Speaker Spike Help

BDR Cones are exact size you need and outstanding. They are flat on top and tapped for 1/4-20 threads commonly used on a lot of speakers. If the speaker is heavy enough then its weight alone will hold things in place and in that case you could use 3 per speaker. Although 4 threaded is better. Also they work great by themselves, but even better with BDR Round Things under them. On carpet or whatever, does not matter. 

Thank you very much, @millercarbon  I will look them up and follow up with you, should I have questions.

I should have made note of this: My speakers are bottom ported and by design, there is a gap (from the floor) front to rear AND a rising angle / tilt rear to front.

I’d like (prefer) to maintain the designer’s height and angle for the speaker. Therefore, spike height, spike diameter, and contact point are all important considerations.

Also, maximum thread size is 1/4-20. Less is better. Metric equivalents will work.

Using @millercarbon 's BDR cone recommendation as an example...

They measure 1 inch high. My max is 7/8th of an inch.

They measure 1.62 inches wide. My max is 1 inch.

@david_ten .
I am a little confused by your post.

B. What do you recommend for securely attaching a flat top spike (the Hemi-Spike has a 1 inch / ~25 mm diameter) to the speaker cabinet bottom?

Do you mean there are no threads at the bottom of the speaker?
B

They measure 1.62 inches wide. My max is 1 inch.

Remember they don't have to go the same place. They can be used anywhere flat so long as they are far enough apart to maintain stability.

Also as far as height goes there are tables you can look up on-line for free to study the effect of port size/length/diameter. Basically what happens is raising the speaker higher reduces restriction of air through the port, which has the same effect as increasing the length or decreasing the diameter of the port. Play around with a calculator you will see real quick what this means. Sitting the speaker flat on the floor will effectively plug the port and make your speaker into a sealed design. The high mid-bass output and fast low bass roll off of the port will become the flat mid-bass output and more gradual low bass roll off of a sealed cab.

If you do this it will in no time be clear that unless you go way high or way low whatever difference you make will be at most about the same as what already changes anyway just with normal speaker placement moves, and probably a good deal less. 

@gdnrbob  My apologies. Hopefully this post will clarify. If it doesn't, let me know.

The front of the speakers have M6 inserts and come with stock spikes and floor protectors.  The rear of the speaker has two 'rubber bumpers' with metal cores, attached via a phillips screw. 

To attach a 'standard' spike with threads (For The REAR), I will need to drill two insert holes and install the threaded inserts. 

Due to the finish of the cabinet, I'll need to use a special bit as well as be very careful so I don't damage the finish. Further, there isn't much room for error in terms of the surface and width and material available for drilling / to drill through. Obviously, I will need to also be careful with the 'hole' angle and the need to match both.

I went with a flat / smooth top for the rear 'spike' to avoid the above. Not ideal, but if it gets me most of the way there... :)

Luckily, the front is setup for easy swapping of spikes, etc.

Can you use a 1" aluminum bar mount across the rear end of your speaker using the existing phillips screw holes and put those spikes as outriggers?  

https://elac-content.s3.amazonaws.com/uploads/2016/01/Uni-Fi-Foot-Web.1349-1500x712.jpg

@imhififan  Your suggestion is an option I have not considered. It is an excellent solution. Thank you!!! 

@imhififan ,
Nice suggestion, but I would be a little concerned if the OP's speakers are very heavy(-he/she doesn't mention the model). Using a screw hole to support a heavy object might damage the wood if it encounters any twist or uneven load. That was the reason I was asking if there were threaded inserts.
Seeing how there are holes for the phillips screws, I would just enlarge them and install some threaded inserts, if there is sufficient material available. Gluing those into the cabinet should provide a better fastening option whether he decides to use a threaded spike or add the aluminum bar you suggested.
https://www.amazon.com/Bolt-Dropper-Pronged-Climbing-Cabinetry/dp/B01MSVU3WF?ref_=Oct_BSellerC_16410701_0&pf_rd_p=0b9c089c-afaa-565c-9502-215de3390c99&pf_rd_s=merchandised-search-6&pf_rd_t=101&pf_rd_i=16410701&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=CAHQ159A1TFF70MHGXX3&pf_rd_r=CAHQ159A1TFF70MHGXX3&pf_rd_p=0b9c089c-afaa-565c-9502-215de3390c99

Bob

@gdnrbob  Good point. Speakers weigh 88 pounds (40kg) each.

@gdnrbob
Yes, if the speakers phillips screws size less than 6mm and without threaded inserts, your recommendation is much better.   
BTW, if using a aluminum bar, lower profile spike will be needed.