Hi efficient speaker, bass problems

Weseixas, that TAD driver I mentioned can cross over easily at 500Hz. So it can be matched with a horn midrange easily enough. I've seen some such horns have good response to 17KHz, although for what I want to call 'hifi' I would want to supplement that with a super tweeter at least.

OTOH you could cross over to a smaller Lowther or the like, but IMO its still nice to have a super tweeter so you can have a wider sweet spot.

Tmsorosk, it may be a language issue, but the appearance is that your post is in contradiction to the title of the thread. In addition, your post mentions

low efficient speakers

and then in the same sentence

less sensitive units

so its hard to know what you are asking. Would you care to try again?

Weseixas, TAD makes high compliance 15" drivers that have free air resonances in the 20s. At least one speaker, the Classic Audio Loudspeaker, has used these drivers to make a 3-way system that is good to 20Hz. It is rated at 97 db.

Weseixas, you wrote:

no one driver is going to go from 30-500+ hz IMO and still produce high sensitivity it would also produce 2 much distortion IMO.

I guess I take issue with this. The TAD driver I mentioned does exactly this range quite easily, and does do at 97 db. Yet it is quite fast and transparent.

But more recently I have heard some field-coil powered 15" drivers that are even faster and more transparent, and cover the same range yet are more like 98 or 99 db (without a horn). It is used in a speaker that got 'Best Sound at Show' in TAS' CES issue a couple of years ago.

Unsound, just FWIW, field coil technology in and of itself has no power limitations any more than regular magnetic systems.

Of course, most of the FC drivers we have seen so far are designed for high efficiency applications, and so do not handle all that much power. The midrange drivers in my speakers are FC and are rated at 50 watts. I would not want to be anywhere near them with that kind of power going through them- they are about 109 db 1 watt/1 meter.

Certainly it is! The slew rate (or risetime) is a measure of how fast the amplifier can respond to a signal. The quicker it responds, the more likely the signal will be processed by the emotional centers of the brain (limbic system) rather than the cerebral cortex. This is where toe-tapping comes from.

Mapman, a damping factor of 1000... well let's put it this way- you won't hear the difference between that and an amplifier with a DF of 50, all other things being equal (which, it seems, they never are...). Its my guess that there are other things that are making that work for you.

Now if running tubes, subjectively there is some argument, tubes have poor damping and hence very little bass control to speak off , a sealed enclosure might be an advantage here, TL too , due to the loading.

Actually in practice the reverse is true. Vented boxes usually need less damping of the driver for optimal response if I have my theory right- so less damping from the amplifier will be needed. So you can have plety of bass control!

No speaker known requires a damping factor of above 20:1. That can be created by any tube amplifier, given enough feedback. However you pay a price for adding feedback- while you get more damping, you also add odd-ordered harmonic distortion, which essentially is audible as brightness and harshness.

So if you want tubes to give you the best they can offer, its in your best interest to use an amplifier without feedback, and a speaker that is intended for an amplifier with a higher output impedance.

The only thing about this is that loop feedback contributes to harshness in transistor amplifiers too. Since the ear/brain system uses the 5th, 7th and 9th harmonics as a means of determining how loud a sound is, messing with these harmonics will cause the system to sound louder than it really is, plus the odd orders are perceived as harshness. So there is a powerful argument for eliminating feedback altogether, as figuring out how loud a sound is is arguably one of the more important rules of human sound perception.

IOW, the model of an amplifier with an output impedance of zero ohms may not hold water, given other real-world issues. So designing a speaker for that may not make a lot of sense either.

Weseixas, actually with many tube amps when you increase the load impedance the output power goes *up* not down.

In the case of transformer coupled amps, this is because the OPT is more efficient. In the case of OTLs (and especially if its a *smaller* OTL), this is because the entire output section is running more efficiently- more power is dissipated in the load and less in the output section.

Bass extension has nothing to do with output impedance. Bass 'control' might, but since damping plays such a minor role here, what really is important is distortion. That's what gets you muddy bass! So if the amp is undistorted its more likely to be perceived as 'control'. Just FWIW.

Anyway, if the speaker was designed on tube amps, its unlikely that a transistor amp will exhibit more 'control'. My impression is that transistor amps in this situation exhibit 'punch' but not a lot of definition or subtlety. I often find myself trying to turn them up to get the same impact I expect out of the tube (in this case, OTL) amp. I guess my point is that so much depends on the interface between the amp and speaker that its very hard to make generalities.

They were made for TVs and got phased out in the 1970s. It just so happened that if wired right, they could be operated with low voltage and high current, and so were useful in OTLs. Today they are pretty rare. The closest thing to them is the EL509, which is not as gutsy.