Something stirs in the Undergrowth

[slowmotion]

I have a sneaking suspicion that you'll end up with an 8" driver and a round low compression midbasshorn to go with the midhorn ......

[rowuk]

My experience with light coned "yellow" 5"-6" drivers has not been good. They do certain things VERY well but have some VERY bad habits too that I was never able to get around. I did have them only in boxes however. The hardest part was the lack of real output around 200-300 Hz - even with a backloaded horn. That type of horn also exhibits transmissionline characteristic and right where symphonic music needs the most, there were problems that I couldn't solve. Actually, I think that the modified Deltalites do much more for me - even over 500Hz.

Thanks for your v.interesting comments. Please post any further results/comparisons you can do .
I can see the bass trade-offs may be complex . In the midrange I'm pretty sure there's something important in this value . There is a sort of very delicate, nuanced delivery on vocals that I've only heard on the light-coned , low RMS drivers like the better Fostex units, AER , and the combination of Supravox/AER, which I really want to have in the system .
However the 416-8B data is very encouraging . I did like the sound of the original Altecs at ETF in Germany .
Like Gary, I will only be running the upper bass / mid driver ( on OB ) over a limited range - in my case even less : about 200 to 1000Hz .

I was looking today for the data on the Tone Tubby, but it seems to have disappeared from their pages ! The Jensen P12N which I've been using for OB experiments comes in at 2.6 approx .

[IslandPink]

I have a sneaking suspicion that you'll end up with an 8" driver and a round low compression midbasshorn to go with the midhorn ......

I see no reason to go back down that route, Jan . The decision has been made . I spent about 3 years on and off trying to get good results out of it. In the light of what we're discussing here, I can't see how reducing the cone motion of a conventional driver even more is going to help the rendition of low-level info, and this is precisely where the sound was at fault. If I could pick an 8" driver with a mylar or aluminium-flexure surround off the shelf and attach it to the horn, it would be a different matter .
If you ( or others ) can make it work, then well done !

[slowmotion]

I could live happily with a 3 way system with 2 x 15" on a large OB,
a good midrange horn + a horn tweeter.

The only reason I want to try a midbass horn is "because it's there".

[IslandPink]

Come over to Wales with a trailer and you can have two almost-finished ones to play with

[Lynn Olson]

My experience with light coned "yellow" 5"-6" drivers has not been good. They do certain things VERY well but have some VERY bad habits too that I was never able to get around. I did have them only in boxes however. The hardest part was the lack of real output around 200-300 Hz - even with a backloaded horn. That type of horn also exhibits transmissionline characteristic and right where symphonic music needs the most, there were problems that I couldn't solve. Actually, I think that the modified Deltalites do much more for me - even over 500Hz.

This is a really good point. Although the resolution and detail of the Lowther-family drivers is seductive, there's a certain lightness of tone that is always there. Piano don't quite have concert-grand scale, male voices lose some depth of tone, and cellos don't sound as full and rich as the real thing. Because it sounds more vivid and interesting, the listener's attention is drawn to the upper end of the musical scale.

This isn't a matter of tonal balance ... it's more a matter of weight, solidity, and tonal depth. This is where 12" and 15" drivers excel, sometimes at the expense of resolution, but that's very much a function of the driver itself. Some big drivers sound dull and flat, while others are lively and full of sparkle.

As for bass horns driven with 5" to 8" drivers, I guess it comes down the tonal qualities of the driver. The horn isn't going to change the "personality" of the driver; it will simply amplify whatever's on the input side of the horn. If it's a Lowther, AER, or Fostex, it will sound like a really big Lowther, AER, or Fostex.

On thing I've noticed is when efficiency goes up, the "responsiveness" seems to go up as well. This seems to happen when BL product is increased, horn loading is employed, or a time-coincident driver array is used.

[waveguide]

My experience with light coned "yellow" 5"-6" drivers has not been good. They do certain things VERY well but have some VERY bad habits too that I was never able to get around. I did have them only in boxes however. The hardest part was the lack of real output around 200-300 Hz - even with a backloaded horn. That type of horn also exhibits transmissionline characteristic and right where symphonic music needs the most, there were problems that I couldn't solve. Actually, I think that the modified Deltalites do much more for me - even over 500Hz.

This is a really good point. Although the resolution and detail of the Lowther-family drivers is seductive, there's a certain lightness of tone that is always there. Piano don't quite have concert-grand scale, male voices lose some depth of tone, and cellos don't sound as full and rich as the real thing. Because it sounds more vivid and interesting, the listener's attention is drawn to the upper end of the musical scale.

This isn't a matter of tonal balance ... it's more a matter of weight, solidity, and tonal depth. This is where 12" and 15" drivers excel, sometimes at the expense of resolution, but that's very much a function of the driver itself. Some big drivers sound dull and flat, while others are lively and full of sparkle.

As for bass horns driven with 5" to 8" drivers, I guess it comes down the tonal qualities of the driver. The horn isn't going to change the "personality" of the driver; it will simply amplify whatever's on the input side of the horn. If it's a Lowther, AER, or Fostex, it will sound like a really big Lowther, AER, or Fostex.

On thing I've noticed is when efficiency goes up, the "responsiveness" seems to go up as well. This seems to happen when BL product is increased, horn loading is employed, or a time-coincident driver array is used.

Lynn, thank you for a very good post along with the previous very good comment from Rowuk. It fits in with my view where I have come up a different side of the pyramid to you. I did say that some people are hung up on Rms. If you know what it is you can use it, but dont intentionally go for high Rms if you dont need it unless say, making a functional PA system. The Rms of 0.44 for the Supraphon is going to come with a penalty. The Altec 416B seems right with the Rms in the lower mid range.

[rowuk]

Actually when I made my chart for 12" speakers, I was surprised that BL, QTS, Fs and RMS did not correlate at all. My experience with BL is that there can be too much energy. That gives the drivers an up tilted frequency response and resonance problems at the upper range of useful frequencies provided by them. That means that I need some type of EQ to compensate for that rising response. That can be acoustic horn EQ or sonically questionable DSP or crossover EQ. Midwoofers with high BL (20 or more) sound really strangled to me......

There is an awful lot to think about before selecting drivers, then you get to listen to them and if you can defeat Beraneks Law for a while, you may even be able to come up with a logical, proper sounding implementation..........

[g3dahl]

That's exactly what I ran into when comparing woofers in my system. When the GPA 416-B sounded so good, I expected the GPA 515-C (stronger motor, everything else the same) to sound even better. It didn't--the rising response came into play. I could have compensated for it, but with the 416 all of the factors seemed to be in perfect balance. So I agree: it's not a simple matter of selecting the driver with lowest Rms.

Of course, using Rms value as a figure of merit didn't ever come into play while considering woofers for use in the system. Instead, it has been a matter of looking back on the results and trying to learn why things came out the way they did. In my case, the subjective audible differences were much greater between the TD15M and GPA416B than what could be explained by the simulations and measurements. Lynn's findings were similar when comparing the JBLs with the GPAs.

Gary Dahl

[Lynn Olson]

Just stumbled across this: http://www.sonicscoop.com/tag/altec-416a/

Not interested in the funky radial/sectoral horn, but the simplified A7 horn section is interesting, along with Steve Durr's comments about directivity-matching (referred to as "Q" in the pro world).

The secret behind the success of the A7 speakers is the high frequency horn which has a relatively high Q of around 15 and likewise so does the horn-loaded low frequency woofer enclosure. This matching of the two horn bells made for an accurate and natural sounding speaker system. Traditionally, it is common to find a high-Q horn such as a radial horn used in most speaker designs with a Q of 12 to 15 and the woofer simply flush mounted in the front board of the enclosure.

This is a complete mismatch, as the low frequency in this configuration has a Q of 1 with little or no directionality match to the high frequency horn, which has very high directionality. Hence the lack of definition in the lower frequencies, and [lack of] smooth transition from the horn to the woofer.

Although the AH425 has broadening directivity in the 700 Hz region (compared to 10 kHz), it's still a long way from omnidirectional. The AH425 is at 4~6 dB down 90 degrees off-axis, and I would guess 10 dB down 180 degrees off-axis. At a guess, the Q at 700 Hz would be somewhere between 4 and 6 (most of the energy goes forward towards the listener).

That makes it a lot more directional than a simple closed-box with a 12" or 15" woofer, which is only slightly directional at 700 Hz, maybe 2~3 dB down 90 degrees off-axis, and maybe 3~4 dB down 180 degrees off-axis.

In simple terms, what do you hear when you walk around the speaker with music playing? Conical horns are almost dead-silent when you're behind them; the room reflections are what you hear, not the direct sound. The AH425, and other LeCleac'h horns have some direct sound when you walk behind them, thus my guess of 10 dB or so.

But direct-radiators (in closed or vented boxes) sound pretty much the same anywhere, just a little duller when you walk behind them. At 300 Hz, they're close to omnidirectional. As a result, they kick more energy into rear and side-wall reflections.

The interesting thing about OB's is they are also more directive than conventional direct-radiators, since they have polar patterns similar to figure-eight microphones.

That said, I'm not in the constant-directivity camp like Dr. Geddes and many of the denizens of the DIY forum. But I do think a sharp frequency-dependent divergence between the total room spectra (the energy radiated into a sphere) and the direct-arrival spectra is cause for concern, since it makes the system harder to balance subjectively.

[steve s]

On thing I've noticed is when efficiency goes up, the "responsiveness" seems to go up as well. This seems to happen when BL product is increased, horn loading is employed, or a time-coincident driver array is used.

My opinion too, is this the acceleration factor, I own far too many vintage drivers, with all of them, the dynamic ability and 'life' to the sound increases with efficiency. I think the mistake made by many is to assume that the acceleration required for the band of the dynamic frequency covered is truly known , if it was i should not find any improvements as efficiency goes up ?

[steve s]

quote="rowuk"]Actually when I made my chart for 12" speakers, I was surprised that BL, QTS, Fs and RMS did not correlate at all. My experience with BL is that there can be too much energy. That gives the drivers an up tilted frequency response and resonance problems at the upper range of useful frequencies provided by them. That means that I need some type of EQ to compensate for that rising response. That can be acoustic horn EQ or sonically questionable DSP or crossover EQ. Midwoofers with high BL (20 or more) sound really strangled to me......

There is an awful lot to think about before selecting drivers, then you get to listen to them and if you can defeat Beraneks Law for a while, you may even be able to come up with a logical, proper sounding implementation..........

I agree with most of that , that rising response is has been well documented Brigg's in the 50's documented it with a chart in one of his books as one of the side effects of increasing motor power.
Nothings without consequence,
I cant say that that high BL driver as mid woofers sound strangled in my experience. Quite the opposite I used goodman's 301's for a while with no issues, a couple of years ago demonstrated at one of our meets an open baffle set up with 12" twin drivers with more a lot more efficiency than the goodman's, that seemed to go down very well.

One of my thoughts on your strangled sound is that the amplification could be an issue, there is a common misconception that the quality of the bass amps is not too important, this has not been my experience,
I'm not sure how you tested your drivers and the amplifiers used, but my view is that as equal(ish) speakers that are armed with more motor power can also be much more revealing in the shortcomings of both what is being fed to them and how they are housed.

[rowuk]

Interesting comments! Maybe some background:
the high BL midwoofers were never used for LF and always had the best amplification that I could provide. Even today, BL with 16 to 20 sounds strangled compared to speakers that get their efficiency with a BL of 10-13 and lighter cones! The issue I believe to be passing the point of diminishing returns. The "too high" motor strength may increase efficiency, but at the same time overdamps the system. The problem is how we view Thiele Small parameters. They are only intended to give us a picture at resonance and perhaps if I would use a midwoofer at resonance, BL could have a positive effect. In the range that I do use the speakers (like horns at least an octave over resonance) the results have not been favorable to sound.

It just turns out to be one of the few parameters that I have been able to correlate to my listening experience. High BL on midwoofers=rising frequency response and restricted sound. I have not found any exceptions out of the Fane, Beyma, Eminence, JBL, Altec offerings.

For many years I have been using a transmission line for the midwoofers tuned to damp the LF resonance peak. I cross over at least an octave above that, so the line is ONLY used for impedance control. The backwave is swallowed in the line. This makes light cones relatively easy to implement as there are no serious resonances in the box to "leak" through the cone.

Never listened to anything from Goodmans.

I agree with most of that , that rising response is has been well documented Brigg's in the 50's documented it with a chart in one of his books as one of the side effects of increasing motor power.
Nothings without consequence,
I cant say that that high BL driver as mid woofers sound strangled in my experience. Quite the opposite I used goodman's 301's for a while with no issues, a couple of years ago demonstrated at one of our meets an open baffle set up with 12" twin drivers with more a lot more efficiency than the goodman's, that seemed to go down very well.

One of my thoughts on your strangled sound is that the amplification could be an issue, there is a common misconception that the quality of the bass amps is not too important, this has not been my experience,
I'm not sure how you tested your drivers and the amplifiers used, but my view is that as equal(ish) speakers that are armed with more motor power can also be much more revealing in the shortcomings of both what is being fed to them and how they are housed.

[steve s]

Goes to show how we all have different ideals in the sound we seek, the lower bl drivers i own may give a nice thud in the lower bass and something in between higher up, but thats not my goal.. unfortunately !

Cheers..

[slowmotion]

Lots of thoughtful posts here lately. I like that.

I have been thinking about IB's for subwoofer use lately.

hmmmm........