[430MAGIC]

So from what I've read in the past, Earthquake SWS 8x seems to be the go-to option for underseat midbass woofers. This is, of course, assuming that no boot "real" sub is going to be installed.

I have booked my car in next week to have the base audio system upgraded to Focal es100k k2 components and a JL audio xd400 v2 amplifier. I'm keeping the OE look by adding HiFi tweeter moldings.

The next stage will be to sort out the bass. I'm debating whether to go with the tried and tested Earthquake SWS or the Audison APBMW S8-4, which are recommended by a well known reputable installer.

What I would like to know is from an acoustical engineering perspective what is the better speaker at reproducing bass frequencies?

I would like an objective (non-biased) opinion based on the acoustical datasheets of each driver.

Earthquake SWS:

Size: 8" high performance sub
Fs: 20-300Hz
Max Power: 300W
RMS Power: 150W
Impedance: 4Ω
Sensitivity: 86.7dB
Qes: 1.372
Qms: 3.158
Qts: 0.957
Rvc= 3.400 Ohm
Sd=22.000m M²
Md= 50.000g
BL=5.837 T-M
No= 0.086%
SPLo= 81.4 dB
Vas= 716.361m Ft3
Cms= 295.150u M/N
Krm= 4.722m Ohm
Erm= 0.687
Mms= 55.805g
Mmd= 53.929m Kg
Kxm= 204.955m H
Exm= 0.257

APBMW S8-4:

Component Woofer
Size mm (in.) 200 (8)
Power Handling
300 W peak
150 W continuous
Impedance Ω 4
Frequency Response Hz 35 ÷ 500
Magnet size D x d x h mm
(in.) 48 (1.89) x 18 (0.71) x 7 (0.28)
Weight of one speaker kg (lb.) 1,21 (2.67)
Voice Coil Ø mm (in.) 50 (2)
ELECTRO-ACOUSTIC PARAMETERS
D mm 159
Xmax mm ±7
Re Ω 3,8
Fs Hz 40
Le mH 0,6
Vas I 21
Mms g 43
Cms mm/N 0,38
BL T•m 6
Qts 0,72
Qes 1,14
Qms 2
Spl dB 88

I'm not an acoustical engineer by any stretch of the imagination but appreciate high-quality sound and do not understand the parameters detailing above, other than power ratings etc.

Any help would be appreciated as I may just go the whole hog on Monday coming!

[RoarinRow]

I've heard good things about both. When I was getting my BAVSound speakers installed the installer said that the Earthquakes delivered deeper bass. He didn't have one that I could listen to. I'm still satisfied with my BAVSound system.

However, for the Audison, I have their 10" subwoofer box in my truck and it totally blows my truck away. The bass and quality is amazing. I bet those APBMW S8-4 speakers would be just as good sound and quality-wise.

[430MAGIC]

Thanks! It's good to know I'm likely going to be satisfied which ever I pick.

Hoping to see if there is a scientific advantage to one of them. If not, it will be down to which is the cheapest and easiest to install!

I know a boot sub will be better ultimately, but I can't lose the space atm.

[Billfitz]

This is the response of the original OEM BMW hi-fi woofer and the others in the same enclosure with the same amp, same drive level, in this case 1.5 volts:



All three are almost identical in the lows below 50Hz. However, most bass content is between 50 and 120Hz, and in that range the BMW driver is decidedly louder. If you're not upgrading the amp the BMW driver is the best of the bunch.

This chart shows the maximum output of those same drivers, which takes into consideration both their electrical and mechanical power limits:



From 70-120Hz the BMW driver remains the loudest. Below 70Hz the BMW and Audison are the same, so there's nothing to be gained from switching to the Audison driver. Below 70Hz the Earthquake is considerably better. However, you won't get that additional output unless you have an upgraded amp that can deliver at least 150 watts per woofer.

This is the type of data comparison that professional audio engineers like myself use to decide on drivers for their projects. I would not invest in any replacement driver, be it a woofer, midbass or tweeter, where I could not do a similar comparison. That requires having the full Thiele/Small specs on the drivers. Luckily for the OP they're available for the Earthquake and Audison drivers, while I measured the specs for the BMW driver myself. Most after market drivers don't list Thiele/Small specs.

[430MAGIC]

That's extremely interesting and useful Billfitz, thanks.

I just want to make 100% sure that your simulated frequency response applies to base systems as well as HiFi systens that are friends in the US get.

The base system has a smaller 6" mid bass driver than the HiFi from what I've read and seen online.

Your graphs would then indicate that my new amp is underpowered to get the extra benefit from the earthquakes opposed to stock drivers. Unless, I bridge the amp and power only the earthquakes. Which means I need another amp to power the focals or to choose another...

Looks like I will see what improvement the 75w RMS brings to the stock driver and make a decision then...

[RoarinRow]

Right, the amp(s) will make all the difference.

[Billfitz]

The Euro/UK bass systems use 6.5 inch woofers, so the results I've shown with the 8 inch OEM hi-fi woofer don't apply. The base system is seriously under powered, so even just an moderately powerful separate amp would make a major difference. The woofers you listed are 8 inch, my assumption is that they won't fit the 6.5 inch enclosures.

[Encanto]

The OEM HiFi woofer response in the above chart does not apply to your Stereo system -those are 8" woofers of completely different construction and response compared to the 6.3" of the Stereo system.

SWS-8 are true sub woofers, the S8-4 are woofers. The SWS-8 will be the closest to a trunk subwoofer that you will get without the trunk subwoofer. What lacks in midbass response -which it is not that much in real life- it makes it up in the sub frequencies. The S8-4 woofers are strong midbass drivers that require a trunk sub to cover the below 40Hz response without distortion.

For your XD amp, SWS-8Xi (2ohms) will perform better than the SW-8X(4ohms). SWS-8 will also fit the best in the underseat OEM enclosures, while the S-8-4 will require a 0.50" spacer to fit -and the OEM grilles cannot be fitted after install. Search and you will find plenty of installs details on these two drivers.

Originally Posted by 430MAGIC

That's extremely interesting and useful Billfitz, thanks.

I just want to make 100% sure that your simulated frequency response applies to base systems as well as HiFi systens that are friends in the US get.

The base system has a smaller 6" mid bass driver than the HiFi from what I've read and seen online.

Your graphs would then indicate that my new amp is underpowered to get the extra benefit from the earthquakes opposed to stock drivers. Unless, I bridge the amp and power only the earthquakes. Which means I need another amp to power the focals or to choose another...

Looks like I will see what improvement the 75w RMS brings to the stock driver and make a decision then...

[430MAGIC]

Originally Posted by Encanto

For your XD amp, SWS-8Xi (2ohms) will perform better than the SW-8X(4ohms). SWS-8 will also fit the best in the underseat OEM enclosures

I'm going to go with the SWS 8, however as I'm using the amp for driving the front focals, I think it's best to get the 4 ohm version ? to keep them wired in stereo and impedance matched...

[Encanto]

Originally Posted by 430MAGIC

I'm going to go with the SWS 8, however as I'm using the amp for driving the front focals, I think it's best to get the 4 ohm version ? to keep them wired in stereo and impedance matched...

So the XD will be driving all 8 speakers? If so then 2ch and 1 crossover of the XD will be wasted on the rear channels.

The best and most effective use of this XD, and any 4ch aftermarket amp, in the Stereo system improvement is to power the front channels with CH1/CH2, and woofers with CH3/CH4 of the XD, and keeping the rear channels powered by the iDrive unit. Then adjust crossovers and gain front/woofers in the XD to taste.

That is exactly what BMW does with their own Alpine OEM retrofit kit, just because it works.

[Billfitz]

Originally Posted by 430MAGIC

I'm going to go with the SWS 8, however as I'm using the amp for driving the front focals, I think it's best to get the 4 ohm version ? to keep them wired in stereo and impedance matched...

That depends on your amp and peripherals. The woofers and midbasses should be separately amplified, with the woofer amp inputs low passed and the midbass amp inputs high passed. The last thing you want to do is to drive the woofers and midbasses with the same amp channel. There's no reason to run the woofers in stereo, as the left/right channel signal content below 100Hz is the same anyway.

[430MAGIC]

Originally Posted by Encanto

The best and most effective use of this XD, and any 4ch aftermarket amp, in the Stereo system improvement is to power the front channels with CH1/CH2, and woofers with CH3/CH4.

This is what my installer will be doing. It's just looking at the amp specs you can either go 2 ohm x4 or 4 ohm x4.

The focals are 4 ohm. So I assume I have to get the SWS 8x rather than the 8xi.

[Encanto]

Originally Posted by 430MAGIC

This is what my installer will be doing. It's just looking at the amp specs you can either go 2 ohm x4 or 4 ohm x4.

The focals are 4 ohm. So I assume I have to get the SWS 8x rather than the 8xi.

All XD are stable down to 2ohms - 2ch can be 4ohms and the other 2ch can be 2ohms. Your planned system calls for a pair of Xi for best bass effect -SWS-8 are not efficient.

[Billfitz]

The difference in the impedance of the midbasses and woofers doesn't matter if they're not being driven by the same amp channel, assuming each amp channel has its own input sensitivity control. Normally one uses the lowest impedance driver that the amp channel is rated for, though that doesn't necessarily make much difference in the end result. In your case with only 75w into 4 ohm capability I would use 4 ohm drivers all around. The problem I see is driving the rear door speakers. I'd be using a six channel amp.

[430MAGIC]

Originally Posted by Encanto

All XD are stable down to 2ohms - 2ch can be 4ohms and the other 2ch can be 2ohms. Your planned system calls for a pair of Xi for best bass effect -SWS-8 are not efficient.

Ok, this makes sense. 2 channels will drive the Focals at 4 ohms 75w RMS. 2 channels will drive the woofers at 2 ohms 100w RMS (that's almost 75% of the SWS 8Xi 150w RMS). Apparently, JL Audio underate their published power figures.

The SWS 8xi will be ordered once I assess the performance of my 1st upgrades( Focals, XD400 v2, front door sound-deading)

The rear speakers will remain powered by the HU. They're high-pass filtered I believe. I've been told with my install and the subsequent Earthquakes, I can leave the rears alone.

Starting to understand this minefield I think..thanks.

[Billfitz]

Originally Posted by 430MAGIC

2 channels will drive the woofers at 2 ohms 100w RMS

Only if you have 2 ohm drivers.

The rear speakers will remain powered by the HU. They're high-pass filtered I believe

I have no idea if that's the case. Technical data about the audio systems is pretty much non-existent. That's to be expected, since as far as BMW is concerned their mechanics have no need for it.

[430MAGIC]

Originally Posted by Billfitz

Only if you have 2 ohm drivers..

Yes, the Earthquake SWS 8xi are 2 ohm:

8" High-performance shallow sub
Power handling: 150 Watts RMS (300 Watts MAX)
2-Ohm
High-temperature voice coil with heat-sink attachment
NOMEX/ROMEX spider assembly
Aluminum bobbin
Protected by 3 U.S. Patents
Mounting depth: 2-1/16"

Originally Posted by Billfitz

I have no idea if that's the case. Technical data about the audio systems is pretty much non-existent. That's to be expected, since as far as BMW is concerned their mechanics have no need for it.
Today 06:10 PM

Makes sense. They only need to swap out OEM components, no need to for any further info other than installation procedure & part numbers.

The rears are high passed I've read, as part of the heavy EQ tuning the base system has - an attempt to compensate for the lack of tweeters.

[Billfitz]

Considering the low sensitivity of the Earthquakes going with 2 ohms is a good idea. I don't think the base HU EQ could be all that much, especially in the bass. EQ eats up power like mad. Every 3dB of boost doubles the power demands on the amp, and the base HU doesn't have much power to begin with. I can't even say if the EQ in the hi-fi and other options takes place in the HU or in the amp, again because there just isn't any technical data out there. I do know that the hi-fi HU is sourced from Harmon, because I saw the Harmon label on it when I had the dash panel off to vinyl wrap it.

[Kevin @ Integral Audio]

Originally Posted by Billfitz

I don't think the base HU EQ could be all that much, especially in the bass. EQ eats up power like mad. Every 3dB of boost doubles the power demands on the amp, and the base HU doesn't have much power to begin with.

You would think, but....there's quite a bit of EQ in the 6-speaker Base audio, and you can quickly see why it falls apart when you turn up the volume. On the order of 10dB (10X power) above average from 50-70Hz is asking a lot of a small chipset amp that is only capable of about 7V max output. It's even worse when you look at how bad the clipping behaviour is.

Note that the front 6.5 underseat and the door mid are paralleled on the front channels.

I can't even say if the EQ in the hi-fi and other options takes place in the HU or in the amp, again because there just isn't any technical data out there.

In the 6-speaker Base audio equipped vehicles, the eq is in the headunit. For the HIFI and h/k and others, it is in the amp, and the HU output signal is flat EXCEPT for the volume-sensitive loudness contour, which takes place in the HU.

I do know that the hi-fi HU is sourced from Harmon, because I saw the Harmon label on it when I had the dash panel off to vinyl wrap it.

Correct, the HU is sourced from Harman Becker. It's actually the same HU regardless of audio system, the differences are all handled thru coding.

[Kevin @ Integral Audio]

Also, I never trust published T/S data. I don't know where those T/S params came from in the OP. The Earthquake numbers were clearly tested by someone (but those are for the 4 ohm 8X, I've pasted the 2 ohm 8Xi below). The Audison numbers look like published data. To be fair I'd trust numbers from Audison alot more than anything from Earthquake (those guys are...disreputable, to put it mildly). We've done extensive testing of most of the available underseats, I've got T/S params for most of them if anyone is interested. What Billfitz says is absolutely correct though, none of the aftermarket woofers will outperform the OEM woofer in terms of efficiency. You can read between the lines for what that means in terms of all the companies selling underseat woofers they claim are louder than the OEM woofers with the factory amp. Physics > Marketing, at least as far as I'm concerned. There is a fundamental trade-off between bandwidth and efficiency - for a given set of constraints, you can play low or you can play loud or somewhere between the two. You can't maximize both. The OEM woofers are crap quality, BUT they are well engineered in terms of being optimized for efficiency.

Also - and I can't stress this enough - T/S params only tell you one thing: they describe the behavior of a driver around it's resonance frequency, i.e. what the roll off of the driver looks like at low frequencies. That's it. They will tell you about the character of the sound at low frequencies, but nothing about the quality of the sound (apart from the freq response portion).

Earthquake SWS 8xi
D 188.0 [mm]
Re 1.85 [Ohms]
Fs 43.07 [Hz]
Zm 14.53 [Ohms]
BL 6.47 [T/M]
Qms 7.038
Qes 1.025
Qts 0.894
Vas 17.200 [liters]
L10k 0.28 [mH]
n0 0.13 [%]
dBSPL 83.17[1W/1m]
Ms 85.93 [grams]
Cms 0.16 [mm/N]

[Billfitz]

Originally Posted by Integral Audio

T/S params only tell you one thing: they describe the behavior of a driver around it's resonance frequency, i.e. what the roll off of the driver looks like at low frequencies.

T/S specs and speaker modeling software are accurate within the realm of pure pistonic response. That generally translates to two octaves above the driver Fs, and all the range below Fs. In the case of a midbass with a typical Fs of 100Hz that's up to 400Hz. Above that you have to use measured response on an EIA standard baffle as shown on the driver data sheets. Where auto sound midbasses are concerned that's a problem, as practically none have driver data sheets. With a sub with an Fs of 40Hz the simulations are fully accurate up to at least 160Hz, which for all intents and purposes is the entire sub pass band.

They will tell you about the character of the sound at low frequencies, but nothing about the quality of the sound

That depends on what you're looking at. If it's only frequency response perhaps, but that's not all that trained engineers look at. Even so, where subs are concerned frequency response and maximum displacement limited SPL account for perhaps 90% of what one might call 'quality'. As my colleague Floyd Toole is fond of saying he has never had a speaker measure good that didn't sound good, and never heard a speaker that sounded good that didn't measure good.

[430MAGIC]

Originally Posted by Integral Audio

Correct, the HU is sourced from Harman Becker. It's actually the same HU regardless of audio system, the differences are all handled thru coding.

Hmmm, this means I could recode my base HU to HiFi or H/K to remove the EQ and get a flat signal.

This would eliminate the need to retune via an expensive DSP (Audison Bit ten) - albeit without other benefits like time alignment etc.

I'm thinking a flat input signal to the amp would make for more accurate sound reproduction. The crossovers for the front Focal tweeters are set to reduce the output (without DSP fitted) otherwise the EQ would be too much (something along them lines).

Most importantly, coding is a lot cheaper!