Woofing "Q"


Todays query pertains to sub matching to a stand mounted two or three way speaker. Irrespective of room acoustics and crossover over or underlaping points and levels. What are the effects of mis matching Q or damping. Is it detremental to match a acoustic suspension sub with a ported monitor or must they both have the same box alignment. This assuming that a sealed box is quicker than than a bass reflex box. I curently am using sealed Yamaha 10m monitors with a Yamaha sub that has two 8 in drivers and a port. It is matched pretty well. The Cary 805c is telling me I need to step up my game, but I don't want to lose my alignment match. Halp before I make a 'greener grass' mistake.
lewhite
Woofer enclosure doesn't matter. You want to get the balance correct, and therefore the loudness of the sub does matter. Any powered sub I know has the means to vary the output. I have found that subs that fire down...or anyway, not directly out are the best for integration.
My Rythmik subs have variable Q. Seamless integration (to my ear) was often possible at more than one "Q" setting. Sometimes, my preferred Q setting changed, depended on other x-over variables (like slope and and x-over frequency). And, even though seamless integration was possible at different Q settings, the overall character of the system definitely changed, depending on which combo of Q and other parameters was chosen.

Generally speaking, I found that it is definitely possible to "mismatch" the Q of the sub and main speaker (when it's wrong, you'll know it), but there is no one perfectly "right" answer. I suspect that some degree of experimentation is probably useful to optimize Q to personal preference. I would personally recommend a sub with variable Q for this reason.

Marty
I understand that level and xover point are adjustable and must be optiomised first but adjustable dampining Now that's a new concept . Marty: is it more noticible to have an over damped sub (lower number) compaired to the monitor or the other way around.
I'm not sure I have a great answer for that. Slightly underdamping the sub can make the system feel a bit more dynamic and punchy, slight overdamping it can make it seem more transparent. Too much damping and things can go dry and lifeless. However, for me, extreme underdamping is probably the worst condition so, twist my arm, and I'll say that underdamping the sub is worse.
If the Q of your sub is a lot higher than your speakers then you will lose detail in the bass and lower mids and the sound will not be as clean and tight.

Sealed subs are really the only way to go if you seek quality rather than an HT sound - but the investment in a sealed sub could be wasted if your speakers are designed with high Q (most speakers with impressive bass extension and small woofers with a port are tuned to a high Q)
Can you adjust the damping of a box,either sub or sat, acousticaly, by putting a 'brick' in the box or a 'sock' on the port? Thanks all for your patient answers

"And may powdered sugar fall gently upon your ears"
Can you adjust the damping of a box,either sub or sat, acoustically by putting a 'brick' in the box or a 'sock' on the port?

You can but it may change the freq response in an undesirable way even if it improves the transient response (group delay)...some subs like the PBUltra13 can have the ports plugged. It is certainly an option but there is a rule of thumb for whether a woofer works best in a ported design or a sealed box...
Shadorne's comment re: "sealed subs only" is probably, as a practical matter, good advice for a music only system, but it may be a bit of an overstatement. The SVS subs he mentions shouldn't be dismissed. Their top model, in it's fully ported configuration, outperforms most sealed boxes on group delay tests. This test usually favors sealed, highly damped designs - but the SVS Ultra shows awfully well. Also, like all ported subs, it offers more deep, clean output capability than a typical sealed box design of similar size and amp power.

That latter item may not be critical for most music (how much musical program material has deep bass info <30hz, anyway?), but it begs a question:

How do you intend to install the subs?

If you're going to roll off the bass to your mains and cross at or above 60ish hz, I'd say sealed boxes are safer bets. If you're gonna run the main speakers full range and "snug up" a sub below their natural roll-off, then it becomes a more open question. Many users on this forum run their subs in this fashion, often rolling off their sub's upper response somewhere below 50hz. In this configuration, a ported box (particularly a good one like the SVS seems to be) may make more sense.

Good Luck

Marty
Shadorne's comment re: "sealed subs only" is probably, as a practical matter, good advice for a music only system, but it may be a bit of an overstatement.

Marty,
Who me ...make an overstatement...never !
LOL - Marty is right - my context is uncompromising bass response. I am not sure where the OP sits, and admittedly for many people "more bass" is better and a low Q device or a sealed sub may sound unimpressively bass light for their taste and $$$ invested.
Shadorne,

Funny, I was thinking the same thing! You and I are the only two posters I can think of who always qualify their statements in a thoughtful and appropriate manner. Yay us!

Marty
I remember a white paper from Dunleavy on multi way speakers and his statement said that the only drivers that should be ported ( hi q) are the biggest ones. Does it make sense that you wouldn't want ported monitor and a sealed sub? idk Or does that only apply to mono amping?
Also I am using a SET amp so doesn't that raise speaker Q because of its hi output impedance. Of the speakers that are going to replace the Yamaha 10m (which are sealed) most of them tout " impressive bass for a speaker this size". Isn't that just another way of saying "kinda loose" Is that something that I want? My room is kinda small and a loose sub seems like it could get out of control real fast.
Lewhite,

I'm pretty sure that trial and error is the only way to be sure that Q is adequately matched. That why I like variable Q subs, whether the Rythmik system, or SVS' open/blocked porting system. Either should allow you enough flexibility to find a good match with most main speakers. Also, both brands are sold direct with a money back in-home trial period. BTW, there may well be other brands out there with this feature, too - so I'm not suggesting that these are your only options. I will note that both appear to be highly regarded and that I'm personally very happy with my Rythmiks.

Good Luck

Marty
I remember a white paper from Dunleavy on multi way speakers and his statement said that the only drivers that should be ported ( hi q) are the biggest ones. Does it make sense that you wouldn't want ported monitor and a sealed sub? idk Or does that only apply to mono amping?

Dunlavy believed in low Q or critically damped designs.

In very large speakers they tend to put very powerful woofers with massive motors (overdamped, Q = 0.5 or less) - in this case the Q can still remain critically damped (Q=0.71) with the addition of the port which also acts to protect the woofer (reduxes excursion and distortion) as well as boosting efficiency by 3 db.

In very small monitors the port is used to increase bass extension and the use of a prototypical small woofer with a small motor means that you are often ending up with a Q of 1 to 1.2 (under-damped). The woofers will tend to have large excursions below port tuning and sometimes visibly popping out by up to an inch in a highly uncontrolled manner which means you get lots of distortion. The roll-off below port tuning is very steep (24 db per octave) so the usable energy below port resonance is very very little.

In a sub - since you are dealing with frequencies from 10 to 90 Hz then it makes little less sense to to have a port tuned at 25 or 30 Hz as the sub will be behave uncontrollably below this port resonance and easily become damaged (even if it sounds louder this way - some subs may have electronic circuits to limit this problem at ultra LF). Better subs are very large and critically damped and have a port tuned extremely low - say at 15 Hz which can be quite effective and gain some SPL without too much risk of sloppy behavior or woofer damage. A critically damped sub (Q=0.71) will work much better with the room (which plays an enormous role below 40 Hz). A sealed critically damped sub will be the most protected from ultra LF (such as 10 Hz) and will sound the tightest or most musical (lowest group delay, lowest distortion and best match to the natural room boost of 12 db/octave in LF), however, it will have LESS SPL output than a ported or under damped design...

Many designers incorrectly assume that because our ears have a lot of difficulty hearing even 20% distortion at 20 Hz then it is OK to have large amounts of distortion in the bass of their speaker or sub wooofer designs. This is a false assumption because you only have to look at an equal loudness curve of our hearing to observe that a mere 1% distortion at an 80 Hz harmonic from a 20 Hz fundamental will sound equally as loud at the original 20 Hz note (even though it is 100 times smaller our ears will pick it up due to their increased sensitivity at 80 Hz).
Best answer so far!!!