Changing a Piezo tweeter to a compression driver

[Wolverinebass]

Not sure if this should go in here or Repairs and Technical issues. Mods to move if you want. However, let's just explain. Both the cabs I use have piezo tweeters. Whilst it was okay when I was just using 4 string basses, the use of 8 and 12 string basses have now shown the piezo tweeters true colours. "Harsh" is not a word that even remotely describes how in your face it is. I can only imagine a pack of dogs howling in front of my front door every time I play the 12 string through it as the amount of 4.5kHz (and above) that I have to cut/shelve to get the sound even remotely passable at the mid point of the tweeter is just frankly stupid. In case some wonder what the settings are like, it's reasonably flat with a boost in the 180Hz region. Listening to the DI out like this it's brilliant. Listening to it after the cabs are taken into account and it sounds as dull as a rusty spoon.

I have no interest in multiple guitar/bass cab setups to get what I want and whilst I don't really want to sell the cabs, I would if I thought I could find something that'd work better for me.

However, one of my mates suggested tearing out the tweeter and replacing it with a compression driver. Now, I've never done this, so firstly, is this possible and secondly is it worth it? Will chucking in something else make the problem ease? Or is it going to be a mess of matching components and all that nonsense?

If anyone's done this, I'd appreciate views.

[Dad3353]

Good evening, Wolverine...

More qualified replies will surely come; meanwhile...
[quote name='Wolverinebass' timestamp='1322434608' post='1450927']...firstly, is this possible...[/quote]
It's certainly possible, although there are a fair number of factors involved. Depending on the cab maker, it is not unusual to have piezos without filtering (they are pretty much insensible to bass frequencies, so don't really need one...). Traditionnal tweeter motors, on the other hand, are extremely sensitive, and take very unkindly to bass or mid frequencies, which 'pop' them almost immediately. Filters are used to prevent these frequecies getting to the tweeter. Good filters are expensive, and need some technical expertise to match correctly to the drivers being filtered.


[quote name='Wolverinebass' timestamp='1322434608' post='1450927']...secondly is it worth it?...[/quote]
Unless you have cab design and experimenting as a hobby (with it's associated expense account...), I would suggest that you may be better served by finding a cab which already has the sound you're looking for. I have no particular recommendations, but doing it yourself could well (unless you're luckier than most...) be disappointing.
Just my tuppence worth; hope this helps...

Edited November 27, 2011 by Dad3353

[LawrenceH]

If the cabs don't have a crossover it might be worth trying one, or even just disconnecting the piezo altogether. Because I could fairly easily, I'd try an active crossover/bi-amp set up just to see what effect that had - would that be an option? If the piezos are operating too close to their resonance apparently this can make them sound pretty nasty, having said that I've never heard one I actually liked...

[Bill Fitzmaurice]

The problem isn't the piezos, its the implementation. But as noted already switching to a compression driver probably won't help. If you find a tweeter harsh you should consider switching to a cab that uses a midrange driver rather than a tweeter. IMO going directly from a woofer to a tweeter with a 4 to 5kHz crossover is a silly idea on the face of it, and is only done because it costs the manufacturer less than half what it does to cross to a midrange driver an octave or more lower.

[Phil Starr]

This depends upon how much twiddling you want to do and which drivers you have. As Bill has pointed out it is probably more to do with implementation than any inherent problem with the piezos.

Most piezos act like a leaky capacitor in terms of load so you can trim down the volume by putting a capacitor in series with them. Try a 2uF polyester and see what it does to the sound. Bigger if you want even more cut and smaller if it is too much..

the other problem I have had with Piezos is that they don't have a very flat response and some are better than others although they all look similar. A lot of the cheap ones only have much output above 4kHz which leaves an empty gap between them and the bass driver. As Bill has said you'd be better with something crossing over at 2kHz or even lower for bass.

My experience is that even fairly cheap coil based tweeters sound better than nearly all piezos though the absolute need to have a crossover makes them much more expensive

[Wolverinebass]

Thanks for the replies chaps. It sounds like the direction you all suggest is the Barefaced Big Twin, Extended Audio Design or an Acme of some description. Not that I'd object to owning any of them!!

However, the problem I have is basically that the treble content of the signal is totally uncontrollable thanks to the tweeters which kind of defeats the purpose of having them in the first place. Using just a DI signal I can easily get what I would consider "normal" settings and things are great. Use a cab and then cut everything above 4.5kHz down to nothing to get the same sound and the DI sounds truly awful.Turning the tweeter down to slightly below half reduces the cut available to zero especially when I'm using a 4 string. According to Markbass, the crossover is set at 3.5kHz. In truth, I probably missed a trick with these as I've only gigged them twice and used them at rehearsals twice. Other than that I've only used the 15 at very, very low practice volumes. More research should have been done methinks....

The other problem is that I don't want to re-set the tweeter when I change basses.

I'm not the most technically minded and to be fair, I'd have to get someone to do any repairs/alterations for me. Whether it's worth it I wonder.

[StraightSix]

AFAIK and I think it has already been suggested, it shouldn't cause any problem to disconnect the Piezo and try the cab like that - if it works how you like, this is undoubtedly your cheapest option

There is talk of a similar problem here: [url="http://basschat.co.uk/topic/68970-markbass-mini-cmd-121p-simplest-of-upgrades/"]http://basschat.co.uk/topic/68970-markbass-mini-cmd-121p-simplest-of-upgrades/[/url]