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Old 7th April 2011, 06:25 PM   #11
ra7 is offline ra7  United States
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Yup, the alphas are excellent value for money.

Godzilla, I love those baffles in the second picture. What wood is that and which finish did you use? Sexy!
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Old 7th April 2011, 06:36 PM   #12
preiter is offline preiter  United States
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Quote:
Originally Posted by sprinter View Post
Sorry, I should have been more specific about the bass part. I plan on bi-amping a separate 15" woofer with a MiniDSP for XO. I would like to be able to xo at 150-200 Hz to the FR for the rest of the spectrum.
Since you are using the MiniDSP anyway you can apply active EQ to your bass drivers, which makes QTS far less of an issue.

The whole point of high QTS in open baffles is to get a boost at FS to counteract the dipole roll-off. But you can do a far better job of this with EQ. Just make sure that whatever drivers you choose have adequate xmax and you should be golden.
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Old 7th April 2011, 08:13 PM   #13
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Originally Posted by preiter View Post
The whole point of high QTS in open baffles is to get a boost at FS to counteract the dipole roll-off. But you can do a far better job of this with EQ. Just make sure that whatever drivers you choose have adequate xmax and you should be golden.
Oh, that simple post just solved a bunch of questions for me. It was all voodoo stuff before. Thanks.

Quote:
I've used the Betsy 8" (qts around .7), Pioneer B20 (qts around .5) and TB 1808 (qts around .4) and they all sounded good on open baffle with Alpha 15's as bass support.
Godzilla, Of these three, which is your fav for listening to vocals/jazz/symphonic (shall we say highest SQ)? Assuming using the Alpha15's. Also, is this setup the single baffle "Betsy/Boomer" layout I've seen on your site?

Quote:
i agree the Alpha's can sound thick and slow in comparison to the main driver if crossed too high in frequency. Keeping it below 100hz (or lower) they sound excellent to me. When i move the crossover higher (around 150hz) they begin to contribute negatively to the overall SQ (lol).
Is it actually possible to cross as low as 100 if I use EQ on a low-Qts 8" FR on a 20" OB? That would clinch it for me. Or would the combination of fs/qts plus edge effects kill it outright at 150 or 200?

Quote:
My favorite combination is the deltalite with AN8, which is a 8" full range driver with a really low Qts. I cross them at about 130 Hz and everything is fine.
ra7, I would love to try the AN8 or Super8. What kind of setup (baffle size, EQ, etc allows you to XO at 130? Could you detail your system for me a bit? That sounds pretty ideal to me.

This is a very helpful thread for me. Thanks.
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Last edited by sprinter; 7th April 2011 at 08:19 PM.
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Old 7th April 2011, 08:45 PM   #14
ra7 is offline ra7  United States
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My baffle is about 24" wide, kind of narrowing towards the top. I used Edge to model and initially, I had thought about offsetting the driver, but in the end decided not to do it. The difference is minimal and I can live with it.

The whole process dates back to about a year or so ago when I started with a big OB - 2x4 - inspired by NP. I thought the big baffle was sort of in the way of the soundstage. So, using edge I reduced its size.... then reduced its size further and finally its down to this size and shape.

I also started with the alpha 15s and they are excellent value for money. I always had my eye on the beta15s though. I got the deltalites for a front horn I'm building with John (carpenter) but for now they are sounding quite awesome in the OB.

I've tried several full range drivers - JX92s, alpair 6 and 12, fe103, fe126, coral alnico 3", tannoy dual concentric CMS6.5, and Audio Nirvana Standard 8. My favorite amongst all these is the AN. The alpair 6 really impressed me but it needs to be crossed higher at about 400 Hz. It is a little too analytical and lacks the realism and musicality that a paper cone provides. The Jordans have just been poor. A lot of people swear by them, I don't know what the fuss is about. The fostex drivers are really good too and I could live with them if I didn't have the ANs.

The 'Q' of a driver is a quality factor. A high Q indicates a big peak in output near resonance (or Fs). This means the magnet is not powerful enough to damp the cone near its resonant frequency. In a sealed box, the enclosed air provides some resistance to the cone when it tries to move excessively near resonance. On a OB, there is nothing to stop this excessive motion. But the baffle roll off counters the excessive output giving an overall flat response. However, you cannot hide the fact that the magnet is not strong enough to damp the cone.

A low Q driver on the other hand has a magnet powerful enough to resist the excessive cone (somewhat) motion near resonance. Add to this the natural roll off on OB and you get less bass compared to a high Q driver. But you can always compensate this by adding more EQ. What you will get though, is a driver that can produce a bass note in music and stop the cone from moving when the note stops.

If you have MiniDSP, you are pretty much set. Just start building and listening. That's where the fun is

Hope this helps.

Last edited by ra7; 7th April 2011 at 08:49 PM.
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Old 7th April 2011, 09:33 PM   #15
ra7 is offline ra7  United States
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Here's a pic of my baffle. This is with the alpha15. An over-zealous dog smooshed in the dust cap
Attached Images
File Type: jpg OB_latest (2).JPG (234.4 KB, 662 views)
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Old 7th April 2011, 10:26 PM   #16
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>>> Godzilla, Of these three, which is your fav for listening to vocals/jazz/symphonic (shall we say highest SQ)? Assuming using the Alpha15's. Also, is this setup the single baffle "Betsy/Boomer" layout I've seen on your site?

I like them all! But they are different. I will try to explain. The TB 1808 is a jack of all trades. It’s detailed, efficient and extended. I think it sounds a little on the mellow side with an emphasis on the middle frequencies. The Betsy is totally different sounding more dynamic, also very detailed (but with less 'tone' than TB) and is more forward with an emphasis on the upper frequencies. The Pioneer B20 is the least detailed and dynamic but I love this driver and wish it were never discontinued. It’s more mellow than the other two and exhibits the least amount of detail emphasizing the lower mids. Of the three, only the B20 requires a tweeter. The TB and Betsy can do without… tho I added one anyway for a bit more of a dynamic sounding treble.

My favorite for Jazz would be the B20 and the TB 1808.
My favorite for vocals would be the TB 1808 and the Betsy.
My favorite for symphonic would be the TB 1808 and Betsy.

TB 1808 is the sweetest and most three dimensional. Sometimes you notice something in the midrange that’s not quite natural. Betsy images a little flat but with punch. It can call attention to itself in the higher frequencies. B20 is mellow without calling attention to itself at all and fatigue free, but it’s the dullest sounding of the group. They are all about the same efficiency… maybe the B20 a little less than the others.

I don’t have an 8” Fostex but love the 6.5” 168s and 165k. Both great drivers… but haven’t had on open baffle… yet. The Betsy sounds similar to Fostex with somewhat less ‘tone’ and a dryer treble as opposed to sweet with Fostex.

Yes, this is the Betsy/Boomer setup using an amp to power the Alpha 15’s. Someone bought a pair the other day to use with their Betsy’s and a small tube amp. It should sound great!

Boomer Open Baffle Speaker Kit

>>> lacks the realism and musicality that a paper cone provides…

Funny how I gravitate towards paper cones too. I’ve tried Kevlar, Poly and Aluminum and prefer paper… always.

ra7... i put something like this on my woofers... sorry about the smooshed dustcap. Maybe you can stick a pin in it and pull it out?

http://www.parts-express.com/pe/show...number=260-375

Those AN's look totally 'no nonsense' and I'd like to hear a pair. I bet your system sounds pretty darn good. Oh, and my baffles are simply unfinished birch ply from Home Depot. I like to sand them smooth. Currently they are in my 13 year old son's room with B20's and a piezo behind that little horn. He loves them!

Last edited by Godzilla; 7th April 2011 at 10:31 PM.
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Old 8th April 2011, 01:40 AM   #17
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ra7 - i found your post >>14 particularly useful. I love to see the interactions of T/S parameters explained and discussed. To others: I've found this page Thiele/Small Parameters particularly informative, especially seeing the formulae for calculating the small sig params, and the 'qualitative description'. Helps to have an idea of how to interpret T/S params without needing to plug a whole dataset into a box sim.
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Old 8th April 2011, 04:06 AM   #18
ra7 is offline ra7  United States
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Quote:
Originally Posted by Godzilla View Post
Funny how I gravitate towards paper cones too. I’ve tried Kevlar, Poly and Aluminum and prefer paper… always.
Yup, I prefer paper too.

Quote:
ra7... i put something like this on my woofers... sorry about the smooshed dustcap. Maybe you can stick a pin in it and pull it out?

http://www.parts-express.com/pe/show...number=260-375
Thanks, that's going to be a life saver!

Quote:
Those AN's look totally 'no nonsense' and I'd like to hear a pair. I bet your system sounds pretty darn good. Oh, and my baffles are simply unfinished birch ply from Home Depot. I like to sand them smooth. Currently they are in my 13 year old son's room with B20's and a piezo behind that little horn. He loves them!
Yeah, they're pretty damn cheap too. In my opinion, they wipe the floor with the competition. At their price, everyone should have one.
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Old 8th April 2011, 06:03 AM   #19
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Originally Posted by ra7 View Post
Hope this helps.
It does. Thanks. Interesting that you decided not to offset your FR. Playing with Edge, it seems to make a big difference, but maybe that just shows that curves and figures aren't everything (insert joke here). I think I'll offset, though.

Godzilla, thanks for the driver critique. I know that it's all subjective stuff, but when you start seeing the same comments repeated from different people, I figure maybe there's something there. I noticed from your pics that you have both an MJK H-frame design system and a single baffle design both employing what looks to be the same FR drivers. Could you compare the two designs? They look pretty much apples-to-apples except for the physical design and that would be a very valuable comparison to have. I'm all set to build an H-frame but having a hard time finding a way to make them with an acceptable AQ for our living room. (I thought a new acronym would be in order here "Aesthetic Quality" since we're having so much fun with them).

I tried to change my PartsExpress woofer order from Alpha to Beta, but they were just shipped today. I guess I'll try them and I can exchange within 45 days if I decide to.
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Old 8th April 2011, 06:22 AM   #20
ra7 is offline ra7  United States
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It does make a difference, but Edge doesn't tell you the driver response. It only tells you how the baffle will react. It's a good idea to still aim for the flattest response in Edge.
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