# 2009-2010

June: Album art presentation by Rich Shelton. Rich is a artist and musician who is fascinated by album art and what it tells us about the relationship between popular music and the graphic art of its packaging. Richard will do a slide show with some of his favorites from his collection of 18,000 albums.

May: Speaker unveiling of new club SB Acoustics setup with all passive crossovers.

April: Audio by Van Alstine partners with Nate's audio (local loudspeaker guy Nate Field) to put on a nice show.

March:

February: Bel Canto demonstrates some new products and high resolution audio recordings - and brings in a fantastic high-resolution, high-sensitivity loudspeaker featuring a fantastic new horn by Peavey. Ceiling tiles were bouncing that night ;)

January: Bring and Brag

December: A special Loudspeaker 101 meeting with Ron Ennenga, and a concurrent Turntable setup meeting with Wally Malewicz of WAM Engineering.

A brief (!) wrapup of the Loudspeaker meeting from a forum post by Ron is as follows:

Alright, just to get things going, here are some more complete,

written answers to some of the questions that I recall were asked at

the meeting. Loudspeakers are a complex topic and a thorough treatment

of just box design could take a whole year of monthly one hour meetings.

If you want to contact me privately with questions, you may also do that.

If there are questions about individual parameters and what they mean, perhaps

the best resource is the thiele small article at wikipedia. It has

reasonably good descriptions of the individual parameters.

1) How does Vas affect box size?

Box size is a function of Qts and Vas for both sealed and vented

boxes.

for sealed boxes .Qtc/Qts=sqrt(Vas/Vb+1) => Vb=Vas/((Qtc/Qts)^2-1)

for sealed boxes box size varies inversely with the square of the

ratio between initial and final Q.

In a vented box the most instructive way to discuss this aspect of box

size is to use a curve fit:

Small-Margolis (1981 JAES article) says box size varies as: Vb=Vas*20*Qts^3.3 and Fb =

0.42*Qts^-0.96

D.B. Keele, Jr says: Vb = Vas*15*Qts^2.87 and Fb=0.42*Qts^-0.9

....so Box size varies approximately with the cube of Qts and in

proportion with Vas. Tuning frequency varies inversely with Qts.

In both sealed and vented, box size is doubled when Vas is doubled,

assuming all other variables remain constant.

2) Will 2 smaller woofers have better transient response than one

larger woofer?

Not necessarily. Transient response (in the sense of step or impulse

responses) is a function of several things. First is high frequency

response and second is low frequency response. A smaller woofer will

generally have better high frequency response so a measured step or

impulse will be sharper (faster) when no crossover is used. Once a

both now essentially have the same high frequency bandwidth. In low

frequency response, the Q and cutoff frequency (or Vb and Fb in vented

boxes) determine the response shape and the resonant behavior of the

speaker. Low Qtc in sealed boxes is often identified as the source of

"fast sounding" bass. I have heard speakers with Q's as high as 1.3

attributed with the adjective "fast" or punchy. I think this is

sometimes due to a bump in the "punch" region 100-150Hz and smaller

woofers are more likely to have this.

Two smaller speakers _with the same response shape_ as one larger

speaker should not sound different at low frequencies from the larger

woofer. Smaller woofers often have higher cutoffs (F3 or Fb), though,

which brings us to a third factor: how the speakers match with the

room. Room resonances tend to decay in times on the order of seconds,

where speaker system resonant decay in normal systems tend to decay in

milliseconds. The room can thus dominate the sound in this area.

Below the frequency where your room has its lowest standing wave ( F=c/

(2*L), where c is speed of sound and L is the room's longest

dimension) the room starts to pressurize and there is a theoretical

12dB/octave gain in response. In practice, leakage and doors to

neighboring rooms reduce this and the resultant is more likely to be

less than this in practice. This gain, when coupled with flat response

speakers, can cause a lifting of bass response that results in narrow

peaks for a vented system, and broader peaks for a sealed system.

Designing the system with a drooping response cna match the room

better and this is one advantage to rolling your own, in that you can

desighn the system for your room, Larger rooms should have less of an

issue with room gain causing bloated bass. In a smaller room, a

dipole source that does not pressurize the room at low frequencies

might be considered.

Another factor is distortion. Distorted bass sounds slow and fuzzy.

Use good quality drivers and don't push them too low.

Another factor is voice coil inductance. Smaller woofers have smaller

coils with lower inductance (usually). Excessive voice coil inductance

can cause response shape changes in the low frequency area that are

not modeled by most software. The result is commonly a bump in the

50-70Hz region that happens to coincide with the standing wave from

floor to ceiling in most rooms.

So the short answer is that bass response is more complicated than

just woofer size. ;)

Various dimension ratios have been put forward as having beneficial

effects for speaker boxes. The usual argument is that they distribute

the resonant modes more evenly. While this is true in an undamped

box, they have a much smaller effect if there is box damping and there

is no effect of frequencies are restricted to frequencies lower than

the standing wave frequencies.. For bass-midrange boxes, even if well

damped, avoiding dimensions that are simple multiples is still a good

idea, but the golden ratio, (phi=1.6180339887499... ;) ), is not some

magic number that is any better than many other ratios. Dimension

ratios are more important in mounting drivers on a baffle. On a

rectangular baffle, the smoothest response results from dimensions

that are different (nonrelated) distances from each of the 4 edges.

Now on to some stuff that I didn't get to expound upon cleearly enough

in the meeting. We are in an awesome era where tools to design

loudspeakers are more affordable and more accurate than ever. The

tools below are free or very cheap. We start with measuring T/S

parameters. Mfg T/S should generally be used as a guide for driver

selection only. Their spec sheets can be very useful for hard to

measure Specs like Cone area (Sd), etc...:

Measurement Software:

HolmImpulse - measures frequency response

Speaker Workshop - measures frequency response and T/S parameters.

Jigs and mics could cost up to ~\$150-200, but can be made for a few \$

if you are handy with a soldering iron and have some parts in a junk

box..

Woofer Tester - http://www.woofertester.com/ costs ~\$160 - measures

driver impedance, and they have more expensive products that also

measure frequency reponse, etc...

Once you have T/S parameters, you can model box size:

Box modeling software:

AJDesigner - simplest http://www.ajdesigner.com/

WinISD (WinISD beta is simpler but less informative than WinISD pro

alpha)

Now to figure out how your box shape will work - only the BDS below

will do nonrectangular and rounded edge modeling.

Diffraction modeling software:

The Edge http://www.tolvan.com/edge/ - Svante also makes a nice

looking inexpensive box modeler called Basta (I have never used)

BDS and many other tools - http://www.pvconsultants.com/audio/frdgroup.htm

Jeff Bagby's Box and Room modeler (just out so pay attention for

Now you measure the response on the baffle and start doing a

crossover:

Crossover modeling software:

Jeff Bagby's PCD (Passive Crossover Designer) - http://audio.claub.net/software/jbagby.html

Speaker Workshop - very powerful, optimizer, etc. (Jeff's tool above

does polar response, though.) SW is also open source:

Various versions of Spice. LTSpice from linear technology is a free

variant very popular with hobbyists

November: ARC Tour - we do a factory tour of Audio Research Corporation in Plymouth Minnesota and listen to some of their new "digital" amps and some very high end speakers in their listening room - more details and pics at our Blog!

October:

September: