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Amplifier under seat? Audio advice needed
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ccihon
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PostPosted: Thu Sep 17, 2015 6:00 am    Post subject: Reply with quote

I have A Rockford Fosgate powered sub in the storage area behind the seat, driven line-level from the Retrosound head unit - it has F/R stereo line outs so I have the sub set for crossover cut-off. The unit is nice as it has a remote gain pot that can be mounted under dash. Currently I have some JBL 6.5s in fiberglass kick panels in the front - they are for now only driven by the head unit. Don't skimp on these speakers in the front. The whole thing is remarkably simple and sounds very clean, even at high volume levels, which are often necessary in a noisy car. The rear seat is naturally "ported" or open to the passenger compartment along the sides of the seat back so the location is nearly ideal, close to the battery, etc. Main drawback is giving up the storage space.

I can also report I am running the original 30A generator with this set up and have no issues with enough power. At some point I may add a small 2-channel amp in the dash area for the JBLs. I don't seem to miss the lack of rear full-range speakers, nor do i want to chop up anything in the back to mount them.
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SirNickity
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PostPosted: Thu Sep 17, 2015 9:09 am    Post subject: Reply with quote

You're better off without rear speakers anyway. The only purpose they might serve is for passengers in the back of a larger vehicle, which is not a concern in a Ghia.

Sometimes auto makers will use small front speakers where room is tighter, and use larger cones in the rear to provide some bass. Not relevant when you get to pick the components and placement.

Other than that, they add complexity and do nothing to improve the sound quality or imaging for the driver and front passenger - and typically just make it worse. In every car I've ever owned, I put the fader on 100% Front. Or pull the rear speakers out entirely.

Now if you add processing to provide "rear fill", like a surround setup, that's a different story. Fun, but not necessary, and most head units (or preamps) don't have anything of the sort.
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ccihon
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PostPosted: Thu Sep 17, 2015 10:09 am    Post subject: Reply with quote

Quite right - just placing an actual passenger in the Ghia rear seat suggests you have no concern for them!
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craigolio1
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PostPosted: Thu Sep 17, 2015 7:22 pm    Post subject: Reply with quote

I used to just run a front stage in my cars. I was taught that's the right way to do it. But I grew to like a couple of speakers in the back. I always back the gain off so that the stage is still up front, but I find it fills it in. Personal preference I guess.

About how much power to run, etc. I may be wrong but I was taught that at regular listening levels your amp is only producing a small percentage of what it's capable of and that its full potential (not max power but it's full rated RMS power) is hardly ever reached, there for making it perfectly fibe to power say a pair of speakers that can handle 75w RMS off of and amp rated for 100w RMS. My last car had a HiFonics Odin, rated at 75/ch, powering a pair of 6" MB Quarts from the '90s... The paper cone ones with the tweeter on a bridge. I had them crossed over at 90hz. They worked for YEARS and I mostly listened at reasonable volumes but believe me, they had their fair share Metallica at offensive volumes. They eventually desintegrated but I wouldn't say I "blew" them. They just died of old age I think. I was certainly over powering them but the whole signal chain was extremely clean. Line driver, 24db/octave crossover, high S/N. It was awesome.

I miss them.
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SirNickity
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PostPosted: Mon Sep 21, 2015 2:26 am    Post subject: Reply with quote

Been traveling, so I missed the reply. Good conversation though, so...

You're absolutely right about rear fill - there's no right/wrong there, it's totally preference. I find the sound of four-speaker stereo to be ill-defined and boxy, but that's just my opinion. I only raise the point at all because I find people tend to think of rear speakers as "just part of the system" when they CAN be left out. Or added back in later if need be. Smile

And about RMS vs. power handling: Matching amps and speakers is kinda hard actually. Power handling of the driver depends on the driver design, enclosure, environment, crest factor of the program material, etc. If you build the speaker/enclosure combo as an engineered system (as in the case of a subwoofer) then you can model its physical power handling characteristics and design the amp's peak output to be less than that.

RMS output is a bit more fuzzy, and really only relevant to thermal handling. Thermals are somewhat harder to predict because it's a cumulative problem - it has a time component. If the manufacturer is being honest (hardly ever the case for either the amp or the driver), and your environment and program material are representative of the test conditions, then you can match them. Otherwise it's a crapshoot.

Like many things, close is close enough, and moderation is the key. You don't run a driver to its RMS limit all the time just like you don't run your engine right up to the redline all the time. So there's a good deal of fudge factor involved, and you can get away with oversizing the amp. You can exceed RMS ratings temporarily, just don't live on that edge if you want your stuff to last.

So yes, as common wisdom suggests, it's usually OK to have that little bit of extra firepower on tap, there's just no real need to. The amp doesn't care if you're running it at the upper end of its output. Transistors run coolest at low output (where the current flowing through them is minimal), and at high output (where their resistance is minimal). It's the middle, linear region that gets hottest. It has to be built to survive that.

For Class D, it hardly matters at all. The switching frequency has more to do with heat buildup than most anything else. In either case, the only part of the amp that is stressed according to output level is the power supply, and if it's not built with a fair bit of margin beyond its rated capacity, then it's a poor amp.

You mentioned that typical output is well below the RMS output anyway - which is absolutely true. Loudness is exponential, which is why audio guys often talk about "the first watt", as that's where casual listening takes place. In a car, maybe the first 10 watts. Wink

All that said, it's mostly an academic argument. Anyone who picks an amp with more than brief concern about the exact power levels (assuming it's enough but not TOO much) is probably spending too much time sweating the small stuff. 40W, 150W, whatever... It's fine, just enjoy the music.
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PostPosted: Mon May 22, 2017 11:49 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

I realize this is an old thread but feel like it might be a short answer and would be better served to be part of this thread:

I've read a few posts about people placing sub boxes and woofers in the parcel deck of a convertible. In many ways this seems like the most logical place and I'd like to do the same, but I've got some concern about placing woofers directly behind the folded down rear window when the top is dropped. Seems like it could lead to destruction of the window or at least muffling/distortion of the bass. Anyone have any experience or advice regarding this? Am I overthinking this?
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crocteau
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PostPosted: Mon May 22, 2017 5:17 pm    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

SambanistaRebel wrote:
Am I overthinking this?
It makes sense to tuck a sub back there, especially if you want the back seat for kids, dogs, groceries, etc. FWIW, when the rear window is down in my cabriolet it's only a few inches from my sub (rear facing JL10W6v2, sealed enclosure, ~500W, pic in gallery) and nothing has broken yet, but I'm not trying to set a record for SPL.
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swavananda
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PostPosted: Tue May 23, 2017 11:15 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

SambanistaRebel wrote:
I realize this is an old thread but feel like it might be a short answer and would be better served to be part of this thread:

I've read a few posts about people placing sub boxes and woofers in the parcel deck of a convertible. In many ways this seems like the most logical place and I'd like to do the same, but I've got some concern about placing woofers directly behind the folded down rear window when the top is dropped. Seems like it could lead to destruction of the window or at least muffling/distortion of the bass. Anyone have any experience or advice regarding this? Am I overthinking this?


I also posted before here:

https://www.thesamba.com/vw/forum/viewtopic.php?t=675222&highlight=sub

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SirNickity
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PostPosted: Tue May 23, 2017 11:42 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

There aren't really a lot of alternatives. What other significant volume of space is there in a Ghia? I guess you could try and stuff it in the trunk... Wink

I wouldn't worry about it. The glass will be fine. If it can handle 40+ years of weather and being on the road, it's not going to have a problem dealing with a little bass. Similarly, the sound will be OK too. Remember: Lots of people keep their sub box locked away in a completely different "room" of their car. Your tunes will find their way around the glass.

If it sounds TOO much different, then you probably have a rattle somewhere, or your crossover point is set too high! Cool
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swavananda
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PostPosted: Tue May 23, 2017 11:59 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

I've had this set up since I got the car 10 years ago. The sound is fine even with the to small of an enclosure and no issues about the glass.
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SambanistaRebel
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PostPosted: Tue May 23, 2017 1:29 pm    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

Thanks for the help. Swavanada, not sure why I didn't get your post when i searched before. Good stuff. Curious if you think you could have gotten more enclosure volume by pointing the sub towards the glass (mounting it vertically)? Do you think a 10 would fit this way even if it had to be leaned back a bit? Thinking if I can mount it vertically and properly port it that the parcel shelf is big enough to provide enough enclosure volume for good bass on a single 10, but just eye balling it at the moment.

However, it's also pointing the wave off the sub directly at 50 year old glass that had me concerned about getting shrapnel in the back of my skull, but sounds like I should just trust the German glass makers more.
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SirNickity
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PostPosted: Thu Jun 08, 2017 12:00 pm    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

You might want to download a copy of WinISD Pro (free) or similar and try modeling box volumes with the actual drivers you're looking at. Or post the T/S params of the driver and someone here can model it for you.

There are a few things to consider with sub boxes:

First, for the most part, the more internal volume the deeper the bass. Small sealed boxes can work well, but they're very inefficient, may require significant EQ to counter the rising frequency response, and I've popped off a dust cap from the internal pressures before. Failure mode is likely to be thermal.

Ported boxes are way more efficient, but they need to be big, and also have to be designed to suit the driver. Pre-fabbed boxes with any old driver that fits is a sure recipe for loud, one-note bass. It'll technically work, and if you've got tin cans for ears, it may even work well enough! Wink

Bear in mind you'll have better results with a good 8 and a well-tuned ported box than you would with a too-small ported box and a 10. You will need to decide whether you're more concerned with extension (<45Hz) or volume though. That determines which driver to use, and what the tuning frequency of the box should be. Those two dictate size of the box. So it can be a bit of an exercise in successive approximation until you find the compromise that works best.

Finally, in a ported box, the tuning frequency also determines a point where the box no longer provides acoustic suspension to the driver, and any program material below that just makes the driver flap itself to death. So you need to ensure your amp or crossover has a steep high-pass filter to remove frequencies below the box tuning frequency.

Assuming that hasn't scared you off... Laughing I would not worry about the glass. It's thick, tough, and won't be affected by vibration. There are no significant pressures involved since it's not part of a sealed enclosure. If anything is going to fail, it'll be mounting rubber and screws. And then, compared to the stress of being in a vehicle, unless you're competing in SPL showdowns, your ears are going to give out before your car does.
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PostPosted: Thu Apr 23, 2020 8:24 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

About to add an amp and speaker box to my 1970 Ghia. What are the typical options with regards to amp location? Seems like under the passenger seat from what I'm reading or integrated to speaker box/enclosure. Is there room under rear seat?
Thx
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PostPosted: Fri Apr 24, 2020 8:36 pm    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

For some reason, I’ve always put mine up front.
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PostPosted: Tue Jun 15, 2021 5:55 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

Dredging up this old thread because it seems like a good place to ask; Do speakers in the rear quarters really matter?

I'm not at all an audiophile, I'm just doing a retrosound head unit. If I did good speakers in the kick panels and a powered bass tube behind the rear seat, would I really notice the absence of rear speakers?
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PostPosted: Tue Jun 15, 2021 6:27 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

In my experience with car audio and home theater, yes. Rear “fill” will greatly improve the listening experience.
I have two 12” subs where the rear seat would be and Revel mids and tweets in an enclosure tucked under the rear tray and DynAudio mids and tweets in the doors. It’s a noticeable difference when I turn off the rear mids and tweets.
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kent70ghia
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PostPosted: Tue Jun 15, 2021 7:10 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

I put a Retrosound unit in my 70 coupe with 6 or 6 1/2 Rockford Fosgate 3 ways in Glass Action kick panel enclosures and I think it sounds great. I am not an audio enthusiast, and just wanted decent sound.
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PostPosted: Tue Jun 15, 2021 7:31 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

Kent did you need an amp to drive those 6" speakers or did you just use the 25watt output from the retrosound head unit?
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PostPosted: Tue Jun 15, 2021 7:51 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

No I didn't use an Amp. The set up was recommended by a Crutchfield rep. We thought it would be good to try without first, and add later if needed. I think it works fine as is, I have run on the highway at 65MPH with windows down and it was loud and clear enough for me, however, I am not a temp thump in the trunk trunk kinda guy.
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PostPosted: Tue Jun 15, 2021 8:31 am    Post subject: Re: Amplifier under seat? Audio advice needed Reply with quote

The speakers are R165X3, 6 1/2 45 watt, 90 watt peak power.
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