[Mayordean]

A question eventually, but first a little background: I'm recently permanently deaf in one ear due to a surgical side effect. For a couple of months now, I despaired at the loss of this hobby until I discovered that both my iphone and computer music server can switch stereo into mono. Things have improved in that I can now hear both channels summed into mono in one ear, but not only is any sense of image gone, but timbre of various instruments is affected to varying degrees on different recordings. I understand that phase issues are largely to blame: when signals from the left are completely out of phase with the right, that sound disappears, and nearly out of phase signals become distorted or diminished in various ways. I am contemplating having a custom IEM built that would put the drivers from both sides into one earpiece, fed by separate left and right channels (or buying the Sensaphonics 221).
 
The question is: am I really going to change anything by doing this, or will the discrete channels simply sum on my ear drum just like mono?
 
I know that I will not be able to recover a stereo image through one ear. However, my understanding (and please do correct me if I'm wrong) is hearing the goodness of stereo sound, both its image and timbre, is based in part on the irregularities of the listening environment. For example, a perfect cube of a listening room will render severe phase (comb filtering) effects because two waves that are 180 degrees out of phase will arrive at the listener's ear at the same time, cancelling each other out. This is the same phenomenon that would happen in summing stereo to mono, So, in getting a custom one-sided stereo IEM, will I not be putting that into the equivalent of a perfect cube since there will be no room for the signals to bounce around before it hits my eardrum?
 
Any wisdom would be most welcome.

 

[JackKontney]

The fast answer to the title question = no. Electrical summation to mono is NOT equivalent to separate Left and Right signals within a single earpiece.
 
You mentioned the Sensaphonics 221 (http://www.sensaphonics.com/221). The 221 is a true stereo device, with a pair of full-range drivers (one for the Left signal, the other for the Right), housed together within a single earphone. The L and R outputs are sent down individual tubes and delivered to the inner ear. There is no electrical summation, and thus no monaural signal. All stereo information is preserved, and the only summation that can be said to occur is acoustical.
 
You question about “cubic room" phase cancellation is somewhat out of place when discussing the deep insertion in-ear environment. Sensaphonics IEMs go past the second bend of the ear canal (significantly further than acrylics and universals), creating a direct path from the earphone to the inner ear. While there is a small “room” of space (approx 1cc in size) beyond the earphone tip, the cancellation effects you fear from the acoustical summation in that space do not manifest themselves to any significant degree.
 
In fact, the severe phasing effects you mention have not been reported by our 221 customers. Quite the contrary — our users report a sense of space (soundstage) with the 221 that cannot be obtained by monaural electrical summation. While certain studio effects (like the movement of an instrument from far left to far right) cannot be replicated for those with unilateral loss, the human brain does a marvelous job of “filling in the blanks” via sense memory, bringing back much of the joy of stereo listening.
 
Like all Sensaphonics products, the 221 earpiece is custom-fit and made from medical-grade soft silicone.
 
Sensaphonics is driven by hearing health, not marketing. We would not offer the 221 if it did not offer significant benefits for those with unilateral hearing loss.
 
Hope this helps.

 

[Mayordean]

This is very helpful indeed. I'll be attempting to make a visit to your hearing clinic when I visit Chicago around Thanksgiving-time.

 

[JackKontney]

Nice! That can be a busy time, so please call ahead to set up your appointment.