New Tweeters for my Mets

[Cressy Snr]

Now I'm afraid it's time to start looking for new tweeters for my Metronomes.

The horn resonance from the FT17H, somewhere right smack in the middle of the "ee" area of most female vocalists is something up with which I am no longer prepared to put.

My budget is strictly limited so none of the more expensive Fostexes, or fancy ribbons can be considered.

I am eyeing up the Eminence APT80 compression driver with horn as a possible answer, and from what I have read on the 'web, folks seem to like it.
words like "smooth" keep coming up regularly. Smooth is my bag as I have very low tolerance for treble issues.

http://www.bluearan.co.uk/index.php?id= ... tAodmVgAfA

It is being heavily discounted by a few pro sound shops.

What does the panel think?

[Toppsy]

Steve,
I can understand your desire to change the FT17H tweeter. It is not one of the smoothest Horn Supertweeters out there but value for money.
Have you seen the FR plot for the Eminence driver?
If not you can download it here: http://www.eminence.com/pdf/apt80.pdf

You will likely have to do some filtering as well as a fixed L-Pad. There is a near 4dB drop in FR plot from 7kH to 10kH before it picks up again quite sharply around 18kH. You'll have to carefully choose the XO point to your Fostex's but as you say from user feedback seems a worthwhile try.

You could consider a Monacor RBT-95SQ / SR for similar monies if you fancy a ribbon in lieu to a horn tweeter. I have several both in stock if you're interested?

[Cressy Snr]

You could consider a Monacor RBT-95SQ / SR for similar monies if you fancy a ribbon in lieu to a horn tweeter. I have several both in stock if you're interested?

That sounds like a good offer Colin.
The thing I like especially about your Edingdales is the treble quality. As we found at your place a couple of years ago, the Edingdales sound very like my Mets, so I have a good frame of reference to be able to reasonably predict what said Mets will sound like with the Monacor treble units.

[chris661]

Hi Steve,

I'd happily lend out the tweeters from my Behringers. They're Seas 1" Ally domes, and are basically flat from ~1kHz to 15kHz, and roll off a couple of dB to 20kHz. Then there's the 26kHz breakup, which doesn't pose much of a problem for us humans.

Something like this:
http://www.seas.no/index.php?option=com ... Itemid=115

I can see the sensitivity might be marginal, but if you'd like to give them a try, let me know.

IIRC they sounded rather good on your valve amps at Owston.


Chris

[Cressy Snr]

Thanks Chris,
I've now bought a couple of Monacor ribbons off Colin, but thanks all the same.

As a stopgap, I have used my JRiver Media Center's extensive DSP to put a mild notch filter in at 3KHz. Looking at the frequency response of the FT17H and the FF225WK and taking them together, both have +3dB peaks at 3KHz which coincide with each other. I could reverse the phase on one or the other of the drivers, to flatten it, but then looking at the graphs, other HF problems then crop up. Truth to tell, my simple 6dB/octave, first order crossover is not steep enough to give sufficient attenuation of the 3KHz peak.

However putting a -4dB trough in, with the JRMC equaliser, has given blessed relief, so until I can install the ribbon driver, I am happy as the proverbial pig in s@*t

I have always been a bit loath to use additional processing, but sod purism, my ears are not ringing.

[IslandPink]

Good !
If you want a passive solution , then have a look at this site, Steve. :
I used it to calc a notch filter for -6db around 3.5kHz for the guitar speaker I'm using on OB at the moment - worked a treat .

http://www.mh-audio.nl/parallelnotchfilter.asp

[Cressy Snr]

Thanks Mark,
I've bookmarked that link for future reference.
It will come in handy, when I get the ribbons.

I think you certainly do need a passive solution for this sort of thing.
After all, if I was making speakers I wouldn't be able to sell them with that peak.

[Cressy Snr]

Well, the ribbons have arrived courtesy of our Colin, so I can start developing the 12dB crossovers.

[Cressy Snr]

OK.
The ribbons are under evaluation on various pieces of music.



I've established the correct phase relationship with the FW225WK widebander.
The right way round as opposed to the wrong way is very obvious.

I'm going to get them fitted properly into the cabs later this afternoon as even after a short time with them playing,
all remaining traces of grit and grain have vanished from the sound.

These are good value tweeters considering the lovely treble quality you get out of them.

I'll post some pics and impressions when I have had some time to audition some more tracks.

At the moment they cross over at 9KHz with a first order alignment so they are 6dB down at 4.5K, which is not steep enough.
OTOH I am not hearing any distortion, but nevertheless I don't want them playing anything below 5KHz as ribbons
are a lot more delicate than hairy- arsed horn tweeters like the FT17H; so there are a couple more jobs to do:

1 - get a 12dB/octave crossover going to protect the ribbon from over excusion
2 - get the 3KHz passive notch filter built into the speaker itself, rather than it being done in software.
I will construct the whole thing so it will sit unseen in the corner, underneath the base arches.

[IslandPink]

Nice work .
If you get the steeper crossover on there you might only need to apply the notch filter to the Fostex.
If so, I can help you work out the best values. The link I provided gives a good starting point, based just on an 8R load, but once you put the real Re and Le for the driver, and simulate it on Spice, it changes a bit , and I reckon you need to adjust the values a bit .
What's the name (model) of this Monacor ribbon ?

[ed]

watching with interest Steve...

I've found them very easy to integrate...with 206s, betsys and seas fa22s

I'm currently working on a sealed box fa22 with them, trying to minimise room interaction.

rbt95 is the model I'm talking about, I think it's the same one Steve is looking at.....there are three models, round, square and up-market

[Cressy Snr]

Yes Mark
As Ed says the tweeter model I have is the Monacor RBT-95.

The Mets are now sans drivers, awaiting the keyhole saw
With the close proximity of the fixing holes to the corners of the rectangular backplate, there is NO margin for error when reshaping the tweeter opening.

Measure twenty times, cut too small, and file until it fits is the philosophy.
Also because of the narrow rectangular aspect of the front opening of the tweeter plate itself, any errors in vertical alignment will stick out like
a sore thumb, and the front baffle slopes front-to-back and side-to-side, making the alignment of the fixing slot highly critical . Oh Gawd

[Scottmoose]

It's not a ribbon Steve, so it's not all that delicate (planar magnetic: a ribbon is a folded ribbon of foil held in a magnetic gap; the Monacor, like, say, a Magnepan, is a flat diaphragm onto which a VC is either attached or printed. They're somewhat more robust). However, you'll get crippling HD if you push too hard, too low. Like most planars, impedance is more or less flat; there's no peak at Fs, so from that perspective, no notches are required.

What will work best depends on whether you do low pass the 225 as well, or just high pass the tweeter & run the widebander wide open. I would also be very careful of taking Spice sims or on-line value calculators too literally, unless you are able to import the actual acoustic responses & phase behaviours into them (since these are almost invariably significantly different from their purely electrical behaviour), especially when diffraction etc. is also factored in. FWIW though, I'd probably be looking at a lowish Q 2nd order electrical high pass at 6KHz as a starting point & adapt from there.

[Cressy Snr]

Hi Scott, I have not decided yet, what to do with crossovers for these tweeters. But.....I now have them mounted on the Mets and working.



The speakers have not been transformed because the widebander is doing most of the work but the improvement in the quality of the treble is striking.

I'll post some more impressions later this evening.

[Andrew]

Nice job Steve, must have been a bit nerve wracking..