Pro's and con's of suspended speakers

[spikey1973]

Hey guys,

i come here to filosophy about the pro's and con's a speakers suspended..
I'm a BsC in photonics from origin but in ative for quite a few years now (different study direction) and most knowledge is degraded..

At his moment I'm building a high end speaker.., the lx mini designed by some one called linkwitz..
as the design is rather functional i am trying to redesign it a little but without degrading the quality of the sound.

one of the eye sore's is the base. so while thinking about a way to redesign that i quickly bumped into the fact that any speaker standing on a floor is not such a good idea as the floor will start acting as a sound board (one floor more than another) so many solve this problem by increasing the weigh of the speakers and making this encrease weight stand on spikes so there will be more energy needed to get that setup to translate its fibration to the floor (sorry if i don't use the right terms, but i prosume you will get the gist)

in the mean time i found the new 'invention' of bluetooth speakers being suspended on a magnetic field.

so i started to think about this suspension and if this would be benefitial of sacraficial sound quality wise.
this is the basic design.

and the following are my thoughts.. please add or contradict where anyone thinks i might be going wrong.
1) i want to suspend it on 6 O-ring like rubber bands around and at the hight of the "rubber coupler" which sits on top of the white pvc pipe and which is the base of mounting the bass driver. this would place it well above center point of gravity.
2) the bass driver is mounted on a closed tube, so a closed system below the membrane. so this would mean it can only transfer approx. 1/2 of it's energy to the air outside the tube. 'causing a vibration in an axial direction to the bass tube.
3) the full-range driver's tube is open.. so the energy on both sides of the membrane can be translate to the surroundings. this would give a rotational movement around the axis is the suspension plane.
and his is what concerns me the most.

the movement will deminish the sound waves amplitude a little which can be caught-up by the amplifier probably without being noticed.

but the axial movent will create a small doppler effect, changeing the sound. on the other hand. the energy is so small and the speaker itself has an inertia that has to be over won that by the time it moves to the signal the signal has changed. shifting the effect of the doppler over the sound waves. losing it's correlation.

so my main thought about this is, will this theoretically alter the signal.. or not.. and ifso.. is there a design alteration one might think of the stop or counteract this.

i know that experimenting with a standard sine wave would be my best option but in practice that is not an option for me. so i want to think things as well as i can over before i start..

kind regards

Matthieu

ps: oh yeah.. the natural frequency of the suspension should be below 20 Hz. no clue how to make sure of this but this.. this needs to be the case.

 

[rcgldr]

2) the bass driver is mounted on a closed tube, so a closed system below the membrane. so this would mean it can only transfer approx. 1/2 of it's energy to the air outside the tube. 'causing a vibration in an axial direction to the bass tube.

Most of the high end studio monitors woofers I'm aware of are acoustic suspension (sealed from behind) for a tight bass. Ported systems tend to muddy the base unless tuned electronic dampening is used (I'm not sure how these circuits are "tuned"). The draw back of a sealed system is the base cone needs to be stronger to handle the higher loads required to generate sound when it's sealed from behind, and they need more power. The end result is a cleaner and tighter base.

In the case of your tube mounted speakers, the tubes could be sealed with acoustic dampening material just below the speaker, but I don't know if the speaker cone will be strong enough to handle the loading related to a sealed system.

 

[spikey1973]

hey rc gldr.

to start.. thank you for your response!

The bass tube system is a closed system, and is properly designed by mr. linkwitz so I'm not even thinking about changing any on this. Indeed they are acoustically sealed with dampening material and also closed up (beside a little hole to aleviate changes in atmospheric pressure. )

the only reason i wrote this down is to explain the situation.. which might have or might not have an influence on the systems behavior when suspended.

which is the real question. how will the systems behavier changes when suspended vs normal situation when it's placed on a foot.

sorry if i wasn't clear about this.

 

[rcgldr]

I'm wondering how much acoustic (base) isolation is already being accomplished by those pvc pipes and the black bases at the bottom of those pvc pipes? Since the base speakers are oriented upward and at a significant distance from the floor, then vertical motion transmitted as sound into the floor would involve the entire column and base vibrating, despite the inertia and whatever dampening the bases on the floor provide. If the floor is the concern, then doing something at the base might be a better approach.

I'm also wondering about the effect of the sound reflected off the wall behind the upper drivers if those are truly open pipes; seems that could result in phase interference. There's no full or partial seal behind those upper speakers?

 

[spikey1973]

I'm wondering how much acoustic (base) isolation is already being accomplished by those pvc pipes and the black bases at the bottom of those pvc pipes? Since the base speakers are oriented upward and at a significant distance from the floor, then vertical motion transmitted as sound into the floor would involve the entire column and base vibrating, despite the inertia and whatever dampening the bases on the floor provide. If the floor is the concern, then doing something at the base might be a better approach.

I'm also wondering about the effect of the sound reflected off the wall behind the upper drivers if those are truly open pipes; seems that could result in phase interference. There's no full or partial seal behind those upper speakers?

yeah well, both of that has been and still is in consideration.. and again is beside the question.

the suspension issue is ONE of the options into doing something about the base.. other options are also taken in consideration. which have been shortly mentioned. 1) spikes, 2) rubber / magnetic feet.. which is similar concept to suspension in at a higher level.

the full range tube will be filled with accoustic dampening fibres.

if you are interested in the design... please visit the linkwitz site and read all about it. Also there is a DSP and several amplifiers involved. but besides that and for now considere the current design to be functionally near perfection.

only the issue of the suspension yes or no is the question.

kind greatings

Matthieu

 

[rcgldr]

So the potential issue with the O ring suspension at the top is that the entire speaker sub-frame and/or sub-frame components will oscillate vertically at their own natural frequencies, generating fixed tones. Rubber O rings would act more like springs than dampers. I suspect this is why the sub-frame is clamped to the pvc pipes, which in turn are clamped to the base, to prevent vertical oscillation of the sub-frame, or to make the frequency below that which can be heard.