Box alignment/tuning - different perspectives

[colofan]

Re: Box alignment/tuning - different perspectives

I prefer Bass Reflex with a sub-sonic electronic filter for Xmax issues. Horn would be great though size for most rooms would be low on the WAF. This is for home theater applications. Diffferent system for music and different room. Even though you can DSP the response flat that is only one location and the more drivers you add the more difficult I believe it is to resolve phase issues coming frmo multiple directions. Also in a home theater most of the action occurs in front of you not around you. Take a space shuttle launch sequence. You used to be able to compare a real event to what was being recorded and if you could reproduce that sound your system has it "right". I know not anymore with movies but a standard that I think stills applies.

Just not a fan of turning my movie room into a massive car system....to each his own like every opinion everyone has one.

[keith_correa]

Re: Box alignment/tuning - different perspectives

FM = Forum member

[Brian Steele]

Re: Box alignment/tuning - different perspectives

I've gotten used to alignments where the passband is tuned as flat as possible, even for small systems. Yes, the bass does sound a bit lean with that type of alignment, but OTOH with a bump in the pass-band at or before Fb, the bass just sounds "wrong" to me.

If I ever want to bump the bass up a bit, that's what the bass knob or EQ is for.

As always, YMMV.

[Jeff B.]

Re: Box alignment/tuning - different perspectives

FM = Frequency Modulation :D

Hmmmmm doesn't seem to fit the context. Somehow I figured it was something like Frequent Mor0n. Which probably fits me fine.

[Tin_Ears]

Re: Box alignment/tuning - different perspectives

There's nothing special about me. I don't even know what an FM is?

FM = Frequency Modulation :D

[Jeff B.]

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.

There's nothing special about me. I don't even know what an FM is?

[Jeff B.]

Re: Box alignment/tuning - different perspectives

A couple comments on rooms and bass. Because rooms are acoustically small spaces at low frequencies all of them have a "Schroeder Frequency". This is the frequency at which the room begins to take over and control the preceived response of the speaker. The Schroeder Frequency is based on the rooms volume and wall / ceiling/ floor surface area, the average absorption coefficient of the surfaces, and the T60 reverberation time of the room.

Based on this formula my family room has a Schroeder Frequency of 197 Hz. Most rooms will typcially fall in the range of 180 - 250 Hz. What happens below this frequency is that the acoustically small dimensions (with respect to the long wavelengths at low frequencies) and parallel walls of the room begin to control the behavior of low frequency propagation. This is where room gain gradually begins to roll-in along with any near-boundary effect, as Allison demonstrated. And, because of the parallel surfaces between walsl and ceiling and floor, standing waves develop with nulls and peaks at different locations in the room.

This is why Pallas (and many others, includeing Toole) recommend multiple subwoofers. When placed properly within the room their combination of peaks and nulls can be made to fill-in and significantly smooth the response in the room. While everything Pallas said is correct, there are a couple of things that change the weighting of these effects.

First, if you are like me you tend to sit in the same place when you listen to music or the home theater. If this is the case, you are likely much less concerned about how evenly distributed your bass response is veruse how it sounds where you are sitting. For me it was not hard to find subwoofer placement that gave me very nice bass where I sit, and I don't worry so much about other places in the room.

Second, when I turn the subwoofers off and listen to speakers with differing bass characteristics from my Continuums that are -3dB around 70hz to my Kairos that reach near 40hz there is most definitely a difference in how the bass sounds in my room. In addition, I can listen to the Kairos both vented and sealed. The differences here are all below 50Hz and it is quite obviously apparent. Even changing the tuning frequency changes the perception of the bass. So, it really isn't correct to say that the F3, slope, and Q of the bass are irrelevant. These are easily seen to make a difference, even when the room still controls much of our perception of the bass.

Now, I don't want to poo-poo efforts made to reduce the room's influence. The method Pallas gave is certainly valid and useful, so are bass traps, Room EQ, and use of dipole speakers to change the pressurization of the room . I'm just saying two things - If you listen in one location it doesn't have to be that complicated, and the differences between different bass alignments can certainly be audible.

Jeff B.

[keith_correa]

Re: Box alignment/tuning - different perspectives

Chris and Pallas, Thanks!

[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

[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

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!

[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

[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

[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.

[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.