Low end support for single driver monitors

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Having built a pair of single driver Fonken speakers from the plans on Planet10-hifi.com I am interested in augmenting them with support in the mid-bass to bass region. The Fonkens are the first pair of speakers that I've constructed, I've found that I really enjoy the woodworking and assembly end of DIY speakers. My overall goal with this project is to have a better understanding of how a speakers design affects it's performance. I've been reading articles and books about speaker design, visiting links found through forums, and playing around with various computer programs such as winISD, I think I've gotten to the point now where I've got a better idea of the many things I don't really know anything about. More then likely it's the tip of a really big iceburg.

So far I've figured out my "design goal" for the speakers: bass units that would be able to run from about 200hz down to around the high 30 or low 40 hertz range, providing tight, fast bass such that it will compliment the characteristics of the Fonkens, in a cabinet that will function as the stands for the Fonkens and mirror the front profile of the Fonken cabinets. Before I go any further I must make it clear that this design goal is most definitely based on the Fonkenwoof that Planet10 (Dave) and Chrisb have referred to a few times, especially in
this post in the full range forum. Rather then ask them for their plans, I'd like to learn more about the process myself, build something that will sound great of which I can be proud of because I've been more involved with it's design. To be honest, I also would like to do it this way because there's a "parachute" of a design from proven designers.

When I get more time I'll add some more specifics of what I'm thinking of in terms of cabinet size, design, drivers, and crossovers. Hopefully I won't wear out my welcome with questions.

Thanks,

Ben
 
Cabinet design

Taking into account the Fonken's footprint and the fact that stands of 26" give the best imaging I've heard so far, I come up with a box of 2566.2 in^3, or 42.0l, as the biggest volume I could fit using the bass units as a stand. This accounts for the 45 degree chamfer of the baffle but ignores volume lost to the thickness of the material used for the cabinet, drivers, and bracing.

I've been using winISD pro to model boxes based on these dimensions. A box, wether vented or sealed, seems to be pretty straight forward to model for a single driver per cabinet. I'm also interested in modeling a cabinet with 2 drivers mounted in a push-push configuration. Is there a program that simulates this scenario? If not, can I infer that they'd react in a certain way when set up like this?

My train of thought is this: I figured out what I want to acheive with this project first (design goal). I know what physical parameters I have to stick with to make the cabinet work within my goal (fitting under the Fonkens as stands) so I know what volume cabinet I'm playing with. Using that volume, I'd start to figure out what driver's would work to give me the frequency response I want. Does that make sense?
 
Ben,

An interesting post. I am following not too far behind you in this process.

I am just finishing off a pair of Fonkens. I too took inspiration from planet10 and benefited from a lot of help and encouragement from Dave and Chris. In the end it was important to me that I participate in the design and I came up with my own Fonken design with a Vb of around 6L (which I have since extended to designs for 8L and 10L). The woodworking has been really enjoyable and although they are not yet 100% finished I am already looking forward to building more.

In my case I'm aiming for something that can be used for Stereo and HT and to this end I am designing the Fonkens to reach down to 80Hz at worse (rear surrounds, requires Vb just around 6L) and perhaps a little lower (front speakers, probably go with Vb of 8L minimum). Then I can add a subwoofer/woofer that takes it from there.

I too am thinking along the lines of both designing and building a sub which would act as a support for the Fonkens. I'm a bit concerned about physical box vibration when using the sub as a support so like you I am considering a two-driver solution to cancel out the box movements. I'll start with one, used to support the central HT Fonken and if I need go to with a pair then I'll build a 2nd and set them up as supports for the L and R.

I've just started my research on this topic and I think you are on a similar tack so I'll be interested to see what you decide on. Note that as I've designed my own Fonken, the physical dimensions of my supports (if they are to match my Fonkens) will be quite different from yours - most likely mine will have a smaller footprint (roughly 21cm x 22cm).
 
I think a subwoofer to augment a FR driver is the way to go. I've heard significant tuneful bass from FR speakers, but it always seemed to come across as somewhat slow. I listen to a bunch of electronic music. I've put together a fairly modest sub (compared to some), and it helps a great deal.

I used the 10" Foster driver NPT-11-083 from Jhidley
http://home.comcast.net/~jhidley/

Along with the Apex Sr. sub amp from Apex Jr.
http://www.apexjr.com/Apexsenior.htm

The driver looked like it had been sitting on its face for too long when I got it, but it performs fine. The amp is probably more powerful than I need. I think the XO freq on it only goes up to 160, it might be nice to have higher if you're going to integrate w/ a smaller driver. For my own use I'm very pleased with both items.

Setup is a sealed box that I computed up based on WinISD. I think it's about 4 cuft, minus bracing and internals. Construction was very simple with 3/4" oriented strandboard. I am always suprised how stiff and solid the box feels. I built it in a weekend. Caulk your seams, I was able to pop mine during testing.

It makes solid sound down to 30 hz. I could have gone deeper ported, but I haven't missed the depth and wanted good impulse response. They augment Fostex 167 metrinomes. While the mets actually got down about equally deep in my room, the sub has MUCH greater authority and impact, while also making things easier for the rest of the system. It took several days of fiddling to get the integration right. Phase knob was important, as was getting past the "LISTEN TO MY SUB MUAHAHAHA" volume phase. Now listening buddies report that it is integrated very well.

I'm very pleased with it. And it was, what, maybe $200 to implement? A bit less? Sometimes I see people in the subwoofer forum talking about "I want to make my first DIY Sub, my budget is $600 or so..." I don't know what to think. Maybe their requirements are much greater than mine? Or they (or I) don't know what they're talking about? Maybe I have put together a sub of uncommon value? Perhaps others desire a weapon of mass destruction, but this setup seems very capable and musical to me.

Now I think with the sub that I could make smaller cabs for the 167's. I'm considering the 167-fonken cab for next summer... Not exactly your own situation, but perhaps interesting info anyway.
 
Look up creative sound solution's web site. On their SDX-7 7 inch woofer it has various box designs for this woofer, both vented and acoustic suspension. I myself build two of these woofers each in one cubic foot parts express pre-built boxes. I did use a seperate subwoofer amps for each side.

I found them very fast, tuneful, and a perfect match for my small line array. I would reccomend that the amps used would have a complete cross over and room equalization. This way you can play with the woofers to blend in with your fonkens. It's a little more expensive than a simple subwoofer, but you get a lot better result.

By the way, I forgot to mention that the subs were acoustic suspension.

-JVA
 
JVA,

I like the smaller size (and cost) of the SDX7 vs the SDX10 but I wondered if it had enough 'gumption' to make a sub. It seems that it would be happier around 150Hz than below 80Hz where I want it. As I know virtually nil about such things can you give a bit more detail on your experience with the SDX7 and your opinion on whether it can do double duty between music and light-home-HT use ?

How does an amp have room equalization ?
 
Gareth,

These speakers have plenty of "gumption" for a medium sized room.
I'm very satisfied how the woofers blended in with the Line array. The sub amp does not have room equalization but does have an equalizer in it and has 10 various controls to boost or bring down the various frequencies from 20HZ to 150HZ. The amplifier (in case you are interested) are Reckhorn 400. Check on their website for information. I used 2, one for each side for stereo effect and I cross over at approx. 100HZ. CSS did sell them and they still may. As mentioned before, Planet 10 has a fair amount of info on these woofer drivers.

Joe
 
Here is a picture of the woofer box ready for the woofers.

Joe
 

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Size-wise the 7's are a better match for what I would need if I built the sub into the supports for my Fonkens. Simply, the 10's wouldn't fit since my Fonkens have a footprint that's too small.

I notice that you are using more than one driver though. I like the idea of doing this. My only gripe is the cost of 4 drivers total if I build a sub into both the L and R speaker stands. I could just build a 2-driver sub into the stand for the centre channel or a single driver into the stands for L and R. Hmmm.

Anyhow - still curious about your opinion on sealed verses vented. And when I say vented I'm thinking of something aperiodic/onken-like in an attempt to get some of the benefit of the LF extension and keep some of the 'tightness' of the sealed box. Am I dreaming ?

p.s. those are some very nicely finished boxes in those photos!
 
frugal-phile™
Joined 2001
Paid Member
JVA said:
On their SDX-7 7 inch woofer it has various box designs for this woofer, both vented and acoustic suspension.

My drawings :)

Bob specced the BR, i did all the sealed. This woofer perfoms really well in a sealed box. The XBL motor allows you to use a little EQ -- i got them done to 25 Hz (14 litre sealed) in room with a touch of boost at 30 Hz. This is actually lower than the TL (when it rises to the top we'll do a sealed one and repurpose the TL). Next is a 4 SDX7 sealed/side for a more exotic mid-tweeter,

There is a minor mod that need]'s doing to the SDX7 at a minimum that greatly enhances its performance.

I consider the SDX7 to do what most 10s do. It won't go as low or move as much air as the SDX10, but it reaches smoothly up to 950 Hz (with the mod mentioned above) which makes it really easy to integrate with a FR, something that is harder to do with a dedicated subwoofer that might reach to a 1/3 of that.

dave
 
Dave,

If I can ask you some follow up questions...

So we start with a sealed box to support a Fonken, and having an internal volume of around 14L with a single SDX-7.

Would the box be stuffed (increase in effective volume) ?

What kind of amplifier power level is needed to get the most from this arrangement ?

What kind of benefit from dual-driver and is the 14L then big enough ?

Why didn't you like the TL approach (was the line heavily stuffed ?) ?
 
Re: Re: Cabinet design

planet10 said:


Can you post a sketch. I was only able to squeeze out 28 litres.

dave

A sketch might take a while for me, but maybe I can show how I came up with that figure.....

26 inch tall cabinet is ~660mm. Ignoring the area lost to the chamfers for a moment, 219mm width x 298mm depth x 660mm height is 43072920mm^3, or 43.1L. To get the volume lost to the chamfers, I took the absolute width of the Fonken cab (219mm) and subtracted the baffle width (137mm) and came up with 82mm to get each chamfer being 42mm wide and 42mm deep. Since each chamfer's a 45deg right triangle, put 2 of them together to get a square 42mm wide and 42mm deep. 42mm squared x 660mm equals 1109460 or 1.1L.

If I did the math correctly, I end up with a cabinet volume of 42.0L. Like I said above, though, this is the absolute volume of the speaker cabinet, not the internal volume taking into account the bracing, driver(s), and the thickness of the cabinet material.

It's also not really practical to assume the cabinet would sit directly on the floor, and I 'd need to figure out how the Fonken would interface with the bass cabinet, so the total height of the cabinet would more then likely be around 600mm tall. That'd be 38.1L.
 
Gareth,

Thanks for reviving this thread. I'd been trying to think it through and started to become confused and disillusioned. Gives me the kick in the a** I needed.

I liked what I'd read about planet10's experiences with the SDX7's, but the $100 a piece price tag got me looking at other options as well. If I'm going to do this project, I'd llike to do it right, which in this case seems to mean 2 of 'em per side, or $400 in drivers alone. I'm hoping I can figure something out for $400-$500 for the crossover and drivers. I'm planning on using a Rotel 980 that I have already, which is rated at 120 watts into 8 ohms, to drive each side of the bass cabinets.

Another driver I'd been looking at is the GR Research M-165X. They go for $45 each; running the T/S parameters in winISD I think I'd be limited to running 1 per side due to the volume constraints I'm looking at. The site claims a -3db of 37.5 hz in a ported design of 1.2 ft^3. I'm pretty sure I could make that volume work and stick to the plan of the bass cabinet staying in the Fonken footprint. Being a ported box, I'm not certain if there'd be a drawback to the shape of the cabinet vs a conventional rectangular design though. Their frequency response also extends relatively high, which I imagine would help it integrate with the Fonken better.

Any thoughts on the GR Research driver?
 
Doesn't anyone question how a low sens carbon fiber cone woofer is suppose to mate so well with a banana paper cone midrange driver, especially when used up higher than 60-75hz, and sometimes even side firing to boot? How is it suppose to be a good thing that the SDX7 can, when treated (of course), reach up to 950 hz when used with any Fostex drivers or the like? Couldn't a person just use another larger Fostex driver crossed lower to mate with the 127,126,108 etc and keep the same family sound?

Dave :)
 
frugal-phile™
Joined 2001
Paid Member
Bigun said:
So we start with a sealed box to support a Fonken, and having an internal volume of around 14L with a single SDX-7.
Would the box be stuffed (increase in effective volume) ?
What kind of amplifier power level is needed to get the most from this arrangement ?
What kind of benefit from dual-driver and is the 14L then big enough ?
Why didn't you like the TL approach (was the line heavily stuffed ?) ?

We have a single sealed 14 litre woofer (with amps built-in to support a pair of uFonken). Box walls are lined with cotton felt, and a light fill of polyfluff.

With a single driver 50W seems to do fine, with a pair somethig with good 4 ohm capability is required. I currently use a 150w amp, but that is more for its current capability than the power.

If you double the driver complement, you should double the volume. Have a look at the charts in the SDX7 doc on the CSS site... i show the SDX7 stuffed into a 3.5 liter cabinet, 14litres for 2 drivers gives a modeled system Q of 0,7, but for extended bass duties, a lower system Q is desirable.

The TL started as a sealed box, but when i put in the side-to-side brace (at an angle), i realized how easy it would be to make it a TL. Being a big TL fan i thot we'd try it. Turns out to be shy on volume, but the biggest issue was that it was too prone to unloading the driver, and when a typical XBL driver unloads to its stops it is not pleasant. The TL ended up being stuffed aperiodic and only gives a measured 5 Hz extension over the Fonken* (FonkenPrime) althou with much more weight.

The 17 litre sealed in Tysen, and the single sealed 14 litre in the 2.1 system both go lower with much less liklihood of unloading.

I have some other 7" drivers i'll eventually load into the TL. but they are doing a sufficiently good job now that i'm loath to move tem out until we get arounfd to replacements and that isn't high in the queue.

*(you really need to add a prefix, or suffix to what you call yours, as to be a Fonken it needs to be my 13 litre box, there is also the tradmark issue, but i'm not going to sweat that... i;d call your box Fonken-inspired).

dave
 
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