Midrange placement

[atropos]

I'm designing the driver layout for a pair of 3-way bookshelf speakers I'm going to build. I've offset the tweeter (a HiVi TN28) so the center of it will be approximately 4 inches from the top, 6-3/8" from one side and 2-3/8" from the other. This is just the closest placement to the Golden Ratio that works for me. I'll be crossing over the midrange (a Goldwood GM-65/8) at 5000hz, and I was wondering if I would benefit at all from offsetting that as well, or is 5000hz too low to make a difference?

[Chris Roemer]

> I'm designing the driver layout for a pair
> of 3-way bookshelf speakers I'm going to
> build. I've offset the tweeter (a HiVi TN28)
> so the center of it will be approximately 4
> inches from the top, 6-3/8" from one
> side and 2-3/8" from the other. This is
> just the closest placement to the Golden
> Ratio that works for me. I'll be crossing
> over the midrange (a Goldwood GM-65/8) at
> 5000hz, and I was wondering if I would
> benefit at all from offsetting that as well,
> or is 5000hz too low to make a difference?

Some would say your imaging would be better with the mid OS as well, so it's directly beneath the tweeter.

[atropos]

http://images.dpchallenge.com/images_portfolio/37930/orig/Copyrighted_Image_Reuse_Prohibited_672390.jpg


So far this is what I got. Aside from being kind of unconventional looking (my wording for ugly) how does it look?

I might just move the midrange and woofer down a bit so I don't need to notch the midrange. The tweeter being that close seems like a good idea to me but I don't know if it'll be worth the trouble.

I'll have to wait until I can order the stuff and then get the stuff before I decide if I can do that--unless someone tells me it's a terrible idea. At the price of the goldwood midranges I could just order an extra two in case it goes horribly wrong.

[atropos]

Oh, one more thing... I was also wondering what other people have used for lining the interior of your vented cabinets?

In your experience(s) what gives you the best results without taking up so much space you need to re-tune your cabinet?

[fwater]

> So far this is what I got. Aside from being
> kind of unconventional looking (my wording
> for ugly) how does it look?

> I might just move the midrange and woofer
> down a bit so I don't need to notch the
> midrange. The tweeter being that close seems
> like a good idea to me but I don't know if
> it'll be worth the trouble.

> I'll have to wait until I can order the
> stuff and then get the stuff before I decide
> if I can do that--unless someone tells me
> it's a terrible idea. At the price of the
> goldwood midranges I could just order an
> extra two in case it goes horribly wrong.

Based on my experience, offsetting the tweeter and the midrange made a perceivable difference. It's hard to tell how much for sure because although the drivers were similar in both enclosures, the two sets were never tested side by side.

IMHO, there may be something (maybe a lot) to gain by using one of the clearance Tang Band speakers if one of your goals is low cost. I've never used a Goldwood midrange, but I imagine it may be inferior to any one of the TB units at just slightly more bucks. A small enclosure would be needed for preventing the woofer from influencing the midrange, but it could be as simple as a heavily stuffed short length of capped PVC.

BTW, it's not so ugly. Heck, a TB midrange (with the sexy phase plugs) could give it some more flare.

[atropos]

> IMHO, there may be something (maybe a lot)
> to gain by using one of the clearance Tang
> Band speakers if one of your goals is low
> cost. I've never used a Goldwood midrange,
> but I imagine it may be inferior to any one
> of the TB units at just slightly more bucks.
> A small enclosure would be needed for
> preventing the woofer from influencing the
> midrange, but it could be as simple as a
> heavily stuffed short length of capped PVC.

I went through probably every driver with the specs I was looking for and this seemed to be the best. The user reviews were quite good, and this one is a sealed back midrange so I don't think I will need a seperate enclosure for it.

But... if there is an audible difference with offsetting the tweeter/midrange, would you know if there ight be an audible difference if I cut a small groove out of the midrange's mounting ring so I could squeeze the tweeter right in next to it? If you havn't seen it, take a look at the tweeter I'll be using. With how small it is, and a small groove cut out of the edge of the midrange, they should be as close as any tweeter ever was to any midrange that I've ever seen or heard of.

<A HREF="http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=297-409">http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=297-409</A>

[Todd G.]

http://www.partsexpress.com/projectshowcase/sc51/main2.jpg


I second the question about the Goldwood. I haven't used it, but I would seriously consider some TB offerings or the Dayton #295-330 even. I wouldn't count on crossing the Goldwood at 5000hz either, but if you're flexible with your crossover points it might not be bad.

> I went through probably every driver with
> the specs I was looking for and this seemed
> to be the best. The user reviews were quite
> good, and this one is a sealed back midrange
> so I don't think I will need a seperate
> enclosure for it.

How do you plan to mount the tweeter? You do realize it is intended to be surface mounted ON TOP of a speaker? (Shown below) Also, it is not the greatest tweeter around. See: <A HREF="http://www.zaphaudio.com/tweetermishmash/">http://www.zaphaudio.com/tweetermishmash/</A> towards the bottom of the page.

I'm just thinking inexpensive here, but the #279-140, 279-280, or ANY of the Dayton dome tweeters would likely be better choices. The small Dayton's could be mounted very close to the mid and they only cost $6.

> But... if there is an audible difference
> with offsetting the tweeter/midrange, would
> you know if there ight be an audible
> difference if I cut a small groove out of
> the midrange's mounting ring so I could
> squeeze the tweeter right in next to it?

[fwater]

> I went through probably every driver with
> the specs I was looking for and this seemed
> to be the best. The user reviews were quite
> good, and this one is a sealed back midrange
> so I don't think I will need a seperate
> enclosure for it.

> But... if there is an audible difference
> with offsetting the tweeter/midrange, would
> you know if there ight be an audible
> difference if I cut a small groove out of
> the midrange's mounting ring so I could
> squeeze the tweeter right in next to it? If
> you havn't seen it, take a look at the
> tweeter I'll be using. With how small it is,
> and a small groove cut out of the edge of
> the midrange, they should be as close as any
> tweeter ever was to any midrange that I've
> ever seen or heard of.

First off, I want to say that I'm not trying to poo-poo your ideas. Part of this hobby is the different designs and endless possibilities. That being said, the drivers that you're looking into are of questionable quality or value. The Goldwood midranges may have gotten good feedback or reviews on their specs page at PE, but many times the people making the reviews have little to no skill or experience in speaker building. Conversly, there are plenty of negative feedback tidbits on many of the well-regarded drivers, usually due to improper implementation and expectations from a generation brought up on hip-hop and I-pods.

The short version is, I beleive that there are better drivers for the money. The TN28 got a very bad review by the very accomplished Zaph, and I agree (I've used it and there's nothing special, even at the price point). Plus, the intended use as a top-mount will make it hard to mount on a baffle. The Goldwood midrange is very cheaply made and probably will not perform as well as even the cheaper Tang Bands. However, this is just advice, don't let me stop you.

BTW, it is not necessary to cut into the midrange's flang to facillitate such close mounting. 4 inches center-to-center is just fine.

[johnastockman]

> Oh, one more thing... I was also wondering
> what other people have used for lining the
> interior of your vented cabinets?

> In your experience(s) what gives you the
> best results without taking up so much space
> you need to re-tune your cabinet?

Some of that egg-crate foam works well. Air can pass through it, so make sure it's not the closed-cell foam variety if you look at Walmart or Kmart. It doesn't increase the apparent volume of the box, just breaks up some standing waves inside the enclosure.

John A.

[zach_t]

1. Play around with the Baffle Diffraction Simulator found over at FRC. You may find that having the midrange a DIFFERENT distance from the sides as the tweeter might be better because the hump from the edge diffraction wouldn't align with each other. Then again, your X-Over may be high enough it doesn't matter.

<A HREF="http://www.pvconsultants.com/audio/diffraction/downloadbds.htm">http://www.pvconsultants.com/audio/diffraction/downloadbds.htm</A>

2. With a 5,000-Hz X-Over, you Center to Center spacing should be 2.7 inches or less.

3. With a 5,000-Hz X-Over, you should above the high level of distortion found in this tweeter. There is a high 5th order peak at 1,750-Hz and the 3-order distortion is highest below 4,000 Hz.

[atropos]

Thanks for those tidbits of useful info. I've since changed my mind about all three drivers, but I'll definetely take your advice on the new design. Much appreciated =]

> 1. Play around with the Baffle Diffraction
> Simulator found over at FRC. You may find
> that having the midrange a DIFFERENT
> distance from the sides as the tweeter might
> be better because the hump from the edge
> diffraction wouldn't align with each other.
> Then again, your X-Over may be high enough
> it doesn't matter.

>
> <A HREF="http://www.pvconsultants.com/audio/diffraction/downloadbds.htm">http://www.pvconsultants.com/audio/diffraction/downloadbds.htm</A>
> 2. With a 5,000-Hz X-Over, you Center to
> Center spacing should be 2.7 inches or less.

> 3. With a 5,000-Hz X-Over, you should above
> the high level of distortion found in this
> tweeter. There is a high 5th order peak at
> 1,750-Hz and the 3-order distortion is
> highest below 4,000 Hz.