Speaker design etiquette

[sploo]

Over the last couple of years, I've been planning to start building loudspeakers for sale (very small numbers, and hopefully 'fancy' artistic cabinets).

Whilst I'm reasonably happy I can build a box, I'm not so hot on the electronics. As a result I'm looking at adapting existing designs - though I understand the crossover has to match the box (baffle step etc.), so may need mods if I use a different box shape. I'd try to match the original internal box volume though.

What I was wondering, is, what is the accepted etiquette of using someone else's driver configuration/crossover?

I know that some driver manufacturers, such as Seas, have designs on their website, and I expect they'd be happy for people to make and sell such units, as they're in the business of selling drivers.

There are however many hobbist designs around on the net (and clones of commercial units). At what point does taking a woofer and treble from a drive manufacturer, and adding a reasonably simple crossover become a proprietary design?

My attitude would be simply to ask the designer for permission, but it occurs to me it'd be pretty hard to protect a driver selection + crossover design, unless you'd done something extremely novel.

I'd be interested to hear people's thoughts - especially from designers and anyone that has a handle on the legal issues.

 

[B_Pay]

A crossover is not patented...most manufacturer's use the same *** thing. I would be more worried about the shape of the box and how it impacts the sound.

 

[Audioholics]

Just don't try to sell them on our forums...

 

[f0am]

Just don't try to sell them on our forums...

Heh i've seen enough of that for one day!

 

[Swerd]

I think your approach is reasonable and is one that some of the better amateur designers encourage. They usually state that their designs are free for non-commercial use, and ask that you to contact them if you do want to sell them commercially. For example: http://www.speakerbuilder.net/web_files/about.htm.

It certainly is true that a crossover design is meant only for the specified drivers and baffle layout. You could easily modify the baffle width, adjust the BSC accordingly, and the result would technically be a different crossover. I do not know whether that would qualify as different by American or British legal standards.

I think what really matters is how many speakers you plan to sell. I do know of one amateur designer whose design was taken directly from his web site, manufactured and sold in amounts that went beyond small. He had to take legal action to protect himself from that kind of commercial exploitation.

 

[sploo]

Just don't try to sell them on our forums...

Clint, the fact there's no smiley on the end of that does worry me a bit!

What I absolutely want to avoid is: a) p!ssing anyone off, b) getting a letter from a lawyer!

My general understanding of speaker design is that the box volume is often dictated (or at least suggested) by the TS parameters of the woofer, and the crossover point is similarly governed by the choice of woofer and tweeter. So, if someone else has used a well known pair of drivers, then surely you're likely to come up with something very similar - allowing for BSC as noted by Swerd.

It's that grey area between stealing, creating something similar due to learning from (and modifying) an existing design, or creating something similar due to independantly using the same design processes and coming up with a close solution.

Swerd - Very interesting info on the speakerbuilder site. My plan is to 'add value' by creating artistic/exotic cabinets, so perhaps the licensing path would be the best way to go - i.e. team up with an experienced designer (for the driver selection & crossover), and concentrate on building the boxes.

I think I'd initially be looking at a handful of units a year (<10). If everything went really well, I could see a distant possibility of a few tens a year (<100), but that's not even on the horizon yet.

 

[Swerd]

Swerd - Very interesting info on the speakerbuilder site. My plan is to 'add value' by creating artistic/exotic cabinets, so perhaps the licensing path would be the best way to go - i.e. team up with an experienced designer (for the driver selection & crossover), and concentrate on building the boxes.

I think I'd initially be looking at a handful of units a year (<10). If everything went really well, I could see a distant possibility of a few tens a year (<100), but that's not even on the horizon yet.

Perhaps you should contact a semi-amateur speaker designer in the USA named Dennis Murphy. His email address is listed on his web site. I mention him only because I know he will retire soon and plans to develop one or several of his unpublished designs into a commercial venture. I have built two of his designs (the CAOW1 and the MB20) and have heard several others. I admit to being an unabashed fan of his designs, but I have no financial or commercial interest in his work.

His web site lists his DIY designs that are free for individual use, but he has participated in the past with other small commercial speaker builders in the US in a similar manner to your idea of adding value by building exotic cabinets. The model 1801b made by Dave Ellis, and several models sold by Salk Sound have crossovers designed by Dennis.

I do not know if he is interested in selling speakers in the UK, but why don't you ask him yourself?

 

[Audioholics]

Clint, the fact there's no smiley on the end of that does worry me a bit!

It just means don't use our forums to sell your speakers. Throughout the years many have seen $$$ thinking they can take advantage of the readers here to sell and talk about/market their speakers.

 

[sploo]

Perhaps you should contact a semi-amateur speaker designer...

Great info Swerd, many thanks.

I've seen Dennis' site before, and Salk Sound, but I didn't know that the Salk units used some of his work. As an aside, given the number of Seas drivers in many of those units (and the 1801b) the prices they're charging look very good to me - especially the great looking offerings from Salk.

I've got some more techniques to learn for making the cabinets, but I think I'll be pursuing some contacts with guys like Dennis in the future.

It just means don't use our forums to sell your speakers...

Understood. I've gained a huge amount from this forum, from understanding cable issues, to room acoustics, to equalisation techniques, so I certainly don't want to stir things up.

Given that I've learnt so much here, I'd love to share what I learn as I go on (construction and box finishing techniques etc). Nearer the time (and assuming I think I've got stuff worth sharing) I'm quite happy to clear any content/tone with a mod before posting.

 

[jcPanny]

Speaker building kits

Sploo,
You might consider a speaker building kit which includes the drivers and crossover components. The intent with these kits is for you do design and build your own cabinet and the designer is getting some of the proffit by your use of the kit.

 

[sploo]

Sploo,
You might consider a speaker building kit which includes the drivers and crossover components...

Buying a couple of kits was actually my introduction into speaker building.

This is a photo taken when I was experimenting with a home built LCD projector: http://spikyfish.com/speakers.jpg. The speakers are from kits (I cut the panels) and the AV rack is something I built after seeing a similar unit on the web (oh, and the centre stand is just something I cooked up). The kits were from http://www.wilmslow-audio.co.uk/ and the towers are particularly impressive.

I wasn't sure about doing what would effectively be a reselling route for an established kit company. What I'm planning wouldn't be a challenge to their business, I just felt it would be a little odd to ask. Couldn't hurt I guess.

The only other thing is that they of course are in business, and therefore need to make a profit on the kits they sell, so you'd be paying a markup on the parts. Of course, they might drop that a bit if you were going to do them some decent business...

 

[Ampdog]

Sploo,

Since your original subject was cross-overs, I would re-iterate what another member said, that cross-over design can really not be patented - it is all quite general, so nobody would be able to challenge you about using their inductors, capacitors, etc. And it is very decent of you to inquire about this!

But there could be an even greater caveat than copying existing designs. A cross-over network can be quite specific to a particular loudspeaker system - box as well as drivers. Not wanting to rain on the parade (or into your speaker box), but with the little experience I had I was shocked to find the peaks/troughs in response of a simple 2-way system when checking with a microphone. Point is that often such a cross-over would have to consist of more than the simple 2xL 2xC network. As you seem to know, driver impedances are anything but simple resistances at frequencies in the 1 - 5KHz region. Get an L.C (especially undamped) with the wrong phase characteristics here, and you might have a sharp peak/dip in the response. In a "simple" 2-way cross-over for not very otherwise drivers, I ended up with 3 inductors, 5 capacitors and 2 resistors. OK, having had a suitable program and impedance graphs for the drivers, I was perhaps a little critical.

As said, not desiring to put you off, but since you seem to want to design a fairly decent product, it would be nice if you could find some way of at least plotting the final response. That need not cost an arm and a leg, in fact I use a fairly cheap microphone that I calibrated against an expensive one. (I do not have an anechoic room, but plot the response on my lawn! It does bring one within the ball-park.) With a little knowledge you could with only that showing say a peak somewhere, begin to try a damping network at that frequency, for example.

Perhaps others could reply here about their experiences with simple cross-overs. Perhaps they could prove me wrong!