Is a 'super tweeter' REALLY noticeable ?

Dear all,

is a 'super tweeter' something we might strive for in high-end audio ?

I mean tweeters which go up 'til 50-70 or maybe even more KHz in frequency.

We all know what's the max. freq. of a CD, we know Nyquist, sample rates, Hi-Res Audio and human hearing (I hear 'til around 16k at the age of 40)..

A friend of mine argued such tweeters might be good (even if the source will never play any signal into these lower 'ultrasonics') because of upper harmonics and we can feel them, allegedly.

What's the truth ? Do they make sense or is that complete BS and we're good with high quality domes, ribbons, AMTs etc. going 'til 20k in average ?

:wave2:
 

Galu

Member
2018-04-17 6:50 pm
Vinyl can reproduce higher frequencies than CD.

Do we hear the difference tones?
 

Attachments

  • Difference Tones.png
    Difference Tones.png
    13.8 KB · Views: 869
This Tuesdays Tech Talk is about speakers with two tweeters

YouTube: The REASON why 2 tweeters wont work!


And yes, it is noticeable. Mine, aligned with rear bass-reflex, about 18 kHz if I am not wrong.
If I followed that video correctly, the ribbon supertweeter with a natural rolloff fullranger was on a puny first order single capacitor crossover. That is a recipe for considerable combing or cancellation problems due to the broad crossover region.

The more I look at Troels Gravesen's SP38/13, the more I like it! :D

It's in a famous tried and tested tradition of the 13kHz crossover:

Spendor BC1:

274995d1333360770-classic-monitor-designs-spendor_bc1_troels_gravesen-jpg


Spendor BC1

B&W DM2 v2:

274994d1333360770-classic-monitor-designs-w_dm2a_loudspeaker-jpg


333571d1362235376-schematics-speaker-crossovers-w_dm-2_ver-ii_crossover-jpg


Do you need ears like a bat to hear the improvement? Especially since CD only goes up to about 19kHz, with steep filtering thereafter? Amusingly, there is some evidence your hearing goes up to about 35kHz. But more the hairs on your cheeks and the hairs on the back of your neck that picks it up. :confused:

IMO, adding a 3/4" supertweeter just makes everything easier lower down. We can cross the woofer lower, avoiding cone-breakup. We can maintain good dispersion and low distortion above 10kHz where a 1" or 1.5" tweeter struggles.

It's not a bad idea. As ever, time will tell. All speakers are compromise.
 
I can't hear anything above 12k (it's an age thing) but I'm sure the average cat would love those frequencies ;)

I can not hear a 18 kHz tone and less but the sound is more airy and better. Why? I do not know. In principle that super tweeter is aligned with the bass-reflex output is for that.

Anyway, my modded KEF Q100 5.25" coaxial loudspeakers sound much better with music, with the high quality recordings I usually listen to. I LOVE them.

BTW: 3-ways with woofer of 27 cm aka 10.6". 91 dB, paper cones. With a sandwich of viscoelastic, acrylic+viscoelastic+acrylic+fiberglass.
 
Last edited:

Galu

Member
2018-04-17 6:50 pm
Super tweeters were introduced to UK speakers during the 1960s, not so much for fidelity reasons, but more to do with avoiding Purchase Tax. (VAT replaced purchase tax in 1973).

Professional products were not taxed and professional was defined as above 8 inches for a woofer or as a 3 way speaker. The addition of a super tweeter therefore allowed a speaker to be classed as a 3 way and hence avoid purchase tax.

Vinyl is quite capable of carrying ultrasonic frequencies. Just look back to the CD-4 quadraphonic system in which the carrier frequency was 28kHz and to the Shibita stylus developed to trace it.

Although some musical instruments can produce ultrasonic overtones, every item of equipment in the recording, mixing, and mastering stages would have to be able to preserve them.

So, it is unlikely that there are any ultrasonic frequencies present in music recordings for vinyl to preserve.
 
Super tweeters were introduced to UK speakers during the 1960s, not so much for fidelity reasons, but more to do with avoiding Purchase Tax. (VAT replaced purchase tax in 1973).

Professional products were not taxed and professional was defined as above 8 inches for a woofer or as a 3 way speaker. The addition of a super tweeter therefore allowed a speaker to be classed as a 3 way and hence avoid purchase tax.

...

274995d1333360770-classic-monitor-designs-spendor_bc1_troels_gravesen-jpg


The Spendor BC1 certainly benefitted from purchase tax exemption, but was also a good loudspeaker.

Here's what the designer, Spencer Hughes said:

Dear Sir,

The Spendor BC1 was not, as it has so many times been described, a development of the BBC loudspeaker type LS3/6. Perhaps a short history of the lead into, and the development, of the two systems may be of interest.

From the very early days, even before hi-fi, the BBC has designed its own monitor loudspeaker systems as commercial systems were not, and most are still not, accurate enough for broadcast work. These designs were based on available units matched by, what were in those days, very complex crossover networks and mounted in custom designed cabinets.

During the mid-1960s, the development work carried out by the BBC had advanced to a stage which was beyond the capabilities of the available paper pulp cone bass units. The decision was taking to investigate the possibilities of using some form of plastic as a cone and surround material. It was assumed that plastic would be a consistent material unlike paper pulp, which to some degree seemed to depend on the mood of pulp stirrer. Over the years it has been found that it was not quite that easy.

The section of the BBC Research Department involved in this operation was headed by Mr. Del Shorter, now retired, with Mr. H.D. Harwood now of Harbeth Acoustics, second in command and myself completing the investigating team.

Some two years were spent making 12in unit cones in a variety of shapes and from a range of plastics; this could be a story on its own. The first successful unit was made from the now well-known Bextrene and used in the development of the BBC studio monitor type LS5/5. his loudspeaker was described in an article written by Mr. H.D. Harwood in the March 1968 issue of Wireless World.

My part, as a laboratory technician, in the operation was to do most of the actual work both on the plastic investigation and the development of the LS5/5. With that experience I decided that it should be possible to make a loudspeaker from scratch in the home environment. With the aid of our electric fire, a compressor working in reverse and an iron bedstead the first vacuum former was built. Bins full of malformed cones were produced before any measure of success was achieved and the first 8in unit was produced. This unit turned out to be almost certainly the first commercial 8in Bextrene driver and still arguably the best.

The first pair of BC1s was constructed using these units and Celestion HF1300 units. The cabinets were smaller than the current model and initial listening tests indicted that the performance could be improved by an increase in size, hence the present design. At this point it was all being done for fun.

The second pair of BC1s was made for a friend who took them to Merrow Sound of Guildford. The third pair was sold to Merrow Sound and Spendor was on the way to a small niche in the audio world.

Now some difficulties were beginning to arise as under the terms of my contract with the BBC, the design had to be offered to them. Fortunately the 'Pop' era had just started and the main request was for more power, so the BC1 was turned down. Around about this time there was a special requirement within the BBC for one pair of speakers about the size of the BC1s. Being a kind soul, I suggested that my design could be used, so I was given the task of producing an official version of the BC1, later designated the LS3/6.

This design used an 8in unit made by Research Department, the Celestion HF1300 and a redesigned crossover. The main change in the crossover was the addition of a large multi-tap autotransformer to allow adjustment of levels between the two units, normal BBC practice at that time.

Some months later BC1s were fitted with an amplifier mounted in the back panel and the 4001G super tweeter added. This addition was for purchase tax reasons, but it did have two extra gains. Firstly, it improved the overall dispersion characteristics, secondly, from the broadcasting angle, it made any 625-line breakthrough to be more easily detected.

Now the LS3/6 was offered to a number of commercial companies and eventually taken by Rogers, then under the control of Jim Rogers. With approval, and a little assistance from the BBC, Rogers added the Celestion HF2000.

As Spendor was now a commercial company it was agreed that a royalty should be paid to the BBC for each BC1 produced. This was in recognition of the work I had done on the loudspeaker whilst still employed by the BBC.

To perhaps prove the order of development of the two systems, it is of note that out of over two thousand BC1s supplied to the professional market there are over six hundred in operation with the BBC and as far as I know very few, if any, LS3/6 speakers.

In addition to the above, the name Spendor is derived from the first names of myself and my wife Dorothy. Mrs. Hughes provided practical assistance in the early days with her coil winding expertise and now as Managing Director is responsible for all accounting, sales and general management. Derek Hughes, the son, another ex-BBC employee, deals with an amplifier design and assists me with research and development and general running of the factory.

Yours,

Spencer Hughes

Mark's Pages › Letter from Spencer Hughes

Here is the modern equivalent, Stirling Broadcast's current BBC LS3/6 homage, using SEAS drivers:

Stirling Broadcast BBC LS3/6 loudspeaker | Stereophile.com

Theory is all well and good, but really we need good ideas. And a supertweeter is not a bad idea at all. :cool:
 

Galu

Member
2018-04-17 6:50 pm
This addition (of a 4001G super tweeter) was for purchase tax reasons, but it did have two extra gains. Firstly, it improved the overall dispersion characteristics, secondly, from the broadcasting angle, it made any 625-line breakthrough to be more easily detected.
I remember reading this Steve. However, I can't seem to find any information on the actual audio frequencies produced by '625-line breakthrough'.

The Coles 4001 unit is available in both 16 ohm (G) and 8 ohm (K) versions from Willys Hifi. Coles 4001G 16 Ohm Super Tweeter - Willys-Hifi Ltd

Correction, 16 ohm version no longer available.
 
Last edited:
I am probably rambling at this deep in the game. 625 line breakthrough probably refers to the PAL TV standard of the late 1970's. You had 625 lines (interlaced) by 30 frames per second of screen refresh on a colour television.

This either comes out to 9kHz or 18kHz of magnetic interference from the flyback inductor in a standard Colour TV set.

It was an unfortunate effect that nearby speakers, unless magnetically shielded, tended to pick up this irritating HF whine. :D

I think this is what Spencer Hughes is referring to.

TBH, I don't lose too much sleep over ancient drivers like the Celestion HF1300, derived from a compression driver. Or the mylar Coles 4001G, derived from an ITT microphone. Here put together in a B&W DM4.

533372d1456309262-b-w-dm4-poor-high-frequencies-b-w_dm4_loudspeaker.jpg


We must move with the times. This, IMO, is a flippin' good derivative of the ancient Spendor BC1:

SP38/13.
 

Galu

Member
2018-04-17 6:50 pm
This either comes out to 9kHz or 18kHz of magnetic interference from the flyback inductor in a standard Colour TV set.
Thanks for pointing me in the right direction Steve.

A tone corresponding to the horizontal line frequency of 15,625Hz (15,750Hz in the USA) caused by interference from the flyback transformer in cathode ray tube (CRT) televisions appears to have been the culprit.

This tone has even been found to be present on recordings made during the era when CRT monitors were used in recording studios. The tone could be picked up by the microphones or be added during the mixing process.