Another PAP inspired OB job

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iansr
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#1 Another PAP inspired OB job

Post by iansr »

So, as alluded to in Colin’s OB thread, I’m in the early stages of making some 3 way speakers that will feature dual 15” woofers on OB per speaker, horn loaded comp driver and a super tweeter. I want to bi amp them so will be using a hybrid crossover; the horn to super tweeter will be passive whilst the woofer to horn will be an analogue active crossover. My aim is to make something really great sounding and I’m prepared to spend a bit on the drivers to that end. More in the next post when I have more time.
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Ali Tait
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#2 Re: Another PAP inspired OB job

Post by Ali Tait »

Have you particular woofers in mind Ian?
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#3 Re: Another PAP inspired OB job

Post by iansr »

Drivers: top of my list for woofers is the AE 15” dipole or LO woofer. I’ve never seen anything but the highest praise for these.
For the CD I’m buying a pair of JBL 2450SL and having Truextent Be diaphragms fitted. Super tweeter, the Fostex 925A.

As a result of researching this approach I’ve fallen in with 2 very helpful horn enthusiasts who, for GDPR compliance reasons :wink: I will refer to as R and M. R is a cabinet maker who has made, amongst other things, some TAD 2404 clones using original TAD drivers. He also makes wooden horns. M is, apparently, a research physicist who has decided to devote a significant proportion of his extensive grey matter to understanding the science of loudspeakers in general and horns in particular. M has designed a horn specifically with the 2450SL in mind, which is a modified version of the Yuichi horn. I’m going to have a listen to the one R has made out of plywood and if I like it then R is going to make me one.
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#4 Re: Another PAP inspired OB job

Post by Ali Tait »

Some nice drivers there, look forward to your progress.
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#5 Re: Another PAP inspired OB job

Post by Dave the bass »

A question from the back of the classroom...

What does PAP stand for?
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#6 Re: Another PAP inspired OB job

Post by IslandPink »

iansr wrote: Sun Nov 18, 2018 8:48 pm Drivers: top of my list for woofers is the AE 15” dipole or LO woofer. I’ve never seen anything but the highest praise for these.
Umm.. I will say that Lynn Olson and Gary Dahl did not like the AE 15" woofer in the 'Beyond the Ariel' project, they both came down heavily in favour of the Altec 416B remakes by GPA. This was more for sealed box low-mid use though. What sort of dB volume level do you play for normal listening ?
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#7 Re: Another PAP inspired OB job

Post by iansr »

The 2 AE drivers I’m considering are specifically designed for OB use so are almost certainly not the ones you are referring to. However I’m not familiar with the GPA ones so I’ll have a look.
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#8 Re: Another PAP inspired OB job

Post by iansr »

That GPA driver has a Qts of <3 and most people seem to recommend a Qts of >8 for OB. The only wisdom I have on this subject is received, so that’s all I have to go on :| ( I have no idea what that emoticon is meant to convey but it seemed appropriate!)
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#9 Re: Another PAP inspired OB job

Post by iansr »

PAP is a reference to the Pureaudioproject Trio 15 speakers which seem to have garnered a lot of love from reviewers and owners alike.
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#10 Re: Another PAP inspired OB job

Post by IslandPink »

iansr wrote: Sun Nov 18, 2018 9:52 pm The 2 AE drivers I’m considering are specifically designed for OB use so are almost certainly not the ones you are referring to. However I’m not familiar with the GPA ones so I’ll have a look.
It was something to do with the joining of the voice coil to the cone, that they said was detrimental to tone. This may apply to some or all of the range, irrespective of magnet strength. Have you got the drivers already ?
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#11 Re: Another PAP inspired OB job

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iansr wrote: Sun Nov 18, 2018 10:09 pm That GPA driver has a Qts of <3 and most people seem to recommend a Qts of >8 for OB. The only wisdom I have on this subject is received, so that’s all I have to go on :| ( I have no idea what that emoticon is meant to convey but it seemed appropriate!)
I think you need to check the numbers again, those don't sound like Qts values. Something like 0.45 to 0.5 is nice for passive use on OB, though many ( not convinced, having been down this road myself ) use 0.4 or 0.3 with EQ.
What I was aiming at above by asking what loudness you were using, was related to power rating and Qms - high Qms ( low Rms ) seems to work better at normal HiFi (room ) levels that PA-style drivers with Rms at 2.5 to 4.0.
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#12 Re: Another PAP inspired OB job

Post by iansr »

Sorry I was being a bit slap dash there and missed out the decimal point; I meant 0.3 and 0.8 respectively. I’ve never measured my typical listening levels so all I can say is that I would class them as being within the normal range for a domestic hi fi set up. I had Quad 989s for a number of years and they don’t go particularly loud. Only rarely did I feel that I would have liked a bit more volume.
BTW have you seen the price of those GPA woofers! And that’s without shipping and import taxes. I know I said I was prepared to throw some money at this but they would have to be extraordinary for me consider spending that sort of money.
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#13 Re: Another PAP inspired OB job

Post by iansr »

PS i haven’t bought the AE woofers yet, but I’m negotiating for some . . .
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#14 Re: Another PAP inspired OB job

Post by chris661 »

Have you bought the JBL compression drivers yet?
I can't find much data online, but it doesn't look like they go particularly low. I'd be looking at EV DH1a drivers for 400Hz-10kHz use (although you haven't specified your intended crossover frequencies yet). A large horn would be needed to provide a decent amount of gain down there. Those EV drivers came out on top compared to some good drivers according to some very thorough testing by Art Welter.
Another option would be the BMS coaxial drivers, which run 300Hz-22kHz from a time-aligned point source.

Will you have any EQ in the chain?
FWIW, I tried OBs for a short while, just as an experiment, and found a low-Q driver (Beyma 15P1200Nd) gave some of the best bass I've ever heard. It needed 27dB of boost to get down to 25Hz, with the associated increases in power levels, but it was amazing to hear.

Chris
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#15 Re: Another PAP inspired OB job

Post by iansr »

Chris
I haven’t paid for them yet but I have found a nice pair of the JBL drivers. The intended crossover point is c.600hz. I’m anticipating some bass boost will be needed for the woofers and that some EQ will be required at various points. Interesting that you got such good bass from a low Q woofer on OB. There does seem to be a minority school of thought that a high Qts is not essential.
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