to deal with

Peaks and Nulls can effect the sound dramatically and need to be measured

If you can try the Test CD test of listening from 200hz down to 20hz ... you should clearly hear the walls vibrating when you hit the right frequencies    

maplegrovemusic

How does one isolate the speakers from a "suspended" floor ? Thought that’s what the spikes are for .

Many get this confused, spikes couple the speaker or stand to the floor, this is fine for cement slab floors, and the best. 

But with any suspended floor the speaker or stand should be de-coupled from it to get the best bass response, as the manufacturer would have voiced it. As they would have been crazy to voice it spiked into a suspended floor acting as a sound board to any bass notes from the speaker.

To de-couple from a suspended floor you need to use an isolating puck or device like a sorbothane filled disc. Like these which you can still use your spikes with 

"Cone/Spike Decoupling Glider"  that are half way down the page.

http://herbiesaudiolab.net/spkrfeet.htm

Or you can substitute your spikes for these "Threaded Stud Glider " a bit further down the page. 

Cheers George

bcgator 

davehrab, I want to clarify something - and I think George had the same idea - the bass response I’m getting, and the resonance, is absolutely not a problem.  It’s not something I’m trying to cure, or eliminate.  

 I think you probably lucked out with a room standing wave problem that just happens to be just below the natural roll off of that 6.9" bass driver, giving you another octave lower perceived bass. Shh it’s free don’t tell anyone, and whatever you do don't move the speakers or you may loose it.

Cheers George