[Billfitz]

If the H-K and L7 part numbers are the same buy whichever you can get for the best price. The higher impedance than the Hi-Fi isn't a problem if you've got the power available to drive them. Performance wise the H-K and Hi-Fi are similar, other than the impedance. The reason why the Hi-Fi have lower impedance is that the Hi-Fi amp has lower output voltage swing, which the lower driver impedance compensates for. The only problem I see with the ribbons, assuming they're otherwise suitable, is mounting them. The DLS look fine, no better than the OEM, but they're a bird in the hand, so I'd use them.

[Zack1uk]

Originally Posted by Billfitz

If the H-K and L7 part numbers are the same buy whichever you can get for the best price. The higher impedance than the Hi-Fi isn't a problem if you've got the power available to drive them. Performance wise the H-K and Hi-Fi are similar, other than the impedance. The reason why the Hi-Fi have lower impedance is that the Hi-Fi amp has lower output voltage swing, which the lower driver impedance compensates for. The only problem I see with the ribbons, assuming they're otherwise suitable, is mounting them. The DLS look fine, no better than the OEM, but they're a bird in the hand, so I'd use them.

Sorry, I want clear, but the l7 and the hifi are different speakers and part numbers. L7 are an aluminium cone. Not sure if the HK are another party number. I've found some other parts and it seems both the all of them are actually 2 ohm and rated to 30w..... My genesis would be putting out 200w into two ohm, whilst the audison ap5.9 would be nearer 75w.

Might revert to using the ap5.9 for the front mids and tweeters and a smaller two channel amp to per the underseat woofers.

[Billfitz]

It's confusing, as I've seen what's referred to as Logic 7 also called Harman/Kardon, Individual Audio and Enhanced Premium, while BMW refers to it as Top HiFi. It seems that the aluminum cones were used in the E series, but not F. Don't sweat the power, what limits output is cone excursion, not the voice coil thermal rating. None of them are going to take more than 40w before heavy distortion occurs.

[F30Mo16]

This is all so confusing to me. I just got a 2016 F30 with Hi-Fi and the bass sucks on a lot of songs. Some songs are good some are bad. Those same songs in my E90 use to give good bass, even on almost anything that got played. I never replaced the 8" subs in my e90 but i did do the bavsound stage 1 speaker upgrades.

I'm really not happy with the F30 bass. What is a quick plug and play? I've seen the bavsound subs but with the e90's people use to say you would have to change the amp as well.

[Billfitz]

The only woofer I've come across that works better than stock is the SWS Earthquake, and it will only work better than stock if powered with at least 150 watts per driver.

[F30Mo16]

Originally Posted by Billfitz

The only woofer I've come across that works better than stock is the SWS Earthquake, and it will only work better than stock if powered with at least 150 watts per driver.

So that means upgrading the amp?

[Billfitz]

It does. Google 'Hoffman's Iron Law'. It will help you understand why the main obstacle to low bass at high levels from our cars isn't the woofer, it's the small enclosure. You can get more output and/or lower response by changing the woofer, but in both cases you also need more power to do it.

[Encanto]

Originally Posted by Billfitz

It does. Google 'Hoffman's Iron Law'. It will help you understand why the main obstacle to low bass at high levels from our cars isn't the woofer, it's the small enclosure. You can get more output and/or lower response by changing the woofer, but in both cases you also need more power to do it.

The enclosure total volume includes the door sills -total volume is about .8cuft. Plenty of subs and woofers play more than fine in that volume.

The problem with OEM bass is not the enclosure volume, it is power and bass frequency response. OEM woofers with aftermarket power can have deeper and louder bass than with the OEM amp. However, OEM woofers are designed for the OEM amp power output and frequency response. So increasing the power and making them play deeper into the bass shows how inaccurate they are. In particular, the F30 woofers (be the 6.5" or the 8") themselves are shallower than in the E90, making them less capable of handling aftermarket power than in the E90 -while keeping the total volume fundamentally the same.

There is no way of having better bass in the F30 than having a trunk sub if OEM/aftermarket woofers are kept powered by the OEM amp, or powering aftermarket woofers with aftermarket power.

[Billfitz]

I know what the total enclosure volume is. I measured the woofer Thiele/Small specs, then I measured its response and impedance in the car, and from that data was able to extrapolate the 0.8 cu ft. enclosure volume. It just happens to be spot on for the best possible results with the OEM driver specs with the available power from the OEM amp. I guess those Harmon-Kardon engineers aren't as clueless as replacement driver sources would lead us to believe, and that's why you're not going to get the fantabulous results they claim by just popping in one of their replacement woofers.

To go lower than stock there are two options. One is a larger enclosure. That option cannot be employed, at least not under the seats. The other is by using a woofer that has Thiele/Small specs that allow it to go lower than the stock woofer in the same size enclosure. The SWS Earthquake has the requisite specs to do so. It's the only driver I'm aware of that does. However, those same specs that allow it to go lower than stock also result in less sensitivity. That's where Hoffman's Iron Law comes into play. That lower sensitivity must be compensated for with more power. And that's why dropping SWS Earthquakes into the car without also increasing the power of the amp driving them to at least 150w per channel would be a waste of time and money.

[johnung]

Originally Posted by Billfitz

I know what the total enclosure volume is. I measured the woofer Thiele/Small specs, then I measured its response and impedance in the car, and from that data was able to extrapolate the 0.8 cu ft. enclosure volume. It just happens to be spot on for the best possible results with the OEM driver specs with the available power from the OEM amp. I guess those Harmon-Kardon engineers aren't as clueless as replacement driver sources would lead us to believe, and that's why you're not going to get the fantabulous results they claim by just popping in one of their replacement woofers.

To go lower than stock there are two options. One is a larger enclosure. That option cannot be employed, at least not under the seats. The other is by using a woofer that has Thiele/Small specs that allow it to go lower than the stock woofer in the same size enclosure. The SWS Earthquake has the requisite specs to do so. It's the only driver I'm aware of that does. However, those same specs that allow it to go lower than stock also result in less sensitivity. That's where Hoffman's Iron Law comes into play. That lower sensitivity must be compensated for with more power. And that's why dropping SWS Earthquakes into the car without also increasing the power of the amp driving them to at least 150w per channel would be a waste of time and money.

Hi Bill,
I appreciate your audio posts. I've got a '15 F30 with the HK system. If I understand correctly, you think the speakers are fine and don't really require replacement. The underseat subs can only be improved in that location by replacing with Earthquakes along with a more powerful amp to drive them.

Assuming leaving the HK speakers in place and swapping the subs for Earthquakes, then what do you see as the amp options? Is there an amp scenario that's relatively plug and play to provide the Earthquakes the power that they need and also integrate with the rest of the HK's? Thanks in advance.

[Billfitz]

I'm not aware of a plug and play amp replacement for the HK, they all seem to be for the Hi-Fi. You should be able to use a generic subwoofer amp with speaker level inputs, driving them with the outputs from the HK.

[johnung]

Originally Posted by Billfitz

I'm not aware of a plug and play amp replacement for the HK, they all seem to be for the Hi-Fi. You should be able to use a generic subwoofer amp with speaker level inputs, driving them with the outputs from the HK.

Thanks for your response. Can you please suggest some specific amp options? It's been decades since I've been involved with car audio so I'm starting from scratch to even know what brands or products to consider. I could really benefit from your experience to determine how to upgrade the HK system by upgrading to the Earthquake subs with a dedicated amp driving them. Thanks.

[Billfitz]

If I was going to buy one this would be a contender:

https://www.parts-express.com/boss-r...fier--265-3983

It's 2 ohm stable, so you can use the Earthquake SWS 8Xi for maximum amp headroom. The wires that normally connect to the woofers from the OEM amp go to the high level input of the new amp. The Boss installation manual should cover the rest.

[Encanto]

Originally Posted by johnung

Thanks for your response. Can you please suggest some specific amp options? It's been decades since I've been involved with car audio so I'm starting from scratch to even know what brands or products to consider. I could really benefit from your experience to determine how to upgrade the HK system by upgrading to the Earthquake subs with a dedicated amp driving them. Thanks.

The HK OEM amp outputs about 35V peak at the woofer channels. The aftermarket amp that you connect directly to those channels must accept up to 40V high-level inputs.

[johnung]

Originally Posted by Encanto

The HK OEM amp outputs about 35V peak at the woofer channels. The aftermarket amp that you connect directly to those channels must accept up to 40V high-level inputs.

Thanks for the heads up. I received a recommendation for the Kenwood KAC-M3100 mono amp. I can end up with 150 watts per sub if I wire two Earthquake SWS-8X 4-ohm subs in parallel. But I can't find any spec about the Kenwood's input voltage. I sent an email request to the Kenwood retailer.

Where do people locate an extra amp in a 3-series sedan installation when the amp is powering the two underseat subs? Ideally I'd like to do an installation where I'm not splicing into BMW cables. This Kenwood amp is pretty small at 6 7/8" wide x 1 13/16" high and 3 7/8" deep. With the battery in the trunk it would seem smart to locate it there, maybe on the left somewhere near the OEM Harmon Kardon amp or on the right near the battery itself. There must be some techniques or materials to mount and hide a small amp?

Then I was wondering if I can run four pairs of speaker wires to the underseat subs. Two pairs would connect to the woofer outputs coming from the OEM amp and the the other two pairs would connect the outputs on the Kenwood amp to the new Earthquake subs. (Maybe someone sells OEM style connectors to make the installation clean?). Of course I'd have to figure out how to take interior pieces apart to figure out the best way to run the wires.

Am I thinking in the right direction or am I way off here? Any input is appreciated.

[onur_sp]

Originally Posted by Billfitz

It does. Google 'Hoffman's Iron Law'. It will help you understand why the main obstacle to low bass at high levels from our cars isn't the woofer, it's the small enclosure. You can get more output and/or lower response by changing the woofer, but in both cases you also need more power to do it.

What do you think about audison apbmw woofers with enough power? or at least giving them 200w rms , is it still gonna be worse than l7 woofers? using them with audison 8.9bit forza amplifier bridged 260w rms but i cant compare with l7's but i guess it should be much better than harman subs.

[Billfitz]

Originally Posted by johnung

Thanks for the heads up. I received a recommendation for the Kenwood KAC-M3100 mono amp. I can end up with 150 watts per sub if I wire two Earthquake SWS-8X 4-ohm subs in parallel.

You're better off with 2 ohm drivers each powered with their own amp channel. An amp with high level inputs shouldn't have a problem handling a high level input. They do so with high input impedance, which reduces the current flow.

What do you think about audison apbmw woofers

They're no better than stock.

i guess it should be much better than harman subs

Why? Where's the data that proves it? If it exists it must be written in invisible pixels.

[johnung]

Originally Posted by Billfitz

You're better off with 2 ohm drivers each powered with their own amp channel. An amp with high level inputs shouldn't have a problem handling a high level input. They do so with high input impedance, which reduces the current flow.

They're no better than stock.

Why? Where's the data that proves it? If it exists it must be written in invisible pixels.

I keep finding mono amps designed to power subwoofers. When you have two separate subs they instruct you to wire them either in parallel or in series. So you are saying that it would be better to buy a 2-channel amp to connect each of the two underseat subs separately and to use the 2-ohm SWS-8Xi.
Why is the 2-channel amp preferred over the two subs wired to a mono amp?

[johnung]

Originally Posted by johnung

I keep finding mono amps designed to power subwoofers. When you have two separate subs they instruct you to wire them either in parallel or in series. So you are saying that it would be better to buy a 2-channel amp to connect each of the two underseat subs separately and to use the 2-ohm SWS-8Xi.
Why is the 2-channel amp preferred over the two subs wired to a mono amp?

I spoke with Rockford Fosgate's technical support. Their model T400X2AD is a compact sized 2-channel amp that will put out two separate 200watt channels into the two Earthquake SWS-8Xi 2-ohm subwoofers.

However the speaker level input ports on the Fosgate amp will handle a maximum of 15v. He said that the maximum on all of the amps that they make is 15v. So if the output from the stock Hartman Kardon amp to the stock underseat subs is really 35v, then a Line Output Converter (LOC) would be needed between the HK amp and the new second amp to reduce the 35v down to under 15v.

He brought up an interesting point. He questioned why a second amp is needed at all to drive the Earthquake subs at 150watts? He said that if the HK amp is putting out 35v to each sub then that must already be at least 150watts. I said that I had read that the HK underseat subs were something strange like 7-ohms. He said that he thought that they were 2-ohms. He said that 18v should roughly equal 150watts.

Has anyone measured or knows definitively if:

1) Stock HK underseat subwoofers are rated at 2-ohms, 4-ohms, 7-ohms or something else?

2) Stock HK amplifier is putting out 35v or something else to each stock underseat subwoofer?

Thanks in advance for any help!

[Billfitz]

Those power amps are primarily intended to drive a single trunk mounted sub, not the dual under seat woofers of a BMW. I could go into further detail covering voltage swing and output device current concerns and more technical stuff that will only serve to cause your eyes to glaze over, but I'll spare you that. But that said the main issue with the SWS subs is that in order to go lower than stock they won't go as loud with the same input voltage. To compensate for that you have to be able to adjust their volume independent of the rest of the speakers. AFAIK the H-K can't do that. I know my Hi-Fi can't. That's where the external amp comes in. As for the 35v thing, I seriously doubt that the H-K amps put out more than 10v on average. No way will they run at 35v continuous, or anywhere near it, as that's 300 watts into 4 ohms, way more than the amp woofer channels are rated for.

[johnung]

Originally Posted by Billfitz

Those power amps are primarily intended to drive a single trunk mounted sub, not the dual under seat woofers of a BMW. I could go into further detail covering voltage swing and output device current concerns and more technical stuff that will only serve to cause your eyes to glaze over, but I'll spare you that.

So basically you are saying that mono amps are designed for one subwoofer, and with two subs the results will be much better to use a 2-channel amp with dedicated 150watt/2-ohm channels to each sub.

Can you provide any clarity on the line voltage that the HK amp (BMW Top Hifi Option 688) is putting out to the stock HK underseat subs, and what the ohm rating is on those subs?

Is using a Line Out Converter between the two amps the only practical solution?

HaHa, having my eyes glaze over makes me feel alive! I live for this stuff! 😀

[Billfitz]

I'd rather two channels working half as hard. The H-K woofers are nominal 4 ohms. You could use a converter to get a line voltage to drive the amp, but it's the same thing as the high level input of the amp. Finding accurate specs on the H-K amp is like herding cats. You would want to run the external amp level high, and keep the bass EQ on the iDrive flat. Each 6dB of EQ boost doubles the amp output voltage, so get the output you want with the external amp, not EQ.