Novice stereo subs project with stereo amp.

[PJeff]

Hi everyone,
I've been wanting to add a sub to my stereo system (SqueezeBox Duet, ONIX SP3(tube amp) and PSB B25's(monitor speakers) for a little while now and I've been contemplating sub kits like Rythmik to name one... But, I also have a Rotel amp (RA-985BX) 100W/8ohms sitting on a shelf and was wondering if it would be possible, as a cheaper alternative, to use it with something like a Reckhorn F-1 Stereo from CSS Audio to drive a stereo pair of not too expensive high efficiency sub drivers and maybe even use the enclosures as speaker stands? I'm thinking 12'' drivers. Performance goal is to have well integrated with really good transient low frequencies for hi-fi music and occasional movies.

What do you think of all this? Would it work?

Cheers,
PJeff

[chris661]

Yeah, it could work, but I think we still need more info...

How low do you want to go? (using headphones and a signal generator is good for choosing...)
What size is your room?
How loud do you want to go?
How big can the subwoofers be?
What's the budget?

For a start, though, I'd begin playing around on winISD.
I use a pair of 8" drivers in a smallish sealed box, with a linkwitz transform circuit, which enables them to go to 28Hz. ESP - The Linkwitz Transform Circuit - if you don't want to go that loud, applying this could be for you.
Unfortunately, there aren't any high efficiency 12" subwoofers. Hoffman's Iron Law means you can have only two of the following: small size; high efficiency; low frequency extension. That applies to cabinets, too...

[PJeff]

Originally Posted by chris661

Yeah, it could work, but I think we still need more info...

How low do you want to go? (using headphones and a signal generator is good for choosing...) fairly flat to 30hz would do it
What size is your room? about 15'x26'x8'high
How loud do you want to go? I do not have a way to measure that but from what I've read I guess 90-95dB max. I don't need really loud capabilities
How big can the subwoofers be? I guess around 3 cu-ft.(As stand mounts it would be something like 22''Hx12'Wx20''D inside dim.)
What's the budget? is 250-300$ realistic (including the F-1Stereo at 124$ but excluding the cabinet) for a clean, dynamic, good transient sound?

For a start, though, I'd begin playing around on winISD.
I use a pair of 8" drivers in a smallish sealed box, with a linkwitz transform circuit, which enables them to go to 28Hz. ESP - The Linkwitz Transform Circuit - if you don't want to go that loud, applying this could be for you.
Unfortunately, there aren't any high efficiency 12" subwoofers. I do not mind a smaller driver... as long as it does the trick... but I was thinking of an economical alternative to something like the AE Speakers Lambda serie if such a thing exist(I do not need it's high frequency capabilities so that's what makes me think there might be a cheaper alternative focussing on the lower end of the spectrum while keeping the high sensitivity???).
Hoffman's Iron Law means you can have only two of the following: small size; high efficiency; low frequency extension. That applies to cabinets, too..

Thanks... that make's a lot of sense!

[chris661]

Unfortunately, 12" is considered small by many...

Given 30Hz as a target (pretty sensible...), a pair of 12" drivers should suffice. A single 12" driver, in a sealed cabinet, would move 8mmp/p (peak to peak) to hit 30Hz at around 93dB.
Dual drivers would half the excursion, so most pro audio drivers will do the job.

I have an Eminence Beta 12, and that does the job well. It has reasonable linear excursion, but (perhaps more importantly) around 99dB@1w efficiency. With a Linkwitz Transform in place, you'll be going at around 40w total output (2x20w seems reasonable), hitting 95dB at 30Hz. The cabinets would be 50 litres each. They're £40 each here, which is a bargain, in my opinion. It's not a driver designed for subwoofer use, but it has enough excusion and power handling to be a good option for a lower budget.

Edit - just noticed your budget. Perhaps either something better by Eminence (or another Pro Audio manufacturer), or something aimed more at the hifi market would be in reach.

The Eminence LAB12 could be something to consider. More excursion, but lower efficiency (still not bad, though)

[Spasticteapot]

I might point out that Hoffman's Iron Law does not say that deep bas has to preclude efficiency. It just says that you need a freakishly enormous box.

I've seen some nice things done with small drivers and tapped horns - you could conceivably build some 30hz horns using Tang-Band 6" subs that you could use as speakers stands. While the efficiency isn't awe-inspiring, it's hard to argue with the form factor.

You can see what I'm getting on about here:
Tapped Horns

[PJeff]

Thank's Chris661 for your input. Your suggestion of the Eminence LAB12 hints me to be a little clearer about my budjet... I'm thinking around 250-300$ for the crossover (F-1Stereo-124$) and TWO drivers. The Eminence Beta12 looks within the budjet...

Thank's Sparticteapot. Wow... pretty impressive for a 6.5'' driver in this Tapped Horn. I'm not familiar with tapped horn but this avenue seams interesting but i'm curious to know anyone's opinion about the advantages AND disadvantages of such a design. I mean there MUST be compromises to be made to get that kind of performance from only a 6.5'' driver!! Here's a little reminder... I'm looking for a clean, dynamic, good transient that will integrate well with hi-fi music.

Two good but very different possible designs here and I need help to make the right choice for my application...
Very good day to you all,

[PJeff]

Also, If anyone has any experience with the Reckhorn F-1Stereo I would appreciate to have your inputs. Is it a worthy device? If I also use the satellite high pass for the monitors, will it deteriorate the signal or should I strictly use it for the subs and try to work with the monitor's natural roll off? Will the lack of phase adjustement will give me headacks for the integration to my system?

A great weekend to you all!

[chris661]

It would be far far cheaper to build something yourself. There are lots of active crossovers out there.
Active Filters Those will cost next to nothing to build on some stripboard or something like that. It would be better to play with $5 of components, than $135 on something that does the same thing. I made the circuit shown above (just the low-pass), and used a 100k stereo pot instead of those resistors. The result was a variable cross-over. This won't work for the high pass. You'll need a variable capacitor for that...

WRT the tapped horn, there's a couple of compromises that I know of... The size is still bigger than a sealed box for the same driver, the construction becomes more difficult (lots of pieces, and the all have to be in exactly the right place). In some cases of horn loading, you can't hear the driver hit the stops, so you have to be careful. Dunno if that applies to tapped horns.
On the positive side, it gives good low frequency extension, and brings efficiency up.
For the TB driver, you can get similar extension from a ported box, but the overall efficiency stays low... (still, by having a smaller cabinet when vented, you could add more later...)

Anyway, I'd cross your monitors over. Saves them going to any excursion when you've got a sub to do the pushing.

Ohhh - just noticed that the frequency response of that TH has boundry gain added (ie, on the floor, up against a wall...). Add that to a sealed design, you can also get pretty low (before even adding a Linkwitz Transform).

Chris

[bjorno]

Originally Posted by Spasticteapot

..I might point out that Hoffman's Iron Law does not say that deep bas has to preclude efficiency. It just says that you need a freakishly enormous box...

Agree, Here is an inexpensive T-TQWT to consider:..

b

[PJeff]

Originally Posted by chris661

It would be far far cheaper to build something yourself. There are lots of active crossovers out there.
Active Filters Those will cost next to nothing to build on some stripboard or something like that. It would be better to play with $5 of components, than $135 on something that does the same thing. I made the circuit shown above (just the low-pass), and used a 100k stereo pot instead of those resistors. The result was a variable cross-over. This won't work for the high pass. You'll need a variable capacitor for that...
Humm... didn't see that one coming but I really like the idea (not only for cost reasons but personal interest)... except that, no matter how easy this could be, I'd need major help along this new experience. I'll have a look around to see if I can find someone I know who could assist me with this... And what difference does it make that the reckhorn unit is powered(powercord and transformer on it) and, from what I can see, the schematic from Linkwitzlab isn't?

WRT the tapped horn, there's a couple of compromises that I know of... The size is still bigger than a sealed box for the same driver, the construction becomes more difficult (lots of pieces, and the all have to be in exactly the right place). I can stretch the size factor if technically justified for better performance. In some cases of horn loading, you can't hear the driver hit the stops, so you have to be careful. Dunno if that applies to tapped horns. Me neither
On the positive side, it gives good low frequency extension, and brings efficiency up.
For the TB driver, you can get similar extension from a ported box, but the overall efficiency stays low... (still, by having a smaller cabinet when vented, you could add more later...)

Anyway, I'd cross your monitors over. Saves them going to any excursion when you've got a sub to do the pushing. Any loss or garbage added to the signal to the monitors doing that? My goal is to eventually change my speakers for something more neutral and transparent that I will build from a proven design.

Ohhh - just noticed that the frequency response of that TH has boundry gain added (ie, on the floor, up against a wall...). Add that to a sealed design, you can also get pretty low (before even adding a Linkwitz Transform).

Chris

With my somewhat limited knowledge, What I'd like is the best performance possible following my basic requirements, with 100W/8ohms stereo and for the budjet I have... ie around 50$-75$ per driver. Already, there seem to have a few possibilities and that's great but I feel the need to elaborate a strategy to help my confusion. Could we adopt a strategy like, for exemple, starting by choosing a driver meeting my budjet and performance requirements and then choosing the type of enclosure to get the most from it...?? This is a simple suggestion to help my little neurons here... How would you guys do that?

Cheers