Spiked my speakers... and didn’t like

WLDock wrote: »

Whats interesting in the audio production / recording world, you see speaker decoupling / isolation more so than and coupling used.

Isolation/decoupling makes sense in a room with multiple pairs of speakers. I can see where having two or more pairs of speakers acoustically grounded to the same plane could cause some coloration issues, even if only one pair of speakers is active at a time.

DSkip wrote: »

Please explain to me exactly how a spike decouples. I’m not picking a fight here.

Spikes create pathways for energy to travel. This in effect is a coupling mechanism.

The small surface area of a spike is intended to not allow floor vibrations to creep up into the speaker, and they also serve to minimize speaker vibrations being transferred to the floor... John is correct.

Think of it this way...you could either set the speaker on the floor and have the entire surface area of the bottom of the speaker transferring (and receiving) vibration; OR, you could remove 99% of that "vibrating" surface area by channeling it via 4 tiny spike tips.

You all can debate the semantics of "coupling" and "de-coupling." I have found that "soft" floors (sub-floors) sound best "spiked" while hard subfloor (concrete/tile) sound best with "soft" isolation; ie, rubber feet.

steveinaz wrote: »

The small surface area of a spike is intended to not allow floor vibrations to creep up into the speaker, and they also serve to minimize speaker vibrations being transferred to the floor... John is correct.

Think of it this way...you could either set the speaker on the floor and have the entire surface area of the bottom of the speaker transferring (and receiving) vibration; OR, you could remove 99% of that "vibrating" surface area by channeling it via 4 tiny spike tips.

"The basis of this idea seems to be that if the contact area was zero (i.e. no contact at all!) then no solid vibrations could pass. Hence if we make the contact area tiny, this approaches zero, so should only allow a small amount of vibration through. Unfortunately, although plausible, this idea may simply be incorrect.

We can understand how the above idea might be wrong by considering another example of the use of “spikes” – a running shoe. Here the purpose is to increase the grip between two objects (shoe and ground) and hence transmit forces more efficiently. This example instantly shows that a cone or spike might not reduce the amount of actual force transmission, but actually help ensure effective transmission. Hence spikes and cones – far from “isolating” – might sometimes give a more effective link for vibrations to pass though."

The spikes "couple" the speaker to the floor, however they de-couple the speaker from floor-borne vibration. That's why I don't like those terms. I think isolation is a better way to categorize spike vs rubber feet; or what I call hard or soft isolation.

RobbyKY wrote: »

I know Polk included the "Bass Brace" threaded attachment point on the rear of these but always though it was just a cover story to prevent liability claims if they tipped over on a child.

I don't think it had anything to do with accident liability. If so, they would have made it a safety requirement or safety recommendation. Tall, relatively shallow depth speakers with high bass output can't help but wobble a bit back and forth due to the push back from the drivers. Bracing to a drywall wall damps the wobble considerably. Bracing to a masonry wall (which is what Polk recommended) stops the wobble.

RobbyKY wrote: »

Have you compared spiked vs braced results during any of your past experiments?

I did listening tests and room response measurements between regular feet, braced and non-braced, here:

https://forum.polkaudio.com/discussion/123136/sda-driver-seals-original-foam-vs-mortite-vs-armaflex-foam/p2

I have done listening tests between spiked and non-spiked, but I didn't do any measurements. Spiked was better than non-spiked. Braced was better than non-braced.

RobbyKY wrote: »

Spiked and braced?

I don't recall trying spiked in combination with braced. The SRS manuals state one or the other is sufficient.

RobbyKY wrote: »

I know many theories float around concerning how far off the back wall these should be for peak performance and found it does make a slight difference to the sound stage I get on one of my set-ups. Just curious how far offset you're running yours?

My 1.2TLs are 11.5" from the rear wall.

@Toolfan66

What kind of floor?

I was told by Matt or Stu or Al (don't remember) that the bass brace was conceived as a way to prevent the speakers from falling in an earthquake, read California. During the development Polk discovered it helped with the bass response. The manual states to use the brace or the spikes, but not both. I found while using the brace I could wiggle the speakers on my hardwood floor, which seemed counterproductive, so I went back to the spikes.

I see no reason why you can’t use both, spikes made a world of difference in sound from every angle, adding the brace didn’t affect it at all, if it did it’s not audible to my ears, and like I said I like how solid they feel with the brace, keep in mind I have added about 40-50lbs of weight to each speaker as well, they are solid and heavy..

From the above linked article.

"At first appearance, it seems plausible that cones under a loudspeaker should reduce the amount of sound energy transmitted between speaker and stand because they reduce the area of contact between the speaker and the stand. In the same way, we might expect spikes at the base of the stand to provide isolation. The basis of this idea seems to be that if the contact area was zero (i.e. no contact at all!) then no solid vibrations could pass. Hence if we make the contact area tiny, this approaches zero, so should only allow a small amount of vibration through. Unfortunately, although plausible, this idea may simply be incorrect."





It is faulty logic to think if you reduce the contact area you reduce the amount of transmitted energy. What they don't understand is that as you reduce the amount of contact area the force pushing down on the contact points increase exponentially. Think of it this way. A 50 pound speaker on a 10x10 inch base (100 cubic inches) is only applying 0.5 psi pressure to the floor. Now if you put spikes on you reduce the contact area to a very small size. Depending on how sharp the spikes are you could be coupling to the floor with hundreds of pounds per square inch.

You can demonstrate this for yourself. Stick your little toe under a speaker without spikes. Then put the spikes on and stick your little toe under a spike. Trust me, you will feel a difference. Then have an assistant start playing music with a lot of bass. I bet you feel plenty of vibrations.

delkal wrote: »

You can demonstrate this for yourself. Stick your little toe under a speaker without spikes. Then put the spikes on and stick your little toe under a spike. Trust me, you will feel a difference. Then have an assistant start playing music with a lot of bass. I bet you feel plenty of vibrations.

Bondage in the stereo room?

audioluvr wrote: »

If you're married, you pay for sex every day....

No married man is having sex every day.

HzTweaker wrote: »

delkal wrote: »

You can demonstrate this for yourself. Stick your little toe under a speaker without spikes. Then put the spikes on and stick your little toe under a spike. Trust me, you will feel a difference. Then have an assistant start playing music with a lot of bass. I bet you feel plenty of vibrations.

Bondage in the stereo room?