Thinking ahead

dynamo

So at some point I plan to start yet another project before finishing the ones before it.

I have thrown this idea around before and since my quad of 8” peerless HDS nomex drivers are looking for a new home, I want to attempt an 8” two way with them, two a side. Likely tweeter would be the RST28F in a waveguide since I have them and they are efficient and kinda robust.

IIRC it was Craig who suggested a possible mtm with the visaton round guide, which I did order. I also have the seos8 in the pile o parts. It seems the seos might offer a little more LF support. I’m open to either and value the visaton suggestion which is why I ordered it. Is one shape better suited for an mtm than the other?

Also, I’d be interested in knowing what all of you would do - MTM or TMM? I’m good with either and am unconcerned about size/height requirements. 

Thanks guys!

jr@mac

2.5 all day. The sheer height of an 8" MTM might be intimidating.

dynamo

jr@mac said:

2.5 all day. The sheer height of an 8" MTM might be intimidating.

Thanks JR, it’s a solid point. Would you mind throwing a TMM vote in the poll. I’ll hash out the 2 vs 2.5 way later if I end up going TMM. I want all points of view and opinions so this is perfect. Just wanna throw out ahead of time I could go contrary to the poll, just gauging the consensus.

Its a whole ‘nother topic, but totally relevant so I’d love to discuss 2 vs 2.5 way. I personally have sworn off 2.5 ways since I could never get my attempt right. I’m sure it is a me-issue and not an issue of the topology though. My first proper diy build is that TMM d27/pl18 combo I was talking about at PETT. Originally it was a Madisound 2.5 way crossover I had them draw up and it just never was quite right (knowing the little I know now) it seemed like a phase issue. I did my own crossover once I learned how and it still seemed not like it should be. With disregard for ctc spacing concerns of the TMM, I did a simple two way crossover and they opened up - alot. The image is massive and they are just right. Ever since this I have determined the on-paper faults of a TMM two way were better than the seemingly proper 2.5 way. Just sharing my experience with that to show my basis for having originally considered a two way only.

What are your thoughts on guides JR?

jr@mac

I thought I had hit submit on the poll, oops. Fixed now.

Guides are fine, if relatively shallow. All too often they end up sounding like PA speakers in a bar. I look at them a lot more as diffraction control. The Visaton guide looks about perfect, and there are plans for a 2.5 way here this summer with one. It is not a panacea for poor tweeters, just offers some diffraction mitigation, and with some tweeters will allow lower crossover points.  

R-Carpenter

Don't look like MTM has much support. I like the idea but they always sounded meh.. to me.

dynamo

I’m totally fine with the TMM format so that’s fine, it is a lot more practical. 

You definitely have a point with the mtm sound sometimes not being quite there. Two speakers in my memory that got it right were the Polk LSi9 (and I normally don’t like the modern Polk sound) and the ProAc D38. My Indy theme build is an mtm and they are still a work in progress.. 

Good input on the guides. I knew the Visaton was suggested for a reason, I just had the seos laying around forever and wanted to get an idea If there was any love for them. I can never get myself to use them for some reason.

This is great guys, I love the advice and suggestions.

AdamM3

Another vote for TMM, although i have had success with mtm before. I think 8's would look better in a TMM and i would lean towards a 2.5 personally.

jhollander

I voted MTM as I think that would look good with the SEOS in a stand mount. TMM with the round Visaton in a tower.  I think the SEOS would have the best off axis performance. 

dynamo

I was also thinking that if I go MTM I’d go stand mount, frankly easier to deal with their height and size if I had to move or transport them. Thanks for the extra input on guide application as well. I understand the general concept of guides, and how it helps match a small tweeter to a big woofer, but don’t really know how to apply that to which shape would be better vertically for an mtm.

6thplanet

Big tower, MTM, 15" passive at the bottom.

dynamo

6thplanet said:

Big tower, MTM, 15" passive at the bottom.

Sounds like a rebound speaker for after a divorce! “Don’t tell me how big I can make my speakers and where I can or can’t put them!” 

6thplanet

"I wear the pants, I build the speakers!!! Now git in thar and make me a chicken pot pie!!"

Ed_Perkins

Said in a high voice since the wife cut off his balls!  

dynamo

Just some visuals to put things into perspective. Sorry for the sideways pic of the mtm.

The woofers are right at home in 0.8 ft3, so 1.6ft3 net per cab to give an idea of what is needed there. 

kenrhodes

I like the last one best. I would put the woofers horizontal.  It looks like a killer combo.

dynamo

Thanks for the input gentlemen. The verdict is a TMM with the visaton guide. Big ass stand mount, started making sawdust today. These shall be named the Zoinkers! 

dynamo

I know, the shop is a TOTAL shit hole right now. I have two non-speaker projects and am building 3 sets of cabs all at once for a backlog of projects. 

here are the cabs. 2ft3 net, used some really nice commercial PB cabinet material I got for 75 cents a sheet at habitat.

PWRRYD

Total awesomeness dynamo!  Double extra bonus points for using the habitat stuff!!! 

joeybutts

Excited for this as I have 6 of these bad boys, and may use them for a new HT front stage. 😁

joeybutts

Gentlemen, do you feel thee would improve efficiency, be more dynamic and offer a more "cinema" sound than full RS designs?  I've had the bug to build something new, more efficient and a more pro audio sound.

Sorry to hijack 😬🤫🤫

dynamo

No hijack at all, totally on topic! I haven’t heard the driver yet so I have no idea. They are efficient, which is a plus. The cone is very thin and light compared to the RS paper drivers, likely having a tone closer to a pro cone than the Daytons, which is heavy and coated on the back.

joeybutts

Sorry dynamo, I have some older RS aluminum designs, khanspires, cjd Dayton rs center and markk rs225/28a as my ht.  They are wonderful and offer great sound, but are more musical than ht sounding. 

But your description sounds like exactly what I'm after and rpb (kim) over at PETT brought a pair of what I believe similar driver design over and I loved the sound.  Eagerly awaiting your design and thoughts!!

dynamo

Yup, haven’t cleaned yet. Got all the holes poked in the cabs. I went with the port on the bottom instead of the back because I prefer bottom ports. I will build the stands to accommodate.

The holes look choppy because they are. Everything I touched today went to hell in one way or another. I was working on some small cabs with some 1” thick walnut crotch (think giant knot) that shattered my first of two upcut bits. Broke my second off too but it was salvagable but no longer long enough to cut holes all the way through so I had to finish them with the jigsaw.

My circle jig also became off so the tweeter recess on these and the walnut baffle is way too big. I don’t care about these but I’m pissed about the walnut ones. I built the entire cab off those two chunks of walnut. I will likely just fill the gap with black silicone, hopefully will just look like a trim ring. 

joeybutts

Any progress on these bad boys?

dynamo

A little, I built the stands out of some scrap oak boards and dyed them. I’ll grab some pics when I get a chance. Hopefully Monday or Tuesday I’ll get back to them. Thanks for checking in!

joeybutts

Absolutely!  Glad making progress and wish something I could do to help.  Eager beaver....

dynamo

Here are the stands. Tops are open for the bottom firing port. I’ll likely put a couple dowels in to couple them to the speaker to prevent sliding off.

dynamo

I fixed up a pair of B-stock RST28-Fs using Wolf’s mod. Different material in the cup as it’s what I had but it works. Ben outlined the steps but I’ll just recap.

Cut off the cup with a cutoff wheel. Remove felt and foam plug.

I used hot glue to seal the jar lid in the screw ring. Stuff a 1” cotton ball in the pole in place of the foam. I used a piece of breathable foam carpet pad in the cup.

I used hot glue to glue the cap on and also used a swirl of it on the cap to help ensure it doesn’t resonate.

Green before, blue after.

dynamo

A few shots of the stands before finish.

Wolf

I thought about the can-lids, and had some in the house. I decided the risk of rusting out, the ferrous qualities, the possible leak or give of the lid/rim seal, and the likelihood of resonance; deterred me from using them. 

I'm surprised your Fs is so high and that the impedance below Fs is rising like it is. Could it be mainly because the chamber is smaller?
One of mine had a ripple in it in the 300 Hz range for whatever the reason. 

I'm really starting to think the QC on the RST28 is poop.

dynamo

Yeah, the fs is high. I couldn’t wrap my head around it and didn’t think about chamber size. If the lids weren’t glued on so hard I’d try to back them off some to open it up. Maybe I’ll apply a little heat to soften the glue. Otherwise I’m running them as is. The magnitude is only 3.5 ohms so I can probably deal with it. I’m using it though since I have it and it is efficient, and probably can take a little abuse. My other choice of my stock of parts is an H1212 but I’m not sure it would keep up.