Impact of BL / Force factor on SQ

[Flint]

After some testing of various drivers in prototype speakers (all open baffles) I have observed that high-efficiency pro drivers seem to give a rich texture to the sound--that is, drums on a Kappalite 3015LF woofer make an extra crisp thump, and tapping noises through an 18Sound 6nd430 can really be startling and immediate. For the bass that texture always sounds good, although this woofer isn't ideal for OB.

As for the 6nd midrange, the texture is not always desirable, because it can really brutalize the eardrums on bad recordings. On the best recordings it's as true to life as I've ever heard through a speaker. I don't have a way to measure distortion but Zaph's tests suggest that any unpleasant character from the 6nd is a property of the recording, or maybe something else in the chain.

My question is whether this texture is related to motor force, because logically it seems like it would be a function of cone mass and BL product. For the two drivers I mentioned above their BL vs. Mms is much higher than non-pro drivers. Most non-pro 6-inch mids have a BL of around 6, whereas the 6nd is 11.

For another comparison, the Dayton RS225-4 has a lower BL than the RS225-8. Since these two drivers are otherwise similar, can anyone report whether the 8-ohm version has more precise bass? I have the 4-ohm but not the 8-ohm to test that.

Hopefully I have not completely misunderstood the meaning of force factor. The point here is to be able to use the BL value and any other parameters to judge whether a driver will have a softer/smoother sound or a more vivid texture.

[Pete Schumacher]

Re: Impact of BL / Force factor on SQ

After some testing of various drivers in prototype speakers (all open baffles) I have observed that high-efficiency pro drivers seem to give a rich texture to the sound--that is, drums on a Kappalite 3015LF woofer make an extra crisp thump, and tapping noises through an 18Sound 6nd430 can really be startling and immediate. For the bass that texture always sounds good, although this woofer isn't ideal for OB.

As for the 6nd midrange, the texture is not always desirable, because it can really brutalize the eardrums on bad recordings. On the best recordings it's as true to life as I've ever heard through a speaker. I don't have a way to measure distortion but Zaph's tests suggest that any unpleasant character from the 6nd is a property of the recording, or maybe something else in the chain.

My question is whether this texture is related to motor force, because logically it seems like it would be a function of cone mass and BL product. For the two drivers I mentioned above their BL vs. Mms is much higher than non-pro drivers. Most non-pro 6-inch mids have a BL of around 6, whereas the 6nd is 11.

For another comparison, the Dayton RS225-4 has a lower BL than the RS225-8. Since these two drivers are otherwise similar, can anyone report whether the 8-ohm version has more precise bass? I have the 4-ohm but not the 8-ohm to test that.

Hopefully I have not completely misunderstood the meaning of force factor. The point here is to be able to use the BL value and any other parameters to judge whether a driver will have a softer/smoother sound or a more vivid texture.

I don't think you can pin any one thing to BL. A good design is a good design, and low distortion, especially with a driver suffering very little compression, will certainly impact "realism." So it's no surprise to me that the more efficient 15" pro driver is more able to deliver that "kick" vs. the much smaller RS225. I'd wager that an array of 4 RS225 would be rather impressive from the impact standpoint.

If a higher BL is able to help deliver higher sensitivity along with linearity from the connected cone and surround, then less compression can result and more realism has a chance of being delivered.

[Flint]

Re: Impact of BL / Force factor on SQ

As a matter of fact I have a side-by-side comparison between quad RS225-4 and dual 3015LF. What I was expecting from the 3015 was that they'd have more depth and authority, because they can move so much more air (like 3x at x-max, and 2x the cone surface). In fact there's not a significant difference in low end extension, at least with my prototype OB's. The notable difference is that the RS225's seem to lack the sharp impact definition, which I wouldn't have known was missing if not for the big dual-15 to make the comparison. Now I'm curious whether using the shielded woofers would improve the bass definition, because they have a BL of closer to 8 versus 6.5 for the non-shielded woofers.

[Pete Schumacher]

Re: Impact of BL / Force factor on SQ

As a matter of fact I have a side-by-side comparison between quad RS225-4 and dual 3015LF. What I was expecting from the 3015 was that they'd have more depth and authority, because they can move so much more air (like 3x at x-max, and 2x the cone surface). In fact there's not a significant difference in low end extension, at least with my prototype OB's. The notable difference is that the RS225's seem to lack the sharp impact definition, which I wouldn't have known was missing if not for the big dual-15 to make the comparison. Now I'm curious whether using the shielded woofers would improve the bass definition, because they have a BL of closer to 8 versus 6.5 for the non-shielded woofers.

I'd be amazed if you could really hear a difference at the same power levels between the arrays of RS225

There's no replacement for displacement.

[billfitzmaurice]

Re: Impact of BL / Force factor on SQ

Hopefully I have not completely misunderstood the meaning of force factor. The point here is to be able to use the BL value and any other parameters to judge whether a driver will have a softer/smoother sound or a more vivid texture.

In cases where you have drivers that are quite similar save Bl the higher Bl driver will tend to have higher sensitivity in the upper half of its passband. Very high Bl, in excess of 25, will tend to choke off bass response. There's been a lot of research into ultra high Bl woofers, well over 30, which can allow good bass from very small enclosures. But that bass requires very long xmax, high Pe and lots of power.

[camplo]

"There's been a lot of research into ultra high Bl woofers, well over 30, which can allow good bass"

vs

" Very high Bl, in excess of 25, will tend to choke off bass response"


Thats confusing....

[billfitzmaurice]

It's not confusing at all when you read the entire passage. There's been a lot of research into ultra high Bl woofers, well over 30, which can allow good bass from very small enclosures. But that bass requires very long xmax, high Pe and lots of power.

[Scarface1]

Bl is different with 4ohm and 8ohm speakers but it's the same anyway , i tought it has something to do with the voicecoil length or something but it is almost the same performance at the end

[Paul O]

As a matter of fact I have a side-by-side comparison between quad RS225-4 and dual 3015LF. What I was expecting from the 3015 was that they'd have more depth and authority, because they can move so much more air (like 3x at x-max, and 2x the cone surface). In fact there's not a significant difference in low end extension, at least with my prototype OB's.

That is because they are open bafle, lowend response drops off at the same rate regardless of driver size or type. Yes a larger baffle = a lower corner but that is going to be a rather subtle difference... you could get the same effect by just making the RS225 baffle the same size as the 215 baffle.
But otherwise your observations align with what I have known for decades.. weak assed low sensitivity drivers cannot do dynamic impact the way powerful pro audio drivers do. I think Pete is right that BL alone doesn't account for all of the difference, but it's not just about SD either because as you demonstrated a stack of room heaters still doesn't equal the pro drivers in that regard.

[Steve Lee]

To compare motor strength of different drivers, use this formula: Bl squared / Re = square Newtons / Watt.

What you want in a closed/vented alignment is a driver with high motor force and low Le [inductance] and low mms [moving mass] plus a large Sd [surface area/displacement].

Loop this video from 4:39 mm:ss to 6:08 mm:ss --> https://www.youtube.com/watch?v=JdQ3mLU5zBE

Then watch the whole thing several times - I found it very helpful and concise.

[camplo]

It's not confusing at all when you read the entire passage. There's been a lot of research into ultra high Bl woofers, well over 30, which can allow good bass from very small enclosures. But that bass requires very long xmax, high Pe and lots of power.

So increasing BL in a small box, provides better bass at the limit of Xmax/Pe...
Thus, increasing BL in a large box, provides better bass, at the limit of Xmax/Pe...

That would make sense to me but somehow this is incorrect?

"But that bass requires very long xmax, high Pe and lots of power." - It sounds like BL can drive low end sensitivity down....but thats about it regarding drawbacks. BL also creates a stronger motor better able to deal with pressures fighting the diaphragm at high excursion and high pressure near F of vented designs

Far more interesting to me, is the why, why does a higher BL create lower sensitivity on the bass side? Makes no sense to me. As far as sound quality goes I would say higher BL can create more accurate bass, potentially. Lower Qes giving greater control over the diaphragm in the face of excursion/pressure......When excursion is minimal below 1-2mm.....Le is the dominate factor


ps- lol at my edits....

[billfitzmaurice]

Model a high BL low Qes driver, which pretty much means a pro-sound woofer with nominal sensitivity of 98dB or higher. It's not that high Bl/low Qes drives low frequency sensitivity down, it's that it increases midrange sensitivity without increasing low frequency sensitivity. On the flip side said high BL/low Qes allows the driver to work well without a midbass hump in a small sealed enclosure, with enough EQ to boost the lows, which eats up excursion and power.

[Steve Lee]

^ That makes things more clear, I think.

[camplo]

It's not that high Bl/low Qes drives low frequency sensitivity down, it's that it increases midrange sensitivity without increasing low frequency sensitivity. On the flip side said high BL/low Qes allows the driver to work well without a midbass hump in a small sealed enclosure, with enough EQ to boost the lows, which eats up excursion and power.

2 drivers with the same Sd, everything else similar but one has high and the other has low BL.....both produce the same spl per mm of excursion. Its just the electrical sensitivity that differs.....you are talking about boosting the lows to match the sensitivity of the mids...you could just as easily attenuate the mids to match the sensitivity of the lows

[billfitzmaurice]

Everything else won't be similar, so the system Q and therefore response will be very different. You can boost the lows or cut the highs but either way to reach high output in the lows will require long excursion and high power.