Home theater rebuild phase 1: Center channel

**BoomieMCT** · **02-28-08, 05:24 PM**

I've been thinking about rebuilding my whole home theater setup for a while. Currently I have a Velodyne CHT speaker setup with two sealed subs I made that use the 12" Dayton Titanic. I enjoy this setup a lot but it has some flaws that I think I can address.

Problems

1. Needs more mid-bass. The Velodyne speakers are two-way sealed speakers with a 4" woofer. While very good for what they are they don't have the mid-bass punch I want in my action movies.

2. Mains need to go lower. The Velodynes have an F3 of 90Hz. While this is fine with my setup (twin front subs keep the bass from being localizable) I'd really like to push that down so they are flat to 80Hz or lower.

3. Center needs better dispersion. I've never been 100% happy with the center chanel. It is a typical MTM type and the horizontal dispersion is lacking. I've done everything I can do to fix this with positioning and it's good - but not good enough.

4. Sub(s) could go lower. Okay, this is probably always true. With EQ my current subs have an in-room F3 of about 21Hz. Bass shakers are all I really need for sub-sonic. I would like to have my subs go low without electronic EQ. This is low priority but something I'll probably address.

5. This isn't a problem but one thing I liked about the Velodynes is that they were pretty insensitive to room placement. I think part of this came from the small woofer and part because they were sealed with highish F3 points.

Philosophy

Since my theater is for movies only (music listening is done in a different room) I can stay a bit focused and not worry about having full range mains. These are nice (especially for 2 channel music) but I'm happy being able to pass all LF to the subs as long as #1 above is met. Right now I'm going to try to have all my speakers have the same F3 to simplify crossing over. This design choice allows me to use smaller drivers which tend to have better dispersion and should allow me to use smaller baffles and a higher x-over point (makes tweeter selection easier).

I've imagined building a set of 2-way speakers based on the Dayton RS125S-8 and an as-of-yet-undetermined tweeter. My experiments with full-range drivers (all in the 3" and 4" range) have impressed me with their good dispersion and the bass that is possible with a modern small driver.

The front L and R speakes would be ported MMTMM's, the center a ported TMMMM that stands on the floor. The surrounds would either be of a similar design to the surrounds described in the Loudspeaker Design Cookbook (one woofer canted down with forward and rear tweeters) or similar to the GR-Research upwards firing surrounds. If I decide to go 7 channel I'll make simple ported TM 2-ways for the rear.

To try to keep these as insensitive to positioning as possible I plan to front port these (almost as good as sealed IMHO).

**BoomieMCT** · **02-28-08, 05:44 PM**

I've started this thread to talk about the center channel. In the previous post I said I'm going to shoot for a TMMMM design using the 5" 8 ohm Dayton Reference driver in a 2x2 parallel / series arrangement. According to Unibox I should get an F3 of just under 60 Hz and a max SPL of 112dB.

The enclosure will be a short floorstander with the tweeter just below the bottom of my screen (why I went TMMMM). To improve dispersion I'm going to make the baffle as narrow as possible (may need a BSC circuit). The internal volume I'm shooting for is a scant 0.7 cubic feet so this will likely have lots of bracing to eat up space. This will also make placing the port interesting - I may try for a slot ported design.

I'm going to shoot for a crossover between 2000 and 2500hz. I really can't say which until I've tested the woofers some. Unlike most of my designs (where I try to get my x-over as low as possible) for these I'm going to see how high I can get away with to make finding a suitable tweeter easier.

Questions I have at this point;

1. Does anyone here have experience with this driver? Are there any things I need to be aware of? I have read it is best not to cross it over 2.5kHz.

2. Any advice on tweeters? I'm looking for something small, in the 90dB efficiency range with reasonably flat response and good off-axis response. Possible candidates so far are the BG Neo3 PDR and the Dayton ND28F. I have no experience with the latter but have used its smaller brother the ND16 with good results.

**BoomieMCT** · **02-29-08, 05:05 PM**

Because the baffles on these are so thin thers is going to be a baffle rolloff right around 1kHz. Because this is close to the crossover point I really wanted to take extra time to deal with baffle effects when designing the crossover.

So I took the CLIO FR and impedence charts from the PE webpage, modified it to represent a 2x2 series/parallel setup of woofers and applied a baffle diffraction adjustment from Edge to make a combined FRD. I did the same thing for the NEO3 PDR. I then dropped these FRD files into Passive Crossover Designer (by FRD Consortium) so I could draft a crossover.

The attachment is my current best. It is a third order electrical crossover that, with the baffle, makes (roughly) a fourth order acoustic crossover. Impedence never drops below 7 ohms (minimum of 6 was my target). Please note the low end of this graph does not represent the final product as the driver data does not include the enclosure. I'm guessing that around the crossover this won't change it much so it should be mostly valid. The porting should reinforce the low end from 200Hz(ish) down to 50Hz(ish).

Anthony has extra Neo3PDR's lying around so I may order the 5" drivers and put these things into a test baffle and see what happens. Hopefully I can do this in a week or so.

**Jason Schultz** · **03-09-08, 03:38 AM**

Hey boom
I would like to comment on your #1 part in the first post. I had the same lack of mid bass punch in my mains (used for movies and music ). I was using a single but powerful 6.5 inch driver in a small 3 way design. It went loud but lacked warmth and impact. It had a f3 of about 90 Hz also. I am convinced that you need at least a good eight inch driver to give you some more slam without bottoming it out. This is what I did and it worked. I used a single seas P21 Rex in a small ported box. and the mid and upper bass it much more present, even When the frount speakers are set to "small" on the receiver. What i am trying to say is I don't think any 5 inch driver has a low enough Fs or enough Sd to be satisfying in the "hard bass" region. Another thing is, a five or six inch driver will have to be ported( I'm assuming you will use a ported enclosure) at around 50 - 65 Hz. this will IMO give you too much port output in midbass and a less tight sound. Ok It might not be so obvious if using the Receivers 100 Hz high pass filter.
You might Find also that your room is soaking up the mid bass. Have you measured your mains in room response? systems response?

**BoomieMCT** · **03-09-08, 09:37 PM**

Quote:

Jason Schultz wrote:

Hey boom
I would like to comment on your #1 part in the first post. I had the same lack of mid bass punch in my mains (used for movies and music ). I was using a single but powerful 6.5 inch driver in a small 3 way design. It went loud but lacked warmth and impact. It had a f3 of about 90 Hz also. I am convinced that you need at least a good eight inch driver to give you some more slam without bottoming it out. This is what I did and it worked. I used a single seas P21 Rex in a small ported box. and the mid and upper bass it much more present, even When the frount speakers are set to "small" on the receiver. What i am trying to say is I don't think any 5 inch driver has a low enough Fs or enough Sd to be satisfying in the "hard bass" region.

Some interesting observations. A few things though; Many people have reviewed this driver and comment on the good mid-bass it can deliver. I have built ported speakers with 6 inch drivers (with much higher Fs's) that have tight mid-bass so I know it can be done. Could there be a problem like you describe? Maybe - but I'm still going to build a prototype to see what happens though! Maybe having four smaller drivers will help out. Honestly I'd love to have three ways with 8 inchers taking the bottom but the current HT won't fit such things. Such is life. . .

Quote:

Jason Schultz wrote:

Another thing is, a five or six inch driver will have to be ported( I'm assuming you will use a ported enclosure) at around 50 - 65 Hz. this will IMO give you too much port output in midbass and a less tight sound. Ok It might not be so obvious if using the Receivers 100 Hz high pass filter.

You may very well be right, but I'm not convinced. According to the Unibox plot above the port output won't be greater than the direct output until 90Hz. If I cross at 80Hz (where I intend to) I don't *think* there will be a problem. I have made similar ported single driver speakers with 3" and 4" drivers (for lower SPL) and haven't had a problem with mid-bass tightness. Again, I'm hoping that by having four in each enclosure will get me the response and SPL I want.

Quote:

Jason Schultz wrote:

You might Find also that your room is soaking up the mid bass. Have you measured your mains in room response? systems response?

Of course! I'm a huge believer in the idea that the room is an important part of the theater "instrument". I've used REQ several times and am on my third incarnation of acoustic treatments. Of course no room is perfect (expecially a basement room) but I'm aware of the unfixable faults of mine and this problem isn't it.

**Brian Bunge** · **03-10-08, 07:02 PM**

This sounds like a fun project! As long as you use a large enough port to prevent chuffing I don't see any reason that you'd have any trouble with boomy bass response.

I personally like the looks of 28L tuned to 50Hz with heavy fill a little better. It gives a more gradual rolloff to the bass and will probably having a little tighter sound if/when you run it full range.

**BoomieMCT** · **03-10-08, 07:15 PM**

Quote:

Brian Bunge wrote:

I personally like the looks of 28L tuned to 50Hz with heavy fill a little better. It gives a more gradual rolloff to the bass and will probably having a little tighter sound if/when you run it full range.

This is something I wondered about - building in a bit of bass roll-off. I may build a prototype enclosure to test this - it's worth the effort as the MMTMM mains will be the same size and tune.

I understand what you are saying about tuning them to run full range . . . except I don't intend to. These are for HT only as I very rarely listen to music in my theater room.

**Brian Bunge** · **03-10-08, 07:18 PM**

Quote:

BoomieMCT wrote:

This is something I wondered about - building in a bit of bass roll-off. I may build a prototype enclosure to test this - it's worth the effort as the MMTMM mains will be the same size and tune.

I understand what you are saying about tuning them to run full range . . . except I don't intend to. These are for HT only as I very rarely listen to music in my theater room.

Well, if you're building them for HT use only and always with a sub, then tune them for max SPL in whatever frequency range they'll be used!

**BoomieMCT** · **03-24-08, 08:59 PM**

I got my four 5" Dayton Reference drivers today. Neat drivers but I'd really classify them as 4" drivers with a large heavy flange. I'm going to steal a BG Neo3PDR from Anthony and make a test baffle. Hopefully I can test my crossover (or use an active setup) this weekend. If all goes well a prototype will follow.

**Jason Schultz** · **03-25-08, 05:33 AM**

I like the idea of four! five inch drivers, this should give you decent surface area for a bigger sound. I'm looking foward to the results.

**Brian Bunge** · **03-25-08, 05:21 PM**

Yeah, I built some bi-pole surrounds with the TB 4" bamboo drivers. The frames of my RS125's are the same diameter as the TB 4's. So I'd call them a 4" driver as well. I've heard one design with them before and they had really good bass output for their size.

**BoomieMCT** · **04-01-08, 10:15 PM**

Just a quick update; the test baffle is done and the drivers are mounted. Tomorrow I hope to run a test with both an active and passive crossover. This baffle is a flat plate so I'll get no good bass data but should get an idea of how to wire up the crossover and how it should sound.

I'm not 100% sure I'm going with the Neo3PDR as a tweeter but I like it and Anthony had an extra lying around for me to use as a test tweet. If it doesn't work I'm going to have to get something else - I have a short list worked up. One benefit of the Neo3PDR is the mounting face is almost the same size as the drivers so it looks cool. I will try to find a way to scrape the BG logo off.

Before someone comments - yes I made my baffle too short. Oops. This is why we test.

**Anthony** · **04-02-08, 11:50 AM**

Is the baffle being too short a mistake, or a feature?

Looks good, are you doing full line 2-way or 2.5 way?

**BoomieMCT** · **04-02-08, 11:56 AM**

Quote:

Anthony wrote:

Is the baffle being too short a mistake, or a feature?

Looks good, are you doing full line 2-way or 2.5 way?

The baffle being short was because I could either use a piece of scrap sand-ply to make this (and be short) or I could chop up a good piece of Baltic Birch and have it fit. For my purposes this will work fine and I assume the large BG faceplate will compensate for the lopped off corners.

I intend for this to be a 2-way, not 2.5. I may play around with a 2.5 setup in PCD but right now I'm leaning to a 2-way.

**DRB** · **04-02-08, 02:03 PM**

I'm a big fan of identical 6.5" 2-way satellites all the way around. Some of the best systems I've heard were done this way. Dennis Murphy's Usher design was used in one of these and it was very effective in a fairly large room combined with a 3 Tempest IB setup.

It is difficult/rare to find an 8" woofer/tweeter combo that is truly suitable for use together.

http://murphyblaster.com/content.php?f=usher2way.html

Good luck!

**BoomieMCT** · **04-02-08, 07:21 PM**

Did a bunch of active x-over tests before I realized the crossover point and levels assumes there was a BSC on the woofers. I'll make that later - I'm tired now. Until then here is the woofer and tweeter on-axis @ two meters with the tweeter at -3, 0 and +3 dB. The BSC should flatten out that woofer "hump".

These parts aren't really broken in yet and because they are set up in (basically) a dipole baffle instead of a vented enclosure I have no bass. Other then that this sounds pretty good. I think the Neo3PDR is going to work out as a good mate to the 5" Dayton References. The other weird thing is that they measure better with the tweeter inverted which is the opposite of what PCD predicts. One reason could be that the active x-over is fourth order electrical wheras I plan to use a third order electrical x-over (combined with the baffle it should end up being fourth order acoustic).

I haven't measured it yet but the off-axis dispersion of these is great - I think this will make an excellent center channel.

**Anthony** · **04-03-08, 08:37 AM**

You should baseline a speaker outdoors and then in your test room so we can see what's a room effect and what might be speaker related.

The only way to really know if the tweeter polarity is going to be correct is to flip it on purpose and look for a deep null, then flip it back and look for a smooth response. If it is just alternating between near flat and a slight null, then your slopes or crossover frequency are probably off from what you simulated.

**BoomieMCT** · **04-03-08, 08:51 AM**

Quote:

Anthony wrote:

You should baseline a speaker outdoors and then in your test room so we can see what's a room effect and what might be speaker related.

The only way to really know if the tweeter polarity is going to be correct is to flip it on purpose and look for a deep null, then flip it back and look for a smooth response. If it is just alternating between near flat and a slight null, then your slopes or crossover frequency are probably off from what you simulated.

<groan> I have no real good way to set things up outdoors.

I did flip the tweeter which is why I know it likes to be inverted. I still think this is because of the different order of the networks simulated vs. tested. I'll simulate a fourth order electrical network to see if it has the same issues. If it does then I know what the issue is.

My main purpose for this test is to see if the driver choices and x-over points sound good to me and to test off-axis dispersion. I'd also like to know if I can get away with a higher x-over to protect the Neo3 more (since I hear they are fragile and easily burnt up).

**Anthony** · **04-03-08, 08:57 AM**

What if you got a really long mic cable?

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