New here with a question

[alg460]

Hi
First post here. A little about me. I'm not an audioholic and I probably have somewhat of a tin ear. I have done some DIY audio in the past an I'll give away my age here. A zillion years ago I built a PACO SA-40 stereo tube amp kit and its matching tuner kit. As far as speakers, many years ago I spent two weeks pay on 2 Bozak B-207 12" woofers with the dual tweeters on the front. I mounted them in some end tables that had a drawer on top. Not only did they sound like crap but when played loud the drawers and everything in them rattled.

Anyway, just for something to do, I'd like to build a set a speakers and see If I can get better results than my blunder with the Bozaks. I do have just about every type of woodworking tool and I work as an electronics engineer. Should be simple. At least I thought it might be.

After reading these forums it seems speaker design is totally complex, way over my head, baffling and sometimes involves voodoo. All this talk of baffle step compensation, cone breakup, notch filters, driver spacing, on axis, off axis, lobes and degrees makes my head spin. But, I have a feeling that all or most of that stuff will not matter for me. I never sit and listen to music from a "sweet spot". Its just on most of the day for background music and once in awhile I like to crank the volume to the point that the walls and floors vibrate during which time I may or may not even be in the same room.

With that said my requirements for these speakers are simple. I need them to sound rich and full at low volume and punchy and clean at high volume. Rich and full at low volume may be a problem for me because my ears just don't hear bass very well at low volume (whatever happened to the loudness buttons on amplifiers). I have 4 cheap MCM 55-1170 6 1/2" woofers that I bought 5 years ago for $5 ea. I'm planning on a sealed MTM arrangement, floor standing - about 30 inches tall with a volume of 2 cu ft. I do have signal generators and oscilloscopes so I might be able to handle building an at least workable crossover.

So my question is, for my listening habits does all that stuff about driver spacing, baffle step etc really matter?

Thanks
Tony

 

[tvrgeek]

Glad you asked, Some folks here are in your position and believe they already know it all! Yes, all that stuff matters. Speaker design is a combination of mechanical engineering, electrical engineering, woodworking, art, craft black magic and a little smoke and mirrors. Mostly just the engineering. But here is the good news: Kits. There are many very well respected designs that will ensure yo get darn good results. Madisound, Menisicus, Zaph, Parts Express etc. I strongly recommend doing a kit or established design first. If you are really determined to use the MCM's, you can buy a crossover design from Madisound done on LEAP simulation. It will be far closer than you can guess. MTM is a very complex design as it relies on very careful mechanical and crossover aliment to control dispersion. I might be more inclined for your description to do an MMT. Don't expect lower than 60 Hz out of that size woofer. Deep bass requires moving lots of air. Big woofers or subs. 60 Hz though is really all most pop music does. Jazz of course is another matter. True 60 Hz is actually pretty low.

Let me give you a hint. A $5 woofer is not worth the price for other than a garage. A decent cheap woofer starts around ten times that much. The cost of the box is no more for good drivers, and the cost of the crossover may be higher to deal with the cheap driver problems.

So, go read bout the published kits and designs.

 

[sreten]

Hi,

Yes it all matters. FWIW speakers don't do rich and full at low
volume and punchy and clean at high volume without EQ.

30" tall is way too low for a MTM unless your adding stands.
2 cuft is big for typical MTM nowadays, and very big for sealed.

Forget about your cheap $5 drivers, not worth the build effort,
you can't build decent speakers by guessing about stuff.

My RS180 MTM Design

In the 2cuft cabinets described here is an idea
Zaph|Audio - Bargain Aluminum MTM

The latter is a cheaper option and could be tweaked to incorporate
a nowadays much higher value tweeter like the Tangband SD1.1.

rgds, sreten.

http://sites.google.com/site/undefinition/diy
(see if nothing else, the excellent FAQs)
The Speaker Building Bible
Zaph|Audio
Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter
http://audio.claub.net/Simple Loudspeaker Design ver2.pdf
FRD Consortium tools guide
Designing Crossovers with Software Only
RJB Audio Projects
http://web.archive.org/web/20090902
Speaker Design Works

 

[Cal Weldon]

Although these are not intended for any kind of volume, I think the OP just wants to make some noise. Can you guy come up with a box size and maybe suggest a tweeter and simple XO that he might just put together and then decide if it's good enough?

 

[system7]

I think you can do something with those:
MCM Audio Select 6 1/2'' Polypropylene Cone Woofer | 55-1170 (551170) | MCM Audio Select
http://www.geocities.ws/CapeCanaveral/Launchpad/2760/dmp.html

Those are closed box drivers needing about 20L (er, 0.7 cu foot) a speaker and about 8" wide. I've knocked up a 5kHz notch filter to tame the nasties above 4kHz. Should work well enough. Adjust the red resistor for level with a typical soft dome tweeter. This is right for an 88dB jobbie.

To series MTM them, double coil and resistor values on bass filter, halve the capacitors. Easy...

Waits for someone to say it's much harder than that! 😉

 

[alg460]

Although these are not intended for any kind of volume, I think the OP just wants to make some noise. Can you guy come up with a box size and maybe suggest a tweeter and simple XO that he might just put together and then decide if it's good enough?

Well I hope to make a little more than just noise but your assessment is pretty much correct. Actually I'm hoping a bug bites me and I go for a better DIY speaker after this. I love building electronic things. I'm a cancer patient and semi retired and wasting a sheet of wood means nothing to me.

A supposedly successful design was made with these cheap MCM drivers. The Adire Audio Bang. The T/S parameters for these are:Vas = 30.48, Qts=.5 and Fs=40. These are probably really junk because my testing reveals that the Fs is really 58hz so I'm off to a bad start at getting any decent bass out of them. I also think the T/S parameters have changed since the Bang speaker was developed because the Bang's cabinet volume seems low for the current specs. I chose these speakers based on the high Qts so that the speaker will be large in size. Unlike most wife's, mine wants them big so that she can put figurines or flowers on top of them. I think I'm in the ballpark for a sealed design at 2 cu ft.

Tony

 

[Cal Weldon]

Thanks Steve.

Tony, is that something that works for you?

Oh, and making noise is a term used to describe non-critical listening, it's not a negative. 🙂

 

[sreten]

Although these are not intended for any kind of volume, I think the
OP just wants to make some noise. Can you guy come up with a
box size and maybe suggest a tweeter and simple XO that he
might just put together and then decide if it's good enough?

Hi,

If the OP just wants to make some noise about 1 cuft sealed
and well stuffed should work for 2 of the MCM drivers.

In the same vein you could use two of these in a MTM :
GRS PZ1016 2" x 5" Piezo Horn Tweeter Similar to KSN1016A | 292-440
Even piezo's can be used better with a little research.

These are cheap and come with x/o's :
Pyle PLST6 1/2" Neodymium Tweeter Pair | 267-748

rgds, sreten.

However I think the OP may be much better off not guessing.
TriTrix MTM TL Speaker Kit Components Only Pair | 300-700
TriTrix MTM TL Speaker Components And Cabinet Kit Pair | 300-702

 

[alg460]

I think you can do something with those:
MCM Audio Select 6 1/2'' Polypropylene Cone Woofer | 55-1170 (551170) | MCM Audio Select
http://www.geocities.ws/CapeCanaveral/Launchpad/2760/dmp.html

Those are closed box drivers needing about 20L (er, 0.7 cu foot) a speaker and about 8" wide. I've knocked up a 5kHz notch filter to tame the nasties above 4kHz. Should work well enough. Adjust the red resistor for level with a typical soft dome tweeter. This is right for an 88dB jobbie.

To series MTM them, double coil and resistor values on bass filter, halve the capacitors. Easy...

Waits for someone to say it's much harder than that! 😉

Thanks for that info. Have you used these drivers before and did you come up with that frequency response plot yourself? By driving these with a signal generator I thought it was my imagination but I definitely heard something strange at around 4500hz and your plot seems to show it.

Tony

 

[alg460]

Thanks Steve.

Tony, is that something that works for you?

Oh, and making noise is a term used to describe non-critical listening, it's not a negative. 🙂

Thanks Cal

Steve's reply was helpful. I got a lot to learn here but I think its something I want to learn. I'm finding it all fascinating. I'm to old now but I think I have the background to figure out a a good part of it.

Tony

 

[system7]

I lifted the measurements from the article I quoted. But it's enough for me to know it's a 6" polycone driver of lowish inductance. The rest is experience.

FWIW, ALL 6" drivers have a peak at 5kHz. Simple matter of the distance from the dustcap/voicecoil to the surround being half a wavelength of sound. It'll be about 3.5cms here. Being damped poly, it'll rolloff a little faster than the paper cone I modelled, but not much, and the notch is a good one-size-fits-all. You might then find 4uF works better in the tweeter circuit. I modelled a narrowish baffle.

You could go for that Adire Audio Bang circuit, but simplify the tweeter section for another tweeter. It's a lower crossover point. 8uF and 0.27mH, wasn't it? Designed for a wider baffle too. But I like mine! 😎

 

[Cal Weldon]

I'm to old now

Well Tony, nothing like something new to make you feel younger.

At 51, I am considered a spring chicken by some here, so... 🙂

 

[badman]

Well Tony, nothing like something new to make you feel younger.

At 51, I am considered a spring chicken by some here so... 🙂

And older than dirt by some others 😀

 

[alg460]

Well Tony, nothing like something new to make you feel younger.

At 51, I am considered a spring chicken by some here, so... 🙂

Well I'm 55 but I've been chemo'd and radiated so I feel old. Some tell me I look young for my age. I'm impressed with the real knowledge here - not just people blurting out unsupported opinions.

Tony

 

[system7]

And older than dirt by some others 😀

Yup, well you can't beat experience, IMO. I read the oldies here most. 😀

The unusual thing about these drivers is the loose foamed surround. This is quite Acoustic Research albeit with a weaker motor in this case. A Qts of 0.5 and a Vas of 30L is Floppy to the max! It's why you are getting that big uncontrolled edge resonance at 5kHz. A purer midrange driver would have a more rigid rubber or cloth surround.

There's a lot to be said for fixing the front baffle to battens here, then you can change drivers and baffle later with ease...
http://www.diyaudio.com/forums/multi-way/223174-interesting-read-i-found-lossy-cabinet-designs-harbeth.html#post3234256

 

[ODougbo]

Are you set on sealed? These 6.5's will shake the room in a vented box. Very reasonably price for such a robust speaker driver.

Anarchy's are back!!

Denovo Audio Anarchy woofer DIY Sound Group

diVine Audio | Ansonica

 

[system7]

Are you set on sealed? These 6.5's will shake the room in a vented box. Very reasonably price for such a robust speaker driver.

Anarchy's are back!!

Denovo Audio Anarchy woofer DIY Sound Group

diVine Audio | Ansonica

Sorry, Doug, much as I respect your ability, you need an oldie to tell you that foamed surround is NOT SUITABLE for reflex. 😀

These cones rely on air spring to get back to centre. It's called acoustic suspension. 😎

 

[alg460]

Yup, well you can't beat experience, IMO. I read the oldies here most. 😀

The unusual thing about these drivers is the loose foamed surround. This is quite Acoustic Research albeit with a weaker motor in this case. A Qts of 0.5 and a Vas of 30L is Floppy to the max! It's why you are getting that big uncontrolled edge resonance at 5kHz. A purer midrange driver would have a more rigid rubber or cloth surround.

There's a lot to be said for fixing the front baffle to battens here, then you can change drivers and baffle later with ease...
http://www.diyaudio.com/forums/mult...ossy-cabinet-designs-harbeth.html#post3234256

Steve

I'm going to go ahead and start planning on building these things and use your crossover even though I'm a little confused.. Would I be better off paralleling the drivers? I don't know what I'm talking about but I think my amp could handle it as its spec'd at 125W at 6 ohms. What would change on the crossover? ODougbo mentioned that a vented design would be better. If I went vented what would change and could I do it in 2 cu ft or so?

Thanks for your help
Tony

 

[alg460]

Sorry, Doug, much as I respect your ability, you need an oldie to tell you that foamed surround is NOT SUITABLE for reflex. 😀

These cones rely on air spring to get back to centre. It's called acoustic suspension. 😎

Looks like I posted a few minutes after you posted this so I guess that answers my question about going vented. Confuses me even more though as the Bang was a vented design. So much to learn.

Tony

 

[tvrgeek]

Thanks Cal

Steve's reply was helpful. I got a lot to learn here but I think its something I want to learn. I'm finding it all fascinating. I'm to old now but I think I have the background to figure out a a good part of it.

Tony

The physics has not changed, just the quality of the drivers and the tools we have available. It is a lot easier to use a PC based sim than my Pickett.