BLH or FAST - what would you do ?

[Bigun]

I'm looking for some opinions...

I have a flea powered SET amplifier and I like the sound. I may build a more powerful one but we're still talking single digit power levels. My current speakers sound fine, but are not sensitive enough and so I have a good reason to build something

I'm currently thinking of two options:

a) Back Loaded Horn - never heard one before but I understand this route gives the possibility of no cross over, reasonable bass extension, possibility of achieving high sensitivity with large (e.g. 8") driver and plenty of 'presence' - downside is box colourations (tradeoff with box size) and less top end extension due to use of larger driver

b) Full Range AssisTed (FAST) - I'd use the SET to driver a full range, possibly OB or Sealed, bottom end supported by a sealed woofer cross-over at 300Hz and I'd bi-amp using a push-pull or SS amp for the woofer. Worry is introducing a line level cross-over into the equation, lower sensitivity of 4" full range driver, and integration of the two drivers

What would you do ?

[zobsky]

If you're a beginner at this and have a flea power amp, .. I'd suggest the "FAST" approach, .. because

1. it is easier to get a hi-eff midrange / treble enclosure in a small volume as opposed to much larger back loaded horn designs. ..because they are harder to get right

2. its hard to drive a back loaded horn with really low power amps (<1 w). You haven't mentioned what you're amp is though.

3. some back loaded horns tend to have a midbass dip, and if end up with such an issue, it's guaranteed to drive you nuts figuring out why some music sounds so good, while other music sounds thin and hollow.

That said, I'm not a fan of sealed or reflex enclosures, generally speaking. See if you can build mini bass horns to augument the mid ranges.

[ra7]

My ANs on OB sound best with at least 20W behind them. I cross them over pretty low at about 130 Hz. The ANs by themselves are efficient, but you need to shelve them when mating to a woofer that is loosing bass on an OB. Therefore, your low powered amp may run out of juice pretty quickly. Of course, it depends on how big your room is and how loud you listen. With a MiniWatt (2.5W) or even the Delite (6W), the sound becomes strained as you turn up the wick. It gets worse with something like a Jordan or an Alpair.

I would consider the econowave option. They are seriously efficient speakers and are pretty much full range. Cheap, efficient and good sounding. Can't beat that. They will of course not give you the full range driver sound, but will certainly play loud with your SET amp.

[chrisb]

IINM you've got a collection of more than a few amps, exactly which one is your favorite sounding of the bunch?

If you've got room for an OB of some sort ( a la the dual driver format popular after MJK's project ), you're more than half way there.

However not all of us (particularly those with a stable of speakers and amps ) have room for such, and more conventional enclosures may still be most practical.
In which case I'd opine that a FAST with something like FE126E XOd as high as 200-300Hz and at least one smallish woofer per side would deliver a great bang for buck in a small footprint. see Tysen (in this case with FF85K in a small tapered aperiodic TL - but the topology would remain)

[Bigun]

Let me answer a couple of questions. My amp is a DIY amp of course [my CELLINI triode amp - I figure it puts out a solid 1W.

I'm using DIY speakers, I have a few choices but currently I'm using a pair of BRs with tiny drivers of only 85dB sensitivity [MARTELLO enclosure for FR88EX. Even with this set up I find listening a pleasure - but it's mostly operated on full volume in the evening with no kids making noises. I think this means I don't need a lot of volume (my home theatre project is a different story altogether and that's where I use my SS amps).

Of all the amps I've built so far, for casual listening, the tube amp is my favourite, I also prefer it to my commercial amps. And my tube amp is not considered a great tube amp either. My next tube amp will use 6S4S tubes if this means anything and I hope to get something more like 3W+ out of it.

I've tried OBs [Apollo OB - ? and like the sound so this may be worth considering.

I'm not all worried about the challenges of building a BLH, I'd likely choose a proven design to mitigate risk on that one.

The Tysen was in my thoughts when I started this thread.

[chrisb]

I guess the next question would be - do you have a particular driver (make./model) in mind for a potential BLH?

I know a guy who knows a guy with some interesting designs - at least one of which is about as simple as this family of enclosures can get.

[chris661]

Hi,

I'd go with FAST, as it takes away the strain on the full-range driver to play bass. When turned up (ie, the cone starts shifting), the BL of the driver will be all over the place.
Couple that with phase modulation distortion, doppler shift and all the rest of the stuff that might happen when feeding a full-ranger low frequencies, and I think I'd take my chances with a crossover...

Chris (who happens to be running a pair of FE126eNs in small folded Voigt pipes, and a couple of TH subwoofers)

[Bigun]

Originally Posted by chrisb

I guess the next question would be - do you have a particular driver (make./model) in mind for a potential BLH?

I don't have a specific driver in mind yet. The more confident I am in the results the more I'd be willing to spend for better quality. My thought was that for a single driver BLH I'd want to go as large as possible before losing the high frequencies to beaming and other limitations since larger means higher sensitivity (and this is a particularly attractive attribute for my tube amp). My guess is that this means something around 6", maybe even 8" since my hearing cuts off around 15kHz these days. With my limited knowledge I'd probably start looking at drivers I've at least heard good things about such as Fostex, maybe even Lowther, and Radio Shack. Just kidding on the last one

Originally Posted by chris661

Hi,

I'd go with FAST, as it takes away the strain on the full-range driver to play bass.

I had thought that the BLH alleviates some of the strain on the driver by providing adequate loading and at the same time it 'amplifies' the bass so that large excursions aren't necessary ?????

I think for a FAST option I'd still want a fairly large full range driver for high senstivity. I'm now wondering if the arrangement should be OB for the full range driver and sealed for the supporting woofer ?

[Godzilla]

>>> Chris (who happens to be running a pair of FE126eNs in small folded Voigt pipes, and a couple of TH subwoofers)

lol Chris... yes, there are more ways to skin this cat and everyone will have an opinion. Your setup kind of deals with things similarly to fast (i'm not even sure what 'fast' is... a sealed up full ranger with a powered woofer on the side or is the woofer running off the same amp?... sorry i don't know?).

With one watt of tube power you can drive any number of efficient back horns using Lowther, Fostex, Audio Nirvana, etc... The larger designs using larger drivers will be the most efficient. You are probably looking at 95 to 98db per watt. Or you can drive a less efficient smaller full ranger like the fe126 (around 91 or 92db per watt?) and power a woofer with another amp. But i think you will get a different sound with these two types of designs. For some reason it seems one watt should equal one full range driver... but that's just me. Also consider you can always add a powered sub if you build a pair of back horns and maximize bass that way. By doing this, you maximize efficiency, dynamics and scale of the overall sound.

But again, there's lots of things that could be done. An open baffle with an efficient full ranger supplemented by powered woofers works really well too...

Some things to look at:

http://www.6moons.com/industryfeatur...marja/cain.jpg

http://www.sixmoons.com/audioreviews...ffers/cain.jpg

http://diyparadise.com/super12.jpg

[planet10]

Originally Posted by Godzilla

... (i'm not even sure what 'fast' is...

Full Range AssisTed (FAST)

FR + helper woofer. Active or Passive. XO typically <400 Hz. Martin's passive OB is a FAST as are at least one of yours

dave