Speaker responsiveness

[AstroSonic]

Quote: "I remember reading somewhere that speaker responsiveness (defined here as the time it takes for the speaker to return to neutral from full excursion) in two otherwise identical speakers is different between the 4ohm and 8ohm versions. I forget which was claimed to be faster (tighter sound?).

Any truth in this?"

4 and 8 ohm versions of the 'same' driver are not really the same. The TS parameters are significantly different. Review the spec sheets for drivers (Parts Express website) and compare 4 and 8 ohm versions of the same driver. You will see that there are more differences than just nominal impedance and Re.

The merits of a particular driver depend on your goals for tone, bandwidth, cab size and maximum volume. If we are really talking about driver damping (Qts), then there really is no direct correlation with the nominal impedance of available drivers and damping. Neither 4 nor 8 ohm drivers are inherently better damped.

Just curious if you have ever heard differences in 'responsiveness', how you would describe them, and what led you to believe that what you heard was due to 'responsiveness'.

 

[Al Kraft]

Quote: "I remember reading somewhere that speaker responsiveness (defined here as the time it takes for the speaker to return to neutral from full excursion) in two otherwise identical speakers is different between the 4ohm and 8ohm versions. I forget which was claimed to be faster (tighter sound?).

Any truth in this?"

4 and 8 ohm versions of the 'same' driver are not really the same. The TS parameters are significantly different. Review the spec sheets for drivers (Parts Express website) and compare 4 and 8 ohm versions of the same driver. You will see that there are more differences than just nominal impedance and Re.

The merits of a particular driver depend on your goals for tone, bandwidth, cab size and maximum volume. If we are really talking about driver damping (Qts), then there really is no direct correlation with the nominal impedance of available drivers and damping. Neither 4 nor 8 ohm drivers are inherently better damped.

Just curious if you have ever heard differences in 'responsiveness', how you would describe them, and what led you to believe that what you heard was due to 'responsiveness'.

Interesting insights as always AstroSonic. As a genuine question (not a challenge or trick), if there are a number of significantly different parameters between 4 and 8 Ohm version of a speaker, does this mean that voicing with a particular cab could also be significantly affected when you get a 4 or 8 Ohm model?

I always assumed (and probably incorrectly) that something like a WA Scout combo that could be had in 4 or 8 Ohm was simply done by substitution of a speaker with different nominal impedance rating. In retrospect that was obviously a foolish assumption as the cab would need to be able to handle either driver and I suppose the driver chosen (4 or 8 Ohm) might actually be different in more ways than necessary to just go from 4 to 8 Ohms in order to perform well in the same cab.

 

[rd2rk]

Just curious if you have ever heard differences in 'responsiveness', how you would describe them, and what led you to believe that what you heard was due to 'responsiveness'.

Never said I could hear the difference, or believed there was one. I read it (here I'm pretty sure) in a discussion about replacing the 4ohm/300 watt BW speaker in an old Peavey Databass (450 watts). They were famous for blown speakers, and that would've taken it down to around 300 watts by itself, and would've allowed me to install an extension jack for a second 8ohm cab. Never got around to it and eventually sold the amp. Don't know what brought it to mind, but thought it an interesting question.

 

[AstroSonic]

Interesting insights as always AstroSonic. As a genuine question (not a challenge or trick), if there are a number of significantly different parameters between 4 and 8 Ohm version of a speaker, does this mean that voicing with a particular cab could also be significantly affected when you get a 4 or 8 Ohm model?

I always assumed (and probably incorrectly) that something like a WA Scout combo that could be had in 4 or 8 Ohm was simply done by substitution of a speaker with different nominal impedance rating. In retrospect that was obviously a foolish assumption as the cab would need to be able to handle either driver and I suppose the driver chosen (4 or 8 Ohm) might actually be different in more ways than necessary to just go from 4 to 8 Ohms in order to perform well in the same cab.

Some of the potentially significant differences are seen in Qts, Le, and Xmax. The lower impedance version often has a shorter voice coil, and so a lower Qts, lower Xmax, lower voice coil mass and lower Le. For example, using the Kappa 15 a (Invalid Link Removed) and c (Invalid Link Removed): The 4 ohm (c) version has a shorter voice coil (with lower Xmax - 2.7 mm) compared to the 8 ohm version (Xmax 4 mm). The 4 ohm version has a greater percentage of its windings (and field) within the gap, resulting in a lower Qes and Qts (0.25 vs 0.33 for the 8 ohm version). The difference in bass response in a given cab depends very much on the cab - volume and tuning. Some alignments are more sensitive to these differences than others. A cab designed for maximally flat response for the 8 ohm driver will be somewhat overdamped (with a higher F3) with the 4 ohm driver. In an attempt to minimize the difference between these versions, the actual impedance is less than the rating would indicate. This can be seen in Re where the 4 ohm version has an Re of 3.7 ohms, while the 8 ohm version has an Re of 5.2 ohms. The 4 ohm version is a 'high' 4 ohms while the 8 ohm version is a 'low' 8 ohms. A look at the impedance minimum, between 100 Hz and 400 Hz will clearly show this, with the 8 ohm version having a minimum of around 6 ohms and the 4 ohm version having a minimum of about 5 ohms. Many players would hardly notice the difference in tone, particularly in highly voiced (bass peaked) designs.

For a player who just wants to change driver impedance (to get full power delivery into a single cab, or to allow two cabs to be used in parallel), they need to assume some difference in the low and mid bass, and in the upper mids and highs. also, the difference in Xmax may add to or reduce the excursion limited power handling of the cab. If the woofer is low passed (crossover) the low pass filter will need to be replaced with an appropriate design. If no low pass filter is involved, the driver can be installed and auditioned. If the bass tone is 'off', then the cab can be modeled and retuned.

Good question about the WA Scout. I wouldn't be surprised if the cab (volume and tuning) was the same, but that the drivers were engineered like the Kappa with a high 4 ohm and a low 8 ohm. I would like to think that the versions were tuned differently.

 

[Al Kraft]

Thanks for the thorough and insightful answer AstroSonic. You're a great teacher!

 

[HaphAsSard]

I always assumed (and probably incorrectly) that something like a WA Scout combo that could be had in 4 or 8 Ohm was simply done by substitution of a speaker with different nominal impedance rating. In retrospect that was obviously a foolish assumption as the cab would need to be able to handle either driver and I suppose the driver chosen (4 or 8 Ohm) might actually be different in more ways than necessary to just go from 4 to 8 Ohms in order to perform well in the same cab.

Good question about the WA Scout. I wouldn't be surprised if the cab (volume and tuning) was the same, but that the drivers were engineered like the Kappa with a high 4 ohm and a low 8 ohm. I would like to think that the versions were tuned differently.

Didn't the Scout cabs have both a port and a passive radiator? If so, perhaps they had identical(ly ported) cabs and two piles of identical radiators with two differently specced weights, one for each impedance version.

 

[AstroSonic]

Didn't the Scout cabs have both a port and a passive radiator? If so, perhaps they had identical(ly ported) cabs and two piles of identical radiators with two differently specced weights, one for each impedance version.

I would like to think something like that: 2 piles. either port tubes or passive radiators.

 

[Al Kraft]

I would like to think something like that: 2 piles. either port tubes or passive radiators.

Actually I think both the 12" versions had a port tube and a passive radiator, as did the 15" versions. However, I suppose someone fairly clever could have found a way to work with fixed volume and made the adjustments with the passive radiator characteristics and/or port dimensions.

 

[Rick James]

4 and 8 ohm versions of the 'same' driver are not really the same. The TS parameters are significantly different.

That's usually true, so that's why I did some searching to find the JBL 2118H and 2118J, which have the exact same specs other than DCR, inductance and impedance.

 

[AstroSonic]

Actually I think both the 12" versions had a port tube and a passive radiator, as did the 15" versions. However, I suppose someone fairly clever could have found a way to work with fixed volume and made the adjustments with the passive radiator characteristics and/or port dimensions.

The tuning can be changed with a different port tube or PR. The port tube would be less expensive.

 

[AstroSonic]

That's usually true, so that's why I did some searching to find the JBL 2118H and 2118J, which have the exact same specs other than DCR, inductance and impedance.

I used the 2118H in small PA cabs designed for voice and guitar/banjo and small venues. They work very well. Not sure how they achieved the same specs. The voice coil inductance is different, with the 16 ohm coil having more inductance. To maintain the same Qes they must have kept the same percentage of windings in the gap (smaller wire?), or increased the gap flux. in any case, they are fine drivers.

 

[agedhorse]

Wire size is different (smaller) on the 16 ohm version. The inductance is different of course, but the important value is the ratio of the inductance to the nominal impedance, often the frequency response curve will differ between versions.

When developing drivers with different impedances, we must always consider a combination of factors. These are the DCR, the winding height, the gap clearance the inductance, the ratio I mentioned above, all with the same motor. It's a juggling act, and sometimes other parameters must be changed (like moving mass) in order to get close enough.

 

[BogeyBass]

I know im getting slower. Not sure if my DCR is near 4 ohms or not

 

[Rick James]

I used the 2118H in small PA cabs designed for voice and guitar/banjo and small venues. They work very well. Not sure how they achieved the same specs.

That's JBL engineering for you, at least back when they did the 2118. JBL had lots of drivers in the 22xx series in different impedance versions, most of them pretty close spec wise, a few identical. The 2225 H&J and 2226 G,H & J are other examples. I bet the reason was since they made their own cabs and wanted to have the same results with different impedance versions of the same cab they took the time to tailor the voice coils to get it.

 

[BadExample]

Never said I could hear the difference, or believed there was one. I read it (here I'm pretty sure) in a discussion about replacing the 4ohm/300 watt BW speaker in an old Peavey Databass (450 watts). They were famous for blown speakers, and that would've taken it down to around 300 watts by itself, and would've allowed me to install an extension jack for a second 8ohm cab. Never got around to it and eventually sold the amp. Don't know what brought it to mind, but thought it an interesting question.

Besides the changes in TSPs, VC depth, tuning getting wrong, and other stuff already brought up, Rick touched on voltage requirements on page 1.

Depending on the amp, this could effect the tone by altering the clipping point of the power section. Desireable or not will also depend on the amp, the system as a whole and the supjective opinion of the player.

More Z means more E to get the same SPL. This can be good if you're a dirty boy, the cab can handle it, and the amp is designed to break up nicely. For me that's another vote for 8ohms... Or even 16.

 

[Al Kraft]

Interesting points BadExample. It would appear that cab impedance differences involves a lot more than just substituting in a different driver and making an appropriate tweak to the crossover. Had I really thought about it, I suppose that should have been obvious.

 

[Al Kraft]

It's a juggling act, and sometimes other parameters must be changed (like moving mass) in order to get close enough.

So thinking back to Rick's post on the first page about the significant level of power available to move a speaker cone (and its connected elements like the VC), from a total system perspective are things like mass, stiffness/compliance of suspension, etc. in the super fine tuning (couple % impact) category, or elements that can make a very significant change in what we hear?

I always assumed (perhaps erroneously) that the mass and the inherent mechanical properties (i.e. spring constant and self damping) of a speaker's moving elements and suspension respectively were quite significant in terms of how a speaker performed/sounded to me as listener. Motor strength and design, VC placement, total excursion, etc. always seemed like something significant.

 

[rd2rk]

Interesting points BadExample. It would appear that cab impedance differences involves a lot more than just substituting in a different driver and making an appropriate tweak to the crossover. Had I really thought about it, I suppose that should have been obvious.

For many of us simple pickers, this electronics stuff is, to paraphrase Arthur C.Clarke, "...indistinguishable from magic".

 

[agedhorse]

Every parameter affects the voicing and LF response. Changing one parameter can improve LF response but negatively impact the voicing. It's a delicate balancing act.

 

[Ben B]

The 4 ohm (c) version has a shorter voice coil (with lower Xmax - 2.7 mm) compared to the 8 ohm version (Xmax 4 mm).

Thanks. I learned something today. I had noticed that many 4 ohm versions of "the same" Eminence driver had less xmax than the 8 ohm version. I wasn't sure why.