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Old 11th January 2009, 01:42 AM   #1
morkyz is offline morkyz  Canada
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Default Customizing manufactured speakers to fit a height challenged AV theatre setup.

Ok, those of you who are purists, please look away. Here is my idea. I have a set of PSB image speakers. My problem is that I love the effciency and bass response of my front tower speakers, a pair of PSB Image T65's, but, they are tall enough that they limit the height of my screen in my home theatre. The speakers are 39.25" high. There exists a shorter T55 PSB Image tower speaker, at about 36-36.25"" high, but, I am hesitating to use it because it is a bit less efficient and has less bass reponse. Yes, I am well aware that I can use a subwoofer with the smaller towers, or with even smaller speakers, and get good bass. The point is that I like the full sound from the tower speakers themselves.

I want a larger screen, and not only that, the throw distance of the room is such that with the projector I am using, I would actually benefit from a slightly larger screen.

Yes, I have thought of other options. I cannot dig the floor down, as I live in a condo townhome. My ownership ends at the concrete basement floor surface. Yes I have looked at other speakers, but none meet my requirements of bass response, efficiency and shorter height. Go figure, as tower speakers with low bass extension are often tall. No kidding. I am even looking at raising the ceiling, but that is proving very difficult to impossible. Not raising the actual ceiling, but simply allowing me to make use of some room in the ceiling joist space.

So, my question is this. Could I take parts and peices from the PSB image speaker line and create a speaker with nearly identical freq response and efficiency, and sound character and yet have it 3 to 5 inches shorter in height?

The speakers and speaker cabinets I have to work with are:

T65 - one 1 inch tweeter and three 6.5" woofers.
T55 - one 1 inch tweeter and two 6.5" woofers in a smaller voume cabinet.
C60 - one inch tweeter and two 6.5" woofers in an even smaller centre channel cabinet.

In all the cases, what I'm trying to do is make a shorter speaker, but maintain or improve on the bass response, and at least hopefully not worsen the efficiency too much.

Here are some examples of ways in which I could do this.

I could take a T55 and supplement it with more woofers in the C60 centre channel cabinets, thereby ending up with as much or more bass reponse in a shorter package. It would require altering crossovers and I wouldn't use the tweeters in the centre channels. I would need to lower the crossovers to avoid lobbing that could occur with putting midrange drivers horizontal.

Without doing any physical work, I could simply take two pairs of T55's and run them back to back as bipoles. Alternatively, I could make one cabinet from a pair of T55 cabinet's. I would possibly not keep the rear facing tweeter and the woofers I would crossover lower. The idea would be a cabinet with 4 woofers so hopefully even lower bass response.

I could take the guts of the T65 and simply build my own shorter cabinet, perhaps out of two sets of T55 cabinets.

I could take a T65 cabinet and shorten it by the amount I need, and fit the drivers onto the new cabinet in a number of ways.

Anyhow, check out the speakers on the psb website and you'll see what I'm looking at. Don't bother telling me that what I'm doing is wrong and I should just build my own speakers from scratch. I know that is an option in my situation, but before I do that, I want to explore this option. I think it can be an interesting and workable option if it is carefully thought out and done properly. I like the sound of these speakers and so I want to maintain the sound character.
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Old 11th January 2009, 10:36 AM   #2
morkyz is offline morkyz  Canada
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Here is another option:

A pair of T55's run off the receivers amp output.

A pair of "woofer" speakers built like this:

C60 centre channel cabinets.
Two 6.5" woofers using the 500 hz crossovers that the T65 and T55 use.
No tweeters.
Drive the 'woofer' speakers off of separate amps.

The idea is to get a shorter speaker with the same or better bass response than the T65's alone. May work since I'm using the same drivers and crossovers but with slightly higher enclosure volume and one extra driver per side.

If I could figure out how to wire 4 woofers to a T65 I'd do it all off the receivers amp.
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Old 11th January 2009, 02:13 PM   #3
Paul W is offline Paul W  United States
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Build a new cabinet for the T65 components with the internal volume lost to height reduction made up in increased cabinet depth. Do not change the baffle or relative driver locations, ports off-center if necessary.
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Old 11th January 2009, 03:02 PM   #4
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I had the same problem as you with tall mains.

Have you thought about a new screen with an AT fabric? I'm using Seymour AV centerstage material. Its good stuff, does very minimal harm to the sound and best of all, is good value. I paid $700 for my screen material including shipping to the UK. From there I glued it to the roller mechanism of my existing screen and that was it.

http://www.seymourav.com/screens.asp

All this is certainly easier and probably cheaper than DIY.
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Old 11th January 2009, 06:13 PM   #5
morkyz is offline morkyz  Canada
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Thanks for the feedback folks. Good idea's. I am not too keen on an acoustically transparent screen, although I suppose I am willing to try it out. I wear glasses and I like things to be as close to perfect visually as possible and also, no matter what anybody says, I still believe that a screen will affect the sound. Again, I would have to test.

I like the idea of building a shorter cabinet for the T65 drivers. Looking at the front baffle, there are many ways I could reduce height. The space between the ports and the drivers allows for 3.75" of height reduction. I could probably pull off a reduction in height of 3.5" without going overboard.

How do I reduce the height of the front baffle? It looks like a matter of cutting it in many many places and re-assembling it by glueing or?

More thoughts on using pairs of PSB Image speaker cabinets:

I think my original thread post was long and complicated, but I still managed to omit a couple of other good options. There are so many ways to do this:

I could get two pairs of T55 cabinets and put the T65 drivers into one pair of the T55 cabinets, except the 3rd woofer would go into the second pair of T55 cabinets. I would not changed the crossovers. Of course, the single woofer in the T55 cabinet would be different, but it should, if anything, give slightly more bass.

I could do the same as above but use two woofers in the second T55 cabinet.

I could use a pair of T55's normally and have a second set of T55 cabinets with a pair of woofers crossed at 200 hz like the woofers in the older 7PT, requiring an amp for those.

The ways to do this seem endless, I guess I need to eliminate some options.

Is there any harm in having woofers side by side horizontally? I could cross-over the second woofer at either 500 or 200 hz or even lower. I know having midrange woofers side by side isn't great, but what about bass woofers <500hz?

thanks again for the advice,

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Old 11th January 2009, 06:39 PM   #6
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Quote:
Originally posted by morkyz
[B]Thanks for the feedback folks. Good idea's. I am not too keen on an acoustically transparent screen, although I suppose I am willing to try it out. I wear glasses and I like things to be as close to perfect visually as possible and also, no matter what anybody says, I still believe that a screen will affect the sound. Again, I would have to test.
I thought the same and imagined that any idea of fidelity would be greatly lost with a screen between you and the speaker. Afterall even a piece of paper over the tweeter does significant damage to the highs.

However after trying it out I found it only only slightly more damaging than speaker grills and nothing like as bad as the paper.

The Seymour fabric is woven type with an open area of a few percent. If I get within around 6 or 7ft I can start to see the perforations. I sit around 9ft away and have no problem. They're pretty tiny. Order a small sample from them to test.

An unexpected upshot and not something I ever really considered was how much better the experience is with the sound coming from the screen rather than to the sides or below it.

Whatever you do, good luck. I know these space problem are rarely easy or quick to solve.
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Old 11th January 2009, 10:14 PM   #7
morkyz is offline morkyz  Canada
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After going through all the options, I have pretty much determined that I've very few choices.

1) Go with a small screen size.
2) Go with smaller speakers.
3) Use an AT screen.

It actually is ok for me to try AT screen, because, co-incidentally, I have found my new setup very bright, overly detailed and revealing of poor source recordings...so, I figure if I try an AT screen, perhaps one side affect may be to soften the sound. In my situation, that may be ok. Kinda odd, because I don't want to miss-match my surrounds speakers. I guess one could put small peices of AT material in front of the surround speakers too, but that's kinda weird.

By using an AT screen, I would end up with a screen about 3 feet from the back wall. The final location will be determined once I decide where my speakers work best (with or without AT). Using an example of setting up a screen 3 feet from the back wall, my seating position will have my head located exactly 10 feet away from the screen when seated. Depending on the viewer and the way they sit, we're looking at 9-10 feet away. Using this setup I also get a good throw distance for the projector. I'd actually chose the screen size based on what looks best in terms of geometry etc. The one bonus is that I'm using a LCOS projector which has a large fill, which means less light loss to the AT screen perforations, and less chance of moire, and no sde due to closer seating.

Anyhow, I'll try it out and see what I get.
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Old 11th January 2009, 11:52 PM   #8
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Here is a thought, though extremely unlikely, maybe the speakers don't use the entire cabinet.

If you look at this PDF from one of Zaph Audio designs, you will see a shelf near the bottom. That shelf set the internal enclosure size.

http://zaphaudio.com/ZDT3.5-enclosure.pdf

I think the reason for this is that Zaph uses off-the-shelf tower cabinets and adjusts them internally to meet his current needs.

To find out, you have to open your speakers up and see if there is a false chamber in the bottom. If so, problem solved, if not, nothing ventured nothing gained.

Again, it is extremely unlikely, but it would solve a lot of problems.

The alternative as suggested by others, it to keep the baffle width the same, and make the cabinets deeper and shorter, but maintaining the cabinet's current volume.

Just a thought.

Steve/bluewizard
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Old 12th January 2009, 04:09 AM   #9
morkyz is offline morkyz  Canada
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Quote:
Originally posted by BlueWizard
Here is a thought, though extremely unlikely, maybe the speakers don't use the entire cabinet.

If you look at this PDF from one of Zaph Audio designs, you will see a shelf near the bottom. That shelf set the internal enclosure size.

http://zaphaudio.com/ZDT3.5-enclosure.pdf

I think the reason for this is that Zaph uses off-the-shelf tower cabinets and adjusts them internally to meet his current needs.

To find out, you have to open your speakers up and see if there is a false chamber in the bottom. If so, problem solved, if not, nothing ventured nothing gained.

Again, it is extremely unlikely, but it would solve a lot of problems.

The alternative as suggested by others, it to keep the baffle width the same, and make the cabinets deeper and shorter, but maintaining the cabinet's current volume.

Just a thought.

Steve/bluewizard
The specs for the PSB T65 and T55 show internal volumes of 43.7 L for the T55 and 65.8 Litre's for the T65, so I believe the T65 is larger. Rebuilding the speakers looks like a lot of work. Not that I'm afraid of work, but it looks like it would be difficult to get it done well so it sounds at least similar to the original T65.
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