Martin, please don't be offended. We all enjoy your contributions here and hope that you continue. Your skepticism is well founded! That was not my point. The point is, without hearing a design it's difficult to judge. On a forum like this it can be difficult to tell the wheat from the chaff. Perhaps I'm in the lucky position of having heard a number of OB projects and met the guys who have built them. They run the gamut of designs and results, that's for sure.
I just happen to know that high Q drivers are not the only way to a good sounding OB. There other approaches that work well. In fact there is a whole other school of design with mid Q woofers and big inductors that sounds good and may be more to the taste of some people.
Maybe there is something to be learned here.
I just happen to know that high Q drivers are not the only way to a good sounding OB. There other approaches that work well. In fact there is a whole other school of design with mid Q woofers and big inductors that sounds good and may be more to the taste of some people.
Maybe there is something to be learned here.
I am not offended at all. I have asked questions. When the questions have been answered I will investigate the predicted results and make some comparisons to a higher Qts design. There is not much to do until that point so no reason to continue posting. When the design is complete I will post the comparison of the calculated results. Then we can list the cost and performance trade-offs and draw some conclusions.
Some more design considerations and thoughts
Next we look at woofer performance abilities... flattening the response of the dual woofers... trading away the excess efficiency at the midrange end with a properly sized series inductor. Trying to end up with a more or less usable flat - extended response down to the 40 Hz area. This is complicated and obviously my writing skills are not the best. Will try to be as coherent as I can...
I personally assume that a speaker of any design type... intended to reproduce most music in a typical residential setting at or close to live levels must be able to play cleanly at 100 DB level (@ 1 meter) down to at least 40 Hz. Of coarse this criteria is way too much for a small near field computer speaker or the like.... again assuming the main duty of the speaker is as above.... there are caveats of coarse... Theater Pipe Organ 32' stops, home theater very LF sound effects and insane rock music levels would not be within this systems capabilities in the very deep bass. Above 50 Hz or so... this system would eat most residential speakers for lunch in terms of shear output potential. But... you would expect that of a speaker of this physical size with two 15" woofers and an 8" midrange. More on size below.
We need to see if we have enough woofer displacement to meet the design criteria above.... So.... Going to visit Mr. Linkwitz's excellent calculator here.... www.linkwitzlab.com-spl_max1.xls we input some parameters... remember... the calculations produced by the calculator are free space... we need to add 6 DB to the results shown to get in room 1/2 space operating values.
Our total piston area (SD) for the two DC-380's will be 1670 sq. cm., Peak excursion is 5.0 mm, & path difference 410 mm (Approx. 16"). We end up with a F equal of about 140 Hz. With out correction for some driver Q induced roll off.... we see enough displacement to produce 100 DB at 1 meter in 1/2 space in the 40 Hz. region. And the large baffle face I will be building (18" W X 46" tall with 6" - 7" wing depth) will... in practice lower the F3 equal a few additional Hz. Just what happens... but difficult to accurately predict. However... we stick with the conservative Linkwitz calculator predictions. Just for drill... a single Emi Alpha 15" can produce an Xmax limited 93 DB on the same baffle in the same 40 HZ region. One of the nice things going for the dual 15's... the extra displacement really pays off.
Now what Martin King astutely reasons in one of his posts is that the Lower driver Q (relative to the Emi Alpha 15) will not only induce an early roll off... a large series inductor will also add (form a broad peak) likely in the 45- 55 Hz region. However in reality... with the dual 15 operating Q being at least .5... (on that large area baffle... it will be more like .55 to .6), the moderate Q induced roll off will start around the mid 40's. And from the upper 30's it becomes a real factor. From about 45 HZ you start a Q induced rolloff transition from the traditional 6 DB/Octave for an OB to a 9 DB/octave... and below about 37 HZ you transition again to a full 12 DB/octave or higher. Driver FS (F2 in particular) and room boundary distances will effect this to various degree's. However... with my design goals I don't care.
The predicted inductor 45-55 Hz hump on paper is significant... but in reality it rarely is more than 2 or 3 DB with a 0.50 or higher operating Q... you just can't hear it. Exactly why this is I can only guess... and one of these days I will work out an evaluation - measurement test and try to figure it out. With baffle wings we are now in cardioid territory. The only time I found this Hump to be an audible problem is with a low Q Paudio 18" coax on a very large open baffle in a hotel room at RMAF. I suspect the hump issue may be exacerbated with large low MMS cones. Only a hunch.
The long and the short... based on my field experience... I will likely see a 1-3 DB roll off at or around 40 Hz and be 2 DB or so fat in the lower - mid 50's. And we must deal with an inefficient system. 84 DBW... give or take. This is where the single Emi Alpha has a big advantage. It will not play loud down low due to it's SD and Xmax limitations... but it will be close to 9 DB more efficient. Dual Alpha's would be great... but the whole point of Jon Pike's original post was premised on whether the Special $35 priced DC-380 could work for a practical OB system.
Need to work out the mid and high end part of the system... and BTW... the system will be passive... amazingly simple passive. More on that later.
Next we look at woofer performance abilities... flattening the response of the dual woofers... trading away the excess efficiency at the midrange end with a properly sized series inductor. Trying to end up with a more or less usable flat - extended response down to the 40 Hz area. This is complicated and obviously my writing skills are not the best. Will try to be as coherent as I can...
I personally assume that a speaker of any design type... intended to reproduce most music in a typical residential setting at or close to live levels must be able to play cleanly at 100 DB level (@ 1 meter) down to at least 40 Hz. Of coarse this criteria is way too much for a small near field computer speaker or the like.... again assuming the main duty of the speaker is as above.... there are caveats of coarse... Theater Pipe Organ 32' stops, home theater very LF sound effects and insane rock music levels would not be within this systems capabilities in the very deep bass. Above 50 Hz or so... this system would eat most residential speakers for lunch in terms of shear output potential. But... you would expect that of a speaker of this physical size with two 15" woofers and an 8" midrange. More on size below.
We need to see if we have enough woofer displacement to meet the design criteria above.... So.... Going to visit Mr. Linkwitz's excellent calculator here.... www.linkwitzlab.com-spl_max1.xls we input some parameters... remember... the calculations produced by the calculator are free space... we need to add 6 DB to the results shown to get in room 1/2 space operating values.
Our total piston area (SD) for the two DC-380's will be 1670 sq. cm., Peak excursion is 5.0 mm, & path difference 410 mm (Approx. 16"). We end up with a F equal of about 140 Hz. With out correction for some driver Q induced roll off.... we see enough displacement to produce 100 DB at 1 meter in 1/2 space in the 40 Hz. region. And the large baffle face I will be building (18" W X 46" tall with 6" - 7" wing depth) will... in practice lower the F3 equal a few additional Hz. Just what happens... but difficult to accurately predict. However... we stick with the conservative Linkwitz calculator predictions. Just for drill... a single Emi Alpha 15" can produce an Xmax limited 93 DB on the same baffle in the same 40 HZ region. One of the nice things going for the dual 15's... the extra displacement really pays off.
Now what Martin King astutely reasons in one of his posts is that the Lower driver Q (relative to the Emi Alpha 15) will not only induce an early roll off... a large series inductor will also add (form a broad peak) likely in the 45- 55 Hz region. However in reality... with the dual 15 operating Q being at least .5... (on that large area baffle... it will be more like .55 to .6), the moderate Q induced roll off will start around the mid 40's. And from the upper 30's it becomes a real factor. From about 45 HZ you start a Q induced rolloff transition from the traditional 6 DB/Octave for an OB to a 9 DB/octave... and below about 37 HZ you transition again to a full 12 DB/octave or higher. Driver FS (F2 in particular) and room boundary distances will effect this to various degree's. However... with my design goals I don't care.
The predicted inductor 45-55 Hz hump on paper is significant... but in reality it rarely is more than 2 or 3 DB with a 0.50 or higher operating Q... you just can't hear it. Exactly why this is I can only guess... and one of these days I will work out an evaluation - measurement test and try to figure it out. With baffle wings we are now in cardioid territory. The only time I found this Hump to be an audible problem is with a low Q Paudio 18" coax on a very large open baffle in a hotel room at RMAF. I suspect the hump issue may be exacerbated with large low MMS cones. Only a hunch.
The long and the short... based on my field experience... I will likely see a 1-3 DB roll off at or around 40 Hz and be 2 DB or so fat in the lower - mid 50's. And we must deal with an inefficient system. 84 DBW... give or take. This is where the single Emi Alpha has a big advantage. It will not play loud down low due to it's SD and Xmax limitations... but it will be close to 9 DB more efficient. Dual Alpha's would be great... but the whole point of Jon Pike's original post was premised on whether the Special $35 priced DC-380 could work for a practical OB system.
Need to work out the mid and high end part of the system... and BTW... the system will be passive... amazingly simple passive. More on that later.
would like to throw these two Jamo drivers in the picture... wonder if they are worth the deal...
Parts-Express.com: JAMO 20392 15" Paper Cone Woofer | JAMO 20392 15" Woofer Treated Paper Cone driver speaker bass
Parts-Express.com: JAMO 20388 15" Paper Cone Woofer | JAMO 20388 15" Woofer Treated Paper Cone driver speaker bass
the 20392 has an xmax of 4 mm and an Fs of 24 Hz... and 93db/W... qts is low.... can this be a substitute for the dayton woofer?
the 20388 has qts of 0.84... hmmm....
4 of those also go at $19 each.... wonder what John, pano and MJK think of these.
Parts-Express.com: JAMO 20392 15" Paper Cone Woofer | JAMO 20392 15" Woofer Treated Paper Cone driver speaker bass
Parts-Express.com: JAMO 20388 15" Paper Cone Woofer | JAMO 20388 15" Woofer Treated Paper Cone driver speaker bass
the 20392 has an xmax of 4 mm and an Fs of 24 Hz... and 93db/W... qts is low.... can this be a substitute for the dayton woofer?
the 20388 has qts of 0.84... hmmm....
4 of those also go at $19 each.... wonder what John, pano and MJK think of these.
I bought two of the heftier looking Jamo 15" and will try them in the H-frames i built. They have a qts of .85 if i remember correctly. I have Alpha 15's in them now. They both appear to be well built drivers. If i can carve out some time (between work and my son preparing for his black belt test, etc.) i will directly compare the sound of the Jamo to the Eminence in H-frames and report back. I have not run the math for the Jamo and will find something to do with it if it sucks... but i suspect it will work well in some future configuration if they fail in the H-frames. I also bought some of the Jamo tweeters and 5.5, 7 and 8" woofers just to play around with and hope to create a 'cheap' Jamo system to enjoy as an alternative to what i have been listening to lately (BIBs using Fostex drivers and a pair of OB speakers using Betsy drivers... different flavors of tasty). Anyway, i already built a pair of speakers using the Jamo closeouts and gave them away to a friend who just moved to a new apptment who needed speakers. They sounded lovely if a little thick and slow compared to what i usually prefer. This may be the Jamo 'house sound'... but not bad at all imo and they certainly play music thru them.
Godzilla
Godzilla
Looks like there may be several of us trying the Jamos. I have four of the 20388's on the way. Their first destination will be a variant of MJK's dual Alpha + FE167 design, with an FE166 standing in because that's what I already own. Looks like they'll need a wider baffle than the Alphas, and still won't go as deep. The Fostex may need to be padded down a tad.
How do you pronounce Jamo, anyway? With a "J", or a "Y"?
Note to Martin - I've heard John's speakers, and they do indeed make bass quite nicely!
Bill
How do you pronounce Jamo, anyway? With a "J", or a "Y"?
Note to Martin - I've heard John's speakers, and they do indeed make bass quite nicely!
Bill
Well remember guys - if those "Yamo" 15s are of a mid Q, you'll need a much bigger inductor than you would use on the Alpha. (tho 2 in parallel would need 1/2 the value of 1 by itself). And you may need to pad down your mid & tweeter to match.
With mid Q woofers on OB you often have to throw away 10-12dB to get the right tonal balance. 2 woofers will help.
Have fun!
With mid Q woofers on OB you often have to throw away 10-12dB to get the right tonal balance. 2 woofers will help.
Have fun!
Here's the current state of my sim for two Jamo 20388's + Fe166E. The baffle is 25" x 40", low pass is 3.5 mH/0.36R + 250 uf, high pass 2 mH/1.18R + 33 uf. All three drivers centered 10" from the outside edge.
The bass rolls off a tad sooner than I see in MJK's Alpha 15/FE103 design, but more gently. Otherwise it looks pretty good to me. The bass won't be an issue if they wind up in the HT system with a sealed sub below 80 Hz.
Whether reality will match the sim, I'll know once I build them. That might be a while, I'm going in for surgery on my left eye next week, and that will have to heal before the sawdust can fly.
Any suggestions?
The bass rolls off a tad sooner than I see in MJK's Alpha 15/FE103 design, but more gently. Otherwise it looks pretty good to me. The bass won't be an issue if they wind up in the HT system with a sealed sub below 80 Hz.
Whether reality will match the sim, I'll know once I build them. That might be a while, I'm going in for surgery on my left eye next week, and that will have to heal before the sawdust can fly.
Any suggestions?
Attachments
Best of luck on the eye surgery - hope all goes well!
My guess - based on what I've done and seen - is that you are going to need a bigger inductor. But that really depends on what the actual Qts of the driver comes out to. I had my doubts about the published specs. The lower the Q, the bigger the inductor you'll need to get a good balance.
My guess - based on what I've done and seen - is that you are going to need a bigger inductor. But that really depends on what the actual Qts of the driver comes out to. I had my doubts about the published specs. The lower the Q, the bigger the inductor you'll need to get a good balance.
Thanks for the sim lousymusician! The Jamo has a lower Fs than the Alpha so i was hoping for more extension but it is what it is. I hope they sound good. Funny how many of us using 'full range' drivers like the Fostex 166, 167, etc have begun adding helper woofers (and sometimes tweeters) and as you mentioned adding a sealed powered sub from 80hz down. LOL, i was thinking similar thoughts with my OB's using Alpha 15's... But the bass IS very satisfying... tactile in fact. In my system it's more about finding the right hand off from the Alpha's to the main drivers. So from a single 'full range' speaker to a FOUR way (sub, woof, full ranger, super tweeter)... at least the crossover is not around 2khz! I expect future projects will use H-frames as 'stands' and plop various 'monitor' type speakers on top of them to hear the latest driver offerings as time goes by. In the meantime, my OB system keeps me company for now and it's nice company even tho it's not as perfect as i'd like.
Good luck in surgery! During recovery you will have time to think about speaker projects among other things.
Godzilla
Good luck in surgery! During recovery you will have time to think about speaker projects among other things.
Godzilla
Dayton DC380-8 on back order....
Just a quick status for the Dayton DC380-8 OB project...
I did order up 4 each of the woofer early Black Friday morning... they were shown to be in stock... but PE... uncharacteristically horsed around and did not enter my order until yesterday... and now the woofers are on B/O until late January. May not see them until early February. So... obviously.... the project will be delayed. I would be interested in hearing from anyone who does receive the 15's as to the T/S parameters they measure... especially any data from WT3. After break in would be best of coarse. I may have some other woofers close to the spec around here to start playing....er.. a designing ... moving toward a three way system.
John
Just a quick status for the Dayton DC380-8 OB project...
I did order up 4 each of the woofer early Black Friday morning... they were shown to be in stock... but PE... uncharacteristically horsed around and did not enter my order until yesterday... and now the woofers are on B/O until late January. May not see them until early February. So... obviously.... the project will be delayed. I would be interested in hearing from anyone who does receive the 15's as to the T/S parameters they measure... especially any data from WT3. After break in would be best of coarse. I may have some other woofers close to the spec around here to start playing....er.. a designing ... moving toward a three way system.
John
Some results .....
For information, these are the results of a quick study I did over the past couple of days comparing the Dayton and the Eminence drivers. I used John's preliminary baffle size (wings assumed to add width to the baffle) and a large series inductior for the Dayton drivers. For the Eminence, I used my standard 2nd order low pass filter. I assumed that Fostex drivers made up the rest of the system.
http://www.quarter-wave.com/Study_Results.pdf
Note, for the single Eminence driver case I increased the input to 2 watts so the system SPL curves achieved the same dB level on the first page. This was only done for the one plot. Everything else uses 1 W input.
For information, these are the results of a quick study I did over the past couple of days comparing the Dayton and the Eminence drivers. I used John's preliminary baffle size (wings assumed to add width to the baffle) and a large series inductior for the Dayton drivers. For the Eminence, I used my standard 2nd order low pass filter. I assumed that Fostex drivers made up the rest of the system.
http://www.quarter-wave.com/Study_Results.pdf
Note, for the single Eminence driver case I increased the input to 2 watts so the system SPL curves achieved the same dB level on the first page. This was only done for the one plot. Everything else uses 1 W input.
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I've now got two Jamos running in a quickie baffle, 24" wide x 40" tall, unbraced 3/4" plywood, no wings. Rough measurements with HOLMImpulse say they are pretty flat to 60 Hz and roll off at about 12 dB /octave below that. They are pretty close to the efficiency of the FE166E, close enough that I need to tweak the crossover considerably before I decide on whether to pad the Fostex down a dB or not. At this point I think they are pretty close to working as planned.
The Fostex is going to need a little more work, I'm getting a 2 octave wide, 5 dB hump centered at 1k, and a narrower one at 3500 that are quite audible. The 1k peak may be baffle related. The next test baffle will be narrower, but with shallow wings. I'll see how that changes things before more crossover changes.
Bill
(Currently working with one eye - the doc says this AM's surgery went well. I'll know more tomorrow. It's very strange being conscious while someone works on the *inside* of your eyeball!)
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