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Old 13th October 2011, 17:45   #1
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Default 8 Ohms Amp

Could someone suggest a car amp capable of 500W or more into an 8 ohm load. Hopefully an amp that has been measured. Bonus points for 6db (2000W) of peak/burst capacity and if the amp is optimized/designed for 8 ohms.

I am aware of the general idea for halving the power output on listed specifications as the impedance doubles but it only works in an *ideal* amplifier, not in reality. I also don't quite trust manufacturer specifications.

I have my eyes on the JBL GTO14001, any inputs/info on the amp and its 8 ohm capabilities would be appreciated. Is its 1200W 4 ohm rating accurate? Seems like the JBL is intended for 2 ohm usage though.

Open to other brands. Budget 20-25k approx. Cheaper is better.

Thanks.
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Old 14th October 2011, 12:16   #2
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Default Re: 8 Ohms Amp

There are no amplifiers which are optimized for 8 ohms, and getting data of the others at 8 ohms is also tough. Whats this 8 ohms bass driver that you want to run on it?
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Old 14th October 2011, 12:29   #3
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Default Re: 8 Ohms Amp

optimised for 8 ohms? I dont get it.

Car audio is usually 4 ohms. Not that an amp that can drive a 4ohm speaker wont drive a 8 ohm speaker in fact it will drive it very nicely (better damping) albeit with a little loss of power.

One thing to remember when using home audio speakers in the car is that car audio speakers have cones and surrounds that are UV treated and can handle the harsh enviroment of a car (dust, humidity, etc..). Home audio speakers do not need to be so rugged.
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Old 14th October 2011, 12:31   #4
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Default Re: 8 Ohms Amp

Never seen a car amp optimized for an 8 ohm load, there may be a few but I'm not sure since I haven't seen one so far. But like Navin said, the jbl amp which is rated at 1200w at 4 ohms will be able to drive the 8 ohm sub at 500w easily.
Which sub are you planning to use? I have seen a few subs that are rated at 8 ohms but these are low powered subs and are meant to be used as a pair, wired in parallel for a 4 ohm load. Rockford P1S812 is one such sub but it's rated at 150 w rms. Never seen a sub that is rated at 500w rms for an 8 ohm load.

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Old 14th October 2011, 13:42   #5
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Default Re: 8 Ohms Amp

I asked for 8 ohms because I wanted to use a pro woofer. Car audio drivers are typically high q and high mms and low sensitivity. The specific driver I had in mind was the 18 Sound 15LW2400 which sounds like a great candidate for a ported box. The reason I chose this driver is because I am looking to maximize my output from 60-120Hz and minimize my output below 40Hz. IMO the low Mms and Qes helps the sound/kick a good bit. To me a pro woofer sounds better and hits harder generally speaking, of course implementation is important. The 8 ohms impedance also is an easier load for the driver,amp and the cars electrical system.

The JBL amp is rated for 1200W into 4 ohms, but I wanted to know if it will actually produce this power? Inflated ratings are common among manufacturers. Conventional wisdom would suggest that the JBL should at least manage 500W into an 8 ohm load even with decreasing efficiency but I wanted to be sure before I went and bought it.
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Old 15th October 2011, 13:02   #6
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Default Re: 8 Ohms Amp

Many years ago, for a similar requirement, I had used two Class AB 2 channel amplifiers in bridged mode to drive 2 Selenium 12" coaxial speakers. It did a decent job, and I knew it was a safe move since its like driving a 4 ohm load in stereo - well within the amp's known capabilities. Cant comment on how the Class D monos would behave with a 8 ohm load. Never tried it.
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Old 15th October 2011, 15:23   #7
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Default Re: 8 Ohms Amp

8 ohms , no way, you can get it. It can be customised.
Contact Sonodyne, it is a kolkatta based co.,
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Old 22nd October 2011, 16:11   #8
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Default Re: 8 Ohms Amp

Thanks for the input B&T.

Could someone confirm the HPF/LPF filter on the GTO14001? Are they both 12db/oct Butterworth filters?
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Old 27th November 2011, 17:59   #9
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Default Re: 8 Ohms Amp

Anyone? Would really help if someone could tell me the filter types on this amp.
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Old 28th November 2011, 16:50   #10
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Default Re: 8 Ohms Amp

Quote:
Originally Posted by 1420 View Post
The specific driver I had in mind was the 18 Sound 15LW2400 which sounds like a great candidate for a ported box.

The JBL amp is rated for 1200W into 4 ohms..Conventional wisdom would suggest that the JBL should at least manage 500W into an 8 ohm load.
Finally someone who speaka-ma-language!

The 18Sound will need a big (100 liter) cabinet. Besides with "only" a 14001 driving it a big cabinet will be required to up sensitivity. Remember this is a PA/Pro driver not something that is meant for car audio.

Then again why am I talking? I used to have a pair of JBL 2245s (B460 bass bins) as part of my "home" stereo before I was married.

Quote:
Originally Posted by 1420 View Post
Could someone confirm the HPF/LPF filter on the GTO14001? Are they both 12db/oct Butterworth filters?
Yup. 12db butterworth.

http://www.jbl.com/resources/Brands/..._Eng_Aug09.pdf

JBL GTO14001 Car Power Amplifier Sm
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Old 1st December 2011, 08:26   #11
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Default Re: 8 Ohms Amp

Quote:
Originally Posted by 1420 View Post
Thanks for the input B&T.

Could someone confirm the HPF/LPF filter on the GTO14001? Are they both 12db/oct Butterworth filters?
The 14001 in fact has no HPF, it is an amplifier built to run low-pass only. It does not even have a pass-thru.

And as you rightly pointed out, it is designed for 4Ω or 2Ω usage. I have used professional audio speakers in cars, in my previous life.

I find their sound to not be optimized for small spaces.
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Old 3rd December 2011, 13:28   #12
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Default Re: 8 Ohms Amp

Quote:
Originally Posted by navin View Post
Finally someone who speaka-ma-language!

The 18Sound will need a big (100 liter) cabinet. Besides with "only" a 14001 driving it a big cabinet will be required to up sensitivity. Remember this is a PA/Pro driver not something that is meant for car audio.

Then again why am I talking? I used to have a pair of JBL 2245s (B460 bass bins) as part of my "home" stereo before I was married.



Yup. 12db butterworth.

http://www.jbl.com/resources/Brands/..._Eng_Aug09.pdf

JBL GTO14001 Car Power Amplifier Sm
Hi navin, I've read some of your posts and you have a wealth of knowledge and it would be nice to hear more of your thoughts on pro audio.

The 3.5 cube box is ideal for a ported enclosure but the driver should perform well for my intended usage in a sealed enclosure around 1.8 cubes. The smaller box would also help limit excursion somewhat and I plan to use duals. Using a ported box would mean I can only use a single cab.

How did you like the 2245s? They have quite the reputation as far as "sound quality" goes but not really durable. I like its replacement, the 2242, much better. A proven workhorse that sounds good and hits very hard by all accounts. I actually wanted to fit one of them in my car but the enclosure would be too large.

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Originally Posted by Sam Kapasi View Post
The 14001 in fact has no HPF, it is an amplifier built to run low-pass only. It does not even have a pass-thru.

And as you rightly pointed out, it is designed for 4Ω or 2Ω usage. I have used professional audio speakers in cars, in my previous life.

I find their sound to not be optimized for small spaces.
Hi Sam, the manual navin linked mentions a high pass though. Is this incorrect? Without a high pass almost any driver is in danger of mechanical damage dependent on various factors. Real world music material would probably not do so but there is a chance. If it indeed does not have a HPF then I am curious as to why it was omitted?
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Old 4th December 2011, 09:18   #13
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Default Re: 8 Ohms Amp

Quote:
Originally Posted by 1420 View Post
Hi Sam, the manual navin linked mentions a high pass though. Is this incorrect? Without a high pass almost any driver is in danger of mechanical damage dependent on various factors. Real world music material would probably not do so but there is a chance. If it indeed does not have a HPF then I am curious as to why it was omitted?
That would then be a sub-sonic filter. While I understand that technically, this too is a high-pass, it isn't what it is commonly referred to as HPF.

I was quick to misunderstand.

Yes there is a sub-sonic filter on the amplifier, effectively making the low pass into a band pass. But I'm rambling.
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Old 4th December 2011, 10:53   #14
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Default Re: 8 Ohms Amp

Where you will have an issue with pro woofer is excursion capability.

OTOH, if you are not looking at puncturing some eardrums, what there is will be good enough. I see you are already reducing output below 40Hz, in which case the pro woofer should be sufficient. Car subwoofers are low sensitivity, high excursion, and high power handling (sometimes).

Of consequence is the higher sensitivity of pro woofers, which means you can get by with less power. A good choice which I was toying with once was the Eminence Lab12, very good performance even in small sealed box with gently reducing output down to 35Hz in cabin. With EQ, it was possible to get a clean enough output down to about 30, with usable power handling and still being reasonably sensitive after accounting for cabin gain.
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Old 5th December 2011, 12:06   #15
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Default Re: 8 Ohms Amp

Quote:
Originally Posted by 1420 View Post
The 3.5 cube box is ideal for a ported enclosure but the driver should perform well for my intended usage in a sealed enclosure around 1.8 cubes.

How did you like the 2245s? They have quite the reputation as far as "sound quality" goes but not really durable.?
Just check the F3 and F10 you get in 2cu. ft. before you build the box. Remember in a car there is a road noise (tyres on road) in the 60-70Hz band so a pro woofer tht sounds nice at home might sound a tad weak in the car.

I never blew the 2245s. They was XOed to a floor standing MTM using Focal 8N515s and MDT. The system could be heard 250m away even if my windows were closed and the air con on. Each sub was powered by a bridged carver 1.5T the MTM was powered by a carver M1.0t and later by a 250W home brew amp (1200VA tranny, 60,000uf filters, and 6 Hitachi MOSFETS per channel). When my friends came over the first question was how much power (they were used to PMPO numbers in the thousands) so I say "30W". And they'd go "only 30W bah". Then I'd turn the system on and part their hair and re-arrange their brains

When my wife came we had to reduce the size of the system. Out went the 2245s and MTM and 1.5Ts. The M1.0t was used to power a pair of subs each using 2 ACI DV12s and new MTMs were built using the ScanSpeak 8546-9900. Still the system could max out my RAT-Shack SPL meter.

Now we are working on a more WAFed system but that is a long story.

Quote:
Originally Posted by Sam Kapasi View Post
I was quick to misunderstand.
The pass through would be considered an "All pass" na?

Quote:
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But I'm rambling.
Ramble on, now's the time, the time is now, to sing your song
We'll be here, at Team-BHP drinking in your words
and blessin' our ears, we'll 'drink' a thousand times, so Ramble on.

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With EQ, it was possible to get a clean enough output down to about 30, with usable power handling and still being reasonably sensitive after accounting for cabin gain.
This is something I was going to suggest. Given that 1420 was going to stuff the woofer in a small box he could use a bit of EQ like a Linkwitz ransform described below. Pro woofers have nice stuff surrounds and hence are better protected against damage from over-excursion so applying a bit of bass boost to them is safe.

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