Thoughts on building a 4 way system

tucmat

Member
2009-07-08 9:27 am
I was hoping to get the forum's input on a project I'm seriously considering. I am not saying cost is not an object, but at the same time I won't be too concerned about a $50 or $100 variance in an aspect of this project. The project I'm considering is a more elaborate version of a design by Troels Graveson (TV) - the Illuminator 5.

Using all Scan-Speak drivers, the driver layout would mimic the layout of the Audio Artistry Beethoven (AA) system: two cabinets per side, the upper cabinet like the AA driver layout and the lower cabinet a stack of 8" or 10" (tbd) drivers. All drivers would be in sealed enclosures. Rather than going thru the exercise of designing/building a crossover network, I intend to use discrete Class D amps along with an active crossover. Here's where I start having questions about the build.

When I'm in Walmart or Best Buy looking at their 'best' speaker cabinets or when I'm in a dedicated high-end audiophile showroom or the audio show in San Francisco, all I see is a variation of a theme. Whether it's a basic Polk Audio or an aluminum Revel or a Wilson WAMM (PRW), all I'm seeing is a 6-sided box with a speaker/driver in one side of the box. The box could be a cube, a rectangular cube or a variation of a free form shape, but functionally all I'm seeing is an enclosed volume with a driver in it. I acknowledge I am grossly glossing over the build quality of the cabinet. I don't mean to get into a discussion of the differences in these cabinets - I get that. From a purely sonic perspective, am I missing something? Is the speaker cabinet sitting in your listening room something other than a stack of boxes with drivers mounted in one side of the box?

I understand passive analog crossovers to be as much of an art as a science to be done correctly. Not wanting to dedicate the investment in time and equipment to learn crossovers, an active crossover/equalization system is currently being considered. The speaker system I'm considering would have 9 drivers per channel. Rather than trying to manage the 4 channels per side phase issues, an active crossover would solve the phase issue - all 4 channels would be in phase with each other. Other than getting the correct frequencies to the correct driver, adjusting for a smooth transition between cut off frequencies and adjusting the loudness between the 4 channels so that the overall sound 'sounds good', does the crossover (active or passive) do anything else?

Regarding the cabinet itself I understand for the most part the how's and why's of building a solid box. Other than correctly matching cabinet volume to the respective driver, does it really matter what the shape of the cabinet volume is? Again, referring to PRV, it appears as if one side must be big enough to mount the driver while providing the correct volume for the driver to 'work'. I will concede that when working with the tweeter and its baffle, there is some consideration necessary for the shape of the baffle given the wavelength of the tweeters output and the reflective qualities of the tweeter’s baffle. Although Troels is adamant in staying with his baffle dimensions and crossover design, when looking at PRV speakers and Troels boxes, I don’t see where baffle dimensions for drivers other than a tweeter is that big of a deal. What am I missing?

In my case, ignorance is bliss. I plan on using quality drivers in stiff, non-resonant boxes sized to optimize driver performance. The drivers will have discrete amplifiers for their respective frequency range. Looking at PRV speakers it doesn’t appear that it’s very important to size the baffle much larger than to provide a sound, structural place for the driver to be placed. The cone of the driver moves in and out when the amp tells it to. As the cone moves back and forth it reacts with the contained volume within the box. Within the box typically is some type of acoustic stuffing to slow down and redirect the sound wave within the box. The sound wave leaving the cone to the outside reacts with the shape of the baffle but doesn’t seem to be affected too much due to the wavelength of the sound wave being greater than the dimensions of the baffle. Regarding the PRV speakers, does their design do anything other than provide an optimal volume in a structurally sound environment for the driver to operate? I again concede I have glossed over cabinet build and finish quality. If you take aesthetics out of the equation and only factor in structural quality and driver quality, what am I missing? I feel as if I’ve thought this out fairly well, but I would appreciate the input from a group that knows a whole lot more about this than I do

Thank you in advance for taking the time to read this somewhat lengthy question, and more importantly your response.
 
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tucmat

Member
2009-07-08 9:27 am
There really is not a valid reason for a 4 way system other than I 'want to'. I'm not concerned with my woodworking skills, so the cabinetry is not an issue. I have some time available for a project like this and look forward to the complexity and challenge of making it work.
 

AllenB

Moderator
Paid Member
2008-10-18 11:31 am
Other than getting the correct frequencies to the correct driver, adjusting for a smooth transition between cut off frequencies and adjusting the loudness between the 4 channels so that the overall sound 'sounds good', does the crossover (active or passive) do anything else?
The difference between active and passive is the implementation, which is a small part of the crossover design procedure. Answering your question involves crossing the line you're trying to avoid crossing.
 

tucmat

Member
2009-07-08 9:27 am
Could you elaborate on 'implementation'? What does a passive crossover do that an active does not do? Same question for an active crossover. 'Better' is a difficult word to use because it is hard to define exactly what better means. Is active better than passive? What makes one 'more better' than the other? Also, referring back to my original posting quoted above, does a crossover do anything besides those operations I've listed?
Thank you for your response!
 

boswald

Member
Paid Member
2014-06-27 3:32 pm
The propagation of sound waves from a driver is determined by the driver's characteristics, the input signal, the crossover filters, support(and diffraction) from(the baffle and) adjacent surfaces, reflections from non-adjacent surfaces, placement in and overall size and shape of the airspace, materials and discontinuities of boundaries.


And probably a few more.


A speaker is better than another when it accounts for more of these factors than another.


My suggestion is that you identify which factors are more important for you in your room(in your preferred placement) playing what you like as loud as you like.


This will require systematic experimentation and study. DSP is wonderful as you needn't buy many slightly different filter components as you experiment, but there is no substitute for experience with solving the problems involved.


There are no crash courses for considered judgement. Sorry.
 
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In experienced hands, the end result is largely the same. Ie, it is other parts of the crossover such as the acoustic connection, which make up the very challenge of a crossover to begin with.

A good active crossover will always outperform a passive. In a passive unit, the driver is an active part of the crossover, whereas in an active system, the driver is passive: all it does is follow the signal from an amplifier.
The impedance and sensitivity of the driver are largely irrelevant to the design.
 
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In 2020 with DSP plus multiple amplifiers these three designs would be worth the effort and cost.

======== WOOD ENVY ==== 4-way using ScanSpeak Illuminator drivers

Taipuu Speakers DSP active speakers - Taipuu Speakers

Taipuu Speakers in Finland showcases solid wood cabinets. Taipuu Speakers are a unique combination of carefully finished carpentry and state-of-the art audio made in Finland. Taipuu has a 4-way design using Scan Speak Illuminator drivers with performance data on their website. The VituixCAD2 cadtool website also models this speaker. Worth the effort to klone this beautiful cabinet and top driver mix.
Since this is a proven (passive and DSP) design with extensive CAD modeling.... "If you build it, they will work"

========= CONTROLLED DIRECTIVITY ====

========= Big Mother F___er 3-way Speaker =====
Tweek Geeks is the Colorado audio Boutique which developed the well reviewed BMF-1 speaker around the Beyma TPL150H AMT horn tweeter. The Faital 12FH530 is the midrange with a 1400Hz crossover, and two side-side counter-force Faital 12RS1066 woofers provide deep equalized bass. Extensive construction pictures are on the web. The BMF-1 stands 43”high x 16”wide x 20”deep.

Getting closer to finishing one enclosure. | Gym, Gym equipment, Treadmill

Two 24Hz equalized 12" woofers allow a modest H46" W18" D18" total 6cuft cabinet. The new Faital 12PR320 was selected for the midwoofer based upon wide bandwidth and great sound quality at an acceptable $230 price.

$14 B-52 PHRN-1014 [Part # 299-2303] 1" Horn 10" x 14" Bolt-On waveguide
$62 Peerless 1.75" DFM-2544R00-08 compression driver
$230 Faital Pro 12PR320 midrange
two $150 Dayton RSS315HF-4 12" woofer (one amplifier per woofer)
-------------------------
$606 for drivers
==========

========== The Final Frontier 4-way =====
new tech DCX464 2-way coaxial compression driver ~$600 + $200 SEOS-24 waveguide
----passive crossover on DCX464
-15" midrange in sealed volume (like Faital 15PR400 AES TD15M bms 15N830v2 )
-two sealed and equalized Fs=18Hz 15" subwoofers like Dayton RSS390HO-4 one amp per speaker


========= CONTROLLED DIRECTIVITY ====
When loudspeakers interact with room boundaries and other acoustically reflective surfaces, the delay between direct and reflected sound waves affects not only the perceived timbre, but also the degree to which believable phantom stereo images are created. If reflected sound waves arrive too soon after the direct sound, they generate spurious directional cues that can spoil the stereo-imaging illusion. The precedence effect offers a remedy for the effect of room reflections on stereo imaging to the extent that the reflected sound is a sufficiently delayed copy of the direct sound, with similar spectral and temporal content, the auditory system will take directional cues only from the direct sound. To make this work we need loudspeakers with frequency-independent polar response (constant directivity) and we need to place them far enough from reflecting surfaces. Toole's research suggests that in a “typical” room, a delay of at least 5ms = 68in will put reflection levels below the threshold where they can be perceived as a second image
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WIKI
"The on axis, free space directivity factor for sound sources with several common free space radiation patterns are as follows: Monopole: DF = 1.0, Dipole: DF = 3, Cardioid: DF = 3, 90x90 Horn: DF=8.27. What this means is that if these three different sources are to radiate the same total acoustic power then if the monopole has an on axis intensity of 1.0 the dipole and cardioid will have an on axis intensity of 3.0 or 4.77 dB greater, and the horn will have an on axis intensity of 8.27 or 9.2 dB greater. Conversely, if the different sources are to have the same on axis intensity then the dipole and cardioid will radiate 1/3 the acoustic power of the monopole, and the horn 1/9 the acoustic power of the monopole. When studying room acoustics and reverberation this means that the "critical distance" from the speaker will be greater for a dipole or cardioid or horn than for a monopole. The "critical distance" is the distance at which direct and reflected sound are equal. The level of the reflected sound, above the modal region of the room, is usually considered constant and proportional to the total radiated power. Thus when sitting the same distance from a conventional speaker and a dipole/horn, the dipole/horn can potentially sound more detailed since at the position that ratio of direct to reflected sound is greater. "
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Both dipoles and horn designs control directivity to reduce early reflections from hard walls and floors. Draw your room floorplan and overlay Left+Right horn 90-degree and 60-degree horizontal polar patterns directed to the listener to see if early wall reflections can be significantly reduced. A tweeter horn with a 40-degree vertical polar pattern will reduce early reflections off your hard floor and low ceiling.
=========
 

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