What's the best 8" fullrange that you've heard?
I noticed that on post 314 that David Pinnegar cuts out the dust cap on full range cone drivers and fits phase plugs.
Although he doesn't seem to go into why, I can imagine the improvement in sound this would have, as the problems I expect are exactly the same .
Steve.
I noticed that on post 314 that David Pinnegar cuts out the dust cap on full range cone drivers and fits phase plugs.
Although he doesn't seem to go into why, I can imagine the improvement in sound this would have, as the problems I expect are exactly the same .
Steve.
Göbel patent
Hi I am new here but intrigued by this.
I found the Göbel patent - not sure if it has been posted but it has a wealth of information on how to build their DML driver.
Original German is here
and I translated it with Google here
There is a lot I still do not understand and so much information there is too much for one post but I will try and summarise the most important points as I see it. I am sure others can add to this and some of you are such nutters (said in an affectionate way) I am sure you will go and try and replicate this ... I will try and incorporate some of this in my first attempt.
1) He uses a laminar structure consisting of the following:
3) Two exciters used each of 25mm coil diameter and 58g mass.
5) 3 similar weights are placed on the rear of the panel for fine tuning but he does not say where (presumably at the worst resonance antinodes)
6) The panel is mounted in a deadened aluminium frame and fixed all around with closed cell foam 2mm thick. Silicone is applied on the edges between the frame and the panel. The intention is to reduce reflections at the edges and increase bass response.
That is most of it but I don't have it quite right. Maybe others can add, especially German speakers. It seems to have done wonders for the overall frequency response (fig 10a). You will need to read it for yourselves and look at all the figures which he references. But I think there is some great material here and not beyond DIY.
He does not say how this whole thing is suspended in the speaker. With the heavy surround there are shades of the art canvas design as well.
Apologies if this has already been posted. I have tried to read the whole thread but missed it if is already known about.
Hi I am new here but intrigued by this.
I found the Göbel patent - not sure if it has been posted but it has a wealth of information on how to build their DML driver.
Original German is here
and I translated it with Google here
There is a lot I still do not understand and so much information there is too much for one post but I will try and summarise the most important points as I see it. I am sure others can add to this and some of you are such nutters (said in an affectionate way) I am sure you will go and try and replicate this ... I will try and incorporate some of this in my first attempt.
1) He uses a laminar structure consisting of the following:
- Core made of light wood with high lignin content, preferably balsa wood. Easy and cheap
- This core is coated with a "pore filler". I am not sure if this is optional or combined with resin. Could this be PVA? I can't really see where he explains this. 15g of "pore filler" for preferred dimensions. Is this per side?
- Epoxy resin is applied at about 9.5g per side (for a 28.6x21.6cm panel see later) and a textile material placed over it (carbon fibre, fiberglass linen weave 58 g/m^2 oriented 45 degrees to core material).
3) Two exciters used each of 25mm coil diameter and 58g mass.
- First is at 42% of transverse dimension and 58% of longitudinal dimension
- Second is at 64% of transverse dimension and 39% of longitudinal dimension
5) 3 similar weights are placed on the rear of the panel for fine tuning but he does not say where (presumably at the worst resonance antinodes)
6) The panel is mounted in a deadened aluminium frame and fixed all around with closed cell foam 2mm thick. Silicone is applied on the edges between the frame and the panel. The intention is to reduce reflections at the edges and increase bass response.
- The frame has a square cross section and appears to be deadened with something like "TEROPHON-112B from Henkel, NOISEX fromDIETZ, NOISKILLER from Rockford Fosgate"
- There is an MDF cover frame over this.
- The mass of the entire frame to (panel + exciters) is preferably about 1:5 to improve bass
- A comb filter is created from the two exciters which creates ripple >=3KHz.
- An "acoustic lens" in the form of a perforated plate made from MDF is placed on the back to counteract this. I think this is created 1-4 cm (1.2 cm ideal) behind the panel. I do not know the hole diameters.
- He also talks about a panel cover with concentric rings over the exciters but I cannot work out where this is in relation to the acoustic lens.
- He adds 2cm BONDUM 800 or similar sound absorbing foam at about 2cm behind the panel to help absorb the back wave.
- He says this can reduce rear wave by 10dB or more in the midrange and high frequencies.
That is most of it but I don't have it quite right. Maybe others can add, especially German speakers. It seems to have done wonders for the overall frequency response (fig 10a). You will need to read it for yourselves and look at all the figures which he references. But I think there is some great material here and not beyond DIY.
He does not say how this whole thing is suspended in the speaker. With the heavy surround there are shades of the art canvas design as well.
Apologies if this has already been posted. I have tried to read the whole thread but missed it if is already known about.
Something that is not in the patent:
At this page Göbel describe "laser cut incisions are designed to eliminate any reflections on the edges". Looking at the picture (attached) there are 13 incisions on each long edge which are angled with random noise around 45 degrees to the sides. For the preferred length of 25.5 cm this corresponds to about 2cm spacing between incisions. The length of the incision looks to be about 2.8 cm. I get this by the right bottom corner showing a right angled triangle with 2 cm sides (so other side is sqrt(2x4) = 2.8cm.
Göbel has clearly gone to a lot of trouble to eliminate reflections from all sides, along with the back wave. This is a departure from most of the other DML panel designs out there. This would decrease efficiency and flatten response. Claimed efficiency of the Epoque Aeon Reference is 86 dB (1W/1m).
I have also attached frequency response. I think this is before and after edge treatments. He crosses over to bass drivers at 170 Hz.
At this page Göbel describe "laser cut incisions are designed to eliminate any reflections on the edges". Looking at the picture (attached) there are 13 incisions on each long edge which are angled with random noise around 45 degrees to the sides. For the preferred length of 25.5 cm this corresponds to about 2cm spacing between incisions. The length of the incision looks to be about 2.8 cm. I get this by the right bottom corner showing a right angled triangle with 2 cm sides (so other side is sqrt(2x4) = 2.8cm.
Göbel has clearly gone to a lot of trouble to eliminate reflections from all sides, along with the back wave. This is a departure from most of the other DML panel designs out there. This would decrease efficiency and flatten response. Claimed efficiency of the Epoque Aeon Reference is 86 dB (1W/1m).
I have also attached frequency response. I think this is before and after edge treatments. He crosses over to bass drivers at 170 Hz.
Attachments
This is 0.5mm carbon fiber plate. It is expensive.
You can buy it here or a number of other places.
Double-Sided Carbon Fibre Sheet; 0.25mm, 0.5mm, 1mm, 2mm, 3mm - Easy Composites
It will not work well by itself.
It needs to be laminated to something. Göbel chose balsa, "pore filler", then epoxy resin, then the CF. He says other textiles also work.
I am choosing Nomex Aerospace Honeycomb
and also planning on trying traditional guitar sound board wood veneers which are much cheaper than CF. Guitar makers use this combination in guitar "double tops".
Then you need a vacuum press. Electric pumps are expensive. I found this hand pump method that works well apparently. Buy the kits here.
A lot of outlay for something that may not work well but I am both compulsive and determined.
PS. From what I can see from the scientific papers the secret is to keep the stiffness very high normal (right angles) to the plane of the panel but low in the plane of the panel so it can bend. It also needs to be as thin and light as possible so big thick planks of wood would not work so well. Guitar double tops are basically where I am starting but I will probably use ideas from Göbel's patent, such as size, edge clamping, rear wave absorption and panel incisions.
You can buy it here or a number of other places.
Double-Sided Carbon Fibre Sheet; 0.25mm, 0.5mm, 1mm, 2mm, 3mm - Easy Composites
It will not work well by itself.
It needs to be laminated to something. Göbel chose balsa, "pore filler", then epoxy resin, then the CF. He says other textiles also work.
I am choosing Nomex Aerospace Honeycomb
and also planning on trying traditional guitar sound board wood veneers which are much cheaper than CF. Guitar makers use this combination in guitar "double tops".
Then you need a vacuum press. Electric pumps are expensive. I found this hand pump method that works well apparently. Buy the kits here.
A lot of outlay for something that may not work well but I am both compulsive and determined.
PS. From what I can see from the scientific papers the secret is to keep the stiffness very high normal (right angles) to the plane of the panel but low in the plane of the panel so it can bend. It also needs to be as thin and light as possible so big thick planks of wood would not work so well. Guitar double tops are basically where I am starting but I will probably use ideas from Göbel's patent, such as size, edge clamping, rear wave absorption and panel incisions.
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hi.
im not sure if fig 9 is the same panel or a Elac patent using Rohacell ?
the translation by google is a little hard to understand.
looking at the patent ,i dont think you could damp the panel anymore if you tried,it looks quite similar to a bmr in that respect ?
DML , in his patent is heavily restricted , practically none existant ?
it would be interesting to hear these panels,but with all that damping im a little sceptical as to if i would like the sound ?
we have two totally different ideas on how to make a good sounding panel , i like to do as little as possible to the panel and he uses every damping method possible.
even the problems in the centre of the coils are heavily damped by a puck and heavy damping from behind by sound damping materials and fibre board with holes drilled into it, this is very similar to old open backed speakers from the 1940s ?
im sure they sounds fine but at an eye watering cost
i did listen to a youtube recording of these some time ago which sounded pretty good ,but it is not the same as being there.
steve.
As a professional audio engineer for over 50-years the most frequent overarching term we use to describe sound is, "Color." Warm, rich, bright, etc.
We never, as a whole seek pure sound but what sounds good to us and hopefully the public at large. We leave "pure," to the audiophiles.
If you have ever tuned a speaker to perfectly flat 20-20,000 your ear may not like it.
If a speaker has a low-mid bump, a HF roll like the Dolby X-Curve that can be a very good thing.
In the end it is all about what it sounds like...
We never, as a whole seek pure sound but what sounds good to us and hopefully the public at large. We leave "pure," to the audiophiles.
If you have ever tuned a speaker to perfectly flat 20-20,000 your ear may not like it.
If a speaker has a low-mid bump, a HF roll like the Dolby X-Curve that can be a very good thing.
In the end it is all about what it sounds like...
I agree the translation looks like he was referring to the Elac patent but when you look at the figures they are virtually identical except all the peaks and troughs have been smoothed out.
I figure the only way that would have happened is if he had the same speaker he made using Elac techniques then applied all the damping that he did on the sides then took the measurements again.
I will have to look up the Elac patent.
I do not know which technique is better. I have not tried either. I am sure I will be one of the nutters I referred to and try both. I have ordered all the bits and pieces except balsa which is easy.
I think by "pore filler" he means something like this.
The Secret To Mirror Like Finishes: Wood Grain Filler
I honestly do not know. He omits that part. I would think hanging is logical but that would be impossible in his Aeon speaker.
I think that needs to be taken in context with the rest of the particular design.
eg. back firing port different to front port but they are both ports (back port not too close to the wall).
In the Aeon patent he is specifically referring to the mass of the frame being in a particular ratio to the mass of the panel plus exciters for bass extension. I do not really get this as it implies the whole lot is free and not fixed. But the Aeon appears to be fixed.
The Aeon is also in a traditional closed box so has no rear wall reflections other than those from a normal speaker. So I figure this type of design where the rear wave is absorbed placement is less critical.
Well, generally it is advantageous to attach the panel to a rigid frame, typically with something elastic and damping between the frame and the panel.
This mostly influences the low frequency end. Boosting and smoothing the low frequency response.
Eric
murry,
Concerning solid wood, I expect tonewood like spruce and the like would be better. Such species are typically less dense and hence provide higher efficiency than most hardwoods. Interestingly, inexpensive underlayment plywoods like revply and sureply work pretty well. I think balsa is also a good candidate, though fragile.
What exactly do you mean by "insulation sound board"?
Eric