Flat Anechoic Measured Frequency Response Speakers

Duke,

The K&H O 500 measurements are absolutely stunning (although the spectral decay plot may be hiding resonances as it cuts off at -25 db)

I have read good comments about these speakers (except they do not play very loud - probably a direct result of their tremendous linearity and even dispersion - as everyone knows you can EQ down to get flat but you lose efficiency).

Do you know what they sound like? I have not heard them.

This excess off-axis energy in the lower treble region is caused by the tweeter having a very wide pattern just above the crossover point, and it's there on most speakers

AHA ....now you have hit the nail on the head in respect of the deficiencies of most speaker designs and especially in contrast to the K&H O 500 you refer too, which has the most beautiful plots I think I have ever seen. WOW.

They were very detailed, but to my ears they sounded forward and a bit bright.

Thanks - although too forward is how many would describe ATC's. The plots indicate these may indeed be a bit brighter in the treble as there is no roll-off at all - beautiful plots on and off axis - apart from a hint of what might be resonance in the metal dome around 16 Khz - I doubt many could hear that but it might add some "glare" - who knows.

Of course as you said with such a perfect response one could simply tone down the treble to get any desired response "nirvana" at all...the key is the balance in on and off axis which remains whatever you do with tone control - beautiful plots!

I recall a thread where there was an argument about the relevance or value of specifications. I can imagine some are rolling their eyes at this current discussion of beautiful looking plots.

For those rolling their eyes, and this is true: Dolly Parton once said that she was best known for just TWO things! Demonstrating so very well that people often see things all too differently. Her answer was, of course,.....her music and her lyrics ;-)

The ATC has a very flat response. Do you find that flat responses sometimes limit the 3rd dimension to the soundstage? In other words, do you find it is more like a two dimensional picture than a three dimensional picture depth-wise?

No not at all. A flat "power response" without the usual treble and bass boost can sound extremely natural and is hard to distinguish from live or real instruments. The vast majority of speakers have a strong off axis response in the bass and treble with a dip in the midrange. Sometimes called the "BBC dip", this has become so popular in consumer speakers since the 80's that a flat power response is rare and is usually interpreted as "forward" or "harsh".

There is a strong correlation to soundstage (although most depends on the recording)...there is a tendency for instruments to sound closer as if they are in the room with you - so you could argue that there is less depth with this pattern - conversely you could argue that other speakers will never reach as forward into the room or close to the listener forever relagated to sounding as if you are at the first balcony....so I think the soundstage moves forwards somewhat but is no less or more compressed than speakers with a BBC dip.

Not necessarily flat, but smooth.

Agreed - exactly! Very few people are aware of this. When I talk about tone control adjustments audiophiles cringe ....but they should not. It is no crime to tweak in this way. In fact a ruler flat on axis response is NOT all that important to our listening pleasure...it is actually the off axis that matters most.....in fact the MOST important thing is that the on axis and off axis behave in at least a uniform way with consistent gentle roll off as you get to wider angles...this is what sounds natural!

What sounds unnatural to our ears is a speaker transducer that has either strong directivity or wobbles and bumps off axis such that the on axis and off axis curves do not all behave together in a smooth way - in many poor designs they often crisscross as the cone breaks up or there is a sharp discontinuity at the crossover region (suckout or sudden abrupt change in dispersion pattern)

See this discussion SM75-150S. You will see the author correctly emphasizes that it is NOT the smooth on axis frequency response that is so important in a driver but the smooth consistent behavior between on and off axis and a wide dispersion.

SMOOTH is the key ingredient. This is why many designers pay so much attention to smooth phase response which is a warning sign of unwanted things going on with the design.

This is generally accepted to be simply good loudspeaker engineering.

Absolutely agree. Dr Toole's experiments helped demonstrate this to the industry..although I believe many designers knew this to be important.

What do you think of the Moulton Labs 8 CD's and course? Do you think it is worth it for non audio professionals (8 CD's = $220 )....above all was it fun, a revelation?

Jkalman,

You have me convinced. I'll order it.