My build - 3 way, tri amp'd in-wall - Guidance

[audiothings]

Hello.

I have built a couple of cheap full-range speakers in the past, nothing fancy... Now I'm building studio for my friend, incorporating three way speakers, custom built into the walls. The room is approx 13 x 19 x 9. I am not at all experienced at this, but I'd like to think I'm playing it safe, because the system will be sealed, externally tri-amp'd with a speaker management processor... I believe sealed designs are safer for the inexperienced builder and the crossover is totally variable, with additional equalization for room tuning... My expectations are modest... I want a bloody loud speaker that doesn't distort at high SPLs. Primary purpose is to impress clients with sheer volume... critical decisions will mostly be made on the powered Mackie two way stand mount speakers... A Genelec or other professional monitor of approximately this configuration will easily work out to 4x as expensive as this system... I don't expect to get anywhere near that level of finesse, I just want a loud, clean system that can serve up enough accuracy to be an alternate reference monitor...

I have already bought the following:

* two pairs of Exodus Ex-Anarchy mid-bass drivers - these will be wired in series (3-4 ohms resistance, if I understand correctly) and be powered by a Peavey IPR 3000 or IPR 1600, depending on advice from the more experienced...

* one pair Tempest X-15 sub woofer drivers... to be powered by a Peavey IPR 3000, for 1000w @ 4 ohms per side.

* I have not bought the tweeters yet, but almost certainly, they will be Morel ET 448, based on their great power handling capability (1000w max)... In the studio, there are untamed high frequencies on a regular basis, and I need the tweeter to be really robust. These will be powered by a Peavey IPR 1600.

The drivers will be crossed over, equalized and protected by a Peavey VSX26. I have measurement microphones and meters.

Some questions:

1) Being an absolute n00b at this, am I making any obvious mistakes? Please remember I am trying to play it safe and keep it simple. I'm not looking for any delicate audiophile quality deal. Just something muscular and honest.

2) Is the IPR 1600 sufficient to power the mid-woofers or is an IPR3000 recommended?

3) The manufacturer (or the guy who answered my mail) suggests that the subwoofer be mounted into a separate enclosure from the mid-woofers and the tweeter... Is this necessary?... I could get a lot more volume for the subwoofer cabinet if I did not have to separate it from the other drivers. Please see attached pics... The one with the walls separating the drivers leaves the sub with a volume of 141L, which will have its -3 dB point @ 18-20 Hz, in room... This is OK by me, particularly since I expect at least 3 dB more efficiency due to 'half space' room loading... However, I'm greedy for the extra volume...

4) This particular tweeter, the Morel ET448, do I have to seal it in a separate enclosure?

5) At this time, I'm thinking cabinet will be made from 1" Bison board, which is a "cement bonded particle board made out of 62 % cement 28 % wood"... Its cost, mass and availability make me think its a good option... Any comments?

6) Any tips to optimize this project?

Thanks,

Jai Shankar.

[BobEllis]

Your midwoofers are 8 ohms nominal. Wiring in PARALLEL will get you 4 ohms nominal. Series is 16 ohms.

The IPR 1600 is well over what you need to power the mids. Consider something in the 200W range. That will still give you more than enough power to destroy the midwoofers.

Sub placement is not optimum high on the wall. you'll get more output and probably smoother overall response with them near the floor. If you're going for that look, it won't kill the sound, but you could do better.

No the Morel does not need its own enclosure.

Bison board sounds interesting, but don't forget the bracing anyway.

Protect your tweeter with a crossover as high as possible and steep slopes. If the midwoofers are smooth enough up high, try a bit over 2KHz. It will be interesting to see what the Anarchy can do.

[audiothings]

Originally Posted by BobEllis

Your midwoofers are 8 ohms nominal. Wiring in PARALLEL will get you 4 ohms nominal. Series is 16 ohms.

Absolutely! My bad...

The IPR 1600 is well over what you need to power the mids. Consider something in the 200W range. That will still give you more than enough power to destroy the midwoofers.

That is the lowest powered IPR there is... don't want to mix and match for logistical reasons... Guess I just gotta be careful not to overload the drivers...

Sub placement is not optimum high on the wall. you'll get more output and probably smoother overall response with them near the floor. If you're going for that look, it won't kill the sound, but you could do better.

I'm looking at it as a 3-way, rather than a sub+sat system... Like "Mains" in any pro studio...

No the Morel does not need its own enclosure.

thank you for the clarity...

Protect your tweeter with a crossover as high as possible and steep slopes. If the midwoofers are smooth enough up high, try a bit over 2KHz. It will be interesting to see what the Anarchy can do.

I was hoping to crossover even higher... lets see how it goes...

Any and all additional inputs welcome...

[BobEllis]

Are you going to use another IPR1600 for the tweeters, too? Two of something smaller might be easier, of course if you want to limit rack space use fine. Put a large value capacitor in series with the tweeter for DC protection. 20-30 uf should do.

How high do you plan to use the Tempests? Check with Kevin, but I suspect that you won't want to run them much above 150 Hz. The higher you run them and the smaller your mid enclosures the better the power handling of your mids. You won't need to go as big as the modeling programs suggest for woofer use. Leave some room for the driver to breathe but stuff the rest of the volume fairly heavily.

Running 6.5" drivers much beyond 2,000 Hz. gets you into beaming issues. Your effective cone diameter is on the order of 13cm. Do a little reading on dispersion vs. driver diameter.

The transition from narrow dispersion 6" (at the top of its range) to wide dispersion tweeter may be noticeable as it causes an abrupt shift in the polar power response. Not to mention that the listening axis response may droop. If you're just going for loud and sounding OK in the center that may be acceptable. Be sure to measure from the listening axis as you develop your crossover settings.

Another issue to consider, since Kevin doesn't publish frequency response data, is the breakup peak of the Exodus' aluminum cone. He says it is well controlled, but you'll need to see how it looks when you measure. You may find that you need to push your crossover down, notch the peak out or both. If you don't get the breakup peak at least 30 dB or so down, it will rear its head as harshness - overall system distortion.

[audiothings]

Originally Posted by BobEllis

How high do you plan to use the Tempests? Check with Kevin, but I suspect that you won't want to run them much above 150 Hz."

Thanks again Bob... I was thinking of 120 Hz and 2.5 KHz as the crossover points... I would have liked to crossover to the mids closer to 200 Hz or more, but the Tempest is a "sub" and not a "woofer" Which is why I went for two midbass drivers per side, as they'll be doing the bulk of the hard work...

The reason why I want to crossover to the tweeter has high as I can, is that, intuitively, the 20-30 watts it takes to drive a tweeter cannot balance out the 1000+ watts powering the other drivers... Particularly given that the tweeter handles much more of the frequency range than the other drivers put together... however I'm beginning to understand that my "intuition" and the laws of physics are often poles apart

Running 6.5" drivers much beyond 2,000 Hz. gets you into beaming issues. Your effective cone diameter is on the order of 13cm. Do a little reading on dispersion vs. driver diameter.

will do sir, thank you for the tip...

[BobEllis]

intuition vs physics - take a look at Rod Elliot's site www.sound.westhost.com for an article about active crossovers and power distribution. There's not a lot of energy up high.

Also, it's about sound pressure out, not power in. If you have a 104 dB/1W horn tweeter and a woofer that takes a kilowatt to reach 104 dB, a 5 watt tweeter amp is plenty. With the Morel, 30 watts will get you over 105 dB. Sort of the same idea as a 100 HP motorcycle being able to out accellerate a 500 HP car.

Don't think raw numbers, think octaves. 2500 Hz- 20,000 Hz is three octaves. If you ask your Tempest to do 20-120, that's 2.5 octaves, and your mids cover about 4.5 octaves.

Most of the acoustic power will come from the mids, but your Tempests will take more electrical power if you use any EQ to get into the 20s. Otherwise, it will take only 150W for either the mids or the Tempests to hit around 105 db

Crossing to the tweeter at 2500 is a little on the high side, but not out of the ballpark. Give it a shot.

[whgeiger]

I have just a little to add to the advice you have already received; so, for the most part, this post will serve to confirm what has already been given.

DIY strategy you are using, crossover before dedicated power amps, will most certainly allow you to maximize the performance of the drivers you select and insure system implementation success.

For a three way system, setting crossover frequencies at decade boundaries (200 Hz and 2000 Hz) would be a good starting point. Try to keep most of the musical fundamentals in the MF drivers.

If the mids beam but are otherwise clean, an easy to build acoustic lens in front of these drivers may mitigate the problem.

The enclosure for the sub can envelope those for the mid and hf drivers, though each driver should still have its own enclosure.

The use of DC blocking capacitors is a must, particularly for the venue you describe.

Best of luck with your project.

Regards,

WHG

[audiothings]

Thanks whgeiger.

Originally Posted by whgeiger

If the mids beam but are otherwise clean, an easy to build acoustic lens in front of these drivers may mitigate the problem.

Do the mids have to be recessed or can the lens be built externally?

Originally Posted by whgeiger

The enclosure for the sub can envelope those for the mid and hf drivers, though each driver should still have its own enclosure.

Of course! such an obvious thing and it never occurred to me... thanks!

Originally Posted by whgeiger

The use of DC blocking capacitors is a must, particularly for the venue you describe.

Could you please elaborate for the benefit of the n00b? I have no idea what you're talking about.

[BobEllis]

A DC Blocking capacitor is the cap I mentioned above - a large value cap in series with the HF driver. It helps protect against turn on/off thumps and the like. For an 8 ohm nominal impedance driver crossing at 2K or higher, 30 uF ought to be plenty to avoid noticeable interaction with your crossover.

You can get clever and use a smaller cap if you use it for one of the poles of your high pass filter. For example if you want a fourth order electrical filter at 2400 Hz, size the cap appropriately and you'll only need 3rd order in your active crossover. The catches are if your tweeter's impedance curve isn't really flat you'll need a zoebel to flatten it and many commercial crossovers are fixed at LR4 electrical slopes. Not sure about yours.

[audiothings]

Originally Posted by BobEllis

A DC Blocking capacitor is the cap I mentioned above - a large value cap in series with the HF driver. It helps protect against turn on/off thumps and the like. For an 8 ohm nominal impedance driver crossing at 2K or higher, 30 uF ought to be plenty to avoid noticeable interaction with your crossover.

Thanks Bob. Are there any disadvantages to putting in this capacitor? Will it change the sound in any way?

You can get clever and use a smaller cap if you use it for one of the poles of your high pass filter. For example if you want a fourth order electrical filter at 2400 Hz, size the cap appropriately and you'll only need 3rd order in your active crossover. The catches are if your tweeter's impedance curve isn't really flat you'll need a zoebel to flatten it and many commercial crossovers are fixed at LR4 electrical slopes. Not sure about yours.[/QUOTE]

As fasr as the VSX 26 is concerned, the available filters are:

Flat, Butterworth 6, 12, 18, 24, 30, 36, 42, and 48 dB/oct.; Bessell 12, 18, 24, 30, 36, 42 and 48 dB/oct; Linkwitz-Riley 12, 24, 36 and 48 dB/oct. The user is free to mix and match filter types to create symmetrical or asymmetrical crossovers.

Also please find attached the impedance curve of the ET448 (which, for better or worse, we have already bought)... There is a sharp peak in impedance around 1 KHz... Do you think these factors will become an issue?

Thanks again,