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Old 24th November 2011, 04:02 PM   #1
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Default ZAPH ZRT 2-way sealed cabinet option

Zaph shows an option for a sealed 2-way ZRT on his site, and comments that a 20 liter cabinet works well. I'd like opinions on whether or not the Parts Express 1cf curved cabinet would work well as an option? The curved cabinet is about 1/4" wider on the front baffle than the 20 liter version shown on his site. Will the larger cabinet volume detract from bass quality?


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Old 24th November 2011, 05:35 PM   #2
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As far as I can tell, he is VERY specific about the baffle dimensions, and less-so about the internal volume. It looks like anything in the 19L-38L range will work, as long as it is sealed. Once you add in a tuned port, things accuracy requirements start to get a lot more stringent.

Anyway, if this enclosure is what I am imagining it to be, then the extra 1/4" in the body probably is not an issue. Do you have a link to the product? He has a FAQ section on his site that states something along the lines of, "If you built a design and it sounds bad, you probably didn't build the baffle to my specified dimensions." So, enthusiast-beware!
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Old 7th February 2012, 06:32 PM   #3
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Default Response curves

A late response, but if I found this thread searching on a related question, others will too.

A great resource page for working examples is Linkwitz Transform Subwoofer Equaliser. Download the spreadsheet hosted there, and play with the last sheet, giving dB response curves in terms of speaker parameters and sealed enclosure volume.

The only place I've found the math is in the two R. Small references in the sealed enclosure chapter of the
Loudspeaker Design Cookbook 7th Edition:

R. Small, "Closed-Box Loudspeaker System, Part 1, 2", JAES, Jan/Feb 1973

The cookbook is, indeed, a cookbook; I wish that there was a decent textbook. These papers can be found online, and use different notation. They still require the reader to solve the equivalent electrical circuit, but the formula given in the appendix agrees to my satisfaction with the formula used in the spreadsheet. Of course, these are ideal curves, not factoring in the woofer response curve itself, which won't be entirely flat. And if we were a more advanced species we'd be using complex numbers instead, to include phase information.

I rewrote the spreadsheets to compare multiple volume options, I and played with versions of the formulas in Mathematica. The bottom line is this: Enclosure volume doesn't matter that much. Larger enclosures are described as "leaner, deeper bass". That's a wine tasting notes version of "it's the bottom curve at higher frequencies, and the top curve at lower frequencies" in the graphs that follow.

I give response curves for different enclosure volumes, for this woofer and the woofer used in the ZA-SR71 speaker project. Clearly, this woofer is larger, and has better bass response.

The curves don't all cross at the same point. If so, this would be a very interesting way to classify woofers for sealed use, as the curves all have the same shape, so one could guess the curve from the "pivot point". However, one could use the approximation given by where the curves cross for two reasonable Q values, as a way to classify woofers. I'd love to see this plotted for either the Madisound or Parts Express catalog, or Zaph's next woofer survey.

The Linkwitz Transform itself is clever, but soon to gather dust as time marches forward. Many of us are moving functionality to the computer source that used to require physical components. For example, a preamp now just needs to attenuate, and there are many other ways of doing that. One can now bi-amp with the computer as crossover. A useful calculation would be the best single parametric equalizer that boosts and flattens the bass response of a speaker, as measured in actual use. I find myself wondering if a speaker port is a clumsy mechanical gimmick, and instead all speakers should be sealed and digitally equalized?

In any case, here are the graphs, and my version of the spreadsheet:
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Old 7th February 2012, 11:39 PM   #4
sreten is offline sreten  United Kingdom
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Your not telling most of us something we don't already know, and can
knock up in about 3 minutes using any drivers given Vas, Fs and Qts.

WinISD is the simplest quickest (free) tool.

anyway back to the ZRT, 49.5L, 30.4Hz and 0.41.
Attached are the options.

Very straightforward, 1cuft or 28L will be more than fine.
1/4" extra width on a rounded baffle is fairly meaningless.

rgds, sreten.

The Seas driver in the SR71 is designed to be used in
ported boxes and its quite clear you don't know why.
There is nothing remotely clumsy about porting.
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Last edited by sreten; 7th February 2012 at 11:45 PM.
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Old 8th February 2012, 02:52 AM   #5
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Originally Posted by sreten View Post
You're not telling most of us something we don't already know
Good! I came to the right place. But why didn't anyone else post graphs, if it's that easy? It drives me crazy when people say things like "leaner, deeper" rather than just showing the curves. One might imagine that the curves vary more than they do, reading what people write.

What's a better reference than the Design Cookbook for understanding these equations? I want to understand them. Having a program do the work for me is numbing, like using a calculator.

What's the formula for the response curve of a parametric equalizer? I'd like to combine that formula with the formula in Small's paper, to build my SR71's sealed and carry out a Linkwitz Transform in software.

Does your software compute the optimum parameters for using a single parametric equalizer to extend the bass response of a sealed enclosure? Or does one need to use a general purpose program like Mathematica or a spreadsheet for such a calculation?
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Old 8th February 2012, 10:24 AM   #6
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Check out the website from the creator! Active Filters

All the math and practical circuits are there..

Just my $0.02
Music is art - Audio is psychoacoustics & engineering
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Old 8th February 2012, 11:28 AM   #7
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Ports always have some level of mid/hf leakage which causes canacelation patterns with the mid/hf emmiter. In addition to that they exhibit group delay and compresion artifacts. On the other hand they reduce excursion to produce a given SPL in comparison to a sealed box when operating in the speakers passband reducing distortion. Zaph cares alot about distortion hence the prevelance of ported boxes.
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Old 8th February 2012, 01:26 PM   #8
sreten is offline sreten  United Kingdom
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WinISDpro (free) and the demo version of Basta! free will iet you play
wth active EQ for sealed and ported boxes. You'd probably find the
Basta! manual (download it free) illuminating.

Having a program do the work for me is numbing, like using a calculator.
That is IMO because your looking at it wrong. I can do circuit design
design using rules of thumb and sensible approximations but a good
SPICE emulator allows you to play with the big picture, not the details.

Use WinISDPro (or Basta!) to investiate the max SPL and max power
handling of the Seas driver in various sealed boxes, the SPL curves
and the power handling changes will both probably surprise you.

If you can sse these curves in your head by looking at equations
your a better man than me, design IMO is proper modelling.
(In this case though it is quite obvious from the equations.)

Do the same again for some vented alignments ...... try an overdamped
vented alignment with a low peaking high pass filter to optimise bass
extension versus the excursion characteristics of the driver in this case.

See the FRD tools stuff in the links below. the linkwitz labs site has
the equations for the LT (bad idea with the Seas driver IMO) and
lots of other stuff to boot.

Shown are some simple options for the SR71 ER18NX : 26L, 39Hz, 0.35.
(the last two numbers tell you your loOking at vented for low bass.)
Frist two are calssic sealed and vented, third a good vented
alignment, and the last the sort of alignment you might
add a Q=2 + 6dB boost at 30Hz for a 6th order alignment.

rgds, sreten.

undefinition (see if nothing else, the excellent FAQs)
The Speaker Building Bible - Techtalk Speaker Building, Audio, Video, and Electronics Customer Discussion Forum From
Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter
FRD Consortium tools guide
RJB Audio Projects
Speaker Design Works
HTGuide Forum - A Guide to Completed Speaker Designs.
A Speaker project
DIY Loudspeaker Projects Troels Gravesen
Humble Homemade Hifi
Quarter Wavelength Loudspeaker Design
The Frugal-Horns Site -- High Performance, Low Cost DIY Horn Designs
Linkwitz Lab - Loudspeaker Design
Music and Design

Great free SPICE Emulator : SPICE-Based Analog Simulation Program - TINA-TI - TI Tool Folder
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Last edited by sreten; 8th February 2012 at 01:32 PM.
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Old 8th February 2012, 02:10 PM   #9
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Originally Posted by kipman725 View Post
Ports always have some level of ... In addition ... On the other hand they reduce excursion to produce a given SPL in comparison to a sealed box when operating in the speakers passband reducing distortion.
One could interpret this as saying that porting a given driver plays louder without appreciable distortion, with better bass response. These are surely democratic attributes of a speaker, as anyone (even with hearing loss) can tell if a speaker plays loud with good bass. I listen at low to moderate levels, at odd hours in a solid-walled apartment building. That last octave of bass is what I hear from other apartments, and by giving it up I've never had complaints.

The ZRT kit is clearly a better choice that the SR71 kit for a sealed enclosure, with better bass response and a lower Efficiency Bandwidth Product. Zaph gives sealed as a ZRT option, but discourages sealing the SR71. The SR71 woofer has an Efficiency Bandwidth Product of 95, at around the upper limit for every cited guideline. On the other hand, I've read dozens of descriptions of EBP, and none of them explain what gets lost at higher EBPs, beyond a vague mention of "performance". I have ample watts available, and I've seen the bass response curves; if EBP goes beyond this, none of these authors appear to know, or at least they're not saying.

Your discussion of excursion gets right to the point. The Loudspeaker Design Cookbook also goes into various issues involved in choosing a sealed woofer, including excursion. The SR71's Seas ER18RNX woofer has a Linear Coil Travel (p-p) of 12 mm, similar to the ZRT's woofer. Does the Qes of the EBP ratio determine how much of this travel is needed for a given SPL? If so, then EBP indeed carries information other than a crude descriptor of the bass response curve.

I ask because I'd like to build the ZRT, but I bought the SR71 kit to learn on, as it cost less. It is described as out of stock at Madisound for the mere reason that the available enclosures aren't ported (easily fixed) and I'm pondering whether to cut those holes, while I wait for better damping materials to arrive. Sealed speakers can be more flexibly redeployed, as one wants those rear SR71 ports away from obstacles.

I understand that Zaph's ported designs are refined. However, to one modern way of thinking, there is something "clumsy" about any piece of hardware that can be replaced by software. That is all I meant; replacing a port by software is the same idea as replacing a preamp by software.

By training I find it very difficult to accept recited advice. I greatly appreciate your to-the-point detail. If one imagines your competing considerations as curves, then perhaps these tradeoffs cross somewhere relevant to my circumstances? Perhaps 12 mm is sufficient linear travel, and at lower listening levels I'd be happier sealed?
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Old 8th February 2012, 02:27 PM   #10
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Originally Posted by sreten View Post
Shown are some simple options for the SR71 ER18NX : 26L, 39Hz, 0.35.

THe SR71 kit comes with ER18RNX woofers, with slightly different specs: 32L, 37Hz, 0.32. Still, your graphs making the idea of playing with this software very inviting. And they may make me come to my senses about cutting the port holes...
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