four inch woofer enclouser?

[dallaire]

Hello, I am building my new center channel speaker using two seven inch woofer and one four inch, maybe two four inch mids and one tweeter. What I am not sure about is should I put the four inch mids in a calculated enclouser or just make sure they are seperated from the six inch woofers. I intend to cross the mids in about 350 or so and rolling them off around 2500-3000 hz. Do you think to get good performance at 350hz that this would require a calculated enclouser? or would that be pointless when only going down to 350hz? Slope is electronic 24db per octave for all drivers.
Thanks,
Dallaire

 

[Iain McNeill]

Hi Dallaire,

A couple of things to remember. The mid drivers must be acoustically sealed from the woofers otherwise when the woofers pressurize the cabinet, the mid cones will get pushed out.

Secondly, if you're crossing over at 350Hz then the mid cabinet needs to ensure good driver performance to at least 175Hz maybe even 80Hz if you're using a low order XO.

However, a small driver with a low Vas (most are) won't take up too much volume in the cabinet. I heard of people gluing tupperware over the mid to good effect. Personally, I make a wooden box for more stiffness.

One option: design the mid box to give the required mid high-pass crossover response and save some caps/inductors (although the bass power would still be dissipated in the mid driver, limiting headroom.)

 

[dallaire]

Hello, Iain thanks for the response. I will be using a dedicated amp for each size of driver with a 24db per octave electronic x-over to seperate all speakers, all Marchand Electronics stuff xm1's to be exact. The drivers finally arived today. So I will start to break them in and begin testing parameters this weekend. I was going to seperate the mids (inside the cab.) using a length of thick cardboard tubing and cut a circle with plunge router for end of mid enclouser. But what I wasn't sure about was if I needed to make the enclouser a specific size so the four inch mids could perform down to 350hz, kind of like you need to make for the six inchers I'm using for the low end part. Also don't know for sure, now that you mention it if I should'nt make the cross point higher on the six to four inch driver, pretty steep slope but not sure. Did not want to cross over in the critical voice range is what I read at Rod Elliots site.. Although six inch woofers do go pretty clean trough to about 1K.

Speakers
Peerless HDS Nomex 6.5 Two
Peerless HDS PPB 4.0 Two
Scan Speak 9500 Tweeter
Ported enclouser
Amps Rotel

Thanks, let me know what you think?
Dallaire

 

[sdclc126]

Have you already bought all the drivers? You don't need 4" mids with 6.5" woofers - you can cross the woofers directly to the tweeters.

But either way it sounds like you're putting a great system together.

 

[Cal Weldon]

If you're in the mood to build test boxes you might want to consider the use of an open back mid. It is isolated from the woofer box but is open at the back. Personally I really like the sound. A mid in it's own enclosure tends to sound boxy to me.
The 6.5" mids here are like that

 

[Cal Weldon]

open back mid

 

[Cal Weldon]

On second thought that might not work. The open back "tube" isn't going to be long enough in a 6.5" woofer box to allow for a 350Hz XO. Mine is XO'd at 500hz.

 

[dallaire]

I have kicked around every type of driver complement I could come up with that would suit my needs. So I decided on using a three way because I've read if crossed electroniclly and each driver size having its own amp that great things could happen! time will tell, currently I have Diffinetive Tech everything. My mains are D'appolito array's with two 6.5's and one 1 inch tweeter all vifa drivers D.T. has used and I think they are "ho hum". I did bypass the factory passives and they do sound twice as good!!! but it seems I have achieved all the performance these drivers have to offer, mid priced at best, not that price makes a good driver, but it does seem to play a role to some extent.
Anyway, the open back approach may be a bit involved for me, carpentry speaking. So I will just try my best at measuring the mids and try to find a suitable enclouser size and conf. I will test mid enclouser prior to final design, for response I mean, using test mic and R plus D program, after all I think it is as much fun to design and build as it is to listen
Thanks agian,
Dallaire

 

[Iain McNeill]

It's been a while since I designed cabs so please, anyone, correct me if I go wrong here.

What I see in the specs is a 4" driver F3 at 100Hz, Qts of 0.54 and a Vas of 3litres.

Cal is right, these are a good candidate for open baffle and you'll get response down to the 100Hz F3 with a Bessel response (i.e. perfect transient response, minimum group delay, nice!) I haven't played with OB (yet) so can't really comment but there is a lot of good feedback on this site.

An enclosure for these would be pretty easy. Even a 3 litre box (pretty small) would only raise the F3 and Qts values a little bit so I think you'll be fine. Worth plugging into some design S/W if you have it. The tube idea is fine - make sure you seal all joints well.

24dB/oct means the driver is out of the picture (<1dB) by an octave below XO so it's all looking very good - like you designed it that way!

afterthought - the 0.5 Qts will roll off very gently and start much higher than the F3 point. You may be better off (in XO performance) by raising the Qts to 0.7 (Butterworth - maximally flat) by using a smaller box and this would get a better XO integration.

 

[dallaire]

Iain, you are correct on the IB setup. I did some testing this morning and found the calulated enclouser was nice and flat plus or minus one db, only problem with my tube enclouser was the fact that the low end was not there very well. I removed the "cap" at the end of the tube and the low end just opened up very nice! So my design now has changed to an open back mid enclouser, I am glad for this forum and educated people on the subject, like yourself! I tried to different quarter inch masonite baffles, just a "mock ups" to see edge effects, think I have this worked out now. I tried to place speakers to leave any frequency problems out of there intended frequency range. When you had suggested open baffle, you were, I assume talking about the four inchers only? I have not measured the six and a halfs yet but have test box built and ready.
Thanks again,
dallaire

 

[patch]

Cal, thank you for posting the pics of the loudspeaker.

I'm interested in the general t/s of the drivers, the particular horn type, and crossover used for it. Regards there!

patch

 

[Iain McNeill]

Your lack of bass when the back tube was closed was probably due to the air suspension effect reducing the compliance of the cone and raising the f3 resonance. This will also have increased Qts towards maximally flat!!

Opening the tube and now you've added a helmholtz resonator to the back of the cone (think bad car stereo). If your music is in the same key as the pipe, you'll have tons of bass! I wouldn't recommend the tube if you're going OB on the mid.

I'm assuming your masonite baffles are quite large (>2-3 feet) in which case 1/4" is a bit floppy. 3/4" MDF or better would improve your measurements I think. If they're smaller then it's probably oK, you just need to watch for the baffle step loss at low freq.


Hey, any chance of ripping the crossover out of your DT's and getting those puppies tuned up? There's nothing wrong with the drivers and carpentry on them! Nothing a little bi-amp action couldn't sort out.

 

[dallaire]

Well, for the masonite, it is just a mock-up to see where the baffle step happens. I'm going to use one inch MDF for the finished enclouser. As for as the tube loading, just because the open back tube "measured" better, you still think I will have problems with it sounding correct? My DT speakers, as we speak have the passives bypassed, and I am using all electrinic, by amped setup for all speakers including surrounds. I just wanted to make some three way designs, it seems two way designs are pushing drivers out of there rec. frequency ranges almost. Don't get me wrong, the DT's sound OK but could be better, I think they were designed with a dreaded 4db hump around 80hz, at least that is how all of the speakers measure, this is gating out the room and reflections, using a $250 calibrated B&K mic with R&D software, so I think they are measured correct. When I place them in the room, and where they need to go that 4db hump turns into about a 6-7db hump!! I think perhaps this was considered a "sellable" design for DT.
Thanks,
vince

 

[Cal Weldon]

Hi Patch,

Those are a throw together party speaker from leftover parts. Two sheets of plywood determined the size.Open mid because I like it. Not much more to tell. XO's at 500 and 3500.

 

[Iain McNeill]

Hi Dallaire,

I'll have to defer to others who have actually built OB speakers. It just seemed intuitively wrong to put a pipe on the back of the speaker. I have read in other threads that some folks think that even wrapping the baffle around the sides to make a U shape (for stability) is bad for OB performance.

 

[Cal Weldon]

Iain,

I tend to agree but the tube allows for better control of the lower frequencies without the need for EQ'ing and has a nice effect when placed about 4 or 5 feet from a wall. It also allows for the use of a piezo (ack!) on the back to make them a sort of bipole omni-directional type. It was a great way to use up old crud. The mids sound so much nicer than had I closed off the tube.