Mark Audio CHR-70 Application Thread

[Nanook]

or ya could always set up a threaded insert on the back (from the inside), and use a suitable length bolt to couple the back of the driver to the back of the box. Just don't over-tighten
preiter: nice looking boxes (and not a bad table either).

[italynstylion]

^That's a wonderful idea. Might look a little funny though.

[Nanook]

...of "Room tunes" fame?

essentially he did the same thing using knock-down furniture connectors, and tightening or lossening them. The furniture connectors connected the opposite sides of the enclosue, thus a "tunable" speaker.

[MJK]

Originally Posted by Nanook

or ya could always set up a threaded insert on the back (from the inside), and use a suitable length bolt to couple the back of the driver to the back of the box. Just don't over-tighten.

I had somebody come to my house once with a speaker that had a nice brass bolt through the rear wall pressing on the back of the driver's magnet. It was a really solid heavy duty cabinet with an 8" full range driver. Unfortunately when I ran some sweeps to measure the electrical impedance, it became clear that the bolt and the back of the driver were "rattling". You could not get enough linear compression between all of the stiff parts to keep everything in contact. Any small motion of the driver's magnet unloaded the bolt and caused a loss of contact. The impedance plot was very hashy, back off on the bolt so it was not touching and it cleared up. I am not convinced that this is a good idea.

[Andrewbee]

Whenever I use the bolt through the cab method I cut a wooden "disc" which is placed between the bolt and the magnet. A small hole holds the end of the bolt and the the disc provides extra support area on the back of the magnet.


Andrew

[markaudio]

Originally Posted by Nanook

or ya could always set up a threaded insert on the back (from the inside), and use a suitable length bolt to couple the back of the driver to the back of the box. Just don't over-tighten
preiter: nice looking boxes (and not a bad table either).

Hi Guys,
This particular idea has just been brought to my attention. Please note the following:

NONE of the Markaudio drivers are designed to take a positive stress load on the rear of the chassis, in particular the motor assembly (back-plate).

This practice needs to be VERY carefully controlled to avoid the risk of distorting the driver. This practice could result in the driver's power-train being pushed out of alignment if you get it wrong.

Cheers

Mark.

[planet10]

Originally Posted by markaudio

This practice needs to be VERY carefully controlled to avoid the risk of distorting the driver. This practice could result in the driver's power-train being pushed out of alignment if you get it wrong

Actuallty this is also true, althou perhaps not as dramatic, with pressed steel baskets & even cast baskets. You do not want to stress the basket.

A bolt also concentates the force, Andrews suggestion of a force spreader is a good one. I'll stick to holey driver braces thou.

dave

[Ian444]

I cut up thin cardboard shims from a manilla folder and glue them against the brace with PVA, each shim is around ten thou (0.25mm), usually I need 1 or 2 or 3. Then mount the speaker while the glue is wet, making sure there is no glue between the back of the speaker and the last shim. Seems to work well. With 10 thou at a time, you can get it just right.

Ian.

[planet10]

That is essentially the technique i use when a holey brace is a little shy (not often) except i'll just use a glue stick.

dave

[Peter Menting]

When I built my Alpair 10 OB's, I Glued a 1" thick Oak "Puck' to the rear of each driver, with a threaded insert at its center and used this to "Magnet Mount" the drivers. It would be easy to bring a threaded rod out of the puck with a locknut, two fender washers and a spring and "load' it against a brace such as the ones that dave uses!

Just a thought.
Pete