Granite Baffles ?

[ronzeman]

Here is my new Morel 1308 Midrange driver in their baffle. The tweeter is a Dynaudio D28-2. These are part of my recent upgrade - update project to my 33 year old Audionics (radford) TL90 speakers.
(No it's not real granite....just corian)

[J.R.Freeman]

Looks nice!

[alan-1-b]

Whether Granite or Corian, so long as it does the job it is fine.
It certainly looks good !
Is Corian difficult to cut, etc ... ?

And that new Morel mid-dome,
it has good Specifications, thus what about it do you particually like ?

I've not tried it, but may if I can get time to design a 3-way.

I hope your TL90 upgrade is sounding as good as you hoped,
or at least on the way to ...

[ronzeman]

Corian is very dense and works easily. I believe the material is well suited for baffle construction..and it comes in a large variety of colors and finishes. I had the "rough" shape cut by a local counter fabricator who has the skills and tools I lack. Simple drum sanding and mounting hole drilling was all I needed to make a very good fit. My one "mistake" was to not have them mirrored...no big deal.

RE: Morel EM1308 Midrange drivers. I bought them on specs and on reputation...and thus far I am not disappointed. The Radford woofer crosses around 500Hz so the extended low freq capability of this dome mid was a good fit. The sound quality is very good. Smooth and effortless. I'm sometimes hearing new musical nuances from my "old" source materials. Please understand that I have been able to listen for less than 2 hours so far...but my initial impressions are very favorable towards the new drivers. They are a keeper.

[R-Carpenter]

Have you by any chance measured that particular piece of corian for resonance and reflectance? If so where and how it resonates?
Thanks, Roman.

[ronzeman]

I don't have the test equipment that would enable such resonance testing at this point. As my rebuild reaches completion I hope to get some folks from the regional audio society to do a few frequency sweeps of the system and fine tune from there.

(Meanwhile...your tas de bois furniture company looks like it could assemble some fantastic looking speaker cabinets ! Nice Work!)

[R-Carpenter]

Thanks, Ron.
The reason that I've asked is because I spend last 3 month testing different enclosures and materials for resonances and reflectance qualities. I've tried sandwiching materials and using cement type fillers and powdered glass. Corian wasn't something I had laying around but I will test a piece of Avonite later on.

[ronzeman]

I am hardly an expert...but I read somewhere in these threads that someone built a transmission line enclosure from 2 inch thick concrete. The box still had vibrations. Looking for the perfect non-resonant / non-reflective material reminds me the old saying about physics.

The study of physics is the study of mass elephants on frictionless surfaces.
GOOD LUCK ! Happy Listening.

PS: TIP OF THE DAY : Go to http://www.soundkeeperrecordings.com/
Buy yourself a copy of " LIFT" You won't be disappointed.

[alan-1-b]

Originally posted by ronzeman
. The Radford woofer crosses around 500Hz so the extended low freq capability of this dome mid was a good fit.

************************************************** **
Please understand that I have been able to listen for less than 2 hours so far...but my initial impressions are very favorable towards the new drivers. They are a keeper.

500 Hz is too low to cross to the Morel EL 1308 !

I am wondering if your short period listening has been only at fairly low Volume levels ?

Other than with some extraordinary cross-over circuit, there will be quite noticeable distortion of the lower frequencies sent to the Morel if it is driven even moderately hard, let alone to high volume level,
or are you listening in a very small room where sound seems loud with low drive levels ?

As well as distortion, there is likelihood the 1308 will be damaged if it is driven hard in the octave below 500Hz.

Have a look at the Specifications/Data sheet for the 1308.

See the large peak in the Impedance Plot centering on its Fs of 320Hz, and the Impedance does not drop to magnitude able to accept a standard x-over till above 800Hz.
Basically what happens is that the electrical interaction between the components in the x-over network and the higher than design spec. Impedance occuring so close to the x-over frequency cause the driver to receive significantly greater signal than would be the case if flat impedance {of the design magnitude} though that area.

Even if your x-over has an impedance compensation notch filter centered on 320Hz, 500Hz is still too low to cross to the 1308.
Look at its specified Xmax, +/- 1mm, that is a very small displacement, quite sufficient for higher frequencies but not for much magnitude of output in the 500Hz region.
Rule of thumb is to cross over at least 1 octave above the Fs of a driver,
and usually 2 octaves above, unless there is some type of Impedance Compensation or mechanical Damping of the Fs' impedance.
For example, the Dynaudio D-28/2 has FerroFluid in its magnet coil gap which causes substantial reduction of what would be an impedance peak at its Fs.
Look on its Spec./Data sheet and you will see the Impedance Plot has only a slight hump at about 1kHz.
This is result of the FerroFluid damping.
Thus the D-28/2 can be got to work with a standard x-over,
presuming one does not cross too low, and how low is "too low" depends on the Slope of the x-over Filter.

For the 1308 I would apply an electrical impedance compensation, and then use a 4th Order x-over at about 650Hz so as to have signal down 24dB at Fs.
Using a Linkwitz/Riley type 4th Order, the signal would be down 6dB at 650Hz, thus the +/- 1mm excursion will cope there.

You can cross over higher than 650Hz, and then use a lower slope filter if you want to, but impedance compensation will still be necessary,
because when you get high enough above the Fs caused impedance slope-down you will then be close to the Voice-coil Inductance caused impedance slope-up,
see from above 1.5kHz region on the Impedance Plot.

There is a range where the 1308 can be crossed to the tweeter.
Studying the Frequency Response Plot, including reference to the 30 degrees off-axis plot, 5kHz or slightly above looks best for a simple x-over, but it could be crossed as high as 6.5kHz, with audible results depending on the Vertical Axis that one listens on.
It could be crossed lower than 5kHz, but crossing lower is more audibly detectable as discontinuity between the mid and treble,
albeit dependant on the type of recordings one primarily listens to.

What cross-over circuit are you using ?

And, what is your Woofer ?
Do you have any Specifications/Data, or Plots for the woofer ?

[alan-1-b]

Originally posted by R-Carpenter

The reason that I've asked is because I spend last 3 month testing different enclosures and materials for resonances and reflectance qualities. I've tried sandwiching materials and using cement type fillers and powdered glass. Corian wasn't something I had laying around but I will test a piece of Avonite later on.

Have you seen the published results for the Aerolam cabinet walls Celestion used years ago for their SL 600 and SL 700
{or SL 6000 and 7000, I have forgotten how many 00s!} ?

Wharfedale used similar in their 708 model about that time.

I'll Post more about resonances when I have sufficient time to.

They cannot be completely eliminated, but can be reduced in both magnitude any number if one chances upon the optimum choice and thicknesses of materials for the "sandwich" !