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Mike's MTM - Tweeter Choice
Mike's MTM - Tweeter Choice
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Old 29th October 2007, 04:49 PM   #1
Mike C is offline Mike C  United Kingdom
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Default Mike's MTM - Tweeter Choice

I hope this will be a quick and easy thread (I've searched and found a lot of useful info).

My MTM design was very much inspired by Zaph's large MTM using XG18 and 27TDFC. I can see why the 27TDFC is a good choice, and therefore I have planned to use this myself.
My present speakers use an earlier Seas soft dome tweeter (H400 or similar), not a bad unit; the 27TDFC is said to be significantly better .... but I should not find it a major 'culture shock'.

However, I'm tempted by the Peerless HDS 810921, and finding it hard to make a choice. The cost difference isn't an issue.

For the 27TDFC:
. used in similar speakers with good results
. crossover designs available for my xover frequency
. low Fs suits a low xover point, suits my MTM well
. measures good, sounds good
. well rated by Zaph and Mark
. better than my present tweeter
Against: Nothing!

For the Peerless HDS:
. has been used with the Seas ER18RNX (not MTM) with good results
. lowish Fs of 700Hz just about OK, but said to be good with a lowish xover point due to good distortion performance at lowish frequencies
. measures good, sounds good
. very well rated by Zaph and Mark
. highly rated by UK dealer audio-components
. 'newfinish' found an improvement with the SS 97000 over the 27TDFC; the HDS seems to be in the same class as the SS? Suggests that the HDS could indeed give an improvement in my speaker. Note that newfinish's MTM is somewhat similar to mine.
Against: not a lot; but I have more to do to get a good crossover, I don't have the help I have with the 27TDFC.

I'm leaning towards the HDS .....

Suggestions welcome. It's down to these two!
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Old 29th October 2007, 07:15 PM   #2
weinstro is offline weinstro  United States
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An interesting problem. I too am pondering this from time to time.

My one concern is the ability to cross over low enough with the 810921, a requirement for an MTM, but Jay WJ assures me that it can. I think the 810921 may have slight advantages in distortion and off-axis frequency response.

In my case, I'll probably buy both, and try.
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Old 29th October 2007, 08:39 PM   #3
Jay_WJ is offline Jay_WJ  United States
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Hi Mike,

Let me tell you about my experience with both tweeters. IMO, the 27TDFC is easier to work with and more neutral in terms of tonality. The HDS tweeter's response is not very linear. It tilts upward as the frequency increases. I think the following, Joe Rasmussen's measurement better indicates this characteristic:

Click the image to open in full size.

In my application, I used a notch filter in the top end. But a crossover can't flatten out its uniqueness, unless you want to throw in a bunch of notch filters, based on your own measurement.

Of course, I enjoy its detailed sound in my Usher 2-way, but I have to admit that the 27TDFC sounds a bit more neutral to my ear.
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Old 31st October 2007, 04:17 PM   #4
Mike C is offline Mike C  United Kingdom
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Thanks again Jay for such informative and helpful comments.

The FR plot is interesting, as it's somewhat different to the one published by Peerless which I've been using for some preliminary modelling of a crossover.

With the HDS, in my modelling so far I have not managed to get the transition from flat to BSC rise to come in as well as I can with the 27TDFC. Of course this is all modelling with inaccurate data, of somewhat limited value.

But when I consider this point, your comments about the Seas being easier to work with, and Joe's FR .... then I'm happy to go with the Seas but consider the HDS at some future time - the face plates are the same diameter.

The build is coming along; I have laminated 3 sides, the front and rear panels are being cut to size for me, and I can borrow a router from a friend.

With my narrow baffle there is little space to offset the woofers, but I'm wondering whether to offset the tweeter. I'll do some research on this and will only ask if I get stuck! :-)

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Old 1st November 2007, 05:26 AM   #5
peter_m is offline peter_m  Canada
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Default Re: Mike's MTM - Tweeter Choice

Originally posted by Mike C

For the Peerless HDS:
. has been used with the Seas ER18RNX (not MTM) with good results

slightly off topic, but where did you hsee this ER18/HDS design?

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Old 2nd November 2007, 09:02 AM   #6
Mike C is offline Mike C  United Kingdom
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I didn't actually see a design, just a comment:


I found that while searching for info on the ER18 - it helped me decide on that .... I guess I half remembered about the HDS though in fact it may not be relevant as it seems it's for car audio, in an active system.
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