[ricardojoa]

If i were to built a my own enclosure, how should i approach in desing the box tunning? Without knowing the outcome of the end result, there could only be expeculation on graphs.
So how do some expert who have built their cabinet have they decided what tunning would be best suited?

Thank you.

[JLM]

Plenty of software out there to design with.  Sealed/ported are the easiest.  Thanks to Martin King's MathCad application you can do also any design you can think of (with enough work).

My favorite is transmission lines (a long tube open at one end with the driver near the other end).  Bass rolls off smoothly (if designed correctly) at 6 dB/octave (same as room gain).  Port output is in phase with driver.  With the right configuration the internal baffle can be sloped to front baffle, so back waves are reflected away (don't come back out through the cone material to smear the sound).  Some say they're big (marginally) or that they're complicated to build (just add baffling inside, the only speakers I ever built were transmission line).  The transmission line bass boxes I built in 1980 were big (6 cubic feet each) but were rated to 114 dB at 17 Hz and sounded magnificent in a 20,000 cubic foot space (driven by a 20 wpc amp), but unfortunately were too much of a good thing (overloaded any room I could afford to put them in).

My current speakers (Bob Brines M18-F200 that uses the mighty Fostex F200A full range driver) do all of the above except are rated F3 = 28 Hz in roughly a 4 cubic foot enclosure.

[ricardojoa]

I have use winisd in the past for automobile subs, but is this good for home midwoofer?
Im trying to go with something simple like a vented or sealed cabinets. The main issue is, even with vented desing, diffferent box volume can result a different alignment and tune differently.
I think in a two, it might have a effect on the way the midrange sound as well.

[richidoo]

WinISD is fine for simulating any speaker box, and the freq range doesn't matter. That is accounted for in the speaker data that you enter into WinISD. It will estimate the proper size of box for any cone speaker. It's just an estimate, every simulator will give a different answer for same inputs. Some simulators sound better than others because they have been optimized with some of the black magic reflex secrets. But alas, those aren't free...

IMO, sealed is much simpler and easier to make it sound good than reflex. It's easy to make a vented speaker for home theater using standard reflex formulas.  "Loud and low!" But to make a vented box sound clean and detailed down low for music playback is difficult. Definitely a dark art learned after many attempts.

Sealed may not play as low as ported, but in most other ways it it is hard to make it sound bad.

In theory, the sound of the midrange is not directly affected by the bass alignment, but sealed and ported have different overall sound due to the different phase response and port noise, and these make you hear the whole speaker differently. But mid frequencies should measure the same because the port resistance rises to infinity above a certain freq and the port stops working. One of the good things about sealed bass alignment is less group delay, which makes the bass sound faster. Depends what you want from the bass: clean and musical is sealed, loud and thumpin is ported.

[planet10]

.. transmission lines...  Bass rolls off smoothly (if designed correctly) at 6 dB/octave (same as room gain).  Port output is in phase with driver... Bob Brines M18-F200

Not true. Without damping a TL is a 4th order system with an ultimate  24 dB/octave roll-off. The use of damping allows more freedom in controlling the roll-off. If a TL is heavily damped -- aperiodic -- the roll-off can be pushed close to 2nd order, 12 dB/octave, but terminus output is very close to zero.

Your Brines ML-TL has a 4th order roll-off.

dave

[planet10]

Another discussion on much the same subjct here: http://www.diyaudio.com/forums/multi-way/255373-i-hate-ported-speakers.html

dave

[Duke]

If i were to built a my own enclosure, how should i approach in desing the box tunning? Without knowing the outcome of the end result, there could only be expeculation on graphs.
So how do some expert who have built their cabinet have they decided what tunning would be best suited?

The "best" tuning frequency depends not only on the woofer parameters and box size, but also on room acoustics and even on the amplifier.   

I recommend preserving as much flexibility as you can when you design the box, perhaps by using multiple pluggable ports so that you can choose from multiple tuning frequencies to fine-tune the system. 

Take as much into account as you can when choosing your tuning frequency - including woofer excursion limits, port airspeed, your best guess about boundary reinforcement, even amplifier damping factor (low damping factors will raise the effective electrical Q of the woofer).   Then choose a porting scheme that allows you the flexibility to either raise or lower the tuning frequency, as chances are your first try will still leave some room for improvement.

I always include some port tuning adjustability in my home audio speaker designs, and there have been times when that capability has salvaged the sale for me because the room acoustics did not work well with the "stock" tuning frequency. 

[G Georgopoulos]

The "best" tuning frequency depends not only on the woofer parameters and box size, but also on room acoustics and even on the amplifier.   

"even on the amplifier" how is that possible?,please explain to us duke?

[JohnR]

George, two paragraphs below the line you quoted he said "amplifier damping factor (low damping factors will raise the effective electrical Q of the woofer)"

[G Georgopoulos]

I still don't get it,what is the damping factor of the amplifier do to system Q of the loudspeaker?
if the loudspeaker sounds different with different damping factors of the amplifier,then we have
screwed up the amplifier!

[Letitroll98]

I'm pretty sure a low damping factor (high output impedance) will alter the frequency response of the woofer.  Not a concern with modern SS amps, but with some tube amps it could make a difference.

[G Georgopoulos]

I'm pretty sure a low damping factor (high output impedance) will alter the frequency response of the woofer.  Not a concern with modern SS amps, but with some tube amps it could make a difference.

If that is the case, tube amplifier designers might take offence at your comment...

if what you're saying is true subjectivists win...

[Duke]

I still don't get it,what is the damping factor of the amplifier do to system Q of the loudspeaker?

The given electrical Q of a woofer assumes that it's driven by a source that has an output impedance of zero ohms.  In practice many solid state amplifiers have an output impedance low enough that it can be ignored.  Some tube amps, in particular specialty tube amps that have little or no global negative feedback, may have an output impedance of several ohms.  This will raise the effective electrical Q of the woofer.  Let's work through an example:

Suppose we have an "8 ohm" speaker, whose woofer has a DC resistance of 5.5 ohms, and a Qes of .27.   We connect it to a single-ended triode amp that has a damping factor of 4, which corresponds to an output impedance of 2 ohms (by convention, damping factor = output impedance of the amp divided by 8 ohms, the "nominal" input impedance of the average speaker).   The new Qes is found by this formula:  [(woofer DC resistance + amplifier output impedance)/(woofer DC resistance)] x Qes = new Qes.   Plugging and chugging, we get [(5.5 + 2.0)/(5.5)]x.27 = .37.  So our new effective Qes is .37.

In my opinion, this is enough of a difference that we should take it into account when we run our modelling program. 

The attentive ubergeek will notice a window of opportunity here:  By using an amplifier with a low damping factor, we can enjoy the high efficiency of a low Qes woofer, plus the superior low-end weight of a medium Qes woofer. 

if the loudspeaker sounds different with different damping factors of the amplifier,then we have
screwed up the amplifier!

I strongly disagree with this statement. 

We simply need to make informed choices about amplifier and speaker pairings.   Or if we aren't quite geek enough for that, we need to pay attention to the recommendations of amplifier and speaker manufacturers, who are geek enough. 

[planet10]

I strongly disagree with this statement. 

We simply need to make informed choices about amplifier and speaker pairings.   Or if we aren't quite geek enough for that, we need to pay attention to the recommendations of amplifier and speaker manufacturers, who are geek enough.

+1. Amplifier and speaker need to be considered as asystem. There is an approprite amplifieroutputimpedance for every loudspeaker. Drive your big Fostex horn with a low output impedance amplifier and it will likely sound thin. Use an amplifier with a high output impedance amplifier (typical SET with zero global feedback, Firstwatt F2), they sound just fine. There is even a school of thot that says very high output impedance amplifiers (current amps) have some distinct advantages over high output impedance amps (voltage amps). The basis of the fact that speakers are current devices and that a voltage amp uses the (usually very nonlinear) impedance of the speaker as an I/V converter.

Unfortunately it is hard to do this as most speakers are designed with the assumption that they will be driven by a voltage amp. This is convienient forbig manufacturing, but means that a huge swath of potential hifi solutions is just ignored.

Having a wide range of loudspeakers and a variable transimpedance amplifier (an ampithan extra knob that dials up a range of output impedance from pure voltage amp to pure current amp) is an eye-opening experience.

dave

[G Georgopoulos]

I remember the days back in 70s and 80s where amplifiers and speakers were different beasts,the speakers in open field where taking measurements with disregards of room acoustics,and it was hard to get good frequency response graphs,yes room acoustics matter but the best speaker must measure well in open field how else can be confirmed it's the best,when in room simply adjust the volume and use some kind of room difuses,back then also the amplifiers were being developed with little more than a resistive load and measure ments were being taken thd df etc..that's what i learned that's what i stick with..

thank you all for your opinions...

[Duke]

...back then also the amplifiers were being developed with little more than a resistive load and measure ments were being taken thd df etc..that's what i learned that's what i stick with..

THD is a failed metric, as far as its ability to predict subjective preference (unless you consider its slightly negative correlation with subjective preference to be a useful predictor).  This from Dr. Earl Geddes, who has conducted extensive peer-reviewed research on distortion perception in partnership with Dr. Lydia Lee. 

And damping factor is not a measure of quality, as some marketing departments would have you believe, but it is a useful metric for evaluating loudspeaker compatibility, as Dave (planet10) describes above.