Box alignment/tuning - different perspectives

[keith_correa]

I'm requesting FM's to post their preferences for different enclosure alignments/tuning with a brief reason why and under what circumstance/condition they would prefer to implement an alignment. Example: I found a post by Jeff Bagby from 2007 where he said this:

It seems to me that the most balanced sounding alignment is based on the f3 and where that falls in relation to the room gain curve. An EBS alignment works very well for a speaker that is "drooping" in the region around 30Hz or so where the room is adding some lift. Flat to 30Hz may sound a little bass heavy here. However, for higher frequency F3's of around 50 or 60 Hz the EBS will tend to sound lean in the same room. On the other hand, if my speaker had an Fs of 50 Hz I would keep it flat and then allow the room to aid the lower frequencies. If my speaker had an F3 that was higher yet, like 70Hz, then I prefer a slightly underdamped response that actually has some lift in the response before it begins to roll-off. It is all about the slope of the roll-off, where it occurs (what frequency) and how it interacts with the room. The lower the F3 the more damped I would make the bass alignment. Conversely, the higher the F3 the less damped I would make it.

This direction is what I'm hoping this thread will take. Hopefully, it will help me/others understand different perspectives and also gain from your vast practical experience.

[thekorvers]

Re: Box alignment/tuning - different perspectives

You may find this post (and thread) interesting: http://techtalk.parts-express.com/sh...55#post1902955

[Jeff B.]

Re: Box alignment/tuning - different perspectives

You may find this post (and thread) interesting: http://techtalk.parts-express.com/sh...55#post1902955

After posting that I was told by a pro designer that I was sharing too many secrets :D

[ernperkins]

Re: Box alignment/tuning - different perspectives

After posting that I was told by a pro designer that I was sharing too many secrets :D

And you continued on with more information in the Sopranos writeup. Jeff, you're incorrigible! And please don't change!

[Chris Roemer]

Re: Box alignment/tuning - different perspectives

Many of my projects have an F3 in the 30-40Hz range. Unfortunately, my listening room (living room) tends to have a rather huge gain ("hump") right around 40Hz (as I believe most rooms do). This is good if you want your double-hung windows to rattle at the beginning of "Dark Side of the Moon", but lately, I'm preferring deeper and cleaner bass.

Now, when using WinISD, I'll select my tuning so the output at 30Hz is as high as I can get it, in relation to its output at 40Hz. So now, I'd prefer a tuning where 30Hz is only -1dB down from 40, instead of, say, -3dB or -4dB down, REGARDLESS of where F3 actually falls, or whether or not the response looks flat or kinda lumpy.

Chris

[thekorvers]

Re: Box alignment/tuning - different perspectives

After posting that I was told by a pro designer that I was sharing too many secrets :D

And you continued on with more information in the Sopranos writeup. Jeff, you're incorrigible! And please don't change!

+1

Jeff, maybe not often enough expressed, but while many people have given valuable time and effort in helping others and improving this forum, your contributions have been priceless in making DIY speaker design and building the state of the art that it is today.

I am sure that I speak for many others in saying that your efforts are and continue to be greatly appreciated!

Thank you.

And I agree. Please don't change.

[Pallas]

Re: Box alignment/tuning - different perspectives

The important thing to remember is that room modes are orders of magnitude more important than the bass tuning. In fact, the bass tuning is basically irrelevant! (Unless, of course, it's really messed up.) One exception is low-tuned ported boxes. They may create audible problems, due to port resonances several octaves above tuning. That's the reason I think PR's are generally worth the cost difference compared to tube or slot vents.

My preferred approach is to go a little different on the "Hoffman's Iron Law" continuum than the conventional wisdom for the mains: little more efficient but with less bass extension for a given cabinet size. Say, closed boxes (always closed boxes - vented mains just add problems, with no real benefits) with fairly low Q (though that's more for psychological satisfaction than because it actually matters) and an F3 in the 50-100 Hz octave. Then for the bass, equalized multiple distributed subwoofers. Sealed/ported/bandpass* only matters if one cares about response below cutoff, because the ported and 6th-or-higher-order bandpass subs will not play below cutoff (though they will be more efficient above cutoff), because below cutoff they go from monopoles to dipoles. Closed box and 4th order bandpass subs will pressurize the room below cutoff, because they stay monopoles.

*Bandpass subwoofers are often mislabeled "horn subs" in forums. A "front-loaded horn" is a 4th order bandpass device, and a "tapped horn" is a 6th-order bandpass device.

[lsiberian]

Re: Box alignment/tuning - different perspectives

I personally aim for low Q systems. I'm not sure I qualify as an FM though.

Jeff B does seem to have quite the fan club here.

[Chris Roemer]

Re: Box alignment/tuning - different perspectives

That's because he wrote the software that 99.9% of the designers here use for XO work.

[PWR RYD]

Re: Box alignment/tuning - different perspectives

That's because he wrote the software that 99.9% of the designers here use for XO work.

And share to all of us for FREE! Not to mention every one of his designs I've heard is stellar. Plus he never ever says "you should build my xyz design" when someone posts the typical question of what design to build. No self promoting necessary, the proof is in the pudding

[mzisserson]

Re: Box alignment/tuning - different perspectives

I personally aim for low Q systems. I'm not sure I qualify as an FM though.

Jeff B does seem to have quite the fan club here.

It's not a fan club. That's what Miley Cyrus has.... Jeff is respected not just for his software, but his knowledge and ability to wield the toolkit of design while simultaneously making it accessible to many who do not have the formal education or ability to grasp the higher level mathematical concepts this truly requires. He basically made this hobby accessible for all. It's respect for a man who has invested more time and effort than necessary who has used his knowledge, skills, and abilities for good when he never had to to help. Respect for the fact that MANY will never have the experience and education he has and are truly thankful he is passionate about the right things. Those who are at the same education and knowledge level of Jeff respect him all the same for the same exact reasons. He will always answer a question, and never asks for anything but for everyone to pursue their journey in this hobby.

Anyway,

Bass tuning is far from irrelevant. Ignoring all else and setting a Fb and look at what the simulation does on a graph will hurt. All considerations should be made. Room curve, T/S parameters, motor strength (Get to know what the relationship between Qms, Qes, Bl, Qts, and Vas) which can tell you a lot about how it will respond under load or with transient response, and most importantly never forget the simulations assume a sine wave at those frequencies at a given wattage and does not represent a complex musical signal. This is where having a clear design goal is important as well. Different turnings are required for different situations: Stand mount, distance from boundaries, room gain curve, X-max curve, amplifiers the speaker may/will be used with all play into the decision. Pallas is right, Port modes can suck! So when designing a vented enclosure it is important to consider port location, port size (as big as you can is not always the best option) and the driver's ability to move the air you are asking it to. At times it seems designing a box is just that.... Making a box. It should be more because you are manipulating what is arguably the most important, at lest the most subjectively noticeable, aspect of the sound. YMMV Just my $0.02

[keith_correa]

Re: Box alignment/tuning - different perspectives

You may find this post (and thread) interesting: http://techtalk.parts-express.com/sh...55#post1902955

Thanks for the link!! I remember reading that a while ago, was searching for it yesterday and could not find it. That thread is epic!

[Pallas]

Re: Box alignment/tuning - different perspectives

***Jeff is respected not just for his software, but his knowledge and ability to wield the toolkit of design while simultaneously making it accessible to many who do not have the formal education or ability to grasp the higher level mathematical concepts this truly requires. ***

+1

Bass tuning is far from irrelevant. Ignoring all else and setting a Fb and look at what the simulation does on a graph will hurt.

The modeled graph means basically nothing compared to what happens when the part goes into an actual room.

But let me revise my original statment: bass tuning is basically irrelevant, if one is willing to use modern methods such as multiple subwoofers and DSP-based EQ guided by decent in-room measurements. I cannot speak for those unwilling or unable to use modern methods, except to say that often subs in a multisub system can be smaller and cheaper than one thinks, and subwoofers can be surprisingly easy to hide in a room if one's DIYing. So it's not too hard for a DIYer to explore modern bass reproduction methods.

I don't even model any more, except to see how much power is required to hit xmax in a given size box. Everything else is a matter for EQ based on in-room measurements.

[keith_correa]

Re: Box alignment/tuning - different perspectives

<snip>Just my $0.02

Thanks for your perspective/philosophy Mike! BTW, your claimed $0.02 goes a VERRRRY long way with us/me :D

[keith_correa]

Re: Box alignment/tuning - different perspectives

Chris and Pallas, Thanks!