Ported M8n MTM designs.....

[Paul H]

It looks like the M8n's should be available in about a week, so it's getting near time to start ordering and building, rather than just thinking about other questions. In the meantime I thought of some other questions.

If the crossovers are built into totally separate boxes from the speaker boxes, how far away from the speakers can they or should they be? (ie do longer wire feeds after the crossover rather than before affect sound quality?) I'm using 12ga speaker wire for feeds before and after the crossover.

Any thoughts on using two thinner but different materials (ie 1/2" ply plus 1/2" mdf, aka 'constrained layer damping') as opposed to the 1.5" mdf? Or is that a 'been there, done that, didn't like it'?

Thanks,

Paul

[ThomasW]

There should be short leads from the XO outputs to the speakers.

If you want to go with CLD that's fine. As big as your cab are going to be it might be a good idea to use some baltic birch ply just to keep the weight down.

For Tibor's speakers we used double 3/4" mdf, that was certainly adequate, but we weren't going for max low bass output.




theAudioWorx
Klone-Audio

[Paul H]

... we used double 3/4" mdf, that was certainly adequate, but we weren't going for max low bass output.

This statement would suggest that the double 3/4" mdf is ok, but not the greatest for low bass output.

I've read a bunch about CLD and other vibration reduction techniques for loudspeakers but seem to find differing opinions everywhere.

I was thinking about either a 2 layer configuration of 5/8" or 3/4" plywood plus mdf, or a three-layer with 1/2" mdf-plywood-mdf, bonded with a trowel-on non-hardening glue.

Does anyone have any specific suggestions for CLD configuration or comments on the above layering?

Paul

[ThomasW]

I was thinking about either a 2 layer configuration of 5/8" or 3/4" plywood plus mdf, or a three-layer with 1/2" mdf-plywood-mdf, bonded with a trowel-on non-hardening glue.

Hey as long as you've got a forklift, the sky's the limit...... 8O

Seriously, the goal is simply to have the Fs (resonant frquency) of the box, out of the passband where the drivers are operating. There are 2 basic approaches to doing that. All MDF = high mass/weight, low Fs. All Baltic ply = low mass, very rigid, light weight, high Fs.

Some studies seem to indicate that CLD isn't all it's cracked up to be. So it's just one grand experiment. We haven't done a lot of experimenting with it.

Tibor's speaker is pretty small and even with the minimal bracing it's a very good box.

Given the larger size of your enclosure, I'd recommend any combination of material that makes a 1.5" cab, but combined with lots of 3/4" Baltic ply interior bracing.

Also if you want 'over the top' then copy the Avalon Acoustics idea where there is a brace directly behind each woofer that actually attaches to the driver's magnet, be careful not to obstruct the pole piece vent. Note that there is a felt gasket between the magnet and the wood brace.




theAudioWorx
Klone-Audio

[Paul H]

Thomas, sorry if my description was muddled and it seemed like I was proposing 7 or 8 layers of 3/4" - forklifts in the house are frowned upon

I keep looking for other cabinet wall ideas but will probably end up at 2 layers of 3/4" mdf. Actually I keep looking at and questioning lots of stuff, but that's a large part of diy speakers, I would think.

Weight per speaker will be in the 180-190 lb range.

I'll use mdf or ply for horizontal bracing with cutouts for air circulation. Bracing will go immediately above the upper woofer, right below the bottom woofer, and right in between woofers, with a cut-out for the tweeter. One or two more braces will go in the bottom half. End result will be a 49" high cabinet with braces spaced approximately 9" to 12" apart vertically (height excludes 6" high base).

Paul

[ThomasW]

Ply is preferred of MDF for the bracing. Ply's greater strength is an advantage in this instance.




theAudioWorx
Klone-Audio

[Paul H]

I see that PE has updated the M8n delivery - from early March to early April.

Still waiting as fast as I can ....

Incidentally, as I recall the crossovers noted here were developed specifically for the M8a. I understand that the M8n's are extremely similar, but are they close enough to use identical crossover values?

Paul

[ThomasW]

I think this was already covered, but I maybe confusing posts in the Arvo vs the ported MTM threads.

The M8n is a drop-in electrical replacement for the M8a, so the crossovers are identical. Physically it has slighly different dimensions, larger diameter and different cutout hole.

Bummer about the change in delivery date




theAudioWorx
Klone-Audio

[Al Garay]

Paul

Have you contacted Solen in Canada? They still list the Hi-Vi M8a in their catalog.

http://www.solen.ca/hiv.htm

It is worth the phone call.

SOLEN INC.
4470 Ave. Thibault
St-Hubert, QC J3Y 7T9 CANADA
Tel: 450-656-2759 Fax: 450-443-4949


Good luck,

Al

[Stevepaul]

I called Solen........They don't carry Hi-Vi anymore. They also don't have any stock left over of any of the Hi-Vi stuff. I called them this morning (3/4/03) to Verify.

I guess we wait until early April to see what happens! :nonod:

Steve

[Paul H]

I was playing around with unibox last night and noticed that the M8n's movement at low frequencies is very high relative to the 5.8mm xmax. It's up around 50-70mm when frequencies get down to 30-40 Hz - visions of M8n's flying across the room

Now I'm aware that 'a little bit of knowledge is dangerous', and that statement could apply to me wrt speaker design. I also know that Unibox will oversimplify real life effects.

But, is there any truth and concern in the Unibox predictions that xmax will be wildly exceeded using an M8n in a full range speaker?

Paul

[ThomasW]

Paul

I don't know about the Unibox model.

I can tell you that I had a pair of the M8aMKIII's (single M8a driver/box) up and running fullrange. Driven by a Ayre V-5x (150/channel/8 ohms) the speakers had enough bass (upper to mid 30Hz range) to vibrate the floor, and the woofers weren't moving very much.....

Tibor's MTM's although in a relatively small seal box, have enough bass that so far he hasn't been modivated to build a sub............. that maybe a SAF thing though.........




theAudioWorx
Klone-Audio

[Paul H]

Thanks Thomas,

I've had long enough time to think about these while waiting for the M8n to be available that I'm wavering on building the ported and might go sealed - smaller cabinet and I'll want a good sub for HT anyway.

That being said I see this morning that M8n's are now due April 23rd at PE, rather than April 2nd previously forecast. They seem to be a month away from arriving, and keep on being a month away no matter when I check.

It'll soon be time to move on to "Plan B", a different set of speakers with drivers that are available. Hmm.. no specific plan B in mind yet though ..

Paul

[ThomasW]

You might try ordering the drivers instead of just looking at the expected availability dates.

One of the people posting on the Arvo thread (stevepaul), received his M8n drivers on March 8th




theAudioWorx
Klone-Audio

[Paul H]

Good suggestion Thomas. I ordered 6 drivers (2 for centre channel also) and various related 'stuff' today.

Paul

[Al Garay]

Way to go Paul. I hope you get them soon.

I recommend you try building extra cabinets, may come in handy just in case there's a problem with some panels. If you are fortunate to have no troubles, you will have an extra set of cabinets to use or sell.

Al

[Paul H]

Way to go Paul. I hope you get them soon.

I recommend you try building extra cabinets, may come in handy just in case there's a problem with some panels.

Al

Problems - how could that happen Actually my challenge for speaker-building is in understanding the electronics and acoustics. The woodworking for cabinets is the relatively easy part for me.

Paul

[Paul H]

Having finally settled on a shape for the speakers, I take back that last post I made about the woodworking not being hard.

The overall height and depth of the cabinet for ported always seemed too big, so I started playing with autocad and drew up a cabinet approx 45" high, 12" wide at the front, 19" deep, 8" wide at the back, with curved sides (about an 18" radius, or 2 1/2" 'bulge' on 19" wide piece). The curved sides result in about 16" max width, without affecting front baffle width. The extra width lets me keep the other dimensions in the range I'd like.

I'm planning on thin sheets and laminating numerous layers to each side - thin mdf if I can find it. Any thoughts on material thickness and type?

Paul

[JonMarsh]

You could look at thin plys, but you might also want to take a look at 1/4" HDF. You can get that in 2' X 4' pieces at most HD's, for example.


Paul, Re the Unibox modeling, I'm curiouis- what kind of input power and output SPL's are you "running" for simulation? Taking an "optimum" extension design from the M8ta, for dual woofers, the internal volume would be ~120-130 liters; this can be tuned to 24 Hz, with a net response at 24 Hz which is - 6dB from the 100 Hz level (anechoic; don't forget, Unibox doesn't model room gain).

With drive voltage equivlant to 50W 8 ohm nominal power (per speaker), (about 100W total at 4 ohms), the vented box SPL (per cabinet) will max out around 110 db before room gain, at one meter from one speaker. Now, let's get conservative, back off on the power 3 dB, and add it room gain and the second speaker- you're still looking at over 110 dB at one meter down to 24 Hz. If that's not loud enough, get a sub!

BTW, that does recommend dual 4" ports; dual flared 3" ports would be a little small; minimum recommended port dia with flares both ends is about 8.5 cm.

How did you come up with 40 mm Xmax? What kind of power level and SPL? And what cabinet and tuning?

Best regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Paul H]

you're still looking at over 110 dB at one meter down to 24 Hz. If that's not loud enough, get a sub!

If that's not loud enough for anybody, they need help with their hearing, not a sub

Actually, I have a sub. I want a full range speaker so that I can listen to stereo music without a sub as I find tough to properly dial in a sub to the mains for music. Now for HT, the LFE's will go the the sub, even after these speakers are up and running.

Back to Unibox, the comment on the max excursion wasn't a complaint about power handling - more of a "what am I doing wrong with this software?" question.

I was running 50W power (100 at 4Ohms), 120-125 litre box size, 25-26Hz tuning, etc, etc - basically the same numbers you just provided (there's hope for me yet ). Then I clicked the "Compare" worksheet, scrolled down and saw cone excursion above 6mm (5.8 is max per spec) at any frequency below 70Hz. Unibox version I have is 4.04, btw.

Paul

[ThomasW]

Don't know if it's available in your area but some of the commercial cabinet shops around here use a product called bender board. It comes in a couple of configurations.

The stuff I had was a ~3/8" thick, 2 layer Laun ply. The layers had the wood grain oriented so they were parallel. They were attached with a flexible glue, and could be formed into a pretty tight circle.

I've seen several people just make their cabinets using 1/4" regular ply. They soak each layer in water, then gluing them in place, one layer after another.




theAudioWorx
Klone-Audio

[PMazz]

For a speaker, I would use 1/8" bending panel. The stuff we use is made from birch veneers and is easy to bend. Allow for some spring back if you need an exact radius.

If you don't really want to make it all yourself, here are 2 sites with pre-formed shapes.

http://www.cubiconcorp.com/shapes.htm

http://www.tapeease.com/4rounds.htm

Pete

[Dennis H]

Here's a sketch someone posted showing the construction of a Swans Diva. 1/2" thick 'barrel staves' sandwiched between two layers of 1/8" sheet.

[Paul H]

Interesting Dennis - I think I'd use that method if the radius I was after was a little smaller.

I ordered everything early this week for the 2 mains and centre, including drivers, electronics, l-pads, flared ports, wire, connectors, etc ... I should be getting parts coming in from various parts of North America within the next week or so.

I ordered 3 bazillion 10uF caps - thanks for the tip Thomas - or should I wait until I see how long it takes to assemble them before I thank you

Paul

[ThomasW]

or should I wait until I see how long it takes to assemble them before I thank you

You might want to wait until after the fact before you thank me... :rf




theAudioWorx
Klone-Audio

[JonMarsh]

Have you ever seen what a "big" crossover looks like before you start to assemble it using a "bazillion" 10 uF caps?

We have....




Still, they're hard to resist, because the price is so "right", and the quality and performance very good. :B


~Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Paul H]

Noooooo.... and it's too late I 've already ordered 150 caps

Actually I did see that picture before, shame on you for trying to scare a new speaker builder like me! Those crossovers are for your three-way arvo. The crossovers I'm doing will only be huge, not monstrous .

I received my first delivery today with tweeters, inductors, some caps and resistors. I'm going to lay out the crossovers on a board this weekend and see how big they will actually be.

Paul

[Paul H]

I haven't asked any really dumb questions for a while, so here goes.

What kind of wiring should be used in the crossovers to connect various components - 12 - 18ga, solid, stranded, speaker wire, whatever's laying around?

Are the speakers (drivers) hooked up by soldering the connecting wire directly to the driver terminals, or should I be looking for clips to connect to the terminals?

Paul

[ThomasW]

We use multi-stranded mil spec (silverplated copper with Teflon insulation) for speaker internals.

I use 12 gauge for the woofers and 16 gauge for the tweeters.

I get mine from ApexJr

We think that soldering the wire to the speaker terminals is the best idea. Soldered joints don't ever vibrate loose.




theAudioWorx
Klone-Audio

[Paul H]

Well I started making the cabinets, received my tweeters and other misc parts, and a big box of 10uF caps.

I've got an LCR meter coming in my PE order in the next week or so. In the meantime I'd like to assemble some of these caps this weekend. I'll fine tune and adjust later if necessary.

What do these GE 10uF caps actually measure out to on average? I'm guessing about 9.5?

Paul

[ThomasW]

Generally speaking, all caps are going to be on the low side of the +/- tolerance spec. Thats because it's using less material, so saving the mfgr money.

I glue up and solder, figuring 10mfd per cap. Then when it's completely assembled, I measure the cluster and add whatever is needed.




theAudioWorx
Klone-Audio

[JonMarsh]

In my experience, as I measure all before assembling, they're typically around 9.75 uF, which is only about 2-1/2% low. That's rarely worth or needing to compensate. But it's a good idea to check. Thomas's idea is quite reasonble, as it's only the complete value that matters. If you're within 2%, that's generally fine.

Best regards,

Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[Paul H]

I'm using an LCR meter from PE, which at least claims a 5% accuracy.

The GE caps are measuring almost dead on 10.0uF (+-0.1), as opposed to the 9.75 that you're typically getting (with a better meter I imagine), the solen 3.9uF caps are measuring 4 to 4.1, and inductors are also measuring about 3 to 4% higher than they are labelled from the manufacturer - this might suggest that the meter is consistently measuring 2-4% higher than the parts acrtually are.

I started putting the caps together with a 25W soldering iron - bad move. After switching to a 45W iron had no problems finishing the caps for the first crossover, so .. Thanks Thomas

Paul

[Ten 99]

Paul,

Would you mind giving some approximation price break down as to what these are going to cost you for the drivers and components that make up the cross-overs? Also, a source for where you purchased your items would be nice.

I'm thinking about tackling a set of these myself, but I'm not 100% sure yet.

It wouldn't be until the summer when I could earliest work on them at any rate.

Chris

[ThomasW]

When we built Tibor's original set of speakers, the total parts cost was ~$650 for the pair. His pair had the more expensive, but now discontinued M8a woofers. As a result building the speakers now should cost less given the significantly lower cost for the M8n woofers.

Almost all the pricing info is covered elsewhere in the thread. Here's a quick breakdown.

The large value caps are made from clusters of the 10 mdf GE caps sold by Madisound. They are $.90ea when bought in lots of 100+pcs

Since Paul lives in Canada he getting his inductors from Solen. The primary US supplier of Solen is Madisound. Parts Express sells a 'Perfect Lay" brand that are probably made by Solen.

The only place to get the Hi-Vi M8n drivers is Parts Express. If you're going to use the VifaXT25 tweeter then again PE has good prices.




theAudioWorx
Klone-Audio

[Ten 99]

Hi Loyd,

Here's info on the 2-way MTM center
...
We'll be making a 3-way center using the Arvo design. So a vertical MTM stack with woofers on either side. Info on that design won't be available until the end of March, when Jon returns to Denver for his next visit.....

Thomas, I'm a real noob when it comes to all of this, and please understand that I have no electrical background at all. I can follow some things pretty decent for a lay person, but I have no engineering skills.

The Arvo Project is a dipole design, isn't it? Just wondering how / if you and Jon did on that 3-way center? Also curious as to how this could be translated into a non-dipole (direct radiating?) setup like the MKIV?

I've got some more questions, but I'll put it in a seperate reply. Trying not to get too many on one and make it too confusing.

BTW, the only non-sub experience I've had was doing a set of these for my parents. They turned out great, and even my wife was impressed.

[Ten 99]

Great. If I'm reading you right, then I could expect to come in about $100 cheaper due to the cost of the Hi-Vi M8n versus M8a costs.

I'm really partial to the shaping of that MkIV T&A that Jon is doing. That's a sexy looking design. If I've followed correctly, that's a ported tower version of the MkIVa?

Sound wise, what is to be expected in the differences between that TM tower and an MTM tower? Also, would there be any benefit to a shap like the T&A but in a TMM configuration? Could the cross-over of the MTM be used in such a creature, or what this just sound like butt? I appologise if some of these Q's are basement level things. I'm just trying to understand and learn a bit about what's going on here, without having get up to my shoulders in it. I'm cool with short and to the point answers, but if you wanted to expound on some theories (that a layman could understand), that'd be cool too.

FWIW, my current speakers are Rocket 750's. I know these are the finest speakers out there, but for the $$, I felt that they were very well made and very nice sounding. Now I'm looking to make myself some speakers that will sound better, and have the look I want to give them.

The only thing I don't like about the M8a/n drivers is the gold anodizing on them. Is it better looking in person? I wish they came in black anodizing. That would be sweet. But those things can be worked around. In the end, looks play a distant second to sound. I'm just trying to keep these things from causing a scowl from the wife.

[Paul H]

Thomas covered all the suppliers I've ordered from.

I'm spending about $2,000 - Wait!! That's Canadian $, for 3 speakers (two mains and a centre) and includes everything - speakers, crossovers, wood, glue, hookup wire, shipping costs, etc, and includes about $300 for LCR meter, additional connections, speaker wire and other "might as well get it while I'm placing orders stuff" that you wouldn't need just to build the speakers.

Cost in US$ before taxes and using $1.33 exchange is about $370 per speaker.

Your pricing will of course vary slightly depending on who you get it from and your shipping costs.

Paul

[Ten 99]

Thanks Paul.

I hope I'm not breaking any rules by doing this. If so, please mark over the information or let me know and I'll edit.

I'm seeing the following driver costs:
Vifa XT25 Tweeters ~$54 each
Hi-Vi M8n Woofers ~$49 each (when 4+ ordered)

FWIW, I just saw the Parts Express has the M8n's due 4/23 (still), but that the M8a's (discontinued) show to be in stock at $93.10 (when 4+ ordered).

I'm expecting the cross-overs to cost in the neighborhood of $150-$200 each speaker.

[ThomasW]

No rules about posting PE pricing here, they are a sponsor of this forum. As a matter of fact if you click through their logo on HT-Guide, when placing an order, it's a good thing for us .........

Yes the M8ta is a variant of the M8aMKIV. Both designs are ported. The goal behind the M8ta is to optimize the total performance. As a result it's a no hold barred speaker.

One could build a faceted MTM version of the M8t,a but doing that could require a VERY large and EXTREMELY heavy box.




theAudioWorx
Klone-Audio

[JonMarsh]

Yeah, you have to have a strong lower back and really be into self abuse to do something like that!

M8a's in stock again? Maybe better order a couple sometime soon...

~Jon




Earth First!
_______________________________
We'll screw up the other planets later....

[ksudar]

Is there any advantage to using the M8a over the M8n? Also, from the pictures the 8a looks to have a yellow cone while the 8n's cone is gold. Is this true, or is it just the picture talking?

[ThomasW]

As has been ask and answered numerous times in threads dealing with the M8a. The M8n is an exact electrical replacement for the M8a. The only difference is that the M8n has a larger cutout hole and larger diameter frame. The cones are identical, so any differences are a function of the photograph.




theAudioWorx
Klone-Audio

[Paul H]

Thomas,

You stated previously that the tweeter hookup is not reversed and have supplied +- naming convention for zobel network. However, this still appears a little confusing. If I trace the schematic from the tweeter back I see the following connections:

Tweeter positive - 3A & 4A at J4 - From HP GND OUT - HP GND OUT - 3A & 2A at J3 - J1 connection 2 (negative).

It would appear from the above that the tweeter positive is essentially directly connected to the negative main input.

Sorry if this is just a matter of semantics and connection naming. I just wanted to double-check as the first set of crossovers is wired and ready for soldering

Paul

[ThomasW]

The zobel board in/out terminal is wired different from the woofer/tweeter board terminals. The zobel board terminal is wired as follows, from left to right
(+) input (1B), (-) output(2B), (+) output(3B), (-) input(4B)

The woofer/tweeter terminal boards are wired...

(+) input(1B), (-) input(2B), (-) output(3B), (+) output(4B)

If you use colored markers to label the terminals, you won't get confused when it's time to attach the speaker leads and other internal wiring




theAudioWorx
Klone-Audio