[hndaaudio]

Hello,

This is what I have in mind for Heils from a AMT 1D:

(2) 15" warrior in parallel,(2) 8" Betsy in parallel-(Thanks to Paul at wildburroaudio for suppling reasonable cost low MMS drivers optimized for midrange-no whizzer !),Large heil mounted on top of approx 18" x 52" x 1.5"- 2x 3/4 plywood.Flat baffle.Configuration WWMMT.Approx crossover 50-60,200,1500.

This is what I need to work out:

Is there an online calculator to determine optimum baffle dimensions ?

If going with the max baffle width of 2.2(or is it 2 ?) x mid driver rule,is it outside diameter of frame,cone dia,cone + surround ?

How to decide whether or not to offset mids ? I have read conflicting info regarding smoothing out peaks.
If so how much offset ? I know a mock up and measurements are the way to go,but failing that,what do you suggest ?

Would you mount the bottom warrior at floor level or raise it up a bit ? response down to 50 without EQ
would be a big plus.

Since the baffle will be 1.5 " thick,will the mid driver holes need to have radius to avoid audible resonance ?

I appreciate any help given.

Clayton

[jeenie67]

  Hi !  A long time ago I bought one, yes only one ESS professional column speaker from the used equipment room at a now long gone high end audio place for $50.  It had a 10" woofer and a Heil AMT mounted in the top portion of the 12" wide x 52" high x 11" deep enclosure. It was a sealed enclosure like most of the vocal columns of the time (1970's). The AMT was a hard plastic box about 6" x 6" x 6" with horizontal plates at it's front opening. Two bolts held it down to the cabinet. The sound of this speaker was, at the time, unbelievable! I really wish my ear was developed to the point it is now back then. All I remember is that it handled the Crown DC-300's I had at the time without a whimper and I used it for my stereo system also using a DIY cabinet with a 12" University woofer and a HF University horn. I've seen one on eBay go for blood money recently.  Just had to say something here....."Tanx"   Jeenie.

[Rudolf]

Is there an online calculator to determine optimum baffle dimensions?

Do you really mean online? Or just freeware? I don´t know of any online calculator for OB.

If going with the max baffle width of 2.2(or is it 2 ?) x mid driver rule,is it outside diameter of frame,cone dia,cone + surround ?

The baffle width for that 2.2 recommendation is the diameter of a circular baffle. This diameter will always be larger than the width of an equivalent rectangular baffle. Without some program (EDGE at least) it will be difficult to determine the exact size. But 2.2x is a gestimate only, not a law. Cone diameter commonly is measured from the middle of the surround to the opposite middle of the surround.

How to decide whether or not to offset mids ? I have read conflicting info regarding smoothing out peaks.
If so how much offset ? I know a mock up and measurements are the way to go,but failing that,what do you suggest ?

If you follow the 2.2 x "rule", no drivers should be offset.

Would you mount the bottom warrior at floor level or raise it up a bit ? response down to 50 without EQ
would be a big plus.

With an Xover of 200 Hz I see no need to raise the warrior. But (linear) 50 Hz without any EQ on a 18" wide OB is pure wishful thinking.

Since the baffle will be 1.5 " thick,will the mid driver holes need to have radius to avoid audible resonance ?

Without measurement you will never know how big the basket induced differences of the rear SPL will be compared to the front SPL. For a 8" mid I forecast the main differences from 0.5-1.5 kHz. So why worry about that tiny resonance.

My biggest concerns are with those two mids in parallel going up to 1500 Hz. It would make this design an absolute no-go for me.

Rudolf

[hndaaudio]

Thanks Rudolf,

I am thinking 2 mids to lower IM distortion and give a bigger sound.Would you expand on why this would be a no go and what would be a better mid setup in such a system ?

What baffle width do you suggest for low end response and would put the mid(s) on a narrower baffle ?

Clayton
 

[hndaaudio]

Hi Jeenie,

Too bad you only got one.Sounds like a screaming deal anyway.Do you remember the model and they were not rear firing ? Don't know if it's true but I have read the great heil has the radiating area of a 8" driver.
They certainly have impressive bandwidth-down to 800.But at that crossover they have a kind a fatique
that sounds too "busy" to me.Hopefully taking about an octave off the low end will have terrific results
but they don't have the texture of a compression driver.

Clayton

[Rudolf]

I am thinking 2 mids to lower IM distortion and give a bigger sound.Would you expand on why this would be a no go and what would be a better mid setup in such a system ?

Hi Clayton,

the distance (center to center) of two drivers should NEVER be larger than the wavelength of the upper crossover frequency. In fact half wavelength would be the acceptable upper limit for most people. Look at the lower graph below. It is a simulation of two 8" drivers (Visaton BG20) on a 30 cm wide baffle with 25 cm distance center-center (EQ by 6 dB lowpass at 700 Hz). The vertical radiation pattern is really bad above 1000 Hz. The situation will be even worse for the crossover to the AMT, because you need to calculate with a center-center distance of more than 30 cm.
You might restrict yourself to just one mid driver. Or you need to attenuate the lower 8" to frequencies below 800 Hz approx.

What baffle width do you suggest for low end response and would put the mid(s) on a narrower baffle ?

For the 8" drivers a baffle width of 30 cm looks acceptable up to 1500 Hz, as the upper graph shows.
WRT low end response: The woofer baffle must be 3 m wide to put the dipole peak at ~100 Hz and give a linear enough response level in itself. In common rooms this is IB. You definitely will need a 6 dB lowpass somewhere to fight the steadily rising response up to 200 Hz.

[hndaaudio]

Very helpful info,Rudolf.

I would be using an electronic crossover,what parts do I need to attenuate the lower 8" below 800 ?

[Rudolf]

...what parts do I need to attenuate the lower 8" below 800 ?

Clayton,

the Betsy and the BG20 http://www.visaton.de/en/chassis_zubehoer/breitband/bg20_8.html are different drivers, but not very much. So you have to take my sims for the BG20 with a grain of salt. If I put a 3.3 mH coil of 0.5 Ohm in line with the lower BG20 (blue) and cross over both drivers electronically at 1.2 kHz with 6 dB/oct, it will result in this response:



BTW: Crossing over electronicaly with 12 dB at 1.2 kHz would be fine too. It will just cut steeper, but will not change the response below 1.2 kHz significantly.

The corresponding graphs for the different directions:



The upward response is still not optimal, but probably the best you can get without resorting to a separate amp for each Betsy. The downward response is waaay better than before.
You will need to put the upper Betsy as close as possible to the AMT and the lower Betsy as close as possible to the upper one. 3.3 mH is my best guess. It could be anywhere from 2.2-4.5 mH, but you probably will need measurements to decide on that.

[hndaaudio]

Thank you for taking the time with this,Rudolf.I see now why a single driver would be preferable.
A tone tubby 12 alnico would be very directional but from what I can gather would be much
better in most regards.

Best,

Clayton