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Old 17th June 2002, 07:47 PM   #21
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Hi Harry,

maybe you're right, but I think it's an interesting question why some amplifiers or op-amp's sound bright while the bode-plot seems absolutely flat between 20Hz-20KHz....

any ideas..

gr,
Thijs
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Old 18th June 2002, 02:47 AM   #22
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Default Thanks Harry

I actually spent hours formulating a detailed response in wordpad outlining all the things I thought might cause different sonic affects. But when I looked at it later I saw there were obvious exceptions, to every one of them. I'm also beginning to understand just how differently we all hear too, so whilst my percertions of a particular 'distortion' mechanism might be valid, how would someone else perceive it? I mean I've never seen two people hear a pair of speakers the same way, and their characteristics/deficiencies are <i>at least</i> 1 or 2 orders of magnitude greater than an amplifier. So trying to answer definitively would really be doing people a disservice.

Cheers
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Old 18th June 2002, 03:51 AM   #23
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Default Topic to vague

Bright
* FET or MOSFET
* Dome tweeters that uses any kind of material. Dome tweeters are too concentrated on one location.
* Horn tweeter are concentrated

Warm
* haven't gotten to this point

Neutral
* Haven't yet set a neutral zone

This topic is too vague. A whole novel of his or her own opinions won't cover this topic.

It is best to accept his or her own psychology of sound. In simpler terms how different people hear sound.

A good designer should take some polls to see if his or her goals on a particular project meets or exceeds their expectations.

In conclusion, there is no perfect amplifier or speaker driver.
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Old 18th June 2002, 03:56 AM   #24
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It's very hard to quantify alot of this even the above comment about MOSFETS is biased .... in class a/b mosfets are harsh, bright and misty but in highly biased SE Class A they can be beautifully warm.
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Old 18th June 2002, 04:10 AM   #25
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Quote:
For SE Class A output stages MOSFET's are SWEET
AudioFreak, remember this post. Its yours.


I try to stay away from any Class-A/B amplifiers, but if I don't know what the AV reciever is bias at. I have to live on what I got.

I have a Class-H AV reciever. With Class-H amplifiers there are sub-classes such as Class-A, Class-A/B, and Class-B. If I'm due to be elecuted. I'll try to poke around in my AV reciever.
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Old 18th June 2002, 04:18 AM   #26
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Yes i remember that post well and i stand by it.... highly biased SE Class A mosfet output stages can be wonderful to listen to. Sweet is slang for great/awesome/beautiful/wonderful.
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Old 18th June 2002, 06:45 AM   #27
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Default Harry might be right?

Only might?

OK........10 to 20 years probably isn't long enough.

Bode plots will only tell you if it will blow up. Not how much RF will muck up those teeny-tiny BJTs in the front-end. I would hope the Bode plot is flat from 20-20,000 Hz.

Jocko
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Old 18th June 2002, 07:46 AM   #28
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Default Sheet rock eh?

... perhaps you meant to use rockwool? Several years ago, while I was studying metals and materials engineering at university (before seeing the light, and switching to electrical ), I did some research into affordable acoustic damping materials. I wanted something other than the professional acoustic treatment products which can cost an arm and a leg... It turns out that ordinary rockwool is one of the very best - better than most foams, with a flatter absorption spectrum and better low frequency absorption properties if I recall correctly. Anyway, rockwool is often used as an office cubicle wall / partition material not only for it's acoustic deadening properties, but also for it's great fire resistance.

What you want in an acoustic damping material is a large porous surface area. Sound absorption in general works by utilizing the viscous shear flow losses (aka "friction") of air volumes in contact with a surface, as the air attempts to flow past that surface. Hence, materials which posess a greater distributed surface area are most effective. This is also why acoustic damping materials work best when suspended out from the wall, as they rely on the movement of air past their internal surfaces. At a fixed boundary you have the peak of a standing pressure wave, or the null point of a velocity wave, depending on how you choose to look at it. With a little thought, you may now also understand why, as you increase the thickness of damping material attached to a rigid boundary, you will begin to absorb lower and lower frequencies better...

If you want some rockwool, you can buy it as a base/ rooting material for hydroponics. Of course, if you intend to outfit an entire room with rockwool acoustic damping, the lads at the hydroponics store might be a little suspicious of someone purchasing such large quantities of the stuff... hehe, perhaps you'll get to meet the local police constable?

Just thought I'd interject with those few random thoughts...
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Old 18th June 2002, 09:07 AM   #29
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Default Re: Sheet rock eh?

Quote:
Originally posted by hifiZen
... What you want in an acoustic damping material is a large porous surface area. Sound absorption in general works by utilizing the viscous shear flow losses (aka "friction") of air volumes in contact with a surface, as the air attempts to flow past that surface. Hence, materials which posess a greater distributed surface area are most effective. This is also why acoustic damping materials work best when suspended out from the wall, as they rely on the movement of air past their internal surfaces. At a fixed boundary you have the peak of a standing pressure wave, or the null point of a velocity wave, depending on how you choose to look at it. With a little thought, you may now also understand why, as you increase the thickness of damping material attached to a rigid boundary, you will begin to absorb lower and lower frequencies better...
Hi hifiZen,

You are definitely correct in saying that viscous sheer flow is the primary mechanism for absorbtion in fiberous materials, however, it's not the only mechanism. Particle movement is also significant and especially in foam, you get helmholtz absorbtion.

You can tune absorbers to deal with particular frequencies by altering the thickness of the absorbing material and moving it 1/4 wavelength away from a solid wall to maximise the absorbtion at a particular frequency. Altering the thickness will tend to spread the frequency range of absorbtion (the thinner the absorber the narrower the absorbtion peak) as well as increasing the amount of attenuation. When you move the absorber out from a wall, what you are doing is moving it into the region of highest particle velocity for a particluar frequency, allowing it to do it's job. There is a slight comb filtering effect with this type of absorbtion as the wavelength changes with frequency, but as the high frequencies tend to be diffused and absorbed very easily in normal rooms, it's seldom even noticable.

Good builders suppliers should have rockwool in sheets of 4'x4' and in various thicknesses. It's a pain to use though, dusty and sheds bits everywhere so it has to be enclosed. If you can't get rockwool, or decide it's too messy and want to use foam instead, make sure it is open cell foam. Closed cell foam is for furniture only. You can tell by pressing a sample against your mouth and blowing hard. If you can blow through it reasonably easily, it's open cell, otherwise keep it for sitting on or packaging.

DocP
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Old 18th June 2002, 03:11 PM   #30
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I achieved the best sound by now by using a class A amplifier with internal computer drive system, my speakers are own build:

2 x 3 way, using:

1 dome tweeter (80W 8ohm) (SEAS)
1 midrange speaker (no horn, but closed design) (60W 8ohm)
1 woofer (120W 8ohm) (JAMO)
(unfortunately I don't know the dB/W/m of the speaker)

and just simple cheap filter (I think 6dB/oct)

box dimensions:

30 cm width
57 cm height
22 cm depth
2 pipes d: 5.5 cm; length = 11 cm

all boards 8mm thick
fill the boxes with rockwool for warmer sound

ideal sound when placed on the floor or in corners (!!!)
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