What do you mean by "cardioid load"? Do you mean the radiation impedance? Or are you interested in the sound radiation dependency on volume velocity, something like that. You are correct that the dipole and cardioid are quite different than a monopole. Being a linear system, the cardioid could be found by a linear combination of a monopole and a dipole, but the coefficients can be hard to establish, especially when real systems are usually not simple cardioids.
hi all,
do you know ONE
and do you can suggest me which ?
thanks
cheers
John K from Musicanddesign and Martin King from quarterwave.com wrote this:
U & H Frame Woofer Worksheet
It's free.
I am running Windows 7 x64, and due to that, I have to use The Edge
Yes, but it doesn't really work that well. It never seemed to match my measurements. I don't think the damping is right. Damping the rear wave is really critical and is best done by measurements as I discuss on my web site.
John
Your comment implies that the results are fairly good if there is no damping, but not so good when damping is applied. Is that correct?
The H configuration should not be too difficult to model, but good damping models are very difficult. Damping is more than just attenuation it is a complex (in the mathematical sense of attenuation and delay, i.e. exp(ia(w)x)) problem that changes with frequency.
The reason that I ask is to see if you know where the errors are most likely to be as I might like to try to get a model that works.
Your comment implies that the results are fairly good if there is no damping, but not so good when damping is applied. Is that correct?
The H configuration should not be too difficult to model, but good damping models are very difficult. Damping is more than just attenuation it is a complex (in the mathematical sense of attenuation and delay, i.e. exp(ia(w)x)) problem that changes with frequency.
The reason that I ask is to see if you know where the errors are most likely to be as I might like to try to get a model that works.
Good morning Dr. Geddes,
I'm explained not well,sorry.
I mean that which Dr. John Kreskowsky has, in the past, proposed as "U-frame" fir his Nao Speaker, if I well remember.
thanks
Cheers
Good morning Dr. Geddes,
I'm explained not well,sorry.
I mean that which Dr. John Kreskowsky has, in the past, proposed as "U-frame" fir his Nao Speaker, if I well remember.
thanks
Cheers
I see. A U-frame is not really a cardioid although with damping on the interior it may approximate one over a narrow range.
I found it necessary to build and test. Different damping material and different configurations of the same material make significant differences. I abandon the U-frame on my last design, the Note II RS, and went H frame dipole with no damping. It just makes the build much simpler for the DIYer although there is a loss of max SPL capability relative to a similar sized U. My current thinking is to use a dipole system down to about 50 or 60 Hz and then go with distributed monopoles as Earl has suggested in the past. With a crossover point around 50 Hz there will typically only be one or 2 dominate modes with the monopoles which are pretty easy to deal with by placement.
I really don't do much with audio any more. I'm very happy with the Note II RS and I have no intensions of designing anything else. I've chased the tail of this dog long enough to know what comes out of a dogs butt. Nothing is going to change that.
I really don't do much with audio any more. I'm very happy with the Note II RS and I have no intensions of designing anything else. I've chased the tail of this dog long enough to know what comes out of a dogs butt. Nothing is going to change that.
Exactly right. It is possible to get a cardioid like response over a reasonable range below the primary resonance of the U-frame with the proper damping. The damping reduces the Q of the resonance and LP filters the rear response. As I show on my web page, this results in the correct phase relation between front and rear response over a limited range. It is also the reason I refer to the system as quasi-cardioid.
NaO U-frame
Thanks for explanation , Dr. Kreskowsky.
But I' m intrigued by propriety exclusive of quasi-cardioid/U-FRAME , as you want name it.
if someone of others DIYer here present,
will be so courtesly to make just a simulation for my wf 52 - 250 Hz ( me too have monopole subs below 52 Hz) I' ll can think better what to do.
CHEERS
Ha, yes; John's documentation is one of the reasons I've never tried building a U baffle. Variable resistance enclosures seem of more interest for cardioid as the working bandwidth's larger. Keyser's here on DIYA and Kimmo Saunisto's KS-585 are a couple examples. Given neither build makes much attempt to approximate a structure of constant acoustic size by varying hole size and damping the results strike me as surprisingly good.
I'm not aware of any design calculators for variable resistance but there are porous absorber calculators for plane wave transmission by infinite, damped perforated sheets which provide some idea of what sort of progressive damping and hole sizing one might start experimenting with.
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