Dr Earl Geddes Summa loudspeakers and kits

[paulspencer]

Many of you will be familiar with Dr Earl's work. I'm posting here to avoid cluttering up his thread here:

DIY Waveguide loudspeaker kit

The kits are based on the commercial versions here:

http://www.ai-audio.com/products_esp10.html
http://www.ai-audio.com/products_esp12.html
http://www.ai-audio.com/products_esp15.html

For background, you may wish to visit:

Gedlee website

Now my questions to Earl:

____________________________________

1. If it were possible to create an ideal polar response, what would it look like on those charts shown on the AI website?

http://www.ai-audio.com/products_esp15.html

If I understand correctly, the polar response of the ESP15 is the best because it's response is flat over a wider range due to the size of the midwoofer allowing a lower xo point while retaining pattern control. However, would it be better if possible to extend that flat off axis response right down to 80 Hz?

2. Let's forget practical concerns. Is it possible to extend this polar response down lower through a waveguide on the midwoofer? Would you consider this an improvement in terms of absolute performance where our concern is purely accurate reproduction? Obviously this would mean a more extreme solution.

3. Could this same aim of extending the flat off axis response lower be achieved in an open baffle design? It would seem to me that the midwoofer could actually achieve an off axis response closer to the waveguide through the side null.

4. I've seen the results of your distortion study that was once on your website. How do you advise making an assessment on the accuracy of a speaker based on measurements? Do we still fail to understand how measurements translate into perceived accuracy? Or do we in fact lack an adequate means of measuring and evaluating accuracy?

Is there a way to measure your Gedlee metric with loudspeakers?

[gedlee]

Originally posted by paulspencer
Many of you will be familiar with Dr Earl's work. I'm posting here to avoid cluttering up his thread here:

DIY Waveguide loudspeaker kit

The kits are based on the commercial versions here:

http://www.ai-audio.com/products_esp10.html
http://www.ai-audio.com/products_esp12.html
http://www.ai-audio.com/products_esp15.html

For background, you may wish to visit:

Gedlee website

Now my questions to Earl:

____________________________________

1. If it were possible to create an ideal polar response, what would it look like on those charts shown on the AI website?

http://www.ai-audio.com/products_esp15.html

If I understand correctly, the polar response of the ESP15 is the best because it's response is flat over a wider range due to the size of the midwoofer allowing a lower xo point while retaining pattern control. However, would it be better if possible to extend that flat off axis response right down to 80 Hz?

IF that were possible (in a practical sense) it would be desirable. Directivity is always desirable if it is controlled. But down into the modal region of a room, directivity is a mute point, and at frequencies below about 500 Hz it becomes less and less subjectively important (in a small room). In a large room it is always an advantage.

2. Let's forget practical concerns. Is it possible to extend this polar response down lower through a waveguide on the midwoofer? Would you consider this an improvement in terms of absolute performance where our concern is purely accurate reproduction? Obviously this would mean a more extreme solution.

I don't think that the compression drivers could go more than maybe 1/2 octave lower on that waveguide without problems. Hence some other approach would have to be used, say an array of drivers, or perhaps cardiod, or some other approach. Would this be a subjective improvement, perhaps, but its not clear to what extent it would be. I would bet on it not being a very significant improvement simply because its so low in frequency (our hearing acuity drops off below about 500 Hz. and we are just not as sensitive to certain critical effects and aberations in rooms and loudspeakers as we are from 500 - 5000Hz, where we tend to be almost hype sensitive at the upper edge). In short this "improvement" would cost a lot, create a bigger and more complex system and net out a small to inconsequencial improvement.

3. Could this same aim of extending the flat off axis response lower be achieved in an open baffle design? It would seem to me that the midwoofer could actually achieve an off axis response closer to the waveguide through the side null.

A cardiod design with a second rear facing driver with some electronic controls could achieve this and an open baffle might be a slight improvement in directivity, but, as I said, its not clear that this is going to improve anything audibly. The open baffle requires a new design of the electronics to correct its falling LF response and the systems efficiency and headroom are degraded. It is a big cost hit in either case.

4. I've seen the results of your distortion study that was once on your website. How do you advise making an assessment on the accuracy of a speaker based on measurements? Do we still fail to understand how measurements translate into perceived accuracy? Or do we in fact lack an adequate means of measuring and evaluating accuracy?

I have absolute confidence in my ability to ***** a loudspeaker design from measurements, so IMO its not the ability to make the measurements that is the issue. For loudspeakers the polar response is critical and you are virtually never shown this critical measurement. Why is that? Well if you've ever seen them for some other designs then you'd know why. Marketing knows better than to show people all the warts in their products. They prefer to show you the gorgeous, but irrelavent axial responses. Nonlinear distortion in a loudspeaker is all but irrelavent, even if its done right. THD or IMD is totally irrelavent for a loudspeaker. For amps and electronics modified forms of nonlinearity measurements are important but again THD or IMD is irrelavent.

Is there a way to measure your Gedlee metric with loudspeakers?

It could be done, but its unimportant so theres no incentive to do it.

You can see that these opinions are quite different than what you usually read in the classic dogma of audio. But you also don't usually read reviews of audio systems like I get either. That has to tell you something. If you always do what you've always done, you will always get what you've always gotten. I get the reviews that I get because I DON'T do whats always been done.