A Study of DMLs as a Full Range Speaker

[moray james]

Hey Steve where do your 1cm thick light (1 lbs/cu ft) eps panels fall in this comparison? Size and low frequency extension? Thanks.

My smaller picture frame panels also goes down to 40hz

 

[spedge]

In my current understanding, a rigid spine interacts in 3 ways with the panel and its exciter:

• as a vertical support to avoid the long term deformation of the exciter spider due to its weight. I have no experience with exciters from Xcite but Dayton Audio like a DAEX25FHE it is mandatory.
• it stops the axial movement of the magnet and so the low frequency magnet resonance with 2 sub consequences:
• a change in the response at low frequency. Not fully clear for me but I think Eric shown the LF extension goes a bit lower with a free magnet. Maybe the free/fixed option of PETTaLS allows to get a better idea.
• a reduction of the distortion in fixed magnet. This is probably true only when the panel is acting without high pass filter. I can be check easily with REW.
• by an acoustic mechanism I not able to describe, the surfaces parallel at the panel on the rear side creates a resonance in the midrange. This already exist with the exciter alone but can be increased with a spider. It is the case in my plywood panel where the exciter is supported by a 10x10cm plywood part.

In addition, the spine is a mechanical problem as there is a risk to modify the exciter magnet position, either in the axis direction or by rotation in the other directions putting the voice coil a bit out the position of minimum distortion.
So the common position is a spider is mandatory for the long term and we can add design in a way not to add constraints on the exciter and of reduce dimensions in the panel plan.
Christian

I have mentioned quite a few times over the years, from my observations of the exciter at low frequencies.
It is clear to me that an exciter that is not braced, has two driving forces.
The braced exciter only has one.
Somewhere ,Below 100hz while the coil is still acting like an exciter should.
The magnet starts to vibrate or bounce causing a resonance.
The magnet is acting like a bass shaker and not like an exciter .
I think if it as being like a helmholtz resonator, increasing the low frequency output.
I used to get quite large amounts of low frequencies from my large eps panels with unmounted exciters, but the only problem was that the panels were shaking all over the place, pretty much out of control.
So I used to roll off the response heavily below 50, 60, 70, 80 or 90hz depending on the panel used.
Otherwise, there would be a considerable bass hump below these frequencies.
On the batman the dark Knight cd for instance, the very low and loud frequencies at about 30hz would set off the exciter (shaker) producing large exciter and panel movement.
Mirroring my transmission line speakers measurements but will a slightly narrower peak.
These are my thoughts.
I hope this helps explain the unmounted exciter performance in the low frequency area.
Steve.

 

[spedge]

Hello moray.
To be honest, I do not pay much attention to the response below 100hz as I never intend to use my panels much below this.
I have posted the frequency response for these panels somewhere on this forum, but I can't remember how low they do go.
But the exciters will vibrate heavily around the 40hz area if pushed but probably without the increased output wanted.
The last thing you want is the panel to start flapping about all over the place out of control.
Steve.