technical question on tweeters

Im thinking of adding some supertweeters to my horns.

According to the catalogue the horns cut off at 18khz. Im sure that this is the case, but I'd equally bet they begin to roll off from about 13khz or so.

A pair of supertweeters set to kick in about 13khz doesnt seem like a bad idea if I can get high quality for a reasonable price.

Audiophile supertweeters have audiophile price tags, so I've had a little look at a few studio manufacturers, and come up with these:

http://www.fostexinternational.com/docs/speaker_comp/pdf/t900a.pdf

They have an 8ohm impedance (like my speakers)

They can be crossed over at anything above 7khz

With an SPL of 106db/w Im guessing their sensitivity will be fine (the speakers are either 99db or 97db efficient from memory..cant remember exactly)

they are top-mounted so dont need to have a box built around them


So!

Can anyone with a bit of technical knowledge tell me if theres something I may have missed?

To get them to work, I'd need a crossover. I was thinking of running a seperate cable from the amp to the supertweeters, and setting the crossover point from that. What would I need to set the level and and the crossover frequency?

From the back panel of the supertweeter Im guessing these tasks need to be done off-board.

 

The cross over point is set according to the component values you use in the circuit, its very easy to work out. Have a look on google etc. for cross over design or something along those lines.
At a guess I'd say to set the level you'd need to put a resistor in line with the input to bring the level down. But thats just a guess.

How much are they btw? They look good.

 

Chris,

I'm shocked on 2 counts, I mean voodoo that doesn't work anmd spending money, careful sir, you'll get a REPUTATION

 

Anex, pardon me for correcting some ignorance but xovers are far from easy to design

Like all audio electronics, its not just a matter of a textbook formula for frequency based on capacitance and inductance, but you have to take into account the specific drive units involved.
These have an acoustical roll off of there own, and added to the electrical rolloff of your xover itself, produce a 'composite' filter charactericstic that will totally skewith any textbook based xover.
Just putting in a 2nd order electrical butterworth or linkwitz riley filter will not give a perfectly integrated loudspeaker system, despite the seemingly perfect electrical one.

Its a combination, not many are aware of this. It requires considerable expertise, experience, equipment and some magic to get right

The ideal is to get a flatish frequency response, which apparently is quite simple, but add this to phase and a nice impedance, becomes tough.

What is interesting is it may sound ok, but designers aim first for measured acceptibility, and there are innumerable combinations of values and configerations that will give this, all different, so you can have measured frequency perfection, all sounding different. Which do you choose? Do you try them all?

the more I read, the less I know.

you should see the maths involved with transformers

kind regards

 

I've been thinking of giving super-tweeters a go – notwithstanding the facts that (a) human hearing (for those of us the wrong side of thirty) doesn't extend much above 15kHz and (b) the frequency response of most CD players is brickwall filtered at 22.5kHz.

Tannoy white paper on super-tweeters that addresses these two points
http://audioloft.com/WPSuperTweeter.pdf

Fostex horn tweeters
http://www.fostexinternational.com/docs/speaker_comp/Horn-Tweeters.shtml


bottleneck

Try crossing the super-tweeter at around 15kHz to 18kHz. A 1uf polypropylene capacitor as a simple first order crossover should suffice. Match driver sensitivities with a series resistor.

This link may be useful.
http://www.mhsoft.nl/spk_calc.asp

 

Yes, I know that. If you are designing a multi-way cross over then it gets complicated, if you are building a single driver x-over at a set cross-over frequency its quite easy to build a working circuit. Changing component values as you go along is simple in this case as there will be very little involved in the circuit.

 

Richard, how come you want to give them a try? after all scientifically its not possible to hear that far up! therefore, its just voodoo and will do nothing?
White papers? no way, give me cold hard facts listenable evidence NOW

 

Believe everything that sounds plausible, dismiss everything that sounds like hi-fi guff or choose the third way. Tis' the path I follow Tony.

 

I haven't bought them yet!

Well, I think if I had tweeters that went up to 25khz I don't think I'd bother, but horns are known for their high frequency roll off, so I don't have to rely on the 'bat frequencies' to gain effect... thats my theory anyway.


someone asked about price.

A very reasonable $328, which including shipping and customs should work out about £250.

They look fantastic for that sort of money don't they?

(I'll probably find out that's ''each'' or something )

 

hey tone...

did you know I 'black pen and swab' my cd's??

am I a voodoo practitioner now?

 

It quite possibly is for one actually, if they're lab series. Definately worth checking!

 

Its a long slippery road, before you hit merlin territory though !!!!
Strange how all the sceptics now have a more open mind, most facinating Captain?

 

yes, typically, sigh, it is for just one.

450 for the pair then.

still, they do do cheaper ones.

here's a link to US $ prices.

http://www.madisound.com/cgi-bin/index.cgi?keywords=fostex

 

I was looking at either the Fostex FT17H horn tweeter (response to 50kHz) or Fostex FT7RP ribbon tweeter (response to 35kHz) at about £30 and £70 each respectively.

Both available from Wilmslow Audio.

Just need suitable 'cans' to house them in.

 

didnt realize wilmslow did fostex.

maybe if I paid them a visit I could earwig a few pairs.

dont know if they provide that kind of service? anyone know them?

 

I was going to suggest you should get some drivers and build your own cabs. I've been yaking on about doing that for ages but people seem to object to me using power tools in my flat. For some reason.
Wilmslow have a good rep from what I've heard but no idea about listening, I wouldn't think so if they are just selling drivers. At that price though does it really matter? Go for the £30 ones to start, it they're a total failure you haven't lost too much, if they're a success you can move up to the more expensive ones.

 

thanks, but I believe in buying the best that I can possibly get when hi-fi is involved.

£30 drive units wouldnt be up to the standard of the rest of my speakers.

If I go for it I'll get the best speakers for the job, even if it means saving up.

 

Obviously its up to you but isn't it better to get stuck with a cheap mistake rather than an expensive one?

 

dont use resistors to compensate for the diffrent driver sensitivety or youll screw up all your xover calculations when you adjust there level,what you want is an L-pad,its a pair of pots wired to adujst the level whilst still keeping impedance (fairly) constant

 

The crossover is the (relatively) easy bit. I'm stuck for a suitable off-the-shelf enclosure. Something cylindrical and made of wood would be good. Bound to be an Ikea gem but I can't find one?