Stage 2

[sploo]

If I understand things rightly, once I get the helmholtz in one piece and start trying various lengths of port to find the correct tuning frequency to nail that room mode, I'll know I've hit it because the amplitude of the 'blade' should to a lesser extent and the ringing time to a greater extent reduce. Only at that point should I start adding glass-fibre or an equivalent absorbant material to reduce the blade-like appearance to a (hopefully) much more rounded lump; in other words reduce the blade's Q. Is this correct?

Sounds logical, but I can't remember for certain atm. I'm pretty sure F. Alton Everest's "The Master Handbook of Acoustics' goes into this in some detail.

Why, when a sub has so much greater positional freedom in a room than the front left and right speakers, do people pursue full-range speakers? I should note that I'm not ruling out the possibility of buying a pair of full-range speakers in the future myself, but I just can't imagine being able to fine-tune any room's response to anything like the same extent as can be achieved with non full-range speakers (or even full-range speakers) and a properly integrated sub.

If you mean a speaker with a full-range driver then it's due to the lack of need for a crossover (passive crossovers are, as I learn more about them, nasty). Also, you get a 'point' sound source, instead of sound coming from multiple centers (as you do with a bass/mid and treble setup).

If you mean a loudspeaker cabinet with sufficient drivers to really reproduce 20-20k with a pretty flat response curve, then I guess it comes down to convenience.

With sufficient room treatment, the position should become less of an issue, but hey, this is the real world - nothing's perfect .

 

[Buckle-meister]

If you mean a loudspeaker cabinet with sufficient drivers to really reproduce 20-20k with a pretty flat response curve, then I guess it comes down to convenience.

Yes, this is what I meant. Given that full-range speakers tend to cost the earth, but that non-full-range speakers can be relatively inexpensive and still reproduce down to say 50Hz, it seems a helluva lot of money to lay down just to obtain an extra few hertz (though I know there's more to a speaker than just it's frequency response) or for convenience.

 

[Ethan Winer]

John,

> bass management low pass for the LFE output is generally 24dB/octave in contrast the the 12dB/octave high pass for the mains, the thinking being that the mains will have an acoustic roll-off of around 12dB/octave at the bottom end anyway so overall the result will then combine nicely. <

Interesting. I've never heard of non-symmetrical crossover slopes. But you mentioned LFE. So is it only the LFE channel that rolls off at 24 dB/octave, or is that also for regular stereo music played through a modern receiver having bass management?

--Ethan

 

[JohnPM]

So is it only the LFE channel that rolls off at 24 dB/octave, or is that also for regular stereo music played through a modern receiver having bass management?

The 24dB/octave roll-off is a bass management feature affecting the LFE/Sub output signal of the processor/receiver, it applies to any content from the main channels.

Handling of the LFE signal in a multi-channel recording can vary between processors. The LFE channel in cinema recordings can have content up to 120Hz. Some processors will pass LFE content directly to the Sub/LFE output without any processing. Others apply a common low pass filter (usually 80Hz) to the LFE content and the redirected bass content from the main channels before it gets to the LFE/Sub output connection, with the result that the LFE content between 80 and 120Hz is lost. Dolby recommend that content producers use an 80Hz low pass on the LFE channel when mixing their Dolby Digital material (especially music) to allow for this. Some processors provide a separate adjustment for an LFE content low pass filter cutoff, independently of the bass management crossover frequency. There are also some processors that offer a choice of bass management crossover slopes.

 

[WmAx]

If you mean a speaker with a full-range driver then it's due to the lack of need for a crossover (passive crossovers are, as I learn more about them, nasty).

Passive crossovers 'nasty'? That is an erroneous conclusion. The only 'nasty' passive crossovers are those that are incorrectly designed for the specific application.

Also, you get a 'point' sound source, instead of sound coming from multiple centers (as you do with a bass/mid and treble setup).

A proper multi-way system will have far better response in all important parameters relevant to audibility as compared to a typical full range driver system.

-Chris

 

[WmAx]

Interesting. I've never heard of non-symmetrical crossover slopes.

--Ethan

Yes, but this only exists in the electrical domain in the circumstance that John set up. The electrical slope cascades with the acoustic slope of the mains(assuming a 2nd order bass alignment on the mains), rendering a 4th order target rolloff.

-Chris

 

[Ethan Winer]

John,

Interesting, thanks.

--Ethan

 

[sploo]

Passive crossovers 'nasty'? That is an erroneous conclusion. The only 'nasty' passive crossovers are those that are incorrectly designed for the specific application.

Perhaps I should clarify what I mean by 'nasty':

I've recently started reading about crossover design, and many articles/books I've found start with roughly the same 'disclaimer': "passive crossovers are not nice - because they're heavily compromised by the behaviour of speaker drivers (impedance varying with frequency etc.)"

All of course then go on to say, "and here's how to design one..."

The point is that I was surprised by just how much time a (passive) crossover designer needs to spend working his way around issues, that are not really to do with the goal of creating a suitable filter, but are simply there to side-step strange driver behaviour.

There's an interesting tutorial by the author of lspCAD on how 'easy' it is to do a digital crossover design using a Behringer DCX2496. He then does a passive design for the same system... it's enough to put you off passives for life .

A proper multi-way system will have far better response in all important parameters relevant to audibility as compared to a typical full range driver system.

Considering the price of some of the higher end fullrange driver systems (comparable to a very good bass/mid and treble pair) I certainly accept that the compromise of fullrange (with no crossover) or multiple drivers (with crossover) favours the latter.

Am I on the right lines though, that a single point source would theoretically be better - assuming you could match the frequency response, distortion etc. of a comparable two/three way configuration?

 

[bpape]

Yes. In theory, a single point source is optimal.

As for passive xovers, they can in fact exibit some 'nasty' behavior in certain circumstances. Active xovers can be superior if done properly. Exceptional passive xovers are not inexpensive to produce either.

I'm not sure comparing a 'typical' full range to a 'proper' multi-way is really apples to apples. How about comparing a typical full range to a typical multi-driver or a 'proper' full range to a 'proper' multi-driver? While multi-driver systems do have some advantages in terms of feeding drivers the ranges that they are most linear and being able to contour the frequency response as part of the deal - there is always a tradeoff.

A properly designed full range system will always be in phase. A properly designed full range system can exhibit much better imaging (not always but in theory it can all else being equal).

Also, there is a limit to what you can do with multi-driver systems. Is a 3 way better than a 2 way? 4 better than 3? 5 better than 4? etc.? At what point are you monkeying around SO much that you've caused issues in the time domain, increased price drastically due to necessary xover complexity, etc? K.I.S.S. principle?

Like anything else, there are good and bad examples of both. Think of the best systems you've heard. From my personal experience, almost to a T they've been simpler systems, many line sources, full range panels, actively crossed systems with a sub and a full range driver like a lowther, a 2 way monitor with just a blocking cap and balance resistor on the tweeter, etc. The ones that did have multi-drivers were usually thing where the drivers were engineered to roll off at a certain point and the xover is only on the bottom end of the driver.

Why do 'monitors' have the ability to 'disappear' into the room? Part of it is small cabinet size. I firmly believe that part of it is also significantly simpler xovers.

When was the last time you heard a 4 or 5 way system that sounded as 'real' as some of the things I've described above?

/rant

 

[Rob Babcock]

I don't think 2-ways sound any more real than multi-ways. They simply trade some flaws for some of their own. When is the last time you heard realistic instrumental scale out of any small to medium two way? I never have, unless we're talking solo acoustic guitar or something sonically "small."

 

[Rob Babcock]

BTW, I think that narrow front baffles are probably the key to the ability of monitors to sometimes 'disappear' sonically.

 

[WmAx]

I try to limit off topic discussion in a specific thread; because at some point it becomes threadjacking. I will reply to the speaker behaviour replies in another thread which I shall start in the Loudspeaker forum in order to not pollute Buckle-Meister's thread further.

The offshoot thread shall be found at the following link:

http://forums.audioholics.com/forums/showthread.php?t=18786

-Chris

 

[bpape]

Agreed - sorry for the rant.