Despite what was said earlier, the Alchemy (Fusion 8) has the correct amount of baffle step compensation in the crossover. It was designed on a 25" stand about 3 feet out from the wall and I targeted a flat relatively flat response from this set-up. I also voiced it with my Continuums and used the standard set of CD tracks that I always use when voicing.
The Tempest and the Alchemy are the post popular designs I have done, and many sets have been made by others. The Alchemy was originally designed as a surround speaker for the Tempest and Zephyrs, however many people started using them in 7.2 systems as main speakers too. All of the feedback I have received has been extremely positive.
Jeff B.
Why is it impossible, and why would you not trust the response graph? Yes, I certainly understand cabinet diffraction - I wrote a paper on just that topic if you would like it. I also wrote software to calculate it as well. But, when I design I don't think in terms of whether I am incorporating baffle step compensations or not. I don't even see how to do that unless the whole design was done in a computer simulation. What I do is attempt to take raw measurements, in the speaker cabinet, positioned in a way that I consider to be typical usage for the speaker, and then design for flat frequency response. Since all diffraction, including the baffle step, is included in these measurements, the crossover will automatically result in the correct amount of compensation.
If you are referring to that fact that I maintained reasonably high efficiency as the impossible part, what you don't see are the raw measurement of the drivers and how they behave on the baffle, nor do you see the crossover transfer functions. The Beta 8-A has an unusual frequency response. Rather than a rising response like most other PA drivers, it is fairly flat on baffle. It is also a bit more efficient in the low-end than it is listed at. Looking at my crossover transfer function there is about 4.5 dB of compensation between 200 Hz and 1 kHz. This is the baffle step range, and I typically set the 200 Hz raw level as my reference. This means that the Alchemy requires roughly half the compensation of most other speakers on a baffle this size (as most would be 8 -9 dB).
Sure the graph you posted above has a bit of marketing in it. It is a gated and spliced response. This is pretty typical of what most manufacturers will show. So here's something most of them won't give you:
Here's the raw response of my Fusion 8 Alchemy. It is placed on a 25" high stand, and set out from the wall about 3 feet. The mic is 1 meter away, directly on the tweeter axis. There is no gating and smoothing is set to 1/48th octave in the measurement. It is also not set to any specific input level, so the SPL is arbitrary and does not mean anything. I do not see that it is lacking any baffle step compensation.
Jeff B.
Hi,
Well all I can say publishing this graph :
Is doing you a disservice as its clearly impossible from the Eminence
flat baffle measurements, and your graph is entirely sensible, but
is way lower sensitivity across the board, as it has to be.
Your graph never really gets above 90dB, which is right for
a 95dB bass driver with BSC, whilst the above never drops
below 90dB and is clearly wrong for a BSC'd 95dB driver.
There is a clear (and misleading) disparity in the representation
of senstivitity of the order of 5 or 6dB. The graph in this post
is impossible, and according to you, simply very wrong.
You say your input level is arbitrary, that is dodging the issue,
I'm saying the above graph is not possible with 2.83V/1m,
without some splicing shenanigans that would imply that
the treble level is not set for proper BSC correction, or
is spliced to totally misrepresent the actual senstivity.
rgds, sreten.
Well all I can say publishing this graph :
An externally hosted image should be here but it was not working when we last tested it.
Is doing you a disservice as its clearly impossible from the Eminence
flat baffle measurements, and your graph is entirely sensible, but
is way lower sensitivity across the board, as it has to be.
Your graph never really gets above 90dB, which is right for
a 95dB bass driver with BSC, whilst the above never drops
below 90dB and is clearly wrong for a BSC'd 95dB driver.
There is a clear (and misleading) disparity in the representation
of senstivitity of the order of 5 or 6dB. The graph in this post
is impossible, and according to you, simply very wrong.
You say your input level is arbitrary, that is dodging the issue,
I'm saying the above graph is not possible with 2.83V/1m,
without some splicing shenanigans that would imply that
the treble level is not set for proper BSC correction, or
is spliced to totally misrepresent the actual senstivity.
rgds, sreten.
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Wait, let me clarify - In the raw graph I posted above the SPL means nothing, it's just a number. It has nothing to do with the sensitivity.
The graph posted at DIYsoundgroup is calibrated to 2.83V at 1 Meter, just as it says. It is not lacking in BSC and it does have 93 dB sensitivity. I even measured it with my Continuums and the Alchemy averages 10 - 11 dB higher than the Continuum. Its calibrated sensitivity places it at 83 dB, just as I would expect it to be. Another way to look at it - the Alchemy's compression driver is rated at 106 dB sensitivity. My crossover is padding it down about 13 dB. It all matches up.
I'm sorry that you feel that my response is impossible, but from my perspective it is clearly not and is real.
Hi,
Well it seems there is no real point taking this further :
http://www.eminence.com/pdf/Beta_8A.pdf
Half space the Beta 8 is about 94dB up to 1KHz.
Domestically I can't see that translating to a 93dB
speaker with BSC, about 90dB would be my guess.
Something doesn't match up, and still doesn't.
The graph shows 94dB 100 to 200Hz, no BSC.
rgds, sreten.
Well it seems there is no real point taking this further :
http://www.eminence.com/pdf/Beta_8A.pdf
Half space the Beta 8 is about 94dB up to 1KHz.
Domestically I can't see that translating to a 93dB
speaker with BSC, about 90dB would be my guess.
Something doesn't match up, and still doesn't.
The graph shows 94dB 100 to 200Hz, no BSC.
rgds, sreten.
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From my view the Eminence Beta-8A indeed reaches a sensitivity of 92-93 dB in the Fusion-8 cabinet. That's quite surprising for a driver with 94 dB in infinite baffle.
However, the response below 200 Hz actually is falling and the speaker really needs a subwoofer. This part of the published response graph is marketing and ignores baffle step.
Attachment: Simulation with a sample crossover.
However, the response below 200 Hz actually is falling and the speaker really needs a subwoofer. This part of the published response graph is marketing and ignores baffle step.
Attachment: Simulation with a sample crossover.
Attachments
I don't measure quite the same response for the driver as is shown in the Eminence pdf. When I design I go by my own measurements. Your simulation is not far off from my actual measurement though. Nice job.
You are correct, in free space it is rolling off by 100hz. I tuned it so there is still some output at 60Hz in-room that isn't too far down, but it was always intended to be mated with a subwoofer. I didn't expect it to be used full-range too often.
Keep in mind that when we talk about the baffle step range it it generally from about 150 Hz and above, up to about 1000 Hz. I tend to use 200 Hz as my reference level. If the response is equalized flat above 200 Hz then the compensation is there. In my family room the Schroeder frequency is 193 Hz, so simulations below that point will not show what is really happening in my room, as its acoustics will control the response. This is why the bass is bit stronger in most rooms than it might seem from the simulation. My goal is a balanced sounding speaker in a typical environment. I do still recommend a subwoofer though.
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Hi,
Well it seems obfuscation of the facts is alive and well.
I still don't believe this graph, though I understand peaking bass
alignments can implement some BSC, and very often do so in
many basic commercial speakers, and as ever YMMV.
For sure for low powered amps if a sub is not involved you want
decent efficiency in the low bass, or you will be very stuffed.
That requires big boxes for relatively small drivers.
At low power you can get away with it.
rgds, sreten.
Well it seems obfuscation of the facts is alive and well.
An externally hosted image should be here but it was not working when we last tested it.
I still don't believe this graph, though I understand peaking bass
alignments can implement some BSC, and very often do so in
many basic commercial speakers, and as ever YMMV.
For sure for low powered amps if a sub is not involved you want
decent efficiency in the low bass, or you will be very stuffed.
That requires big boxes for relatively small drivers.
At low power you can get away with it.
rgds, sreten.
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There's no peaking bass alignment. I actually have the bass tuning overdamped. The baffle step compensation is accomplished in the crossover using a relatively large first inductor that creates a 4.5 dB drop from 200 Hz to 1 khz. You're making all of your comments on a response that does not, unfortunately, match what I got for the woofer on the baffle. I haven't played fast and loose with any facts. I have simply shown a spliced half-spaced response curve that is accurate for what it represents.
This assumes that the manufacturers measurements are the correct one. I must say that I trust Jeff's measurements more since manufacturers specs are prone to be misleading and incorrect.
Regards
/Göran
Manufactures are usually pretty good with half space sensitivities though, esp when combined with measured T/S params.
As sreten says, you can't start out with a ≈94dB half space driver and end up with a baffle step compensated design of any more than around 90dB, it simply defies the laws of physics. So something isn't right with the response that shows ≈93dB for the finished speaker.
As sreten says, you can't start out with a ≈94dB half space driver and end up with a baffle step compensated design of any more than around 90dB, it simply defies the laws of physics. So something isn't right with the response that shows ≈93dB for the finished speaker.
Hi,
Well that implies the Beta8 is a stunningly efficient driver,
way better than the Eminence specs, and hits near 99dB
half spaced at 200Hz. Keep digging the hole you are in.
rgds, sreten.
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I'd rather go for a drink with Jeff Bagby, and shoot the breeze about some of his designs, which for understandable reasons he doesn't discuss in minute detail here, rather than argue about minutae. It's all about the sound.
For sure, his Alchemy has some significant bass coil inductance, perhaps around 3mH in the filter though politeness stops me revealing it all further. Pi speakers manage to match an Eminence Beta 8A with a regular 90dB tweeter. I've used Eminence drivers before, and they certainly have some very good qualities. Including vented polepieces.
It's also going to benefit from the significant rise in midrange level that is a result of shunt capacitance. For all that, I think it would be slightly bass light, as is my efficient Sony E44 project
I took on board some of Troels' ideas here: TQWT-
This type of speaker works very well. The corrugated paper surround and acoustically transparent cloth dustcap are good things, IMO. Along with the cone type tweeter. 🙂
For sure, his Alchemy has some significant bass coil inductance, perhaps around 3mH in the filter though politeness stops me revealing it all further. Pi speakers manage to match an Eminence Beta 8A with a regular 90dB tweeter. I've used Eminence drivers before, and they certainly have some very good qualities. Including vented polepieces.
It's also going to benefit from the significant rise in midrange level that is a result of shunt capacitance. For all that, I think it would be slightly bass light, as is my efficient Sony E44 project
An externally hosted image should be here but it was not working when we last tested it.
I took on board some of Troels' ideas here: TQWT-
This type of speaker works very well. The corrugated paper surround and acoustically transparent cloth dustcap are good things, IMO. Along with the cone type tweeter. 🙂
I'm in no hole. I have refrained, but you are the one who doesn't really know what is going on here with this speaker. Everything I have posted has been honest. You have based everything you have said on a picture and what you think must happen, but I don't believe you have worked with the Beta-8, nor measured the Alchemy.
Speaker design has a lot of variables. I have been doing this a long time and there are a lot of my speakers out there with independent measurements on them. I currently design / consult for eight different speaker companies, so there is lot out there. I measured the drivers myself in the box, on a stand. I designed the crossover for flat response; I compensated in whatever way was necessary to achieve that. I measured the final response in a listening room as I would expect the speaker to be used.
I measured the sensitivity under controlled conditions. I have even measured the sensitivity and response of other speakers with the Alchemy. As I said earlier, measured side by side the Alchemy measures a full 10 dB more efficient than the Continuum. The Continuum is an 83 dB LS3/5a type loudspeaker. There are dozens of sets of these out there, and they have been verified. I don't think anyone would find their rating abnormal, but the Alchemy is 10 dB more sensitive than it, not 5 db. That's just a secondary confirmation, that's all.
It would all be much clearer if I posted the raw measurements of the Beta-8 on the baffle, showed the crossover design process and circuit schematic, its transfer functions, and how it all ended up with individual measurements, but since this is a commercial design and those belong to Denovo Audio I'm not going to do that. You're welcome to discuss this with the Engineers at Eminence if you want. I can give you their names. I know them well and have done system design work for Eminence. I work closely with them.
I've shared about all I can. At this point I don't think there is much hope in bringing a clear understanding to this picture. You are convinced that you understand my speaker better than me, and I will just have to let it go at that.
Jeff
A fair reply, Jeff. I'm sorry you've run into some over-critical and perhaps ill-informed comments here. 😱
Can you tell me something before I embark on a wild goose chase? Do you think I have a chance of matching my current favourite 90dB Monacor HT22/8 cone tweeter with an Eminence Beta 8A?
HT-22/8
Can you tell me something before I embark on a wild goose chase? Do you think I have a chance of matching my current favourite 90dB Monacor HT22/8 cone tweeter with an Eminence Beta 8A?
HT-22/8
HaHa, me an' sreten is all friendy these days. We's all workin' as a team toward enlightenment. 😀
Mere toilers in the vinyard an' all that. 😎
But I think there's a point where this whole business starts to make sense. An Jeff is doubtless at that point. Along with Joachim, Lynn, Gornir and Juhazi, who I like a lot, and always read with interest. These guys have really built some good stuff. 🙂
To get back on-topic, there is an aspect of Paul Carmody's Overnight Sensation that makes me uneasy. I think he did it for cost and simplicity, but IMO the 0.22uF tank on the bass coil should have a series resistor around 22R to avoid being overly deep.
Trouble with overly deep notches, which here is to reduce metal cone breakup, is they push up the range above the notch frequency. You're also going to mess up the good phase and energy storage correction that a correctly designed notch can bring.
Trouble with overly deep notches, which here is to reduce metal cone breakup, is they push up the range above the notch frequency. You're also going to mess up the good phase and energy storage correction that a correctly designed notch can bring.
Attachments
I don't really see why not. I'm not really familiar with that tweeter, but I looked at the link. Why is it a favorite, if I may ask? Anyway, it shouldn't be hard to match these two drivers up just fine. There are always trade-offs. In the post by Dissi above he gives a pretty good idea of what I was doing in the Alchemy - to keep the sensitivity as high as possible I give up some bass response (this is not the same as ignoring baffle step, as I am flat to below the step frequency). The Alchemy was originally designed as surround speaker and I expected it to be mated with a subwoofer. The room can help the bass quite a bit though. If I wanted to target more bass extension with the driver then I would likely pull it down a couple more dB. The Beta-8 is not going to give you a lot of bass though. That's just not what it was designed for.
Jeff
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