Tuning cabinets lower than speaker Fs...

[Eric Moesle]

FWIW, I LOVE, LOVE, LOVE threads like this . . .

As for the initial question, why bother detuning your cab, such an intrusive act, when the easy route is to use a power amp such as the QSC PLX line which permits you to switch to highpass at either 30hz or 50hz, problem solved???

I've recently set mine at 50hz, and my bass sounds the SAME to me at high volumes, except for a bit of "thinness" on the low B string at C# and below . . . and that's what I was aiming for in order to protect my 10" drivers . . . let the PA handle those frequencies for me.

 

[Magman]

That sounds like a handy feature (the high pass). Some places don't have very good PA's though. Some of the bass rigs owned by people on this board, if duplicated into stereo would be far better than the PA's lurking in many bars&cafes around the country

I find the whole subject of speaker design, acoustic physics and music very interesting, even though a lot of the math goes above my education.

I think its great how playing a musical instrument can tie in all sorts of other interesting things - science, computers, carpentry, psychology etc.

FWIW, I LOVE, LOVE, LOVE threads like this . . .

As for the initial question, why bother detuning your cab, such an intrusive act, when the easy route is to use a power amp such as the QSC PLX line which permits you to switch to highpass at either 30hz or 50hz, problem solved???

I've recently set mine at 50hz, and my bass sounds the SAME to me at high volumes, except for a bit of "thinness" on the low B string at C# and below . . . and that's what I was aiming for in order to protect my 10" drivers . . . let the PA handle those frequencies for me.

 

[Magman]

I think Bill has been pretty clear that the Tuba is not 'extra' efficient with the deeper lows.
Though - if 2 tubas were placed together, or it is placed in the corner of a room, this can change, as size of 'virtual horn' is increased?
Is the concept of how a roman audiotorium works based on the horn principle again? (the acoustics in some of those ancient places are supposed to be very good at amplifiying sounds on the stage area).

I'm thinking now for first project I'll 'just' build a big 15 sq ft cabinet, tune it to 30hz or 25hz with an emminence kappa 18 and be done with it. I'd have full range rig.
There is the problem of the kappas upper resonant peak though, but eq could get rid of that - or crossover and making the cabinet full range: but scope of project starts increasing.

Please understand I'm not in any way disputing your design, or how efficiently it operates. My heartburn is with the self-annointed Galileo who claims or infers a horn operating flat to 30 or 40 Hz in a small box. It just doesn't happen. The proof is in the response plots, which they will never publish.

 

[billfitzmaurice]

I could go to great length in defense of the Tuba 24, but as those who've actually built and played through it are more than satisfied with how well it works I'll defer that chore to them, as it is one which they seem quite pleased with.

All the frequency plots for all my designs have been/are published; I have nothing to hide. Try to say the same for commercial speaker manufacturers, most of whom won't even provide the T/S specs on their 'proprietary' drivers (probably sourced from Eminence anyway).

Tuba 24s response was specifically tailored for the real world needs of electric bass and PA. Over a period of two years RTA measurements were done at a 6,000 seat concert venue. Over 60 concerts featuring major national and international acts were measured, and the results showed quite conclusively the primary SPL demands on electric bass lie from 60 to 100 Hz. While output is required to approximately 32 Hz, there is no need for flat response to very low frequencies. In fact, average requirements at 40Hz are some 20dB lower than those at 80 Hz. However, the average electric bass loudspeakers sold today are not capable of delivering even this level of performance, and those that do operate to 40Hz do not do so with anything approaching the sensitivity level of Tuba 24.

As to the possibility of a small horn that operates flat to 40Hz, if 3.6 cu ft qualifies as a 'small box' then such a horn does indeed exist; it is the Tuba 18, which will be published in AudioXpress Magazine (along with SPL charts) this fall. Corner loaded it runs with 105dB/watt sensitivity to 40 Hz, with an f10 at 28Hz. According to traditional theory this level of performance is impossible. Since I'm listening to this impossible speaker at this moment I have no qualms with being compared to Galileo, though Da Vinci is my personal idol.

 

[Magman]

What happens if the Tuba 24 is corner loaded?

I could go to great length in defense of the Tuba 24, but as those who've actually built and played through it are more than satisfied with how well it works I'll defer that chore to them, as it is one which they seem quite pleased with.

All the frequency plots for all my designs have been/are published; I have nothing to hide. Try to say the same for commercial speaker manufacturers, most of whom won't even provide the T/S specs on their 'proprietary' drivers (probably sourced from Eminence anyway).

Tuba 24s response was specifically tailored for the real world needs of electric bass and PA. Over a period of two years RTA measurements were done at a 6,000 seat concert venue. Over 60 concerts featuring major national and international acts were measured, and the results showed quite conclusively the primary SPL demands on electric bass lie from 60 to 100 Hz. While output is required to approximately 32 Hz, there is no need for flat response to very low frequencies. In fact, average requirements at 40Hz are some 20dB lower than those at 80 Hz. However, the average electric bass loudspeakers sold today are not capable of delivering even this level of performance, and those that do operate to 40Hz do not do so with anything approaching the sensitivity level of Tuba 24.

As to the possibility of a small horn that operates flat to 40Hz, if 3.6 cu ft qualifies as a 'small box' then such a horn does indeed exist; it is the Tuba 18, which will be published in AudioXpress Magazine (along with SPL charts) this fall. Corner loaded it runs with 105dB/watt sensitivity to 40 Hz, with an f10 at 28Hz. According to traditional theory this level of performance is impossible. Since I'm listening to this impossible speaker at this moment I have no qualms with being compared to Galileo, though Da Vinci is my personal idol.

 

[Petebass]

FWIW, I LOVE, LOVE, LOVE threads like this . . .

+1.

 

[billfitzmaurice]

What happens if the Tuba 24 is corner loaded?

It will get an additional 3dB of sensitivity below 62Hz. Tuba 24 was designed specifically for where it would usually end up being placed, which is freestanding, so corner loading doesn't do much for it. The ratio of the horn path length to mouth area is small, so it gets the maximum SPL possible with no boundary reinforcement. This is completely opposite to the home theatre/autosound Tubas that use a long path length and small mouth for maximum LF extension and boundary reinforcement and/or cabin gain to achieve the desired sensitivity.

Tuba 24 has a response curve that differs completely from other speakers in that it is stepped. Like a typical 15 or 18 box it delivers it's highest output from 60 to 100 Hz. However, other speakers have response that falls in a linear fashion below Fb; Tuba's doesn't. It drops in sensitivity by about 10dB at 50 Hz, where it levels off down to 32Hz, so that the full range of fundamentals are covered down to a low B, but with the lesser SPL actually required. Thus the Tuba 24 maintains an SPL/watt of 90dB at 32 Hz, whereas the typical electric bass 1x15 or 1x18 cab is lucky to deliver even 80 dB/watt at 32Hz.

 

[alexclaber]

This is all really interesting stuff Bill, and certainly a very different approach to my power sucking Acmes!

It appears that horn speakers can use the room boundaries to extend the horn size and thus efficiency and LF response. Is it possible to achieve this with direct radiating speakers or do the boundaries simply affect the lows in a full-space, half-space, quarter-space manner?

One reason I'm asking is that I tend to place my vertical Acme stack in the corners of room, not too close to the corner, maybe 1.5'-4' away, to help throw the lows further out into the room. Of course, this may just be psychosematic (sp?!). Are there any ways to calculate room benefits for such an example?

Alex

 

[McHack]

Horns have been around for a VERY long time... For any of you audiophile types, that are into home stereo/theatre... you've probably heard of a company called Klipsch...

Same deal... Just slightly different. I think speaker manufactuers get away from Horn design speakers, as theres more labor into building one that a standard box w/ drivers & such...

 

[billfitzmaurice]

It appears that horn speakers can use the room boundaries to extend the horn size and thus efficiency and LF response. Is it possible to achieve this with direct radiating speakers or do the boundaries simply affect the lows in a full-space, half-space, quarter-space manner?

Yes, the effect works for any source, though it works best when the radiating area of the speaker is fairly small; it doesn't do much for Tuba 24 as that box already has a large radiating area (at 530 square inches more than that of two eighteens). But you need to be tight to the wall, or reflections off it will actually kill the bass. For instance, at 4 feet away you get an out of phase reflection off the wall at 70 Hz which can easily suck out as much as 25dB. In general with small radiating areas you can expect 6 to 9dB of room gain below 100 Hz from corner placement.

I think speaker manufactuers get away from Horn design speakers, as theres more labor into building one that a standard box w/ drivers & such

Absolutely true. When choosing whether to sell speakers built the best way or the cheapest way, guess which option is more profitable? Of course, horns are still offered. Check out the EAW Super Subs. Then check out the price on them. You can still buy quality, but it's gonna cost ya.

 

[Magman]

Standing waves are problem in general... my studio is the basement. At about two foot from my monitors sub-50hz rolls off hard because of a standing wave, I have to move my chair back about 2-3 feet to check kickdrums etc, but at that distance 80-100hz is dipped.
Its great we can have very poweful home studios with computers etc nowadays, but the fundamental different between them and a proffesional studio is the rooms less than the gadgets.

People spend huge large sums of money on flat reference systems, but as far as I can tell the biggest inhibitor to a flat system is the room acoustics, which can't be fixed with expensive speakers.

Yes, the effect works for any source, though it works best when the radiating area of the speaker is fairly small; it doesn't do much for Tuba 24 as that box already has a large radiating area (at 530 square inches more than that of two eighteens). But you need to be tight to the wall, or reflections off it will actually kill the bass. For instance, at 4 feet away you get an out of phase reflection off the wall at 70 Hz which can easily suck out as much as 25dB. In general with small radiating areas you can expect 6 to 9dB of room gain below 100 Hz from corner placement.



Absolutely true. When choosing whether to sell speakers built the best way or the cheapest way, guess which option is more profitable? Of course, horns are still offered. Check out the EAW Super Subs. Then check out the price on them. You can still buy quality, but it's gonna cost ya.

 

[Magman]

Yeah, just think of those old grammophones (the non electrical ones).... whats the needle attached to?... a big horn!
Is the horn the fundamental amplification system?

Horns have been around for a VERY long time... For any of you audiophile types, that are into home stereo/theatre... you've probably heard of a company called Klipsch...

Same deal... Just slightly different. I think speaker manufactuers get away from Horn design speakers, as theres more labor into building one that a standard box w/ drivers & such...

 

[billfitzmaurice]

the biggest inhibitor to a flat system is the room acoustics, which can't be fixed with expensive speakers

Quite true, but between carpet, wall treatments. proper speaker placement and a 31 band digital EQ with auto RTA you can do a lot.

needle attached to?... a big horn!

Is the horn the fundamental amplification system?

Yes. And with a tuba or trumpet or any other brass instrument what turns the squeek of a mouthpiece into music is also a horn. And it was ram's horns that brought down the walls of Jericho. Some things just can't be improved upon.

 

[bgavin]

As to the possibility of a small horn that operates flat to 40Hz, if 3.6 cu ft qualifies as a 'small box' then such a horn does indeed exist; it is the Tuba 18, which will be published in AudioXpress Magazine (along with SPL charts) this fall. Corner loaded it runs with 105dB/watt sensitivity to 40 Hz, with an f10 at 28Hz. According to traditional theory this level of performance is impossible.

Paul Klipsch discovered the beauty of corner loaded horns 60 years ago. The wall boundaries act as extensions of both the air column and the mouth perimeter. It doesn't work unless placed in a corner.

Does your upcoming Tuba 18 article show response in half space also, or just in a corner?

 

[billfitzmaurice]

Does your upcoming Tuba 18 article show response in half space also, or just in a corner?

Results are shown for half, quarter and eighth space loading, along with nearfield response and impedance charts. The response is similar to that of a Klipschorn, though since it is intended as a sub I made no attempt to extend the midbass response higher than 200Hz. The box is considerably smaller than a KHorn but is able to achieve the same LF extension. PK was severely restricted in what he was able to do because of the limitations of the drivers available to him. Modern high Xmax high Bl drivers allow the use of taper geometries and throat impedances that simply weren't possible even ten years ago.

 

[bgavin]

As you point out with all the good drivers available... why choose a Beta 10 for your Tuba 24?

 

[billfitzmaurice]

The Beta 10 works just fine to moderate volumes, and actually is more sensitive than many far more expensive drivers I tested in the design. It's perfectly clean with 100 watts input, and with its efficiency and bandwidth that means it is well able to outperform the average 1x15 or 1x18 driven with 300 to 400 watts.

I don't recommend the Beta 10 for very high power/very low frequency applications. The Beta 10 remains reasonably linear above 60 Hz or so to its 250 watt limit, but from about 60 Hz on down it does suffer from serious power compression above 150 watts input. For maximum LF output with no power compression right to its 300 watt rating I recommend the Eminence HL10a.

At 10 watts input the Beta 10 is about 3dB more sensitive broadband than the HL10a, but at 40 Hz with 250 watts input the HL10a does not suffer from power compression and is 7dB more sensitive than the Beta 10 as a result. At those levels the Beta also suffers from throat distortion associated with the power compression; the HL10 a does not.

Other tens with a higher Bl product would have less power compression problems than the Beta, but none have anywhere near the Xmax of the HL10a, with the exception of some tens designed for subwoofer usage in direct radiators and bandpass boxes, and those have too low an Fs for horn loading.