|26th March 2008, 08:45 PM||#31|
Join Date: Mar 2008
This is getting to be fun!
I definitively see your your point for operating the midrange outside the baffle step area so to speak.
I guess my consideration for crossing the midrange over low comes from another angle....
In the 200-2kHz range, the ear identifies the direction of sound by time, i.e. the time difference between a sound reaching each ear.
So my "philosophy" is to use one driver (midrange) dedicated to handle this frequency range. Making two (or more) drivers share this range will inevitably reduce the quality of the stereo imaging.
A bit less scientifically, my second rationale is that the transient response in the lower midrange is probably best reproduced by a smaller unit with a lighter membrane.
As I'm planning for a 3-way active set up, I expect to be able to manage baffle step issues with the help of electronic filter equalization.
And at the end of the day, I'm not striving for a perfectly flat frequency response (room acoustics mess that up anyway), dynamic response and good stereo imaging is more interesting.
Very interesting to learn that you got a F3 of 25 Hz in a 140L box!
That would be great!
Why didn't I get that result from my simulation and what software were you using to model??
The original midrange of the speraker is a SEAS 4,5 unit.http://www.seas.no/images/stories/vi...aheet/h143.pdf
I must admit that the response curve for this unit looks incredibly flat and the efficiency is also good. However, considering the fact that it falls short on low frequency capacity (for my intended use) and the fact that a number of interesting new (and presumably better) midrange units have been developed over the last 30 years, they will have to go.
The tweeter is an early SEAS dome long since discontinued, probably this one.http://www.seas.no/images/stories/vi..._dome_h107.pdf
I have allready decided to try the new Seas DXT tweeters.
Now, for a new midrange, I'm currently a bit lost....
I'm strongly leaning towards SEAS units since I know that they are generally high quality. Also, there is an element of patriotism I must admit, and having an all-SEAS design seems kind of cool..
There seems to be a lot of reference out there in terms of frequency response and distortion, but how can one judge a drivers capability of giving good transient response??
This one looks interesting though...
Efficiency match is not the prime concern, again an active design gives me some room for adjustments here, but as I'm looking to design a system capable of effortlessly reproducing dynamic music at "realistic" sound pressure levels, a total slouch efficiency wise is not necessarily all to desirable. (using two midranges in stead of one migh be a way out though...)
|26th March 2008, 09:33 PM||#32|
diyAudio Member RIP
Join Date: Nov 2003
Location: Brighton UK
No. the port tuning frequency I reckon is best is ~ 25Hz.
f3 is 40Hz, f6 is 30Hz and f10 23.5Hz.
FWIW I do not think the midrange unit is shabby, the problems
and solutions have not changed much, though troels g does
suggest the MCA15, which has a very similar reference efficiency.
Tweeters though have definitely moved on. 27TDFC is very good.
We obviously do not see eye to eye as to the point of a large
efficient speaker. With lots of power on tap in a active 3-way
TBH I cannot see the utility over a proper subwoofer driver.
Now if your amplifier was :
You'd kill for a large efficient 3 way with great bass.
Going nowhere near the bass driver limits ? Who cares ?
That is not the point ....
|26th March 2008, 10:15 PM||#33|
Join Date: Mar 2008
Oh! My stupid, and I can't even figure out how to edit my post to get rid of that extra http!
Anyway, those interested enough are probably capable of editing the URL as required....
Yes, the midranges are as far as I can judge fairly good units. After all, mine were manufactured back in '78 and I believe its perhaps only a couple of years since they were discontinued by SEAS. A design running for almost 30 years must have had something going for it!
As you say, there has probably been few quantum leaps in midrange technology over the past years, perhaps except for the more (seemingly) successful metal cone designs.
I decided to go for the DXT tweeter as I find the directivity control feature very interesting.http://www.seas.no/index.php?option=...184&Itemid=179
Perhaps not so much not seeing eye to eye as having different priorities towards one wants from a speaker system....
At the moment I have Two Coral flat8 fullranges in voihgt horns assisted by Coral H-24 horn tweeters above 8kHz, and an active sub crossed over at 80Hz. Absolutely not linear and probably full of other flaws, but very engaging and dynamic reproducers of music!
You might say I'm looking to achieve something with the same level (or perhaps even better) dynamic transient response together with improved stereo imaging and power handling offered by 30 year newer technology.
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