That's running full range, it can handle much more in this application, since it doesn't have to produce any bass.
🙂
MJK said:
Scottmoose said:
I was more refering to a loss in spl of bass/midbass which happens due to cancellation of front and rear wave, but this apparently doesn't mind (more or less) due to high q of those alpha's and width of the baffle, right? Do you think that such high crossover point could be done with Eminence Beta15 ?
The natural response of a baffle is to roll off the low bass by having the rear wave combine with the front wave destructively, the smaller the baffle the higher in frequency the roll off starts to occur. A high Qts driver will mitigate the roll off to some extent. A lower Qts driver, say less than 1.0, will compond this effect by rolling off the low frequencies just due to the nature of having a low Qts. Unless you use a second amp to boost the low frequencies of a low Qts driver, strong bass response will be difficult to achieve in a moderately sized baffle using passive crossovers.
Sure it can be done, but the Beta will not produce as deep a bass response as the Alpha in the same baffle without a second amp. That is the conclusion I came to in my article and what can be seen in the plots comparing the Alpha, Beta, anf Gamma drivers.
I'm starting a build off of MJK's article, but I'm concerned about having the wide range driver only 30" off the floor. Usually a tweeter is around 42" - won't the soundstage have a funny perspective so low? Any suggestions?
cuibono said:
You usually try to get the HF unit at ear level when seated. Statistically this is 36". I try to target 33-36", but have some happy at 30", any lower and i try for a bit of tilt-back.
Keep in mind that with the beaming typical of a FR you may not want to listen on axis.
Your height when seated in your favorite chair and quite a few other factors play into this.
dave
I guess I'm tall - slouching in a low chair, my ear is a 44"...
But your numbers sound good to me. Can you tilt the baffle back to correct for both HF driver height and time alignment with the LF driver? If so, what is the rule of thumb?
Thanks for the ideas...
But your numbers sound good to me. Can you tilt the baffle back to correct for both HF driver height and time alignment with the LF driver? If so, what is the rule of thumb?
Thanks for the ideas...
MJK said:
Hi,
Maybe a dumb question but would it be possible to position the Beta driver closer to back wall than Alpha?
Peter
If I read the graphs correctly a narower baffle say 16 inches wide and a driver with a Qts of .30, like the Gamma 15, would give you more or less a 12 dB/ Octave slope up to around 500 Hz. If actively crossed over with 12dB slopes at 20 Hz the driver would be pretty flat out to about the 500 Hz range where it would then begin to roll off.
I know the intent of the article was to use passive x-overs but looking at the graphs it looks like the lower Qts driver would be good for active x-overs and bass output toward 20 or 30 Hz.
Great article by the way. I was having difficulty getting the results I desired using a closed box and actively crossing at 20 to 30 Hz because the woofer wouldn't extend high enough, about 200Hz, to mate with my midrange driver. The article has renewed my interest in my current drivers. Can you smell the sawdust?
BDP
Thanks for the positive feedback.
Once you add an active crossover and more amps a number of different trade-offs become available. A low Qts driver can be used for bass but recognize that more power is required and the associated problems with pooring more power into a driver's voice coil need to be considered. For right now, I am concentrating on passive OB systems becasse that is what I think most DIYers would be interested in building. I have a couple of desings that are a little more high end that I hope to build, measure, and document.
I have three identical 200 W SS amps and a digital crossover so eventually I will return to putting together a system that takes advantage of that collection of gear.
That could be simulated and investigated further, I don't know off the top of my head. You could give it a try if you are really intersted.
Sure, I think some tilt would be acceptable. I have no idea what the max tilt would be before you run onto problems.
If you are 10 feet from the speaker and the driver is 14 inches (44 - 30) below ear level.
atan(14/120) ~ 6.6 degrees
which is not too big of a tilt. I bet it would work just fine.
The speakers that my friend and I built are being tilted back via the "L" brackets on the baffle connected to the base in such a way that the 103's are directed right at the listener's head.
I can personally attest that in the early hours of operation, this might not be... optimal.
I heard them for the third time again yesterday and there was a significant improvement. I'm trying to not go over there too often to avoid my ears "getting accustomed" to the sound the speakers are producing. Despite some assertions that full range drivers don't break in in the sense that some claim, I'm finding that they do - and it takes a long time, unfortunately. I'm holding off on modifications to the drivers so that the changes noted will be due to the mods and not break in, but I won't be able to hold off much longer. I feel the itch to tweak...
🙂
I can personally attest that in the early hours of operation, this might not be... optimal.
I heard them for the third time again yesterday and there was a significant improvement. I'm trying to not go over there too often to avoid my ears "getting accustomed" to the sound the speakers are producing. Despite some assertions that full range drivers don't break in in the sense that some claim, I'm finding that they do - and it takes a long time, unfortunately. I'm holding off on modifications to the drivers so that the changes noted will be due to the mods and not break in, but I won't be able to hold off much longer. I feel the itch to tweak...
🙂
The MJK baffles are now at my house, in a familiar acoustical setting. The FE103s need to be attenuated 2 or 3 dB. I grabbed some 2 watt 22R and 1.8R resistors and soldered them in. BIG difference. I'm sure the values are not optimal (I happened to have them), but the attenuation is required IMHO. Try it, you'll see.
best regards,
PSz.
EDIT: I just remembered this from Martin's article:
"The other interesting feature of Figure 3 is the apparent 92 dB/W/m efficiency of the Fostex FE103E driver. For this study, assume that this portion of the SPL response will be 2 dB lower matching the manufacturer’s data sheet."
best regards,
PSz.
EDIT: I just remembered this from Martin's article:
"The other interesting feature of Figure 3 is the apparent 92 dB/W/m efficiency of the Fostex FE103E driver. For this study, assume that this portion of the SPL response will be 2 dB lower matching the manufacturer’s data sheet."
MJK said:
Hi Martin,
First I'd like to thank you for a very informative article.Info about OB's is scarce is general, there are not many explanations around,(besides Linkwitz lab) and we are hungry for more knowledge in this area. Still lurking in the dark, we hope that you and Nelson Pass will pave the way for us...
Regarding passive vs. active OB's, I think that passive OB's may not be much more appealing than active ones. At least it is not for me. First, I have a spare SS amp, and it shouldn't be more difficult for the most DIY-ers to obtain a second SS amp. Then we would need an active crossover,and we are done. Almost. That what I thought when I stated building my OB's. Look here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=110452
I don't want to hijack this thread, but I'd greatly appreciate an article and a thread about active OB's and trade-offs involved there...
I still did not manage to get mine to sound good, and I am still scratching my head...
Hope I am not asking too much,but could you please run a simulation of that OB (Visaton b200+Eminence Beta 15 on a Visaton NO box baffle) and give a hint about a crossover points/slopes that might work?
Sorry if I am behaving like a kid who'd like to eat the pie before it's baked...
Regards,
Vix
Vix,
I think you should run the simulation(s), the tools are available for a very modest fee. Either my worksheets or John K's spreadsheet would probably do the job nicely. Then you can simulate over and over again and make changes to see what works and what does not work. No more wandering in the darkness. You would learn much more that way compared to me doing the simulation. It is really very easy to do these calculations.
I have two more passive designs I am working on. I will most likely do the full build and measure job before making them avaialble, please don't hold you breath I work very slow in the building phase. Then I will most likely look at active options. But I still believe that a passive design will attract more DIYers then an active design.
I think you should run the simulation(s), the tools are available for a very modest fee. Either my worksheets or John K's spreadsheet would probably do the job nicely. Then you can simulate over and over again and make changes to see what works and what does not work. No more wandering in the darkness. You would learn much more that way compared to me doing the simulation. It is really very easy to do these calculations.
I have two more passive designs I am working on. I will most likely do the full build and measure job before making them avaialble, please don't hold you breath I work very slow in the building phase. Then I will most likely look at active options. But I still believe that a passive design will attract more DIYers then an active design.
I had a couple of spare Fostex 108E Sigamas so I decided to try Martin’s OB project. Sweeping a sine wave through the speakers confirmed my initial listening impressions. First, the bass wasn’t as low as I expected it to be. In my room, it starts rolling off at about 60 Hz. However, if I turned up the bass control on my pre-amp all the way, the bass goes even lower than my 166esr swans. Second, I noticed that the Fostex driver was too loud – it definitely needs an L-pad. Even without the L-pad though, I prefer these speakers over my swans. They already show signs of greatness! Thanks Martin, for a nice introduction to open baffles. I am now addicted to OB!
Out of curiosity (I also plead temporary insanity for trying to get another octave of bass), I ordered four Lambda 15 inch dipole drivers from Acoustic Elegance. They have an Fs of 21.7 so they should give me all the bass I could want...as long as I use active EQ.
Sincerely,
Rich
Out of curiosity (I also plead temporary insanity for trying to get another octave of bass), I ordered four Lambda 15 inch dipole drivers from Acoustic Elegance. They have an Fs of 21.7 so they should give me all the bass I could want...as long as I use active EQ.
Sincerely,
Rich
MJK said:
One vote for the passive version. My wish is they will have higher sound fidelity but not much bigger size. Which also mean high WAF.
😀
Sam
May I point to my recent design along the lines of MJK's article and also with the help of his Math Cad models: http://www.audiocircle.com/circles/index.php?topic=46951.0 .
It may be of interest.
/Erling
It may be of interest.
/Erling
Anyone else have a go at this? My Alphas arrived damaged so I'm stuck at the starting gate. (To the credit of Parts Express, they shipped me a new pair the same day I called them to report the problem.)
Scott.
Scott.
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