Hi efficient speaker, bass problems

Atmasphere, 50 Watts is not very high, but, if they are indeed 109 dB watt/1 meter your point is well taken. That is, if that's the free standing sensitivity.

Apparently in reply to my post above, Timlub wrote: "Extension, dampning and efficiency are the tradeoffs. The vectors go in different directions. The op questions grip vs eff. The extension is not. as I understand. part of the query. But I'm all in for a free lunch of any kind. Elucidate."

Sorry for the late resopnse; I didn't check back in on this thread until just now.

First let me say that high damping is not necessarily desirable in and of itself; it is the in-room frequency response that we want to optimize because that is what correlates best with subjective preference. An overdamped speaker sounds... overdamped.

Suppose we have a fairly low-Q woofer in a considerably larger-then-optimum vented box. Let's say we're tuning to the upper 30's, giving us a -3 dB point in the upper 30's with a steep rolloff below that. With typical room gain, we're getting down to the mid 30's.

Now let's drive this same speaker with a low-damping-factor tube amp, but without changeing the tuning frequency. Boom! Quite literally - we now have a broad 2 dB hump across the middle of the bass region, and we've managed to push the -3 dB point south a little bit. So far this isn't a net improvement, but we're not done yet...

Let's drop the tuning frequency to the upper 20's, which elminates any peaking and gives us extension into the lower 30's before room gain. We're on the right track.

Now let's factor in room gain, and push the tuning down into the mid 20's. We get a nice gentle rolloff across the bass region that is approximately the inverse of room gain, and real-world extension into the upper 20's. In contrast, before our low-damping-factor amp came into play, we could have expected extension to the mid 30's after room gain.

This isn't hypothetical. I manufacture this speaker, and chose my woofer and box size and port system with all of this in mind. The scenario I've described doesn't necessarily play out with all high-efficiency speakers.

Duke

Hi Duke,
Not overly important, but your last post was responding to Lewhite.
Tim

Hi Duke,
Well after you got my attention by putting my handle in your post, I read your post thoroughly. I see your point completely and can see this happening, but won't that same speaker create frequency dips in some rooms? and/or do you recommend this speaker for certain types of rooms or placement?

You're absolutely right Timlub - my bad! It was indeed Lewhite I was responding to! Thus dissolves my illusion of infallibility...

Okay to answer the questions which I think actually did come from you this time, the subject of room interaction dips (and peaks) is almost a different topic from the one I addressed. One could argue that a speaker which goes deeper is likely to have more peaks and dips simply because its wider bandwidth gives the room more opportunity to screw things up. But beyond that, I don't see any reason why a low-tuned box with a low-damping-factor amp would result in a room-interaction dip. If you're talking about a sag in the bass response above the tuning frequency, actually that's more likely to happen using a conventional amplifier with a low-Q woofer that's in a somewhat oversized vented box. If you have a modelling program, the effect of low damping factor is to raise the apparent Qes of the speaker (without correspondingly lowering its efficiency... hence, a "free lunch").

Oversimplifying a bit, you can get bass boost from boundary reinforcement or from a low output impedance amplifier. The two can work in your favor, or work against you... but if you can adjust the tuning frequency of the box, that can help a great deal.

Now since you brought up the topic of dips, I'll bring up the topic of peaks, so now we're talking about peaks and dips, which arise from speaker/room interaction. They are inevitable. My preferred technique for addressing them is to use four small subwoofers scattered asymmetrically around the room. This way each will produce a different peak-and-dip pattern at any location in the room, because each is a different distance from each of the room boundaries (in the horizontal plane anyway), and the sum of these multiple dissimilar peak-and-dip patterns ends up being pretty darn smooth. Now if we're talking about two speakers and no subs, one way to introduce some of this staggering/smoothing effect is to place the port on the rear of the speaker, at a different height than the woofer. Toe this speaker in fairly aggressively, and the woofer and port are each a different distance from the room boundaries in all three dimensions! Of course the port is fairly close to the wall in this scenario so it's getting a lot of boundary reinforcement, but that's been taken into account in the design stage (and/or the port's tuning frequency is user-adjustable).

In my experience paying all this extra attention to room interaction makes more of a difference in small rooms than it does in large ones.

Since I've been referring to free lunches here and there, let me mention one more that comes along with low damping factor tube amps (like those atmasphere makes): Their characteristics help to partially counteract thermal compression. Thermal compression arises when the voice coil heats up, and when that happens its resistance rises. Taking an extreme example here, at high power levels your 8-ohm woofer may become, in effect, a 10-ohm woofer. Not only does it take more power to push your woofer, but a high-damping-factor (constant voltage) amplifier will actually put out less wattage into that increased impedance, making a bad situation even worse. On the other hand a low-damping-factor amplifier will put out the same or perhaps even somewhat increased wattage into the higher impedance! So if you plan on pushing your speakers hard, and you hate dynamic compression, you might look for speakers that work well with that type of amplifier. Not that this is the biggest of free lunches out there, but it's at least on the menu.

Imho, and as we all now know, I'm hardly infallible...

Duke