[nullspace]

Thanks for the report. It's on my list of tweaks to try as well.

Regards,
John

[FJK]

Thanks John for sharing your work.

As you know I originally contacted you to get a handle on the Jensen field coils you used on a previous project on your website. You mentioned they were a pain due to many being faulty. Then I guess you were using the Fertins field coils before the TT's.  I'm still a little fixated in doing a crossoverless DIY open speaker and wonder if those two field coils might be better for this or did they also have unacceptable peakiness in your opinion.

Also wondering if you find the tone and naturalness that others speak about with field coils, not be much different from what you have found the Tone Tubbys can provide.

 

[nullspace]

The Fertin 20EX are really nice. I still have them and don't have any intention of getting rid of them, even if they are boxed up and stored in the attic. They actually measure really well; ruler flat up to about 4-5khz, then peaking about 4-5db at 11khz before rolling off quickly from there, if I recall correctly. They definitely have the natural, relaxed tone field coils are reputed to have. But, I don't have the current model and the ones Fertin is selling now are much different than the ones I own.

I like my latest efforts better, though.

Regards,
John

[FJK]

That says a lot given the price difference between the Tone tubbys and the Fertins.

Can I also presume the Tubbys can provide higher spl levels than the Fertins or previous Jensens (I know you are running two TT's per baffle but assuming you were only using one)?

[nullspace]

Factor in the required crossover, horns, compression drivers, and I don't know that my current setup is any less expensive than my Fertin setup.

The current speakers play much, much louder before distortion sets in than the Fertins did. Part of that is that I didn't highpass the Fertin; if I had stuck with them, I would've added a 1st-order 200hz filter. Here, the ~80hz fs for the TT12s helps keep excursion managable.

Just about any prosound driver will play louder with less compression than the typical audiophile driver.

Regards,
John

[FJK]

The spl requirement is somewhat important in my large listening room so I think I will just have to give the the Tubby's a try and order a pair.

Thanks again.

[Lazz]

Hello John.Can you tell me why you used 2 TT per baffle.instead of just one for midrange and xover to the woofers.Thx Lazz.

[nullspace]

Hi Lazz,

Certainly one could use just one TT12 and then run the woofers up to 300hz or so, but I decided I'd rather add the second TT12 and get the mains to cover down to 100hz. Just a personal preference, I suppose, no real reason.

Regards,
John

[Telstar]

Hi Lazz,

Certainly one could use just one TT12 and then run the woofers up to 300hz or so, but I decided I'd rather add the second TT12 and get the mains to cover down to 100hz. Just a personal preference, I suppose, no real reason.

Regards,
John

Makes perfect sense to me

Why not the 10"? Should extend more on the HF (cant find a graph)...

[ttan98]

There are no manufacturer's FR graphs that I known of for 10" or 12" or even 15" TT drivers.

[nullspace]

Why not the 10"? Should extend more on the HF (cant find a graph)...

A couple of reasons, I suppose. First, the 12" is more efficient and I really wanted a speaker close to 100db/watt. And, I don't need the midbass to go higher than 1.2khz -- the compression driver I'm using is plenty comfortable playing that low. Really, I'd rather the crossover be lower rather than higher. If I thought I had a chance at getting a 15" driver and a 1.4" compression driver to co-operate and cross over at 700-800hz, I'd have gone that route. Of course, that's a whole nother story...

Regards,
John

[Telstar]

Why not the 10"? Should extend more on the HF (cant find a graph)...

A couple of reasons, I suppose. First, the 12" is more efficient and I really wanted a speaker close to 100db/watt. And, I don't need the midbass to go higher than 1.2khz -- the compression driver I'm using is plenty comfortable playing that low. Really, I'd rather the crossover be lower rather than higher. If I thought I had a chance at getting a 15" driver and a 1.4" compression driver to co-operate and cross over at 700-800hz, I'd have gone that route. Of course, that's a whole nother story...

Regards,
John

Thanks. It makes perfect sense. I s'pose the 10" is also not able to go fullrange (i.e rolloff after 15k), so a 3 way is the right use of it.

The 12" TT looks to me as a perfect midrange for a Prometheus-style ob.

[nullspace]

Maybe, maybe not. I don't know the particulars, but if I'm not mistaken the Bastanis Prometheus uses the 12" drivers pretty high, more like a widerange driver + helper tweeter. That's pretty demanding of the 12" driver.

I'll attach the measurements I took on- and off-axis (0 to 35degrees) of the TT12 -- the dB scale is relative, btw. I'll leave it to you to draw your own conclusions. For me, I wouldn't use it above 1.2khz, and really that's stretching it, because of cone breakup and directivity issues. But, as others have noted, the breakup is pretty benign if you do something about the rising response. And, some people don't bother much with controlling for directivity. Horses for courses, I suppose. Many people hold the Prometheus in very high regard -- I've heard them and I thought they were nice but not my cup of tea, so my design has gone in a different direction because of my priorities. To each their own.

Regards,
John

[nullspace]

I still need to work on the (sub)woofers. As expected, the mains rolloff around 100-120hz. I have something in place now, but it's not worth discussing. I have a quartet of OB15 from the nice fellows at AE, and I'm looking forward to getting baffles made and the active filtering built up. I already have the boards back from ExpressPCB and components have arrived from Mouser.

Hi All,

Just to wrap up, I finally got the AE OB15 plus active filtering up and running. The stereo (sub)woofer controller consists of volume control -> open baffle compensation -> 2nd order lowpass -> 2nd order highpass at ~28Hz with variable Q -> phase correction. It took me about half an hour on Saturday to dial in the woofers. Crossover to the mains turns out to be ~120Hz, and the woofers are pretty flat to 30Hz - except for a 8dB suckout between 40 & 50Hz. Here's a picture of everything piled into my living room:



Also, I've posted an update at my site; you can check it out here.

Regards,
John 

[nullspace]

I posted this in The Lab, but what's a little cross-posting between friends?...

I built a prototype to see if I could pull together a fullrange open baffle speaker. It's a 2.5way -- mids and treble are as before, Beyma CP380M + AH!1000 conical horn and ToneTubby 12" AlNiCo. The .5 is now a 4x Eminence Kappa-12A. Initial listening impressions are generally positive, and I'll be pulling out the measurement gear later today.



Ran the freq. measurements. Strong down to 50hz, then rolls off very quickly thereafter. A little shy of expectations, but hopefully after the Eminence drivers break in a bit the suspensions will loosen up and Fs will drop closer to the book value of 45hz.

With such a larger baffle than I had previously been using, the ToneTubby now reaches <200hz. Consequently, I'm crossing over the .5 much lower, more than an octave lower. This is as I had planned, but I had not expected that with just one TT now covering 200-400hz, the mids are quite a bit more clear. A nice bonus.

Regards,
John

[ttan98]

Nullspace,

The bass must "sound" awesome with 4 bass drivers per speaker. A big room is a must as well, otherwise the sound will swamp over by bass response.

[Telstar]

I built a prototype to see if I could pull together a fullrange open baffle speaker. It's a 2.5way -- mids and treble are as before, Beyma CP380M + AH!1000 conical horn and ToneTubby 12" AlNiCo. The .5 is now a 4x Eminence Kappa-12A. Initial listening impressions are generally positive, and I'll be pulling out the measurement gear later today.

Oh, I had almost forgot the Tone tubbies! Would they go lower than 200hz? (lets say 80hz, using a pair of 12")?

Also, reasons for the change from the AE to th Eminence kappa?

[nullspace]

The bass rolls off early, around 50hz or so. In my smallish room of 13'x18', the bass is very nice -- tight, dynamic, and without any overhang. I do miss the extension offered by the AE drivers, though.

Only reason is that I wanted to see if I could do a non-biamp'ed, fullrange open baffle. I suppose my success depends on your definition of fullrange. I'm looking at a bandwidth of 50hz-16khz at around 97-98db/1W. Nothing wrong at all with the AE drivers, they're great -- but not efficient enough to work in the context of this project.

Regards,
John