dipole speaker
Warning: this is not about HIFI, this is about fun.
There is no shortage of loudspeakers in my home but I mainly listen to streaming radio and that does not sound too well on good speakers (in fact the better the speakers the worse it sound).
Like many people I am charmed by the sound of an old radio. Now old radios have nothing to do with hifi, still some of them sound very pleasing so I thought instead of 'upgrading' I should 'downgrade' to capture some of that vintage experience.
As it happens I'm dragging around a 30x180 cm piece of multiplex for the last 20 years for which I never found any use. A dipole speaker is just that, a flat panel with a speaker. A full range speaker should do the job, in line with the vintage experience. Some googling revealed that this indeed is possible, there are however some serious drawbacks.
In theory this is the one thing you should never attempt to build, there is a serious issue with the acoustic short circuiting of the lower frequencies. The roll-off is 6dB/octave however and this is not difficult to compensate.
There is a nice piece of software available on the net to calculate such a system.
Before you can simulate something you have to decide the driver dimensions. At first I wantd to use an elleptical speaker to add to the vintage experience but unfortunately the suitable model from visaton was not in stock so I settled for the visaton BG17.
The simulated results where promising.
Oddly the best result (in my opinion), the smoothest curve; is achieved when you place the driver off center (the green curve).
The red curve is for a centered driver.
My tube buffer has a mono channel with a vintage LM201 opamp. I modified the circuit to lift the bass 10db.
This provides the necessary 6dB/oct lift to compensate the open baffle (up to 70 Hz when in the 200Hz position). I did not expect to get any meaningful result below 70 Hz.
I set out to build the whole thing.
Now how does this sound? To be honest, it works but needs a lot of tweeking. When you look at the speaker curve you see that the speaker itself needs some additional lift below 150 Hz which leaves you with something like 20 dB of compensation. Moreover to get rid of some harshness I had to cut some midrange as well.
In these eco-times this is not very responsible and I really hate to push 50W into a system where 0.5W would normally be enough.
But then I had this silly idea to put a carton box over the speaker.
This has a very strange effect, the harshness I fought with is almost completely gone and the bass came to life.
I opened the 'bottom' of the box to preserve the open baffle idea.
Finally I only use the bass compensation and a little mid cut from the winamp equaliser (which is really not very good I hate to say) and I'm very pleased with the result.
Other than that it is also a nice piece of conversation...
There is no shortage of loudspeakers in my home but I mainly listen to streaming radio and that does not sound too well on good speakers (in fact the better the speakers the worse it sound).
Like many people I am charmed by the sound of an old radio. Now old radios have nothing to do with hifi, still some of them sound very pleasing so I thought instead of 'upgrading' I should 'downgrade' to capture some of that vintage experience.
As it happens I'm dragging around a 30x180 cm piece of multiplex for the last 20 years for which I never found any use. A dipole speaker is just that, a flat panel with a speaker. A full range speaker should do the job, in line with the vintage experience. Some googling revealed that this indeed is possible, there are however some serious drawbacks.
In theory this is the one thing you should never attempt to build, there is a serious issue with the acoustic short circuiting of the lower frequencies. The roll-off is 6dB/octave however and this is not difficult to compensate.
There is a nice piece of software available on the net to calculate such a system.
Before you can simulate something you have to decide the driver dimensions. At first I wantd to use an elleptical speaker to add to the vintage experience but unfortunately the suitable model from visaton was not in stock so I settled for the visaton BG17.
The simulated results where promising.
Oddly the best result (in my opinion), the smoothest curve; is achieved when you place the driver off center (the green curve).
The red curve is for a centered driver.
I set out to build the whole thing.
Now how does this sound? To be honest, it works but needs a lot of tweeking. When you look at the speaker curve you see that the speaker itself needs some additional lift below 150 Hz which leaves you with something like 20 dB of compensation. Moreover to get rid of some harshness I had to cut some midrange as well.
In these eco-times this is not very responsible and I really hate to push 50W into a system where 0.5W would normally be enough.
But then I had this silly idea to put a carton box over the speaker.
This has a very strange effect, the harshness I fought with is almost completely gone and the bass came to life.
I opened the 'bottom' of the box to preserve the open baffle idea.
Finally I only use the bass compensation and a little mid cut from the winamp equaliser (which is really not very good I hate to say) and I'm very pleased with the result.
Other than that it is also a nice piece of conversation...
edge simulator
linkwitz lab
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