Beyond the Ariel

[Pano]

JohnK - very impressive- thanks! Never quite seen it put that way. =)

How did you figure the EQ? The low end looks simple, to top end does not.


Maybe Lynn is looking for a way to do that acousticaly, instead of electricaly?
Having heard Gary's system, I can certainly say it's one of the cleanest I've ever heard in over 30 years. Quite amazing. No exotic/expensive drivers, either.

[mige0]

[i]
The only other enclosure I can think that puts first priority on minimization of stored energy is the B&W Nautilus tapered-pipe design. [/B]

Lynn, do you have any reliable data on that?

My experiments and own measurments - a pretty long time ago - didnt show any significant improvement for that kind of "inverse horn" shape.

Also I haven't heard of a Nautilus DIY fan community comparable to the Carlson coupler idea for example (but also haven't searched for to be honest) which for sure would exist if there is *anything* of interest on this principle (besides the cool shape).


Michael

[Overkill Audio]

Hi Telstar,

Thanks I have sent you the photos, enjoy!
The Acrylic cabinets were my first experiments and used good but not great bass / low mid drivers, two per side of the 8inch Seas Excel W22EX 001 run in parallel to give 4 Ohms and 91dB sensitivity.
I now use 10 or 12 inch paper coned drivers with 3 or 4 inch voice coils and 96dB plus sensitivity.
The in room -3dB was a genuine 30Hz to 33Hz using some EQ cut (not boost!) as I used the power amp level settings to boost the whole 100Hz to 350Hz band these drivers were covering and then cut down by approx 7dB a peak from about 150Hz to 250Hz if my memory is correct.
The principal being acieve desired in room response with the minimum of EQ intervention. ie rather than boost the low end, cut the top end by starting from an elevated power amp level setting.
Martin Collums (UK speaker guru and reviewer) loved them!

Cheers

Derek.

PS I will post a reply to your twin Manger question on the Manger thread you suggested as I dont want to go off topic here.

[mige0]

JohnK, where you'd put the limits to the min phase axiom for speaker-enclosure systems?

Vented - transmission line - horns, etc still min phase?

Michael

[Sheldon]

Originally posted by Overkill Audio
The principal being acieve desired in room response with the minimum of EQ intervention. ie rather than boost the low end, cut the top end by starting from an elevated power amp level setting.

This a distinction without a difference.

Sheldon

[gedlee]

Originally posted by john k...
As Earl knows we have different positions on drivers and MP response. First let's distinguish between a minimum phase response and a minimum phase system. A minimum phase response, to me, simply means that the amplitude and the phase associated with that amplitude can be related by the Hilbert-Bode transformation. A minimum phase system would then be a system with output characterized by the same H-B relationship between amplitude and phase. In a simple electrical or mechanical system where there is only a single output this is straight forward. However, for a loudspeaker driver the output can be a function of the observation point. That the response varies with position doesn't preclude that the response at any observation point is MP. The problem with a driver is complicated because, even in the case of a perfectly rigid piston, we can think of the radiated sound as being the sum of the radiated energy form an infinite number of sources distributed over the surface of the piston. Each of these sources moves with the mechanical velocity of the piston and in so-far as the mechanical system is linear and MP, then so is the motion of each of these sources.

When we are far from the piston and on axis, all the sources sum in phase and thus the on axis response is a direct indication of the mechanical motion of the piston. However, when we move off axis the distance from each source (on the piston surface) to the observation point varies. As the wave length become shorter we start to see the development of a nonuniform polar response due to these path length differences. The system remains linear and the response is typically still MP relative to any observation point even though it may be different from the on axis response.

Since the on axis response is indicative of the piston motion, any anomalies in the on axis response are indicative stored electromechanical energy in the driver. Thus is we eq the on axis response to correct these anomalies we correct for the stored energy. We will still suffer the change in the off axis response due to the distributed nature of the sources over the piston surface. But the applied EQ will correct for the stored energy in the electromechanical system.

The off axis anomalies generally have little to do with stored electromechanical energy in the driver. They are just the consequences of the finite size of the driver radiation at frequencies with wave length on the order of, or smaller than the driver circumference. The only way to deal with this is to limit the use of the driver to a frequency range where is has constant directivity.

I presume that some of you will say, "what about breakup?" That is another issue, but not so relevant as good design would limit the use of a driver to well below any region of breakup.

John

I don't think that I disagree with you as much as I'd say that MP applied to a three dimensional problem is not meaningful. Here is why. Lets say that the axial response is MP and that we correct it to be flat, whatever that takes. And lets say that the off axis responses are also MP and correctable to flat. These are both points that you made that I don't disagree with. But the problem is that these two corrections are not the same. There is no single correction that can make BOTH points flat at the same time even if both points are MP individually. So in a three dimensional problem even if any given point is MP they are not MP with respect to each other. I think that this is more a failure of the concept of MP application to 3-D fields than anything else.

[Overkill Audio]

Hi Sheldon,

Not with the DEQX, for two reasons.

(1) With the DEQX the lower in frequency any signal manipulation is implemented the more demanding it is on the DEQX software.
For example the latest HD version running at 96KHz can not cope with a 80Hz crossover point using Linear Phase filters, you have to drop to 48Khz where there is no problem.

(2) The main IO manager page where yo set the basic levels between drivers is a "blanket" DSP ie there are no more or less calculations required to set the low mid driver at +5dB than there is to set +1dB or -2dB etc.
The software has better resolution at slightly higher frequencies due to the programe priorities of Latency Vs resolution.
The DEQX is far from perfect, but most of its compromises can be worked around.

Basically you can run out of computing power if you set it up the wrong way or.... you can get more out of it by setting it up correctly. Have I just said the same thing in two different ways....!!?

Hope this helps

Cheers

Derek.

[john k...]

Hi Earl,

I don't disagree that the MP corrections would be different under certain conditions. I just don't consider that the issue because it is more of a limitation of the design being directional. Take the post I just made above where I looked at the dipole impulse response both on and 30 degrees off axis. Both cases use the same EQ function and the impulse off axis is just about as good as on axis. It would actually be better if I lowered the crossover point. The reason it is as good as it is, and why if would improve with a lower x-o point, is because the dipole response for the bandpass I chose is almost CD. The lower x-o point would yield even better CD. The magnitude changes off axis for the dipole by a scale factor, but the shape of the response (the transfer function), which is what matters for the MP, does not. The point being that if the response is truly CD then only a single eq is required for the entire 3-d space. You of all people should appreciate that. If the system response is MP (i.e. and transient perfect x-o is used) then a single Eq function will correct the response in both amplitude and time over the entire CD window. Sort of another reason why CD should be a design goal.

[john k...]

Originally posted by panomaniac
JohnK - very impressive- thanks! Never quite seen it put that way. =)

How did you figure the EQ? The low end looks simple, to top end does not.


Maybe Lynn is looking for a way to do that acousticaly, instead of electricaly?

Having heard Gary's system, I can certainly say it's one of the cleanest I've ever heard in over 30 years. Quite amazing. No exotic/expensive drivers, either.

The eq is designed using SoundEasy's Digital Equalizer. It allows the user to specify a target acoustic response and then given the driver's raw amplitude and phase response it computes the required filter transfer function to meet the target.

The measurements I presented are acoustic measurement. They were obtained by "playing" the SE developed digital filter (also part of SE's capability).

I uses this DE function in all my preliminary designs. Then I optimize passive or active analog circuits to emulated the digital filters as closely as possible. It's a very powerful tool.

I am sure that Gary's woofer system sounds great. So does my NaO woofer system. From Lynn's description they are pretty much the same design concept, originally due to Kalusche, 1950 and then further analyzed by Holmens (1986) and by Backman (1999) as I stated below.

By the way, Lynn's comment, "They're almost acting as if they were very short transmission lines..." In fact, that is exactly what they are, short,well damped TL's. The role of the damping is two fold: 1) damp the TL resonances and 2) act as an acoustic low pass filter.

[john k...]

Originally posted by mige0
JohnK, where you'd put the limits to the min phase axiom for speaker-enclosure systems?

Vented - transmission line - horns, etc still min phase?

Michael

Vented and TL's are certainly MP. Horns, well I'm not an expert on horns by any means. But from what little I have read the phase velocity can be frequency dependent in a horn which would imply departure from MP at the mouth if the response at the throat is MP. How significant this is, I don't know. Perhaps Earl can address this.