Hi,
I was asked by a friend why his Madisound BK-20 pair (fitted with TB W8-1808s instead of the Fostex) sounded so different from his previous speakers. Being a scientific fella, he wanted to know if the "different" was "better"... and despite the can of worms, I took a listen.
They sound bad. Off. Displeasing.
So much so that after an ad-hoc test of frequency response, I decided it was a great opportunity to play with the near-field scanner (that I never get to use...) since it is one of the few modules that can be used with a full system. (n.b. I've measured the drive in question free-field before and know it's, QC issues aside, not at fault)
I'm probably not supposed to post the actual graphs and measurements, so my 2-cent synopsis is that the response is very direction sensitive, a few degrees this way or that and the frequency response is all over the place. It's not just beaming, the problem is well down to 400Hz or less, and the best part is that it doesn't just scale with amplitude, it just morphs and changes in a wondrously non-linear way.
So I felt somewhat vindicated, but then wondered if there was anything to be done. I will admit I don't have a lot of back-loaded horn experience.
Is it simple or intractable or somewhere in between? (It did occur to me that swapping out 1808 for 1772 might help?)
I was asked by a friend why his Madisound BK-20 pair (fitted with TB W8-1808s instead of the Fostex) sounded so different from his previous speakers. Being a scientific fella, he wanted to know if the "different" was "better"... and despite the can of worms, I took a listen.
They sound bad. Off. Displeasing.
So much so that after an ad-hoc test of frequency response, I decided it was a great opportunity to play with the near-field scanner (that I never get to use...) since it is one of the few modules that can be used with a full system. (n.b. I've measured the drive in question free-field before and know it's, QC issues aside, not at fault)
I'm probably not supposed to post the actual graphs and measurements, so my 2-cent synopsis is that the response is very direction sensitive, a few degrees this way or that and the frequency response is all over the place. It's not just beaming, the problem is well down to 400Hz or less, and the best part is that it doesn't just scale with amplitude, it just morphs and changes in a wondrously non-linear way.
So I felt somewhat vindicated, but then wondered if there was anything to be done. I will admit I don't have a lot of back-loaded horn experience.
Is it simple or intractable or somewhere in between? (It did occur to me that swapping out 1808 for 1772 might help?)
Could be that using an entirely different driver than the BLH was designed for is at least part of the problem?
You trying to put driver with requirement volume of 60 liters into 3 liters horn's chamber.
1808 designed for bassreflex enclosure, 1772 designed for folded horn, but also requires of 10-15liters horn chamber!
1808 designed for bassreflex enclosure, 1772 designed for folded horn, but also requires of 10-15liters horn chamber!
Oh wow. Just noticed how different the Qts of the 1808 is. Must have measured a 1772 last time and not an 1808. Or there's huge variance?
The 1808 is clocking in at about 0.5...
How are you getting the 10-15 litre number for the 1772?
EDIT: Borrowed a FE206En from a bass-reflex enclosure I forgot I had. Polar response still weird, but not total garbage. Especially if I back the thing up far enough.
The 1808 is clocking in at about 0.5...
How are you getting the 10-15 litre number for the 1772?
EDIT: Borrowed a FE206En from a bass-reflex enclosure I forgot I had. Polar response still weird, but not total garbage. Especially if I back the thing up far enough.
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It depends what it is you are looking at.
1/ The BK20 isn't the greatest example of a folded bass horn on the planet. It's designed to be simple, and produce reasonable midbass with the intended / design driver. It was a Nagaoka design for the Japanese market, which has specific requirements that don't necessarily carry over to other situations all that well.
2/ The BK20 was not designed for the 1808, which is completely inappropriate for that load, as is the 1772 (albeit better, as far as the box goes. Marginally. In the same way that some parts of the RMS Titanic are marginally less underwater than others).
3/ The resulting mismatch of either of those two drivers with a [not all that brilliant, and substantially undersized] bass horn inevitably produces poor results. Laws of physics. The response under anechoic or 1/2 space conditions will be all over the shop; I'm not sure I want to know what it would be like under real conditions.
4/ If you're expecting pretty polar graphs from an 8in wideband driver with sub-cones, forget it. They can do some things well, but that's not one of them. Nor is a ruler-flat frequency response. If that's the criteria, save yourself the time & look elsewhere because this sort of wideband driver isn't going to give you it.
1/ The BK20 isn't the greatest example of a folded bass horn on the planet. It's designed to be simple, and produce reasonable midbass with the intended / design driver. It was a Nagaoka design for the Japanese market, which has specific requirements that don't necessarily carry over to other situations all that well.
2/ The BK20 was not designed for the 1808, which is completely inappropriate for that load, as is the 1772 (albeit better, as far as the box goes. Marginally. In the same way that some parts of the RMS Titanic are marginally less underwater than others).
3/ The resulting mismatch of either of those two drivers with a [not all that brilliant, and substantially undersized] bass horn inevitably produces poor results. Laws of physics. The response under anechoic or 1/2 space conditions will be all over the shop; I'm not sure I want to know what it would be like under real conditions.
4/ If you're expecting pretty polar graphs from an 8in wideband driver with sub-cones, forget it. They can do some things well, but that's not one of them. Nor is a ruler-flat frequency response. If that's the criteria, save yourself the time & look elsewhere because this sort of wideband driver isn't going to give you it.
To add to what Scott said, the BK20 is a well over 2 decade old design from before the genre was revolunionized by pretty accurate modeling software.
The W8-1808 wants a WAY bigger box than the FE206 so performace wil be greatly compromised.
dave
The W8-1808 wants a WAY bigger box than the FE206 so performace wil be greatly compromised.
dave
How do you define 'best' for your application? If you can give us an idea of your size, position, amplifier & taste requirements for an enclosure, we may be able to home in on what might be closest to an optimal solution for that particular situation.
To add to Scott’s query, which dual cone driver? What amp? Size constraints? Capentry skills (what are you willing to tackle)?
dave
dave
I don't understand why. If they're your measurements . . . . . .
I'm not being combative, I just don't understand.
Thanks
Like said, that TB W8-1808 needs a big 125L ported cabinet tuned to 40Hz to be good, not a horn. A smaller sealed can also work, but with less bass response (somewhere in the mid 50's Hz) but even then the box is still 50 to 60L big. So in this horn this will never work.
Hmm, as stated, not use them full-range, but as a wide range mid driver in a three way; otherwise unless there's one I'm not aware of, wait for someone to design the correct BLH.
For small room/near-field apps, one of the full size MLTLs folks have done and drive them with an impedance matching SET amp.
There's other alignments too, from small high power rated to OB, but depends on the needs of the app.
GM