Ask an Acoustic Engineer (me)

[MegaG]

Thanks for the quick response, the tweeters haven't been installed yet as I was actually trying to get a baseline and make sure everything was ok before I install them. So far the midbasses look fine. I even ran the factory speakers through DATS.

I've only heard the sweeps from the DATS and some music (fullrange) at very low volume when I ran foobar by mistake not realizing my DATS was still connected and it would play right through it. Volume was very low so I don't think it would have been damaged by the full freequency range it saw and what I heard was too low to judge sound quality. This was all after my testing so issue existed previously.

The one with the choppy response was from the Buzz and Rub test which I have ran several times, the Fs may change but the results don't, I will get one value well below spec and one near it and the driver will fail (failure is based on repeatable from one to the other based on a set tolerance, I was using the standard tolerance of 40% for Fs, its 100% for Zmax)

I bought them through Crutchfield so shorterm I may just get them wired up to test in the car sitting on the dash before I even modify the A-pillar, long term, I've been thinking about getting a 12V system set-up in the shop, so far I just haven't wanted to invest in the power supply because I would want something large to run Amps, not just a HU.

Thanks for your insight, I definitely need to give them the benefit of the doubt until I get them installed and dynamically tested properly...

[DirtyBumOAK510]

Do ohms affect sound quality?
For instance, if one was to run a Stevens Audio MB-6 2 ohm vs 4ohm version, is there a difference that only has to do with ohms?
I realize many subwoofers have DVC versions and D2 has a different t/s than a D4... But is there an inherent loss that happens when choosing to run a d2@ 1 ohm as opposed to 4 ohms?

[Justin Zazzi]

Do ohms affect sound quality?
For instance, if one was to run a Stevens Audio MB-6 2 ohm vs 4ohm version, is there a difference that only has to do with ohms?
I realize many subwoofers have DVC versions and D2 has a different t/s than a D4... But is there an inherent loss that happens when choosing to run a d2@ 1 ohm as opposed to 4 ohms?

That's a tricky question that can be looked at from many angles like efficiency of how tightly packed the voice coil windings can be and what that means, the motor efficiency factor BL^2/Re and how it relates to waste heat generation, damping ratio and influence of speaker wire as the voice coil Re approaches zero, eddy currents and their effects, how the number of turns effects the inductance of the coil, what side effects you get from running your particular amplifier at different impedances, and so on.

Ohms, all by themselves, don't have much to do with sound quality or performance when all else is equal. At the consumer level and even the serious enthusiast level, there are very few tradeoffs that would be noticeable. I can think of only two that we might actually notice:

1) Amplifiers usually make more power at lower impedances, so that's a noticeable thing when you have your woofers wired the right way to take advantage of it.

2) If you have one speaker that comes in a 2Ω and a 4Ω version with all else being equal (or you wire your D2 in 1Ω or 4Ω), then the lower impedance voice coil might have less inductance because it might have less turns. Some people might notice a difference on some particular setups.

Other than that, I think all the other considerations (might?) be important to a designer trying to get every ounce of performance from an exceptionally challenging build, like trying to build a subwoofer inside a laptop.

........ all that said, I would be thrilled to learn something new if you all know something else!

[goatpanda]

I understand that there are many different factors that go into a cone driver's design. But I've been wondering, are there any generalizations (ie: pros/cons) that can be made for different cone profiles? I sometimes see mention of straight, curved, parabolic and flat cone profiles. I bet there are tradeoffs to each (like all things in speaker design), it would be cool to have a basic understanding of why a designer would choose one over the other.

Btw thanks Justin for starting this thread and continuing to respond to it!

[DirtyBumOAK510]

Can two matching drivers share the same airspace in a closed box? I'd searched all around the home audio forums and there seems to be an ongoing battle between this.
Let's say I buy to 10 inch subwoofers, they each call for a half cube. I put both subwoofers in a one cube box. Do you need to separate them with a partition? Or can they share the same airspace? this is also assuming that one of the drivers doesn't blow out and end up working as a passive radiator for the other one....

One thing that is definitely an unknown is whether they share the exact same TS parameters... Which almost certainly they would not.

[rton20s]

Can two matching drivers share the same airspace in a closed box? I'd searched all around the home audio forums and there seems to be an ongoing battle between this.
Let's say I buy to 10 inch subwoofers, they each call for a half cube. I put both subwoofers in a one cube box. Do you need to separate them with a partition? Or can they share the same airspace? this is also assuming that one of the drivers doesn't blow out and end up working as a passive radiator for the other one....

One thing that is definitely an unknown is whether they share the exact same TS parameters... Which almost certainly they would not.

I'm sure Justin will be along with a much more detailed answer, but the simple answer is yes. Two like drivers can share the same air space and two drivers in 0.5cf each is approximately equivalent two the two drivers sharing 1.0cf. Also no two drivers will have exactly identical T/S parameters across the board, but any drivers made under decent QC standards should be "close enough" across the line.

[Jdunk54nl]

I'm sure Justin will be along with a much more detailed answer, but the simple answer is yes. Two like drivers can share the same air space and two drivers in 0.5cf each is approximately equivalent two the two drivers sharing 1.0cf. Also no two drivers will have exactly identical T/S parameters across the board, but any drivers made under decent QC standards should be "close enough" across the line.

Any speaker can share the same airspace as long as the airspace takes into account how much each needs. It isn't as simple as one would think though. For same drivers working together it seems you can just multiply the airspace by number of drivers. For different speakers, it becomes harder.

I know the few bookshelf speakers that I was looking at making, all of the speakers shared the air space. This is fairly easy in a 2way setup with a tweeter, but throw in a 3 way or a low crossed full band 2way and it becomes harder. That is where I get to be uncertain about how to combine speakers without portioning the box, which seems the easiest solution, but does usually come at a cost of physical size.

[Grinder]

Any speaker can share the same airspace as long as the airspace takes into account how much each needs. It isn't as simple as one would think though. For same drivers working together it seems you can just multiply the airspace by number of drivers. For different speakers, it becomes harder.

I know the few bookshelf speakers that I was looking at making, all of the speakers shared the air space. This is fairly easy in a 2way setup with a tweeter, but throw in a 3 way or a low crossed full band 2way and it becomes harder. That is where I get to be uncertain about how to combine speakers without portioning the box, which seems the easiest solution, but does usually come at a cost of physical size.

While I'm not sure what you mean, and while I'm certainly no expert, I think I can safely state that an open-basket midrange or fullrange, for example, should not share the same airspace with a woofer - lest the cone of said midrange/fullrange be passively acted upon by the positive and negative cabinet pressures created by movement of the woofer cone. I think this is why it is particularly desirable for all drivers sharing the same airspace to be at least nominally identical, so that the forces of each driver are in balance and their cones move actively as one.

I think I've got that at least approximately correct. Looking forward to Justin's expert guidance.

[rton20s]

I'm with Grinder on this one as well. While it isn't uncommon in either home speakers or vehicle applications to have drivers of different designs and purposes to share air space, it is far from "best practices."

Now we just sit back and wait for Justin to show back up.

[RocketBoots]

Please excuse my ignorance. Can a midrange that is part of a set (mid + passive XO + tweet) be switched out for a different mid? Will anything suffer? Thanks.