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Old 2nd January 2003, 06:50 PM   #11
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kingdaddy !

You´re right of course !

I´ve never considered to build a speaker with passive x-overs by the same reason.
Passive networks is hard to calculate and of course there´s the temperature-effect. Cheap of course........
Active ones are very easy to realize but is more expensive.

The reason for my first thread is:
Even if you buy a high quality speaker with lots of magnet (low Qts) and construct/build a vented loudspeaker, which would give a comparly low Qc ( about .4) in sealed box´s you´d get a slight rise (+3-6 dB) in the 70-100 Hz region due to reflexes.

For my coming project, I´ll use the Scan-speak 21W/8554 and up to now the box-volume would be in the region of 30-45 liters (vented or not). With the box situated in an ordinary room of 25 sq.m it will most likely give unwanted reflections, mainly from floor and walls, which give gives a more bumpy bass (70-100 Hz) but the low bass will be reproduced up to the level that corresponds to the room area (frequence wave-length).
I haven´t decided yet if it´s going to be vented or sealed but if vented, I think a fb of about 35 Hz will be best since acoustic mass in tube otherwise will be too heavy= undistinct bass.
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Old 2nd January 2003, 08:20 PM   #12
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Partly agree kingdaddy,

When we are talking about Qms, Qes ant Qts concerning loudspeakers, indeed damping is involved. This concerns the intrinsic high-pass 2nd order characteristic of a loudspeaker and is of relevance if the speaker has to produce sound down to and below fb. This is usually only the case for woofers. With mid speakers and tweeters you stay far above fb in general and damping is not much of concern.

IMO stablity and the capability to drive complex loads with ease of an amplifier is of more importance than damping factor of the amp. The 20W MF David amp (A1) drives a Rogers TML with much more ease than a 100W Denon 4400 for instance.

So yes I agree for woofers but not for mids and tweeters. It is my experience that passive x-overs at the x-over frequency between mid speaker and tweeter give better sonic results than active x-overs. This is probably due to the limited GBW product of an op-amp?

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Old 2nd January 2003, 09:03 PM   #13
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Some of this is probably over my head so I can’t comment, but I do know from experience that all drivers including the Tweeter will benefit form direct coupling to the output of the Amp, also the newer Op-Amps that are available today have very little if any of the problems of just a few years ago.

I’ve had at least 2 different pairs of speakers with simple Butter-worth even order Passive filters that sounded quite nice, but once I replaced the Passive device with a either a 3rd order Active (Nak 200H) or a 4th LR (Marchand) it sounded much tighter and the transients were far better and the Attack of the mid-bass was superior, and none of these were operating in the true LF range, even the highs were much cleaner and more articulate. Also it seemed to have much less cone movement during loud passages. And maybe this isn't exactly what Dampening is but I know it's closly related, and I'm quite sure that all drivers benifet from direct coupeling.
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Old 2nd January 2003, 09:15 PM   #14
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Only a contribution to the active-passive debate:

Previously I built an active 3-way system where the power amps were very basic. GBW wasn´t more than 1MHz and their current-capacity wasn´t that good; suffered from a .33 ohms emitter resistanses. All the same; they do sound very good. Probably because the tight coupling between speaker and amp.

Presently, I´m planning to use a Op-amp, namely LM3886, which also have limited GBW (2MHz) but they can deliver typically 7 A of current (depending on power-source). Better not use this LM3886 up to it´s power limit though since suffers from the SPiKe-circuit. Many DIY have used it and have reported good results.
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Old 3rd January 2003, 10:32 AM   #15
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Hi,


Quote:
I’ve had at least 2 different pairs of speakers with simple Butter-worth even order Passive filters that sounded quite nice, but once I replaced the Passive device with a either a 3rd order Active (Nak 200H) or a 4th LR (Marchand) it sounded much tighter and the transients were far better and the Attack of the mid-bass was superior, and none of these were operating in the true LF range, even the highs were much cleaner and more articulate.
Here you are comparing filters with totally different characteristics. That’s not fair. A simple Butterworth filter is of no use for high-end purposes and is of no good whether it is implemented passive or active. LW filters with a Q-factor of 0.5 are sounding much better. The 1st order + higher order combo’s are also interesting. Also the filter characteristic of the speaker unit itself is important, no matter if you filter passive or active.

For clarity, when I am talking about GBW I am not talking about the power-amps but about the op-amps used in the filters. I did do a lot of “3-amping” in the past and used the BB’s 2604 op-amps with good results for the filters. But yes there are better ones out there nowadays.

Quote:
Presently, I´m planning to use a Op-amp, namely LM3886, which also have limited GBW (2MHz) but they can deliver typically 7 A of current (depending on power-source).
The LM3886 is a very good amp for multi-amping. I did use them a lot. But for the tweeter you need to use a good PP coupling capacitor anyway. The slightest DC on a tweeter will do not any good.

The big advantage of multi-amping is that you relax the headroom requirements of each amp. This gives much more apparent dynamics because there is less chance an amp will clip. Also there is less IM distortion produced in the power-amps.

I am myself more on the track of using a good class-AB amp for the basses and a fine pure class-A for the mid/highs.

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Old 3rd January 2003, 12:37 PM   #16
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Quote:
originally posted by bjed
Most woofers do reproduce high-bass a bit "bumpy" due to floor/wall reflections. The added damping is requested to make high-bass sound more accurate/rigid/dry.
Floor/wall reflections have to do nothing with cone damping. They depend from room geometry and its acoustical properties , speaker baffle size/shape and finally speaker placement. No way that You can influence this significantly by just changing damping of the driver.

Quote:
originally posted by Pjotr
I Have good results with taming the Q of a (closed) box by using an electronic bi-quad compensation filter like that of Linktwitz: http://www.linkwitzlab.com/
Also so have I. Here some of my experiences with it:
http://www.diyaudio.com/forums/showt...072#post103072
BTW: the Linkwitz transform circuit does not work with BR-enclosures, only sealed.

Quote:
originally posted by kingdaddy
So any method of increasing dampening seems wasted to me when most of all the driver control is being robbed by de-coupling the Amp's outputs to the driver's inputs via passive crossover networks.
What concerns damping of drivers that usually do not operate down to their resonance frequency (mid/high drivers) I can agree with what said Pjotr:
When we are talking about Qms, Qes ant Qts concerning loudspeakers, indeed damping is involved. This concerns the intrinsic high-pass 2nd order characteristic of a loudspeaker and is of relevance if the speaker has to produce sound down to and below fb. This is usually only the case for woofers. With mid speakers and tweeters you stay far above fb in general and damping is not much of concern.

In contrary to him I´m convinced that active drive of mid/high is beneficial though. At least this counts for moving coil drivers due to the "voice coil temperature modulation" Pjots mentioned already. But there are other aspects also due to more relaxed operation of the power-amp (IM-modulation, power). Damping plays only a minor role in this.

Quote:
originally posted by Pjotr
Here you are comparing filters with totally different characteristics. That’s not fair. A simple Butterworth filter is of no use for high-end purposes and is of no good whether it is implemented passive or active. LW filters with a Q-factor of 0.5 are sounding much better. The 1st order + higher order combo’s are also interesting. Also the filter characteristic of the speaker unit itself is important, no matter if you filter passive or active.
IMO You can`t generalize that Butterworth filters are bad for high quality audio and LR filter are always good respectively always sound better. It all depends from the application, drivers/ enclosures etc. etc. You can`t view the filter isolated from the hole concept and say 12dB BT or whatever is bad (maybe it`s bad for a particular case but in another it`s good). BTW: Q=0.5 is only true for 2.order (12dB) LR-filter whereas 4.order LR-filter(24dB) is nothing less than two cascaded 2.order Butterworth filters (Q=0.7)

Bjed:
Your Scan-speak 21W/8554 is a very fine unit. If I were You I would decide for what Rodd suggested - a sealed box design(with the Linkwitz transform circuit if You want to go active).
Whatever You decide, closed or vented active or not - it will have little influence on the mentioned room reflections issue.
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Old 3rd January 2003, 03:11 PM   #17
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quote:

Floor/wall reflections have to do nothing with cone damping. They depend from room geometry and its acoustical properties , speaker baffle size/shape and finally speaker placement. No way that You can influence this significantly by just changing damping of the driver.
---------------------------------------------------------------------------------

But of course you´re right about room-geometri and so on.

I can´t totally agree with you about influences: For instance, the use of equalizer´s will give the opportunity to correct those phenomenoms (i.e. level-adjustments of certain frequences). Another way is to decrease levels passivly (i.e. better damping) at the source, right ? That is easy when using sealed boxes (i.e. lower Qc) but harder when using vented boxes since port will interfear. Another way is correct electronicly (i.e. the use of Linkwitz transform circuit) but again only in sealed boxes.

But you´re right, the influence can only be done marginally since physical conditions always contributes. Corrections should always be done in several areas; first physically and after that by changing source.

All I´m saying is that by increase of damping together with other physical alterations will affect sound, especially in bass-region.
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Old 3rd January 2003, 04:38 PM   #18
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Lightbulb "better damping" or..... "higher attenuation"?

Hi bjed:

Now I begin to realize what You mean with "damping".
I think in this case the correct English terminology for what You mean is "attenuation" or "gain" vice versa.
Isn`t it?

If so, even an equalizer is only partially suited for correcting room reflection issues. For instance You can do little with it about waves that cancel due to interference. This is a wave that bounce back from a wall/floor, arrives again out of phase and mix (interfere) with the directly emitted wave from the speaker and thereby gets attenuated or even almost canceled.

I still don`t get it what sealed/vented or high/low Qtc should have to do so much with the room reflection thing.
Probably just another language related problem between two people not talking in their "mother-tongue"
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Old 3rd January 2003, 06:55 PM   #19
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cocolino:

That´s just the case; interpretating ones language. Since english have more more meanings to one expression than the swedish language (rather the opposite, in fact).........Anyway, I´ll try to choose words better: Being a swede makes it a bit harder to explain the problem, styntesis, abstract, suggestion, solution and conclusion.

By means of dampening, it makes things a lot easier to adapt to a certain "normal" acoustic situation. It gives a bit of "headroom" to work with, so to say.

I´ve syntiziced some situations and, afterwards, used the solution in a construction with some success. Success in subjective meaning since all listeners is subjective, right ?
Youngsters would probably not agree (due to other priorities).

Conclusion so far: use low Qc (or equivalent) in moderate listening room´s areas.

This means, if you work with BR enclosures, that even the Q of helmholtz-frequence will benefit.
I´ve also tested some solutions where I´ve inserted dampening-materials in the port, with some positive experiences, and that´s really a derivate between BR and sealed boxes of course.

:-)

The first question: to use cone- or electric-dampening was really a way to "stick the neck out" since i haven´t tried it out. I thought, perhaps someone have.....
Now my father shouts: "We used cone-dampening back in the 60´s with great luck and if I remember right, even in the 70´s".
Well, in those days, speakers were not that good, but they did what they did with small means and acomplished something even then................


Come on everybody; comments ?!
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Old 3rd January 2003, 07:27 PM   #20
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damp·en (d²m“p…n) v. damp·ened, damp·en·ing, damp·ens. --tr. 1. To make damp. 2. To deaden, restrain, or depress. 3. To soundproof. --intr. To become damp. --damp“en·er n.


In terms of Electrical dampening the meaning from what I know is best explained as the Amplifiers ability to control the movement of the drivers Cone.

Any components between the Amp's output and the drivers cone will no doubt affect and degrade the ability of the Amp's output stage to control the movement of the drivers cone / Voice Coil.
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