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Old 6th November 2008, 11:57 PM   #11
jol50 is offline jol50  United States
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One of my trunks when I was building a baffle....
Click the image to open in full size.

Also IB subs only take about half rated max power, they xmax before thermal is an issue. The subs I run are 300rms each and 150rms if IB. I have 420 on all of them and can not xmax them even clipping, but shakes my roof like crazy. My intent was to hit 20Hz and they do. My trunk is about 14cf so these 12s are near getting boxed, if I put some stuff in trunk it starts to tune them higher.

Those 8 ohm IB subs are for HT use IIRC, of course they will work in a car. You have to be careful, an auto IB tuned sub will often account for "cabin gain" and tune it higher for more power handling. If you want 20Hz that is not the way to go. Don't know about you but I can get rid of 20Hz way easier than finding it. Just model them in a huge box like 50cf or so. IB always has a rolloff so subs that are tuned lower are better, until you lose too much efficiency....it is a balance.

A .87cf sealed box with a single 10" took more usable space out of my trunk than these four 12s with mountains more output down low. They are kind of heavy, that is a negative so wanting to try pair of 15 instead should be near same output....which is more than I need actually. If I crank these I can't hear the 4x85rms on the highs, it is not even close.

I've taken a liking to the kenwood class d amps, they are priced right for the power in 800-1K rms area. Not the best amp but not bad IMO when you are talking budget.
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Old 7th November 2008, 04:03 AM   #12
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Quote:
Originally posted by metaverse


Whats the deal with the "Znom : 8ohm"

Quote:
Don't worry too much about impedance.
Seriously, don't sweat it.


Quote:
with the Infinite Baffle setup would I basically be using my trunk as my box - with the Sub in a bracket of some sort right behind the rear seats?
Yep, just like in jol50's pic. True, this will not actually be an IB for the woofers referenced. But, it will be an appropriately sized leaky box.

First, get to know your trunk personally. Remove the bottom carpet, and the trim panel that against your rear seat. Remove the side panel trim, or pull them back so you can see the naked structure you have to work with.

Does your back seat fold down? I had a '92 SE, and that series had a fixed rear seat.

Now, envision a large flat piece of wood against the seat just like in jol50's pic. Measure the area, and note the areas where it you will be able to screw it in.

The '92 had a horizontal brace across the middle of the opening. I was able to attach to that, both sides and the top. The gas tank was under the floor right up against the seat, so no drilling down there.
In addition, there was a small hump on the right side. I had to cut a notch in the baffle to clear that. The baffle was large enough for a 15, with a couple inches clearance top and bottom.

Measure well and look for such details before ordering anything.

There is no need for walls or anything else. You can tweak stuff like that later if you desire, but it's not necessary.

And be warned -large woofers are heavy. The baffle will need to be anchored well and stiff enough to hold up. Your arms will get tired while you are crammed in the trunk holding the woofer up with one hand while screwing it in with the other.

As mentioned, 2- 12's will work, so will 2 or 3-10's. You'll get more punchy bass, less output, and noticeably less around 20Hz from smaller woofers. Those 15's are built with a good balance of low fs, high qts, good efficiency, good excursion, and healthy suspension for large box/IB operation.


After measuring, let us know what you think?

jol:
Quote:
Don't know about you but I can get rid of 20Hz way easier than finding it.
I like the way you said that!
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Old 7th November 2008, 04:03 AM   #13
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Quote:
Originally posted by jol50
One of my trunks when I was building a baffle....
Click the image to open in full size.

Also IB subs only take about half rated max power, they xmax before thermal is an issue. The subs I run are 300rms each and 150rms if IB. I have 420 on all of them and can not xmax them even clipping, but shakes my roof like crazy. My intent was to hit 20Hz and they do. My trunk is about 14cf so these 12s are near getting boxed, if I put some stuff in trunk it starts to tune them higher.

Those 8 ohm IB subs are for HT use IIRC, of course they will work in a car. You have to be careful, an auto IB tuned sub will often account for "cabin gain" and tune it higher for more power handling. If you want 20Hz that is not the way to go. Don't know about you but I can get rid of 20Hz way easier than finding it. Just model them in a huge box like 50cf or so. IB always has a rolloff so subs that are tuned lower are better, until you lose too much efficiency....it is a balance.

A .87cf sealed box with a single 10" took more usable space out of my trunk than these four 12s with mountains more output down low. They are kind of heavy, that is a negative so wanting to try pair of 15 instead should be near same output....which is more than I need actually. If I crank these I can't hear the 4x85rms on the highs, it is not even close.

I've taken a liking to the kenwood class d amps, they are priced right for the power in 800-1K rms area. Not the best amp but not bad IMO when you are talking budget.
Thanks for the info ... And the pic , thats a beautiful sight - ALL THAT TRUNK ROOM!!!

Do you have any other IB subs you would recommend , ones that are less than 8ohms?

I'm loving the idea of the extra trunk room and sound quality but at the same time its seeming like this IB situation isn't quite as straightfoward and easy as I thought ... maybe i'm just getting overwhelmed ...

Either way , i'm thinking if this is something I can easily do than i'm all for it.

Besides that i'm going to just grab the Titanic and a premade box from partsexpress and amp ...

I'm stressing myself out over this LOL. I just want order my stuff and go but at the same time this idea of extra trunk space and using my trunk as the box itself is really holding me in place.

One question about the IB setups - How would I go about sealing off everything ?? Some type of industrial glue or something?
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Old 7th November 2008, 04:16 AM   #14
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Quote:
Originally posted by metaverse



I'm loving the idea of the extra trunk room and sound quality but at the same time its seeming like this IB situation isn't quite as straightfoward and easy as I thought ... maybe i'm just getting overwhelmed ...


One question about the IB setups - How would I go about sealing off everything ?? Some type of industrial glue or something?

Don't stress. Basically, just cut a rectangle-ish 3/4" board with a couple of circles in it, and screw it down. Two 3/4" layers glued together wouldn't be out of line for the big woofers.

No need for sealant or glue, but I do try to cover as much as possible with the board. Don't leave any large gaping holes.

If you want to get obsessive over sealing things up, do it later while enjoying the music.
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Old 7th November 2008, 04:54 AM   #15
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Sorry T, I missed your post while I was posting!

Thanks for sticking with me in this journey ...

Quote:
Originally posted by tsmith1315
Seriously, don't sweat it.
What amps do you have in mind to power that one Dayton 15??

Quote:
Does your back seat fold down? I had a '92 SE, and that series had a fixed rear seat.
I'm 95 percent sure it does NOT. But I will be double checking ...

Area's for screwing into - Am I just looking for wood and plastic and thin metal ... What should I be on the look out for?

:::

On another note , if this baffle thing turns out to be too much for me than I was thinking this for a setup :

Speaker would be the Dayton TITANIC MKIII 12" ...

Amp would be this Lanzar 2 channel - bridged[maybe]:
http://www.parts-express.com/pe/show...number=267-808

And , assuming this wouldn't royally mess everything up , as i've read crappy boxes can do , this 12" vented box [maybe]:
http://www.parts-express.com/pe/show...number=260-630

PS. For all the 2 channel amps i've checked out ... Under the Bridged section is always says "XXX watts MAX @ 4 ohms when bridged"

Should I assume this "MAX" wattage when bridged isn't even close to the RMS , like in any other situation?
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Old 7th November 2008, 05:32 AM   #16
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Quote:
Originally posted by metaverse


What amps do you have in mind to power that one Dayton 15??

Any good bass amp that will give it about 300W or more. I can recommend good old school amps (like the one ppia600 pointed to), but can't comment on newer or class D amps.


Quote:
Area's for screwing into - Am I just looking for wood and plastic and thin metal ... What should I be on the look out for?
Sheet metal only, no plastic. Wood won't be there.

Quote:
Should I assume this "MAX" wattage when bridged isn't even close to the RMS , like in any other situation?
Unfortunately, that seems to be the case these days. "MAX" wattage is a useless figure, and should be completely ignored. RMS is the only way to compare.

Quote:
Speaker would be the Dayton TITANIC MKIII 12" ...
That's a tough 12".

They don't specify a port frequency for that box? It's important, and shouldn't be considered generic. That will greatly influence the low frequency response, as will where/how you place it in the trunk. Maybe PE can give you more details.

I'll look at it in the AM and see approximately what port frequency would give you good low-end extension.
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Old 7th November 2008, 06:34 AM   #17
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Hey Tim ,

I ended up doing some research on the 8ohm driver into a 4ohm amp ...

There was a guy in a post on a different site that said something to the effect of "The amp doesn't have a choice what load its going to take , the speaker determines that" ...

He then went onto say "therefore if you put an 8ohm speaker into a 4ohm amp , it would pretty much cut the RMS in half ..."

Now if thats true ... And I then took what Jol50 said about the RMS of speakers in an infinite baffle only being able to get up to half of their RMS value as it is ...

Then I would need a monoblock amp that could deliver , roughly , 350w RMS@4 ohms to power the 8ohm Dayton 15" to half of its RMS which would be 175 ... and it would be safe and stable and nothing would break or burn ... ???

Or is the halfing of the RMS in a baffle setup only applicable to Jol50's speakers for X reasons ??

:::

All of that aside I took Jol50's advice and started tracking down a Kenwood monoblock class D amp and found this baby for a good price w/free shipping at the same place i'm going to get my Clarion Headunit from :

http://www.onlinecarstereo.com/CarAu...roductID=19352
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Old 7th November 2008, 01:50 PM   #18
ppia600 is offline ppia600  United States
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..Or just get the two channel earthquake like I mentioned above and use an 8 ohm. Then when you get used to that level of bass, you can add another 8 ohm. Seriously, its better to buy a used american made high quality amp than a cheapo new amp. And buying a mono amp is a waste of power if you plan on only running it at 4 or 8 ohms. If you only wanted that much power you could get a better quality amp with lower power for less $.
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Old 7th November 2008, 04:57 PM   #19
jol50 is offline jol50  United States
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Depend on what way you go, with IB you will not need as big an amp. I only say Kenwood because in the realm of budget amps they are actual brand name, one of the few 850/950rms class D you can get used to your door for <100, they seem efficient when I test, use pretty good parts in the high power sections. There are other budget amps too and you are more likely to have problems with any budget amp.

With IB you want more cone area and need less amp. How much output do you need? A 15 in a box is capable of a lot of output, IB less but can give nice SQ and get really low like a large ported. The infinity 12s I have model more output at 20Hz when IB than many subs, that is why I liked them plus they were a deal at the time. If you are talking stock speakers about any 15 IB should put out more than you need, let alone a good 15 like suggested here.

Another issue is if you are going to max out IB subs you need a subsonic on them, some sub amps have them built in I've seen some newer alpines do. Other amps have adjustable, some crossovers and HU have them. If you don't beat it hard as possible then not such an issue.

The only new amp I have bought in last decade I don't like for my use, its that kicker in the photo. It works but high side is not working out for some reason. Subs run great though. I prefer older amps also but like class D for subs, mostly because I can do less power wiring and less power issues to deal with. I would add that under about 4-500rms it matters less and old amps run subs nicely at that level. In all the years I've done this I rarely pick X item and am happy with it in a car, or have to swap to verify it works good, so that is just the way I do my systems. But if an IB sub is not perfect you can EQ or crossover it to a better place. Planning and modeling are great and all, but for me after that its faster to swap stuff.

I like lots of lows, I would model all those 15s in my trunk size and likely pick the one that went lowest unless it had quite low efficiency. In a sense for IB your pick of sub is the box tuning you would do for a box sub. Yes, I have lots of trunk room! I like IB, been running it for long time when I could. For years I ran four 10s on old 12v rated 2x75rms amp, equal to about 2x100 to 125rms in newer amps I'd guess. That was all those 10s would take back then. With IB when it hits xmax you are done, no matter what power you put to it to get there....that is often half or less than rated. That is because you don't have a box to hold the cone back. A more HD speaker will have stiffer spiders and suspension, thus take more power to reach xmax when IB. The Qms can tell you some about that, on the other hand when it gets to xmax you are pushing that much air no matter the power. You can use a larger amp just don't over drive the subs, you have to look at them at max output to see what they are doing....power ratings don't mean anything IB it is all about mechanical movements.
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Old 7th November 2008, 07:37 PM   #20
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Quote:
I ended up doing some research on the 8ohm driver into a 4ohm amp
There isn't really such a thing as a 4 ohm amp. Maybe that's a source of confusion?

Quote:
"The amp doesn't have a choice what load its going to take , the speaker determines that" ...
Correct, in that the speaker system is the load the amplifier will be required to drive.

Quote:
"therefore if you put an 8ohm speaker into a 4ohm amp , it would pretty much cut the RMS in half
For RMS *power*, that's true. The amp is a voltage multiplier that will deliver whatever current is needed to produce the output voltage across the speaker. From Ohm's law, twice the load impedance would require half the current for a given voltage, therefore half the power is delivered.

But, the trees are beginning to obscure the forest...

OK. While impedance is an important consideration in general, a specific target impedance is not when choosing a woofer for a standard car sub application.

First, a 4ohm speaker is not really 4 ohms. Speaker impedance is polynomial function, not a constant. It will vary considerably with frequency, and be at itís highest value at resonance in sealed or IB/OB. Ported or transmission line systems will exhibit two peaks.

Letís look at the spec sheet for that Eminence Lab12, a 6 ohm woofer.

At 100Hz, itís impedance is about 5.5 ohms. Sounds about right, huh?
At 50 Hz, the impedance is just over 8 ohms. What? I thought this was a 6 ohm woofer.
At 40 Hz, the impedance is 11 ohms. OKÖ
At 30Hz, itís 30 ohms. Thatís right, 30 ohms.
And near resonance at 25Hz, the impedance is just over 100 ohms. Hmm.


These values will drop when the woofer is enclosed, as anything that interacts with the cone movement will affect the impedance of the system. For example, in a ported system impedance dips to a minimum (nearly the DCR value) at port resonant frequency where cone motion is at a minimum and motion of the air mass in the port is at maximum.

So, donít nitpick over a couple of ohms when selecting woofers. Other things are usually more significant.

Another side to the storyÖ Speaker efficiency and frequency response.

Doubling the amplifier power theoretically gives you an additional 3dB in output. Conversely, to raise output 3dB requires twice as much input power.

Remember that the earlier comment about sensitivities of those IB 15ís being ~10dB higher at 20Hz? Well, it takes a *lot* of additional power to even out that difference at 20Hz. Even if your amp was only delivering half the power into the larger 15, SPL would be higher in the 20-40 Hz range.

So, donít nitpick over a couple of ohms when selecting woofers or amplifiers. There are exceptions of course, but this situation isnít one of them.

You already have the car. Pick a woofer to fit the car. Pick an amp to fit both the woofer and blend with the rest of the system.

jol50 summed it up well:
Quote:
If you are talking stock speakers about any 15 IB should put out more than you need, let alone a good 15 like suggested here.
They only need to keep up with a stock Bose system. This is supposed to be fun. After it's all in: tweak, learn, and repeat.

And whatever you decide to do, donít spend too much, relax, and enjoy the trip!
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