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Old 29th November 2001, 03:26 PM   #21
Bill F. is offline Bill F.  United States
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FWIW,

the drivers I'll be using are the Parts Express #269-469 full-range 4in. 150-16KHz, 90dB/W/m, 15W max pwr, 8ohm. I got two cases of 32 at about 70 cents for each driver, including shipping!

My latest thought is to put 32 of them into a rectangular open baffle array of 4x8 on each channel. The middle 16 (rows 3,4,5,6) will be full range while the top/bottom 16 (rows 1,2,7,8) will be rolled off at about 300Hz. These panels should have flat response from about 150-10KHz, 102dB/W/m efficiency, and 200W+ power handling. I imagine it'll end up looking (even sounding?) like a large planar!

(For lower bass I'll add a dipole woofer section of 4 15" drivers per channel, biamped. For HF, I'm planning to cross this array over around 4KHz with a high-efficiency horn tweeter to further cut down on any beaming/comb filtering nonsense...So I guess it'll be triamped.)


The rectangular array should create less comb filtering than a line array and will also spread the Q of the dipole baffle dimension-related fpeak (similar effect to baffle step).

I'd like to wire the array 2(series) by 8(parallel) for both the rolled-off and full range halves. This will yield a nominal impedence of 1-2 ohms (frequency dependent).


So, I guess you could think of the amp in question as a low wattage, high current mid/bass amp. As such, ultimate frequency extension isn't crucial.

Bill
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Old 29th November 2001, 03:31 PM   #22
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Default cool idea

Interesting idea!
With 104 db/1w speakers, you would need only 1 watt output per channel from your amp. If you want more headroom, maybe assume a 2 watt power amp. This would give you more available power than you probably will ever use.
Assuming 1W = 104 db. then 2 W should give 110 db. More than enough.
In order to get 2 watts across 1/4 ohm, you would need peak current of: I*I*(.25) = 2watts =: sqr.(8)= 2.83 amps per channel peak.
The Zen amp would seem like a great candidate if it wasn't for its 1 ohm output impedence. With 2.83 amps available, 1.6 watts of the 2 watts output would be lost across the amplifier output impedence, leaving about .5 watt for the speaker.
Thats not factoring in any milliohm impedence added by cables etc.
You will need either an amp with a very low output impedence,(very high damping factor), or tremendous current reserves.
mg16
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Old 30th November 2001, 02:40 AM   #23
PassFan is offline PassFan  United States
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Unhappy 104spl 1w/1m

I see were you came up with 104 db. You started with a 90 db driver and added 3 db for every doubling of the drivers. You must also double the wattage to maintain your 3 db increase. You must double the drivers and the wattage to increase 3 db. So, you wouldn't wind up with 32 drivers with a 104 db spl at 1w/1m, as each driver would require 1w to maintain its original 90 db spl rating. It would be 104db spl at 32w/1m. Bear in mind, at 2m you will lose 6 db, at 4m the loss is 12 db. 104 db is not that loud. Normal conversation is usually in the 80 db range. The formula, (Watts = log x 10) will give you the db increase for whatever wattage you decide to use. This will be added to your 104 spl at 32w/1m. At the risk of offending I am assuming a lot, but bear in mind I'm only trying to help and would like to see you succeed. Good luck.
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Old 30th November 2001, 02:52 AM   #24
PassFan is offline PassFan  United States
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Talking Correction

Normal conversation is around 60 db. Heavy traffic on a crowded street is 90 db. Also, an increase from 1w to 2w would yield an increase of only 3 db. Hope this helps.
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Old 30th November 2001, 09:27 AM   #25
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104dB is indeed LOUD... ... normal listeing level are more like 90dB.... further more, I know that a 4x12" speaker is louder then a 1x12"speaker driven by the same amount of power.. so some there is a increase in efficiency.. could anyone explain this....

thijs
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Old 30th November 2001, 10:43 PM   #26
PassFan is offline PassFan  United States
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Depending on the situation 104 db can be both loud and not loud. If I were in a quiet environment 104 db would be loud. Do we really think about sound levels of 90 db when were walking down a busy city street? 3 db represents a volume increase of double, but the human ear can't perceive it. The human ear requires a 6 db increase to perceive any increase at all. It doesn't sound like its twice as loud does it, but in fact 6 db is more than twice as loud, yet it takes as much as 10 db for the ear to perceive it as twice as loud. The decibel is a logrithmic scale as is your ears hearing ability. The difference between 100watts and 1000watts would be 10 db. The 104 db spl also represents the volume level 3' away from the speaker. If you move to 6' it drops to 98 db. If you move to 12' it drops to 92 db. If you have a big listening room and your 24' away, guess what? It's not really that loud after all is it? As to your speaker question, The difference is in the resistance of your different speaker setups. If the resistance is lower for your 4x12's then the amp will attempt to put out more power. Theoretically an amp at 100watts into 8 ohms will put out 200watts into 4 ohms. It's generally less due to a number of things. Hope this clears up my earlier statements.
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Old 1st December 2001, 05:49 PM   #27
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Skippy,
Given decent conditions, I can hear less than 1 dB differences. 3 dB is <i>easy</i> to hear.

Grey
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Old 1st December 2001, 08:18 PM   #28
PassFan is offline PassFan  United States
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Grey:
Where do you live, in an anechoic chamber?
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Old 1st December 2001, 10:01 PM   #29
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Near enough...a basement with 4" concrete floors and three out of four walls being cinder block.
Actually, aside from that, I've taught my ears a thing or two. I've said it elsewhere, but can't remember the thread. People who lose their sight find their hearing increasing in acuity to compensate. The trick is to do this without having to lose your eyesight. Try this:
At night, with the lights out, navigate your home by sound alone. No cheating. The first few times you try it, you'll hit the jamb of the door you were trying to go through. (Keep your hands out in front of your face so as not to get a bloody nose.) It's embarrassing; you thought you could hear, but discover that you can't. But keep at it, and you'll find yourself able to <i>hear</i> walls and doorways and such. (Open doorways are quieter than walls--the sound that hits them doesn't reflect and come back to your ears. Not to mention there are often tiny sounds in the other room that are different than the room you're in, another person's breathing, clocks ticking, etc.)
For extra credit, try to hear the furniture. Don't laugh--most furniture these days is loaded with foam and covered with fabric. It's a black hole for sound. If you hear a profound silence in front of you, go slowly, there's a couch there.
It also helps if you're a musician accustomed to playing by ear (jazz or rock here, classical, for once, has to take a back seat).
<i>Concentrate!</i> It will soon become second nature.
Don't blame me if you start hearing flaws in your stereo you never recognized before. It's expensive to learn to hear.

Grey

[Edited by GRollins on 12-01-2001 at 04:03 PM]
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Old 2nd December 2001, 04:42 AM   #30
PassFan is offline PassFan  United States
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Cool Guru

There was a review of an ear training program in this months issue of audio xpress. Claimed to be able to teach frequency recognition as well as a few other things. I like to close my eyes and dim the lights when I do any listening. I like to shut down the senses that I don't need to hear with. I believe it makes a difference. My wife doesn't understand it. She can't hear a 6db difference either.
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