Thomas,
In your BMR builds, did you add any "ring masses" or locate the voice coil at a particular radius ratio in order to "balance the modes" as they describe in the Tectonic literature and patent?
Eric
https://tectonicweb.wpenginepowered...9/05/Tectonic_BMRWhitePaper_Rev2.0_2019-1.pdf
https://patentimages.storage.googleapis.com/1d/e6/29/d4bdc6e58aff65/US7916878.pdf
Hi Thomas
Harking back to the BMR mod :
1/ is the voice coil former very thin/weak?
I thought that with the vent holes, it may be necessary to stiffen the former, perhaps with balsa ribs, and maybe a light weight internal ring.
2/ did you drill and tap the rear magnet plate to screw mount the motor to the spine?
3/ how did you wire up the 6 exciters?..IE what is the terminal impedance.?
4/ how clean is the HF performance?
I was musing on the possibility/usefulness of adding a single BMR unit to a panel like yours to enhance HF by penetrating the panel and using a roll surround around the outside of the BMR frame connected to the panel, and feeding the same signal to all.
5/ In hindsight, do you think you could use 4 exciters instead of six?
Thanks
Eucy
Wouldn't using light stuffing like fibrefill or a cotton ball in the former stop cavity resonance?
Eucy
As I mentioned in my post on the BMR units I have, the ring masses have been economised down to 3 straight strip masses. Not ideal
Eucy
Thanks Eucy,
I hadn't really been thinking about BMR's much lately until I saw @Sandasnickaren's pics of his small round BMR's, so your post didn't catch my attention originally.
I wonder if it's the same on their larger units? Their white paper seemed to suggest that they prefer designs that require 3 or 4 ring masses. I'm thinking that those three straight strip masses only count as one ring mass, but I could be wrong.
Eric
The problem is that anything loose and fluffy does not present a linear force if it touches the back of the panel where the VC is bonded to the panel, and it causes various kinds of mechanical distortion.
But even worse than that, it migrates into the pole gap and eventually causes coil scraping and even more distortion.
In my last iteration I used a layer of thick double-sided tape cut to fit and placed onto the magnet (used non-magnetic, plastic tweezers to place it.)
But that was not enough. I think I'll use several layers next time.
No, I haven’t add any ring masses. I was planning to but never came around to do it. They sound well enough. The VC former diameter was given by the chosen exciter, so no. The edges are done according to their patent.
But, I should re-measure them to see if there are any eigenmodes to worry about. The FR response picture I appended in the earlier post have 1/12 smothing which might hide the eigenmode spikes. I cant find the original measurement file. Large spikes in FR with very high q-values is not necessarily something we can hear due to the way our hearing is working.
Thomas
Veleric.
If I remember correctly from reading this patent some time ago, the third outer ringe was removed as the rubber surround was placed in this position, to replace it.
So only the two inner rings were used.
Pity they did no feel the need to sort out the inner coil area peak at above 10k.
Steve.
If I remember correctly from reading this patent some time ago, the third outer ringe was removed as the rubber surround was placed in this position, to replace it.
So only the two inner rings were used.
Pity they did no feel the need to sort out the inner coil area peak at above 10k.
Steve.
It only took a couple of minutes last night to cut up the can after drinking it 🍺🤪 and applying it to the panel with a very small piece of blu-tack.
The frequency in the 2k to 10k area was increased by about 5db to 10db.
I will send some pictures, and will probably cut the whizzer size down to see if this reduces the dB?
But I must admit sounds such as Bells and metal clanging were very clean and clear sounding .
Not harsh or distorted, I have heard worse from ribbon tweeters.
I was trying to find sounds and music that would show up problems, it was clearer and brighter ,certainly, but I was impressed at just how good it sounded.
I will have to compare this with the coffee whizzer , maybe even another recording?
Not bad for another free upgrade 😉
Steve.
Jaxboy.
Just remembered I took some frequency plots just showing the whizzer increase in the 2k to 10k area.
It sounds much better than it looks, honest😀
And if you have hearing problems this could be a plus benefit.
I have heard hi end audio that sounds bright but also painful sometimes.
It's nice to have the brightness without the pain 😁
The trouble with whizzer cones is trying to match the efficiency of the whizzer to the panel for a flat frequency response for general use,( no volume control ).
Steve.
Just remembered I took some frequency plots just showing the whizzer increase in the 2k to 10k area.
It sounds much better than it looks, honest😀
And if you have hearing problems this could be a plus benefit.
I have heard hi end audio that sounds bright but also painful sometimes.
It's nice to have the brightness without the pain 😁
The trouble with whizzer cones is trying to match the efficiency of the whizzer to the panel for a flat frequency response for general use,( no volume control ).
Steve.
Attachments
1, It’s thin but not weak. I dont see a need to strengthen it. Obviously the magnet must be supported. I did a ”max test” when was measuring the speaker. I made a misstake using Rew at max volume with a 300W amplifier…The only thing that happened appart from a slight tinitus was that one of the VC glue bond to the panel failed.
2, There is allready a M4 hole.
3, 2 in serie and then parallell approx 5,5 ohm
4, pretty clean. But, comparing to my smaller ”göbel” panel and the ”BMR” the Göbel panel is cleaner. I’m not sure about the reason for this as the göbel is open and the BMR is mounted in a wall (closed box) and they have different exciters and number of exciters. So it might be benefical to try something like your suggestion.
5, Haven’t considered it. But, my first protype used 5 with the same panel size (one placed in the center) and the rest in the corners. I beleive its important to get a symmetrical drive in the pistonic mode. Which is not really optimal for the DML mode. I’ve been contemplating an idea that I saw in one of tectonic patents where they had a varying stiffness of the panel.
Thomas
How high up on the can did you go? That is, how tall is the whizzer? Is it a standard drink can? I really appreciate your doing this for me. You are so accommodating for me and so many others to do such experimenting for us.
Jaxboy.
It's OK ,no problems.
Pictures of the can and cut out whizzer .
Plus the coffee whizzer in the first picture.
As you can see I have left the lip on the can whizzer , so far , as I preferred it left on the coffee whizzer.
But I will be cutting it off later, a bit at a time , for the smaller whizzer and dome tests.
Steve.
It's OK ,no problems.
Pictures of the can and cut out whizzer .
Plus the coffee whizzer in the first picture.
As you can see I have left the lip on the can whizzer , so far , as I preferred it left on the coffee whizzer.
But I will be cutting it off later, a bit at a time , for the smaller whizzer and dome tests.
Steve.
