I gather that for bass extension, a fairly high Qts of around .7 is important in an OB. However, I keep seeing recommendations for drivers with rather low Qts, say around .2 to .3 in OB application (Fostex especially).
Assuming a bass-augmented system with an active crossover goal of about 200 Hz (150 would be better) and an OB size of about 20"-24", what kind of Qts value could one get away with, say for a 8" driver? Is there a tool to help determine this that includes the Qts factor as well as cone size?
I'm having a lot of trouble finding many examples around 8", at least 90 dB (SE tube friendly), inexpensive (under $100 each) with a higher Qts and with a good reputation for sound quality. However, if I could get away with a .3 Qts, that opens up the field a lot. If not, it looks like the Betsy is the best option so far but I would like a few more options to choose from if possible.
I'm starting to think that maybe a smaller driver would be okay too, but power handling for a largish room has been a concern of mine. Dispersion seems adequate on a 8" for me so far.
Assuming a bass-augmented system with an active crossover goal of about 200 Hz (150 would be better) and an OB size of about 20"-24", what kind of Qts value could one get away with, say for a 8" driver? Is there a tool to help determine this that includes the Qts factor as well as cone size?
I'm having a lot of trouble finding many examples around 8", at least 90 dB (SE tube friendly), inexpensive (under $100 each) with a higher Qts and with a good reputation for sound quality. However, if I could get away with a .3 Qts, that opens up the field a lot. If not, it looks like the Betsy is the best option so far but I would like a few more options to choose from if possible.
I'm starting to think that maybe a smaller driver would be okay too, but power handling for a largish room has been a concern of mine. Dispersion seems adequate on a 8" for me so far.
well, i think it will roll off at Fs/qts, not including the open baffle dipole roll-off.
And to me, a driver will have a dip at 1129/distance front to back (but it fill in farfield according to stereophile's measurements of the Jamo open baffle), then there will be a peak at half that frequency (front wave 90 degrees out of phase adding to back wave) then response falling till it hits mass corner then vanishes.
I had about 8" of cone area on an open backed box. The shortest distance (front to back) was 38", I liked it, excellent midbass compared to most speakers that had no baffle step. That put the Feq (+3 to 6db) hump around 180hz. It was liveable to me.
Listening to fostex plus 15" on youtube on a narrow baffle, I hear a severe lack of midbass (not much below 400hz).
Largish room (15' x 18') sitting 12' away, I need at least 8" of cone area plus sub. And I'd like to see a full range get down to 200hz for a crossover point.
The betsy is said to be great for the price. You may want to notch that 5-10db spike near 3-4khz though.
Norman
And to me, a driver will have a dip at 1129/distance front to back (but it fill in farfield according to stereophile's measurements of the Jamo open baffle), then there will be a peak at half that frequency (front wave 90 degrees out of phase adding to back wave) then response falling till it hits mass corner then vanishes.
I had about 8" of cone area on an open backed box. The shortest distance (front to back) was 38", I liked it, excellent midbass compared to most speakers that had no baffle step. That put the Feq (+3 to 6db) hump around 180hz. It was liveable to me.
Listening to fostex plus 15" on youtube on a narrow baffle, I hear a severe lack of midbass (not much below 400hz).
Largish room (15' x 18') sitting 12' away, I need at least 8" of cone area plus sub. And I'd like to see a full range get down to 200hz for a crossover point.
The betsy is said to be great for the price. You may want to notch that 5-10db spike near 3-4khz though.
Norman
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What do you expect for SQ?
I see guys using qts of .3 but they're not getting any bass to speak of or are augmenting with subs or bass bins.
To my way of thinking don't expect SQ out of any 8" fr with less than .7 qts and as a stand alone don't expect to get any lower than maybe 150hz without sacrificing mids and highs which is ob's appeal.
Read Gainphile's site. He's done the most with OB.
I see guys using qts of .3 but they're not getting any bass to speak of or are augmenting with subs or bass bins.
To my way of thinking don't expect SQ out of any 8" fr with less than .7 qts and as a stand alone don't expect to get any lower than maybe 150hz without sacrificing mids and highs which is ob's appeal.
Read Gainphile's site. He's done the most with OB.
If you are going to augment your full range driver with a bass driver, the Qts of the full range driver is almost irrelevant. Fostex, AN, Lowther, just about anything works.
I'm using a single Eminence Deltalite 2515 per side. Qts=0.38. It needs a little bit more EQ, but it literally whopps the Alpha15s ***. Check out troels site for more info on OB with this driver.
To me, low Qts drivers mean powerful magnets and light cones, a combination which usually results in better sound compared to high Qts drivers.
I'm using a single Eminence Deltalite 2515 per side. Qts=0.38. It needs a little bit more EQ, but it literally whopps the Alpha15s ***. Check out troels site for more info on OB with this driver.
To me, low Qts drivers mean powerful magnets and light cones, a combination which usually results in better sound compared to high Qts drivers.
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.
Thanks Norman for the Fs/Qts formula. That's the math I was missing. I can use Edge for the baffle stuff.
Bluto, I just don't know about the SQ factor. Is your concern that 8" is too large to give a satisfactory SQ with a low Qts? Do you think that a smaller FR would be better in that regard? I know a lot of people do prefer smaller FR drivers in this kind of application and that is one factor I still am struggling with.
CLS, good points. Thanks
ra7, what can I say, your answer just made my life a lot easier. I think I'll go with it! What do you think of Bluto's concern about SQ of a low Qts 8" FR?
Thanks Norman for the Fs/Qts formula. That's the math I was missing. I can use Edge for the baffle stuff.
Bluto, I just don't know about the SQ factor. Is your concern that 8" is too large to give a satisfactory SQ with a low Qts? Do you think that a smaller FR would be better in that regard? I know a lot of people do prefer smaller FR drivers in this kind of application and that is one factor I still am struggling with.
CLS, good points. Thanks
ra7, what can I say, your answer just made my life a lot easier. I think I'll go with it! What do you think of Bluto's concern about SQ of a low Qts 8" FR?
I was a bit critical to Troels speaker when someone put it in the Ultimate OB gallery - multiway forum. The Deltalite should be much better than the Alpha no doubt but it's limited X-max will not allow something like 100 dB in the lowbass without overloading, in OB that is. Upper bass would not be a problem.
I have substituted my Alpha15s for Acoustic Elegance IB15 with excellent result. See post #467 here: http://www.diyaudio.com/forums/multi-way/123512-ultimate-ob-gallery-47.html#post2433427 and this link: The BlindStone OB . Also AE IB15 is about half price of the Deltalite.
/Erling
I have substituted my Alpha15s for Acoustic Elegance IB15 with excellent result. See post #467 here: http://www.diyaudio.com/forums/multi-way/123512-ultimate-ob-gallery-47.html#post2433427 and this link: The BlindStone OB . Also AE IB15 is about half price of the Deltalite.
/Erling
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First off, I don't know what SQ is.
Sprinter, you can try the Beta15s, which have a low Qts, and while they may not be built to the same quality as the deltalites, they will give you a taste of what low Qts bass sounds like. The Alpha15s sound thick and slow in comparison.
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. With regard to SPL and excursion, I doubt you'll ever exceed the maximum specifications. You'll be in trouble with your neighbours before you break the driver.
NP had his Lowthers crossed to the beta15 at 80Hz LP and 120Hz HP. So make what you will of that.
Sprinter, you can try the Beta15s, which have a low Qts, and while they may not be built to the same quality as the deltalites, they will give you a taste of what low Qts bass sounds like. The Alpha15s sound thick and slow in comparison.
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. With regard to SPL and excursion, I doubt you'll ever exceed the maximum specifications. You'll be in trouble with your neighbours before you break the driver.
NP had his Lowthers crossed to the beta15 at 80Hz LP and 120Hz HP. So make what you will of that.
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. There was not any drastic change in settings for the Alpha's. The baffles were about 20" x 20" sitting on top of H-frames. I also used them all on baffles about 20" x 44" to good effect. When i turn off the woofers bass drops drastically. I hope to get around to trying smaller drivers (4" like many tend to use). I also have a pair of ceiling speakers mounted in an open baffle setup that have a qts of 1.6. Subjectively they have the same amount of bass (down to about 100hz) whether they are in a sealed, ported or on an open baffle.
When simulating responses on open baffles 20 x 20 the drop off is similar regardless of qts (around 250hz unless using a driver with a qts of 1.0 or more, which will extend deeper). On 20 x 44 baffles the bass response extends to about 150hz for drivers with qts below 1.0.
Does any of this make sense? lol
>>> The Alpha15s sound thick and slow in comparison.
Hi ra7, SQ is short for Sound Quality. I don't always know the acronyms but i do know that one. Also, 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).
If i was using an equalizer i'd look into the higher priced, higher excursion 15" woofers even with lower qts. But for my applications the Alpha's do the job. They go low enough on open baffle and crossed appropriately, i think they are awesome! I don't doubt the better SQ of the more expensive and more robust products out there.
When simulating responses on open baffles 20 x 20 the drop off is similar regardless of qts (around 250hz unless using a driver with a qts of 1.0 or more, which will extend deeper). On 20 x 44 baffles the bass response extends to about 150hz for drivers with qts below 1.0.
Does any of this make sense? lol
>>> The Alpha15s sound thick and slow in comparison.
Hi ra7, SQ is short for Sound Quality. I don't always know the acronyms but i do know that one. Also, 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).
If i was using an equalizer i'd look into the higher priced, higher excursion 15" woofers even with lower qts. But for my applications the Alpha's do the job. They go low enough on open baffle and crossed appropriately, i think they are awesome! I don't doubt the better SQ of the more expensive and more robust products out there.
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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.
Oh, that simple post just solved a bunch of questions for me. It was all voodoo stuff before. Thanks.
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?
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?
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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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.
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.
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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/showdetl.cfm?Partnumber=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!
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/showdetl.cfm?Partnumber=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!
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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.
Yup, I prefer paper too.
Thanks, that's going to be a life saver!
Yeah, they're pretty damn cheap too. In my opinion, they wipe the floor with the competition. At their price, everyone should have one.
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.