GPA 15" can also be 8 or 16 Ohm, worth pulling one out to check unless you can get hold of US builder man
1 Like
I like those. Just enough to tell everyone you’re on the hifi spectrum.
They are SE 6B4G mono blocks, so good for about 3.5W per channel, to go with some v v large and v efficient Cessaro horns
Something like that would probably be enough for the Goto mids and tops, whilst the bass apparently needs quite a bit more.
Ideally @Jim can get some input from the designer on what he thinks works, but it would also be useful to know the sensitivity and impedance plot to understand the challenge.
Know what the crossovers are doing would also be useful 
1 Like
This is always going to be the challenge on a multiway horn system with high efficiency compression drivers, and bigger (different requirement) bass drivers.
Splitting them into two (more easily solved) issues makes sense but will need a suitable crossover.
I guess Jim would be able to get away with something more simple (cheaper) on the top end, as it won’t need to be full range, and then needs to find something to match (the character) for the bottom end…
Doing a few searches it looks like John Sheerin did the prototypes for Ming Su, he has an email address on his website
The Goto project is down near the bottom of the page
1 Like
Yes, the bass units John Sheerin used were Goto then, I think Ming Su changed them as Jim has GPA’s. Finding out what the bass units are will be instructive. Perhaps then using an active / digi xover would allow a crossover point to be identified and the the passive xover adapted accordingly? (As well as trialing LF amp and HF amps)
I’m honestly really baffled by these speakers. For example, my room is at most 10% smaller than Jim’s, volumetrically, yet 25WPC can drive just two 15" drivers to create tight, foundations-damaging bass with suitable material.
Why then would someone design a no-expenses-spared set of speakers, using four 15" drivers that apparently can’t do the same thing? Why would they make them a single crossover design, if the power needs of the drivers they used are so very different? LF drivers should be hilariously easy to drive - as a general principle, the notion that the drivers have to make massive excursions only applies if you’re using tiny, weedy little diaphragms to do something they’re not really suited to because you’re designing for domestic acceptability: for that you need lots of wattage and lots of current. These shouldn’t need it.
Is this perhaps the root of the issue?
2 Likes
Could he stick a meter across the bass bin terminals and measure the DC resistance?
2x 8ohm parallel = 3-4ohms
2x 16ohm parallel = 6-8ohms
2x 8ohm series = 12-16ohms
2x 16ohm series = 24-32ohms
1 Like
He may have designed them for a specific amp the customer had, guess something like a Kondo 211 amp would drive everything ok?
1 Like
GPA took on much of the Altec machinery etc, they ‘re make’ Altec drivers’ Most vintage 15" Altecs I know like 30W+ depending on vintage (More modern ones a lot more)
1 Like
Jim needs to buy an Ongaku 
1 Like
25WPC Push pull?
fixt 
1 Like
I’ve not had the pleasure yet of hearing one quiet enough to use with horns.
1 Like
Not one that has been fettled by @sjs though
That M7 went from hummy and crackly to absolute dead silent on 105dB horns
I have heard one with Vox Paladiums which was just about quiet enough
1 Like
And that’s what would make me look elsewhere.
Could be worth checking to see if all the bass speakers are correctly wired in phase.
4 Likes