Quality speaker enclosures

[The Boogie Man]

:) In quality speaker enclosures, ( insert list here ) where does the quality stem from? And dont just reply with "your wallet" :D Is it the quality of the driver or a combination of the driver/ horn ( in full range ) or the cabinet design, or the magic black box controller?

I'm sure it's probably a combination of all of the above, but at what percentage?

ie would a wonderful cab design overcome a mediocre driver, or vice verser, would a digital controller transform a cheep set of cabs.

 

I'm not asking about "in a specific enviroment" as any cab can be made to sound good or bad in any setting, but when placed next to each other and then described as good and bad.

 

This isnt a " I'm looking to buy etc" type question but a genuine enquiry into the science of speakers. So comon white coats on and no dumbing it down coz I'm a muzo, :) well ok, dumb it down a bit :D

 

Baz

[Chris Hinds]

Disclaimer: This is my opinion not written in stone scientific fact

 

In truth quality sound comes predominantly from the factor you wanted me to ignore, system design and deployment. I thought I ought to just briefly mention why it is significant. You can have the highest quality box with the best drivers ever but use it in the wrong way, ignoring the surroundings and you will have bad sound. Very few people take into account this when they choose a system. The person doing the set up makes all the difference - are speakers pointing at walls? Has the system been set to avoid comb filtering between areas, are highly reflective areas masked off, have you done something inventive to solve a problem. You only have to look at the big companies like Clair-Showco or Ratsound in the USA to see some of the really inventive things they are doing. Dave Rat is doing the current RHCP tour using L'Acoustics V-DOSC and clever arrangements of subs that allow him to channel the low end where he wants it to go using depths of subs time aligned around the stage. Clair pioneered the use of what is arguably the most advanced DSP in the world - the Lake Contour and used it in conjunction with their own design Prism and i4 systems to get better results. Both are highly original (and expensive) approaches that are taken by people who are at the very forefront of sound, and for me in the most fascinating area of it. So I'd say half of the overall responsibility for sound quality in real world venues comes from this - which is why in truth why, while some people prefer one box over another, you can get good results on any of the premium systems.

 

Looking more at the design of the box as we must for the tools so the system designer/engineer can use them to do the job. There are generally three things a box aims to provide:

 

1. Controlled coverage

2. High SPL in the coverage area

3. Even frequency/phase response.

 

The trouble with these three is that generally they conflict wildly with each other. You can pick two out of three and get them, getting a compromise of all three is more of a challenge.

 

Horn design is intrinsic to getting even coverage, take a look at the moulds for a Turbosound Aspect horn and you'll see just how much effort companies now have to go to in order to get every sound path the same length so that coverage is truly even. Most systems have a very significant on-axis beam (think Peavey HiSys) while off-axis varies wildly. D&B and the like try to ensure their speakers sound as good as possible off axis as well as on axis. Pattern control to low frequencies is regulated by the size of the horn outlet, and is a factor of the linear horn dimensions and the wavelength of the signal. Line Arrays use the length of the array to effectively create pattern control to lower frequencies, though they make use of off-axis comb filtering to reduce spill outside the designed coverage area and increase SPL in the coverage area.

 

High SPL can be generated using drivers with long excursion and good control. The more air you can move the louder it can get. The choice of drive is connected to the horn and the Thiele-Small parameters of that driver. More expensive drivers offer better control and are more responsive than cheap units. In the lower frequency range the design of the cabinet interacts with the driver to control the frequency response of the box, in particular the lower limit of the box. If you try to put the wrong driver into a poor shaped box you end up with nasty resonances in the box that can damage drivers or affect output.

 

I deliberately put frequency and phase response last because it's simply the one we know best how to correct. In creating horns and cabinets that control the pattern well we create waveguides that accentuate certain frequencies while killing others. We can correct that easily using a parametric equaliser, or even an analogue circuit in a passive crossover. The so called magic black boxes that are DSPs enable us to correct frequency deficiencies for a speaker to allow us to achieve the overall aim. A DSP can't correct for a box that has no pattern control, though it is possible in large arrays to 'steer' the output to some extent using dsp, this falls apart at higher frequenciess. Nor can a DSP give you more level than the speaker can produce. What it can do is enable you to design a box for mainly high SPL and accurate coverage and then correct the anomalies of frequency response using filters. The better DSPs even offer filters than minimise the phase impact of the corrections. Just about every premium grade speaker manufacturer now uses DSPs to do this kind of correction for their system, in the case of speakers that can run passive as well (JBL SRx, Martin Blackline etc etc) similar eq correction to that which is programmed into the DSP is inside the speakers themselves in the crossover boards.

 

Of course all that about EQ flies in the face of Audiophile opinion because it uses equipment and components in the signal path to correct inherant non linearities in the speaker design. The fact is that a speaker for large scale reproduction has very different aims to that of a speaker for home use, and the objective is not to have sound in a single seat sounding good but to make sure it sounds good for every single one of the 30,000 people in the arena or 500 people in the theatre.

 

Edit: Percentages!

 

If I had to pin percentages I'd say:

Box design - 25%

Horn design - 25%

Driver selection - 25%

Crossover/DSP settings - 25%

- That was helpful eh

 

Hope that's of some use,

 

Regards

 

Chris

[Jivemaster]

There has to be an understanding of Quality as- Degree of fitness for purpose -

 

Manufacturers place themselves in the market place and for different purposes within their field. A studio monitor while a quality speaker for its purpose would be a failure in concert hall or arena! People who care about sound have to suit the system for the application, then bring out the best for all the audience.

[The Boogie Man]

Chris,

So a good quality speaker design in effect "directs" the sound wave into a tight dispersion, a good driver forces the sound wave futher along your chosen path ( higher spl ) and the dsp "fixes" the changes to the soundwave frequencys that squeezing the soundwave causes?

 

Baz

 

Cheers Jivemaster,

I understand what you mean, "horses for coarses"

But the question would still be viable when comparing any speakers, monitors or foh.

I'm trying to fathomn what makes a good speaker "good" and if it is a single componant of said good speaker or a sum of it's parts.

cheers

baz

[Chris Hinds]

So a good quality speaker design in effect "directs" the sound wave into a tight dispersion, a good driver forces the sound wave futher along your chosen path ( higher spl ) and the dsp "fixes" the changes to the soundwave frequencys that squeezing the soundwave causes?

That's reasonably fair, but the driver also influences the response of the speaker, you can only correct with DSP if the driver can produce those frequencies anyway - you can't make the speaker go lower/higher using DSP. I'm sure someone better versed than me will come along shortly...

 

Regards

 

Chris

[Simon Lewis]

Baz,

 

How in depth do you want to go? To do any justice to your question would require a seriously long post, and it's probably easier to point you to a technical paper or book, than to take up bandwidth here...

 

Simon

[SeanT]

It is possible to make a speaker that will function at moderate SPL with no crossover nor electronics - however the speaker is very large (and horn shaped)

It is then possible to add a subwoofer to said speaker and only reinforce the sound that is CONSIDERED non-directional - this will require a simple crossover and some math - the cabs can get smaller and less gruesome straightaway.

It is then possible to add additional drive units in enclosures so that each unit is reproducing the ideal range of frequencies using passive crossovers - however usually the cabinets are modified in such a way that it sounds "nice" with only two or three drive units (and one or two crossover networks)

You can of course make the shift to active (line level) crossovers and bi or tri amp, this is more efficient and is used effectively by manufacturers to make enclosures smaller (but requiring more expenditiure on amps and control circuitry) - check out D&B for an example of a very small potent setup using some dsp and lots of funky looking amps (that cost a packet...)

Or you can split everything up and throw dsp, room eq and lots of amps at it - this is how we produce impressive sound on a very large scale (except for outdoor events where there is an emphasis on size and power)

 

An interesting case study is of course of a system shunned by hifi enthusiasts and people with perfect pitch but ideally suited to PA - check out how BOSE do it :( - particularly the 802/302 systems with panaray controllers - we use it and it makes some noise and is practically indestructable (no little tweeters, no crossovers, nothing to go wrong but the amp and controller!!)

[The Boogie Man]

Cheers simon, If you have links to online articles or books, that would be great.