matching speaker impedance to reciever

[LilBassGuy]

I have posted this in a different section, but I think this section is more appropriate, so forgive me for the double post.

I have decided to build one of the many MTM projects I have found on the internet, but I am not sure which ones have a high enough impedance to suit my reciever.

The reciever manual says speakers must be 8 ohms or greater.

http://www.circuitcity.com/ssm/Sherwood-Stereo-Receiver-RX-4105/sem/rpsm/oid/121266/rpem/ccd/productDetail.do#tabs

The projects I am considering building are:

http://zaphaudio.com/BAMTM.html

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=302-930

http://ascendantaudio.com/Arbiter_MTM.html

I know the parts express project says nominal impedance is 4 ohms so I guess that one is out of the question. How can I find the impedance of the other two projects?

Thanks!

[joecarrow]

Zaph's project looks like it's 4 ohms, based on his graphs. The Arbiter project is also probably 4 ohms, since it used two woofers. MTM projects generally have two eight ohm woofers in parallel, for a nominal 4 ohm load.

If you want, you could build one of the projects and try it with your receiver- it might not cause any problems. Your link to the Circuit City page didn't work, so i don't know which receiver it is. It's possible that a low impedance speaker could break your receiver. It might be a good time to upgrade your receiver.

[LilBassGuy]

wow i can beleive i suck that bad at the internet links fixed

thanks for the reply...as far as upgrading the reciever is concerned, that is really my last option since I just bought the thing to build this little system. Would be silly to get rid of it already, although i guess it is silly to buy it without doing a little research first.

I would, however, hate to spend 4 - 500 bucks on one of these projects to see it not work as I want, I would rather find drivers that might make it work as is.

Question: When it comes to determining the overall impedance of the system, do we just consider the two woofers, or does the tweeter and crossover components (resistors, inductors, and capacitors) also have an effect on the "nominal impedence" of the loudspeaker?

[joecarrow]

Are you really sure you need an MTM project? Many projects with a single woofer sound just great. I have the Modula MT for home theater, and it's plenty loud enough for me. I sit about 8 to 10 feet from the speakers. I'm sorry to say it, but you'll probably have to spend at least double what you did on your receiver to get something that will be happy with the loads presented by the majority of MTMs.

Here's another idea- what about getting some Insignias and performing a few modifications on them?

http://zaphaudio.com/Insignia.html

Best Buy Insignia 6 1/2" Bookshelf Speaker

You'd spend $50 on the pair, maybe $75 or $80 total with mods. It would be something to listen to while you save up for something more impressive. Of course, free holiday shipping at parts express is awfully tempting right now...

One more idea- check out used gear. It's very possible that there will be more good stuff available on the used market after the holidays. Just because speakers are old doesn't mean they don't sound good.

Whatever you do, I wish you luck. Only a year and a half ago I didn't think I'd even be able to afford the Modula MTs. I finally got a raise, and after many months of saving (you can't just blow money on electronics after a raise, can you?), I did it. Boy am I glad I did- a good project with a decent receiver really brings the movies and music to life!

[LilBassGuy]

Thanks for another reply! Glad someone is actually talking to me

And no, I dont NEED an MTM, i just figured that the extra cone area and special design would make them more appropriate to be a couple of mains for my little HT project.

I really did not want to just buy a pair of speakers, and getting something cheap now to upgrade later is what I have been doing my whole life. Its time I actually put a little money into this thing (looking to spend up to 500 on the pair).

I do know that the arbiter project (linked in the first post) has two 4 ohm midwoofers wired in series to give an 8 ohm nominal load. That, AND these things seem to be well liked on other forums. Problem is I think they are priced per speaker, which brings the grand total to around 550 bucks if i buy prefab enclosures (which I will).

So it may behoove me to find an MT project, but it must sound powerful enough to be a main speaker, and sound nice and clean for my music.

[joecarrow]

How large is your room, and how far away from the speakers will you be listening? That will help us figure out what "loud enough" is. Also, are you in a house, or an apartment? "My own house"-loud is totally different from "Apartment with neighbors on three sides"-loud.

Also, you can get by with smaller main speakers for movies if you have them set to "small" on the receiver, and have a decent subwoofer.

[LilBassGuy]

Room size will be relatively small, as it will be in an apartment. I guess I have always thought there was a difference between "big" sound and "loud" sound. I figured that with two main woofers per side, I could keep the actual volume low while still maintaining a large, powerful soundstage. Like, I would have to turn a MT setup LOUDER to acheive the same large soundstage. That probably didnt make sense.

BUT, it will go into an apartment, but I am not sure my receiver has a "small" setting. I guess I should start browsing some basic MT projects. Maybe I can find one that will be suitable for my mains in an apartment building.

[LilBassGuy]

So, to recap, the room is average sized apartment room, not as small as a bedroom, but not as large as a living room in a house. I would be sitting on a couch about 6-10 feet away (guess).

[joecarrow]

The two woofers won't really play any lower, or with a "bigger" sound- they just have the ability to play bass sounds louder. It makes sense what you're saying, I think. I remember a long time ago, I could tell the difference in sound between a "big" speaker and a "small" speaker... but now I've sort of trained my ears to tell that the "big" speakers tend to play lower frequencies, and play all of the bass frequencies somewhat louder. This is generally referred to as sounding warm.

In my opinion, an MT project with a sub will give you more than enough sound. The benefit of the sub is that it fills in the lower frequencies, letting the overall sound seem bigger. I use the Modula MTs without a sub, but I don't listen that loudly. I really only miss the sub during movies, but my neighbors probably appreciate that I don't have one.

Oh, and about your original question- the woofers, tweeter, and all of the crossover components (the way the are wired) come together to create an impedance. This is a resistance that varies with frequency. You'll see on the graphs that a speaker might be 4 ohms at 300 hz, and 16 ohms at 2khz, with some other changes along the way. The minimum impedance is what you have to worry about when it comes to figuring out if your receiver will be able to handle it.

[LilBassGuy]

So are you saying that the mininum impedence is what is created by the woofers? Is that usually where the impedance curve reaches its minimum value?

Also, what you say about big sound makes sense. The warm thing makes sense also. Guess I didnt know quite how to word it, but I think you hit it right on.

How much did that modula cost you to build? It sounds like it might fit the bill here if its within the price range. AND the impedance range...

[joecarrow]

Unless the crossover is doing something strange- yes, the minimum impedance is generally in the range covered by the woofers, and could be estimated by looking that the woofer's impedance and if two of them are wired in series or parallel.

I forget exactly how much I spent on the Modula MTs, but it would be possible to build the pair for under $500. It might even be possible with the Parts Express boxes since free shipping is under way.. but it will be very hard. Do you already have a router, or know someone who would be able to help you out? My friend loaned me a router, but it was hard to get the work done in my apartment.

Also, the Modula MT is a 6 ohm load. Your receiver should be able to handle that fine, but you will also probably notice an improvement if you were to upgrade.

[LilBassGuy]

router? for what?

Oh wait, I think its for modifications to the box isnt it? I could get access to one, my dad's got loads of tools. As far as 6 ohms is concerned, does that mean its a 6 ohm driver?

Grr. I just need a find a solid 8 ohm MT project that costs around 400 to build. I know its out there, i just need a little time to do some research. If you can think of any that you have read good reviews about, lemme kno!

So why dont you run a sub? Is the bass from those Modulas so good that you dont need it?

[Dennis H]

You won't find an easier load than the Modula MT with the Seas tweeter. It's an honest "8 ohm" speaker. All 8 ohm nominal speakers dip down to 6 ohms or lower at some point. Quoting Jon, the designer, "Last, the impedance curve. Pretty much anything should be able to drive this, except a crystal radio."

[joecarrow]

You need a router so that you can flush-mount the drivers. You can't just cut the holes with a jigsaw. Actually, you could cut the holes with a jigsaw, and then cut thin sheets of HDF to bring the face of the baffle flush with the edge of the driver. You'd need to take care to put a spacer under the rim of the tweeter to bring it in line with the front of the woofer.

Sorry if I gave too much worry over the MT- I really should have remembered what Jon had said about its impedance.

Why don't I run a sub? Two reasons! First, I'm in an apartment and I don't want to bother the neighbors. Second, I haven't been able to sneak one past my girlfriend yet.

I can hear output from these speakers below (I'm estimating, but have some confidence) 40 hz, maybe into the low 30s. I have them a little close to the wall and in a corner, so that helps. It's certainly adequate for pop music, and only during really dramatic classical music and movies do I feel like I'm missing out.

After I move, I'm certainly getting a sub. That could be a few years, though, so I'm interested in a "stealth" sub until then. That's difficult, since it would have to be physically small and able to operate mostly below 40 hz.

[LilBassGuy]

Ahh so your just being kind to your neighbors then...how sweet!

I am just going to assume my neighbors like loud music like me

Actually, I am going to build a small sub to supplement my mains, but keep the gains on the amp low enough to where I aint rattling too much (I GOTTA have that low end )....maybe I will get lucky enough to have neighbors that dont mind...I do hate it when some idiot is blasting his stereo tho, so I will try and respect everyones noise preferences to the best of my ability.

As far as physically small subs go, I remember alot of people liking the small tangband 8inch neodynium drivers...I think they threw them in a small ported enclosure (enclosure was SMALL)...I doubt that would give you the low end extention you desire, but it certainly fits the size (and budget!) requirements.

[joecarrow]

Right now I'm thinking that I can fit a 12" woofer into a small sealed box- maybe 0.5 cubic feet- and use a linkwitz transform circuit and a 500 watt BASH amp to get my bass. Considering how loud I listen to movies and how close to the sub I would be sitting (maybe 6 to 8 feet) it might just do the trick.

Of course I'm considering a Dayton Reference sub, but it could really be ages and ages before I get to build the doggone thing. I guess I'll just live without it until I'm in a house where I can turn it up and hide a really big sub. If you can tolerate a somewhat larger ported box, you could do quite well with even a 10" driver and less power. That's the way to do it if budget is a bigger consideration than a girlfriend who doesn't share the enthusiasm.

[LilBassGuy]

Haha. Luckily my girl is supportive of my ambitious desire to find great clean sound. She wants to be able to throw in her favorite flick and be completely drawn in, and she likes a sub when theres explosions or helicopters and what not.

Haven't decided what sub design I want to follow yet. I am thinking 500 W RMS would be a bit too much power for a small apartment. Then again, I want the sub to at least be able to keep up with whatever mains I build.

By the way! I am trying to decide between these two designs, as both seem to fit my needs. If ya have any input, I would be greatful to hear it.

http://www.zaphaudio.com/audio-speaker17.html

http://zaphaudio.com/audio-speaker12.html

[joecarrow]

The reason I'd need 500 watts is if I built a small sealed box that doesn't produce any bass, and then EQ'd it back to flat. The particular type of EQ used for this is a little bit more than just a frequency boost, and they call it a linkwitz transform. Here's a nice article on the subject, if you're interested:

http://sound.westhost.com/linkwitz-transform.htm

The whole point is that you're giving up efficiency for size, and the price you have to pay is a more powerful amplifier.

About Zaph's projects- I haven't read either of those in a while, but I trust the guy as a speaker designer and I've only ever seen him tell it like it is. If you're definitely building a sub, I'd go for the smaller project. You'll save money on the enclosures, and probably get a slightly better midrange.

One word of caution- neither project uses shielded drivers, so you'll want to be careful with how close to the TV they go.

[LilBassGuy]

That is one thing I was worried about, because this will be used for a basic 2.1 setup. Granted, I am pretty sure I should have enough room to pull each one a foot or two away from the TV, I am still worried about how far they should be to prevent damaging it.

I do know I am leaning towards the project with the smaller woofers for two reasons: I do plan on building a sub eventually AND that project includes a softdome tweeter which is my preference over the usually harsher sounding metal dome.

[technimac]

LFE with no sub??

Here's a possible solution...BassShakers!



I have four mounted under the couch and two under the loveseat. Both are hooked up series/parallel for 4ohm load that is powered by a 150Watt Buyout Audiosource subamp. Everyone who sits on the couch or loveseat comments on how "great" the "subwoofer sounds" - even when (my actual sub) is only "cranked up" to 30% or so.

For a situation like yours, particularly where there are neighbors above/below and beside you, this is the ideal solution - for movies especially. Not for music necessarily - although live concert DVD's are very impressive.

If you place your "BassShaker enabled" couch on thick felt pads (with hardwood floors) most of the LFE will be isolated (to the couch). A small/high quality "sealed" sub would fill in the rest.
The result - you'd be happy and so would the neighbors.

BTW, I run 4 Modula MT's (Seas TBFC/G version) and am amazed at the quality of sound they produce (extension down into the 30's), even in my large (21'x35') open-plan listening area. They're positioned less than one foot from the CRT TV and there are no problems. You can get a shielded Seas TDFC to use in the MT's, and the RS 180 is already shielded.

Hope you find answers to your question.

[LilBassGuy]

Thanks for the post!

Just curious, what is the TBFC/G version? I found this thread:

https://www.htguide.com/forum/showthread.php?t=13154

of the Modula MT speakers and I just want to make sure I am looking at the right project.

So you say that LESS than one foot away from your TV, you have no issues? This just might be acceptable to me

[joecarrow]

I have the Modula MTs about an inch from my TV. Hey, there's the post with my BOM! https://www.htguide.com/forum/showpo...&postcount=326

I just added cabinets, drivers, and estimated shipping from Madisound- and I think you could get everything for under $500. Of course you still need tools like a router with circle jig and a soldering iron- but the soldering iron can come in handy later. I've complained about this before, but our cat loves to chew on cables. I've saved more than one cable and power adapter with the soldering iron, so it's kind of paid for itself.

I don't think the bass shakers are for me right now. We have a couch that's much nicer and newer than I would have picked on my own, and I don't think I could get clearance to bolt any shakers to it. I should probably pick some up, though, since it looks like most of the Aurasound ones on the market are surplus and discontinued.

[technimac]

I don't think the bass shakers are for me right now. We have a couch that's much nicer and newer than I would have picked on my own, and I don't think I could get clearance to bolt any shakers to it. I should probably pick some up, though, since it looks like most of the Aurasound ones on the market are surplus and discontinued.

Hmmmm....Know what you mean Joe. Our couch is $$$leather, but the good news is that the BassShakers are invisible (except for the wire leading out from under to the SubAmp). Oh, and once my wife experienced .....let's put it this way.... the LFE experience 8O .... she was an instant convert.

Now she's often the first to invite friends to "sit down and watch this scene". :W

In fact, she commented the other day that the couch has probably appreciated in value since the BassShakers were installed. :T

[LilBassGuy]

ahh thanks for the BOM, that helps alot!

and yes, maybe bass shakers would be the way to go, but would I have to buy a completely seperate amp to power them or just wire them up with the subwoofer?

I have tools like soldering iron and my dad has a router, and most likely the circle jig I would need. And under 500 bucks means it sure fits my budget...and I read so much nice things about them...

[technimac]

Standard BassShakers are rated 25W@4ohms driven. A 150W@4ohms sub amp is perfect. You want a separate amp from your sub, but you can use a "Y-splitter" to feed the LFE signal to both amps.

Try this amp:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=300-804

OR this one:

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=300-750

Either will leave you with lots of head-room to add more BassShakers if you wish to.

Cheers, Bruce

[LilBassGuy]

nice and beefy...where do you mount the plate amp if its not going on a sub box?

[technimac]

Right! The amp will mount nicely on the backside of that new matching end-table you're going to build to put at the end of the couch under which the BassShakers are mounted. :W
Even a small frame that can sit on the floor will do. :B