[Viridian]

Hey All,

I've been enjoying listening to my Pioneer 12" Coaxes in OB for a while now and have really been enjoying them. However, I want to try something new that will also be tube SET friendly.

The two OB options that I am considering are along the lines of:
1. using a HempConed JBL D130 widerange with a phenolic diaphragm horn tweeter passively brought in at the D130 rolloff. The D130 is very well regarded as a midrange and the hemp version from aBrounSound is supposed to be super yummy.
2. using a 6" FR driver, like the Pioneer PE-16M, widerange, with some sort of bass support underneath. Along the lines of Lowther America's Tiny Baffle http://www.lowther-america.com/page2/page12/page20/page20.html

What would be the advantages/disadvantages to each configuration that I should consider? I'm sure that directivity will be an issue with the first option, right? Also, Option1 will be WAY more efficient.

Thanks for the help,
Erik

[Viridian]

I would delete this topic if I could.

Mark?

[JohnR]

Oh. Why delete it?

I'd probably go with option 2, if you like the sound of the widerange driver. Assuming an active crossover?

[Viridian]

Thanks John for your reply. I guess I was feeling that the project wasn't esoteric enough to garner much attention.

I'm thinking along the lines that you expressed, wide-band up top with some bass reinforcement. AS much as I like the idea of the D130, and it's potential dynamics and hemp musicality, it seems to be the more difficult implementation for a simple guy like myself and would not end up in the "simple" category.

[Viridian]

Oh, and most likely passive XO on the first try at least. MiniDSP is surely attractive but I like my DAC and wonder if guys have modded the MiniDSP at all. Like converting it to NOS?

[mcgsxr]

Geez, if I had to delete projects that were not at the cutting edge, I would have to cut all my OWN!   

Glad to see your concept, I have not tried the miniDSP, but lots of folks seem to gravitate towards it, and I can see why, when I google it.

I am still running active Xover via an older Reckhorn piece, but happy enough with it.

[JohnR]

AS much as I like the idea of the D130, and it's potential dynamics and hemp musicality, it seems to be the more difficult implementation for a simple guy like myself and would not end up in the "simple" category.

It's just that you may need bass support anyway with the D130. I see it's a 15" but it depends on baffle size and drivers specs as to whether you would or not.

Oh, and most likely passive XO on the first try at least. MiniDSP is surely attractive but I like my DAC and wonder if guys have modded the MiniDSP at all. Like converting it to NOS?

You wouldn't be able to modify the built-in DACs per se, but you should be able to connect something eg TDA1543 chips directly to the IIS outputs of the board. I haven't done it (or read of anybody doing it) but it looks feasible.

[Viridian]

You wouldn't be able to modify the built-in DACs per se, but you should be able to connect something eg TDA1543 chips directly to the IIS outputs of the board. I haven't done it (or read of anybody doing it) but it looks feasible.

Now there's an idea!

And you've got me thinking of the D130 again. Dang it.

[JohnR]

Well, refining the DACs is also something you can do later once you have the basic design and baffle/crossover sorted out. Did you decide which way to go?

[Viridian]

Hey John,

I've decided to go with a small widerange driver, the 4.5" Pioneer PE-12 and implement an H-frame(idea from MJK's passive 2way) with my 12" PAX30G in it for bass/lower mid support. Plan to cross at 300 Hz simply because that is where the PE-12's start to roll off. The H-frame should drop efficiency(!) of the PAX30G to be a better match for the PE-12. But it might still be too efficient. I like the PAX30G's as according to manufacturers spec they don't really start to roll off until 80Hz. I've had the best ever bass in OB from those drivers. I was going to try the LowtherAmerica's tinybaffle funky crossover scheme and see how that works.

Any thoughts?

[Viridian]

PAX-30G graph:

PE-12 graph:



I think I may have trouble bringing the PAX30G down to match. What a problem to have!

If this is in fact the problem then I'll have to try something creative to boost the PE12, like the dipole waveguide I've threatened to build for the last couple of years. Bill Woods called it a "boffle" when I asked him about it.

[el`Ol]

Higher sensitivity of the woofer is no problem for OBs. That can be compensated by the crossover (crossover point of the woofer lower than that of the fullranger). See http://www.quarter-wave.com

[JohnR]

Hey John,

I've decided to go with a small widerange driver, the 4.5" Pioneer PE-12 and implement an H-frame(idea from MJK's passive 2way) with my 12" PAX30G in it for bass/lower mid support. Plan to cross at 300 Hz simply because that is where the PE-12's start to roll off. The H-frame should drop efficiency(!) of the PAX30G to be a better match for the PE-12. But it might still be too efficient. I like the PAX30G's as according to manufacturers spec they don't really start to roll off until 80Hz. I've had the best ever bass in OB from those drivers. I was going to try the LowtherAmerica's tinybaffle funky crossover scheme and see how that works.

Any thoughts?

Sounds like a good plan to me As el Ol points out you could lower the woofer lowpass rolloff to compensate for dipole rolloff and match sensitivities at the same time. I'm not doing that myself but it makes sense as a concept and is what the MJK projects do as I understand. I myself am heading off into active DSP territory at present. I'd suggest though that being able to do some measurements would be indispensable.

[Viridian]

Ok, I get what you are saying about the lower XO point. However, look at the plot of the PE-12. I need to XO at around 300Hz. My PAX woofer isn't going to see any baffle induced rolloff in an H-frame until much lower than that. Am I wrong? I have not tried to match dissimilar sensitivities before.

I do have a rudimentary way of measuring. I have a quite good iPod app with RTA and FFT that will help.

[JohnR]

The idea with a higher sensitivity woofer is to use a series inductor to roll it off at a much lower frequency than the actual "crossover" frequency. The frequency of rolloff / size of inductor needs to be such that, at the actual crossover frequency, the effective sensitivities (woofer with series rollof inductor, and FR driver) will be matched. This early rolloff also compensates for the dipole loss. The JX92s OB project on MJK's website works this way, here is the direct links -  http://www.quarter-wave.com/Project08/Project08.html

I think it's worth investing a bit to get a measurement capability. I've made much more rapid progress since doing so, anyway. The program (REW) is free, you also need a mic (preferably calibrated) and mic preamp/USB interface.