can i turn my house into a horn?

In all seriousness, very low frequencies can damage buildings. I remember hearing about a helicopter landing pad near an army base and they kept getting damaged foundations because of the ultra low frequency vibrations from the helicopter blades.

Then there is:
The orgasm frequency
The shit yourself frequency
The stomach explode frequency and finally
The heart chamber frequency

 

What is it, and which subwoofer do I have to buy for it?

 

I havn't found it yet, the PMCs didn't do it for my last girlfriend

 

right that's me fXXked

in all seriousnessess, you've thrown me into a right spin there, bud
i've been stomping hard and thinking furiously since i read your post, cos it confirms something i'd been worrying about- bass from above, and whether it would sound right
i've a few ideas that i'm asking about on the IB forum
i'll keep you posted
many thanks
gav

 

any views on electronic delays?

i may need to allow for the subs being up to 6 feet behind the mains

mounting them level is proving difficult

the idea of eq's horrifies me. can i have a delay without smegging the sound?

where's tenson when i need him...?

gav

 

Be patient

I'm afraid I don't see any very easy way to truly solve the issue, but I'll have a try. It would not be hard if you wanted to delay the subs, but to delay the mains is harder since it is more quality critical.

One way of doing it would be to use a very high quality ADC after the pre-amp, then use a digital delay (~5ms for 6'), then a nice DAC and then on to the power amps. The signal to the subs goes direct from the pre-amp.

Another way that is better, but requires a big system change is to take the signal from your transport, put it through the digital delay and then on to your DAC, pre amp, power amp and main speakers. Then you take another line from the transport (could be looped thru from the digital delay but without any delay added, something like the Behringer DEQ2496 can do the job) and pass that to another DAC without it being delayed and that goes to the pre-amp, another power amp and subs.

The problem here is that you need a pre-amp which can control the volume of 4 channels (2 for the subs and 2 for the mains). Such a pre-amp can be done, I have one which does 6 channels for my digital active system using 6 S&B TX-102 transformers and a custom built 24 position switch from Greyhill. Music First Audio might be able to make something similar.

It depends how attached you are to your preamp and if you even use a digital front end with a DAC.

Yet another option is to use an analogue active all pass filter (phase shift) before the power-amp of the subs. However, this is not the same as a true time delay on the mains. It can get the two signals to arrive in relative phase at the Xover point, but the subs will still actually be delayed by their physical offset.

Another similar option is to position the main speakers and subs so that they are exactly 180degrees or 360degreese or 540degrees etc... delayed at the Xover point. If you crossed at 100Hz then the main speakers could be 1.72m, 3.44m, 5.16m etc.. in front of the subs. With a sharp Xover (24dB/Oct or greater) that should not cause too significant an issue.

I would probably try the all pass filter on the subs as a first course of action. Depending on the amount of delay and at what frequency this may or may not be audible. A lower Xover is better in this case. I expect someone like Oedipus knows more on that subject.

Having said that, one of the advantages of a large IB sub is minimal group delay and that would go out the window with that 6' delay between the mains and the subs, whether or not it is supposed to be audible.

As for the EQ… well I am horrified that you would not use it

If you have a digital source (transport and DAC) then you can place the EQ between them in the digital domain and get practically nill negative effects. Also, it can do the digital delay at the same time if you were going for the option with the 4chanel pre-amp.

Or, you could place it in the line of just the subs, but that would introduce yet more delay (~1ms) so you would need to Xover even lower.

 

I've completely changed my tune on the topic of eq, room correction in general... be it in the analogue or digital domain.

.. it is just that too much eq can be worse than none at all.. like salt and pepper on your dinner

 

Delays can be a problem, in my case the distance from the sub to my ears is about half the distance from my main speakers to my ears and yet the sound from the sub arrives after the mains, not normally a problem as I only use the sub for movies, but irritating if I use it with music. Given that your mains go down to around 25hz you may end up the same as me and only use a sub for movies as there really isn't much bass in that region on music anyway.

 

are the speakers capable of giving a flat response to 25hz in room?

 

no, they are -6db @25 hertz

 

Tenson, i'm still assimillating your reply...but my source will primarily be my turntable, which rules out the digital option

i'm planning to change my pre-amp, so this is a possibillity. i had been minded to buy david's, along with his power amp and speakers...i understand that the spec of the pre can be modified. i will make enquries

it seems easier to rely on physical positioning to acheive correct time alignment?

gavin

 

Well yes, if you can place them so they are time aligned that’s great But having the subs 6’ back from the mains is certainly not time aligned. Even placement as I suggested will only get you phase aligned at the Xover point, they are not time aligned.

If you use a TT and don't want to digitise the signal then you simply are not going to get time alignment without placing the subs and mains in the same place (or one above the other). You can't really do a time delay with analogue technology. All you can do is get them phase aligned. In which case the best bet is probably to get them as close to each other as possible while still getting good sound from each of them, and then using an all pass filter to adjust the phase of the subs to match that of the main speakers at the Xover point. Using a very sharp filter is a good idea because with this method it will only be phase aligned at one frequency point - either side of this frequency you will be going out of phase again.

By the way, this might prove interesting reading - http://sound.westhost.com/pcmm.htm

 

You need my pmcs for that Markus not tensons titchy one!

 

Titchy one? From the lack of plural form, we are not talking about my speakers, right?

 

Those too

 

i ran my ideas past the IB forum,and they're unanimous that i should stick with the ceiling mount approach

this makes time alignment considerably easier. i can mount above the mains.
i'm also considering an "outey" rather than "inney" to help timing.
perhaps this will address some if the problems encountered by GaryG

so, two cubes, one above each main. probaly a little inside, rather than directly above.

2 x aurasound 18's in each cube, back to back in order to gain from cancellation effect & reduce any structural impact
i'm minded to fire them across the room rather than straight at me and straight away. again, this is to (hopefully) improve percieved phase and timing.

i could build a line array pointing directly at me, but this configuration can lead to negative side effects, structural damage being the most serious.
apparently the sound of rushing air can also interfere with sq (!)
so a cube manifold would appear the best way to go
this should hopefully remove the need for most of the (scary) electronics mentioned

gav

 

One of my loft mount arrangements was a cube manifold with 2x15" drivers directly above my main speakers slightly closer to the left speaker rather than central between them, if I could have stopped the resonance problems with the ceiling against the joists I would probably have stuck with it, however, experimenting with temporary enclosures I found the best location for integration with the mains to be a driver right next to (preferably underneath) each main speaker, wish I had the space to implement that.

Regards
Gary

 

that makes sense- if i could i would use that configuration, however i have a solid concrete floor.

i've a couple of questions:

did you build an inney or outey?

how high was your ceiling?

many thanks

gavin

 

The cube version was an 'outey' with a ceiling height just under 8ft.

Regards
Gary

 

ok, ive gone a bit quiet, here's why:

i'm paying for my main speakers till the spring

i've reached the (obvious) conclusion that i need to move in and site my main speakers before i can then work out where to site the sub(s)

i'm also going to need another pair of ears cos it's a two man job working out the best place to mount. one person needs to sit in the listening position, and another to hold a sub box in the location proposed. that way any problems can be heard before install.
tenson, could be a job for you if you're interested?
you'll have a good chance of selling me some of your room conditioning gear too....

ps on the drivers, aurasound are working on some 15's, that may be ready by the time i am!

gav