Rear located IB

[collo]

I read somewhere that locating a sub at the rear of the room when the mains are at the front can cause problems with response in the crossover region.

Does anyone know how severe this can be?

I'm trying to find a location for an IB without resorting to roof-mounted or under-floor options which would upset the neighbours.

According to REW, the best response is achieved with a pair of IB's firing into the rear of the room either side of the listening position.

This would allow the subs and the noisy EP2500 to be located in a study

regards
Collo

[Wayne A. Pflughaupt]

Welcome to the Forum, Collo!

The BFD/REW Forum is for questions directly related to that, so I’m redirecting your thread to our DIY Subwoofers Forum, where you’ll get more informed responses.

From what I’ve seen at the Cult of the Infinitely Baffled Forum, rear-room placement is highly discouraged. I know they have some good reasons for it - poke around a little and I’m sure you’ll find it.

Regarding the disturbing the neighbors issue, I can’t find it now, but I saw a thread on another Forum about that the other day, and the general consensus was that an attic will absorb most of the sound. Anything that does get out will be at such a low volume it won’t bother them inside their house.

However, it looks like you’re contemplating something other than an attic install, so it’s hard to say without any more particulars.

Regarding the noisy amp, you can put it anyplace you need to. Assuming you would be using a BFD to equalize the sub, you could use a balanced output to the amp. That will allow you as long a cable run as you need.

Hope this helps at least a little.

Regards,
Wayne

[collo]

Thanks for that quick response Wayne.

I'll have another look through the FAQs at The Cult to see if I can find that info on rear location.

I'll also have another think about roof mounting.

To measure how well that might perform, could I put my current sub in the seating position and use a pole to get the meter up high near where a proposed outlet would come through the ceiling?

That tip on balanced wiring for a long run sounds like a good 'un.

regards
Collo

[Wayne A. Pflughaupt]

To measure how well that might perform, could I put my current sub in the seating position and use a pole to get the meter up high near where a proposed outlet would come through the ceiling?

Yup, that’ll work. That’s actually the technique they recommend at the IB Forum to get an idea of what your response will be.

Regards,
Wayne

[Chrisbee]

ThomasW once posted an image on The Cult forum of a ragged trace due to phase problems between the rear subwoofer and the main speakers.

Regarding the noise problem: My wife regularly comes in from gardening and tells me quite voluntarily that the IB is very quiet outside compared with her SVS cylinder.

I watched Matrix 1 yesterday rather loudly while my wife pottered in the garden. She said she could hardly hear the IB at all outside. We live in a very quiet rural area so traffic noise is certainly not masking the sound.

That said, the IB output travels very well indoors so may well inconvenience neighbours within the same building. As long as they are separated by a few yards from your home you should be okay. An attic manifold enjoys the heaviest damping from lots of thick fibrous roof insulation.

[collo]

Thanks for that Chrisbee.

I've done a heap of measurements, and found that swapping the screen and seating position, places the mains next to the manifolds of a pair of IB's and gives a great response.

I've written it all up on my website but I'm still short of the 10 posts needed to give out the URL.

While I was at it, I did the "meter on a pole" trick and measured each of the inter-rafter positions across the room at ceiling height. I then picked the best position and worked my way along the room. Only one spot gave a good response.

Since I'm looking at 12 * 15inchers, I'll need a pair of manifolds, so I'm going to go with the "through the wall" option.

regards
Collo

[Chrisbee]

Keeping the IBs and mains together makes very good sense.

12 x 15"s sounds like a great plan if you have the available volume in the room(s) behind.

Remember that you'll have to multiply Vas (for a single driver) by the number of drivers x a minimum of 4 to maintain sound quality.

(12 x 4) = 48 x Vas. This is a safe minimum and more rear volume is better.

6 drivers could be run in sets of 3 x 4 Ohms in series for 12 Ohms per channel on a dual mono (stereo) amp. A nice safe load for continuous high levels so the amps would be cruising.

Or the 2 sets of 3 could be paralleled for a more normal impedance of 6 Ohms with the amps bridged. This wouldn't make much difference in the real world unless you like claiming impressive numbers of watts driving your IB.

Opposed driver manifolds are a good idea to minimise mechanical vibration.

Though I can't help feeling you are going to sense rather more of the acoustic vibration with that much woofage!

[collo]

Each manifold will run off one channel of an EP2500.

Three parallel circuits, each of two drivers in series gives a 3ohm load.
Normal usage wants 335w per side, but Xmax wants 850w per side which is about what that amp should do at 3 ohms.


Total Vas is 150 * 12 = 1800 litres or 1.8kl

The room the backwave will vent into is 3m * 4m * 3m approx, giving 36kl for a factor of 20.

I'm hoping the vibration won't be too bad since the design excursion is only 12.5mm one-way. (That's why I need 12 drivers)


I've got that link for anyone who's interested in a look at my graphs:
Using REW to find best IB location

[Otto]

Hi Collo,

Sounds like fun! That's quite a few drivers. I had a browse through your web page. How did you decide on the Viper drivers? I used the Mach5 18s, primarily because they were cheap. I'm not a driver expert. However, the limited xmax of the Viper seems to be limiting your results in the sims. Is it hard to find other drivers in Australia?

Even with the driver you are using, I might think you could get away with fewer than 12. You might be surprised by the amount of bass you will get from that setup. Enough to be scary, I would imagine.

Good luck and have fun!

[Chrisbee]

I just did a quick conversion. $80 Aus dollars is only £32 (in real money)

Using a lot of drivers is a great way to get high SPLs from lots of displacement with limited Xmax. Doing it the "American way" with fewer longthrow drivers would cost far more with freight and taxes.

If you ever hear suspension noise from 12 of those Vipers it could be the last thing you ever hear before they scrape you up with shovel!

I still prefer 3 drivers in series per channel.

Great website BTW!

[Hakka]

There's a member here called Norpus, he has 2 IBs, one at the front and one at the rear. He'd be a good one to talk to about it. You can also find him on either of the Aussie HT forums.

[collo]

Thanks for that feedback Chrisbee

We don't have a lot of drivers to choose from here in Australia. All the popular drivers mentioned on the overseas forums are way too expensive here. There generally is no importer, so bringing in just a few costs heaps because of the weight.

The Venom drivers I've modelled are widely available here through Jaycar, a local electronic components supplier, and are affordable.

Another builder here has used these drivers and recommends keeping to +/- 12.5mm excursion. Even though this is low, multiplying by the Sd for a 15inch driver is about the most affordable way to get displacement.

Going two parallel circuits each of three drivers in series gives 6 ohms per channel, which would extract around 625w per channel from an EP2500 - enough to meet the cruising needs, but a bit short of the 850w to push out to Xmax on the peaks! It's all about maximising the headroom.

I have to wait a few more months to get the drivers, but will start on the manifolds and room mods soon.

As you say, it should be a lot of fun!

[Chrisbee]

collo wrote:

We don't have a lot of drivers to choose from here in Australia. All the popular drivers mentioned on the overseas forums are way too expensive here. There generally is no importer, so bringing in just a few costs heaps because of the weight.

The Venom drivers I've modelled are widely available here through Jaycar, a local electronic components supplier, and are affordable.

Another builder here has used these drivers and recommends keeping to +/- 12.5mm excursion. Even though this is low, multiplying by the Sd for a 15inch driver is about the most affordable way to get displacement.
:

We have exactly the same problem obtaining IB drivers in Europe. Freight charges for big heavy drivers from the US + 1/3 the total cost in taxes all adds up.

I was able to obtain the last 4 x AE IB15s in Europe (as far as I know). I paid £GB pounds for US dollars + European freight but no taxes. Not too bad really except that two drivers were cosmetically poor. These AE drivers only have 16mm Xmax.

Getting more drivers for more bottom end "welly" is now probably impossible due to AE's reported demise. I would have liked to bring the total number of drivers up to eight with a ceiling manifold.

It's a shame Parts Express doesn't have a presence over here or Down Under. The PE IB15's aren't a million miles from the AEs in spec.

Bulk buying might make a further dent in the price if you could get some Ozzy IB fans together in a power buy.

You'll just need a forklift to move the crate.

[norpus]

collo wrote:

I read somewhere that locating a sub at the rear of the room when the mains are at the front can cause problems with response in the crossover region.

Does anyone know how severe this can be?

I'm trying to find a location for an IB without resorting to roof-mounted or under-floor options which would upset the neighbours.

According to REW, the best response is achieved with a pair of IB's firing into the rear of the room either side of the listening position.

This would allow the subs and the noisy EP2500 to be located in a study

regards
Collo

Hi Collo

When I use my rear single IB alone, I need to cross it over around 40Hz to make it unlocatable - at 60 it is just locatable. (When using both front and rear subs, 60Hz is fine) I also use sub amps with phase control which the amp manufacturer helped me setup when we commissioned them.
Front mounting would be preferable although I can recommend one at each end sounds good at my place

[collo]

GDay Norpus,

The lowest frequency my AV amp (Pioneer VSX-D711) will crossover is 100hz, so your info adds more evidence that rear mounting would not be a good idea in my case.

I'm happy to re-arrange the room to get this response (no filters):



This was measured using an existing sub that rolls off below 25hz. The red and green curves are for the two manifolds which will be at the front of the re-arranged room. exiting adjacent to the mains.

The current stage of the project is to clear the other side of the wall. It has full width racks six foot high, chock-a-block full of gear! - two days work so far and another to go!

Then I can chase out the studs and start on the manifolds.

[terry j]

collo

am interested in your progress.

Had a quick look on your site and here, forgive me if you've said it and I missed it, but what are the dimensions of the room in which your IB's will play??

I'm pondering the installation of an IB, but have quite a few constraints on what I can do.

The one I'm querying at the moment is my music room has a volume of around 190 m/3, and of course that begs the question of how many drivers do I need?!?!

At the end of this week am visiting Melb, and whilst there I will avail myself of a massage of a very special kind, courtesy of a front and rear mounted pair of IB's at chez Norpus ha ha and hooray!

At the very least I can see if the IB sound is to my liking and then carry on from there.

I originally only wanted to do a floor mounting of 4 or 6 woofers behind me ( architectral aesthetics) but am really starting to think that won't be anywhere near enough for my room.

Anyway, will keep planning and see if these hurdles can be overcome.

The absolute pits would be to totally fall in love with Norps sound, and then find that in the end I can't do an IB !!!!!!!!!!!

[norpus]

Terry I am sure we'll find a way for you
Make sure you bring your plans and piccies with you so the Melbourne team can paw over them
I'm sure 6 15s should be enough - thats about the equivalent of mine so you should get a good idea
Looking forward to your road trip

[collo]

Hi there Terry,

I originally had the room dimensions on the drawings of the room layout, but took them out for the sake of simplicity. I'll put them back in.

The room is 5.5m wide * 4.4m deep * 3.175 high. It is open to a hall that is 4.1m long * 1.4m wide, same height. This gives a volume of around 90 m^3

The backwave will be contained in an adjacent room 3.9m wide * 3.9, same height, for a volume of around 48 m^3

I suspect I've gone for a bit of overkill, but all my previous subs have sounded great running flat-out. I wanted something that had enough headroom to "set and forget"

Given that your area is double the size of mine, I doubt four drivers will do it for you. I'm sure norpus will show you the light...

regards
Collo

[collo]

There be holes....(screen will go where chair currently is)

There be drivers...

Manifolds are taking shape....

I'm starting to get just a little bit excited...

[Sonnie]

Even with the lower xmax... I think this is still going to be awesome. I can't wait to see the response and hear your thoughts.

[Chrisbee]

Should collo be allowed to play with so many toys at the same time?

He appears to have far more than his fair share!

[collo]

mmmmmmmm....toooooooys....

[kesa32]

Hi collo, hows it coming along mate?....are you going to run bracing in the manifolds at all?

should be good with that many drivers, it will be interesting to see how they perform.