RMAF Loudspeakers?

As a point of reference, a vented speaker of one cubic foot internal volume and 90 dB/1 watt/1 meter efficiency will be -3 dB at about 44 Hz, assuming good boundary reinforcement from one room surface (woofer close to floor, for example). Different loudspeaker modelling programs may give slightly different results, but this should be in the ballpark.

If we factor in moderate boundary reinforcement from the two closest walls and the ceiling, we can extend that to perhaps 35 Hz.

If we put the speaker up on a stand way out in the room, our -3 dB point could end up closer to the 55 Hz ballpark.

Here's how you can make use of this point of reference:

If we want to lower the -3 dB point by 1/3 octave, we'd have to either trade off 3 dB of efficiency or double the box size. Put another way, if we double the box size we gain 3 dB of efficiency or 1/3 octave of bass extension. Put yet a third way, in order to gain 3 dB of efficiency we'd have to either double the box size or trade off 1/3 octave of bass extension. Or some combination thereof.

To calculate the frequency that would be 1/3 of an octave lower you multiply by .793; and to calculate the frequency that would be 1/3 of an octave higher you divide by .793.

To estimate box size, assume 3/4" thick walls and then deduct 10% from the gross internal volume to allow for bracing, driver magnets, and ports.

If anyone sees significant errors in these numbers please feel free to make corrections.

Different speaker manufacturers make different assumptions about the room's contributions, and the information above will allow you to estimate how much room contribution the manufacturer is factoring in. Recognize that you probably are not comparing apples-to-apples when you rely exclusively on specs from different manufacturers. In general, a smaller speaker cannot be both more efficient and have deeper bass than a bigger one if they use the same type of enclosure and both are competently designed. There are exceptions where a designer trades off bass extension for transient response, but that's another topic for another day.

Duke
dealer/manufacturer

Duke - Are you the only manufacturer who is hampered by these physical parameters or do they influence all speaker makers regardless of claims to the contrary?

Tvad - I achieved what you are seeking by contacting Bill Woods and ultimately buying his AH300 horns. When combined with B&C 50 mm compression drivers, these horns provide a remarkably coherent voice ranging from 400 Hz up to 14Khz. I mounted mine on top of a pair of JBL L-200 cabinets using only the LE 15B woofers and cabinets and bypassing the inboard horn and passive crossover. Mine are actively crossed over by a DBX Drive Rack but the native crossover divides the signal at 800 Hz and works pretty well with less complexity and less expense than my arrangement.

I'm sure you won't see Bill at RMAF but the Oswald Mill system that was there last year uses the same horn as does the Cogent system. Chris Brady of Teres turntable fame uses them too.

My frequency response is limited at the low end at about 50 Hz. and on top at about 14 Khz. This might be a deal breaker for you but I don't find it to be very limiting at all. Efficiency is limited by the JBL woofer which I'm guessing to be about 97 db. Maybe Duke can give a better estimate of that. The cabinet is 5 cu.ft. and ported. You may have better bass cabinet options in your area than the JBLs I already happened to own.

Not sure if you can get to hear a pair of Lamhorns
They seem to fit your sonic characteristics

I heard them at FSI in Montreal - Very nice sounding speakers

Hey kurt
I see you went back to Tonians Again
You still have the Lamhorns

Hi Macrojack, ya got me... I'm among the few manufacturers dumb enough to be limited by physical-world constraints.

Seriously, I'll admit that it's possible to manipulate the shape of the frequency response curve in the bass region to give the perception of louder & deeper bass than would normally be possible, or to use resonances to boost the apparent bass (a sound that decays slower will be perceived as louder than a sound that decays quickly even if both have the same peak SPL), but there will be tradeoffs that are likely to be perceived.

[As an aside, in general I believe we should base our designs on perception, not strictly on measurements, because we listen with ears instead of with microphones; but measurements can be a very reliable tool if we can reliably extrapolate perceptions from measurements.]

The real-world in-room picture does include some complications and mitigations that can explain discrepancies between the published figures of different manufacturers. When speakers are positioned so they get a fair amount of boundary reinforcement (like on the floor and near a wall but not in a corner), we can expect approximately 3 dB per octave boost below 100 Hz or so. In other words, the deeper a speaker goes the more the room helps it out. This is more complex than the boundary-reinforcement situation I described in my post above, which was streamlined a bit for the sake of brevity.

The point-of-reference numbers I gave can be reproduced by anyone using a speaker modelling program, and are based on the Thiele-Small parameters. Midband efficiency may be higher, but usually it's the efficiency in the bass region that sets system efficiency because otherwise the tonal balance is off unless boundary reinforcement is used to restore it.

Some manufacturers design for and specify placement up against the wall or in a corner, and in my opinion that is perfectly legitimate. Some manufacturers give an "in-room" spec which includes several dB of broadband reverberant field contribution, and in my opinion this is justifiable (if they disclose it) but does work against making an apples-to-apples comparision. Finally, some speakers because of their configuration have significantly different sound propagation characteristics that make it impossible to adequately measure them by the same yardstick. For example, a line-source speaker's SPL will fall off by 3 dB per doubling of distance (under anechoic conditions) rather than by 6 dB per doubling of distance, so a 1 meter measurement will under-state such a speaker's real-world efficiency at the listening position.

Macrojack, which JBL woofer do you have? I suspect that in your 5 cubic foot box it's one of those cases where the designer has traded off some theoretically available (based on box size and efficiency) extension in favor of better transient response and better in-room behavior once boundary reinforcement is factored in. If so, in my opinion this is the ideal way to design a vented-box woofer system for use in a home - namely, not shooting for deepest-loudest-possible bass, but going for a more shallow roll-off that starts higher up.

By the way, JBL's specs for their woofers are conservative. If their specs say 97dB, that's what a modelling program and a careful measurement will confirm.