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Old 17th July 2012, 05:33 PM   #31
qusp is offline qusp  Australia
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hahaha awesome, yet another contraption to 'blow one's mind'
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Old 17th July 2012, 07:46 PM   #32
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The subwoofer is wimpy in this application. It is bare like a turtle outside its shell. Its direct output [towards the ear] and that reflected from the piezo tweeter are just right for a good tonal balance. This combo loudspeaker is capable of high sound pressure to literally "blow one's mind/brain". Surprisingly, it is a precise brute which is easy and fast to assemble and dismantle. A "breadboard" loudspeaker of sorts. Best regards.
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Old 19th July 2012, 12:41 AM   #33
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I have a Threshold S150 [voltage source amplifier or VSA] which is my reference. This 20 year-old is a testament to the genius and excellent craftsmanship of Mr. Nelson Pass. Are the floor 'loudspeakers -pseudo headphones' I described above worthy to be driven by this superb amp? Why not? In this S150 application, I am assessing the performance of this hybrid loudspeaker system with an excellent performing amplifier. In a second comparative application I replaced S150 with a Class A transconductance DIY amplifier. Both amplifiers do not use corrective overall loop feedback. The attached [refined] schematic shows the experimental set up. One voice coil [shown as #1] is driven [the load] by either the VSA or the TCA. Voice coil #2 is a floating power generator which independently drives the piezo tweeter. Both voice coils simultaneously travel in the magnetic field. But; voice coil #2 piggy backs on the travel of voice coil #1 in the field. The orientation of the loudspeaker drivers on the floor is the same as described above. The key findings were:
  • The hybrid loudspeaker sounded great with VSA and TCA. Great means pleasing to my ears, and detailed
  • The tonal balance of the hybrid loudspeaker due to VSA was richer in the low end than the high end.
  • By contrast the tonal balance of the hybrid loudspeaker due to TCA was richer [and quite detailed] in the mid -high end than the low end.
  • The hybrid loudspeaker is fully acceptable for music listening.
NB. Condition the hybrid loudspeakers with a medium power musical signal before the so called "critical" evaluations.
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File Type: pdf SubPiezo001.pdf (37.1 KB, 18 views)
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Old 22nd July 2012, 07:02 PM   #34
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Serendipity at work! Refer to the pdf in the above thread. What is the fidelity of the power signal emanating from coils #2; say with Threshold S150 driving coils $1? You guessed it; Hi. I used GRADO SR80i [coils #2]for this experiment. I was not laying down on the floor with my head between the erect subwoofers. To my surprise, GRADO sounded superb; full range, spacious and clean. I have earbuds which are shy in the bass. I stuffed'em in my ears, laid on the floor with my head between the subs. The music was full range. Bass and treble were strong and detailed. Ditto with a a low-cost pair of headphones [also bass shy] which sat on the outside of my ears. Here is the value of this set up:
  • Easy to implement and low cost too.
  • I created a Hi Fidelity [noise-free] headphone port for S150
  • No DC offset. Headphones are protected.
  • Why build or use a dedicated headphone amp? The existing power amp is more than fully adequate.
  • High impedance headphones [e.g. 600 Ohms] will be easy to drive. You have a powerfull amp.
  • Extends the frequency range of ear buds, and over-the-ear headphones.
The two DIY transconductance amps I have also worked very well. However they are intrinsically hummy which annoyed me at this closeness of the drivers.
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Old 1st August 2012, 06:07 PM   #35
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Default Moving Coil Transconductance Headphone Driver

What's new and interesting? Do you have a Transconductance Amp [TCA] ? Mr. Pass [www.firstwatt.com] has popularized them. The output stage of a TCA [a la Pass] is generally the opposed drains of MOSFETs. There is not a loop feedback [to the front end] which lowers the desirably [and needed] high output impedance of the TCA. Please consult the attached schematic for the following discussion. A TCA drives one voice coil of a two-voice coil subwoofer [12"]. The second coil moves [has to] in a synchronous manner with the energized first coil connected to TCA. This second coil is the "Moving Coil Transconductance Headphone Driver [MCTHD] . The headphone is the load to this second coil and is connected in parallel [with coil #2]. The subwoofer driver is not enclosed. In my experimental setup it hangs freely from the ceiling and out of the way. Take a look at the 3 graphs in the attachment. The top one is the impedance curve of the first coil [or voltage drop across it = Vo] and is typical of any woofer. The one below it is the impedance curve [and also voltage drop across it] of the second coil loaded with the headphone. It has the same characteristic shape of the top one for coil #1. This is the important part. The headphone is driven by a signal of the indicated shape which is primarily the impedance curve [or voltage across it] of coil #1. There is a boost in the low end between 100 Hz down to 20 Hz. There is also a gradual [and substantial] boost of the mids and highs. I have a pair of GRADO SR 80i headphones. They sound totally different [dull] from the situation of being driven the normal way with a voltage source amp. They came alive when driven by MCTHD. The highs are brilliant and the low end is well-defined but light and tight. I found the highs too bright [strident] for my taste. So I toned them down with a 0.1 uF polypropylene cap in parallel with each headphone. Thus I made my new and improved pair of headphones by manipulating the drive signal to them.

Note that a faint sound emanates from the subwoofers which in my set up are ~10 feet away from where I sit. The headphones sounded mostly the same with me in the room with the hanging subs and outside the same room with its door closed.

Treat your ears to new flavor of music.
Attached Files
File Type: pdf SubHeadphone1.pdf (38.5 KB, 23 views)
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Old 1st August 2012, 07:25 PM   #36
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Quote:
Originally Posted by kctess5 View Post
I'd be tempted to get a pair of over the ear hearing protection sort of headphone type things and mount a 3" tang band driver in it making sure to get a good seal. The things you mentioned earlier about low excursion and distortion would all be true
I did so some 35 years ago and used eliptical FR speakers. Had to tweak air permeability of the earmuffs for best bass response.
I've seen a interesting project in the russian "Radio" magazine. Can't remember if it was orthodynamic or ESL. Must do a search in the basement.
What effect will have the intense magnetich field of the speaker magnets on blood sirculating in ears and brain? Is blood magnetical?
Antoinel Did you licenced your nice helmet phones from Jecklin? ;-)

Last edited by franzm; 1st August 2012 at 07:37 PM.
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Old 2nd August 2012, 11:05 AM   #37
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Default Moving Coil Transconductance Headphone Driver

What about Doppler effect? (Sound from piezo speaker being reflected on the moving woofer cone). Could this be used in a benefical manner, i.E. to cancel some distorsions?
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Old 2nd August 2012, 11:50 AM   #38
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Quote:
Originally Posted by franzm View Post
I did so some 35 years ago and used eliptical FR speakers. Had to tweak air permeability of the earmuffs for best bass response.
I've seen a interesting project in the russian "Radio" magazine. Can't remember if it was orthodynamic or ESL. Must do a search in the basement.
What effect will have the intense magnetich field of the speaker magnets on blood sirculating in ears and brain? Is blood magnetical?
Antoinel Did you licenced your nice helmet phones from Jecklin? ;-)
Is Jecklin Dr. Jeckel? Hahaha. I believe the magnetic field of a loudspeaker is mostly focused in the voice-coil gap. Other loudspeakers may have a magnetic shield. Blood has Iron in the 2 and 3 + oxidation states [in the protein Haemoglobin]. It is paramagnetic and is influenced by magnetism. I did experiments in college using transition metal solid compounds in an intense and localized magnetic field to determine whether the valence electrons in the D- orbitals of the metal ion were high or low spin. I believe the answer had units of BM [Bohr Magneton].
Please add more details and ask more questions. Maybe the setup improves the frequency response of hearing. Would'nt this be something?
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Old 2nd August 2012, 12:03 PM   #39
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Quote:
Originally Posted by franzm View Post
What about Doppler effect? (Sound from piezo speaker being reflected on the moving woofer cone). Could this be used in a benefical manner, i.E. to cancel some distorsions?
It may be beneficial as you mention above. In a second experiment, the tweeter [piezo and an 8 Ohm Pyle Pro electrodynamic] were vectored perpendicular to the subwoofer [minimum Doppler]. Got fully satisfactory results too. I also measured SPL in this pseudo enclosure with a Radio Shack "Realistic" model analog meter. For a realistic and comfortable listenning experience, the meter [C-weighting and Fast] registered 60-75 dB with occasional peaks at 80 dB. I believe these values are safe during an hour worth of music enjoyment.
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Old 2nd August 2012, 07:01 PM   #40
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Originally Posted by Antoinel View Post
Is Jecklin Dr. Jeckel?
Joerg Jecklin - Wikiphonia
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