Attack of the Clone

[philip]

After two years of solid research and reading of the diyaudio.com pages, I’m finally ready to begin my own project. I’m probably only going to do this once, so I want to get it as good as I can. Reading up on speakers, I was taken by various attempts to “clone” commercial products, namely the Wilson Audio WATT/puppy combo; this speaker became my benchmark in performance and looks. As my drivers are totally different, any resemblance will be in looks (and hopefully performance) but what the heck!

I really like what Tony Gee does – he puts a lot of design into his projects – and so want to use the drivers and crossover of the “Tempo” (Seas tweeter, Vifa PL18WO mid) but in a closed box of ~15L for the top half. For the bottom half I want to use the Seas L22RN4X/P ported in a ~30L enclosure. This would be a 2.5-way loudspeaker (like some of Tony Gee's other projects) with a 1st order low-pass filter and zobel correction on the woofer. So far so good if you're only using one woofer, but here's where it gets interesting. I want to use two woofers. Is this possible?

I have no idea how to wire this. If I run the 2 L22’s in parallel, the sensitivity goes up way above that of the Tempo. If I run them in series then I now have a 16ohm load vs. the 8ohm of the uppers and who knows what will happen. So what do I do? I need the help of the diyaudio.com community because I really want to make this work. Thanks for any help in advance,

Philip

[planet10]

Originally posted by philip
I’m probably only going to do this once

It is VERT hard to do it only once... not only is it addicting, with what you learn building the 1st one, you just know how to build the next one better

I want to use two woofers. Is this possible?

What XO point were you thinking of? If less than 200-250 Hz you really should be thinking active woofers -- then the relative sensitivities don't matter.

dave

[philip]

Yeah, you're probably right, just reading about speakers is addicting. I mean build an all out project when I say do it once, this stuff isn't cheap. I've built a few kits so far but have been saving and planning for this special one so want to do it right.

The crossover point is not decided, but could be anywhere from ~150 like the real thing upwards. Tony Gee's Andromeda (1 x focal 13kx) uses 300Hz I think, and ~500Hz I think for the Geers EveII which he helped design (1 x ss 8"); these are examples of other series 2.5 way projects I know. Either way, two main considerations deciding the range of the crossover would be the roll off of the Vifa PL18 and the wierd cone action of the metal cone at higher Hz. I anticipate choosing a crossover point in the range of 150-300, maybe closer to 300. I could use the L26 to overcome this problem, but I really like the look of the 2x8's and they model a bit better for my purposes. I want to keep this project passive to maintain their versatility and because I like the concept of an integrated speaker i.e one input, speaker does the rest.

Philip

[planet10]

Originally posted by philip
I mean build an all out project when I say do it once

Something i always try to talk people out of... you are likely to find that building up a couple simplier projects 1st will actually save you money...

dave

[philip]

Maybe I need to back the train up a bit and ask a different question. This is about sensitivity. Before I knew much I would have said just run the two L22's in paralell and then cross them over to the upper speakers. However, I have heard that when you run two speakers in parallel their sensitivity increases by 6dB. That's what's stopping me. What are the effects of running two woofers in series (16ohm load) or parallel (4ohm load) on sensitivty?

The reason I am confused is because if you look at many mtm designs, you have 2 woofers in parallel being crossed over to a tweeter, often of similar sensitivity. If there is a massive sensitivity boost by running two woofers in paralell, then the speakers should not sound right, but mtm's sound great. What is going on in this situation?

Philip

[philip]

p.s. I know this has been discussed before with the general conclusion that in theory running two woofers in paralell raises sensitivity by 6dB. However, previous posts discuss additional factors such as driver spacing and baffle step but are ambiguous as to their effects on sensitivity.

Philip

[planet10]

Originally posted by philip
I want to keep this project passive to maintain their versatility and because I like the concept of an integrated speaker i.e one input, speaker does the rest.

I always figured separate powered woofers were more flexible.... even a couple plate amps would do the job.

dave

[planet10]

Originally posted by philip
I have heard that when you run two speakers in parallel their sensitivity increases by 6dB

Depends on your amp... again better just to have a separate amp -- and if you are crossing as low as you suggest, often cheaper. Certainly a much higher probability of better sonics.

dave

[philip]

Hey man, yeah, I'm sure separate powered woofers would sound great - I've heard that biwiring can really make improvements. However, there are many factors, not all of them related to speakers, that have led me to a single-amp design. As for the 2 8's, part of that is just me.

Anyways, I've been doing a lot thinking about this design. I know that it isn't recommended that you attenuate a woofer because of the high power involved, but I had an idea: Instead of using one attenuation circuit for the two woofers combined, what if I was to attenuate each woofer separately, so that their overall circuit was attenuated. For example, the sensitivity of the upper system is 87dB/1W/1m. What if I was to attenuate each of the L22's from 86 to 81, so that when run in parallel they achieve 87dB. I don't have an excessively powered amplifier, nor would I be running them at loud volumes so I don't know if this would be a problem in my case. Would this work?

Philip

[planet10]

Originally posted by philip
Would this work?

Not without affecting the sonics... the phrase "suck the life out of the music comes to mind". If you don't go active on the bottom, keep the XO 300 Hz +

dave