mounting a woofer by the magnet

I hope to get some feedback from some of the guys who having been building for a while. There is an article at the linkwitz.com website about how to mount a speaker. It is probably most common that a speaker is mounted to the baffle board in the traditional method using the bolts or screws outside the suspension. It seems that woofers and some midrange units that have a stamped steel basket are subject to some output losses due to some vibrations and or resonances in the basket itself. However, if the driver is mounted by the magnet inside the cabinet these losses and be almost eliminated.

My concern is that the wooden frame that holds the speaker by the magnet might hinder the sound waves coming from the rear of the cone and thus reduce the efficiency of the bass reflex design, ( or TL design for that matter ), resulting in less output.

Has anyone used this method of mounting the woofer at the magnet? And if so, do you really hear a positive sonic difference?

And what about woofers and midranges that have a cast aluminum frame? Perhaps they might also be better sounding if mounted at the magnet ?

Thank you. :)
 
A couple of opinions:

The speaker parameters that are published are most certainly derived from a test unit with a conventional mounting, you may need access to acoustic tools to confirm you haven't messed up the desired results.

The outer ring of the woofer must be connected by an air tight means to the front baffle thereby complicating your suggestion.

If you mount by way of the magnet structure IMHO the mountng should not protrude past the outside diameter of that structure. Cone drivers radiate pretty much identical signals off the front and back of the cones. You do not want the rear wave to bounce off the magnet mounting device and flow forward through the pretty acoustically transparent cone material to the listener. It will be time smeared and not all frequencies will reflect the same.

Other than that, most agree that greater woofer mounting stiffness has positive acoustic results.
 
First I want to correct an error, the website is linkwitzlab.com. There are some impressive graphs to back up the subject of the article, "how to mount a speaker".

Another idea was mentioned to me just recently. It is to have a "compression pole" mounted between the rear of the magnet and the back of the cabinet. I would assume that the pole would
attach to the center of the magnet and run straight back to the rear of the cabinet , where it would attach to a support that is already being used to hold the back panel more firmly in place. This too would help to reduce any resonance or vibrations because of the flex of the speaker basket.

If the magnet has a vented pole piece, then the compression pole could be drilled out so that it is hollow. This long, small diameter void could be stuffed with a dampening material to absorb the vibrations coming thru it from under the voice coil dust cap.

In any event, the compression pole and the magnet mounting frame could both be coated with a sound absorbtion material to reduce sound reflections that could hinder performance.

Also, I think that there could be a way to clamp the magnet mounting brace from the outside of the cabinet using long bolts.
This way, the speaker could first be clamped down using the standard screws or bolts located outside the suspension in the traditional method. And then the magnet clamp to secure the speaker internally could be tightened up with a socket wrench or cresant wrench.

It just seems to make sense that, if there are more attachment locations to secure the woofer in place solidly, that it will make for a more efficient set up, as long as the internal magnet mounting brace does not hinder any sound waves coming off the rear of the cone.

Comments ? Suggestions ? Ideas ?
 
it makes sense

Well I think its time to try it.
It makes alot of sense I have been thinking about using shims and glue and wedge the magnet against a crossbrace.
another way of doing it would be to use 9/16 inch bolts and Tnuts and have an expanding pole squeezing up against the magnet....
I guess its such a hassle that only freaks like us even consider it.
 

mac

Member
2003-05-26 1:49 am
Seattle
I recently used Linkwitz' Phoenix style mounting for my dipole mid woofers.

Although I didn't conduct any measurements to verify improved performance, I can subjectively tell that there is less energy being transmitted into the baffle.

Btw, This is SL's article on alternative baffle mounting: http://www.linkwitzlab.com/frontiers_2.htm#N.

[IMGDEAD]http://cornucopia.sytes.net/~mike/projects/ono/P3120354sm.JPG[/IMGDEAD]
 
You might want to take a look at my implementation, it works quite well (the speaker is NOT under compression, unlike the Phoenix).

http://www.htguide.com/forum/showpost.php4?p=133401&postcount=17

Mac, where did you source that profile that you use on the back of your drivers? A very clean and minimal implementation.

Ron
 

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Those are some nice cabinets ! You have creative minds to come
up with various methods of securing the woofers.

I have a question for transducer. Those are real nice woofers you have mounted in the cabinet. The magnets are quite large, but what interests me more is the cones. Do those woofers have metal cones ? What are the cones made out of ? What is the diameter ? Do you have thiel specs on them? And are they available to the general public?

I am quite interested in metal cone woofers and hope to gather more info as time permits.

Thanks
 
barth2102 said:


I have a question for transducer. Those are real nice woofers you have mounted in the cabinet. The magnets are quite large, but what interests me more is the cones. Do those woofers have metal cones ? What are the cones made out of ? What is the diameter ? Do you have thiel specs on them? And are they available to the general public?


Thanks

The woofers are HiVi M8A, 8" aluminium/magnesium cones. I don't have the t/s specs handy. I bought them from Solen in Quebec, but I believe that Parts Express also carries them.

Ron
 

sqlkev

Member
2004-03-24 7:43 am
714
mac said:
I recently used Linkwitz' Phoenix style mounting for my dipole mid woofers.

Although I didn't conduct any measurements to verify improved performance, I can subjectively tell that there is less energy being transmitted into the baffle.

Btw, This is SL's article on alternative baffle mounting: http://www.linkwitzlab.com/frontiers_2.htm#N.

[IMGDEAD]http://cornucopia.sytes.net/~mike/projects/ono/P3120354sm.JPG[/IMGDEAD]


Mac,
Can you tell me what type of material you used to sandwich between the woofers and the steel rib?
How did you attach that foamy part to where it is?

I'm still puzzled as to how the steel bar from behind can hold up the 2 woofers. I would imagine that if it's 1mm or 2mm off, there would be at least some buzzing.
 

mrsteve

Member
2005-08-03 7:37 pm
Magnet Mount

I used Mr. Linkwitz' Orion mid-driver mounting modification as my model, as his Phoenix mid-driver mounting scheme seems to present too much reflective surface for the backwave to interact with.

My mount consists of a thick "hockey puck" that's the same diameter as the O.D. of the magnet.
The MDF "puck" is secured to the magnet with PVC construction adhesive...and is also held in place with a press-fittted sleeve I laid up in glassfibre set in polyester resin.
So, in my case, the backwave "sees" only a sixteenth of an inch of extra material, the fibreglass sleeve, and the shelf bracket I bolted to the MDF puck.

The midwoof is, of course, sitting on a foam-tape (weatherseal) gasket.

In other words, my solution is almost exactly like Mr. Linkwitz' solution...only a bit different...and -ahem- a bit more secure.

No, I DON'T have a camera, sorry. More money for speaker projects!
;)