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-   -   Hi-End Sealed MTM Bookshelf Design? (http://www.diyaudio.com/forums/multi-way/125902-hi-end-sealed-mtm-bookshelf-design.html)

treytexag 5th July 2008 06:25 PM

Hi-End Sealed MTM Bookshelf Design?
 
I've done a number of hours of searching and reading. I've looked at a number of the big name designs out here that we all talk about here and on other forums, but I can't seem to find what I'm looking for.

I want to build a pair of sealed cabinet MTM's to go on a shelf for 1/2 HT and 1/2 Music listening - budget ~$1,000 plus or minus. I'd also like to build a matching center channel. Anyway, since these will be back in a corner, probably <12 inches away from back and side walls, I wanted to do an un-ported enclosure. Also not sure how to cut back on BSC, since they'll be near the back and side walls. I'm already running a 15" Bash amp driven sub, nice output down to 20Hz when listening to my Stereophile Calibration CD's.

Anyway, looking for a very nice MTM in a sealed enclosure that I can sit on a shelf against walls. The Parts Express 1.0 cubic foot (28.3 liter) enclosure would be a nice cabinet to use. I like the Eros MkII design, seems like nice drivers, Vifa PL18s and SS 9500 tweets. Anybody done these in sealed enclosures?

Zaph Audio has some nice MTM's using the Vifa XG18 / Seas 27TDFC, but it's ported too. Don't know how to change the XO and BSC to adjust for sealing the cabinet.

Anybody know of proven designs for a hi0end sealed MTM bookshelf? Thanks alot for your help gents.

Treytexag
Houston

KS 5th July 2008 09:19 PM

You might email Danny Ritchie at GR-Research. Has has speaker plans and kits that are not currently listed on his web site.
http://gr-research.com/index.asp

crazyhub 5th July 2008 09:54 PM

Jay's DIY Loudspeaker Project:

http://www.geocities.com/woove99/Spk.../Usher_MTM.htm

Quote:

The Parts Express 1 cu. ft. cabinet can also be used for a closed alignment---1 cu. ft. happens to be a box volume usable for both vented and sealed designs. This closed cabinet gives a -3 dB point of 71 Hz with a box Qtc of .64; see predicted bass response in closed standmounting cabinet. This response will be ideal when the speakers are used with a subwoofer crossed over at 80 Hz using an AV receiver's active crossover. If a crossover frequency lower than 80 Hz is desired, vented designs will be more appropriate.
;)

treytexag 6th July 2008 12:12 AM

Great responses gents. Thanks. A couple of follow up questions.

On Jay's website for the Usher MTM he makes the following comment:

"In fact, an MTM design can easily be created if a corresponding TM design is already built and tested. Only thing that needs to be considered is a little different baffle step loss and diffraction."

Is this a true statement universally men, or was Jay only talking about this design? In other words, can I take any existing TM design and get help on the BSC and diffraction for a good speaker?

Other question, how does the Usher Usher 8945P compare to the Vifa PL18, and how does the Peerless 810921 HDS tweeter compare to the Scanspeak 9500?

Thanks allot guys, appreciate the help. If anyone has any other suggestions on a sealed high end MTM bookshelf, please do share.

Thanks,
Trey

Jay_WJ 6th July 2008 01:25 AM

The Vifa PL and SS 9500 are excellent drivers but a bit old designs by today's standard. Particularly the Usher 8945P has much lower distortions than the Vifa PL thanks to its advanced motor. And according to Mark K and Zaph's tests, the 810921 has lower distortions than the SS 9500 below 2 kHz, which is important for an MTM application.

I can provide a reduced BSC crossover for my Usher 8945P and Peerless 810921 MTM design. Send me an email if you're interested.

BTW, does your receiver have an auto EQ function like Audyssey?

Jay_WJ 9th July 2008 01:33 AM

Trey,

If you have a limited budget, I can also provide an MTM version of my Dayton RS180/Seas 27TDFC 2-way design. This crossover can be modified to have reduced BSC.

BTW, if you have an auto EQ like Audyssey, fine-tuning or voicing of a speaker is a moot point. So, subtle FR differences between TM and MTM designs are no longer meaningful in this case. The method I use for crossover simulation is more than adequate to provide a sufficiently good result. So, you may want to focus on drive units' quality for your MTM. As for the quality of drivers used, you will be hard pressed to find a better MTM design than my Usher/Peerless design.

treytexag 9th July 2008 02:08 AM

BTW, I'm runing a Marantz 7002 with the Audessy setup. Marantz sends all the LFE at 80 Hz to a 15" sub driven by a 500 watt BASH amp. I have a 5 channel amp coming Thursday, to help drive lower ohm speakers.

Thanks again.

Treytexag

treytexag 9th July 2008 04:31 AM

Jay, thanks so much for responding, you too kind. I really want to go the other way, larger budget. Looking for a sealed MTM using very nice drivers, perhaps like Seas Excel and Seas Milenium tweets - perhaps. I only mention the Seas because I've heard those and they sound excellent, in an TL design anyway. I'm looking for a proven design that folks have built and tweaked. What are your thoughts?

BTW men, thanks again for all the great posts here. I've lost serious sleep reading here and not sleeping!!

Treytexag

Jay_WJ 9th July 2008 04:45 AM

Quote:

Originally posted by treytexag
BTW, I'm runing a Marantz 7002 with the Audessy setup.
Okay if this is the case, as I said above, subtle voicing elements such as pinpoint-accurate BSC and tweeter padding in so-called "proven" designs are a moot point since your Audyssey can handle them.

I believe my Usher 8945P/Peerless 810921 in a sealed PE 1 cu ft cabinet with a reduced BSC crossover is what you're looking for. How can I say so? Take a look at Zaph's driver test pages:

http://www.zaphaudio.com/6.5test/compare.html (for 6.5" midwoofer tests)
http://www.zaphaudio.com/tweetermishmash/compare.html (for tweeter tests)

I'm not sure you can read these measurement charts. What you need to see in these pages is various 6.5" midbass drivers' and tweeters' harmonic distortion measurements, because harmonic distortions in the drivers' operating ranges are motor-induced property that cannot be corrected by crossovers or EQ no matter how well the crossovers are designed. Click the "Harmonic distortion" tab. You'll see each tested driver's harmonic distortion sweep over a frequency range. What you want to see in these graphs is the levels of the 3rd order (blue line) and 5th order (grey line) harmonics since they are generally considered to be acoustically obtrusive.

For 6.5" drivers, compare these levels across drivers in a frequency range from 100 Hz to 2 kHz to see how low the levels are. Compare the Usher 8945P's distortion levels to other drivers'. You can easily compare any two drivers by toggling between them. You'll see that the 8945P is one of the best performers regardless of price. Only the Scan Speak 18W8531G can rival the 8945P---overall, the 8945P's distortion levels are slightly lower. It is better than Seas Excel, Seas Prestige, Peerless, and Dayton. For example, compare the 8945P and the Seas CA18RLY (a bigger brother of the CA15RLY used in many existing designs). You'll see the 8945P's distortion levels are significantly lower than the CA18RLY.

The same thing applies to the Peerless 810921 HDS tweeter. For tweeters, compare their distortion levels in a frequency range from 1 kHz to 4 kHz because this range determines a tweeter's real-world performance. You'll see that only tweeters that measure (ever slightly) better than the 810921 are the Scan Speak 6600, 7100, and 7000. But I don't think this small difference is much audible. Note that there are no Seas Excel tweeters that outperform the Peerless 810921. Even the Seas Prestige line 27TBFC/G and 27TDFC measure better than the Seas Millennium.

In sum, I don't think you'll be able to find any existing DIY MTM designs---even if they luckily meet your exact requirements: can be used in a sealed 1 cu ft cabinet and with reduced BSC crossover---that have lower system harmonic distortions than this 8945P/810921 MTM design. With respect to drive units' quality, this design is top-notch regardless of price. This is the reason why I described my 8945P/810921 2-way as "truly high-end" in my web page. And I'm proud of what my crossover design does for this driver combination. :)

-jAy

Calvin 9th July 2008 09:32 AM

Hi,

this is a design, that could be just the right! ;-)
http://img150.imageshack.us/img150/2...01kleinvt7.jpg

This design is intended to be placed close to a wall. It shows high efficiency (93dB@2.83Vq1m) and allows for high dynamics.
It can play in small rooms (>12m²) and allows for small listening distances. In large rooms (>30m²) and freely standing it should be supported by a large sub below ~60Hz. It uses a pair of the Vifa 17WN225-8 in 12.5L BR each. As CB it would show a Qtb of 0.7, so it should be no prob to build it as a CB with similar dimensions (H60*W24*D30cm). Though it is a quite not a stylish new driver this is one of the very best 17cm drivers you could use. Equally linear response, smooth rolloff, low distortion and good efficincy are nearly impossible to find in this size class, especially not with an similar price tag attached to it.
The Tweeter is a horn loaded XT25. Besides increasing efficiency and reducing distortion the horn offsets the driver ´backwards´ which leads to an excellent step response. Directivity is high of course, but on the other hand this decreases the part of early reflections which is useful for a bookshelf box.
The crossover needed is simple and doesn´t need tons of parts as other designs ;)
Unluckily I lost some of my measurements but here are some of the left ones.
Distortion level at 96dbSPL@1m:
http://img77.imageshack.us/img77/693...bsplxu2.th.jpg
At this high level of SPL distortion is very well arranging around0.3%. One can clearly see that the tweeter distortion consists of nearly only K2.

Impedance
http://img77.imageshack.us/img77/442...iimpyi2.th.jpg
It is a 4Ohm speaker, with low phase shift. Combined with the high efficiency this is very easy to drive even with Tube amps.
I drive it with a KR340 (SE-Triode with ~20W) which is a combination made in heaven ;)

Step response
http://img112.imageshack.us/img112/4...stepmy3.th.jpg
The ´time aligned design´ and lack of resonances in freq-response clearly show in this excellent step reponse.

midwoofer freq responses wo crossover
http://img401.imageshack.us/img401/6...respkt1.th.png

and here the same with crossover
http://img88.imageshack.us/img88/708...bampzf1.th.png

The tweeter wo crossover
http://img180.imageshack.us/img180/2389/ht0lk2.th.png

Crossing over takes place around 2-3kHz. The tweeter features a higher crossover frequency (electrically than acoustically), thereby ´equalizing´ the raising amplitude response. Besides getting a linear amplitude response this reduces power stress on the tweeter, reduces distortion, increases the dynamic range and sounds smooth but more lively than the pure tweeter. Too you don´t need any resistances to get the efficiency down to woofer level...less parts count..better sound :D

jauu
Calvin


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