Fault finding an issues with a tweeter array... Is there a right way to check?

[rwillett]

I was kindly given a bass cab, which appears to be an Omni 10.5. This looks a well made cabinet with four piezo electric tweeters and a decent speaker. 

 

There is a toggle switch on the back which looks like it switches the four tweeters in and out. 

 

Playing through the cabinet with a Warwick Gnome V2 works well and there are no issues with the main speaker. However toggling the switch appears to make no impact on the sound. I do not hear any higher notes or any change in sound quality. I've tested the toggle switch and that works fine.

 

Opening the speaker up, and looking at the toggle switch, I can see a simple 'crossover' resistor which according to my multimeter measures the right value. I also note that when I got the cabinet a tweeter cable was disconnected and I *think* I put it back in the right place.

 

 

 

 

I'm trying to work out if there is a wiring mistake somewhere OR one or more tweeters isn't working. The tweeters are buried in the cabinet amongst all the foam but it appears to me before I trace the wiring that they are in series and parallel, I'm guessing that this is to present either 8 Ohms or 4 ohms to the cabinet. The tweeters have no information on them apart from a sticker saying 0807. Goolge doesn't help here.

 

I'm aware that piezo electric speakers cannot be easily measured by the ohm rating but should be measured by their capacitance OR by putting a small battery across the tweeter terminals and listening for a click OR by connecting them to a low powered amplifier and seeing if they work.

 

I happen to have a dedicated capacitance meter but no matter which tweeter I measure I get a reading of 0.641 when set to the 2uF range on the meter. 

 

I'm way out of my depth here and and contemplating just junking the four tweeters and trying to get four other tweeters that might work. However I have no idea what the current speakers are and so I may be making things worse. I have no issues soldering any new tweeters, but I can easily see myself being back where I started from and absolutely no further forward and £30-£40 down and a lot more frustrated. I don't know if the tweeters are 4 ohm or 8 ohm or could be something else and I certainly don't want to blow up up Gnome. 

 

One thing that occurs to me is to simply find the two wires that feed the tweeter array and put a small (and cheap) amp onto them to see if it makes a sound. However not sure if a small little amp is the right approach. 

 

Any advice on what the next steps should be is greatly welcomed.

 

Thanks

Rob

 

 

Edited 9 hours ago by rwillett

[Hellzero]

Eminence speakers have a sticker on the side of the magnet.

 

Furthermore, there should be a filtering capacitor somewhere before the piezos, if not, the first low frequency note will have destroyed them...

[Hellzero]

Here you can calculate a simple RC filter for your cabinet, if you can't find any information about the Eminence "woofer", you can protect your piezo tweeters by using 4000 Hz as the pivot frequency.

 

https://www.digikey.co.uk/en/resources/conversion-calculators/conversion-calculator-low-pass-and-high-pass-filter

 

[bertbass]

Ask Bill  fitzmaurice.  The cab is his design.  All the information you need can be found here, https://billfitzmaurice.info/  and you can buy the plans for your cab on the site as well then you'll have all the info you need.

 

I can tell you that there is no crossover in the cab and that the resistor is there to prevent ultrasonic oscillations.  The piezos have to be the right ones and that the cab is designed to use only those tweeters anything else won't sound right or have the right dispersion.

[Hellzero]

Here's a thread about a BFM Omni 10.5, looks like there were as many options you wanted for the line array of tweeters.

 

 

 

And another one here: https://billfitzmaurice.info/forum/viewtopic.php?t=11085

[Hellzero]

Now I understand why there's no filter in this @Bill Fitzmaurice design...

 

Here are the specs of this Goldwood GT-1016 tweeter:

 

Power handling: 50 watts RMS/75 watts max * Frequency response: 3,500-27,000 Hz * SPL: 94 dB * Manufacturer model number: GT-1016 * Dimensions: A: 5-3/4", B: 2-3/4", C: 2".

[rwillett]

4 hours ago, Hellzero said:

Eminence speakers have a sticker on the side of the magnet.

 

Furthermore, there should be a filtering capacitor somewhere before the piezos, if not, the first low frequency note will have destroyed them...

@Hellzero

 

The thread about the crossover, oddly enough from @neepheid, is here https://www.billfitzmaurice.info/forum/viewtopic.php?t=26505 

 

I believe that the view from Bill was that nothing else is needed for his design apart from the resistor. I'm no expert here, hence this thread

 

Certainly the box as it came to me had nothing more complicated than a square resistor as shown in the picture. It may well be that it should have had something more complicated in place and has never worked, but given the (high) quality of the build. I suspect it has worked properly in the past. I have nothing to back this up, but would love to get this small cab working to its full potential. 

 

@bertbass

 

Thanks for this. That phrase "the resistor is there to prevent ultrasonic oscillations" rings a bell as I have read that in Bills forum as I've been investigating this further. 

 

I appreciate all the help, I'll try and work out what to do next.

 

Thanks

Rob

[rwillett]

16 minutes ago, Hellzero said:

Now I understand why there's no filter in this @Bill Fitzmaurice design...

 

Here are the specs of this Goldwood GT-1016 tweeter:

 

Power handling: 50 watts RMS/75 watts max * Frequency response: 3,500-27,000 Hz * SPL: 94 dB * Manufacturer model number: GT-1016 * Dimensions: A: 5-3/4", B: 2-3/4", 😄 2".

 

Those tweeter specs are helpful, thank you. My problem is that nobody in Europe appears to stock the Goldwood. GT-1016. 

 

There is this thread from 2007 (!) on alternatives

 

https://billfitzmaurice.info/forum/viewtopic.php?t=11162

 

The following are supposed to be alternatives, but I can't find anyone who can confirm they are good alternatives and work.

1.  Pulse PLS00306 <-- Can't find anywhere near to me
2. Monacor MPT-016 <-- Available at Thomann (https://www.thomann.co.uk/monacor_mpt_016.htm) Quite expensive each.
3. GRS PZ1016 NPeople have claimed that these are a replacement and the model number indicates at least a relationship to the Goldwood but are 4Ohm as opposed to 8Ohm, noit sure if this is an issue TBH. Available at https://www.soundimports.eu/en/grs-pz1016.html

I have been offered something from a kind basschatter so will enquire there first.

 

Also it may well be that the issue with all of this is a simple wiring issue and a fault finding check may find the issue. My issue is still that I'm unclear on how to fault find a piezo speakers.

 

Thanks

Rob

[Hellzero]

@Bill Fitzmaurice will be here soon to help you, don't worry.