[JohnR]

For what matters I agree enterily with Rudolf that the Nelson Pass baffle is more or less a gimmick, not really thought over in the light of proven knowledge. You won't get around the EQ problem and effeciency gain would probably be small. So what you are set with in this design is more or less a flat baffle with some introduced problems in how frequency response will be. So it is not really an advisable way.

I suppose what Rudolf is hinting at in his answer is the Ripole concept which deals with pressure loaded units but that in it's really useful application is more of a subwoofer solution.

Does a ripole actually give efficiency gain? It's baffle is so small that it looks like it would be a lot worse (lower output) at low frequencies.

[Rudolf]

Does a ripole actually give efficiency gain? It's baffle is so small that it looks like it would be a lot worse (lower output) at low frequencies.

In fact there can't be a efficiency gain. There has to be an efficiency loss - it is inevitable.
This has been explained over at diyaudio.com by sreten (in a rather direct way) and by johnk (more politely).
The reason for building such "slot-loaded" dipole devices has never been increased efficiency. It is all about compact size, impulse compensation and lowering Fs (in the case of "ripoles" - intended as subwoofers).
It has been shown that the AMT effect as proposed by Dr. Heil doesn't work as advertised. AMTs simply have their Sd folded in an accordean way. If you calculate efficiency with a smaller Sd than there actually is, you will see a gain in efficiency.

Rudolf

[Chops]

If Chops would follow people with SOME "slot-loading" experience and not a once-in-a-lifetime experiment by Papa Nelson, he would have found that the general recommended slot area is 1/4-1/3 Sd for drivers with Xlin < 5 mm, and no less than 1/3 Sd for drivers with Xlin = 5 mm and more. Rear slot opening should be 1-1/2 Sd. Optimal numbers depend on Vas values and need a simulation with AKABAK or another precise simulation program to be calculated with sufficient precision.
AFAIK the idea is that drivers with a "loose" suspension should see more air resistance from the slot than drivers with a stiff suspension.

Chops' waist would effectively lower the slot cross area, but would do nothing WRT resonances.

Rudolf

I somewhat know the basics such as you stated above. It does help that you added some numbers in there.

I think I should answer my question above myself. For what matters I agree enterily with Rudolf that the Nelson Pass baffle is more or less a gimmick, not really thought over in the light of proven knowledge. You won't get around the EQ problem and effeciency gain would probably be small. So what you are set with in this design is more or less a flat baffle with some introduced problems in how frequency response will be. So it is not really an advisable way.

I suppose what Rudolf is hinting at in his answer is the Ripole concept which deals with pressure loaded units but that in it's really useful application is more of a subwoofer solution. Now you settled on the Alpair 10.2 and some reasonably slim baffle width, I assume. And you are also quite right given your recent hearing experience that the fullrange response will begin to decline about 300 Hz with those reasonable baffle widths.

So here is one kind of answer: I simulated 4 (6 is not possible with the MJK   software) Indian Woofers arranged in two groups with two units parallel in each group and then these groups are serially conected. I simulated those in an U-frame MJK-way in a 7.5 " deep (baffle excepted) U-frame with inner measures 26 x 18 ". That is to make place for another pair of woofers to use all 6 per side. To add the extra woofers just connect one each in the parallell groups to make two 3 groups.

On top of the U-frame is placed a flat baffle of 14 x 18 " dimensions the Alpair put 10" up in the middle. Crossover was set to 100 Hz 2 nd order LR for the woofers LP and 250 Hz HP also LR for the Alpairs, a kind of standard MJK simulation. I, given Chops equipment, would advocate to use 6 woofers per side for greater margin. I don't think that adding the woofers would alter anything but giving more bass output, (about 3.5 dBs) so it is just to adjust bass SPL to the Alpairs.

Now here are the results, Baffle picture first:



and then response:



/Erling

Sorry Erling. I didn't mean to look over your first post. Lots of great info in your second post. I'll have to consider something similar to this maybe if the "SLOB" doesn't pan out. Also, the current baffle size is ONLY for break-in. I will not be using these baffles on the final design.

Does a ripole actually give efficiency gain? It's baffle is so small that it looks like it would be a lot worse (lower output) at low frequencies.

In fact there can't be a efficiency gain. There has to be an efficiency loss - it is inevitable.
This has been explained over at diyaudio.com by sreten (in a rather direct way) and by johnk (more politely).
The reason for building such "slot-loaded" dipole devices has never been increased efficiency. It is all about compact size, impulse compensation and lowering Fs (in the case of "ripoles" - intended as subwoofers).
It has been shown that the AMT effect as proposed by Dr. Heil doesn't work as advertised. AMTs simply have their Sd folded in an accordean way. If you calculate efficiency with a smaller Sd than there actually is, you will see a gain in efficiency.

Rudolf

As far as efficiency is concerned, (which seems to have been all the complaints in NP's thread), I could care less about that. I'm going to have two dedicated plate amps powering these, so power and/or efficiency isn't an issue. All I care about is the end result... The sound quality.

Three things that attracted me to this design...

1) The ability to lower Fs and raise Qts
2) The ability to be somewhat compact in size
3) It's a somewhat unique design using multiple drivers

[Chops]

Erling, it almost seems as though the design you present above is similar to this design, which I rather like a lot.

http://www.musicanddesign.com/UE_OB.html

[Rudolf]

...
2) The ability to be somewhat compact in size
3) It's a somewhat unique design using multiple drivers

This is an example how four woofers per side could be arranged:

[scorpion]

Hi Chops,

I thought perhaps I was a bit too offensive in putting out that question for you, which of course I already had thought of an answer for.
Indeed, a U-frame could be made looking a lot like JohnK's design by hiding woofers behind some nice grillclothing and letting the Alpair shine on top.

/Erling

[Chops]

Hi Chops,

I thought perhaps I was a bit too offensive in putting out that question for you, which of course I already had thought of an answer for.
Indeed, a U-frame could be made looking a lot like JohnK's design by hiding woofers behind some nice grillclothing and letting the Alpair shine on top.

/Erling

No, no, no! You weren't being offensive at all. You are just giving me more options to consider, which is a good thing! Trust me when I say that I appreciate all the trouble you went through to do those simulations.

[Chops]

After much consideration, I have decided to go in a different direction with this project and am abandoning the slot baffle. I am now going to go with dual 12" drivers per side in an H-frame. The 12's I'm getting are from Danny Richie. Pretty much, I'm going to be building the entire bottom half of his GR-Research V2's, same 12" Eminence drivers and same SA-1 amps.

At least this way, I KNOW what the end results will be. Solid, detailed usable output down into the mid-20's in an attractive, slim design that looks like it's going to be smaller than the SLOB design. In fact, the V2 is physically smaller than Siegfried Linkwitz' Orion's!

So needless to say, I won't be needing these Peerless India drivers anymore.

[WC]

Still going to use the MA Alpair 10.2 for the top?

[Chops]

Still going to use the MA Alpair 10.2 for the top?

Yes I am. Why?

[WC]

Just curious. I am planning to use the same driver in a different speaker build in the future. Based on what you said earlier about it, it sounds like it will work well.

[Chops]

Not that anyone is keeping up with this anymore, but here's a quick and dirty update...

I'm listening to "Radiohead - OK Computer - Let Down" (FLAC file) right now and these Alpair's are sounding excellent! Large, full, detailed and LOUD! Ultra-clear sound! I've never heard Thom Yorke sound so good before. Deep, wide sound stage and Thom up front and center... IN MY ROOM! And yes, these are still on the small 12x12 baffles and crossed over at 40Hz!

I think the Alpair 10.2's and Monarchy Audio SM-70 Pro amp are a perfect match.

In other news, my drivers and amps from GR-Research will be here tomorrow.

[WC]

So are you running the amp as a stereo amp or as monoblocks?

[Chops]

So are you running the amp as a stereo amp or as monoblocks?

In stereo. I just have the one amp. I almost bought another one shortly after getting this one but didn't. It was the same exact amp internally but with different writing on the front and different rack handles.

[Chops]

Got a couple of boxes in today with "GR-Research" packaging tape all over them! 

[danvprod]

Did you ever end up finishing these? I'm in the process of putting together a H-frame + Alpair 10.3 on OB, just about to start the breaking in phase.

Would love to know what became of this project.