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Elite Shackster
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Discussion Starter · #1 ·
Ive played with sealed and ported designs so decided to get stuck into a pr design. The design needs to be kept fairly compact considering we are using an 18" driver, so pr's seem to make sense. The design will use an Fi 18" Q series driver with 500 watts input, and 2 AE 2100 pr's. The cabinet is around 175 litres and the end result will be an 18 hz tune. I will be making provision for an amp swap, just to keep options available, which I'll explain in a minute.

The amp is going to be a mofset based 500 watt amp with a built in HPF which I'll spec and have added. Its a plate amp to try keep this design an all in one box, so basically as close to a commercial sub as is possible. The driver will be front firing with dual opposed pr's and the plate amp on the rear. I am going to add in a Bi-amp speaker terminal, and wire the plate amp to one set of terminals, while the driver will be wired to the second set. Jumper bars will make the final connection. If I decided to add in a more powerful external amp later, I can then simply remove the jumper bars and connect the new amp to the second set of terminals, simples :D

As is typical for me, I got a 3D model complete and have added these below for people to have a nosey at. Any input is welcome :T
 

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Hi Dan,

That's an odd looking curve with the alignment down 10db at 20hz. I always thought it was best to be -3db at tuning frequency. Obviously you have room gain to add but what if you don't get much.

Just a thought. What are your thoughts on this. Always good to try something new with different drivers.

cheers

Graham
 

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Elite Shackster
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Discussion Starter · #7 ·
It is a little unusual but dont take that TFM as the end total result. The spl chart tells the real output story, and the TFM is probably more representative of what I guess you would call the Q in a sealed sub. Using the 18" driver in this cab is going to give a lot of upper bass impact that ist normally associated with low tuned ported cabs. This will still give good output down to 15hz (which is within design goals). Ive looked at using a 15" driver and I think that curve is less desirable. Its less smooth with -3 around the same point, but uses more cone excursion.

FWIW, the -3 on the AE's I ran was about 45 hz, but it still went flat to 10hz in room to 105db. I actually think a higher -3 is probably better for music based on experience so far, and with a good large driver the lw end will still be there anyway.
 

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Elite Shackster
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Discussion Starter · #8 ·
Just noticed the WinISD file I uploaded is wrong. You need to change the cab volume to 175 litres.
 

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Dan,

It makes little difference really but I must not get any room gain in my subs as my model is pretty identical to my actual turn outs. Its the way it goes some times but I couldn't wish for anymore bass really.

cheers

Graham
 

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Elite Shackster
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Discussion Starter · #10 ·
Well this will replace a PBU, with the goals being matched performance with better SQ and musicality. It should fulfil that goal pretty well. I'll be sure to keep this one updated as I go :T
 

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It's looking even easier to surpass the performance of the mighty SVS PB13 ultra.

I just did a ported Q18 tuned to 18hz with slightly more power in the same size box gave the same results but with a much much less group delay.
Port velocity is not a problem so I see no real gain apart from the extra expense off two PR's. I guess you already have these.

cheers

Graham

P.S: A 4 FI IB3 IB is growing on me!
 

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Elite Shackster
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Discussion Starter · #12 ·
Group delay is just the same according to my WinISD, so not sure what your doing there. Also, dont forget that a 175 litre ported cabinet is larger than the outer dims of this one. Pr's are about minimising box size and nothing else, and that what they are doing here. I did already have the pr's, so there is no cost to this build from using them.

Size wise, a ported cab is worse, all other things are equal.
 

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Dan,

With essetionally such a small box size I don't see the real gain from PR's apart from the lack off so called port noise from the port. I did a simulation (attached) with a 175l ported sub tuned to 18hz and with 800 watts input power came out exactly the same. If PR's are about min sizing box size then why is it the same. I relate to PR's simply to rule out port noise but they like anything still have limits. If a PR essentially acts like a port which I thought does but without the noise then what are the gains in this small box.

If group delay in winisd is not a function we should be looking at then why is it there.

Please don't take this personally, its just my opinion. But please advise me if I am very wrong.

cheers matey

Graham
 

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Elite Shackster
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Discussion Starter · #14 ·
First question is are you using the 2010 model of the driver, as your model comes out slightly differently from mine. If not you can grab it from the data base we have here.

Now, your model has over a meter of porting which would need to be included in the cabinet, and that is additional size I dont want. Cab volume may be the same, but your box would be physically larger. Granted its not massively larger, but the cab I have designed is max and thats that, so to port it I would have to reduce cab volume, which is not desirable, especially when at the bottom end of what the driver wants anyway.

I dont know why your questioning the use of the group delay tab, I didnt say dont use it. What I said is that in both a ported and pr model, the GD is virtually identical, so there is no difference between ported and pr in that sense.

As I said, the idea with pr's is to remove the required cabinet size needed to house the porting. This actually helps in this particular case. There are pros and cons to both ports and pr's, but generally speaking, pr's do remove the thing ports can suffer that we dont want, like compression and noise artefacts etc. Their main attraction in this case is so I hve the maximum usable volume from this sized cabinet, which basically had to have a footprint no larger than an Ultra and could be no more than 700mm high.
 

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Elite Shackster
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Discussion Starter · #15 ·
On further inspection Graham, there looks to be something wrong with your driver file, at least on my machine, as it shows the sub gives a flat response up beyond 50khz, which it just wont do. Not sure whats going on there.
 

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Elite Shackster
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Discussion Starter · #19 ·
Well there has been a slight development on the driver front that means the start of this build is put back a little, but it should be worth it in the long run. Basically Fi have a new driver on the way I am waiting for that should be ready very soon. As soon as I can get the specs for the new drivers, it will be modelled and the build will begin.
 

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Dan,

Just to let you know if you don't already know, its under another name. They have 4 new drivers coming out. 2 high excursion drivers and 2 IB drivers.
These are based on HT specs so are applicable to home theatre applications.

Its gonna take alot to beat the FI Q drivers.

Exciting stuff.

cheers

Graham
 
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