Tempest Woes

[jbandpc]

I've built a sealed box - a little less than 5 cubic feet - for an Adire Audio Tempest (15"). It sounds good, but I can't help but think the bass could be tighter. I used 3/4 inch MDF for the box and it's fairly well braced. I'm going to add 1/4 inch High Density Fiberboard (material like clipboards are made of) to the outside to try to help.

Can anyone offer any other suggestions? Maybe a different driver? Should I try a 12"? Or a different 15"?

I'm using a Rythmik Audio 350 Watt amp, which replaced an Adire Audio 250 Watt amp. (They sounded similar in this regard.) The room is about 20' X 12' X 8'. I want to focus mainly on tight bass for music (jazz), but I actually USE it more for home theater, so 'extension' is on the priority list - below 'tight'.

Thank you,
Philip

[bogoes]

There is no reason a sealed Tempest with a good 350W amp should sound flabby. I'm gonna guess that what you're hearing actually has more to do with the integration of the sub and your main speakers or with room modes. Are your main speakers ported or sealed? How are they crossed (i.e. mains running full and sub crossed with amp lowpass at xxHz, or mains running as small on receiver and sub playing wide open off LFE channel)? Also, what size is the room you have this in? Carpet or hard floor, etc?

Give us a couple more details and we can help some more.

Good luck.

[jbandpc]

Sorry. I was trying to be thorough, but I guess I left some stuff out.

My mains are ported bookshelf-style speakers (the AR.com diy's) and their placement is far LESS than ideal. The room is about 20' X 12' X 8' but there are two double-door-sized opennings. The room has carpet. The crossover duties are being handled by a Harman Kardon AVR-7200 and I have the crossover point set to 60Hz. The sub is down-firing and is near only one wall (not in a corner).

I wouldn't say that the sound is flabby, just not quite as tight as I had imagined it would be.

Thank you!
Philip

[Timn8ter]

I won't claim this to be the ultimate solution, perhaps others can comment on my suggestion. I don't like the sound of the mid to high Q sub boxes either. I think you need a bigger box to get the Q down to .6 or even .5.

[GRollins]

The bass will not get appreciably tighter. Assuming that you mean what I mean when you say tighter (you'd be amazed how many people say tight when they mean deep), you're pretty much stuck with the sound that you've got now. I'm not saying that it won't change at all, just that the "tightness" isn't going to get better just by stiffening the cabinet.
Timn8ter's suggestion will change the sound considerably, but if anything will make the bass more loose. As a general rule, you raise the Q if you want it to sound tighter.
Okay, now on to "extension." I've said it elsewhere, but people keep buying these drivers and ending up dissapointed, so I'll say it again: They ain't flat. Period. They have a broad peak in the 80-100Hz range and slope off at about 6dB/oct south of that. The end result is that your 20Hz response is a good 12-15dB lower than you think it is from the simulations. Don't argue with me...measure it. This is not some subtle, tweak, golden-ear thing, this is a real problem. Your only realistic option is to EQ the booger to get that bottom end up to a reasonable level. You'll burn valuable amp power getting there, but it can be done--trust me on this one, I've got twelve 12" Titanics (a similar driver). There are other options, but they get much more complicated.

Grey

[Timn8ter]

Hmmmm....I'm thinking increasing the box size from ~140L to ~230L will lower the group delay, hence "tighter" bass. Am I wrong?

Not wanting to quote Adire I went instead to Vandersteen.

In subwoofer engineering terms, system Q is the product of a complex mathematical equation derived from driver, electrical and enclosure parameters. In practical terms, it relates to the character of the bass response. A low Q subwoofer sounds highly damped and very tight. A high Q subwoofer produces a warm loose bass with more energy in the most audible bass range. The trick has always been to try to find the subwoofer with the Q that best matched your listening room and personal tastes.

.5Q = slightly overdamped, tight jazz sound
1.2Q = significantly underdamped, mass-market HT sound

[GRollins]

First, let's define tight. Most folks I know define tight as meaning that a drum has punch; a definite start and stop. Loose bass is wobbly or rubbery sounding, lacking in definition.
Now think of it in terms of what the driver's cone is doing. Once the cone starts moving--let's say it's a drum thwack--it will obey basic Newtonian physics and tend to keep moving. There are several braking forces at work, but one of the primary ones is the pressure or lack of it behind the cone. In an extreme case, let's say a 12" driver in a box of really small volume, like the size of a shoe box, as the cone moves forward it will create a substantial vacuum in the box, hence, a braking force. Likewise, if the cone moves backwards, it will compress the air, which will in turn resist the movement of the cone. Again, a braking force.
Large enclosures work oppositely.
Are we in agreement so far?
Okay, the only remaining thing is to posit that a woofer that's flying around uncontrolled produces loose, rubbery bass. It loses definition. One that starts and stops on a dime is tighter.
If Vandersteen defines tight and loose differently, all bets are off.
All things being equal, a smaller cabinet (higher Q) will produce a hump before the response rolls off. The rolloff comes much earlier than it would in a larger, low Q cabinet. Now, whether you call this "more energy" or not is in the eye of the beholder. That hump can get pretty noticeable. If your focus (like a lot of car stereo/rap peoples') is on the mid-bass, then, sure, it's 'more energy.' If, on the other hand, your goal is deep bass, you're going to say that it actually decreases the bass. The bass began a 12dB/oct rolloff at a much higher frequency. It's kaput by the time you get to 20Hz.
In the case of a driver in free air (I'm using free air here as a stand-in for a really large cabinet, i.e. one of infinite volume), the rolloff will be much more gradual, and will start somewhat lower. The slope will be closer to 6dB/oct leaving more capability at 20Hz compared to the higher Q cabinet--but less at higher frequencies.
So, which one is "more bass?"
Depends on your point of view. Me? I look for 20Hz. This car stereo boom-boom thing is for kids. Grown-ups know better. Or should, anyway.
By which you can assume that I disagree with Vandersteen's definition of tight. To me "more energy in the most audible bass range" is commercial-speak for "sells more speakers."
To put it another way, I've been using a paint recently that says something to the effect that "due to the extreme purity of the components in this paint, it will take more coats to get good coverage on your wall." Say what? Anyone who knows anything about paint will tell you that a good paint has sufficient pigment to cover in fewer coats, not more. Yet these guys are trying to make low quality sound like a desirable thing. Needless to say, had I realized just how poor this paint was before I bought it, I'd have picked something else. Now I'm stuck with trying to make a silk purse out of a sow's ear.
Oh, one other thing. The response of these drivers in a "properly sized" Thiele-Small enclosure already looks like that of a low-Q speaker. Increasing the cabinet size will only decrease the deep bass further. Granted, this isn't directly related to the tightness, but it's not going to help with extension at all. Now, you could decrease the size of the cabinet, which would bring up the bass somewhat. You'd have to cut and try, because the simulations have already failed miserably. The problem here is that the low end would be lumpy, then rolloff at a higher frequency. At a guess, I'd say you could achieve something approaching flat response if you were willing to accept a rolloff begining somewhere in the range of 45 to 60Hz. Your 20Hz response would still be way down. Bummer, eh?

Grey

[robertwb70]

room treatments would help alot

DIY some broad-band absorbers from rigid fiberglass panels for the corners

[johninCR]

Do you have the driver voice coils wired in series or parallel? Series wiring results in an Le 4 times as high as parallel. I've yet to hear a dual coil sub that didn't sound much better wired in parallel because of this. Check out Adire's paper about woofer speed.

[rnoble]

I'm running a mid-Q sealed tempest. What I found was that the sound changed quite considerably over the first 80hrs. After running it in for around that long and tuning in to my mains the sound was awesome.

You have everything there, just needs a little tuning and possibly experimentation with room placement and/or parametric eq.