[Bob in St. Louis]

I understand Martin and won't hold that against you (that's a wee little joke there  ).
I read your paper when you released it and understand your justification for using the Alpha. As much as I love the Augies, I wasn't taking this as a cheap opportunity to shill them to Alex, I just wanted to let him hear a simular bass driver in OB (to the best of my knowledge, he's never heard OB bass??)

Bob

[MJK]

OK, I understand. I thought you might be trying to liquidate your Augies so you could buy some Alpha's and use the leftover cash to go back to SS amps. 

[Bob in St. Louis]

 ................ .........Not on your life Mr. King. 
Nosirree.
I believe the phase goes something like, "You can have my drivers when you pry them from my cold dead fingers".
{Some liberties taken with the phrase to suit my needs, of course.} 

Bob

[MJK]

So how are you planning to pay for the SS amps?

[Bob in St. Louis]

I really have no need to buy any more amps. I've got 40wpc of tubes from 80Hz and up, 270 watts of SS from 40Hz to 80Hz, and 800 watts from 40Hz down to the 'Brown Note'.
Honestly, I love what I have and have no desire to change back to SS for the mids/uppers.
I'm happy enough in what I currenty have to feel confident in saying no amount of 'forum buzz' will cause me to switch back to SS for content above 80Hz.

Bob

[Graham Maynard]

Hi AJ,

I think that TerryO was referring to transconductance. 
Bipolar transistors especially just do not do voltage to current at all linearly without NFB.
Nelson Pass has shown extended driver range capabilities with current drive;  do a search for his " cs-amps-speakers " .pdf.

I also think it likely that non-global-NFB current drive reduces driver 'shout' and 'sibilance' when compared to SS drive, though I personally prefer SS and then cope with such aspects differently.

Cheers ....... Graham.

[mark@marktwain]

Hi guys,

Sorry for the interruption.

Martin, I was wondering if the crossover and baffle specifications you posted for the DX2's would also work with PM2C's?

Thanks,
Mark

[MJK]

Mark,

The PM2C would also work without any concerns if you are using an active crossover. I have used the PM2C in my Lowther OB and it works very well with the two Eminence Alpha 15A woofers per side with about +2 dB of boost applied to the woofers.

The passive crossover works for the DX2 and PM6A drivers because both of these drivers are about 95.5 dB/W/m and the two Alpha's are about 96 dB/W/m best case. The PM2C driver is just over 97 dB/W/m so I would be concerned about a passive crossover and the Lowther being just a bit too bright. You could try it passively and if it was a little out of balance add a very small series resistor to the PM2C to bring it down a little in SPL/W/m.

Martin

[sts9fan]

Martin,

in your linked PDF do you have the drivers off center?  am I reading it correctly that the center of each driver is 30inches?

[Retsel]

I have some suggestions about where to mount the DX2s on the baffles (I built a set of Basszillas).  You should mount the DX2s about 3/4 the way up on the baffles with the baffles standing tall (4 feet tall, 2 feet wide).  These baffles are a little short, but they will do for testing sakes.  I suspect that the baffles are not wide enough to get down below around 500 hz or so, so you can check this and maybe add some short wings (i.e. 4 inches) off the back (flared out 120 degrees from the back). 

You will have to measure the frequency response to see if yoiuwill need to adjust the frequency response with some sort of crossover circuit. 

You will have to high pass the Lowthers to protect them from excessive movement, probably at about 150 hz. 

Even if you don't need or want deep bass, you will still need woofers because 150 hz is way to high to have anything that sounds like music, unless if the only thing you like to listen to are cymbals....

Retsel

[MJK]

in your linked PDF do you have the drivers off center?  am I reading it correctly that the center of each driver is 30inches?

The worksheet was something I put together a couple of months ago to look at a different question, which is another story of its own, which required modeling the baffle offset in the geometry plot. But if you look at the dimensions and the picture you will see that the model is for a baffle 48" tall and 24" wide. In the pictures the drivers are all centered in the baffle with the two Alpha 15A woofers 10" and 26" off the floor and the Lowther DX2 30" off of the floor. That is the geometry that produced the SPL response plots shown in the linked simulation. You can change the wiggle created by the Lowther to a more uniform wiggle over a slightly wider frequency band by offsetting the Lowther 2" towards one baffle edge. This requires the baffles to be made in mirrored pairs. It is a trade-off that anybody building the design can think about and decide if they want the added complexity.

Martin

[AJinFLA]

Hi AJ,
I think that TerryO was referring to transconductance. 
Bipolar transistors especially just do not do voltage to current at all linearly without NFB.
Nelson Pass has shown extended driver range capabilities with current drive;  do a search for his " cs-amps-speakers " .pdf.

Hi Maynard,

I quite aware of what Terry was referring to as well as Nelsons designs. What I was looking for was some evidence of audibility in the form of scientifically acquired data via controlled tests, not audiophile ghost tales (which while quite amusing, are otherwise utterly useless anecdotal hearsay).

I also think ...
...it likely that non-global-NFB current drive reduces driver 'shout' and 'sibilance' when compared to SS drive, though I personally prefer SS and then cope with such aspects differently.

Well, soundwaves don't care much for what you and I think .
Now is this audible reduction visible in the frequency domain, or is this one of those audiophile effects that bypass soundwaves/pinna and are beamed directly into the cranium?

Btw, Bob, MJK is giving you sound (no pun intended) advice. My only comment there is that I still find it incomprehensible how folks can be building "holes in a piece of wood" and not utilizing the free software that exists just for DIYers, such as The Edge and xlbaffle, or very low cost MJK and JohnK programs. These are plug-a-few-numbers from widely available driver specs that a 10yr old (my nephew) can do.
Just remember that while an offset (mid) driver may result in slightly smoother on axis simulations (and possibly measurements), it will introduce polar asymmetry and possible worse off axis smoothness - neither of which is normally desired.

cheers,

AJ

[Bob in St. Louis]

I still find it incomprehensible how folks can be building "holes in a piece of wood" and not utilizing the free software .........

I have these two soft fleshy things that tell me I've done a pretty good job so far.
Who knows, maybe someday while I'm poking holes in plywood using my time tested methods, I'll let my nine year old son plug-a-few-numbers from widely available driver specs and he can design baffles for his own room. Wouldn't that be cool.   aa

Bob

[Graham Maynard]

Hi AJ,

You opening another can, or just stirring the pot ?  LOL.

Wonder if you saw this thread. 
Much still needs to be investigated, but it won't affect what hear.

 http://www.diyaudio.com/forums/showthread.php?s=&threadid=121344&highlight=

Cheers ...... Graham.

[AJinFLA]

I have these two soft fleshy things that tell me I've done a pretty good job so far.

But of course. As predicted http://users.ece.gatech.edu/~mleach/beraneklaw.html

Who knows, maybe someday while I'm poking holes in plywood using my time tested methods, I'll let my nine year old son plug-a-few-numbers from widely available driver specs and he can design baffles for his own room. Wouldn't that be cool.

Maybe. But will he think it's cool that his dad is now hanging out in his son's room all the time listening to his son's more adeptly designed and better sounding loudspeakers? His son's friends?

Hi AJ,
You opening another can, or just stirring the pot ?  LOL.

Of beer? Always. Don't cook much myself.

Wonder if you saw this thread.   http://www.diyaudio.com/forums/showthread.php?s=&threadid=121344&highlight=

I had crossed his site long before and yes I did follow the thread from the beginning.

Much still needs to be investigated, but it won't affect what hear.
Cheers ...... Graham.

I've been saying that about audiophiles for a long time
But I will leave those type of investigations to those properly qualified in psychology.
While I continue my own or study others investigations that involve audibility....in the electro-acoustic domain.

cheers,

AJ

[Bob in St. Louis]

But of course. As predicted http://users.ece.gatech.edu/~mleach/beraneklaw.html

There's nothing better than confirmation ones choices were correct. 

[AJinFLA]

There's nothing better than confirmation ones choices were correct. 

Yep.
Like your tubes, it's a perfect way to avoid any NFB whatsover.

cheers,

AJ 

[Bob in St. Louis]

Oh, I like NFB, it's helps me advance. As long at it's constructive NFB of course.
If it's not constructive, I'll soon tire of it and discount it as drivel. However, I will play with it a little bit just before I pitch it in the trash.
Just for the fun of it. 

But we're no longer talking about "Lowthers on Ply", we've managed to stray.
Back to the topic at hand please......

Bob

[scorpion]

Hi Bob,

I think you are home. Three holes in the baffle for 2 Alpha15s and the Lowther. Nothing to stop Alexis to have an OB as good as Martin J King's.
There are a lot of favourable mentionings of Alpha15 as bass-OBs including my own, and indeed it is a kind of Silver Iris. So can you listen to that speaker I think you will stand the Alphas, as we other do. I would also choose the Augie on a number of occasions including IB, but here sensitivity is to low to allow a passive design. It would be quite anothet thing if an active system was discussed but even then I think you would have to use two Augies per side.

I will also sharply agree with AJ in stating: It is almost a sin not use the good software for loudspeaker construction now available, be it an enclosure or OB !
It doesn't take the magic out of design, but it allows you to start out good with something that your own intuition, fantasy and knowledge might improve. 

PS ! Perhaps I should also say that my first choice of crossover capacitors in the signal lead definitively wouldn't be Solens.

/Erling

[Bob in St. Louis]

Alright Erling, good deal. Thanks for the information man!
Not sure Alex wants $600 in bass augmentation but we'll see.
Looks like it's time I have a chat with him and see which direction he wants to go.

I will also sharply agree with AJ

Well what I have to say about that is............Oops, gotta go.......my sock drawer is on fire. Nevermind. Bye.

Bob